After briefly reviewing our recent progress on 3D laser nanoprinting based on two-step absorption instead of two-photon absorption, we review our recent work towards designing and realizing elastic and acoustic metamaterials exhibiting roton-like dispersion relations via nonlocal interactions. Previously, rotons were restricted to correlated quantum systems at low temperatures.

Metasurface design methodology combined with both mature and emerging manufacturing approaches have led to a new generation of robust and high-performance array antennas that can satisfy large market demands. Here, we review the basic waveguide-fed metasurface architecture and discuss current trends.

In this paper, a high gain antenna based on low profile metasurfaces is designed and numerically analyzed. The operation principle is the same of series fed Continuous Transverse Stub (CTS) structures, but in comparison to prior designs, radiation efficiency and compactness are improved by feeding the radiating aperture with a planar lens working in reflection. The lens can be realized using a pin-type metasurface, resulting in a fully metallic construction. The radiating aperture is realized by etching slots in the upper wall of a parallel plate waveguide loaded with corrugations; this solution provides an almost frequency- and scan-independent active impedance, resulting in wideband performance for all the pointing directions. Furthermore, because of the axial symmetry of the feeding structure, the antenna has the capability of generating multiple beams from the same aperture while maintaining excellent port decoupling.

In this contribution, we discuss the possibility to exploit functionalized metasurface coats wrapping wired antennas for manipulating their radiation pattern. Through a proper design of the Huygens metasurface coating, the quasi-cylindrical wave front of the field radiated by the antenna is locally transformed into a plane wave, leading to the generation of multiple or single radiating beams from the original omnidirectional pattern. The semi-analytical model of the device is presented, and some relevant examples are provided.

Needle radiation can be achieved if a large number of multipoles are appropriately combined together. However, the practical realization of multipoles and their combinations have only recently been considered. The physics and engineering of mixtures of multipoles will be given in my presentation. Initial practical prototypes will illustrate the viability of the concepts.

The ability to obtain dynamic control over an antenna radiation pattern is one of the main functions, desired in a vast range of applications, including wireless communications, radars, and many others. Here, an antenna design with optically controlled beam steering is demonstrated. The design is based on cylindrically arranged passive dipole elements loaded by a switchable impedance circuit. The circuit encompasses a bipolar transistor, controlled with a fast photodiode. An active broadband element is placed at the center of the structure. The experimental device can be switched between 6 states at an almost MHz rate. Each radiation pattern is demonstrated to have a 6dB of differential gain, while the overall footprint of the antenna (2r/λ = 0.5-0.6) is rather small. Fast switching between optically driven reflectors allows achieving scanning and cover the entire 2π azimuth section. The current architecture is a step towards obtaining high-quality scans over the whole three-dimensional space.

This paper describes the application of higher symmetries to enable broadband operation of Reflecting Luneburg lenses (RLL) at Ka-band. The structure at hand consists of two vertically stacked parallel plate waveguides (PPWs) of circular shape. An azimuthally symmetric graded index (GRIN) medium in the bottom PPW serves to address the rays along curvilinear paths such that, after reflection in the boundary, they emerge collimated in the top PPW . Owing to the symmetry of the medium, one can generate plane waves with arbitrary directions by simply changing the azimuthal position of the source in the bottom layer. In this work, we explore the implementation of the GRIN medium by loading higher symmetric unitcells consisting of metallic posts. This solution allows one to mitigate frequency dispersion, thus increasing the operational bandwidth of the lens. The proposed architecture constitutes a metalonly, low-profile beam-former that provides full azimuthal scanning over the whole Ka-band

Slow light devices are one of the key components in photonics, yet common slow light devices are limited by their large footprints and susceptibility to disorder. Here, we demonstrate that topological slow light in synthetic spaces can tackle these challenges and provide slow light over extremely compact footprints.

The robustness of topologically protected few-particle states may open new horizons for quantum technologies. We study topological properties of a one-dimensional array of qubits coupled with their nearest neighbors via alternating connecting elements: either an inductance or Josephson junction. By deriving the circuit Hamiltonian, we demonstrate that the presence of coupling Josephson junctions gives rise to the effective photon-photon interactions inducing a non-trivial topological phase of bound photon pair accompanied by an in-gap topological edge state. Studying the effective Su-Schrieffer-Heeger model, we predict the interaction-induced topological transition.

Here we introduce a new technique, time res olved vector microscopy, that enables us to compose entire movies on a sub femtosecond time scale and a 10 nm scale of the electric field vectors of surface plasmon polaritons. Depending on the shape and geometrical phase, in combination with the helicity of the excitation beam, topological plasmonic quasiparticles are created: skyrmions, merons, as well as quasicrystalline excitations. We observe their complete field vector dynamics at subfemtosecond time resolution.

We have developed a succinct approach for using homogenisation to derive explicit estimates for the properties of topologically protected edge states. Our approach uses transfer matrices to reduce the wave transmission problem to a set of difference equations, which can be handled concisely using high-frequency homogenisation. This gives estimates for the eigen- frequency and the decay rate of topologically protected edge states. We use a medium based on the Su-Schrieffer-Heeger model to demonstrate the method and show how it can be extended to more complex geometries.

In this work it is shown that nonreciprocal structures with continuous translation symmetry can have an ill-defined topology. In particular, it is experimentally verified that the topology of a ferrite can be effectively regularized when an air layer is adjoined to the relevant material interface. Furthermore, it is experimentally demonstrated that ill-defined topologies can be used to create energy sinks where the electromagnetic fields are massively enhanced.

Here we demonstrate that strong coupling between topological photons with phonons in hexagonal boron nitride (hBN) offers a new platform to control and guide hybrid states of light and lattice vibrations. The observed topological edge-states of phonon-polaritons are found to carry nonzero angular momentum locked to their propagation direction, which enables their robust transport.

Electron-photon interactions in ultrafast electron microscopes are routinely used to probe material excitations with a high spatial resolution using external laser excitations. Here, we provide the first proof of concept experiment that internal radiation sources based on electron-driven photon sources can be used for phased-locked correlative electron-photon spectroscopy, providing a tool for spectral interferometry with electron microscopes.

Electron energy loss spectroscopy is often utilized to characterize localized surface plasmon modes supported by plasmonic antennas. We address its mediocre spectral resolution by analyzing the spectral and spatial distribution of the loss probability simultaneously. In this way, we resolve nearly degenerate modes supported by a pair of plasmonic discs.

We study lasing in plasmonic arrays composed of quadrumers of gold nanoparticles combined with organic dye molecules. We show that the lasing mode is a quasi-BIC mode of high Q-factor and out-of-plane polarization. In our system, the edges of the array provide a leak mechanism for the quasi-BIC to be observed: this leads to a stronger lasing emission from the edges than from the bulk. By combining theory with polarization-resolved measurements of the lasing emission, we show that the lasing mode has a topological charge. Our results highlight the potential of lattices made of multiparticle clusters for the design of new high-Q-factor topological modes that can enhance light-matter interactions and reduce lasing thresholds.

Over the past three decades, graphene has become the prototypical platform for discovering topological phases of matter. Both the Chern C∈Z and quantum spin Hall υ∈Z2 insulators were first predicted in graphene, which led to a veritable explosion of research in topological materials. We introduce a new topological classification of two-dimensional matter – the optical N-phases N∈Z. This topological quantum number is connected to polarization transport and captured solely by the spatiotemporal dispersion of the atomistic susceptibility tensor χ. We verify N ≠ 0 in graphene with the underlying physical mechanism being repulsive Hall viscosity. An experimental probe, evanescent magneto-optic Kerr effect (e-MOKE) spectroscopy, is proposed to explore the N-invariant. We also develop topological circulators by exploiting gapless edge plasmons that are immune to back-scattering and navigate sharp defects with impunity. Our work indicates that graphene with repulsive Hall viscosity is the first candidate material for a topological electrodynamic phase of matter.

We propose an analytical framework combining transformation optics and Feibelman d parameters to investigate the nonclassical effect in complex plasmonic structures. On the one hand, transformation optics allows an analytical solution for the optical response of a complex nanostructure. On the other hand, the d parameters incorporate most of the quantum effects of electrons, such as nonlocality and electron spill-out. Therefore, combining these two ingredients enables an analytical approach to the nonclassical effects of mesoscopic plasmonics. We further extend our analytical tool to the case of noble metals and charged particles. Our method is not only an accurate and efficient tool but also a general routine to explore the light-matter interaction in complex mesoscopic plasmonic systems.

We explored a system of strongly coupled mid-infrared localized plasmon modes and phonon polaritons using far-field infrared spectroscopy, state-of-the-art monochromated electron energy-loss spectroscopy, numerical simulations and analytical modelling, which together enabled a detailed analysis of the response of a system accommodating several coupled modes.

In this work, we use a high-throughput screening method combined with optical Mie theory to evaluate the performance of more than 2000 materials and discover a new promising material, boron phosphide, which has so far been elusive. We prepare boron phosphide nanoparticles and experimentally demonstrate that they support Mie resonances across the visible and the near ultraviolet using both far-field optical measurements and near-field electron energy-loss spectroscopy.

We report an extended family of diffraction-free super-toroidal light pulses, the exact solutions of Maxwell's equations, allowing propagation-robust skyrmionic topologies that persist over arbitrary distances.

A conventional optical cavity supports modes which are confined because they are unable to leak out of the cavity. Bound state in continuum (BIC) cavities are an unconventional alternative, where light can leak out, but is confined by multimodal destructive interference. BICs are a general wave phenomenon, of particular interest to optics, but BICs and multimodal interference have never been demonstrated at the nanoscale. Here, we demonstrate the first nanophotonic cavities based on BIC-like multimodal interference. This novel confinement mechanism for deep sub-wavelength light shows orders of magnitude improvement in several metrics. Specifically, we obtain cavity volumes below 100x100x3 nm3 with quality factors about 100, with extreme cases having 23x23x3 nm3 volumes or quality factors above 400. Key to our approach, is the use of crystalline hyperbolic dispersion media (HyM) which can support large momentum excitations with relatively low losses. Making a HyM cavity is complicated by the additional modes that appear in a HyM. Ordinarily, these serve as additional channels for leakage, reducing cavity performance. But, in our experiments, we find a BIC-like cavity confinement enhancement effect, which is intimately related to the ray-like nature of HyM excitations. In fact, the quality factors of our cavities exceed the maximum that is possible in the absence of higher order modes. The alliance of HyM with BICs in our work yields a radically novel way to confine light, expected to have far reaching consequences wherever strong optical confinement is utilized, from ultra-strong light-matter interactions, to mid-IR nonlinear optics and sensing applications.

We show that the magnetic modulation of the Near-Field response induced by an external magnetic field in complementary rod-slit arrays made out of a Giant-Magneto-Resistance material (GMR) can be higher than the Far-Field counterpart in specific points close to the metasurface. This can be exploited to improve the sensitivity of molecular sensors.

Metal-polymer interfaces are used widely in satellite missions as they show extreme thermal isolation and elevated interface strength. In space, robust interfaces between nanomaterials are essential as thermal gradients and strain may result in device failure. Here we show flexible metafoils with ultrastable plasmon resonances allowing transmission of visible radiation while reflect the unwanted infrared responsible for device heating. Electromagnetic and nanomechanical simulations confirm our experimental findings showing extreme robustness with strains up to ~20%, equivalent to thermal expansion in temperatures of >10000 K. Such space solar isolators can be used along with photovoltaic panels allowing optimum interplay with visible light for efficient charging. Resilient ultrathin metasurfaces are highly desirable for mechano-optical applications in harsh environments ensuring small footprint and lightweight devices.

In this talk, I will discuss our recent progress in the area of polaritonics and its role in advancing the field of metamaterials and metasurfaces. Tailored material resonances, based on excitons, phonons, or electronic transitions, can be strongly coupled to electromagnetic waves in engineered metasurfaces, unveiling new degrees of freedom for the control of light-matter interactions. In particular, I will discuss how, as the degree of lattice symmetries in the involved materials and in optically engineered structures is reduced, new opportunities emerge in manipulating light and matter at the nanoscale.

Acoustic tweezers exploit ultrasonic acoustic radiation forces, and sometimes acoustic streaming, for contact-free, bio-compatible, and precise manipulation of particles from millimeter to sub-micrometer scale. Acoustic tweezers typically use multiple sources to create standing wave patterns that can trap and move objects in ways constrained by the limited complexity of the acoustic wave field that can be generated from an array of simple sources that are generally removed from the area of trapping and manipulation. We report here our efforts to develop metamaterial structures for new approaches for acoustic tweezers for trapping and manipulating small particles in water. We first demonstrate a 3D acoustic tweezer in fluids that uses a single transducer and a PDMS acoustic lens. Three-dimensional trapping is achieved by combining the radiation force for trapping in two dimensions with the streaming force to provide levitation in the third dimension. Second, we demonstrate spatially complex particle trapping and manipulation inside a boundary-free chamber using a single pair of sources and an engineered structure outside the chamber that we call a shadow waveguide. The shadow waveguide creates a tightly confined, spatially complex acoustic field inside the chamber without requiring any interior structure that would interfere with net flow or transport. Controlling acoustic fields with local metamaterial structures significantly expands the capabilities of acoustic tweezers.

Metamaterials typically leverage coupled local resonances to achieve target wave properties. An interesting exception is provided by interlaced wire media, which instead rely on a finite number of quasistatic modes to control the spatial dispersion of lower dispersion branches. Here, we introduce their mechanical counterpart. We leverage oligomodal geometries to induce extremely large non-local effects into deep subwavelength phononic branches. We start by showing how oligomodal vertex models predict the zero-frequency content. Then, we use a spring-mass model to investigate how mechanical zero modes affect the finite-frequency spectrum. We also discuss how deforming the unit-cell mechanism impacts the band structure. Finally, we validate our theory with full-wave simulations and preliminary experiments.

We proposed a four-leaved rose shape mechanical metamaterial that does not suffer from stress concentration and shows a wide range of effective Poisson's ratio and stiffness. We implemented a programmable design of shape morphing of rose structures, verified it numerically and experimentally, and explored its potential applications.

Elastic metamaterials have much promise in terms of vibration control, energy harvesting and soundproofing from urban noise. This talk will discuss recent results and the potential for devices.

We use machine learning to solve the forward and inverse design problem for 2D periodic linearly elastic metamaterials. We focus on a single Cauchy-elastic isotropic constituent material and voids within and on square-shaped symmetry of the metamaterial unit cell. We consider generative adversarial networks (GANs) and variational autoencoders (VAEs).

Metamaterials can perform sophisticated computations. We demonstrate experimentally that these capabilities extend to speech classification, a paradigmatic artificial-intelligence task. We fabricate a neuromorphic phononic metastructure that distinguishes between pairs of works. Our design process combines reduced-order modelling with machine learning to efficiently optimize the structure against a large speech corpus.

The simplicity of leaky wave antennas makes them suitable for some of the scenarios of the new communication systems. Additionally, the scanning with frequency that is inherent to these antennas is a property that can have also interest in some radar systems. The increase in frequency of the new communication networks has motivated the development of new technologies. Among them, gap waveguide technology is a cost-effective solution for millimeter wave frequencies. Its use for designing leaky wave antennas based on the use of the groove version will be reviewed in this work. On the other hand, 3D printing technologies have exploded in the last years and, in this work, the potential use of this technology to design leaky wave antennas based on corrugated surfaces implemented with dielectrics will be presented.

Near-field resonant parasitic based Huygens sources have been of interest in many antenna applications recently. Here, it is demonstrated that the frequency of operation of a sub-wavelength, metamaterial-inspired Huygens dipole antenna and, hence, its cardioid pattern, can be adjusted across a broad bandwidth using tunable lumped reactive elements.

A 2-D TEM-wave-fed modulated reactance surface on a grounded dielectric substrate for leaky-wave antenna application is presented. TM-polarized leaky-wave radiation is excited by the TEM parallel-plate waveguide mode. Complete tangential fields over the aperture are built and optimized to satisfy the power conservation condition to find all-reactive surface characterization. A 10-wavelength-long uniform aperture for broadside scan is provided as a numerical example and verified by full-wave simulation.

A well-known issue related to sparse or clustered phased array is the rise of grating lobes (GLs) when scanning away from the broadside direction. In this work, a novel methodology to address the issue of reducing these grating lobes through the use of a Huygens’ type meta-surface (MTS) placed above the phased array is proposed. The meta-surface elements are designed in such a way as to locally compensate the phase difference between the field radiated by the array and an ideal linear phase front for a pre-determined pointing direction of the array, while maximizing the magnitude of their transmission coefficient in order to minimize the insertion loss of the meta-surface.

While topological properties of electromagnetic waves are commonly associated with photonic (i.e. periodic) structures, it has been recently demonstrated that even continuous media such as magnetized plasmas can support topologically protected one-way edge states. We demonstrate that, under some circumstances, such waves can be damped even without any dissipation, i.e. for a purely Hermitian permittivity tensor. Such damping is attributed to localized resonances in the inhomogeneous transition region between topologically trivial and nontrivial domains. Despite such damping, backscattering remains suppressed owing to topological protection as shown in the figure above, where surface waves are propagating around a sharp corner. More complex magnetic field geometries, such as helically-winding field lines, will also be discussed.

Bi-anisotropic metawaveguides (BMW) are a versatile platform for realizing quantum Hall, quantum spin Hall and quantum valley Hall effects for electromagnetic waves. We utilize these photonic topological insulators (PTI) to realize a chaotic graph system whose statistical properties fall into the universality class of the Gaussian symplectic ensemble (GSE). The bonds of the graph are built with spin-momentum locked edge modes between quantum spin Hall (QSH) and quantum valley Hall (QVH) PTI BMW media. The built-in two fold degeneracy and time-reversal invariance make QSH/QVH PTI systems a good platform to simulate the symplectic ensemble, which should describe time-reversal invariant spin-1/2 complex (wave chaotic) systems. Numerical simulations of the graphs show Kramers degeneracies of the modes and the spectral level spacing distribution is found to be in agreement with the GSE predictions. An experimental realization of the QSH/QVH tetrahedral graphs is fabricated, operating at 24.5 GHz. To reveal the Kramers degeneracies of the realized graph, it is cooled to cryogenic temperatures while monitoring the complex Wigner time delay of the structure. The statistical properties of the realized graph will also be presented.

We study the signatures of topological light confinement in the leakage radiation of two-dimensional topological photonic crystal cavities that feature the quantum spin Hall effect at telecom wavelengths. We examine the scaling behavior of mode spectra, observe band-inversion-induced confinement, and demonstrate hallmarks of topological protection in the loss rates.

Metamaterials with topological order uncover a broad range of promising tools for backscattering immune propagation and robust localization of waves of any nature. The description of such structures is based on the symmetry analysis of Bloch modes, which requires either a thorough analytical study or multiple numerical simulations, which is especially cumbersome when studying topological transitions. Here, we propose an alternative strategy to detect the topological transitions by inspecting the effective material parameters behavior of photonic subwavelength structures.

Thanks to an optimized nanostructures arrangement, we report on temperature increase of more than 250°C by impinging a plasmonic device with a 532 nm laser beam. This significant temperature value is due to strong confinement of electric field enabled by covering gold nano heaters with a layer of polymer + dye. A chopper-modulated impinging wave adds a new control mechanism enabling a fine control of the thermal response. In this configuration, the proposed device reveals a maximum temperature variation of 60°C in a period (10Hz frequency). This feature can be exploited in the design of novel systems for application in nano medicine and nano chemistry.

We present a method for realizing polarizing gap plasmon metasurfaces operating in reflection at near-IR and mid-IR via direct laser structuring, i.e., highly-ordered laser induced periodic surface structures on nanometer-thick metallic films. The approach produces metasurfaces with very well-defined, tunable resonances and polarization sensitive resonant absorption response.

We present our recent advances in the theory Plasmonic Parametric Resonances (PPR) in nanoparticles and extended structures supporting propagating modes. PPR originates from a temporal modulation of the dielectric properties of the medium adjacent to a metallic surface. The rich dynamics of these physical systems can lead an efficient energy injection into the surface plasmonic modes supported by the metallic regions. When the permittivity modulation is induced by a pump field exceeding a certain threshold intensity, such field undergoes a reverse saturable absorption process which suggests the viability of these effects for optical limiting applications.

Gap-plasmon metasurface absorbers can efficiently generate energetic hot electrons owing to their ability to squeeze and enhance electromagnetic fields in confined subwavelength spaces. However, it is very challenging to fully comprehend and quantify the dynamics of hot carriers in these emerging plasmonic configurations, mainly due to their ultrafast time decay. Their non-equilibrium temperature response is one of the key factors missing to understand their short time decay and ultrafast tunable absorption performance. In addition, although the dynamics of hot electron relaxation processes have been extensively studied for extended metallic surfaces, very little is known about these processes in plasmonic nanoscale systems. In our talk, we will present the temperature dynamics of hot electrons and their transition into thermal carriers at various timescales from femto to nanoseconds by using the two-temperature model, which will be applied for the first time in the gap-plasmon metasurface nanoconfiguration. Additionally, the hot electron temperature and generation rate threshold values will be investigated by using the hydrodynamic nonlocal model that is more accurate when ultrathin nanogaps are considered. The derived temperature dependent permittivity of the used metals will be used to demonstrate the ultrafast transient nonlinear modification of the presented plasmonic metasurfaces making their absorption spectrum tunable in the femtosecond timescale before plasmon-induced lattice heating is established in picoseconds. The derived ultrafast transient change in absorption can be useful in the emerging field of time-variant nanophotonics. Finally, we will examine the damage threshold of these plasmonic absorbers under various pulsed laser illuminations, an important quantity to derive the ultimate input intensity limit that can be used in various emerging tunable and nonlinear optics applications. Our work elucidates for the first time the role of hot electron generation and temperature dynamics in the ultrafast tunable response of gap-plasmon plasmonic absorbers that can be used to improve the performance of a plethora of emerging applications, such as photocatalysis, photovoltaics, nonlinear optics, and photodetection.

Using realistic classical models of microscopic Amperian electric and magnetic dipoles, it is proven that the Einstein-Laub macroscopic electromagnetic force on a volume of dipolar material, and the Abraham macroscopic electromagnetic-field momentum in that volume correctly equals the sum of the microscopic electromagnetic forces on the discrete dipoles and the total microscopic electromagnetic-field momentum, respectively, in that volume.

The rest-frame electrodynamics of slowly rotating metamaterials is explored using the framework of polarizability theory and discrete-dipole approximation, developed to hold in the rotating structure frame of reference. A new class of rotation-sensitive metamaterials is defined and discussed. In contrast to the usual perception of a metamaterial as a structure whose electromagnetic measures of interest are related to spatially averaged or collective observations, we suggest new measures for rotation sensitivity that focus on selective inclusions or meta-atoms response. Multiple scattering supported by metamaterials play a pivotal role in establishing the materials rotation sensitivity. These new materials can be used as rotation sensors that may outperform the conventional Sagnac loop gyros. Thus, while multiple scattering effects usually hamper the Sagnac loop sensitivity, here they may suggest performance enhancement.

One of the most fascinating phenomena in general relativity is the black hole, and the associated Hawking radiation, which predicts that escape from the hole can be possible for relativistic particles under certain conditions. This phenomenon has been recently highlighted by a quantum condensed matter analogue, using a microscopic lattice model of a Weyl semimetal with tilted nodes. Here, we are motivated to imitate black hole Hawking radiation in a purely classical-mechanical system. We propose a coupled double chain model featuring frequency dispersion that coincides with the tilted Weyl semimetal band structure near the vertices. The resulting directional inter-site couplings can be realized by an active mechanical metamaterial with an underlying programmable feedback network.

In this work, we design a new negative Poisson's ratio mechanical metamaterial based on the deformation characteristics of traditional materials and optimize its structure to enhance its mechanical properties. This work can provide a reference for the design and engineering applications of negative Poisson's ratio mechanical metamaterials.

We demonstrate that in-gap topological boundary modes can become fully extended by the inclusion of non-Hermiticity in the form of non-reciprocity. These extended modes occupy the entire bulk lattice. Moreover, by introducing a non-uniform distribution of non-Hermiticity, the topological modes can even be shaped into a wide variety of forms. The effects are realized in both one-dimensional (1D) and two-dimensional (2D) topological mechanical lattices with active components.

It is known that waves can undergo negative refraction. However, negative refraction systems known to date are symmetric, since they cannot distinguish between positive and negative angles of incidence. Exploiting a metamaterial with a 2d-chiral unit cell, we demonstrate that such symmetry can be broken. Our study specialized upon a mechanical metamaterial operating at GHz frequency; however, the phenomenon is based on general wave theory concepts, and it can be exported to any frequency and wavelength scale for any kind of linear waves.

We present a broadband multiresonant graded meta structure for piezoelectric energy harvesting at low-frequency vibrations <100 Hz. The device combines a graded metamaterial with beam-like resonators, piezoelectric patches and a self-powered, switch-less interface circuit with rectifiers. Furthermore, we actively cancel boundary reflections occurring at the ends of the graded meta structure to better analyze the modulation of the propagating wavefield within the structure.

In recent years, novel research areas have been developed in the field of photonics: metamaterials and nanoplasmonics. By utilizing the ideas developed in these research areas and using specially-designed materials, unusual electromagnetic properties such as artificial magnetism, negative refractive index, cloaking and squeezing photons through subwavelength holes have been demonstrated. These novel fields need new material fabrication techniques, especially bottom-up approaches such as self-organization. Two novel bottom-up manufacturing methods will be presented: (i) method based on directionally-grown self-organized eutectic structures [1]; and (ii) NanoParticles Direct Doping method (NPDD) [2, 3, 4] based on directional solidification of dielectric matrices doped with various nanoparticles. In both of these methods we can easily use all available resonant phenomena to develop materials with unusual electromagnetic properties. Eutectic composites are simultaneously monolithic and multiphase materials forming self-organized micro/nanostructures, which enable: (i) the use of various component materials including oxides, semiconductors, metals, (ii) the generation of a gallery of geometrical motifs and (iii) control of the size of the structuring, often from the micro- to nanoregimes. On the other hand, the novel method of NanoParticles Direct Doping enables doping of dielectric matrices with various nanoparticles (varying chemical composition, size and shape) and with the possibility of co-doping with other chemical agents as eg. optically active rare earth ions or quantum dots. In both cases we apply one of the crystal growth methods - the micro-pulling down method - to create the material. Utilizing described above methods we demonstrated (i) volumetric material with localized surface plasmon resonance tunable at visible wavelengths [5, 6]; (ii) enhanced linear and non-linear optical processes in the material exhibiting LSPR and co-doped with erbium ions [7]; (iii) volumetric matrix-nanoparticles-based materials with plasmonic resonances at visible and IR wavelengths based on silver (Ag) [1], antimony-tin-oxide (ATO) and titanium nitride nanoparticles (TiN); (iv) matrix-nanoparticles-based composite with enhanced photoluminescence at the telecommunication frequency of 1.5 µm; (v) material with subwavelength transmission at IR frequencies [8]; (vi) material with anomalous transmission [9]; (vii) bulk SERS materials [10], (viii) materials with enhanced Faraday effect; and (ix) materials for phonoanodes in photoelectrochemical cells for generation of hydrogen [11, 12]. New achievements in this field will be discussed.

We demonstrate optically tunable control of nonlinear metasurfaces: the control pulse photoinjects free carriers in the nanostructure, which in turn induce dramatic permittivity changes at the band edge of the semiconductor. Our results can lead to the development of ultrafast, all optically reconfigurable, nonlinear nanophotonic devices for a broad class of telecom and sensing applications.

Near-infrared to ultraviolet wavelength conversion can be achieved in a chalcogenide-based metasurfaces: the combination of high-field localization and phase-locking allows one to circumvent the high absorption typical of the ultra-violet frequency range. We investigate nonlinear third-order processes triggered in the near-infrared by the excitation of quasi-bound states in the continuum, and investigate them when the metasurface is illuminated by TM- and TE-polarized light. Our findings suggest that the resonance quality factor is not necessarily a good predictor of nonlinear processes’ efficiencies.

Modern photonic devices rely on nonlinear optical effects to carry out their functionalities. Yet, the realization of efficient nanoscale nonlinear optical components remains a chimera. In this talk, we explore three strategies based on the exploitation of plasmonic systems that might allow to overcome the main challenges and pave the way for all-optical integrated circuits.

We investigate a perovskite semiconductor cavity where a highly nonlinear coupling of orthogonally-polarized modes enables the realization of spin multistability and polarization switching. In the bistable regime, we discover a breaking of detailed balance: the path and time the system takes to spontaneously switch from one state to another is direction dependent.

In the field of acoustic wave, frequency conversion has technical limits that the nonlinearity of a general medium is not large enough and the generation of undesired frequency components are unavoidable. In this study, we propose a metamaterial-based frequency converter that can overcome the technical limits in acoustic frequency conversion.

The contacts of conductors with rough surfaces and random distributions of asperity heights and sizes of the contact areas are studied. The self-consistent analysis of the contact junctions is performed for arbitrary waveforms and packets of harmonic signals.

Topological band theory has guided findings and analysis of various robust crystalline wave platforms. However, amorphism, in the form of nonlocal structural disorder, falls beyond the framework of Bloch theory. Here, we explore the interplay between amorphism and Floquet topological networks. We demonstrate that the anomalous phase can persist at any level of amorphism. The Chern phase, on the other hand, undergoes a trivial Anderson localization at small levels of unstructured disorder, just like topological trivial insulating networks. This confirms the superior robustness of the anomalous phase even in amorphous settings.

Higher-order topological insulators have recently emerged as an important topic of topological phenomena in condensed matter, photonics, acoustics, and cold atom lattices. Here, we propose a photonic lattice comprising waveguides with degenerate orbital modes which hosts unusual higher-order topology, and describe a higher-order Fu-Kane orbital pump based on it.
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See arxiv preprint https://arxiv.org/abs/2111.01224.

 

We introduce and provide recent results on several topological structures in electromagnetics and acoustics. Beginning with a discussion of numerical techniques which we have provided to the public for analyzing the structures in inverse space and real space, we illustrate several approaches for identifying interesting properties of periodic structures and defects. This has led us to understand how topological effects such as spin-momentum locking can be seen in structures that would appear to be trivial, how their non-trivial nature can be exposed, and specifically how to use this understanding to create protected interface states. Examples of such structures have been developed in both photonic and phononic domains. Originally assumed to be a limiting case of valley type structures, we now understand their true nature in terms of symmetry indicators. We will show recent 2D implementations, as well as current work on 3D versions in the form of screw discontinuities in hexagonal close packed or diamond type lattices. It is also possible to create terminal interface states by adiabatic transformations which we call Vernier or zipper type structures, which have important applications for topological laser cavities in the optical regime, and efficient interfaces between conventional and topological waveguides in the RF regime. By introducing nonlinearity, we can also create self-induced bandgaps for mitigating effects of high-power signals. Finally, we will discuss recent work on topological plasma structures including measured results demonstrating nonreciprocal behavior.

Here, inspired by the response of standard MOSFET transistors, we propose a new mechanism to obtain a nonreciprocal and non-Hermitian electromagnetic response based on the interplay of material nonlinearities and a static electric bias. It is found that the linearized response is nonreciprocal, and most strikingly, it is either ”gainy” or ”lossy” depending on the relative phase of the electric field components. We present a simple design for a magnetless electromagnetic isolator relying on an idealized “MOSFET-metamaterial”.

We analyze the guided waves on cylindrical metasurface magnetized perpendicular to the cylinder axis. The magnetic bias yields dependence of the surface conductivity on the angle φ. Using an analytical model, and full-wave simulations, we show this structural asymmetry, combined with magnetization induced nonreciprocity, yields modes which dominantly propagate on opposite sides of the cylinder depending on their propagation direction.

We study the physics of wave propagation in non-reciprocal scattering networks, namely artificial wave media composed of multi-port non-reciprocal scatterers connected by transmission lines. We show that these systems can be described either by regular-3 reciprocal graphs, or by oriented Eulerian graphs. From graph theory, we can understand the occurrence of an anomalous topological phase, different from the usual Chern phase found in 2D topological insulators, with one-way edge modes in each band gap. We will survey the anomalous physics of these edge states in periodic and aperiodic, Hermitian and non-Hermitian, planar and non-planar networks. We will show that these anomalous edge modes survive any level of scattering, phase, and structural planar disorder, and present microwave experiments to confirm our findings.

We will review recent advances in the design and application of atomically thin polaritonic materials, including nonlinear effects, novel methods for in/out-coupling to light, and quantum aspects such as the realization of a new class of quantum-phase materials.

On-chip integration of semiconductor light sources would benefit from near-field handling of the emission with a subwavelength spatial resolution. Here we present a fully near-field photoluminescence study of semiconductor light sources, with a surface plasmon interference device used for the excitation and scanning near-field optical microscopy for the collection.

Babinet’s principle is not valid in general for plasmonic complementary metasurfaces because metals are not good conductors and sample thicknesses are not negligible respect to other tiny details of the unit cell. Nevertheless, we demonstrate that it is possible to recover its validity under a suitable election of materials and sample thickness. Namely, we show numerical results for several complementary designs made of silicon and silver for which the validity of Babinet’s principle in infrared is only confirmed when the thickness is about 13 nm.

Two different routes for realizing spatiotemporal optical metasurfaces that would enable manipulating optical fields with ultrahigh spatial and ultrafast temporal control with external stimuli are discussed using our recent advances in this area. The considered configurations represent electrically controlled optical metasurfaces operating in reflection, with the applied voltage influencing either the gap between a piezoelectric MEMS mirror and an optical metasurface or the refractive index of a thin electro-optic crystal layer sandwiched between nanostructured electrodes. Experimental demonstrations of dynamic beam focusing and complete control of the state of reflected light polarization are reported.

Plasmons in nanostructures offer extraordinary properties. To take advantage of them, it is crucial to identify them among all absorption modes of structure. To that end, we propose the energy-based plasmonicity index (EPI) to quantify previously unattended characteristics of plasmonic response.

Nanophotonic design principles can enable self-stabilizing optical manipulation, levitation and propulsion of ultralight macroscopic-sized (i.e., mm, cm, or even meter-scale) metasurface ‘lightsails’ via radiation pressure from a high power density pump laser source. Here we examine stringent criteria for the lightsail materials design, thermal management, and dynamical stability, and discuss lightsail design and first experimental steps in characterization of small (<1 mm) microscale lightsails.

Superlenses enable deeply subwavelength resolution imaging beyond the diffraction limit, yet their performance is fundamentally limited by material loss. We show that excitations at complex frequencies can address this challenge and experimentally demonstrate enhanced resolution in an acoustic metamaterial lens.

In this work we study electromagnetic properties of a resonator recently suggested for the search of axions – a hypothetical candidate to explain dark matter. A wire medium loaded resonator (called a plasma haloscope when used to search for dark matter) consists of a box filled with a dense array of parallel wires electrically connected to top and bottom walls. We show that the homogenization model of wire medium works for this resonator without mesoscopic corrections, and that the resonator quality Q at the frequency of our interest drops versus the growth of the resonator volume V until it is dominated by resistive losses in the wires. We find that even at room temperature metals like copper can give quality factors in the thousands, an order of magnitude higher than originally assumed. Our theoretical results for both loaded and unloaded resonator quality factors were confirmed by building an experimental prototype. We discuss ways to further improve WM loaded resonators.

Electro-optically tunable active metasurfaces that enable dynamic modulation of reflection amplitude, phase, and polarization using resonantly excited materials and phenomena are powerful design elements for meta-imaging and computation. We describe the role of such active metasurfaces as cascadable elements in lens-less and single-photon imaging systems.

We show that resonant gain-involving metamaterials can offer a novel path to chirality sensing, facilitating the detection of ultrathin layers of chiral substances and the discrimination of different enantiomers in circular dichroism measurements.

Bound states in the continuum (BICs) enable extreme wave-matter interaction, which can be utilized in many applications such as lasing, sensing and energy harvesting. One inherent problem of BICs is that they require large periodic structures and/or materials with exotic properties such as epsilon-near-zero materials. In this work, we realize a localized BIC supported in a single resonator, which is based on simple and abundant materials. The localized BIC is realized by imposing suitable boundary conditions around the resonator effectively achieved with a simple rectangular waveguide, and holds strong potential in sensing of small perturbations and impurities in tiny drops of water.

There are two kinds of exceptional points in waveguides, depending on the absence or presence of loss and gain. We discuss both kinds and how the coalescence parameter is used to measure the degree of degeneracy. We show applications like sensors, delay lines, distributed amplifiers, antennas, lasers, and oscillators.

Incandescent sources such as hot membranes and globars are widely used for mid-infrared spectroscopic applications. Their emission properties can be tailored by means of resonant meatsurfaces. Controlling the spectrum and directivity has been reported. Here, we will report recent advances demonstrating amplitude modulation faster than 10MHz and emission of circularly polarized radiation.

We demonstrate that layered strongly correlated materials can be tailored to sustain a wide spectrum of electronic heat transport regimes, from ballistic, to hydrodynamic and diffusive. The temperonic crystal, a metamaterial made of correlated materials working in the hydrodynamic regime, is introduced to control the wave-like thermal transport.

Metamaterials with temporal modulation of constitutive parameters have recently emerged in the scientific spotlight, featuring the novel concept of temporal boundaries. That idea was recently expanded to case of dispersive temporal boundary, Although changing only one constitutive parameter. Here, we study the case in which the temporal boundary drives both constitutive parameters from dispersionless to a dispersive state. We demonstrate the simultaneous generation of waves propagating in two different dynamical regimes, double-negative and double-positive.

<p> We present two methods for cloaking objects from thermal measurements that use active sources instead of metamaterials. One method deals with the parabolic heat equation [1], in which case active sources need to completely surround the object to cloak or mimic. Another method [2], for which the sources do not completely surround the object to cloak, relies on the frequency domain formulation of the heat equation as a Helmholtz equation with complex wave numbers. This second method extends the active exterior cloaking for waves modelled with the Helmholtz equation in [3] from positive wavenumbers to complex ones [2]. We point out the second method can be applied to waves in dispersive media.</p>

Embedded eigenstates are non-radiating eigenmodes sustained by open structures and compatible to radiation in terms of their momentum. This phenomenon allows several interesting applications, including sensing, filtering, field confinement and lasing. This response has been studied in quantum, electromagnetic, optics and photonics. However, few investigations have been made on the possibility of realizing embedded eigenstates in acoustics. In this paper, we discuss the generation of embedded acoustic eigenstates in Fabry-Perot metasurface-based structures. The effect is verified both theoretically and numerically using two arrays of Helmholtz metasurfaces with optimized separation distance.

We introduce an efficient way of the modal selection in acoustic cavities by means of a resistive wiremesh. We study the behaviour of the complex eigenfrequencies with the variation of the wiremesh impedance and position. We obtain the conditions of the optimal selection of the desired modes and absorption of the undesired ones.

We theoretically predict and experimentally demonstrate near-infrared to ultraviolet frequency conversion of conventional light beams and optical knots in nonlinear optical metasurfaces, enabled by a phase-locking mechanism between the pump and the inhomogeneous portion of the third harmonic signal.

We demonstrate enhanced visible sum-frequency generation in doubly resonant GaP metasurfaces. Record conversion efficiency is achieved in the metasurface by the excitation of high-Q waveguide-type bound state in the continuum resonances with non-trivial polarization dependence and diffraction order control.

We developed a simple yet effective approach to design and optimize the third-harmonic radiation of silicon metasurfaces combining a sampling method with Monte Carlo simulation. Our results demonstrate a significant enhancement of the radiated third-harmonic intensity of the metasurfaces compared to that reported in literature.

We will present optical properties of vaterite nanoparticles and discuss their appearance in a natural environment. We will show that the controllable infusion of gold nanoseeds into polycrystalline sub-micrometer vaterite spherulites gives rise to a variety of electric and magnetic Mie resonances, producing a tuneable mesoscopic optical metamaterial - “golden vaterite”. Optomechanical properties of vaterite particles in application to laser-driven drug delivery will be demonstrated.

Thermoacoustic amplifiers are analyzed in the framework of nonreciprocal Willis coupling. The closed form expressions of the effective properties are derived, showing that an applied temperature gradient causes nonreciprocal Willis coupling. A coalescence point in the k space and the opening of an amplification gap at low frequency are exhibited.

We study phononic states in networks of nanomechanical resonators coupled via temporally controlled radiation pressure. Inducing particle-non-conserving squeezing interactions allows investigating the interplay between broken time-reversal symmetry and controlled non-Hermitian dynamics. We report tuning of higher-order exceptional points through geometrical phases, chiral phononic amplification, flux-dependent cooling, and phase-sensitive nonreciprocity.

Temporal symmetries and energy are deeply related concepts. Within this context, this talk discusses some intriguing opportunities (and limitations) at the intersection of nonreciprocal/time-varying metamaterials, thermal photonics, and energy-related applications, from enhanced absorption/emission and zero-point-energy effects in time-varying dispersive materials, to violations of Kirchhoff’s thermal radiation law in current-biased media.

We observe experimentally in a one-dimensional phononic lattice two wave phenomena associated with time-varying material properties. For harmonic modulation of elastic properties, we demonstrate the opening of a wavenumber band gap. For a Heaviside-like modulation, we demonstrate the 'temporal refraction' of waves incident on the temporal boundary.

This paper addresses the problem of wave scattering at a moving interface formed by a space-time modulation step. Specifically, it derives, using the technique of frame hopping with Lorentz transformation, the formula for the corresponding critical angle beyond which the transmitted field is evanescent. It shows that this angle is smaller (resp. larger) than 90 degrees (position of the interface) for a modulation that is codirectional (resp. contradirectional) to the direction of wave propagation, and that the critical angle versus the modulation velocity function monotonically decreases to zero at the velocity where the incident wave cannot catch up any more with the interface. The theory is illustrated and validated by full-wave FDTD simulation.

We propose and computationally investigate a metasurface with correlated positional disorder and covered with a conformal gradient-index structure for the purpose of light management in solar cells. When integrated into a prototypical Silicon solar cell, we observe a broadband reduction in reflection when compared to either high-index nanostructures without the gradient layers or an optimized conventional planar anti-reflective coating. We discuss this superior reflection-suppression in the long-wavelength using a helicity-preservation framework.

Photonic bound states in the continuum are spatially localised modes with infinitely long lifetimes that exist within a radiation continuum at discrete energy levels. These states have been explored in various systems where their emergence is either guaranteed by crystallographic symmetries or due to topological protection. Their appearance at desired energy levels is, however, usually accompanied by non-BIC resonances, from which they cannot be disentangled. Here, we propose a new generic mechanism in a double-plasma to realize bound states in the continuum that are induced by first principles, free of other resonances, and robust upon parameter tuning.

We discuss the analytical and computational issues associated with the automatic design of metasurfaces, which we call here “machine design”. The core of the talk will be a formulation to effect the design using only the (equivalent) currents, yet enforcing passivity, losslessness and realizability constraints along with radiated field mask requirements.

Epsilon-near-zero (ENZ) materials have attracted attention for more than a decade. With a lot of advances in their functionalization it also has come an understanding that most of such natural materials exhibit high intrinsic losses at optical frequencies. Therefore, as an alternative, index-near-zero (INZ) materials are currently being investigated. The use of nanostructured dielectric materials with specific mode profiles, which effectively provides very small modal indices, is considered a potential solution. We report on such system, which has been designed, fabricated and characterized recently. Quasi-bound states in the continuum are involved to minimize the radiative losses of INZ modes.

Metal-Insulator-Metal nanocavities sustain Epsilon-Near-Zero resonances with tunable wavelength via the thickness of the dielectric layer, and their resonant modes can be matched with the absorption and emission bands of light emitting nanocrystals. We discuss the implementation of such metamaterial photonic cavities in light-emitting devices such as perovskite LEDs.

Recent research has numerically shown the possibility of manipulating the elastic properties of wood plates through periodic hole patterns. In this work we focus on experimentally testing these results, changing the stiffness and density of Spruce Engelmann plates, a traditional wood for guitar soundboards.

In this paper some methods to achieve antenna beamforming with metasurfaces are described. Both transmissive and reflective metasurfaces are presented that synthesize the aperture fields by exciting auxiliary evanescent fields. The capabilities of metasurfaces to precisely control the far-field radiation pattern are demonstrated through various design examples and full-wave simulations.

We propose a pillbox antenna in combination with a geodesic lens at 60 GHz. The antenna is implemented in a dual-layer parallel plate waveguide. The waves from a geodesic lens in a first layer, after being reflected by a parabolic mirror connecting the rims of the two layers, enter a second layer and illuminate the radiation aperture. Since the lens produces a virtual focus, the reflector works as if it is fed from that a further location, making the system more compact.

Analysis of the energy transfer between two dipoles near a conductive plane in the microwave range as an analogy of the Forster Resonant Energy Transfer (FRET) between two quantum emitters in the optic. The ways to control it by shaping the environment to the desired effects

In this contribution, we investigate the angular response of planar deflecting metasurfaces and show that the angular stability of their meta-atoms does not allow to engineering the lens behavior vs. the illumination angle. Then, we show how the metasurface geometry can be exploited as an additional degree of freedom to enhance its overall spatial dispersion and obtain different response with the impinging angle. A relevant example, involving the use of the deflecting lens for phased antenna arrays is also discussed.

In this paper, we focus on the alignment of the dielectric and plasmonic resonances of VO2 nanostructures at near-infrared wavelengths. Such resonance alignment, which can be applied to a tunable perfect absorbing grating, is demonstrated on an array of VO2 nanostructures.

Topological phases of matter, despite their abstract origins, have led to a plethora of promising applications from waveguiding over lasing to antennas and beyond. Here, we show that in a diatomic chain of electromagnetic resonators that is host to topological edge states, wireless links may be established by coupling these. They significantly outperform the conventional, monoatomic chains when it comes to signal power and offer robustness against perturbations due to topological protection. These results may be of use in applications where signal power is of concern, such as underground or underwater links.

We experimentally demonstrate that a magnetic uniaxial wire medium lens formed by a racemic periodic array of helical-shaped metallic wires behaves as the magnetic dual of the standard wire medium configuration formed by a set of parallel straight metallic wires, enabling the channeling of the subwavelength details of the magnetic field of near-field sources. The experimental results are validated by numerical simulations.

Being able to understand how optical forces emerge from the interaction of light with matter is paramount for controlling the motion of nanoparticles as well as powering nanomotors. The purpose of this work is to uncover the physical mechanisms at the origin of these forces and show how they can be engineered. We demonstrate that the interplay between symmetric and asymmetric multipolar modes in a Kerker-like fashion is responsible for asymmetric scattering, which results in a time-average non-zero optical force and possibly optical torque.

We present our recent theoretical and experimental studies for controlling topological properties of photonic crystals by loading functional materials. The first example is GST-loaded Si photonic crystals, in which we aim for the photonic topological phase transition by the phase change of GST. The second example is graphene-loaded Si photonic crystals, in which we control topological chiral properties, including an interplay of exceptional points and polarization singular points, by manipulating non-Hermitian properties.

We study an elastic continuous half-plane endowed with distributed gyricity, which is capable of breaking the reciprocity of wave propagation. First, we determine analytically the dispersion properties of the system, and we observe a clear non-symmetry in the eigensolutions for positive and negative values of the wavenumber. Successively, we demonstrate the non-reciprocal behaviour of the gyroscopic continuum by performing an independent finite element computation, which shows a non-symmetric response of the medium to an external excitation. The results of this work can be employed in the design of mechanical splitters, that can channel wave propagation into predefined directions.

We demonstrate a multi-functions meta-device for imaging and all light level depth-sensing. A combined light field imaging and structured light system based on meta-lens array is developed with the support of deep learning.

We demonstrated an orbital angular momentum (OAM) microlaser that structures and twists the lasing radiation at the microscale, which can provide an additional OAM-based information dimension to meet the growing demand for information capacity. By harnessing the synergy of total momentum conservation, spin-orbit interaction, and transient optical gain dynamics, we have further achieved ultrafast reconfigurable chiral light emission with the desired topological charge at a single telecom wavelength.

In this talk we will review our recent results on surface waves on time-varying boundaries. We consider boundaries with spatially uniform but time-modulated macroscopic reactive surface impedance. Analytical results and numerical simulations reveal possibilities to amplify surface waves, nearly stop their propagation, convert them to waves propagating in space, and other interesting effects. First experimental results confirm the amplification effect.

Here, we show that spacetime modulations provide an exciting route to realize the elusive Tellegen medium response. We describe an analytical formalism to homogenize anisotropic spacetime crystals in the long wavelength limit. It is found that spacetime crystals with suitable symmetry can have a giant Tellegen-type response. The nonreciprocal Tellegen response enables not only interesting applications, such as unidirectional transmission and electromagnetic isolation, but also to probe exciting new forms of light-wave interactions.

We explore a class of temporal metamaterials characterized by a time-varying dielectric permittivity waveform of duration much smaller than the characteristic wave-dynamical timescale. For these {em short-pulsed} metamaterials (SPMs), we study the interaction with an electromagnetic wavepacket, and we identify intriguing configurations for which analog-computing functionalities (first and second derivatives) can be attained. Our proposed SPMs can be viewed as the temporal counterpart of spatial metasurfaces and may open up new perspectives within the framework of space-time metastructures.

Structures which appear to move at or near the velocity of light contain singular points. Energy generated by the motion accumulates at these points into ever-narrowing peaks. In this paper we show that energy is generated by a curious process that conserves the number of photons, adding energy by forcing photons already present to climb a ladder of increasing frequency. We present both a classical proof based on conservation of lines of force, and a more formal QED proof demonstrating the absence of unpaired creation and annihilation operators. Exceptions to this rule are found when negative frequencies make an appearance Finally we make a connection to laboratory-based models of black holes and Hawking radiation.

In this work we will discuss our recent and ongoing efforts in exploiting time-dependent media using rapid changes of permittivity and/or permeability to induce temporal boundaries that lead to spatial boundaries. We will show how such temporal boundaries can be exploited to create a spatiotemporal boundary. It will be discussed how this mechanism may enable a feature that we call spatiotemporal focusing of the wave propagating within such medium.

A model for a deep-subwavelength direction-of-arrival (DoA) sensor with enhanced performance and sensitivity is developed, by incorporating time-modulation into the sensing system. Using an analytical model and equivalent circuit models, we analyze and discuss the physical mechanisms responsible for the enhancement. We show that time-modulation allows us to flexibly control the response of our system and accomodate to variations in the incident frequency. This new degree of control lets us incorporate the currents from higher generated harmonics into the sensing scheme, to extract more accurate information about the impinging wave.

In this talk we report on recent theoretical explorations in the context of time-varying media, aiming at offering a few perspectives on the peculiarities and symmetries inherent to wave scattering from abrupt, continuous, periodic, chiral and dispersive temporal inhomogeneities, as well as their implications for distinct forms of wave amplification, localization, nonreciprocity, frequency modulation and harmonic generation. Finally, we will showcase recent experimental advances on frequency generation and shifting in time-modulated indium tin oxide experiments.

We present our detailed analysis for the impulse response of the dielectric polarization in linear time-varying (LTV) media, providing a path for a generalization of the Kramers-Kronig relations for such LTV platforms.

We describe a thermal metasurface platform that combines local and nonlocal scattering to achieve complete control over the wavefront of thermal emitted light.

Nonlinear holograms can be realized by spatially modulating the nonlinear coefficient of ferroelectric crystals. These holograms are already used in classical nonlinear optical processes, for shaping the spatial and spectral properties of the generated light. Here we extend the application of these devices to the quantum optics regime, in order to shape the correlations between signal and idler photons in spontaneous parametric down-conversion.

In this talk we will present results of experimental characterization of anomalous reflectors of two types: conventional phase-gradient metasurface and non-local metasurface. Measured results are compared with analytical and numerical models.

In this work, we demonstrate in a proof of concept experiment the ef f icient noi se absorption of a 3-D printed panel designed with appropriately arranged space-coiling labyrinthine acoustic elementary cells. The labyrinthine units are numerically simulated to determine their dispersion characteristics and then experimentally tested in an impedance to verify the dependence of absorption characteristics on cell thickness and lateral size. The resonance frequency is found to scale close to linearly with respect to both thickness and lateral size in the considered range, enabling tunability of the working frequency. Using these data, a flat panel is designed and fabricated by arranging cells of different dimensions in a quasi - periodic lattice, exploiting the acoustic “rainbow” effect, i.e. superimposing the frequency response of the different cells to generate a wider absorption spectrum, covering the required frequency range between 800 and 1200 Hz. The panel is thinner and more lightweight compared to other sound absorber solutions, and designed in modular form so as to be applicable to different geometries. The performance of the panel is experimentally validated in a small -scale reverberation room, and an absorption close to ideal values is demonstrated at the desired frequency of operation. Thus, this work suggests a design procedure for noise-mitigation panel solutions and provides experimental proof of the versatility and effectiveness of labyrinthine metamaterials for tunable medium- to low-frequency sound attenuation.

In this presentation, I firstly show the intrinsic natures and advantages of the information metasurfaces, including the reprogrammable and real-time control capabilities of EM waves and information operations. Then I introduce the recent advances in combining the information metasurfaces and AI technologies, which generates the intelligent metasurfaces. I will present the AI-based intelligent imagers, microwave camera, and programmable AI machine based on multi-layer information metasurfaces and optical neural networks.

In this contribution, we explore the possibility of tailoring the response of a reflective metasurface (MTS) according to the composite vortex theory, i.e. the judicious superposition of different vortex modes. An analytical analysis of the problem is reported and the results for an example of practical interest are discussed. The proposed approach could find application in the design of Reflective Intelligent Surfaces (RIS) and, thus, in the implementation of a smart electromagnetic environment.

<p> Abstract – We report the design of space-time reflective metasurfaces composed by an alignment of elements that can exhibit an In-phase (I) and Quadrature (Q) reflective response. Space-/frequency-domain manipulations of the reflected field can be achieved by properly designing the dimension of the I-/Q-areas and their time sequence across the metasurface. For example, we demonstrate that the positive first-order harmonic of the reflected field can be shifted in frequency, but maintained fixed in propagating direction, while, in other directions, the negative first-order harmonic can be easily controlled by changing the dimension of I-/Q-elements. Reducing the dimension of I-/Q-areas, the first order harmonic can be used for beam scanning by pre-designing the start time of the modulation element. We report the comparison between our analytical and numerical results, demonstrating that space and frequency domain manipulations of the reflected fields can be simultaneously obtained. The proposed metasurface has potential applications in wireless communications, radar camouflaging, and cloaking.</p>

Electromagnetic metamaterials have realized exotic effects which are challenging to achieve with other approaches. Although novel electromagnetic responses have been made, the conventional forward design process is fundamentally limited, and therefore designs explored to date are limited. I will discuss how deep learning based inverse methods can overcome constraints of the current design approach, and will highlight their prospects for future novel applications.

Modulated metasurfaces (MTSs) can be efficiently used to guide the propagation of surface-wave (SW) wavefronts or to gradually radiate the power carried by a SW. These two complementary mechanisms can be applied, respectively, to design beam-formers and antennas capable of addressing some of the needs in emerging millimeter wave wireless and future networks beyond 5G. More precisely, we will present the use of modulated metasurfaces for the design of high-gain antennas and broadband beam-formers. We will also show how the later can be efficiently combined with the former to provide multi-beam operation.

In this paper, we build on EFIE direct inversion approach by adopting Gaussian Rings sub-domain basis functions to determine MTS antennas IBC for getting desired radiation. This choice allows for freedom to define problems on circular/annular domains, considerable spatial resolution and reduced computational burden in system matrices construction.

In this paper we present a novel approach for the design of a reflecting inhomogeneous lens; i.e. a lens which, in combination with a circular corner reflector, focuses a point source to the far field. This task is accomplished by using a congruence of circular ray paths; next, the phase tracing technique permits to retrieve the wavefronts and to numerically find the refractive index distribution inside the lens volume. In this particular case, the choice of circular ray path permits, by a uniformly distributed ray curvature, the minimization of the refractive index range variation inside the lens.

Metasurfaces (MTS) are thin layers of subwavelength elements which are employed to control the wavefront of guided waves and reflected waves and the transformation from surface wave (SW) to leaky waves (LWs). A class of MTSs is constituted by self-complementary MTS (SCMs), singlelayer metal patterns floating in free-space whose elemental cell remains invariant after complementary inversion except for a rotation of the elemental periodic cell in the MTS plane; here, “complementary inversion” means interchanging the metal pattern with the free space. The concept of SCM can be also extended to impenetrable type of boundary conditions, modifying the shape of the elements with the objective to maintain the basic properties of reflection/transmission and/or SW dispersion. The application of SCMs to antennas opens new possibilities, especially for microwave antennas in dual-polarization. In this talk, various examples will be presented, which include gaussian horns, surface-wave based antennas, flat reflectors, optical control of the reconfigurability, and propagation which is robust against backscattering. Particular attention will be given to anisotropic SCMs, which are constituted by a “self-dual” alternance of inductive and capacitive complementary strips. They support orthogonally polarized surface-wave modes with the same phase velocity in the principal direction of propagation. The isofrequency dispersion curves of these modes are hyperbolas, and therefore these SCMs belong to the category of hyperbolic MTSs. The hyperbolas may degenerate in same cases into almost straight lines, which implies that the velocity of energy transport is constantly directed along the complementary strips at any frequency and for any possible phasing orthogonal to the strips. In this circumstance, the SCM can be conveniently used to design dual-polarized leaky-wave antennas by modulating the impedances of the complementary strips. Each strip behaves as a channel, which can be independently fed with the desired phase and amplitude. We demonstrate here that these antennas exhibit a strong decoupling between both co-polar and cross-polar channels, even when the distance between strips is electrically small. This increases the performance of the antenna, especially in azimuthal beam scanning.

Topological phenomena in photonics and metamaterials have attracted considerable interest of pertinent communities because of fundamental interest and great potential for applications. However, most topological systems studied over the last decade have been linear. Here we present our recent theoretical and experimental results in nonlinear topological systems including nonlinear coupling to a topologically protected edge state, nonlinear tuning and control of parity-time symmetry and non-Hermitian topological states, nonlinear higher-order topological insulators, and emergent nonlinearity induced topological phase transitions.

I will present an overview of the work of my group on nonreciprocal and non-Hermitian photonics and present our vision of how an electric bias can be used to sculpt electromagnetic interactions and obtain strongly nonreciprocal and non-Hermitian material responses.

We study the phase transition of nodal lines in photonic crystals. Using a dielectric double diamond structure, we characterize the stability and instability of nodal lines using both non-Abelian charges and Euler classes. Then, we numerically investigate the topological phase transition of nodal lines by controlling structural perturbations.

Beyond the three generations of metamaterials, space-time metamaterials provide the important capability of dynamically manipulating the electromagnetic wave. By controlling the structure parameters, the metamaterial can exhibit non-reciprocity. Because multiple time-varying parameters are involved, characterization of the time-modulated metamaterial can be computationally challenging. In this paper, we propose a space-time modulated metamaterial waveguide that breaks the reciprocal transmission. Additionally, we use a deep neural network (DNN) to predict the scattering coefficients with a small error. The results show that DNN successfully predicts the forward and backward transmission with high accuracy.

We provide a theoretical description of light scattering by a spherical particle whose permittivity is modulated with twice the frequency of the incident light. Such a sphere acts as a finite-size photonic time crystal and permits optical parametric amplification. We show that the control of the temporal modulation strength provides a qualitatively new route to spectrally overlap different parametric Mie resonances in the sphere for controlling its far-field pattern and satisfying the Kerker scattering conditions.
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See arxiv preprint at https://arxiv.org/abs/2202.11138

Here we show that a time-varying capacitance can be in general used to mimic a static inductance, capacitance, or resistance having arbitrary values. Next, we analyze stability of a simple circuit that contains resistance and emulated negative capacitance. Finally, we show an application of our theory to metasurfaces.

Foster’s reactance theorem is one of the most important theorems of network analysis, dictating the analytical properties of impedance or admittance functions of passive, linear and time-invariant networks. Due to its generality, Foster’s reactance theorem is a starting point for deriving other fundamental results, like the Bode-Fano criterion. Here, we show how this fundamental result can be extended to time-modulated networks and discuss the conditions under which it can be broken.

This paper presents Generalized Space-Time Electromagnetic Metamaterials (GSTEMs), where ‘generalization’ refers to nonuniform-velocity (or accelerated) modulation, as the next potential frontier in metamaterials.

In this presentation, I will highlight recent efforts in our group for the use of nonlocal metasurface elements for optical imaging applications and electrically-tunable metasurfaces.

Optical metasurfaces, made of subwavelength arrangements of nanostructures, have relied on resonant phase scattering occurring in Mie resonators or ultrathin pillars. Symmetry-breaking arguments and topological properties of the associated non-Hermitian matrices representing the metasurfaces provide new guidelines for achieving 2π phase coverage in transmission and in reflection.

Programmable radio environments parametrized by reconfigurable intelligent surfaces (RISs) are emerging as a new wireless communications paradigm, but currently used channel models for the design and analysis of signal-processing algorithms cannot include fading in a manner that is faithful to the underlying wave physics. To overcome this roadblock, we introduce a physics-based end-to-end model of RIS-parametrized wireless channels with adjustable fading (coined PhysFad) which is based on a first-principles coupled-dipole formalism. PhysFad naturally incorporates the notions of space and causality, dispersion (i.e., frequency selectivity) and the intertwinement of each RIS element’s phase and amplitude response, as well as any arising mutual coupling effects including long-range mesoscopic correlations. PhysFad offers the to-date missing tuning knob for adjustable fading. We thoroughly characterize PhysFad and demonstrate its capabilities for a prototypical problem of RISenabled over-the-air channel equalization in rich-scattering wireless communications. We also share a user-friendly version of our code to help the community transition towards physics-based models with adjustable fading.

One-dimensional waves guided along the boundary between two complementary metasurfaces have been theoretically and experimentally demonstrated in microwaves. However, it is rather a challenging task to scale down the structures to made them work in mid-infrared because Babinet’s principle is usually violated. To circumvent this issue, we propose to use thin films of silicon and silver with thickness about 13 nm in which case the validity of Babinet’s principle is recovered.

In this work, we present several devices designed using narrow waveguides operating near cutoff and emulating an epsilon-near-zero metamaterial. The high electric field confinement inside the narrow channel is exploited to sense deeply subwavelength dielectric bodies inserted inside with transverse dimensions of just 0.04lambda0 and height 51030. The scope of ENZ metamaterials goes beyond sensing devices and can also serve to implement other devices such as graded-index metalenses operating at terahertz frequencies.

Metamaterials with near-zero values of permittivity, known as epsilon-near-zero (ENZ) media, enable promising applications in electromagnetic wave manipulation such as in sensing and lensing. However, ENZ media present a challenge in transmission due to impedance mismatch with other media. Here, we show how unidirectional transparency can be achieved using an ENZ medium emulated via a rectangular waveguide operating near the cutoff frequency of the dominant TE10 mode when combined with parity-time (PT) symmetry techniques. Theoretical studies based on transmission line theory, eigenvalue problems, and full-wave numerical simulations are performed, showing unidirectional transparency and ENZ behavior when working at the exceptional points (EPs).

Wireless power transfer, defined as the transmission of electromagnetic energy without the need of physical connectors, requires reliable and stable solutions for charging high-power devices such as electric vehicles while causing no danger to humans, animals, plants, and so on. We address this challenging problem and propose a unique technique based on the use of metamaterials with extreme parameters to enable targeted and protected wireless power transfer. We design epsilon-and-mu-near-zero (EMNZ) metasurfaces that transfer energy if and only if both the transmitter and receiver are equipped with them. This technology will be used in targeted wireless power transfer systems, particularly when high power is required, such as electric vehicles.

For too long the functionality of optical devices and systems has been severely restricted by the very limited range of refractive indices at the disposal of designers. A simple increase of the value of refractive index by 50% can result in disproportionally large improvement in performance. With that in mind, I explore what are the fundamental limits that limit the scope of refractive indices as a function of wavelength, explain why higher index materials have not yet materialized and point out a few tentative directions for the search of these elusive materials, be they natural or artificial.

Nonlinear and electro-optic devices are present in many applications: light sources for microsurgery, green laser pointers, or modulators for telecommunication. They usually use bulk materials such as glass fibres or high-quality crystals, difficult to integrate or scale up. Here we will present our recent advances on bottom-up photonic assemblies of randomly oriented nanocrystals and how we can produce electro-optic and nonlinear signals. First, barium titanate metalenses synthesized by a sol-gel technique will be demonstrated. Then, we will show how the electro-optic response in assembled nanostructures can be as strong as certain other perfect crystalline structure. Finally, we will describe the more fundamental aspect of random quasi phase matching at the nanoscale.

We demonstrate an electrically tunable, ultrafast, nonlinear, terahertz absorption modulator operating at 2.3 THz. The device consists of a uniform graphene sheet placed on a Au- grounded ionic liquid substrate. Nonlinear modulation is assessed via self-action when the THz field strength increases from 145 to 654 kV/cm

Sub-wavelength dielectric resonators can be designed to highly confine the incoming light fields in their interior, strongly amplifying intrinsic nonlinear responses. In this work, we propose the use of Gallium Phosphide nanostructures with high-Q and low-Q factor resonances for efficient frequency conversion and sub-100 fs all-optical switching, respectively.

This work presents a systematic study towards the demonstration of high-performance tungsten diselenide (WSe2) and molybdenum disulfide (MoS2) field-effect transistors (FET), by engineering the metal-semiconductor junction. We design the metallic electrode based on the work function difference between the metal and the semiconducting two-dimensional layer. Here we report high-quality ambipolar transfer characteristics in WSe2 FET using In/Au electrodes. The temperature dependence emphasizes less thermally activated behavior at high source-drain bias. Current-voltage characteristics of MoS2 based transistor with Cr/Au contacts show switching from Ohmic to Schottky type behavior at low temperature.

We demonstrate an electrical control of the propagation of guided exciton-polaritons, using a DC electric field. We observed an electrical controlled reflection and transmission of the polaritons in the waveguide. We exploit this technique to demonstrate a transistor-like behavior of the polaritons in the waveguide.

Molecular optomechanics seeks to leverage the mechanisms underlying surface enhanced Raman scattering (SERS) to realize the physics of cavity optomechanics, but with molecular vibrations at IR frequencies. I will discuss the efforts at AMOLF to realize sideband-resolved and waveguide-integrated molecular optomechanics.

Recent years have witnessed a lot of interest in time-varying media. They have provided an interesting platform to explore new physical concepts such as nonreciprocity, subluminal and superluminal phase velocity, high-frequency generation, to name a few. Here, we exploit time-varying dielectric media to convert electromagnetic pulses to uniform electrostatic field distributions. Specifically, we show how a dielectric block experiencing a temporal variation of its permittivity can trap an incoming electromagnetic pulse in the form of electrostatic energy. Numerical results of this new wave phenomenon based on the time-dependent platform are provided.

Recently, time-varying electromagnetic structures have been extensively investigated to unveil new physical phenomena. In this direction, one of the important and historical topics is studying temporal discontinuities in these structures. Here, we consider fast changes of bianisotropic media. Specifically, we focus on introducing a temporal interface between isotropic chiral and dielectric media. We show that due to the discontinuity in time, interestingly, a linearly polarized electromagnetic wave is decomposed into forward right-handed and forward left-handed circularly polarized waves having different angular frequencies and the same phase velocities. This salient effect allows splitting light to two different polarization states with high efficiency. Hopefully, our findings will be useful as a possibility to control polarization states of light.

Temporal metamaterials are attracting a huge interest from the scientific community, thanks to their capability to explore the temporal dimension together with the spatial one as a new degree of freedom for tailoring anomalous scattering process. In this contribution, we present and discuss our recent results on the achievement of temporal interface by modifying the boundary conditions of a parallel plate waveguide. The propagating wave perceives the sudden change of effective medium within the waveguide and an effective temporal interface is thus induced. We provide analysis of the scattering problem and give close form solutions for the frequency shifts, scattering coefficients and static field configuration, emerging from the interface.

It is highly desirable to break the diffraction limit on the resolution of optical devices and achieve subwavelength focusing. Despite numerous solutions that have been developed throughout the years, a practical method to obtain subwavelength focusing without the generation of undesired sidelobes is a challenge to this day. We have developed a feasible strategy to achieve this goal based on the concept of perfect lens.

We consider active metamaterials that mimic non-Hermitian quantum systems. Such systems are being extensively researched, focusing mainly on their topology and bulk-boundary effects. However, little attention is devoted to their dynamical stability properties, which are crucial for implementation. Here, we explore the stability of a simple, yet fundamental non-Hermitian system.

In this paper, it is shown that circularly polarized leaky-wave antennas based on a one-dimensionally modulated anisotropic impedance exhibit a complete suppression of the open-stopband when the beam is scanned through broadside, in contrast with what happens in an isotropic periodically modulated impedance surface. This general behaviour is illustrated here by using a homogenized penetrable impedance model to compute the leaky-wave dispersion. As a consequence, leaky-wave antennas based on modulated anisotropic metasurfaces are able to scan from backfire to endfire without any frequency region of high attenuation.

In recent years novel transparent conducting oxides have emerged as near-zero-index materials for photonic applications. In the near infrared spectral region, where this class of compounds has a real index approaching zero, optical nonlinearities have been proved to be exceptionally high and potentially disruptive for a broad plethora of applications. Giant nonlinear frequency conversion, unitary refractive index change, and bandwidth-large frequency carrier shift have been demonstrated by using optical pumping. However, despite these remarkable results, the perfect domain of application for zero-index optics is still unclear. Here we will discuss the most recent and relevant results involving low refractive index systems also trying to frame the best optical configuration to take full advantage from the slow-light properties of these materials.

We demonstrate numerically and experimentally that metallic films placed on top of epsilon-near-zero (ENZ) substrates become narrowband and efficient thermal emitters. Our experiments show that ENZ-based emitters feature a narrow linewidth whose frequency positioning is robust against variations in the geometry of the system and the observation angle.

We investigate two types of chiral meta-media: (i) combining optical activity with birefringence, leading to a new kind of Bragg-like reflection from a homogeneous medium, (ii) combining structural chirality with optical activity, leading to a ‘reverse’ circular Bragg phenomenon where light that is contra-handed to the medium is strongly reflected.

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This presentation will discuss advances and future prospects in manipulating light at the nanoscale using plasmonic nanoparticle lattices. These metasurfaces support hybrid resonances known as surface lattice resonances that show both light scattering and localization properties. First, we will describe the expanded scope of plasmonic lattices based on exquisite tuning of topological symmetries and surface engineering of the nanoparticles. Next, we will highlight how the nanoscale cavities combined with quantum emitters show unprecedented nano-lasing properties. Finally, we will discuss how this platform is opening new opportunities from ultra-long range and strong coupling to photoelectrocatalysis to auto-regulatory materials.

Dallenbach layer is composed of an electrically conducting magneto-dielectric substance backed by a perfect electric conductor sheet. For such linear time invariant layer, Rozanov has established a fundamental bound on the absorption efficacy over a predefined bandwidth given the thickness of the layer. This relation is inapplicable when the layer is composed of a magnetically conductive material. Here we generalize the bound for this case, and moreover explore theoretically and experimentally a practical metamaterial realization that gives rise to effective magnetic conductor behaviour and thus exceeds the Rozanov bound.

Current and next-generations of communication systems demand for high-data rates devices with enhanced coverage and compact dimensions. We present here a dual-polarized, differentially fed, metasurface leaky-wave antenna for dual-polarized and full-duplex applications. The design is based on a slotted substrate-integrated waveguide designed to excite two orthogonal polarizations and to provide differential feeding. The antenna is constituted by a partially reflective surface placed on the top of a dielectric substrate and it operates around 24 GHz, providing satisfactory impedance matching, isolation greater than 50 dB, and maximum realized gain of the order of 18 dBi.

Recent theoretical proposal of a self-oscillating single-loop non-Foster antenna is complemented by experimental verification. The measurements on scaled prototype (a loop smaller than /10, operating in 10-60 MHz RF regime revealed self-oscillations tunable across 1:2.2 bandwidth. Such a loop is promising candidate for unit cell of future active metasurfaces.

In the first part of this work, we overview the previously proposed structures of quasi-optical THz components for controlling wave fronts and polarization using self-complementary metasurfaces. In the second part, we study the operation of finite self-complementary structures as metasurface-inspired multi-port antennas. We propose a new decoupling approach in which dipole scatterers of the metasurface are considered as driven antenna elements, while the complementary slots between them serve as resonant and passive decoupling elements.

Omega bianisotropic metasurfaces (MSs) are invaluable for wave control. However, an impediment to their general deployment is the requirement that the power flow be locally conserved across the surface. Attempts to achieve this have included introduction of auxiliary fields in the solution, the determination of which is often nontrivial. Power-flow conformal MSs have been shown to mitigate this need by judicious deformation of the surface profile, but the solution was restricted to impenetrable MSs. Herein we extend this concept to allow transmissive beam manipulation, facilitated by our recently proposed Fabry-Perot MS platform. As verified via full-wave simulations for asymmetric beam splitting, such configurations could readily implement nonlocal field transformations, paving the path to perfect field molding in transmission.

<p> A technique is presented for the design of printed-circuit unit cells in aperiodic metasurface environments. The method begins with a matrix equation governing electromagnetic scattering from a homogenized metasurface design. The matrix equation is used to find the local electric field exciting the printed-circuit unit cell geometry and to compute the electric field scattered by the printed-circuit unit cell onto its neighbors. A printed circuit geometry is found which scatters the same fields as the homogenized unit cell when excited with the local electric field computed from the matrix equation. A finite-sized, wide-angle reflecting metasurface is designed and realized with printed-circuit unit cells using the new approach. It is shown that the local periodicity approximation cannot be used to accurately design the printed circuit unit cells of the finite, wide angle reflecting metasurface.</p>

Reconfigurable metamaterials have shown to be integral to the future of next-generation antenna systems. However, current technologies such as origami, varactor, and pin-diode based designs can be limited when deployed into real-world applications. On the other hand, compliant mechanisms, when integrated with conventional metamaterial antenna technologies, can expand the available design space, and overcome the limitations of these conventional solutions. To this end, a compliant mechanism iris-based antenna is presented with continually varying frequency reconfiguration capabilities to demonstrate the efficacy of the approach.

Tuning of the acoustic/elastic properties of metamaterials is particularly important, as it allows to solve critical issues, such as the dynamical change of the position of the stop band frequency of acoustic/ultrasonic devices, the modulation of the focal point of acoustic lenses, the adaptation to changing environmental conditions and so on. In this work, we present a novel active acoustic metamaterial whose transmission spectrum can be deterministically and reversibly tuned by light stimuli, in different configurations and applications.

In this talk I will describe our recent progress in the field. Some specific examples are the enhancement of interactions between light and thin layers of materials, such as hyperbolic metamaterial cavities and other nanostructures, leading to enhanced light emission and enhanced photodetection. I will also discuss some of the limitations and the opportunities of metalenses in imaging applications. Finally, I will demonstrate tunable metasurfaces via mechanisms such as the electro optic effect and MEMS

A four port Edge-Line Coupler (ELC) based on Parity Time-reversal Duality (PTD) symmetry has been designed. The coupler connects four PTD bifilar edge lines (BELs), which are intrinsically matched due to the PTD symmetry. Each port is strongly coupled with a second port, strongly decoupled with a third port, and weakly coupled with a fourth port. This ELC can be elec- tronically controlled by applying a switching circuit which imposes open or short conditions on the two opposite sides of the structure. Switching simultaneously the open and short circuits reroutes the signal to a different port, while maintaining a good input matching and the same level of coupling with the fourth port.

The next generation of wireless communications within the framework of 6G will be operational at the low THz frequency band. Although THz systems will dramatically enhance several performance indicators such as the data rate, spectral efficiency, and latency, exploiting such technology is challenging. Electromagnetic waves confront severe propagation losses including atmospheric attenuation and diffraction. Thus, such communications are limited to line-of-sight scenarios. In 5G networks, Reconfigurable Intelligent Surfaces (RISs) are introduced to solve this issue by redirecting the incident wave toward the receiver and implement virtual-line-of-sight communications. In this paper, we aim to employ this paradigm for 6G networks and design a graphene-based RIS optimized to perform at emph{multiple} low atmospheric attenuation channels. We investigate the performance of this multi-wideband design through numerical and analytical analysis.

Line waves are recently discovered wave objects that can propagate along suitably designed planar impedance discontinuities, and can effectively channel the electromagnetic power along one-dimensional tracks. Here, we review some results from recent and ongoing studies in this emerging field, with special emphasis on leakage and coupling effects.

An homogenization theor y of space time metamaterials will be presented. This framework will unveil regimes of synthetic motion yielding different physical properties such as light dragging or non-reciprocal and chiral amplification mechanisms.

We introduce a multiple purpose experimental platform for ultrasonic wave manipulation. It allows us to rapidly adjust the Young’s modulus and the attenuation level of a medium by local heating using a digitally controlled laser beam. Experiments show reconfigurable focusing, divergence, and collimation of ultrasounds.

Emerging metamaterials formed by space-time modulation involve interfaces that conjunctly move in space and time. This creates a fundamental discretization issue in numerical methods such as the Finite Difference Time Domain (FDTD) method. This paper highlights this issue and resolves it using a numerical frame-hopping scheme. This scheme is validated by comparison with exact analytical results from previous works.

Time-varying metamaterials are artificial electromagnetic material whose properties dynamically change over time. When refractive index of the whole medium is modulated in step-lie fashion, the propagating wave is scattered due to the change of material properties realizing the temporal analog of a spatial interface. Recently, we studied the scattering taking place in a time-varying metamaterial exhibiting a single, double, and multiple interfaces over time. In this contribution, we review our recent results, focusing our attention on the temporal counterparts of conventional dielectric slabs and multilayered structures. In addition to design several types of optical and electromagnetic devices exploiting the temporal dimension instead of the spatial one, we also report the analysis on temporal interfaces induced by a sudden variation of the boundaries within a guiding structure, allowing giving close form solutions for the frequency shifts, scattering coefficients and static field configuration, emerging from this kind of temporal interface.

<p> Direction-of-Arrival (DoA) estimation is fundamental for establishing and maintaining communication between two terminals while one is moving with respect to the other. DoA estimation methods typically make use of several antennas and huge computation for tracking the target. Here, we propose a low-complexity DoA estimation method based on a single antenna in combination with a space-time modulated metasurface. The proposed approach exploits the unbalance in amplitude of the received fields at broadside at the frequencies of the two first-order harmonics generated by the interaction between the incident plane wave and the modulated metasurface. This is possible thanks to the breaking of the spatial symmetry of each order harmonic scattering pattern, which allows determining the DoA of a plane wave with extreme accuracy. The computation and hardware complexity is extremely lower than conventional DoA estimation methods based on antenna arrays, but still ensuring good estimation accuracy.</p>

In this paper we suggest an optimization-free design of spatial wave filters that is based on a WKB inversion of the reflection by a smooth temporal profile of the dielectric constant ϵ(t) of a spatially homogenous medium.

In this presentation, we will discuss the implementation of a metamirror capable of focusing reflected fields with theoretically infinite resolution. For the design of such metamirror, we consider the so-called power flow-conformal surfaces that allow theoretically arbitrary shaping of reflected waves. Our solution provides a feasible strategy for various applications, including plane wave to cylindrical wave transformation.

In this paper, we show that using an chiral body-centered-cubic cell, we can design a chiral simple-cubic metamaterial crystal which exhibits chiral phonons for all phonon propagation directions over a broad frequency range combined with a nearly isotropic acoustical activity.

In this talk, I will demonstrate second-harmonic generation (SHG) via nonlinear interaction of double topological valley-Hall kink modes in such PhCs. I will first show that two topological frequency band gaps can be created around a pair of frequencies, ω0 and 2ω0, by gapping out the corresponding Dirac points. Valley-Hall kink modes along a kink-type domain wall interface between two PhCs placed together in a mirror-symmetric manner are generated within the two frequency band gaps. Importantly, through full-wave simulations and mode dispersion analysis, I demonstrate that tunable, bidirectional phase-matched SHG via nonlinear interaction of the valley-Hall kink modes inside the two band gaps can be achieved. In particular, by using Stokes parameters associated with the magnetic part of the valley-Hall kink modes, we introduce the concept of SHG directional dichroism, which is employed to characterize optical probes for sensing chiral molecules.

We demonstrate a time-dependent dielectric metasurface with sub-cycle dynamics coupled with a photoexcited electromagnetic source comprising a self-assembling distribution of surface nanostructures in black Silicon. We show non-trivial phenomenologies arising from the ultrafast photoexcitation acting as a temporal discontinuity, affecting the nonlinear response responsible for terahertz emission.

This paper demonstrates the ability to localize a non-emitting object in a disordered medium. This task is non-trivial due to multiple scattering events leading to complex multipath wave trajectories. Several wavefront shaping techniques can obtain the object’s position in the turbid media. Unfortunately, they usually require complicated calibration techniques to localize the object successfully. The complexity of the calibration and measurement can be eased by exploiting the machine learning approach for the decoding part. By training the neural network (NN) on the spectral responses of different positions of the scattering particle in turbid media, the NN can predict the actual position with deeply subwavelength precision (1/20 of free-space wavelength). In our conference presentation, we will demonstrate our findings supported by the semi-analytical and experimental results in the microwave domain.

We present the simple and effective method of quantization lobe reduction in 1-bit intelligent reflective surfaces. We show that significant quantization lobes which appear in the case of a 1-bit reflectarray under plane wave incidence can be reduced by shifting reflectarray parts in the direction perpendicular to its plane.

We review our recent efforts in the design of intelligent metasurfaces to be implemented in smart electromagnetic environments for future wireless systems. In particular, we present intelligent metasurfaces: a. implementing analog signal processing, and b. enabling a new generation of intelligent antennas. Some examples are presented and critically discussed as elementary bricks of the smart electromagnetic environments to come.

Optically transparent dual-band frequency selective surfaces (FSSs) are promising candidates to address the specific design challenges posed by the Internet of Things (IoT). This contribution demonstrates their potential by discussing different configurations of the two FSS designs on an innovative optically transparent surface material. First, a single-layer dual-band FSS is presented. Then, in the second design, the modular multi-layer technique is applied to achieve dual-band performance, enabling invisible integration into optically transparent polyvinyl chloride (PVC) surface material. The transparency, compactness, integrability, and high-performance dual-band stability of both designs in different operating conditions make them ideal for IoT applications.

We exploit the interaction of TEM pulses within networks of interconnected waveguides to perform high speed decision-making processes. Two possible examples of decision-making processes are presented to demonstrate our technique namely a comparator and a pulse director. A thorough theoretical examination of our system is carried out and supported via numerical simulations, showing an excellent agreement.

The rapidly emerging Smart Electromagnetic Environment (SEME) paradigm is expected to revolutionize the design and the deployment of future wireless communications systems. In such a framework, electromagnetic skins (EMSs) will play a key-role to enable an almost-arbitrary tailoring of the complex EM interactions arising within a wireless propagation scenario. This invited talk is aimed at providing a showcase of some of the most recent developments in this field as well as an overview of the envisaged future trends according to the authors' vision.

In this work, we present simple acoustic metagratings that can split normally incident beams into two or three reflected beams. By controlling the groove parameters and manipulating the reflectance of different diffracted waves, the mirror reflected wave is suppressed for two-beam splitting case and allowed for three-beam splitting case.

The vibrational waves in one-dimensional random systems containing double-negative acoustic metamaterials were studied. Localization of waves in these multilayer systems was numerically clarified. The role of mass-near-zero medium in random acoustic metamaterial multilayers was also discussed.

Water constitutes an alternative high-permittivity material for use in microwave technology. Various water-based devices, including antennas and metasurfaces, have been demonstrated, albeit are with limited efficiencies due to the lossy nature water. In this work, we investigate use of metal and water to realize hybrid resonators with more efficient forward scattering properties. The resonators are subsequently employed to design a simple metasurface transmit-array which refracts 50 % of the power of a normally incident wave at an angle of 32°. The proposed resonators and metasurface have a great potential in view of their simplicity and price for alternative components for microwave communication systems.

We propose a one-dimensional composite mode converter to realize mode conversion between symmetric mode and antisymmetric mode in different frequency ranges. The proposed converter is composed of two different phononic crystals. The proposed device and design method promote the applications and experimental research for nondestructive testing, imaging, and RF device.

In consideration of a growing interest in analog optical computing, we design a metasurface processor operating in transmission mode, which has its structural symmetries selected to provide angular asymmetry of the scattering response. The MS has been fabricated and an experimental characterization is underway to ensure correct functionality.

Magnetic Co/Pt superlattice metamaterials are studied using frequency-domain microwave spectroscopy under dc magnetic fields. A decrease in Co thickness brings about an increase in damping parameter while the g-value is almost constant. The tunability of magnetic resonance damping is an advantageous to realize time-varying magnetic metamaterials at magnetic resonance frequencies.

A driven and modulated non-linear Kerr photonic cavity is modelled numerically. We demonstrate that temperature-induced fluctuations can be used as the noise source for stochastic resonance (SR). We show that, at SR, the outgoing power at the modulation frequency is significantly enhanced.

Plasmonic metasurfaces are two-dimensional diffractive arrays of plasmonic nanoparticles that support dispersive lattice resonances. Here, we consider ‘active’ metasurfaces, where the plasmonic arrays are covered with a gain waveguide medium, and the pitch of the arrays is designed such the K-point photonic band crossings overlap in energy with the bandwidth of this gain medium. We investigate Dirac cone dispersion of the second and first-order K-point, and we report spontaneous symmetry breaking when these points are brought to lasing. These findings are important for the understanding of lasing modes in hexagonal and honeycomb plasmonic arrays, and support us in our aim to demonstrate predicted rings of exceptional points around the K-points of Parity-Time symmetric metasurfaces with a pump-probe setup.

We present a dielectric metasurface color filter designed to separate primary colors by manipulating the polarization of radiation. The principle of the color filter operation allows for subwavelength pixel pitch and an additional option to filter the spectrum of complementary colors.

We report Si-based nanohole array structures for biosensing applications. These photonic crystal structures were fabricated by the combination of deep-UV lithography and dry etch techniques. The fabricated structures support guided modes for near-infrared wavelengths, which can be used for the detection of analyte molecules bound to the surface.

In this work we study the interplay between nonlinearity, dispersion and dissipation in a periodic acoustic waveguide. The latter phenomena may lead to the formation and propagation of interesting nonlinear waves such as solitonscite{sugimoto_review,kinezoula_gap,hamilton,Remoissenet}. The system under consideration here is composed by a simple waveguide with periodically varying cross sections, presented in Fig. ef{physical setup}. The periodicity is employed in order to induce dispersion, while the nonlinearity is evoked using a high amplitude source leading to an amplitude dependent correction of the sound celerity. We are not only interested in the generation and propagation of acoustic solitons but we also wish to evaluate the influence of strong linear and nonlinear dissipation in the solitary wave charecteristics, since such phenomena are usually observed in airborne acoustics.

Here we study a simple continuous medium - magnetized plasma - that possesses Weyl points which arise at the linear crossing between longitudinal plasmonic modes and transverse helical modes. The topological properties of this medium will be characterized by a first principles method. Specifically, a photonic Green’s function formalism will be used in order to study the influence of these three-dimensional linear degeneracies in terms of the topological charge. The application of this method is discussed below.

We consider resonant frequency and quality (Q) factor of accidental and symmetry-protected bound states in the continuum (BIC) in bilayer resonators consisting of dielectric wires. We investigate dependence of Q-factor and frequency on structural disorder. The change in frequency is more affected by the x-axis disorder for both accidental and symmetry-protected BIC. The y-axis disorder affects much on Q-factor of a accidental BIC and, contrary, the x-axis disorder has a stronger affect on a Q-factor symmetry-protected BIC.

A correlative approach is allowing us to characterize structural, optical, and chemical properties of individual CsPbBr3 nanocrystals with a high lateral resolution. With this method, we are able to experimentally retrieve the dependence of the peak emission wavelength on the characteristic dimension of the nanocrystal on a single nanocrystal level.

Analytical systems such as microfluidic chips and sensors can be used everywhere, for example to monitor blood sugar or the presence of antibodies to covid. So, it is significant to make such devices compact and miniature. However, as the size of functional nodes decreases, their properties also change dramatically. The characteristics of nanostructures may differ from the characteristics of bulk systems by tens of times. Therefore, it is very important to locally investigate the physicochemical properties of that kind of nanoobjects. The ideal tools for the sort work are the Tip-enhanced Raman spectroscopy and Raman thermometry which have high resolution.

The optical response of an heterostructure made of WS2 flakes on top of an array of gold nanoparticles is measured at different temperatures. The result is a weak interaction between excitons and plasmons generated by the poor spill out of the electromagnetic field outside the plane of the NPs array.

The search for new materials for plasmonics and nanophotonics is justified by the need to create miniaturized optical nanodevices with unique properties in one nanostructure. High-entropy alloys have many material properties due to the peculiarity of the internal structure and multicomponent nature. These facts make such systems promising for nanophotonics. This paper presents the results of the experiments on the femtosecond laser ablation of a bulk material in an inert medium to create sphere-like nanoparticles of various sizes. Dark-field spectroscopy studies have demonstrated the presence of natural resonances in nanospheres, as well as their behavior with variation in the size of nanoparticles. We believe that the obtained results are perspective for creation of nanophotonic systems with extended functionality.

We present a new method for two-dimensional quantitative imaging near-field phase distribution. We use the phase-shifting digital holography and we replicate it for the interference of SPP waves which is detected by the scanning near-field optical microscope.

We present a new approach to determining the local glass transition temperature (Tg) of a nanosized PMMA polymer deposited on an array of TiN:Si structures. Under the action of laser radiation in plasmon resonance conditions, the TiN structures play the role of heat nanosources. Localized heat may cause a temperature change higher than the glass transition temperature. This effect offers a unique opportunity to investigate local phase transitions of different materials. We demonstrate that Tg detection of nanosized polymers can be performed using plasmon nanostructures and Raman spectroscopy. This approach enables remote monitoring of thermal phenomena at the nanoscale

The optical Raman cooling implies enhanced anti-Stokes scattering compared to Stokes scattering. Plasmon-enhanced Raman scattering in a layered insulator-metal-insulator (IMI) system occurs due to the modification of the local density of electromagnetic states (LDOS) near a metallic layer. Due to the fact that both eigenmodes with frequencies below the plasma frequency are surface modes and the high-frequency mode is delocalized, energy is capable of dissipating into free space through anti-Stokes scattering. In this work, we carry out the numerical simulation of LDOS for IMI structures with a varied thickness of the metallic layer. Our work is a step towards the development of structured photonic materials for optical cooling of solids.

A proof-of-concept semi-analytical demonstration is presented for practically implementable boundary-tunable metasurface antenna. Proposed antenna consists of reverberating planar parallel-plate waveguide with two via layers on the boundary. Different radiation pattern can be generated by electronically switching vias in the inner boundary layer. This arrangement allows to select different measurement modes necessary for interrogating a scene in the computational imaging framework. The advantage of this design is increased beam diversity compared to the passive frequency tuned approach while maintaining a planar configuration. The performance of the antenna is verified by analysing the singular values of the waveguide modes inside the antenna.

The design and modeling of a non-reflecting metasurface has been carried out, which makes it possible to transform an incident linearly polarized electromagnetic wave into a transmitted wave with elliptical polarization close to a circular one. At the same time, the reflection coefficient of the wave is close to zero in a wide frequency range, since the metasurface is similar to the free space in its wave resistance. The resonant elements of the meta-surface (meta-atoms) are two-turn planar spirals with balanced dielectric and magnetic properties. Such spirals exhibit radically different properties regarding waves with right and left circular polarization. The metasurface as a polarization converter has strong chiral properties, since it contains planar spirals of only one direction of twisting, and can be manufactured within the framework of printed circuit board technologies.

We show that band-limited light fields can exhibit superoscillations simultaneously in space and time, which can oscillate faster that the highest harmonics of their space-time spectra, and verify such behavior in super-toroidal structured pulses.

We demonstrate the focusing of electromagnetic waves to produce a photonic nanojet (PNJ) at the output surface of an engineered high refractive index dielectric particle placed on top of an optical fiber and being surrounded by a cladding material.

We propose tunable graphene-based multisensors sustaining absorption efficiency exceeding 95% in the terahertz domain. Due to the graphene components, the absorption frequency is tunable with gate voltage. The perfect absorber can operate as a refractive index sensor with a sensitivity around 54.54 μm/RIU. More importantly, it can be operated as a temperature sensor with the sensitivity of 13.75 μm/K. Due to the high sensing performance, the structure has a great potential for chemical applications.

The presented work addresses an easy to manufacture and applicable vibroacoustic metamaterial for thin-walled sheet metal structures commonly used for industrial machines and their housings, which are often subject to vibration and the cause of noise. The work involves the numerical stop band prediction, the elaboration of an easy to manufacture vibroacoustic metamaterial compound and its experimental validation on a sheet metal structure. The vibroacoustic metamaterial is attached to the structure using a magnetic film. Two stop bands occur in the frequency range of 1800 - 4000 Hz.

We explored numerically the application of mechanical wooden metamaterials to modify the sound properties of the Cajón Peruano. We studied different patterns of elliptical holes in the soundboard, decreasing its density and manipulating the radial and longitudinal Young’s moduli. Finally we investigated the role of the whole geometry in the acoustic pressure and we found that, depending on the size and orientation of the ellipses we can achieve very different responses for even small density variations.

Recent research has numerically shown the possibility of manipulating the elastic properties of wood plates through periodic hole patterns. In this work we focus on enhancing those results by studying how heterogeneous (non-periodic) hole patterns change the elastic properties of Spruce Engelmann plates, a traditional wood for guitar soundboards.

The presented work addresses a modification of a circular saw blade with a vibroacoustic metamaterial structure. The sound emitted by a saw is mainly due to the structural behavior of the circular saw blade, that is excited by the sawing process. A suitable and easy integrable vibroacoustic metamaterial is elaborated and a numerical stop band prediction is performed. Validation measurements are carried out in terms of structural dynamics and acoustic emission in the non-rotating state. The stop band occurs in the frequency range of approximately 2600 - 3700 Hz.

It has been recently shown that thin wooden plates can be used as substrate for mechanical metamaterials. These could be used in classical guitar soundboards to achieve better sound radiation. We investigate the structural integrity of a metamaterial instrument by means of finite element simulation.

A design flow for radiative cooling thin-film multi-layered metamaterials based on genetic algorithms is presented. Such method can be generalized to other infrared applications and has designed three radiative coolers with a net cooling power as much as 61 Wats per square meter.

We present a framework that can be used to study two-photon spontaneous emission processes of an emitter near nanostructures beyond the electric dipole approximation. It is relevant for current nanocavities, is based on the classical computation of Purcell factors and is applied to an emitter close to a silver nanodisk.

Light-matter interactions in chiral structure can induce strong polarization selectivity. Specifically, an optical activity in a form of polarization rotation and a circular dichroism may be controlled by the the mirror symmetry breaking of the unit-cell geometry. We design and experimentally investigate plasmonic metasurfaces with spatially varying chiral geometry and demonstrate how this architecture may lead to a geometric Berry phase. Our designed structure produces a polarization-dependent diffraction of nearly linear states. We experimentally examine the diffraction orders and show that they are topological in nature. Moreover, the influence of various geometrical factors is also investigated.

In this paper we experimentally demonstrate SHG enhancement in thin 1D periodic plasmonic nanostructures in the infrared spectral range. Due to properly designed plasmonic resonances that occur inside these structures, the obtained conversion efficiencies go up to the 10^-7 W^-1 range. Moreover, by engineering the dimensions of the plasmonic nanoantennas the resonance modes can be spectrally shifted.

Periodic and quasi-periodic linear and nonlinear mechanical metamaterials are designed by solving inverse design problems which include forward problems implemented as finite element method problems, and an inverse problem proposed as a transient optimization problem solved using the Nelder-Mead algorithm to control nonlinear elastic waves in solids.

It is generally accepted that the enhancement of optical nonlinearity in ENZ media requires that the real part of permittivity is equal to zero. In this work, we show, theoretically, that this condition is valid only for those excitation wavelengths that are far from the electronic/phononic resonance.

We report the optical characterization of a gold nanohole array plasmonic chip based on the simultaneous detection of surface plasmon resonance and plasmon-enhanced fluorescence. The measured fluorescence spectra show a change with respect to the reference ones that can be associated to field enhancement effects due to the plasmonic modes.

We present the exploitation of classical optics techniques to design plasmonic meniscus lenses for focusing surface plasmon polaritons (SPPs). We adapted the lens maker equation to incorporate the effective refractive index of SPPs then designed and evaluated a silicon nitride meniscus-shaped block positioned on a gold slab working at 633nm.

Reciprocal space engineering allows generating quasicrystalline structures with the desired transport properties. This study demonstrates a regime of wave localization at a selected frequency in the two-dimensional structures. The quasicrystalline structure is designed for two polymer materials with low contrast between them. We also use an antireflective coating on the surface of the structure to reduce the reflection of the incident wave. For such a structure, the length of the sides at which the localization effect reaches maximum intensity is investigated. The results of numerical modeling show that starting from a certain size value the localization effect acquires a stable level.

Abstract – In this study, we present the refractive index sensing by using the lattice mode in the Au nanodisk array. The rationally designed Au nanodisk array shows the Fano-like asymmetric line-shape due to the interaction of the LSPR of the individual Au nanodisk and the lattice mode. The sharp resonant feature of the lattice mode is shown in the abrupt change of transmittance spectra, and this spectral feature shifts to the longer wavelength when the refractive index of the top filling material increases. The lattice mode in the Au nanodisk array shows twofold larger refractive sensing sensitivity compared to the case of LSPR in the single Au nanodisk. These results suggest the feasibility of the Au nanodisk array for use in sensing application.

The paper presents a system for the IRS beam steering using a computer vision algorithm based on TinyYOLOv4 neural network. We demonstrate that combination of IRS and computer vision algorithms can be used to find beam patterns that optimally redirects the base station signal to the mobile user equipment.

This research overcomes the limitations of flexible metasurface by proposing a new geometry that enables around 100% stretchability. The new design decouples the stress concentration from the metal-substrate interface to the substrate, providing reversible resonance tuning even with 100% strain, which is otherwise impossible with conventional active metasurfaces.

An improved harmonic generation with time-modulated graphene layers is numerically investigated in the present work. In particular, the simulation of a plane-wave propagation towards two graphene layers is performed at the millimeter-wave spectrum. The 2D material's electrostatic bias field that controls the chemical potential, is sinusoidally altered in time and the optimized selection of the setup parameters highlights the frequency generation.

We theoretically investigate with the help of the finite element method the interaction between aluminum pillars erected on top of a silicon substrate in the low frequency range. Our interest is to control and manipulate the propagation acoustic waves through a linear chain of pillars for frequencies in the [0, 2] GHz range. We show that two pillars can interact together in near field through the excitation of their resonant compressional eigen mode. We then investigated the resonant modes of a finite linear chain of N pillars and demonstrate the propagation along the chain of pillars deposited on the half-infinite substrate.

We introduce an approach to signal routing that enables reflectionless in coupling of signals as well as programmability of the routing functionality. Our unconventional device concept leverages the high modal overla p of a wave chaotic system in combination with the hundreds of degrees of freedom of a programmable metasurface. We also report preliminary experiments that implement our concept “over the air” inside a 3D disordered metallic box in the microwave domain.

We demonstrate electrical tunability of lithium niobate metasurfaces supporting quasi-bound states in the continuum (qBIC) exploiting the electro-optic effect. Thanks to the high spectral selectivity of the qBIC, we can sizably shift the resonant mode with a weak refractive index modulation that results from an applied voltage.

We propose a self-activating optical limiter device based on a multilayer film structure featuring a dielectric substrate, a metallic and a Vanadium Dioxide (VO2) film. By exploiting the phase transition in VO2, the device optical transmittivity is reduced by ~70% with a recovery time of 5 ns.

A design method for passive omega-type bianisotropic metasurfaces is extended by removing the need for two different copper trace shapes. Given a desired far-field power pattern, physically realizable unit-cells are designed and verified through simulation to perform the required transformation from incident field to fields satisfying the desired far-field criteria.

We discuss a technique for fabricating hyperbolic metamaterials through the dewetting of block copolymer/homopolymer blend thin films. We show photon sources can exhibit a strong lifetime reduction when coupled with proposed structures, whose spectral response is tunable by varying their height. We think this system could open up new opportunities for several optical applications.

In this work a labyrinth metageometry operating in the THz band is experimentally tested as Polycyclic Aromatic Hidrocarbons detection and identification, with a design able to detect different concentrations and distinguish between different compounds at the same concentration.

We study the effect of losses on the resonances of an all-dielectric metasurface with ideally high quality factor resonances in the THz frequency range, considering realistic materials. We also study the effect of losses in the different elements of the structure and how making the substrate thinner changes its performance.

This paper presents the analysis and design of a bidimensional Fabry-Perot leaky- wave antenna (LWA) with improved frequency scanning response for direction finding applications in the 5 GHz Wi-Fi frequency band. The use of Frequency Selective Surfaces (FSS) as the contour of the Fabry-Perot antenna is proposed. An efficient analysis of the antenna dispersion based on the Transverse Equivalent Network (TEN) of the TE and TM modes is used in the structure to optimize the design for its application in amplitude-monopulse radar techniques for angle estimation.

This paper presents the design of a metalens based of the Pancharatnam-Berry (PB) principle applied to half-wave plate (HWP) metasurface allowing the manipulation of wavefronts with circular polarization conversion by rotating the elements that composed the metasurface. Two methods are investigated to design the metalens: the first one consists in compensating the phase of the antenna used with the metalens and the second one consists in aligning the metalens focal lens with phase center of the antenna. The metalens unit cell is designed at 132 GHz and is composed of two H-shaped aluminum elements printed on both faces of a thin polypropylene slab. The metalenses obtained by the two different methods are combined then with a horn antenna to test their properties. Both solutions present an excellent behavior at the working frequency.

In this paper, a flat hyperbolic lens-corrected H-plane horn antenna is designed at 300 GHz using Groove Gap Waveguide (GGW) technology. A GGW horn antenna is employed to feed the metamaterial lens placed in a parallel plate waveguide (PPW), in order to increase the directivity in the direction of propagation. Both devices, the metalens and the GGW antenna, achieve excellent radiation results when combined together.

Designing passive structures that perform different operations on different electromagnetic fields is key to many technologies. We present a semi–analytic method to design multi–functional metamaterials. To demonstrate our method, we design a device that operates at optical wavelengths and beams light into different directions based on source polarisation.

We demonstrate a femtosecond laser-induced printing of all-dielectric silicon nanoparticles onto polypropylene substrate as a promising fabrication method for a modern design of security tag development. The optical properties of resonant silicon nanoparticles and its spatial distribution within an array of nanoparticles are excellent for a forensic security feature authentication.

In this work, we explore and demonstrate how Petri-nets (PNs) can be exploited to represent linear equations. Such feature is then applied to graphically model the propagation of electromagnetic (EM) pulses within waveguide junctions. PNs have been used in a wide range of research and industrial scenarios to study dynamic systems such as designing asynchronous circuits and chemical engineering, here we exploit features of PNs to represent TEM square pulses in waveguide junctions. In this realm, as new approaches to computing with photonics may require modelling large systems that may need computationally intensive techniques, we discuss how PNs can provide a fast, efficient, and visual modelling of EM pulse propagation within a network of interconnected waveguides. This work represents a step towards allowing individuals from varying areas of expertise to contribute via a common visual language to the future of photonic computing systems and control.

We theoretically studied radiometric and spectral imaging chain of an hypothetical spaceborne satellite, in the presence of 4x4 metaxel super cell based image sensors. Many parts of our imaging configurations are the same as the operational Pleiades-HR satellite except the novel image sensors. The main figure of merit (FOM), signal to noise ratio (SNR), is found as SNR_scene=67 for the synthetic ground truth image and SNR_albedo=35 for average earth surface reflectance equal to albedo=0.2. This satellite, GOKAY-1A, shows images limited by the telescope optics due to the superior performance of image sensor elements (metaxel supercells) that reduces image sensor unit cell size from 13μm to 1.32μm.

Fundamental bounds on electromagnetic scattering from subwavelength structures play an important role in estimating the performances of many wireless communication devices. An appealing approach to increase a scattering cross-section is accommodating several spectrally overlapping resonances within a structure. However, numerous fundamental and practical restrictions have been found and led to the formulation of Chu-Harrington, Geyi, and other limits, which provide an upper bound to scattering efficiencies. Here we demonstrated several superscatterer designs and their implementations, which allow surpassing those limits by orders of magnitude. Genetic algorithms for optimizing arrays of wires and split ring resonators were developed and resulted in ever observed performances. Apart from the fundamental importance, the developed superscatterers are attractive elements for deceiving low-frequency radars.

Ultra-wideband antireflection coating is desirable for a variety of applications. In this study, we report that, by applying a simple design of metallic metasurfaces to the two-section Chebyshev transformer, the ∼100% relative bandwidth can be sustained with a ready tunability of the working frequency band. Such tunability stems from the interplay between the metasurfaces, while the ultrawide bandwidth is contributed by the carefully designed Chebyshev transformer. In addition, its broadband mechanism is explored that a non-resonance or weak resonance of the metasurface shall be implemented.

We present a method to produce bent light beams known as photonic hooks. This is done by engineering a pair of dielectric particles immersed in free space and exploiting the particular diffraction and scattering characteristics of each particle.

Some filters for rectangular monomode waveguides are researched. They are based on metasurfaces composed of resonant subwavelength slots. It has been possible to verify, by means of numerical simulations, a significant improvement of their performance by just introducing several resonators in the cross section and certain mirror symmetry which avoid the splitting of the resonance frequency when elements are vertically stacked.

Several phenomena and applications of self-complementary metasurfaces have been studied in microwaves and sub-THz ranges like filtering, polarizing, and guiding of surface waves. However, it is rather a challenging task to scale the structures to work in mid-infrared because Babinet’s principle is usually violated. We have numerically demonstrated that it is possible by using a 13 nm-thick film composed of silicon and silver.

We provide an analytical formulation to model the propagation of elastic surface waves interacting with a generic distribution of mechanical oscillators arranged atop an elastic half-space. Our framework can correctly capture the multiple scattering effects induced by the collective dynamics of resonators, and thus can be used in different engineering contexts, from the design of novel surface acoustic wave devices to the interpretation of structure-soil-structure interaction problems.

Our research focuses on the simulation of coupled Helmholtz resonators (HRs) and their scattering properties for their further utilization as a sub-wavelength constitutive unit of acoustic meta-surfaces. Since local resonators have a narrow response band, our goal is to extend the effectiveness of this system for the control of low-frequency sounds. In our previous simulation works, we studied the ideal behavior of the resonators and their near and far field scattering distributions. Two distinct modes were detected showing symmetric (S) and anti-symmetric (AS) pressure behavior. In this paper, we consider the effects of viscous damping and discuss how the resonances can be affected as a function of the geometrical parameters.

We review an approach based on Riesz projections for the computation of eigenfrequency sensitivities associated with optical resonances. The Riesz projections are accessed numerically by computing contour integrals in the complex frequency plane. The corresponding scattering problems allow the application of direct differentiation.

We study TEM-wave propagation in a parallel plate waveguide with a graded transition between a lossy right-handed material (RHM) and an impedance-matched lossy left-handed material (LHM). The transition between the two media is graded along the direction perpendicular to the boundary between the two materials, and the permittivity and permeability vary according to hyperbolic tangent functions. We obtain exact analytical solutions to Maxwell's equations for lossy media, and the solutions for the field components confirm the expected properties of RHM-LHM structures. Finally, we perform a numerical study of the wave propagation over an impedance-matched graded RHM-LHM interface, using COMSOL, and obtain an excellent agreement between the numerical simulations and analytical results.

A generalized analysis to determine the Cartesian electric and magnetic field components of anisotropic biaxial media based on kDB formalism and coordinate system is introduced. The approach solves for each characteristic eigenwave within kDB system before transforming the fields back to Cartesian coordinates. This formulation accounts for arbitrary plane wave propagation angles in biaxial media and allows for ease of boundary condition enforcement.

By linking a semi analytical stacking algorithm with a modified genetic algorithm we developed a computationally efficient optimization tool for the inverse design of stacked metasurfaces. During optimization not just the composition but also the number of the individual layers is adjusted simultaneously. The method enables us to inversely design layered metasurface stacks in a matter of seconds avoiding thousands of rigorous simulations in the process. he algorithm is applicable to any objective that can be expressed via scattering matrices in far-field approximation. The algorithm performance is demonstrated and validated via a rigorous simulation showcasing two examples

Using tools from the homogenization theory, we provide new effective transition conditions based on surfacic susceptibility tensors that can be used to obtain the macroscopic behavior of electromagnetic metasurfaces. Validation of the effective model is provided by means of FEM simulations in three dimensions.

A design routine for engineering plasmonic metasurfaces based on a customized particle swarm optimization algorithm implemented in a commercial FDTD software is proposed. Providing to the algorithm the relevant optical and morphological parameters, it returns the optimized geometrical parameters tailored to the required usage and compatible with lithographic processes.

In this paper, we analyze the reflection from a reconfigurable intelligent surface with the finite element method. The control parameters of the surface are modeled with impedances. We tune the control parameters to have a propagating mode delivering significant power dissimilar from the specular. Furthermore, we repeated this analysis for different period sizes

This report presents a 2D magnetoinductive waveguide fabricated with a recently developed method based on fused deposition modelling and liquid Field’s metal injection. The resonance of each resonator has a quality factor of 130. In the waveguide, each element is coupled to its neighbours, resulting in an over 200MHz bandwidth.

The scattering and absorption properties of the plasmonic antenna can be adjusted by adding a dielectric layer. In this work, we have studied the effect of the thickness of dielectric layers. We have numerically investigated the scattering and absorption of meta-antenna and experimentally realized two sets of samples with 10 and 20 nm of the dielectric layer. The absorption of the meta-antenna is blue-shifted by increasing the layer while the scattering remained fixed. Therefore, better control of the absorption mode will allow the use of these antennas separately for imaging and efficient plasmonic absorbers.

<p> We qualitatively compare the effective description of metamaterials using non-local constitutive relations to a description based on induced multipole moments. This facilitates the understanding of the physical meaning of the coefficients appearing in such non-local constitutive relations and establishes a clear link to the properties of the unit cell from which the metamaterial is made.</p>

We study the occurrence of Fano resonances in a subwavelength dual-period grating with some symmetry breaking. By combining classical Homogenization and matched asymptotic technics, we derive an effective model capable of accurately capture the scattering behaviour and allows us to explicitly explain the resonant mechanisms.

This paper reports on the dispersion properties of glide-symmetric parallel plate waveguides, loaded with dielectric layers that are separated by perforated metallic plates. The coupling between the layers is controlled by varying the side length of the square apertures in the separating metallic layers. The importance of the coupling on the dispersion properties of the structure is highlighted.

Structures with heavy-tailed distributions of disorder occur widely in nature. The evolution of such systems, as in foraging for food or the occurrence of earthquakes is generally analyzed in terms of an incoherent series of events. But the study of wave propagation or lasing in such systems requires the consideration of coherent scattering. We consider the distribution of wave energy inside 1D random media in which the spacing between scatterers follows a L'evy $alpha$-stable distribution characterized by a power-law decay with exponent $alpha$. We show that the averages of the intensity and logarithmic intensity are given in terms of the average of the logarithm of transmission and the depth into the sample raised to the power $alpha$.

<p> This work examines various multiconductor transmission-line (MTL)-based Fabry-Perot resonators at microwave frequencies. It is demonstrated that an unloaded MTL supporting two modes with a particular set of properties akin to those of the canonical dark and bright modes may support a frequency comb response consisting of either Lorentzian or Fano-like resonances, depending on its excitation. It is then shown that promotion of modal coupling through the periodic insertion of capacitors causes the system to support both types of resonances simultaneously, or hybrid types, depending on the style of loading.</p>

In this study, we report the possibility of a VDW heterostructure composed of double-layered hexagonal AlP and GaAs using a first-principle calculation-based DFT. The heterostructure is a semiconductor with a direct bandgap of 0.18 eV, which can be tuned and enhanced using external effects like exerting strain and electric field.

We report on an analytical approach to describe the transmission function of a parallel plate switchable cavity based on VO2 films that can be used as an optical sensor in the THz region. This allows to optimize the system characteristics and study its sensing properties in a simple way, without resorting to full-wave simulations so as to reduce computational complexity and keep at the same time a high reliability of results.

The changing balance of forces at the nanoscale allows nanomachines that can alter optical properties of metamaterials with electromagnetic and acoustic forces and heat. We report new metamaterials that explore optical parametric phenomena for controlling light with light in such media.

In this study, we consider a nonlinear one-dimensional lattice that transmits only tensile waves and sustains solitary waves. The introduction of a gyroscopic effect, through the action of a spinner attached at the central node, leads to the possibility to tune the transmision and/or reflection. A numerical solution derived from an algorithm implemented in matlab shows the tunability of the gyroscopic ``gate''.

Achieving active tunability of light and matter interaction is of great interest as it opens a new avenue for exploring various high-performance photonic devices. In this prospect, developing a novel way to achieve active tuning of a strongly coupled system is vital. Here, we demonstrated an active tuning of the coupling strength in a strongly coupled system comprised of a thin ITO film as epsilon-near-zero (ENZ) material and gold nanorods as plasmonic resonators. The incorporation of these two components exhibits strong coupling that manifests as spectral splitting in the transmission spectra in the near-infrared spectral range.

In the integer quantum Hall effect, the transport of electrons is completely immune to the presence of defects and disorder. In this talk, I will explore the implications of this “topological protection” to photons (rather than electrons) in fabricated dielectric structures, particularly in the nonlinear domain. I will use arrays of waveguides to show that in 1D nonlinear photonic Thouless pumps, solitons are transported in a quantized way; this is perhaps a counterintuitive result given that there is no sense in which solitons “fill” a band. Under certain conditions, solitons are also transported in a fractional way.

We show that it is possible to tune Second-Harmonic Generation by breaking symmetry of plasmonic nanoantennas with tips. By exploiting advanced control over the geometry of the antennas, we compare efficiency of asymmetric antennas with one tip and their symmetric counterparts. Excellent agreement between experiments and simulations is demonstrated.

We show how a single plasmonic resonant nanoantenna can be used to induce and control fast insulator-to-metal transition in nanoscaled regions of a VO2 film

Due to unique penetration and absorption properties of terahertz wave, terahertz imaging systems have been extensively studied for real-time, high-resolution, and accurate imaging systems. In particular, through the terahertz spatial light modulator (SLM), it is possible to construct a terahertz single-pixel imaging system offering potential commercialization of terahertz imaging technologies. In this work, transmission-reflection dual-mode terahertz spatial light modulator (SLM) is presented using electrically tunable metasurface based on ion-gel gating graphene metasurface. By applying differential driving voltage on SLM, simultaneous acquisition for transmissive and reflective images on different objects was successfully demonstrated using the proposed dual-mode SLM with high accuracy.

The angle and polarization tunability of the optical Kerr effect in hyperbolic multilayer metamaterials with different metal filling fraction is demonstrated. A model is proposed to predict the angle- and polarization-dependent nonlinear parameters considering the optical anisotropy and the local intensity enhancement within the metamaterials.

<p> Recent progress in metasurface research has enabled new classes of structured light and inspired new applications. We review ongoing efforts in these areas with focus on meta-optics that can remotely control the spin and orbital angular momentum of light in 3D. Devices of this kind may find use in optical trapping, micromanipulation and sensing. We also present new holographic technique — dubbed holographic light sheets — for generating 3D structured light for AR/VR and discuss new directions in creating time-varying optical vortices with dispersion-engineered metasurfaces.</p>

We realize 3D microstructured liquid-crystal elastomer metamaterials via two-photon 3D laser printing. During printing the local liquid-crystal director is aligned by electric fields. Infiltrating the structures with an absorber dye after printing makes the elastic properties of the metamaterials tunable by light from an LED.

We show preliminary results of the fabrication and acoustic characterization of air-actuable quasi 2D mechanical metamaterials, based on an elastomeric matrix with cylindrical holes connected to each. By injecting or extracting air, these metamaterials change their mechanical properties. As a result, a soft mechanical metamaterial is obtained, with tunability properties.

We report on various methods to actively tune and passively tailor the optical properties of conducting oxides and nitrides, for dynamic nanophotonic applications. We demonstrate great tailorability in the epsilon-near-zero (ENZ) response of transparent conducting oxides (TCOs) such as aluminum doped zinc oxide (AZO) and polycrystalline cadmium oxide via yttrium doping. We also investigate the strong thickness dependence of the optical properties of both TCOs and polycrystalline titanium nitride (TiN). Employing the Berreman modes of TiN and AZO films on the same platform, we demonstrate variable switching speeds of an optically-pumped metasurface. Building upon our work with the transient optical properties of optically doped zinc oxide, we demonstrate phase and polarization shifters made with ZnO. To develop photonic time crystals, we investigate the fastest material response to an optical pump in aluminum-doped zinc oxide, showing sub-10 femtosecond rise time. Our approach paves the way to novel device design and the study of novel optical phenomena with ultrafast tunable and tailorable materials.

One of approaches to the development of specialized software suitable for designing curved metasurface structures is to adapt an existing planar analysis tool. This paper discusses extension methods based on estimation of either the EM field within the multilayer curved structure or on estimation of the equivalent metasurface current distribution.

<p> Advances in nanoscience and material science are accelerating the rate at which we can create new materials. But, quite often, experiments are ahead of theory due to the challenging multiscale and multidisciplinary character of the experimental systems. In here, we present a novel methodology which, starting from ab-initio quantum mechanical molecular simulations, allows to compute the electromagnetic response of macroscopic photonic devices containing molecular materials.</p>

Can a zero-thickness susceptibility model be used to model impenetrable, fully-reflective metasurfaces? Considering a simple case of a ground plane with a dielectric coating, we find a set of susceptibilities which serve as characteristic parameters which are able to predict the scattering response for TE-polarized fields incident fields.

Large-scale metasurfaces represent the possibility for dramatic enhancement of optical functionality. In this talk, we show how to exploit the mathematical structures of Maxwell’s equations to (1) enable rapid design of large-area metasurfaces, and (2) identify fundamental limits to what such metasurfaces can achieve. The former relies on quadrature corrections to otherwise ill-conditioned DDA equations, while the latter relies on the sparsity of differential operators. Together, we can find superior design reaching the limits of metasurface-mediated light-matter interactions.

We introduce a spatiotemporal version of coupled mode theory (STCMT) capable of elegantly capturing the unique wavefront-shaping behaviors of diffractive nonlocal metasurfaces. This work extends conventional temporal coupled mode theory (TCMT) by explicitly including spectrospatial properties of the scattering from aperiodic devices.

<p> One of the main advantages of bianisotropic metasurfaces is their capability to produce asymmetric scattering depending from which side they are illuminated. For most applications, these metasurfaces are expected to be illuminated with a single source at a time. However, in applications with simultaneous illumination by two or more sources, bianisotropic effects can be replicated by exploiting coherent illumination. In this talk, we discuss how asymmetric scattering can be realized for a planar 180° hybrid junction using bianisotropic metasurfaces with omega response and non-bianisotropic metasurfaces under coherent illumination.</p>

We propose a time-modulated metasurface enclosure for microwave imaging to shield the imaging domain from outside interference and to enable creating quantitative images of the relative complex permittivity profile of the object being imaged under the Sommerfeld radiation boundary condition without the necessity to utilize high-loss coupling fluids.

Periodic structures are widely used to control waves and improve energy harvesting performance. We proposed a double-focusing flexural wave energy harvest platform consisting of a gradient-index lens and an elastic Bragg mirror. The results show that the output voltage and power are 1.5 and 2.3 times higher than the existing gradient-index system.

We demonstrate a meta-optic based neural network accelerator that can off-load computationally expensive convolution operations into high-speed and low-power optics. End-to-end design is used to co-optimize the optical and digital systems resulting in a robust classifier that achieves 93.1% accurate classification of handwritten digits and 93.8% accuracy in classifying both the digit and its polarization state.

In this contribution we show the study of nanophotonic chiral platforms made of compact arrays of 3D chiral nano-helices for biosensing applications. The high sensing abilities have been obtained by a deep study on optical and structural characteristics of these systems, carried out with the aim to optimize their interaction with the surrounding medium. Large chiroptical effects, originating from single element optical resonances, can be engineered with the collective effects when they are arranged in periodic arrays. Biomarker detection up to femtomolar range is demonstrated even in complex biofluid matrix.

The maximization of the electric field inside biological tissues can be advantageous in several applications, and it can be achieved using a proper matching layer. Here we propose an analytical method for the design of matching layers consisting both of solely dielectric and of dielectric and metasurface.

By using orthogonal linear-polarized photons, images with tailor-made second-order polarization coherence are generated from metasurfaces. The metasurfaces provide arbitrary control on the coincidence as correlated, anticorrelated, or uncorrelated signals. The demonstration allows imaging based on two-photon interference and polarization coincidence signals between object to reference channels.

Fifth generation (5G) and beyond communication systems open the door to millimeter Wave (mmWave) frequency bands to leverage the extremely large operating bandwidths and deliver unprecedented network capacity. These frequency bands are affected by high propagation losses that severely limit the achievable coverage. A promising solution to improve the coverage without increasing the number of installed mmWave base stations is based on the concept of the Smart Electromagnetic Environment. This concept exploits the features of new relatively simple and inexpensive network nodes that are judiciously planned to minimize the total installation costs while at the same time optimizing the network spectral efficiency. This talk will provide an overview of the main challenges of the mmWave frequency bands, a description of the current solutions and the vision on the Smart EM Environment, with a focus on hardware and network-related aspects.

We present the design and study of a device that exploits a simple four waveguide junction waveguide structure (with 2 stubs and an input and output waveguide) with the ability to compute the temporal derivative of incident electromagnetic wave signals. The physics behind such structure will be discussed and demonstrated numerically working with both modulated and unmodulated incident signals. Without loss of generality the device is presented operating at a 4.5 GHz central frequency and all numerical simulations are in excellent agreement with theoretical calculations.

In this work we design a cloak for Rayleigh and Love waves. We apply transformation elastodynamics to obtain the requisite mechanical properties for a 3-D cloak having a triangular cross section. Dispersion analysis and time-harmonic simulations are conducted to validate the performance of the cloak. Finally, symmetrization techniques of the elasticity tensor are applied to approximate the properties of the cloak by using isotropic composite materials.

A reconfigurable intelligent surface (RIS) is a planar structure that is engineered to dynamically control the electromagnetic waves. In wireless communications, RISs have recently emerged as a promising technology for realizing programmable and reconfigurable wireless propagation environments through nearly passive signal transformations. With the aid of RISs, a wireless environment becomes part of the network design parameters that are subject to optimization. In this invited talk, we focus our attention on communication models for RISs.

We show that the resulting fabricated structure deviates from the designed structure for 3D metamaterials created using membrane projection lithography, a variant of stencil lithography, depending on the metal used during deposition. This loss in pattern fidelity correlates with the melting point of the metal used.

We present an artificial orthotropic metamaterial, based on nanopatterned silicon nitride membranes. By using an asymmetric nanopatterning, we modify the mechanical properties of the membranes, changing both their effective Young’s modulus and intrinsic strain. As a consequence, we experimentally observe strong changes both in frequency and shape of the normal modes of mechanical oscillation of the membranes.

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Metamaterial and metasurface devices (i.e., meta-devices) have shown tremendous potential for disrupting conventional RF and optical system design due to their ability to tailor the propagation of electromagnetic radiation in a desired fashion. Meta-devices are generally synthesized from “meta-atom” building blocks which are optimized to meet a certain set of user-designed performance criteria. Meta-atom optimization often requires the use of full-wave electromagnetic solvers which can make the process computationally challenging, especially when a large number of design parameters are used to define the meta-atoms. To this end, inverse-design strategies based on multi-objective optimization and deep learning which seek to efficiently explore the vast space afforded by nanofabricated meta-devices are presented.

An electromagnetic inverse source algorithm, which was developed to infer the macroscopic properties of metasurfaces from desired power patterns for 2D wave propagation, is extended to the 3D configuration. This inversion algorithm takes the desired power patterns on two perpendicular far-field cuts, and outputs the required equivalent currents on the surface of the metasurface. The required metasurface macroscopic properties can be subsequently found.

In this work, the design of a locally lossless and passive anisotropic metasurface performing an anomalous refraction and a linear-to-circular polarization conversion is presented, by using a numerically efficient surface field optimization. The metasurface consists of the cascade of three patterned metallic layers, modeled through homogenized impedance sheets.

Micro and nano fabrication allow complex optical structures, but design and control is challenging. Fortunately, advances in complex interferometric circuits show that, with good choice of circuit architectures, programming, stabilization, and control can be straightforward, allowing self-configuration without calibration or calculation and with adaptation to problems in real time.

A neural network is trained to infer the magnitude and phase components of a linear line source array from a given desired power pattern. The tangential fields produced by this array are then utilized by an integral equation based algorithm (equipped with surface wave optimization) to design lossless and passive reflectionless omega-bianisotropic Huygens’ metasurfaces to transform a known source into fields that satisfy the desired power pattern.

We study a reflectionless transformation of an incident Gaussian beam in which the transmitted beam increases its waist. In two examples with different output beam widths, the optimization results were verified by full-wave simulations with a transmission efficiency of over 90% for a triple-impedance-layer representation of the structure.

We numerically investigate the focusing properties of an acoustic metasurface consisting of a line of pillars of elliptic shape on a thin plate. We report on the influence of the ellipticity parameter on both monopolar compressional and dipolar bending modes of the pillars. We show that both resonances can be superimposed for a particular choice of this parameter and allow a phase shift of 2in the transmission coefficient of an incident antisymmetric Lamb wave We then study the interaction of such a wave with a line of pillars with a gradient in their ellipticity and show the capacity of this structure to focus the transmitted elastic wave at different targeted points.

Dynamic control over a reflected wave phase makes it possible to deny an interrogating radar system from obtaining the instantaneous velocity of a moving object. Furthermore, this approach allows creating an impression that a stationary object is moving. Here, a scattering phase screen, assembled from an array of dipoles with varactor diodes placed in their gaps is studied experimentally and theoretically. Modulating the voltage drop on the varactors allows controlling the reflected phase. By temporally modulating the voltage, the Doppler phase shift produced by the motion of the scatterer can be completely compensated, creating the illusion that the moving target is stationary. Similarly, by properly modulating the scattered phase in time, Doppler and micro-Doppler shifts can be produced in the resulting echoes, which can deceive the investigating system. The proposed method opens the door for the use of smart time-dependent materials for passive jamming applications.

Metasurfaces arose as a new platform for designing flat optical components, which can control light phase and amplitude at nanoscale dimensions and pave the way to substitute conventional bulky optics with compact, light and cheap flat optics solutions. One of the key development directions for metasurfaces is to make them dynamically tunable so that the obtained optical function can be switchable in time, opening a wide verity of different applications in optoelectronics. In this presentation, I will review our recent progress on developing dielectric metasurfaces with individually tunable nanoantenna pixels and their potential applications for light detection and ranging (LiDAR) and 3D holographic display technologies.

We report the inverse design of ferroelectric-dielectric metamaterials with three dimensional optimized topology that can reach higher tunability than the bulk material. The effect is attributed to local field enhancement in the unit cell when a voltage is applied.

A reconfigurable microwave reflectarray metasurface (MS) is investigated for beamforming applications. The reflected beam direction is changed by applying external dc voltages, which create a reflection phase gradient on the structure. The studied MS comprises a chess-board-like array of metallic patches placed over a grounded dielectric slab with metallic vias connecting the patches to the controlling lines. Tunability is achieved with nonlinear capacitive loads (varactors) inserted between the corners of the metallic patches. The MS is studied analytically, numerically and experimentally, from which reshaping of the radiation pattern is observed according to the applied control voltages on the MS elements. It is shown that the proposed MS-based reflectarray with just 3-by-10 elements is already sufficient to redirect the beam in different directions.

We present and discuss the all-optical reconfigurability of metalens optical response as a consequence of thermoplasmonic induced changes of the local refractive index. Since the orientation-dependent optical properties of liquid crystals can be controlled with external stimuli, this technology can enable dynamic control of the metalens optical response.

The T-matrix is the most comprehensive representation of an object’s optical properties. Once known, many photonic materials made from these objects can be described. The T-matrix can be calculated classically for macroscopic objects or quantum-chemically for molecules. This allows a unifying description of natural and artificial photonic materials presented here.

We experimentally measure the extinction and the thermal emission of disordered Metal-Insulator-Metal metasurfaces. By using hierarchical Poisson-disk distribution with various densities, as well Kirchhoff’s law, we can retrieve the extinction and absorption cross-sections of the resonators. Results show that the absorption cross-section is of the order of the diffraction spot area.

The manipulation of the phase profile of a mechanical oscillation on a surface allows to control the propagation of the elastic waves. Metamaterial structures can be used to form gradient index phononic crystal. The introduction of partitions in the structure to separate different layers grants full phase control in the propagation direction: the phase delay of the wave propagated in a layer depends only on the local refractive index. A detailed design procedure that is valid in a general way for any kind of mechanical lens is proposed, together with the specific case study of a converging lens that focuses a 600 kHz plane wave at a distance of 10 mm on silicon.

In this paper, dielectric metasurfaces are proposed as engineered substrates for Surface Enhanced Raman Spectroscopy (SERS), for the detection of small biological particles, such as proteins or viruses. The advantages offered by these structures, with respect to conventional plasmonic surfaces, are discussed and the expected Enhancement Factor (EF) is derived. The exploitation of optical trapping for operation in solution is also discussed.

Moiré metasurfaces offer unique possibilities, but their full potential for photonic applications has yet to be explored. An analytic investigation of the photonic band structure for two strongly coupled, linear arrays of identical atoms reveals tunable resonance locations based on the choice of a Moiré parameter.

We study acoustic propagation in a waveguide loaded with resonant side-branch channels. In the low frequency regime, effective one-dimensional models are derived in which the effect of the channels are reduced to jump conditions across the junction. When the separation distance is on the scale of the wavelength, which is the case that is usually considered, the jump conditions involve a single channel and acoustically induced transparency (AIT) occurs due to interferences between the two junctions. In contrast, when the separation distance is subwavelength, a single junction has to be considered and the jump conditions account for the evanescent field coupling the two channels. Such channel pairs can scatter as a dipole resulting in perfect transmission due to Autler-Townes splitting (ATS). We show that combining the two mechanisms offers additional degrees of freedom to control the transmission spectra. Application to perfect absorption supported by experimental results will be discussed.

Remote contactless sensing and position localisation of conducting objects have vast applications ranging from in-situ quality control in 3D printing to medical diagnostics. We employ a metamaterial array of coupled resonant meta-atoms and localise metallic objects using the time- domain reflectometry of slow magnetoinductive (MI) waves. An analytical model based on the evaluation of group velocity is verified by the experimental data. For the first time to our knowledge accurate single and multiple defect localisation is demonstrated, opening up possibilities for real-time contactless monitoring of inhomogeneous conductive environments.

We have shown that double wire medium support two mode with hyperbolic isofrequency contours, one of which provides high transmittion and can be used to create a planar gathering lens. Both numerical simulation and experimental measurements are present.

<p> Metasurfaces and metastructures will be presented that perform mode conversion. Mode conversion refers to the process of converting one set of orthogonal input modes to a corresponding set of orthogonal output modes. Specifically, metasurfaces for radiation control will be described as well as metastructures for the control of guided waves.</p>

This paper proposes a new technique for improving impedance matching in waveguide ports and irises using the high index mode of locally resonant metamaterials below the bandgap. Using this subwavelength focusing method, named metamaterial port (meta-port), we can improve the matching in a step discontinuity, such as coupling the wave from propagative waveguides to evanescent filters. As examples, we utilize resonant pins inside a rectangular waveguide above the cut-off (9-18GHz) to realize a wideband matching solution in miniaturized microwave filters. Our solution improves the transmission from an iris and reduces reflections at the waveguide ports, which may find applications in a wide variety of miniaturized meta-devices.

The wire media (WM) slab is proposed and investigated in the paper for the broadband digital imaging. The suggested mechanism is based on the transfer of near-field of the discrete sources via parallel channels of the WM slab to the far-field region up to 5λ. The channels are formed as the groups of adjacent wires of WM interfaces. By the suppression of the canalization regime the transfer in wide frequency range up to 4 GHz is supported. The digital post-processing that was applied for the E-field distribution at the WM’s output interface shown the perfect recognition of the transferred digital image with subwavelength resolution.

Modern wireless communications require agile and dynamic control of electromagnetic radiations to achieve spectrum and energy efficiency. Technical challenges include the development of novel materials with low loss and high tunability, ultrathin and flexible devices with low cost manufacturing. In this talk, I will introduce the framework of Software Defined Materials (SDMs), meaning their properties can be modified and updated by simply uploading computer software. SDMs will positively impact the environment, as devices built from them will use less energy and emit less carbon dioxide. I will first introduce some new approaches based on machine learning aimed for new material discoveries; robust design of control network to support SDM becomes more sophisticated but important, a new approach inspired by wireless mesh network will be presented. Finally, the demonstration of real-time SDMs will be presented with both numerical and experimental results.

We present an effective medium approach for the study of metamaterials made of cylindrical scatterers/meta-atoms. The approach is based on the well-known to the Solid State Physics community Coherent Potential Approximation (CPA) method and it is able to accurately describe the metamaterial response well-beyond the quasi-static regime. As is developed in our work, the effective medium approach is applicable to systems/metamaterials comprising of simple-, coated- and multicoated-cylinders, as well as metasurface-coated-cylinders. We demonstrate here the power of this approach in the case of polaritonic cylinder systems, where we observe a rich metamaterial behaviour, including frequency regions of engineerable negative permittivity, negative permeability, negative refractive index and hyperbolic response.

We present a novel method to retrieve local effective material parameters of a material made from periodically arranged scatterers described by their T-matrix. By fully considering the interaction between the multipoles of the scatterers inside the lattice, the exact wave number dependent renormalization of the dipoles is incorporated.

<p> We introduce an effective medium approach to characterise the dynamic response of a generic dispersive space-time crystal in the long-wavelength limit. It is shown that the effective theory captures the dispersion of the first photonic bands and that the effective response can be active or present negative stored energy.</p>

Metasurfaces placed in a glide-symmetric configuration have unusual properties: wider bandwidth, higher density, stronger magnetic response compared to their non-glide counterparts. We give explanations of these different behaviours by using various modelling methods proposed in the last years to tackle the design of innovative devices.

We develop a connection between the spatial symmetries of metasurface scattering particles and the components of the corresponding effective material tensors. This is achieved by combining the fundamental properties of spatial symmetries of the electromagnetic fields with a multipolar formulation of spatially-dispersive constitutive relations. This work may prove to be significantly useful for metasurface modeling as it greatly reduces the complexity of the problem by removing all material components that are not consistent with the shape and symmetries of the scattering particles. It also provides a strong physical foundation to investigate phenomena such as achiral chirality.

We study the propagation of acoustic waves through a thin bubbly screen. The analysis is conducted in the time domain and preserves the non linear response of the bubbles; it provides an effective model involving a jump of the normal velocity coupled to an equation of the Rayleigh-Plesset’s type for the bubble radius. Numerical implementation of the effective model allows us to discuss the influence of the distance between bubbles within the screen and that of the non linearities.

A spatially modulated, conformal printed metasurface cloak on a grounded dielectric substrate is designed for large free-standing objects. The metasurface converts the incident wave on the lit side into surface waves and guides them along the surface before recovering the incident wave on the shadow side. The scalar reactance profile is realized as a length-modulated array of printed copper strips on a grounded dielectric substrate. The cloaking performance is verified by full-wave simulation of the physical design.

We show how the non-conformal distortions of optical space are connected to the refractive index distributions of isotropic dielectric non-Hermitian media. Using this insight, we design and numerically demonstrate the operation of a broadband unidirectional invisibility cloak. Remarkably, the presence of gain and loss lifts the usual requirement of near zero refractive index values for such cloaks. Our framework provides an unexpected bridge between the fields of transformation optics in isotropic media and non-Hermitian photonics.

A new paradigm for the detection of invisibility cloaks is introduced. The proposed technique is based on diffraction tomography, which smartly processes hitherto overlooked information, resulting in a drastic sensitivity enhancement and enabling us to image the cloak, which is surprisingly exposed even at its design frequency.

By engineering light absorption in dielectric nanoantennas, we explore new opportunites for the manipulation of temperatures at the nanoscale as well as the design of tunable metasurfaces.

We will report zero-bias, uncooled, filterless photodetectors in mid-infrared exhibiting colossal discrimination ratio, close-to-perfect CPL-specific response, a zero-bias responsivity of 392 V/W, and a detectivity of ellipticity down to 0.03-degree Hz-1/2. Our approach employs plasmonic nanostructures array with judiciously designed symmetry, assisted by graphene ribbons to electrically read their near-field optical information. It highlights the potential of hybridizing metasurface and semimetals for miniaturized polarimetry.

Epsilon-near-zero materials have been shown to be as one of the most promising optical materials in the recent years as the electromagnetic field inside media with near-zero permittivity has been shown to exhibit unique optical properties. I will review our recent studies on the active linear, nonlinear, and emission properties of conducting oxide and metallic nitride epsilon-near-zero materials.

Put your abstract hereHierarchical structures with constituents over multiple length scales are found in various natural materials like bones, shells, spider silk etc, all of which display enhanced quasi-static, but also dynamic properties [1]. This paper provides an overview of numerical and experimental studies on biological and bioinspired structures with interesting wave attenuation properties, including hierarchical (diatom-like) [2], spiral-shaped (cochlea or shell-like), frame (spider-web-like) metamaterials [3, 4]. The role of viscoelasticity, which is essential in biological materials, is also discussed [5]. Results highlight a number of advantages through the introduction of structural hierarchy. Band gaps relative to the corresponding non-hierarchical structures are mostly preserved in both types of structures, but additional hierarchically induced band gaps appear in some cases, and hierarchical configurations allows the tuning of the band gaps to lower frequencies in others, with simultaneous structural weight reduction effects. We show that relatively simple and lightweight structures like hierarchical or spider-web inspired frames are amenable to a high degree of tunability using a limited number of geometrical parameters, e.g. local beam cross sections variations or localized masses in nodal points. Additionally, we explore the possibility of combining another typical characteristic of biological systems, which is adaptability to the environment (i.e. dynamic tunability), with bioinspired designs. We propose to do this using 3D-printed photo-responsive polymers, which can reversibly change their Young’s modulus at selected locations by up to 30% upon laser illumination [6]. The combination of the two strategies (bioinspiration and tunable polymers) can provide new tools for the design and fabrication of a wide variety of metamaterials with novel properties, which can be tailored for practical applications.

Spider orb webs are versatile multifunctional structures with optimized mechanical properties for prey capture, but also for transmitting vibrations. The versatility of such a system mainly derives from its variable geometry, which can be effectively used to design phononic crystals, thus inhibiting wave propagation in wide frequency ranges. In this work, the design of spider web-inspired single-phase phononic crystals through selective variation of thread radii and the addition of point masses is proposed, determined through the use of optimization techniques. The obtained results show that spider web geometry displays a rich vibration spectrum, which by varying its geometric characteristics and adding localized masses can be tailored to manipulate wave modes, and the resulting two-dimensional phononic crystals present wide complete band gaps generated by Bragg scattering and local resonances.

We demonstrate a high-rate directional single-photon source at room-temperature. This is achieved by binding a single colloidal quantum dot to a nanocone resonator located at the center of a bullseye antenna.

We predict and demonstrate experimentally, for the first time to our knowledge, the generation of spatially entangled photon pairs through spontaneous parametric down-conversion from a metasurface incorporating a nonlinear thin film of lithium niobate covered by a silica meta-grating. We identify the spatial entanglement of the photon pairs through violation of the classical Cauchy-Schwartz inequality. Simultaneously, the photon-pair rate is strongly enhanced by 450 times compared to unpatterned films.

This work presents our recent results on isolators suitable for quantum systems. We first discuss the isolation effect obtained by a suitable combination of quantum nonlinearities and symmetry breaking. Then we discuss a novel approach to tunable isolation based on twisted bilayered Weyl semimetals. The approach enables highly efficient tuning of both direction and value of isolation with the relative rotation of Weyl semimetals.

Integrated photonic technologies are essential for efficient generation, manipulation, and detection of quantum states of light and can potentially enable a high density of on-chip photonic qubits and the level of performance required for the practical realization of various applications in the quantum domain. Our group recently discovered bright, stable, linearly polarized, and high-purity sources of single-photon emission at room temperature in scalable platform based on SiN. We also show how the enhancement of the light-matter interaction with plasmonic materials can shorten the spontaneous emission time to beat the dephasing time and achieve coherence even at non-cryogenic temperatures. Our findings spark further studies of quantum emitters toward deeper understanding of their nature, deterministic formation, and scalable integration with on-chip quantum photonic circuitry. We also demonstrate how hybrid quantum sensors with record-high sensitivity can be developed, by employing spin qubits controlled by light and coupled via magnons.

We present an alternative scheme for obtaining effective power dissipation in planar composites, extending the recently proposed concept of metagrating (MGs), sparse arrangements of polarizable particles (meta-atoms), to realize multifunctional absorbers. In contrast to typical metasurface solutions, where periodicities are limited to half of a wavelength at most to avoid high-order Floquet-Bloch modes, we purposely consider large-period MGs, relying on their proven ability to effectively mitigate spurious scattering. The absorption process is thus implemented via precise engineering of the mutual coupling between numerous individual scatterers fitting in the enlarged period, with these additional degrees of freedom further utilized to enforce the perfect absorption conditions for multiple excitation angles simultaneously. The resultant devices, utilizing a standard printed circuit board configuration obtained semianalytically while featuring relaxed fabrication demands, exhibit high absorption across a wide angular range, useful for radar cross section reduction and energy harvesting applications.

In this contribution, I will discuss the implications that glide symmetries have in the electromagnetic properties of periodic structures. These special properties have a significant impact in microwave and antennas, leading to advantages for ce rtain applications. For example, glide symmetry can be used to reduce the dispersion of periodic structures, to enhance their anisotropy, to widen their stopbands , and to enhance the magnetic/dielectric properties.

Conductivity is an important parameter whose detection has applications in multiple areas including metallurgical industry, coatings design, additive manufacturing and biomedical engineering. This paper proposes a contactless method of conductivity detection which does not affect the integrity of the sample under study, based on monitoring changes to both the resonant frequency and the quality factor of a split-ring resonator. We achieve a full-range conductivity detection with an error lower than 10% across 8 decades of the conductivity values ranging from 0.03 S/m to 6.107 S/m. Analytical results for conductivity dependence are verified by numerical simulations and by experimental data.

We present a new torque sensor concept based on tunable millimeter wave metamaterials. The readout is done by means of a frequency modulated continuous wave (FMCW) chip. We show numerical simulations of the sensor effect and provide the proof of concept by means of a demonstrator.

We demonstrate a novel approach to realize optical neural networks by condensing the layered computations into a singlet of metasurface device, which provides task-specific transformations of signals for recognizing the identity of an optical object.

We demonstrate that single-layer dielectric metasurfaces can operate as multi-functional polarisers. We perform topological optimisation of nanopatterns for angle-selective transmission of different linear or circularly polarised light waves. We predict high transmittance and extinction ratios for both normal and strongly oblique incidence angles, demonstrating flexibility in matching diverse application requirements.

Conventional 1D grating based Guided-mode resonance (GMR) is a strongly angle sensitive phenomenon which is useful in some applications like sensing. But when we need angle insensitive absorption, for example in solar cells or photodetectors, the angle dependence is not desired. One can eliminate this problem by carefully choosing a 2D GMR structure. In this work, by adopting a double-exposed e-beam lithography approach we fabricate a hybrid 2D metasurface based GMR. We experimentally demonstrate that by using a quasi-square lattice metasurface we can have an angle insensitive absorption band which can be useful in perfect absorption broadband applications.

Metamaterials and metasurfaces provide a rich playground for both passive and active manipulation of phase and polarisation of light. In this talk, we present an anisotropic metamaterial platform for local control of polarisation in complex vector beams, including radial and azimuthal beams. The induced transformations of vector beams, topological properties and applications, as well as ultrashort pulse management will be discussed.

The dynamics of current elastic metamaterials is described using dozens of macroscopic material parameters grouped into mass density, stiffness and Willis tensors. Recent research has shown that most of these parameters could be controlled in complex structures such as active metamaterials, Willis media, and space-time modulated metamaterials, but methods to extract all the parameters and, more importantly, provide insight into the new physics enabled by these metamaterials are currently needed. This presentation will outline a new method to extract all the material properties of complex media from scattered elastic fields with convolutional neural networks (CNNs). Remarkably, we will show that edge diffracted scattered waves typically avoided by current analytical methods contain significant information about the dynamic behavior of matter, and this information can be learned by CNNs and extracted through analysis of the trained CNN. The approach will be illustrated experimentally in scenarios involving elastic and acoustic metamaterials.

Machine learning (ML) is now widely used for a variety of important tasks. To improve ML performance, several computational architectures have been investigated whose physical implementations promise compactness, physical robustness, and low energy cost. Here, we experimentally demonstrate an approach that uses a nonlinear disordered cavity as a complex reverberant acoustic environment for the physical realization and enhancement of the computational power of a type of ML known as reservoir computing (RC). We realize the required fading memory of RC systems by leveraging the internal memory of sound-propagation and the intrinsically large feedback of disordered structures to increase the expressive power and reduce the total size of proposed RC. In addition, the use of reconfigurable nonlinear electroacoustic resonators on the cavity's top side allows us to enhance the reservoir size and, as a result, the performance of the acoustical reservoir computer. We show the efficiency of our approach on a challenging benchmark problem: forecasting chaotic time series.

We propose a novel complete bandgap mechanism created by overlapping a flexural and longitudinal bandgap to attenuate the propagation of all mechanical waves. We designed a chiral metabeam with such a bandgap mechanism and observed the complete bandgap. This bandgap mechanism can be applied to vibration shielding systems.

Metamaterials with exotic dynamic properties enabled by careful curvature design is illustrated. The designs include minimal surfaces inspired by the Schwarz P surface with symmetry breaking topological defects, and smooth curvature profiles designed to emulate known waveguiding effects on thin membranes with spatially varying curvature.

We present a novel theory (generalized matching theory) to realize the perfect transmission of obliquely incident elastic waves across dissimilar media. The perfect transmission across dissimilar media is possible if an anisotropic layer satisfying specific conditions is inserted between them.

Through an interface between different media, achieving both impedance matching and wave tailoring has been impossible via previous methods. Here, we suggest a double-unit elastic metasurface composed of two mass-spring systems, phase modulator and impedance matcher, to detour the constraint on various phase shifts and impedance matching. The proposed metasurface is numerically and experimentally validated.

An increasing amount of research is being devoted to improving the spatial resolution of photo-polymerization in direct laser writing technique allowing the fabrication of complex 2D and 3D nanoscale devices. Among the various possibility, we used a metal/ insulator/ metal/ insulator (MIMI) planar multilayer to upgrade a standard two-photon direct laser writing (TP-DLW) process to hyper resolution thanks to its uncommon feature as extraordinary transmittance, zero reflectance, giant dephasing, and epsilon-near-zero permittivity. The improved resolution opens new possibilities in the nanofabrication of next-generation nanoscale devices such as metalens, flat optics and photonic circuits to name a few. Having reduced the voxel size by about 89% in height and 50% in width, we fabricated an apochromatic broadband metalenses with extended focal length and depth of focus, and numerical aperture of 0.087. The full capability of the achieved hyper resolution are exploited by fabricating a flat detailed basrelief of Da Vinci’s ”Lady with an Ermine”.

Conventional fluorescence microscopy with tunable lenses suffers from the challenges of mechanical complexity and large bulk size. We solve the problem using a newly developed technology empowered by compact lightweight Moiré metalens with tunable focal length.

Direct writing with a focused electron beam is an extremely powerful tool for fabricating 3D nanostructures in a mask free single step process. While its flexibility and the accuracy of the resulting nanostructures are unprecedented, the complex chemistry of the process and the deposited material presents a long standing problem. Here we will provide an overview of the state of the art and derive new approaches to improve process performance.

In this work, we aim to design a uniquely compact converter and detector for circularly polarized light based on plasmonics, which will be essential for future applications in quantum optics and metamaterials. The proposed structure consists of a vertically oriented gold double helix coupled to a planar two-wire transmission line on a substrate. The helix acts as a sensitive antenna for circularly polarized light, while the plasmonic transmission line guides two different modes depending on the incident polarization state. We developed direct fabrication protocols: while the helices can be directly written by electron-induced deposition, the plasmonic waveguides can be cut from single-crystalline gold flakes utilizing focused ion beam milling.

In our work we present a way to harness the well-known Rayleigh-Plateau instability of multiple fluid threads placed within a curing elastomer solution to rapidly manufacture elastic mechanical metamaterials.

In this work we introduce the concept and uses of Meta-Atoms (MTAs) in Electromagnetic metamaterials. MTAs take the form of metallic or dielectric meso scale cuboid inclusions which could be 3D-printed in multi- layered metamaterials with different periodicities. Potentially these meta-atoms could be varied in constitution and geometry to augment a variety of artificial magnetodielectric properties. The effect of their periodicity on the effective EM properties (constitutive parameters) is examined by placing the 3D- printed samples in a waveguide or on a resonator. Some of these structures have been applied in engineering applications such as 3D antennas, filters and microwave lenses, prototypes of which will be shown.

The global digitalization and the recent rise of artificial intelligence-based data-driven applications have directed their vectors towards terabits per second (Tbps) communication links. The existing 5G communication architect cannot fulfill this demand due to bandwidth scarcity, which has stimulated innovative technologies with a vision of 6G communication. Terahertz (THz) technologies have been identified as a critical candidate for the emerging 6G communication with the potential to provide ubiquitous connectivity and remove the barrier between the physical, digital, and biological worlds. Nonetheless, the existing THz on-chip communication devices suffer from scattering loss, bending loss, limited data speed, and lack of active tunability. Here, I will describe a new class of active on-chip THz topological devices consisting of broadband single channel 160 Gbit/s communication link, built on Silicon Valley Photonic Crystal. Silicon topological photonics will pave the path for augmentation of CMOS-compatible terahertz technologies, vital for accelerating the development of 6G communications that would empower societies with real-time terabits per second wireless connectivity for network sensing, holographic communication, cognitive internet of everything, and massive digital cloning of the physical and the biological world.

We show how to achieve single-photon control via a synthesized optical magnetic response without metamaterials, using quantum-mechanical electric dipole transitions of naturally occurring atoms. We demonstrate how arrays of atoms can be designed to absorb, store, and emit single photons and realize a quantum atomic Huygens' surface that allows for extreme wavefront engineering. The response can be further controlled by the quantum state of an optical cavity, generating entanglement between the cavity and the array, and hence the cavity and transmitted light.

We outline a procedure to compute input-output relations in any linear lossy multiport network, allowing for the analysis of quantum interference. Additionally, we study the excitation of a Wilkinson Power Divider (WPD) with nonclassical states of light. We demonstrate that a WPD grants access to different quantum coherent absorption events.

Quantum metamaterials enable new forms of light-matter interactions, which can be harnessed for the generation and exchange of nonclassical light states. In our talk, we will review our recent advances in the field of quantum metamaterials for nonclassical light emission, including dimension-dependent radiative processes in near-zero-index media, nonperturbative decay dynamics metamaterial waveguides and strong magnon-optical photon coupling via material dispersion engineering.

We develop a holography-based design approach for molding photon emission with distinct directional and polarization characteristics. We demonstrate the efficiency and versatility of the developed approach by analyzing different hybrid SPP-QE coupled metasurfaces designed for generating photons with desirable polarization characteristics propagating in various off-axis directions.

We propose an on-chip integrated photon source emitting well-collimated photons with high-purity circular polarization, based on hybrid plasmon-quantum emitter (QE) metasurfaces consisting of anisotropic bricks arranged as Archimedean spiral gratings coupling to quantum emitters. The outcoupling efficiency attains up to 97.8% (with S3 > 0.9), demonstrating a near-perfect circular polarization.

Materials not in thermodynamic equilibrium can exhibit negative static electric susceptibility χ(0). In this paper, we investigate the limit of negative χ(0) that can be possibly achieved. Since, χ(0) can be related to the microscopic properties of material, as suggested by the famous “Clausius-Mossotti” equation, we study the classical model of dipolarisable entities for three Bravais lattices and explore their negative χ(0) limits. Possible application of such materials is also discussed.

We present a scheme supporting an exceptional point of degeneracy (EPD) using connected resonators without gain and loss. One resonator contains positive components, whereas the second resonator contains negative components. We show a second-order EPD where two eigenvalues and eigenvectors coalesce. This circuit can be used to make ultra-sensitive sensors.

In this talk, we will present the exotic coherent perfect absorber-laser (CPAL) formed by on parity-time (PT)-symmetric metasurfaces, and its application in high-performance sensing and cryptography.

We explore experimentally, numerically, and analytically a time-dependent system created by a time-modulated active control on a loudspeaker. We model analytically this system with a transmission line having a time-varying acoustic resistance. This strategy could be used to design and implement various wave manipulation systems, such as acoustic circulators, among others.

A concept of negative (non-Foster) inductance with very robust stability properties is proposed. Proposed device is based on compensated passive RC structure and it is very convenient for microelectronic realization since it does not contain any inductor. Basic idea is verified by realistic circuit simulations of negative inductance designed for operation in UHF band. Foreseen applications are in active metamaterial/metasurface structures.

In this talk I will compare the physical backgrounds of non-Foster elements and time-varying elements, as well as the recently introduced time-varying route to none-Foster elements. I will argued that combination of both approaches leads to some novel devices that use both linear and nonlinear time-varying non-Foster effects.

Hyperbolic metamaterials exhibiting direct-transition from type-I to type-II in the mid-visible region are realized and demonstrated for the first time. They are characterized using angle resolved transmission and reflection measurements, exhibiting supercollimation effect at 589 nm. the use of perovskites as the dielectric materials facilitate the introduction of optical gain leading to active hyperbolic metamaterials.

Optical resonators leading to very high field enhancement have greatly gained interest in the SEIRA domain. Perfect absorber Helmholtz-like structures have been presented as good candidates to create sensors, as they lead to strong field confinement in relatively large volumes and demonstrated experimentally the enhancement of a targeted absorption peak of 2,4-dinitrotoluene by 15%. We show in this work that an over-coupled Helmholtz-like structure can achieve four time greater absorption enhancement of not only one but of several vibrational modes over a very large wavelength range. The assemblage of such broadband optical resonators could therefore lead the way towards the development of simple and versatile infrared fingerprint sensor devices.

We studied circular dichroism (CD)in hexagonal and square arrays of elliptical nanoholes etched in thin metallic layers. CD resonances in transmission and absorption spectra fall in Extraordinary Transmission peaks and are associated with surface plasmon-polaritons at the interfaces with the metal. The conditions for maximizing the CD are determined.

The arbitrary manipulations of fields and waves for analogue and quasi-digital computing processes has become a new paradigm for computing applications in recent years. In this talk, we will show and discuss our most recent findings in this field by exploiting light-matter interactions for fundamental decision-making processes (such as if-then-else) and analogue computation of temporal derivatives.

In recent years, the arbitrary control of electromagnetic waves enabled by metamaterials and metasurfaces has opened interesting avenues to explore alternative wave-based computing paradigms. Notably, analog optical computing is becoming a powerful tool for fast and energy efficient processing of mathematical operations. In this work, we will present our recent progress in the neural networks design of multilayered metamaterials capable of taking the temporal derivative of normally incident modulated temporal signals.

We demonstrate an optical hydrogen sensor based on Al2O3 dielectric grating, WO3 gasochromic oxide and Pd catalyst. The use of ultrathin (1-2 nm) palladium film has decreased losses and enhanced sensitivity. Sensor durability was studied.