Since the development of diffractive optical elements in the 1970s, major research efforts have focused on replacing bulky optical components by thinner, planar counterparts. The more recent advent of metasurfaces, i.e. nanostructured optical coatings, has further accelerated the development of flat optics through the realization that resonant optical antenna elements can be utilized to facilitate local control over the light scattering amplitude and phase. In this presentation, I will start by showing how passive metasurfaces can start to impact Augmented and Virtual Reality applications. I will discuss the creation of high-efficiency, metasurfaces for optical combiners for near-eye displays, OLED displays, and eye tracking systems. I will also briefly highlight recent efforts in our group to realize electrically-tunable metasurfaces employing nanomechanics, tunable transparent oxides, microfluidics, phase change materials, and atomically-thin semiconductors. Such elements are capable of active wavefront manipulation for optical beam steering and dynamic holography. The proposed optical elements can be fabricated by scalable fabrication technologies, opening the door to many commercial applications.

Dielectric nanoantennas represent a new versatile platform, which can be used to generate and enhance light emission at the nanoscale. In this talk, I will review our recent progress on using dielectric nanoantennas and metasurfaces for enhancing LEDs and achieving directional nanolasers of different geometries.

Tunable optical metasurfaces have a number of remarkable properties that are promising for potential applications in telecommunications, holographic displays, and spatial light modulators, to name just a few. In particular, integrating nematic liquid crystals (LCs) with dielectric metasurfaces has been established as an efficient tuning approach. Here we provide an overview of our recent advances in this research field.

We realized all-dielectric halide perovskite metasurfaces with giant chirality. Record-high circular dichroism and degree of circular polarization of luminescence are illustrated,based on different design principles, which prove thathigh refractive index halide perovskite metasurfaces rival conventional dielectric platforms for low cost, active metadevices

<p> Metasurfaces are key to manipulate electric and magnetic fields at the nanoscale. Being able to link the response of the individual scatterers the metasurface is made of, while considering accurately their interaction in the lattice, to the macroscopic response of the entire metasurface bears great potential for their design. Here, using a multipolar method, we provide rigorous analytical expressions for the diffraction of light from metasurfaces and metagratings at normal incidence. We restrict ourselves, for brevity, to isotropic constituents and scatterers up to quadrupolar order. With these analytical expressions, we identify scatterers and their 2D arrangement that form metasurfaces with diffraction characteristics on-demand. We demonstrate the applicability by designing a metagrating that perfectly cancels the zeroth-order transmission and diffracts all the light to the four first-order diffractions.</p>

Quasi bound states in the continuum (quasi-BICs) are expected to trigger significant advances in sensing and non-linear optics. Here, we perform a higher-order multipolar analysis of an all-dielectric metasurface that sustains a quasi-BIC resonance. Initially, we design a unit-cell comprising a cluster of dielectric spheres that sustains a quasi-BIC and arrange this unit cell periodically to form a metasurface. Scattering from the metasurface is analytically studied via the T-matrix method where we consider up to a quadrupolar multipolar order. Calculations of the effective polarizabilities reveal the impact of coupling among multipole moments with the same or different order on the excitation of the quasi-BIC mode. Our approach provides a comprehensive physical understanding of the underlying phenomenon.

Good waveguides need transparent materials. We show that this paradigm can be overcome by using two parallel High Contrast Gratings (HCGs) at grazing incidence. Using silicon-on-insulator (SOI) technology, we succeeded in guiding visible light in the plane of a silicon chip over centimeter distances.

We design elastic and acoustic 3D metamaterials supporting roton-like acoustical dispersion relations. For this type of dispersion relation, the wave’s frequency starts off proportional to the wavenumber and exhibits a local minimum at a finite wavenumber within the first Brillouin zone. This behavior can lead to broadband lossless backward waves and multiple partial waves at a given frequency and is accomplished by tailored third-nearest-neighbor interactions.

Localization of waves is studied by means of multiple scattering theory in a (2D) arrangement configuration. Studied structures belong to the so called twisted lattices. Results found show that, for a given frequency, there are localized modes for a discrete set of rotation angles, analogous to the recently studied angles for 2D materials such as graphene. The properties of these clusters whenever the rotation angle approaches a commensurable angle or a really small one are related to the dipolar interaction between scatterers. While the presented results are valid for any type of wave, flexural waves in thin elastic plates have been numerically studied and successfully explained in terms of the interaction between pairs of scatterers. The studied structures are shown as promising candidates for the design of tunable wave-trapping devices.

Twisted bilayered systems such as bilayer graphene have been shown to exhibit a series of remarkable properties ranging from superconductivity at magic angles to the manipulation of topological polaritons. However, the experimental observation of these concepts is often limited by the requirement of two physical layers and the fine control of their twist angle and coupling. We here illustrate that single-layered systems with Moiré-type modulations can exhibit wave physics behavior previously illustrated in bilayer systems. In particular, we study flexural waves in elastic plates with resonating pillars arranged according to a square lattice, whose heights are modulated by a twisted anisotropic modulation. The anisotropic modulation of the resonating attachments produces hyperbolic waves at selected frequencies, which exhibit an overall rotation following the twisting of the modulation. The simplicity of the presented approach opens new possibilities to manipulate and induce topological transitions between elliptic and hyperbolic phases driven by Moiré patterns in a variety of physical systems.

We experimentally realize a theoretically predicted laser-beam scanner based on a topologically protected twist-edge-state in a 1D diatomic chain of 3D chiral metamaterial unit cells. This progress has become possible by a novel casting fabrication approach leading to high-quality 3D silica microstructures. We find mechanical quality factors of the topologically protected twist-edge-state resonance as large as Q=2,850 at around 278 kHz resonance frequency.

Here we employ machine learning techniques to explore combinatorial metamaterial designs. We show that a CNN is able to classify, with high accuracy, which configurations support line modes. This suggests that the network has correctly learned to identify the set of design rules for the presence of a line mode.

In this paper, the accuracy of two popular finite element based methods for calculating dispersion diagrams of periodic metamaterials is compared. The study reveals that the wave finite element method tends to result in higher accuracy for more coarsely meshed models as compared to the shift cell operator method and that care should be taken when using the shift cell operator method for accurate stop band predictions using dispersion diagrams.

The metamaterial paradigm has opened new opportunities for gathering an unprecedented control on the spatial-temporal properties of various physical fields, including acoustic and elastic waves. Although a variety of metamaterial arrangements and designs have been proposed so far, most of them possess a static nature, i.e. their frequency response cannot be modified, once fabricated. However, 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 band gap frequency, 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.

Spider orb webs are versatile multifunctional structures with optimized me- chanical 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 prop- agation in wide frequency ranges. In this work, we propose the design of spi- der web-inspired single-phase phononic crystals through selective variation of thread radii and the addition of point masses, determined through the use of optimization techniques. Our results show that spider web geometry displays a rich vibration spectrum, which by varying its the 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 optically tunable control of second-harmonic generation in all-dielectric nanoantennas: by using a control beam which is absorbed by the nanoresonator, we thermo-optically change the refractive index of the radiating element to modulate amplitude and phase of the second-harmonic signal. For a moderate temperature increase, sizeable modulation is demonstrated; the large tunability of the single meta-atom response paves the way to exciting avenues for reconfigurable homogeneous and heterogeneous metasurfaces.

We demonstrate the modulation of a dielectric metasurface of lithium niobate with the linear electro-optic effect. We show a modulation enhancement of two orders of magnitude for driving frequencies up to 2 MHz and with less than 1 V peak-to-peak voltage. We observe a correlation between the transmission and the modulation amplitude in the vicinity of the optical resonance in the visible region.

We study free electron nonlinearities in heavily doped semiconductors, which have recently emerged as low-loss and tunable materials for plasmonics at mid-infrared frequencies. We develop a hydrodynamic description that takes into account contributions up to the third order, usually negligible for noble metals. Our model predicts that nonlinear optical phenomena caused by free electron dynamics could overcome intrinsic semiconductor nonlinearities by two orders of magnitude. In this context, we demonstrate that, despite showing zero second-harmonic generation efficiency, a semiconductor slab can generate a cascaded third-harmonic signal (due to second-harmonic filed interactions) comparable to direct third-harmonic generation. Moreover, we suggest a possible experiment to observe such effect.

We develop a new approach based on quasi-BICs to develop chiral metasurfaces exhibiting nonlinear circular dichroism (up to 99.9%) and high conversion efficiency (0.01 W^-2). Tuning mode interference allows selective linear and nonlinear circular dichroism.

In this work, we develop an approach aimed at the enhancement of stimulated Raman scattering (SRS) using ENZ media. It has recently been demonstrated that various nonlinear effects can be enhanced when a real part of the dielectric permittivity is equal to zero. Intuitively, one can assume that this condition remains valid for the case of SRS. We theoretically show a modification of the condition which permittivity must meet to achieve the ENZ-driven enhancement of SRS.

We propose a BIC-based nonlinear optical system for giant SHG from monolayer MoS2 on a silicon metasurface. About 600× of SHG enhancement from monolayer MoS2 on a resonant metasurface is shown relative to suspended monolayer MoS2. Moreover, we exploit an eigenmode expansion approach to express second-harmonic power.

We demonstrate highly efficient second harmonic generation from dielectric metasurfaces based on gallium phosphide platform, utilizing quasi-bound-state-in-the-continuum resonances. In particular, we demonstrate an efficiency of 0.1 %/W using pulsed laser at an intensity of 10 MW/cm2 and 5e-5 %/W using continuous wave laser at an intensity of 1 kW/cm2.

Electromagnetic (or microwave) encoders are chains of inclusions (metallic, dielectric or apertures) on top of a dielectric substrate containing a certain identification (ID) code. This paper briefly reviews several strategies for the design of microwave encoders, including the readers, and points out some potential applications.

We propose a comprehensive field-based semianalytical method for designing fabrication-ready multifunctional periodic metasurfaces (MSs). Harnessing recent work on multielement metagratings based on capacitively-loaded strips, we have extended our previous meta-atom design formulation to generate realistic substrate-supported printed-circuit-board layouts for anomalous refraction MSs. Subsequently, we apply a greedy algorithm for iteratively optimizing individual scatterers across the entire macroperiod to achieve multiple design goals for corresponding multiple incidence angles with a single MS structure. As verified with commercial solvers, the proposed semianalytical scheme, properly accounting for near-field coupling between the various scatterers, can reliably produce highly efficient multifunctional MSs on demand, without requiring time-consuming full-wave optimization.

We present the design, fabrication, and anechoic chamber characterization of a proof-of-concept multifunctional microwave metasurface, relying on a printed circuit board loaded with commercial-off-the-shelf resistors and capacitors that shape the response in 4-12 GHz. The same type of board is loaded with different loads realizing different functionalities: absorption, steering, polarizing.

In this paper, the use of a metasurface to improve the radiation properties of a Substrate Integrated Waveguide based slotted antenna is proposed. The design process of a 8 slot antenna following a Chebyshev distribution is presented and its performance is compared with that of a conventional one. The results demonstrate the improvement in the radiation performance that can be achieved, without affecting the bandwidth.

We present the numerical design of a dielectric Electromagnetic Band Gap (EBG) mode launcher-converter for high-power coupling of the accelerating mode in Dielectric Laser Accelerators (DLAs).

In this paper, we study the behavior of miniaturized high-order waveguide filters, constructed by loading a hollow metallic waveguide with resonant pins, to form a locally resonant metamaterial. Such composite pin-pipe structure supports a guided mode with adjustable bandwidth below the resonance frequency of the pins. We show that the position and bandwidth of this subwavelength mode are decoupled from the arrangement of resonant inclusions. We experimentally demonstrate the customizability of the bandwidth and the robustness of the passband against geometrical scaling. Our prototypes, which are an order of magnitude smaller and lighter than traditional filters and compatible with standard waveguide ports, may find applications in future satellite systems, for 5G or internet over satellites.

Over the past two decades, metamaterials have introduced a new paradigm for harnessing light-matter interactions from the nanoscale to macroscale at the level of single photons to flux of intense light. In this talk, we will present our work on interfacing quantum emitters, such as color centers in hexagonal boron nitride with planar metamaterials (also known as metasurfaces) for imaging and sensing applications.

We show that active and parity-time symmetric metamaterials can offer a novel path to molecular chirality sensing, facilitating the detection of even minute amounts of chiral substances and the discrimination of different enantiomers in circular dichroism experiments.

In this work, we studied the multipolar resonances for SERS substrates comprising of Ag-nanoparticle (Ag-NP) arrays grown in anodic aluminum oxide (AAO) nanochannels and their roles in affecting the signal amplification and the background noise. In addition, a duel-resonant system consisting of Ag-NPs embedded in a sinusoidal-shaped AAO/Al substrate was also investigated. The grating structure enables the excitation of surface plasmon polaritons (SPPs) to further couple with the generated hots spots between adjacent Ag-NPs and meanwhile provides a diffraction dispersion which is beneficial for spectral detection.

Accessing sub-wavelength information about a scene without manipulating its near field is a fundamental challenge in wave engineering. Yet, it is well understood that waves reverberating in complex media are sensitive to minute perturbations on a scale set by their dwell time. Modern coded-aperture imagers leverage the degrees of freedom (DoF) offered by complex media as natural multiplexor but do not recognize and reap the fundamental difference between placing the object of interest outside or within the complex medium. We show that in the latter case, deeply sub-wavelength information is encoded in the multiplexed measurements that can be decoded, for instance, using deep learning. We link the efficiency of deeply sub-wavelength information encoding to the waves’ dwell time. We demonstrate our findings in microwave experiments harnessing the configurational DoF of a programmable metasurface inside a chaotic cavity: we localize a sub-wavelength object with a resolution of λ/76 using intensity-only single-frequency single-pixel measurements.

Molecular optomechanical springs self-assembled in nanometre-scale metallic cavities allow extreme optomechanical coupling and single midinfrared photon sensitivity. Here we achieve frequency upconversion of 9-10μm mid-infrared incoming photons to visible photons via SERS in doubly-resonant metasurfaces.

In this talk we provide an overview of recent developments in the field of parity-time symmetry and supersymmetry with emphasis on exceptional points. The use of other type symmetries in photonics will be also discussed.

In this presentation, we will be discussing the physics of exceptional point degeneracies and we will be implementing them in the mechanical framework for the realization of a new class of micro-electromechanical accelerometers and electrodynamic actuators.

Typical sensors detect small perturbations by measuring their effects on a physical observable, using a linear response principle (LRP). It turns out that once LRP is abandoned, new opportunities emerge. Here, we propose a sublinear optomechanical sensing scheme which is rooted in Wigner’s cusp anomalies (WCA): a frequency-dependent square-root singularity of the differential scattering cross-section around the energy threshold of a newly opened channel. WCA square-root hypersensitivity can be applied in a variety of sensing applications, besides optomechanical accelerometry discussed in this paper. Our WCA platforms are compact, passive, and are not subjected to quantum-noise effects (unlike some recent proposals based on exceptional points) and, if chosen, can be cavity-free.

We propose a high-sensitive circuit scheme based on an exceptional point of degeneracy (EPD) using two LC resonators coupled with a gyrator, capable to provide two real frequencies when perturbed. We present the conditions to obtain EPDs in this circuit and the extreme sensitivity to system's perturbations.

The paper presents two analysis methods of curved metasurfaces based either on the estimation of EM field distribution in the vicinity of considered metasurfaces (Mode Matching approach), or on estimation of the equivalent current distribution at the metasurface (Method of Moments).

We report on the formation of high-Q localized states in finite arrays of Mie resonators overcoming the previously predicted values by at least two orders of magnitude. The effect becomes possible due to the destructive interaction of two band-edge modes and the cancelation of their far-field radiation. The interaction between the modes becomes possible due to non-monotonous dependence of the dispersion close to the band edge provided by the condition of degenerate band edge. Moreover, we observe that the formation of high-Q states is accompanied by the simultaneous resonant suppression of $N$-order multipoles, where $N$ is the number of elements in the array.

Electromagnetic waves at grazing incidence onto a planar medium are analogous to zero energy quantum particles incident onto a potential well. Typically such waves are com- pletely reflected in this limit. Here we explore dielectric profiles that support optical analogues of ‘half-bound states’ to allow for zero reflection at grazing incidence. We use the theoretical framework of supersymmetric quantum mechanics to obtain such profiles.
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Fragmenting of dielectric metasurfaces is found to affect their dipolar and lattice resonances. As the result, spectrally-stable, high-Q, odd dipolar resonance mode is formed in addition to red-shifting of even mode, associated with lattice resonances.

Abstract – Time dependent systems do not in general conserve energy invalidating much of the theory developed for static systems and turning our intuition on its head. This is particularly acute in luminal space time crystals where the structure moves at or close to the velocity of light. Conventional Bloch wave theory no longer applies, energy grows exponentially with time, and a new perspective is required to understand the phenomenology. In this letter we identify a new mechanism for amplification: the compression of lines of force that are nevertheless conserved in number.

We derive the dispersion relation of eigenmodes propagating in a time-varying and dispersive medium. We use these eigenmodes to analytically study the scattering of light by a sphere made from a time-varying and dispersive medium. These results are compared to full-wave optical simulations and excellent agreement is observed. With that, we provide tools and outline a path towards further explorations of light scattering by time-varying finite particles.

Time-varying metamaterials and metasurfaces have unlocked a novel way for electromagnetic waves to interact with artificial materials. In this contribution, we present an overview of the recent components and devices based on time modulation of artificial media, surfaces, and illumination signals for achieving time-domain devices, magnet-less non-reciprocity, doppler cloaking, frequency conversion, and virtual energy accumulation into open cavities, respectively.

We formulate a spatiotemporal plane wave expansion method to calculate the effective photonic band structures of time-varying photonic media. We exemplify a time-varying photonic crystal whose permittivity is spatially discrete and temporally sinusoidal. We show driving-induced opening of frequency and momentum gaps and breaking of mirror symmetry in the photonic band structures.

We present here a novel technique of cloaking. The related cloak is based on spacetime curvature induced by an accelerated perturbation, without any transfer of matter. First, we point out an accelerated moving perturbation modulation is an alternative to mass and moving matter for spacetime curving. Next, we outline the theory of this cloak which, following the general theory of relativity, consists in mapping the wave cloaking trajectories to a spacetime-modulation metric so as to determine the required spacetime refractive index profile. Then, we describe a practical implementation of the cloak, consisting in an SiO2 slab modulated by a circular wave pump. Compared to previously reported cloaks, the proposed cloak is immune of the issues of narrow bandwidth, single polarization, restricted cloaking size, and complex or impossible implementation. Given its unique features, this cloak should soon find its way to real-world applications. This work represents, to the best of our knowledge, the first report of spacetime curving based on perturbation modulation, without any motion of matter.

We present some recent advances in the field of coherent perfect-absorber and laser for elastodynamics and acoustic waves. This intriguing effect is enabled by PT-symmetry breaking condition. The results show that the sensitivity and resolvability of the CPAL-locked sensor may go well beyond the traditional acoustic sensors.

The presented work addresses an industry-oriented design process of vibroacoustic metamaterials for automotive components with enhanced acoustic properties. A vibroacoustic metamaterial design for further use in a vehicle door is developed and experimentally investigated. Production of the vibroacoustic metamaterial from sheet metal is done using punching and bending techniques.

We derive analytically and verify experimentally the Willis coupling closed-forms of simple one-dimensional asymmetric and reciprocal resonant structures made of Helmholtz resonators and plates. The coupling terms of the derived analytical closed-forms are analyzed in each of the three configurations.

A nonlinear mass-in-mass periodic system, whose unit cells are connected by means of anharmonic springs, can be equivalently represented via an anharmonic periodic chain of an effective mass-spring system. The effective mass, the band gap and the dispersion relations are calculated for a nonlinear seismic and periodic metamaterial.

We present a topology optimization for biphysical cloak that can render an object unobservable form both electromagnetic and acoustic waves. Three objective functions are minimized simultaneously for the scattering cancellations of E and H polarized waves and acoustic wave.

Two different configurations for realizing electrically controlled optical metasurfaces operating in reflection are introduced: piezoelectric MEMS mirror integrated with gap surface-plasmon based metasurfaces and Fabry-Perot resonator based on a thin electro-optic crystal layer sandwiched between nanostructured electrodes. Experimental demonstrations of electrically controlled beam steering and focusing are reported and discussed.

Many phase-change materials (PCMs) feature a unity-scale refractive index change upon transition from their amorphous to their crystalline phase. This optical contrast has been widely applied in active photonics, ranging from metasurfaces for beam steering to multi-level photonic memories. To boost the applicability of PCMs for a broader wavelength range two restrictions have to be overcome: the intrinsic absorptive losses for wavelengths below the mid-infrared present in the most prominent PCMs as well as the diffraction-limited feature sizes of the switched PCM areas. Here, we discuss our developments towards addressing these challenges by applying PCM nanoparticles and tip-induced switching.

We report a theoretical investigation of thermal performance limits of reflective gate-tunable conducting oxide metasurfaces illuminated with high power density laser beams. We show that conducting oxide metasurfaces can withstand the power densities required for many applications, such as free space optical communications, light detection and ranging (LiDAR), as well as laser-based additive manufacturing.

We are developing an environmentally insensitive hollow-core optical ring-microresonator with an ENZ metamaterial as cladding. Our concept is to use an ITO epsilon-near-zero (ENZ) metamaterial that we developed as the waveguide cladding to form an air or vacuum core ring-resonator. The idea is to make an intrinsic environment-insensitive cavity/ resonator device.

Here, we investigate a heterostructure supporting embedded eigenstates (EEs) governed by phonon-polariton resonances in anisotropic quasi-2D MoO3 layers in the IR spectral range tuned with a relative rotation of the layers. We demonstrate that the structure can be tuned from an almost perfect reflector to an almost perfect absorber and back near the EE state. The approach paves the way to reconfigurable absorbers, quasi-coherent thermal emitters and other active photonic elements.

We propose to retrieve the optical response of Mie resonators in the harmonic and time domains thanks to their eigen-frequencies. We derive the modal expansion of the S-matrix from which we obtain the optical response in terms of eigen-frequenices. Emphasis will be placed on the analysis of anapoles and times dynamics of dielectric cavities.

We report modeling and experimental characterization results of the propagating photonic bound states in a silicon-on-insulator (SOI) metastructure. The photonic bound states in the metasurface can be excited by the interaction between the discrete resonant modes and the incident wave. The calculated dispersion diagram shows anticrossings with continuous spectral narrowing at surface normal- and oblique-incidence excitations. In the presentation, we will discuss the measured spatial and spectral responses of the reflected beam from the fabricated SOI metastructure.

We demonstrate an extremely nonlinear all-dielectric metasurface that employs intersubband polaritons to achieve a second-harmonic conversion coefficient of 5 x 10-4 W-1 and second-harmonic power conversion efficiency of 0.015% at nominal pump intensities of 11 kW/cm2. Furthermore, through heterostructure design, we achieve microscopic control of the nonlinearity and demonstrate suppression or enhancement of second-harmonic generation by controlling the polarity of the resonant χ(2).

Subwavelength resonators provide the foundation of modern photonics, optics and acoustics. The high-Q-factor optical resonators allow achieving extreme energy confinement, enabling a vast number of applications. It includes strong light-matter interaction, low-threshold laser and enhanced nonlinear harmonic generation. Here we present a new method of how such high-Q states can be achieved in subwavelength particles in both photonics and acoustics.

Nonlinear optical phenomena in nanostructured materials have attracted much attention due to their wide range of applications, including sensing and novel light sources. Here, we review the recent progress of nonlinear frequency mixing in high-refractive-index dielectric metasurfaces. We focus on the enhanced nonlinear frequency mixing in two types of material platforms, namely III-V semiconductor metasurfaces and single-crystal transition-metal-dichalcogenide metasurfaces. Such nonlinear metasurfaces offer exciting prospects for infrared to visible conversion for imaging and night vision applications.

In this work, we will review our recent progress in development of active optical metasurfaces in the quasi-static and time-modulated operation regimes. In particular, we will emphasize the novel features offered by time-modulated metasurfaces and compare their performance in beamforming and pattern synthesis against their quasi-static counterparts.

In this work, we derive the Green's function for finite elastic beams with spatiotemporally-modulated material properties. We show for the particular case of flexural wave modes in a finite beam that spatiotemporal modulation of the Young's modulus can lead to the splitting and shifting of the resonances.

We exploit two phenomena for temporal metamaterials where the permittivity is changed from an isotropic case to an anisotropic tensor. We will show how such temporal variation of permittivity can lead to: (1) real-time change in the direction of energy propagation, and (2) under certain condition, to the temporal analogue of Brewster angle. We provide full physical insights of this phenomenon demonstrating, numerically and analytically, how it can be exploited for real time beam steering of electromagnetic waves.

In this talk, I discuss our recent research efforts on some new classes of temporally modulated metamaterials (chrono-metamaterials), with particular focus on (i) non-Hermitian time-varying media, and their application for broadband perfect absorption and one-way propagation along a synthetic dimension; (ii) drift-biased materials mimicking moving media at optical wavelengths, which enable breaking temporal symmetries without the need for magneto-optical effects or complicated space-time modulations; and (iii) enhanced quantum optical effects in time-modulated electromagnetic environments. Our findings highlight the many opportunities offered by time-varying metamaterials for both classical and quantum electromagnetics and photonics.

In this contribution, we present our recent results on the study of the propagation and design of the scattering response exhibited by a temporal metamaterial, i.e. artificial material whose electromagnetic properties are suddenly and dynamically changed over time. We focus our attention on the temporal counterparts of conventional dielectric slabs and multilayered structures. The first is realized through two sudden media switching during the propagation of the wave, which enables a scattering response like the one exhibited by a conventional spatial dielectric slab. In case of more than two switchings, we realize the temporal counterpart of multilayered structures. We demonstrate that by properly selecting the application time of each media realizing the temporal metamaterial, it is possible to design several types of optical and electromagnetic devices exploiting the temporal dimension instead of the spatial one.

A transmission line terminated with a time-varying capacitor charged up with a DC voltage source is investigated to transform electrostatic energy to dynamic energy and for energy accumulation.

We will discuss computational algorithms based on deep neural networks that can accelerate the design and simulation of nanophotonic devices.

Metamaterial and metasurface devices (i.e., meta-devices) have shown tremendous potential for disrupting conventional RF and optical components due to their ability to manipulate the propagation of electromagnetic waves in a tailored fashion. These meta-devices are generally synthesized from building blocks known as “meta-atoms” whose properties are engineered to achieve a specific electromagnetic response. In order to maximize the performance of these meta-atoms, numerical optimization techniques are often employed in conjunction with rigorous full-wave electromagnetics solvers due to their complex behaviors and the lack of established design rules. In this presentation, inverse-design strategies based on multi-objective optimization are introduced and used to realize high performance 2.5D and 3D meta-atom building blocks which can be used to synthesize a variety of meta-devices.

In topology optimization, the quality of the solution depends critically on the parametrization of the problem, and thus a multitude of such parametrizations have been proposed. In this work, we develop a holistic view of such parametrizations and explore how implicit and explicit biases affect the resulting designs.

We present a design framework for metasurface that uses a hybrid approximate solver for Maxwell's equations, which separates the comptutation for the metasurface's nano-scale and macro-scale, and thus makes large-diameter inverse design tractable on a laptop. We further demonstrate experimental realizations of ultra-large-area metasurfaces designed using this framework: (1) a lens with extended depth of field with a millimeter diameter, and (2) polychromatic lenses with diameters of up to 1 cm.

We present a method how to mitigate bad scaling of physics-informed neural networks (PINNs) by subdividing the problem between smaller coupled PINNs, alleviating one of the downsides of PINNs: large computational costs. We discuss these applications in context of forward and inverse scattering problems.

Inverse design techniques have become indispensable tools in the push toward the development of practical metamaterial-enabled devices. These tools frequently employ some type of multi-objective optimization scheme and/or deep learning algorithms. Several examples will be showcased where these tools have been successfully applied to the inverse design of electromagnetic metadevices.

We present a 3-dimensional fully natural sonic crystal composed of Aegagropilae that are spherical aggregates resulting from the decomposition of Posidonia Oceanica. The fiber network is first acoustically characterized, providing insights on this natural fiber entanglement due to turbulent flow. The seagrass fibrous spheres are then arranged on a principal cubic lattice. Band diagram and topology of this structure are analyzed, notably via Argand representation of its scattering elements. This fully natural sonic crystal exhibits excellent sound absorbing properties and thus represents a sustainable alternative that could outperform conventional acoustic materials.

Lattice-type materials offer lightweight and tailorable solutions for the design of phononic crystals and elastic metamaterials with low-frequency attenuation. Structural hierarchy, i.e., combining elements at different length scales, on such structures yields to an additional design degree of freedom. In this work, we propose phononic crystals made of spatial frames to design one- and two-dimensional periodic structures inspired by a spider web-based structure. Our results show that the proposed hierarchical structures show promising advantages in opening and enhancing band gaps when compared to their non-hierarchical counterparts.

Patterning is one way to design topological metamaterials without the need of external excitations (such as external magnetic fields or Coriolis effects). Is it possible that the biological world, in its millions years of evolution, stumbled across such patterns, and that it uses topological edge modes for its behavior? This talk will present theoretical and experimental work on the microtubule which is part of the skeleton of living cells. Topological mechanical systems, such as existence of flat bands on a seam and topological pumping, will be presented in the biological context. Phys. Rev. Lett. (2009) 103, 248101 Phys. Rev. Lett. (2020) 125, 225501 Phys. Rev. Lett. (2020) 125, 224301 J. of Phys. D. (2019) 53, 025401

We leverage the unique properties of anisotropic, colorimetric metasurfaces to scale down the complex manipulation of light and selectively visualize disease-relevant fiber density and orientation in biological tissue. Ranging from Alzheimer’s disease to heart disease, fibrosis or cancer, we discuss the potential of metasurfaces to yield rapid, precise, low-cost diagnostics.

I will describe an experimental technique developed in our lab – Metasurface-Enhanced Infrared Reflection Spectroscopy (MEIRS) of live cells – used to interrogating the effects of various chemical compounds on cellular membranes and cytoskeleton. Several early successes of the technique will be presented: (a) the ability to distinguish between cancerous and normal cells using cell line models, (b) spectroscopic detection of the effects of various compounds that target the membrane and the cell adhesion, and (c) combining MEIRS with dielectrophoresis (DEP), thereby enabling spectroscopy of non-adherent cells.

Fields from silicon photonics to metasurface optics are employing an unprecedented number of structural degrees of freedom in nanophotonics. An emerging critical need is an understanding of fundamental limits to what is possible, analogous to Shannon’s bounds for digital communications. Here, we describe a general framework of conservation laws which enable identification of fundamental limits for analog optical computing, large-area metasurfaces, perfect absorbers, and beyond.

Classical and quantum photonics with superior properties can be implemented in a variety of old (silicon, silicon nitride) and new (silicon carbide, diamond) photonic materials by combining state of the art optimization and machine learning techniques (photonics inverse design) with new fabrication approaches. In addition to making photonics more robust to errors in fabrication and temperature, more compact, and more efficient, this approach is also crucial for enabling new photonics applications, such as on chip laser driven particle accelerators, and semiconductor quantum simulators.

There exist only two fundamental factors determining the strength of all optical phenomena. First one is the light-matter interaction strength which is defined by very strict oscillator sum rule The other factor is the light-matter interaction time that can vary within very large range. All the existing and proposed techniques for enhancement optical phenomena such as photonic crystals, microcavities, plasmonics, polaritonics, exceptional points, epsilon-near-zero materials, Fano resonances, slow light, hot carriers, and others can be simply interpreted as interaction time extenders. I will also show that enhancing the strength invariably comes at a cost of narrower bandwidth and high loss – life is full of tradeoffs and compromises.

We derive fundamental limits to the refractive index of any material or metamaterial, given only the underlying electron density and either the maximum allowable dispersion or the minimum bandwidth of interest. We also identify low-loss, metal-based metamaterials exhibiting sizeable increases in refractive index over the current best materials.

An investigation on the upper limits of achievable gain for antennas based on radially inhomogeneous (gradient index) lenses is presented. This will let us provide design guidelines in terms of appropriate dimensions and material dielectric properties for achieving the optimum performance of gradient index lenses. We have seen that an upper limit of 80% aperture efficiency is obtained for any feed/ lens combination.

Discovering unconventional optical designs via machine-learning promises to advance on-chip circuitry, imaging, sensing, energy, and quantum information technology. In this talk, photonic design approaches and emerging material platforms will be discussed showcasting machine-learning-assisted topology optimization for thermophotovoltaic metasurface designs and machine-learning-enabled quantum optical measurements.

We present our recent work on realizing photonic topological phases using photonic crystals and metamaterials in two parts. In the first part, 3D topological semimetals by combining chiral and hyperbolic metamaterials will be described. We show that such materials can support either Weyl nodal points or Weyl nodal surfaces depending on the spatial symmetries. In the latter part, we present our theoretical modelling on 2D topological phases using coupled dipole method.

The equations that describe the dynamics of physical systems are often invariant under translations in time. It has been suggested that the time symmetry may be spontaneously broken such that classical dynamical systems may exhibit motion in the lowest energy state, forming a time analogue of space crystals. Here, I introduce a classical-type model for an electron with time-crystal type features and which predicts spin and some wave-type features of electrons.

Dirac surface electrons in topological insulator crystals show a natural chiral response to circularly polarized light due to spin-momentum locking, manifested by the generation of circular photogalvanic currents. Patterning of achiral and planar-chiral metamaterial designs on the surface of topological insulator crystals allows enhancing and controlling direction of the intrinsic photogalvanic currents.

We propose a two-dimensional TI realized over a single ring resonator exploiting acoustic pumps and electro-optical modulators. In our system, the synthetic dimensions are represented by the range of discrete optical modes supported by the ring resonator and their azimuthal angular order. Gauge fields responsible for the topological order in the synthetic lattice are realized by an array of racetrack couplers next to the resonator. Based on our platform, topological bulk and edge bands in the time-resolved transmission spectra are demonstrated, and topologically-protected nonreciprocal frequency conversion as well as the amorphous topological phase transition can be realized in synthetic dimensions.

We present a square-lattice photonic crystal that supports chiral topological photonic surface states at the interface to free space. Such unidirectional, back-scattering-immune surface states, as opposed to topological states at the interface between band-gap materials, allow to simplify the design of out-coupling from surface modes to functionalized radiated fields.

Low-noise detectors of mid- and far-infrared (IR) photons have numerous applications in security, medicine and material analysis. In this talk I will propose a novel platform for upconversion of IR (and possibly THz) photons into the visible or near-infrared (VIS/NIR) domain using nanoscale optomechanical cavities, and will present our recent experimental progress toward this goal.

We present photonic funnels, novel material platform that combines hyperbolic dispersion and conical geometry to achieve efficient optical coupling between nano- and micro-scale areas. We realize photonic funnels at mid-IR frequencies in all-semiconductor “designer metals” and explore the roles of geometry- and dispersion-engineering for controlling focusing, emission, and extraction of light.

Interlaced wire media are metamaterials consisting of two 3d cubical lattices of connected wires embedded one into another. These media support electromagnetic waves with longitudinal polarization within a very wide frequency range starting from zero frequency. In this work we investigate the dispersion properties in the case of symmetrically shifted lattices with the same radii of wires and demonstrate that in this case the metamaterial supports low-frequency modes with very large wave vectors and unprecedented spatial-dispersion-induced anisotropy. The revealed effects demonstrate extremely high spatial dispersion in the metamaterial at low frequencies.

We present the experimental evidence of giant optical anisotropy in natural van der Waals metamaterials. To do this, we made correlative far- and near-field characterizations validated by first-principle calculations that reveal a huge birefringence of 1.5 in the infrared and 3 in the visible light for layered transition metal dichalcogenides. Our findings demonstrate that this remarkable anisotropy allows for tackling the diffraction limit enabling an avenue for on-chip next-generation photonics.

Scattering phenomena in small structures have been widely studied across different fields, including photonics and acoustics, for wave manipulation, yet scattering phenomena in conventional materials are fundamentally limited by passivity and power conservation. Here we demonstrate that excitations at complex frequencies can overcome these bounds.

Here, we revisit the issue of optical forces by stepping out to the complex frequency plane and considering its dynamics upon complex excitations. We show that tailoring the time evaluation of the light excitation field allows pulling force for a Fabri-Perot resonator. This effect is linked to virtual gain, which can be achieved by exponentially decaying excitation signal weaker than the outgoing signal that carries away greater energy and momentum flux density.

The use of a machine learning assisted framework significantly speeds up image acquisition in photon antibunching based super-resolution microscopy. The technique is compatible with a CW excitation regime and applicable to a wide range of quantum emitters.

<p> We demonstrate metrology and odometry (detection of change in position over time) with resolution in the nanometric - picometric scales by analyzing electrons or topologically structured light scattered from the nanostructures using artificial intelligence. We show how these techniques can be applied to characterization and optimization of nano-opto-mechanical metamaterials and the fundamental studies of dynamics of thermal motion and the physics of phonons in photonic nanostructures.</p>

We explore the role that the electron wave function plays in cathodoluminescence emission when an external laser pulse is synchronized with the electron probe at the sample. We show that modulated electrons lead to a partial suppression of the cathodoluminescence, while its complete cancellation is achieved in the point-particle limit.

Hyperbolic phonon polaritons (HP2) in anisotropic polar Van der Waals (vdW) crystals can sustain extremely large polariton momentum and feature low Ohmic loss, thus boosting light-matter interactions at deeply subwavelength scales. Herein, we report the observation of hyperbolic phonon polariton vortices (HP2V) in natural hyperbolic vdW crystal-hBN, highlighting exotic photonic features, such as spin-orbit interactions. HP2Vs are highly tunable because of the complex interplay among various degrees of freedom. The demonstration of HP2Vs enables the processing and delivery of information with low loss and large capacity in mid-infrared (mid-IR) range. Their deep-subwavelength scale renders them ideally suited to promote the development of super-resolution imaging systems, ultracompact mid-IR sensors, and other miniaturized nanophotonic devices.

Reconstruction of an object based on its far-field scattering pattern is an ill-posed problem placing fundamental limits in imaging and microscopy. Here, we show that a neural network processing of far-field scattering patterns allows shape classification of deeply subwavelength objects (<λ/2) with accuracy better than 90%.

With the excitation of surface plasmon, the light can be confined to nanometer scales. However, we show that by using highly anisotropic media the interface plasmonic mode can be tuned at will, either expanding or compressing. For the compression of surface plasmon, we demonstrate a substantial compression by a factor of 7. Finally, the flat dispersion relation of this compressed surface mode leads to an application in superlens.

In this paper, practical implementation of metasurfaces providing perfect anomalous reflection is discussed with reference to metasurfaces consisting of a metallic cladding over a grounded dielectric slab. The derived solutions are implemented through a distribution of patches and full wave simulations are performed to confirm their effectiveness.

This work reports the application of higher symmetries to the design of a Reflecting Luneburg Lens (RLL) with broadband response. RLLs consist of two stacked parallel plate waveguides (PPW) of circular shape, where the bottom PPW is filled with an azimuthally symmetric graded index (GRIN) medium, so that the fields coupled to the top PPW take the form of a plane wave. In this work, the GRIN medium in the bottom PPW is implemented by unit-cells consisting of metallic inclusions with higher symmetry. This type of unit cell achieves the required equivalent refractive index profile with reduced frequency dispersion, thus increasing the operational bandwidth of the lens. The proposed architecture can be used as beam-former for complete azimuthal scanning in a wide frequency range, while benefiting from the robustness and low-losses of metal-only structures.

Coherent illumination allows additional flexibility over metasurface functionalities, with coherent perfect absorbers as one typical example. However, most of coherent metasurface devices are based on spatially uniform metasurfaces that offer a limited control over scattered waves. In this talk, we present an idea of coherent asymmetric absorbers with periodic surface impedances. The proposed metasurface can function as a perfect retroreflector for coherent incidences from one side and as a perfect absorber for incidences from the other side.

We present universal analytical criteria for the quasi-normal modes (resonances) of lossless reciprocal 2-port systems to systematically design symmetric or “antimetric” scattering responses, emphasizing compact high-order standard filters. As an application, we design microwave metasurface bandpass or bandstop elliptic filters with various orders and bandwidths.

Crossbar nanoelectronic architectures, which are at the heart of today’s memristive and phase change random access memory technology such as ReRAM and PCRAM, presents a unique structural platform not only for providing ultrahigh device packing and simple interconnect configuration in electronic systems, but also for the realization of reconfigurable and randomly addressable metamaterials. We show here that these periodically arranged three-layered structures can be designed to display multiple Fano-type optical resonances spanning the visible to near-infrared (400≤λ≤1700nm) range of wavelengths.

Electrically small Huygens dipole antennas and their unidirectional radiation properties and their applications will be reviewed. Examples of the progress in realizing multifunctional and reconfigurable Huygens source designs will be described. Applications such as wireless power transfer (WPT) and wirelessly powered sensors will be discussed. The development of linear arrays of Huygens dipole elements to achieve high directivity, steerable beams for 5G and beyond applications will be emphasized. Measurements of their prototypes confirm their simulated performance characteristics.

Plasmonic antennas are capable of enhancing the coupling of light and matter due to their strong electric field confinement. At room temperature, where dephasing is the dominant contribution to the linewidth of a solid-state emitter, studies of plasmonic coupling have usually concerned incoherent interactions, e.g. a Purcell enhancement [1]. At low temperatures, however, the resonant coherent scattering from the emitter becomes significant and another regime of plasmonic interactions can be observed: here, not only the plasmonic particle changes the interaction of the emitter with light, but the emitter can influence the scattering properties of the plasmonic particle. In an extreme case, a single molecule can fully suppress scattering from a (much larger) plasmonic particle, rendering it effectively transparent [2]. In this presentation, I discuss an experiment, where a single organic molecule partially cloaks a large gold nanoparticle [3]. We will also demonstrate a significant enhancement of a single quantum dot coupled to a plasmonic nanogap antenna, leading to the observation of an ultrashort fluorescence lifetime, less than 38 ps, limited by the instrumental response function. Moreover, by controlling the position of the quantum dot with respect to the nanogap antenna, we can tune the system from the weak coupling to the strong coupling regime leading to spectral splitting in the fluorescence spectra [4]. The hybrid plasmonic system discussed in these experiments provides a promising class of active quantum metamaterials for efficient harnessing of the quantum properties of atoms and molecules. If time allows, I will also mention a theoretical proposal for novel quantum metamaterials with magnetic response at optical frequencies [5]. [1] K. Matsuzaki, et al., Sci. Rep 7, 42307 (2017). [2] X-W. Chen, V., Sandoghdar, M., Agio, Phys. Rev. Lett. 110, 153605 (2013). [3] J. Zirkelbach, et al., Phys. Rev. Lett. 125, 103603 (2020). [4] H-W. Liu, et al., in preparation. [5] R. Alaee, et al., Phys. Rev. Lett. 125, 063601 (2020).

Resonant structures implemented with superconducting metamaterial transmission lines coupled to artificial atoms provide a novel platform for exploring multimode circuit quantum electrodynamics. We present measurements of superconducting qubits coupled to such metamaterial resonators and discuss applications in analog quantum simulation and quantum memory in the microwave regime.

We experimentally demonstrate a levitating optical resonator coupled to an optical fiber. We measure a quality factor (Q) exceeding a billion in a 10 micron radius cavity, implying a dimensionless Quality/Volume (Q/V) factor of 4.1 million, which is the highest ever recorded.

Asymmetric absorbers for sub-kilohertz low-frequency sound are constructed, with dynamically adjustable frequency, broadened operating frequency ranges, and excellent ventilation performance, which provide new technical means for the suppression of low-frequency sound.

Optical holograms can modulate light wavefronts to generate visible images. In the same way, acoustic images can also be synthesized by holograms, shaping the areas where mechanical waves present a high amplitude, and areas where the media is at rest. We present acoustic holograms based on metasurfaces for emerging therapeutic applications of focused ultrasound for the non-invasive treatment of neurological disorders. When targeting acoustic beams into the brain, accurate focusing is mainly limited due to the strong phase aberrations produced by the refraction and attenuation of the skull. Acoustic holograms can overcome these limitations by synthesizing aberration-free ultrasonic fields of complex spatial distribution inside the skull. Our results show that, using low-cost 3D-printed holograms, ultrasonic beams can be focused not only at a single point, but overlapping at one or various target structures simultaneously, e.g., left and right hippocampi. Designs are validated by ex-vivo and in-vivo experiments to produce a bilateral blood-brain barrier opening in mice for drug delivery, and complex thermal patterns for localized hyperthermia. Other complex fields such as vortex beams for trapping small objects can also be synthesized inside the human skull. These results open new paths to spread emerging therapeutic ultrasound applications including blood-brain barrier opening, hyperthermia or neuromodulation using low-cost systems.

We show that broadband three-dimensional isotropic chiral metamaterial phonons can be obtained along two conceptually different approaches: By orientational averaging or by using accidental degeneracies. The latter approach allows for simple truss-based cubic-symmetry architectures that are readily amenable to 3D laser printing on the micrometer scale.

By using the nonlinear self-demodulation of two confocal vortices, we report the generation of acoustic vortices of deep sub-wavelength dimensions. A helicoidal acoustic source with two different slopes is used to generate two primary focused vortices beams with finite amplitude of different frequencies and topological charges. The self-demodulated vortex presents the spatial distribution of the main vortices with a sub-wavelength size when compared to its wavelength. Nonlinearity enables the generation of focused vortex beams of tunable topological charge in the far-field whose characteristic size is 22 times smaller than its wavelength

We report broadband metasurfaces to control sound diffusion in the far field by the scattering of acoustic vortices. By encoding the holographic field of an acoustical vortex, these metasurfaces result in structures with spiral geometry. These metasurfaces inhibit specular reflections in the far field because all scattered waves interfere destructively in the normal direction. The scattering function is then unusually uniform because the reflected waves diverge spherically from the holographic focal spot. By triggering vorticity, energy can be evenly reflected in all directions except to the normal and, as a consequence, we observe a mean correlation-scattering coefficient of 0.99 (0.98 in experiments) and a mean normalized diffusion coefficient of 0.73 (0.76 in experiments) over a 4 octave frequency band. These spiral metasurfaces are extraordinary candidates for generating diffuse sound reflections for room acoustics, underwater acoustics, biomedical ultrasound, or particle manipulation devices.

In this paper, arguments are provided to support that, in passive media, the imaginary part of the permeability can take positive and negative values.

By using digitally virtualized atoms as building blocks, we experimentally demonstrate temporal effective medium for acoustics where the resonating properties of metamaterial atoms are modulated in high speed in time comparing to the signal frequency. We also establish the effective medium formula in the case with frequency dispersive constitutive parameters.

Here I will present a theory of homogenisation of space-time metamaterials, which yields expressions for the effective permittivity, permeability and magnetoelectric coupling in the long wavelength limit. The derived parameters show that synthetic motion can result in giant bianisotropy and the dragging of electromagnetic fields down to the quasistatic limit and without any moving matter.

We discuss the reliability of non-local constitutive relations to homogenize an electric dipolar lattice. By systematically varying the ratio of period over wavelength, we investigate twoaspects. First, we demonstrate the superiority of using the non-local constitutive relation overa local model in predicting the optical response of the model system. Second, we investigate thebreakdown of the ability to homogenize the material towards shorter lattice constants for both constitutive relations. This breakdown can be explained with the spread of excitation acrossthe lattice due to pronounced near-field interactions for ever decreasing periods. This workquestions the requirement to have periods sufficiently small to homogenize a given metamaterial;instead it suggests an optimal period at which this homogenization is possible.

Wire media and waveguides can be modelled as a spatially dispersive media. By varying the structure we make the electric field obey Mathieu’s equation. These corrugated structures can be used as slow wave structures either to produced EM fields or accelerate particles. Our method prescribes the precise variation needed.

We show that exceptional points in non-Hermitian systems with three degrees of freedom can exist in the form of cusps linked by exceptional arcs of second order exceptional points. We discuss the topological protection and characterization of such features.

We discuss the relation between Hamiltonian and Liouvillian exceptional points (EPs) in non-Hermitian systems with parametric noise. Conclusions for the performance of EP-based sensors are drawn.

We observe non-Hermitian dynamics in networks of nanomechanical resonators that is controlled through optomechanical interactions. This allows imparting both particle-conserving and -non-conserving (squeezing) interactions. Their interplay establishes a non-Hermitian Aharonov-Bohm effect, which allows controlling non-Hermitian dynamics through synthetic fluxes.

We establish angle-resolved thermal emission spectroscopy as an alternative platform to characterize the intrinsic eigenmode properties of non-Hermitian systems, which can directly map the dispersion of metacrystals within the light cone with high angular resolution for exceptional points, bound states in the continuum, and non-Hermitian Fermi arcs.

We present the experimental and theoretical investigation of nonlinear metasurfaces from lithium niobate, gallium arsenide, and metasurfaces hybridized with monolayer TMDs featuring multiple resonances. We show that the second-order nonlinear interactions in metasurfaces enable tailorable harmonic frequency generation as well as entangled photon pair sources by spontaneous parametric down-conversion.

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: i) multi-resonance mode matching, ii) exploiting surface quantum effects and iii) heavily doped semiconductors.

By utilizing solely quantum-mechanical electric dipole transitions of naturally occurring atoms, we propose how to synthesize collective optical responses of optically active magnetism. We apply the technique for generating toroidal dipoles and a quantum Huygens’ surface for focusing and steering light, and entangled quantum superposition states.

We experimentally and numerically investigate the nonlinear emission properties of non-centrosymmetric gold nanoantennas when simultaneously excited with two pump beams at 1550 and 775 nm

Metamaterials have played an important role in generating and detecting data-carrying orbital-angular-momentum (OAM) beams in different frequency regions. This presentation will explore the achievements of and challenges to OAM-based optical, THz, and millimeter-wave communication systems, including: transmission, turbulence compensation, link design, causes and mitigation of modal crosstalk, and classical and quantum encoding.

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 the vector beams, topological properties and applications will be discussed.

How far can we go in shaping the luminescence of quantum emitters? Here, we make an assembly of colloidal quantum dots spontaneously emit vector vortex beams, which are swirls of light whose construction usually requires the coherence of lasers due to their non-zero angular momentum and singular field structure.

By tailoring local and global geometries of plasmonic vortex generators we experimentally show how a change in circular polarization handedness of light imposes arbitrary large switching in the delivered plasmonic angular momentum. We generalize our approach to create and control complex topological fields. Our results provide tools for plasmonic manipulation and could be utilized in lab-on-a-chip devices
Media link(s):

See arxiv preprint (https://arxiv.org/abs/2102.06033)

 

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.

Dielectric metasurfaces have emerged as a promising platform for light manipulation with sub-wavelength resolution and high efficiency. In recent years, significant efforts are being made towards transitioning from purely passive devices to ones allowing dynamic control of the wavefront. In this talk, we will present our recent results in this direction, with an emphasis on interfacing metasurfaces with liquid crystals for visible light applications. We will show functional devices in which one or few resonators are individually addressed, and which bring the next generation of spatial light modulators with sub-wavelength pixel sizes a step closer to reality.

In this talk, we present our most recent advances in the development of reconfigurable metalenses, focusing on two original technologies. The first approach relies on dynamically controlling the distribution of refractive index in the close vicinity of a silicon metalens by means of an engineered micro-resistor embedded in a thermo-optical polymer. Our second approach to reconfigurability relies on an optomechanical control. Upon illumination with a control beam, the meta-atoms forming the lens mechanically rearranges inducing a change of focus.

We present all-dielectric metasurfaces for various applications in the mid-infrared wavelength spectrum, ranging from biosensing and spectral filtering to optical wavefront and polarization control. Additionally, we experimentally demonstrate how the concept of static Huygens’ metasurfaces can be extended with phase change materials to obtain active control of optical phase while maintaining high transmission efficiency with subwavelength spatial resolution.

We report an all-dielectric active metasurface with high efficiency at the C-band (1.55µm) for beam steering applications. Our design exhibits high reflectance of >30% and is based on localized guided-mode resonances supported by the metasurface. Our calculations show that the proposed metasurface can steer the beam up to polar angles of 32° while maintaining high efficiency of >30%. Our metasurface can be used in future chip-scale light detection and ranging systems as well as for free-space optical communications

Photonic topological insulators offer the possibility to eliminate backscattering losses and improve the efficiency of optical communication systems. Despite considerable efforts, until recently, a direct experimental demonstration and quantitative characterization of robust, lossless energy transport in compact topological insulators operating at near-infrared frequencies was challenging. In our studies, we combine the properties of a planar silicon photonic crystal and the concept of topological protection to design, fabricate and characterize an optical valley Hall effect enabled topological insulator based waveguides and resonators.

Hybrid topological-photonic guidance of light translates concepts from the field of topological matter to that of photonic crystal fiber arrays. Finite element simulations demonstrate the effectiveness of the proposed designs for localising energy in finite arrays in a robust manner. Potential applications reside in the generation of topological photonic crystal fibers for long-haul communications.

In this talk I show how to find materials supporting topological edge states through extending the concept of the refractive index. Rather than compute a topological invariant, we compute the refractive index as a function of propagation direction, finding that zero index in a complex direction corresponds to one-way propagation. As well as providing an alternative viewpoint, we find a circulation dependent local density of states, an optical instance of the Atiyah-Singer index theorem, and a re-interpretation of spin--momentum locking.

In this work we study the response of a wire array embedded in a material with gyrotropic response. Using effective medium theory and full-wave simulations, we characterize the scattering of electromagnetic waves by the metamaterial. We show that the metamaterial can be operated in a regime where the reflectivity can be significantly different for angles of incidence linked by parity, so that for “positive” angles the waves are strongly absorbed and for “negative” angles the waves are mostly reflected.

We provide a review on recent advances on the concepts, analysis, simulation, experimental implementation and applications of nonreciprocal metasurfaces. Having known limitations and drawbacks of magnet-based nonreciprocity, we present two major nonmagnetic approaches for the realization of nonreciprocal metasurfaces, that is, transistor-based nonreciprocity and time modulation.

To address the near-infinite design space of all-dielectric metasurfaces, we invert the design process through the use of artificial neural networks (ANNs). These ANNs orchestrate complex eigenmode interactions present in the metasurface, designing devices with coefficients of reflection greater than 99% over a range of wavelengths of more than 450nm.

Recent progress in topological mechanics has revealed a family of Maxwell lattices that exhibit topologically protected floppy edge modes. These modes lead to a strongly asymmetric elastic wave response. In this paper, we show how topological Maxwell lattices can be used to realize nonreciprocal transmission of elastic waves. Our design leverages the asymmetry associated with the availability of topological floppy edge modes and the geometric nonlinearity built into the mechanical systems’ response to achieve the desired nonreciprocal behavior, which can be further utilized to form a phonon diode via the addition of on-site pinning potentials that blocks the linear transmission and only allows the signal to transmit in one way. Finally, the nonreciprocal wave transmission can be switched on and off via topological phase transitions, paving the way to the design of cellular metamaterials that can serve as tunable topologically protected phonon diodes.
Media link(s):

Published paper at PRB 101, 104106 (2020)

We demonstrate the theory and experimental realization of hyperbolic media and zero-index media by controlling the structural dispersions of a planar waveguide, which is filled with anisotropic dielectrics and arrays of metal wires. We further discuss some intriguing physics realized in such systems, including waveguide decoupling and static field analogue.

<p> In this work, we demonstrate theoretically and experimentally the ability to classify and reconstruct subwavelength acoustic images from far field measurements using a machine learning approach, combined with a locally resonant metamaterial lens placed in the near field. In contrast to other near and far field microscopy techniques that also overcomes the diffraction limit but often use invasive markers or complicated image post-processing, the proposed deep learning approach, once trained, represents a rapid, noninvasive method. Importantly, we show that the relatively large amount of absorption losses present in the resonant metamaterial largely favors the learning and imaging process. With a learning experiment using airborne sound, we recover the fine details of images in the far field, with features at least thirty times smaller than the acoustic wavelength.</p>

The engineering of meta-atoms with tailored-made resonances and scattering patterns has been made possible in the recent years by bottom-up approaches. We show how we used nanoparticle chemistry and self-assembly to produce nanocolloidal optical resonators exhibiting strong magnetic resonances and scattering tunability. In particular, we have synthesized clusters of gold nanoparticles using an emulsion-based formulation approach and shown that they are strong tunable Huygens sources.

We report the interesting physics of different deeply subwavelength layered heterostructures and how they allow to control light-matter interaction at the single nanometer scale. Layered metal/dielectric structures allow to span a broad physical realm which goes from hyperbolic metamaterials (HMMs) that support a wide landscape of plasmon polariton excitations to Fano resonances in thin film nanocavities.

The refractory metal-oxide semiconductors are an overlooked platform for nanophononics that offer alloys with high melting points and tunable optical constants through stoichiometry changes and ion intercalation. We show that these semiconductors can form metamaterial coatings (metacoatings) made from a set of highly subwavelength, periodic metal-oxide layers (≤20nm) with a varying and graded refractive index profile that includes a combination of high and low refractive indices and plasmonic layers. These metacoatings exhibit vibrant, structural colour arising from the periodic index profile that can be tuned across the visible spectrum, over large lateral areas (meter scale) through bottom-up thermal growth techniques.

Photovoltage excited by circular polarized light is demonstrated on a periodic arch structure engraved in a Au film. Wavelength dependence shows that the response is significant in very wide wavelength range, which is ascribed to the robustness of geometric phase in the structure.

We develop and realize experimentally dielectric metasurfaces delivering an order-of-magnitude responsivity enhancement in monitoring of deviations around arbitrarily chosen elliptical polarizations by implementing specially tailored non-conservative transformations.

Laterally structured Metal-Insulator-Metal nanocavities as micro/nano pillars exhibit cavity and dipole resonances. The dependence of these modes on the pillar diameter is demonstrated using FDTD simulations and experiments.

A general design approach for wave-transforming metasurfaces based on complete interface and boundary field synthesis is presented. To the propagating spectral components that define a given wave transformation function in a reflective or transmissive mode, evanescent auxiliary waves are added to every impenetrable boundary and penetrable medium interface. They are optimized such that each interface is characterized by a pointwise passive, lossless surface reactance.

In this contribution, we summarize some of our recent results about the design of dipolar and multipolar all-dielectric metasurfaces featuring advanced wave-manipulation effects. We focus our attention on both dipolar and multipolar metasurfaces and we show how it is possible to engineering their complex scattering response for designing several electromagnetic devices, such as angular filters, optical forward scatterers, high-Q passband filters and polarizers working for extreme angles of incidence.

Periodic phase-gradient metasurfaces (PGM) have been successfully used to produce anomalous reflection and refraction for small and moderate bending angles, but are not capable of efficiently producing wide-angle effects. For anomalous reflection, this limitation is overcome herein by coating the PGM with layered slabs of homogeneous (non-periodic) dielectrics, which serve to suppress the unwanted Floquet components of the scattered field. The required slab-widths of these multi-directional anti-reflective coatings (MDARC) are analytically determined for given dielectric constants, and their effects are verified by full-wave calculations. The PGM-MDARC combination provides a surprisingly simple structure for perfect anomalous reflection.

We introduce here a novel type of cloaking, based on a circular concentric meta-waguide structure, where the metawaveguides are bent waveguides with porous metasurface walls. In contrast to the cloak implementation reported in~[1], which only emph{approximates} the ideally perfect transformation-optics cloak because of prohibitive fabrication complexity, this cloak is designed ab initio for optimal cloaking, and offers therefore largely superior performance. Its combined simplicity and performance arguably makes it the most practical existing cloak reported so far.

This paper presents two different design methodologies to cope with the somehow unexplored design of dual-band modulated metasurface (MTS) antennas with circular shape. In the first approach, one overlays two different modulations. Each modulation is appropriately chosen to provide a broadside beam for one of the bands and a very weak radiation for the other frequencies. The second approach builds on the active region modulated MTS concept, recently applied to broadband designs. In this case, the periodicity of the modulation at the central region of the aperture is selected to radiate at the high frequency band. In turn, a larger periodicity in the outer annular region provides the broadside beam at the low frequency band. Both approaches are compared and their advantages and drawbacks, discussed.

In this paper we present a novel technique for the design of inhomogeneous refractive index only dielectric lenses, which resort to the calculation of a complex holomorphic potential function through a boundary value problem. The potential real part isoline represent wavefronts while imaginary part isoline represent Geometrical Optics (GO) rays. By resorting to the eikonal equation the isotropic lens refractive index is directly retrieved from the numerical solution of the integral equation formalizing the boundary value problem.

Engineering artificial structures with desired wave propagation patterns has been perfectionized. A plethora of techniques help us to design materials that are either ready for industrial deployment or offer us versatile platforms to explore fundamentally new physics. Dissipation, often seen as a foe when trying to observe new phenomena now lends itself as a powerful new tool opening up the road to an entirely new set of topological effects in architectured materials.

We address an optical pressure/temperature nanosensor by designing and numerically simulating Metal/Insulator/Metal nanopillar arrays covered an Ag film. The gap plasmon resonance is highly sensitive to the distance of the nanopillar to the Ag film, which allows optical sensing of pressure/ambient temperature by the change in color of the device.

Plasmonic nanoantennas offer intense confinement of light, to volumes even below the diffraction limit. We adopt a quasinormal mode approach to reveal the strong facet morphology dependence of rhombicuboctahedron-on-mirror near-field charge distributions, as well as far-field out-coupling. Thus allows for structural identification from far-field measurements.

Improving solar cell efficiency is crucial to meet the ever-growing global energy demand. Here, we present a wide-angle and polarization-independent design of broadband plasmonic metamaterial absorbers. We report 96.9% average absorption over 400–1100 nm wavelengths. An integrated design of broadband absorbers into photovoltaic-modules could significantly enhance solar cell efficiency.

In this work we propose a new type of metagrating solution based on a combination of two diffraction gratings embedded inside the waveguide. We demonstrate that the proposed design has high intensity across a wide angular range and can be used as single waveguide full color combiner for AR application

In this work we compare optical Tamm states in the 1D and 3D opal-like plasmonic-photonic crystals. The distribution of the electric field within these structures shows a larger confinement of the Tamm mode field in the opal-like structure. This mode exhibit the polarization sensitivity in case of the opal-like crystal.

Various device applications utilizing left-handed behavior in photonic crystals have been discussed for photonic integrated circuits. Small footprint and low operation voltage is possible by band-to-band transition for modulators and switches. Sensitivity and response time can be improved by inserting an air gap for the sensor applications.

<p> Two-dimensional metamaterial photonic crystals composed of dispersive left-handed materials and right-handed medium were investigated. Using finite-difference time-domain calculations incorporated into an auxiliary differential equation (ADE-FDTD) method, the conditions for a bandgap to be maximized were explored.</p>

We report on ultra-broadband toroidal dipole excitations in dielectric particles under illumination with Flying Doughnut pulses. We show that the toroidal dipole forms the dominant contribution to the particle’s optical response over two frequency octaves and for a wide range of geometrical parameters and sizes.

Coherent anti-Stokes Raman scattering is a well-known tool in molecular spectroscopy. In this work we combine CARS with surface plasmon enhancement on a periodic metasurface. We focus on one particular tuning possibility that is available after the metasurface fabrication. We achieve CARS signal enhancement factors of the order of 10^{18}.

We present a theoretical model based on the quantum hydrodynamic theory and present its numerical implementation to probe second-order nonlinear optical properties of metal surfaces. The proposed method can efficiently handle the realistic (exponentially decaying) profile of equilibrium charge density of a metal. In the spectral analysis of Na and Ag thick slabs, we observe strong resonances induced by the electron spill-out from the metal surface. These resonances can be exploited to enhance the second-harmonic conversion efficiency by several orders of magnitude.

We study plasmonic structures and their applications for enhancing emission and detection. By making use of the advantages of surface plasmon polaritons and semiconductors, we developed new types of detectors which show record-high room temperate detectivities from mid-infrared to millimeter waves. By varying the shape or dimension of the resonators, the emission intensity in the semiconductor quantum dots can be monitored and significantly enhanced.

Metasurfaces infiltrated with liquid crystals have become a particularly promising means of tuning their optical properties, due to liquid crystals’ large and broadband optical anisotropy. In order to fully explore the parameter space of broadband all-dielectric liquid crystal tunable metasurfaces in the visible, we undertake a comprehensive study based on TiO2 nanoresonator superarrays, sweeping geometric parameters and operating in the visible spectrum. We demonstrate both thermal and electrical switching, and visualize the resonance change caused by either the orientation or phase change of liquid crystal, which provides a practical library for the rational design of all-dielectric tunable metasurfaces controlled by the surrounding medium.

We report an epsilon-near-zero (ENZ) material based polarization-insensitive electro-tunable metamaterial absorber, which comprises a patterned-metal–insulator–metal based nano-structure. The numerical simulations show that coupling of electrically-induced ENZ-mode to the gap-plasmon resonance-mode enables more than 80% average absorbance over 1500–1800 nm wavelength regime and ~10-dB modulation-depth at 1550 nm.

Flight of insects surprises researchers for many years as contradicting conventional laws of aerodynamics. Three-dimensional modeling of different flight conditions revealed key peculiarities of the flow generation around wings and proved that most of them are driven by the wing architecture formed by a proper combination of rigid and flexible materials. Here, we study the influence of the architecture of an artificial bio-inspired wing on noise generation during a flapping flight and use the metamaterial concepts to control the produced noise. The outcomes of this study are of importance for engineering applications of flapping wings.

Acoustic screens based on sonic crystals constitute one of the most promising technological bets of recent years in the field of environmental acoustics. Sonic crystals are defined as new materials formed by arrays of acoustic scatterers embedded in air. The design of these screens is made using powerful simulation models that provide reliable results without the need of expensive experimental testing. This project applies the finite elements method in order to analise an acoustic barrier that includes (Helmholtz) resonators in its scatterers, and studies the interference of the sonic crystal with the effect of the Helmholtz resonator, depending on its orientation with the acoustic source.

Acoustic metamaterials with unusual properties have attracted much attention owing to their capability in controlling sound propagation. In this work, the acoustic properties of polymethyl methacrylate (PMMA) material based triply periodic minimal surfaces (TPMS), including Schoen's F-RD, Gyroid, and Fischer-Koch S surfaces are numerically studied. The simulation results show that these three different TPMS lattices have multiple bandgaps in the frequency range between 200 and 2000 Hz. In the sub-700 Hz frequency range, they commonly have a bandgap with a central frequency of nearly 500 Hz and a bandwidth of nearly 400 Hz. However, in the higher frequency range between 800 Hz and 2000 Hz, the bandwidths of bandgaps are much different from one structure to the other. For example, the Fischer-Koch S-TPMS lattice shows the widest bandgap with a bandwidth of more than 200-Hz, but the F-RD TPMS lattice shows the narrowest bandgaps with a bandwidth of less than 50-Hz. This study is potentially applicable for low-frequency sound attenuation applications.

Propagation and attenuation of sound through a layered periodic phononic crystal with viscous constituents is theoretically studied. Using the Navier-Stokes equation, the dispersion of sound for fluid-fluid and fluid-solid layered structures is analytically obtained. Frequency and angular dependence of attenuation is analyzed and the anomaly related to acoustic manifestation of Bohrmann effect is explained.

Resonant tunneling method for subwavelength imaging has prospective application in near field cases. But due to diameter modulation factor the fabrication of such kind of lens is more complex than Fabry-Pérot (FP) resonance based lens. As primarily the theory of resonant tunneling lens is based on cylindrical hole, we extended it for square shaped parallelepiped hole. Therefore, at this work we have mainly proposed a way for shape conversion which might be used as a handy tool regarding fabrication perspective.

We theoretically investigate the interaction between aluminum pillars erected on top of a semi-infinite substrate of silicon. Our interest is to control and manipulate the propagation of the surface acoustic waves through a linear chain of pillars.

In this paper double single and double modes TVAs are used in order to improve the vibroacoustic performance of flexible rotating rings. The Coriolis effect leads to a split of the stopbands generated by double modes TVAs with an overall positive impact on vibroacoustic performance.

Owing to their ability to mitigate elastic vibration, Triply Periodic Minimal Surfaces (TPMS) based metamaterials are numerically studied. The elastic bandgaps in two lattice structures, Primitive and Schoen’s F-RD, are obtained through an eigenmode study and the relationship between the filling fraction and band structures is discussed.

Precise control of elastic waves is a challenge for many applications in the field of mechanical vibrations, ultrasonic inspection and energy harvesting. Graded arrays of resonators on elastic substrates recently revealed superior performances for broadband wave trapping and mode conversion. In this study we present elastic waveguides able to govern waves at different scales exploiting rainbow reflection, trapping and mode conversion. We investigate whether these mechanisms, and the associated control, can be used for energy harvesting or signal conversion devices.

Active systems are not constrained by the principle of energy conservation, allowing for the emergence of a wide variety of wave phenomena not observable in ordinary passive matter. By implementing simple and local non-conservative interactions between constituent particles within a network, complex collective behavior can result, providing new avenues in material design.

The study of invisibility cloak with metamaterials has attracted great interests since 2006. In this article, we develop and analyze a time-domain finite element method for solving a carpet cloak model. Numerical simulation is presented.

High-index dielectric mechanical pieces constitute an important source of signal losses in radio frequency systems due to scattering effects. In this study, we propose to camouflage a dielectric scatterer by tuning it with buried metasurfaces. The impact of a high-index dielectric scatterer with respect to a low-index dielectric reference is defined in terms of its induced field ratio (IFR). The IFR of the scatterer can be controlled and minimized via the geometric parameters of the buried metasurfaces’ elements. Full-wave simulations are carried out at 4 GHz and the obtained results validate camouflaging of a dielectric scatterer. Metasurface-tuning is an easily implementable, frequency transposable solution to camouflage non-transparent, dielectric mechanical pieces in radio frequency systems.

An optically transparent three-dimensional microwave metamaterial absorber based on compact standing-up rounded lattice array is presented. The absorber has ultra-wideband, wide-angle absorption and polarization-independent properties. Our theoretical investigations and simulations demonstrated that the compact standing-up resistive patch arrays can not only excite multiple standing wave modes to obtain ultrawideband absorption, but also enhance the absorption bandwidth progressively with the increase of the incident angle for the oblique transverse magnetic. Both the simulations and the measurements indicate that the proposed absorber can achieve ultrawideband microwave absorption with efficiency over 90% and 95% in the frequency band of 3.5-31.8 GHz (fractional bandwidth, FBW=160%) and 4-31GHz (FBW=154%), respectively.

In this work, we propose, design, and evaluate three types of : three types of metasurfaces using tripod-shaped unit cells when working as thin-film sensing devices. The three meta-atoms of the proposed metasensors are a simple solid tripod, a hollow tripod, and a hollow tripod structure with arms. The best design showed a mean numerical sensitivity of 1.42 × 10−4 nm for extremely thin samples, meaning an improvement of 381% with respect to the initial designs. These results highlight the importance of using metastructures with complex geometries that enable high-intensity electric field distributions over the whole metasurface.

In this contribution, we present our recent progress on printed leaky-wave antennas for W-band frequencies (75-110 GHz). Most previously reported planar leaky-wave antennas for this frequency range require complex and costly manufacturing methods. By using a refined synthesis method based on coarse discretization, we facilitate manufacturing with standard printed circuit board processes. We demonstrate the versatility of the approach by fabricating and characterizing different tapered leaky-wave antennas with very low side lobe level. The experimental demonstration includes comprehensive near-field and far-field characterization.

In this work, we experimentally demonstrate an ultrathin bi-layer HWP with a transmission efficiency of 90.15% and a thickness < λ/13. A numerical analysis along with the measurements confirmed the device’s ability to convert a CP wave’s handedness at 87 GHz.

We study theoretically the resonant suppression of THz wave reflection from a layered superconductor tunable by dc magnetic field. We show that it can tune the reflection-vs-angle dependence in order to get an ordinary single-dip one or a specific double-dip one associated with the hyperbolicity of layered superconducting metamaterials.

Aggressive discretization by discretizing a metasurface into as few elements as required, can benefit the metasurface design with significantly enlarged unit cell size and lower requirement for impedance/phase coverage. Aggressive discretization allows one to design a metasurface with simple structure, which will potentially lead to high efficiency and broadband performance.

Put This paper presents the design of a bidirectional same-sense circularly polarized (CP) antenna using the metasurfaces. The antenna is composed of two metasurfaces and a ground plane with etched slot sandwiched between the two substrates. Each metasurface is made up of an array of 2 × 4 corner truncated patches placed back-to-back at the top and bottom of the antenna.

We demonstrate the viability of designing a polarization rotator surface using metaparticle surrogate modeling and genetic algorithm optimization. A kriging surrogate is constructed to model the polarization conversion ratio (PCR) of a polarization rotator metaparticle with three degrees of freedom (geometrical parameters). The input to the kriging model is provided by 125 full-wave simulations sampled using the hyper Latin hypercube sampling algorithm, and surrogate model is used to construct the cost function for the genetic algorithm. As an illustrative example, an optimization target is set for PCR greater than or equal to 0.85 over the frequency range 10 to 12 GHz. The result from the optimization algorithm is compared to full-wave simulation and very good agreement is observed.

In this manuscript, we propose a novel transmissive metasurface capable of dynamically controlling the phase of linear polarized waves at the microwave regime. The local phase control is dynamically obtained with the help of individually controlled varactors and PIN diodes inserted in the metasurface unit cell. Moreover, we show that the proposed metasurface can be used to generate zero- and first-order microwave Bessel beams with high efficiency (90%).

This contribution proposes a band-pass non-Foster negative inductor. Its stability properties are superior to those from standard designs, including possibility of achieving overall negative inductance. Proposed band-pass negative inductor is based on Negative Impedance Converter (NIC) of Open Circuit Stable (OCS) type. Stability analysis revealed that there is inevitable trade-off between generated negative inductance and achieved operating bandwidth.

The existence of non-radiating sources with high reduction of far-field radiation and accumulation of electromagnetic field in the near-field zone is crucial for various branches of science from medical imaging to dark matter. Here a non-radiating electric source consisted of an ultra-high permittivity dielectric hollow disk excited by an electric point-like dipole antenna placed inside the disk is studied. We theoretically demonstrate that such a system supports anapole state with radiation suppression to the far-field. The radiation suppression is obtained by destructive interference between the point-like dipole antenna's radiation and the hollow disk's induced current.

Advances in time modulation of metamaterials and RF components can support the realization of efficient and stable impedance matching of electrically small antennas (ESA’s) that overcome the Wheeler-Chu limit and significantly improve ESA radiative efficiency and bandwidth. In this paper a full Floquet analysis of a resonant RLC circuit with a time modulated capacitance (varactor), as an initial configuration of basic impedance matching network, is performed [4]. . Rather than driven by an external signal, the varactor is pre-charged, the battery removed and the shorted circuit allowed to freely resonate. This is done in order to analyze the impact of the varactor modulation frequency fm on the fundamental resonant frequency f and the higher order modes found in the time modulated circuit, and how this affects the effective resistance of the circuit and consequently Q and bandwidth of power dissipation.

A proof-of-concept demonstration is presented for a planar boundary-tunable metasurface antenna for computational imaging (CI). The proposed antenna consists of a parallel plate waveguide with perforated slots in the upper plate and pixelated boundaries comprising of PEC and PMC. By tuning PEC and PMC boundary combinations, diverse beams are generated due to the excitation of different waveguide modes. This planar configuration guarantees adequate diversity of the measurement modes for CI as well as facilitating a simplified biasing configuration. The advantage of the proposed configuration is demonstrated by comparing the diverse beam patterns and Singular Value (SV) spectrum of the current configuration with the previously reported frequency-diverse passive approach.

We experimentally studied the room-temperature polarization-resolved electrical conductance of multilayer graphene-based films using a home-made terahertz time-domain spectroscopic polarimetry system. The conductance increases nonlinearly with an increase in the graphene layer number and reaches, for ~76 layers, 0.06 S for the real, and 0.03 S for the imaginary part, respectively.

Carbon films prepared by chemical vapor deposition method are widely used in the oil industry as protective layers of optical fibers in harsh environments. The carbon layer thickness required to insure hermeticity of optical fiber depends on the structure of carbon coating. In this work via Raman scattering spectroscopy method we investigate the effect of the precursor gas on the structure and chemical properties of preparing carbon films.

The new MoS2 precursor solution was formulated to print MoS2 atomic layers by a electrohydrodynamic jet printer. The solution-synthesized MoS2 thin films were controlled to obtain atomic layers without chemical vapor deposition. The precursor solution was applied in an EHD jet printing system to obtain 100 µm patterns, which was used for active layer in TFT applications. The EHD jet-printed MoS2 TFTs had a high current ratio of approximately 5.0×106, a good mobility of 19.4 cm2 V-1 s-1.

We present random lasing action on a two dimensional (2D) active surface incor-porated with randomly distributed air holes: responsible for coherent multiple scattering andcouple out the radiation normal to surface

We will present the fabrication of self-assembled metasurfaces made of sub-micron complex colloidal resonators, engineered to scatter visible light strongly forward. The structure and optical properties of both individual resonators and assembled metasurfaces are studied by electronic and atomic force microscopy, X-ray and light scattering techniques and by reflection and transmission measurements. We will show how we can relate the assembled metasurface properties to the surface density of the assembly and to the inner structure of the resonators.

In this study, a dielectric metasurface hologram that adopted single-crystal Si for the meta-atom was fabricated. The phase distribution was calculated using the angular spectrum method and represented by arranging octagonal c-Si pillars with varying widths with the resolution of 8192×8192. Successful projection of the 3D image was confirmed.

A multicolor holographic animation was designed and demonstrated by using dielectric metasurface hologram that consists of silicon nanopillars at the wavelengths of 445, 532, 633 nm. The hologram is fabricated on a silicon on sapphire (SOS) substrate by electron beam lithography.

It has been predicted theoretically, confirmed experimentally and using model validation (for the microwave range) that for a metamaterial consisting of electrically conducting rectangular omega resonators on a dielectric substrate, it is possible to convert an incident linearly polarized electromagnetic wave of the THz or microwave range into a reflected wave with circular polarization. Samples of metamaterials have been designed and manufactured to observe the indicated polarization conversion effect.

Novel optical devices employing photonic crystals (PhCs) and metamaterials have an abundance of potential applications including optical computing, telecommunications, and (micro-LED) display technologies. We demonstrate measurement of the photonic band structure of a PhC by energy-momentum (E-k) spectroscopy by wavelength- and angle-resolved cathodoluminescence (WARCL) stimulated in a scanning electron microscope (SEM).

We describe studies on photothermal heating of a PMMA polymer films using a refractory plasmon TiN metasurface. Under cw laser irradiation plasmon enhanced light absorption of TiN nanostructures converted into the heat, which causes a change in the ambient temperature. This enhanced temperature may induce phase transitions in homogenous polymer or liquid crystal films, which will allow registering local thermal transitions such as glass transition temperature or melting. Thus, we are investigating the heating of a PMMA polymer film to temperatures above the glass transition temperature by a TiN metasurface under cw laser illumination for further measurements of the local glass transition temperature.

This paper presents simulation study on metamaterial spiral resonator of three different topologies (circle, square and hexagon) for relative permittivity calculation of unknown material. Depending on topology and dimensions, strong evanescent field is created. This exhibits stop-band characteristics at resonance. Structures are individually studied under plane wave excitation using microwave simulation software (HFSS and CST). Sensing is realized using standard solid dielectric materials available in material library of simulation software.

Achromatic super-resolution lens with large numerical aperture (NA) in terahertz(THz) regime is in urgent need in THz imaging and telecommunications. However, the previous proposed approaches to achieve super resolution lens suffer from severe chromatic aberrations,limited bandwidth and efficiency. In this paper, enlightened by Maxwell’s fish-eye lens, a THz semicircular gradient solid immersion lens is proposed. Highly efficient (above 89%) achromatic(0.22THz-0.58THz) superfocusing with full width at half maximum around 0.20λ and large NA of 2.0 have been achieved. Theoretical analysis reveals that electric field enhancement at the lens/air interface contributes to super focusing

We experimentally simulated a cosmic string through the spatially varying shift of a Dirac cone in deformed photonic graphene, and observed a bound vortex fermion generated by the gauge field of this cosmic string. Furthermore, such photonic lattices can simultaneously generate and transmit optical vortices on integrated chips.

The previously developed heuristic uniform theory of diffraction (UTD) corner and wedge diffraction coefficients for a thin lossless anisotropic slab are generalized and applied for predicting electromagnetic scattering by a lossy/lossless multilayer anisotropic slab. The effective reflection and transmission coefficients of a multilayer slab are used in the heuristic formulation to determine the scattered fields. The heuristic coefficients derived for a thin slab are applied to a multilayer slab with a finite thickness. Numerical results are provided for various scattering problems that demonstrate validity of the heuristic formulations for a multilayer structure.

In the present paper, we claim that utilization of metamaterial technology in imaging sensors would yield significantly better quality spaceborne camera images. Metamaterial based subpixel elements (metaxels) will enable modulation transfer function (MTF) optimization in order to maximize MTF values at mission specific spatial frequencies of interest and corresponding MTF area (MTFA) increments. We numerically demonstrated an initial design and performance analysis of a metaxel array. The pixel aperture MTF values at the Nyquist Frequencies are 64% and 62.3% for the rectangular and metaxel cases. These results will yield significant enhancements in image quality of satellites as the almost the same MTF values obtained with significant size reduction.

We consider all-dielectric quasicrystal structures with magnetic responce. Quasicrystal structure with octagonal symmetry are constructed. We calculate field distribution. Homogeneous mode confirms metamaterials regime in quasicrystal lattice.

We analyze here the properties of radiation and coupling of an array of square open ended waveguides (OEW) with an alternance of PEC and PMC boundary conditions. This array structure satisfies the parity time-reversal duality (PTD) symmetry property for inversion of two cross-sectional axes. As a consequence of the PTD symmetry, each waveguide supports a mode protected against backscattering for a certain class of defects. The OEW has been designed to operate at the 5G frequency range (3 – 4) GHz. An infinite array of these OEW exhibits wide angle (0°-90°) active impedance matching over a large bandwidth together with a good isolation between the cross-polarized ports.

We propose the study of subwavelength self-focusing solitons in hyperbolic metamaterials: nanoscale periodic structures consisting of alternating conductive and insulating layers. The self-focusing solitons supported by such media result from an interplay between tunneling of surface plasmon modes and nonlinear self-trapping. Therefore, dynamics in these systems, arises from the balance between periodicity, nonlinearity, and surface plasmon polaritons. A 0.18 μm self-focusing fundamental soliton has been achieved with a Purcell Factor of 178.4 thus making such a metamaterial a promising candidate for sub-diffraction focusing imaging, collimation of optical beams, information processing, high quality signal in high-speed applications, bulky waveguides in integrated photonic circuits and laser diode collimators. Finally, we report an intrinsically high-resolution at the ENZP regime down to 80 nm which clear resolve nano- and micro-entities.

There is growing interest in time-dependent materials. Most models for these materials assume constant permittivity and permeability, which is not valid when considering loss. We demonstrate that lossy materials predict non-physical results. We derive the correct boundary conditions necessary for wave propagation in a time-dependent media.

The phase singularity in open optical systems known as exceptional point has revealed exotic functionalities such as ultrasensitive sensors and laser beam unidirectionality. Nevertheless, the properties of such highly-sensitive systems can be affected by unwanted perturbations during the fabrication process. We analytically derive the conditions to reach an exceptional point in a perturbed pair of coupled ring resonators, where both resonators can be perturbed by different scatterers. A numerical example is employed to verify the proposed analytical method.

We have developed a theoretical model to explore optical bistability in a onedimensional array of coupled micro-ring resonators with Kerr nonlinearity. The Kerr nonlinear effect leads to the self-phase modulations and cross-phase modulations in each ring resonator.We describe the nonlinear topological system by temporal coupled mode theory and solve it numerically in time domain.

We propose a novel strategy to implement electromagnetic topological states exploiting bianisotropy, which is manifested in spatial-inversion-symmetry broken meta-atoms. In this case, the effective coupling between two meta-atoms is controlled by their mutual orientation which allows for flexible tuning of topological properties of arrays.

A novel synthesizing procedure is introduced and employed to extract sub-optimal cloaking devices. Their performance is compared with fundamental bounds found using a convex optimization approach. The optimization method is based on a method-of-moments paradigm utilizing rank-1 updates of the structure iteratively performed based on a greedy algorithm. This approach produces locally optimal shapes and its incorporation into a global search strategy is described and applied. As compared to classical topology optimization schemes, no post-processing is required. Two canonical problems are solved and presented.

Rapid fluctuations of graphene carrier density due to strongly confined surface waves and the subsequent nonlinear response are studied in this work. Initially, the influence of the carrier density on graphene chemical potential is investigated thoroughly and a properly modified FDTD algorithm is introduced to evaluate the dynamically varied graphene surface conductivity. Numerical results highlight a considerable second-order nonlinearity besides the standard third-order one.

We show that a homogeneous high-index dielectric sphere can exhibit an effective negative permeability. Specifically, we analitically demonstrate that a high-index dielectric can support Mie resonances, where the electromagnetic spatial distributions outside the sphere accurately reproduce the spatial profiles of magnetic localized surface plasmons, generally excited by negative permeability subwavelength particles.

Photoinduced chiral force microscopy is used to detect chirality of nanoparticles by measuring photoinduced forces. Beams with RCP and LCP can be used but certain challenges are overcome using azimuthally-radially polarized beams (ARPBs). Then we report how light with maximum helicity, called optimal chiral light can be used to detect chirality of nanoparticles.

Following our recent discovery of the Hyper Rayleigh Scattering Optical Activity (HRS OA) effect[1], further developments and related, new nonlinear chiroptical effects will be reported. HRS OA states: “Upon illumination with circularly polarized light, the intensity of light scattered at higher harmonics depends on the chirality of the scatterers”. [1] J.T. Collins, et al. Phys Rev. X 9, 011024 (2019)

We experimentally demonstrate and theoretically verify spectrally tunable, extremely large, and ultrabroadband circular dichroism by designing new hybrid nanohelical metamaterial configurations operating at technologically important visible to ultraviolet spectrum. The demonstrated ultrathin optical metamaterials are expected to provide a substantial boost to the broad fields of classical and quantum optics.

Knots have been put forward to explain various physical phenomena due to their topological stability. Nevertheless, very few published works have reported on their unique combination of strong chirality and rotational symmetry. While conventional optically active materials are composed of chiral molecules, which usually lack symmetry, a meta-molecule that is intrinsically isotropic and simultaneously exhibits strong optical activity has not yet been reported. Here, we introduce a knotted meta-molecule that possesses both rotational symmetry and strong chirality. The chirality of the meta-molecule exhibits optical activity corresponding to a 90° polarization rotation of the incident waves. More importantly, arising from the continuous multi-fold rotational symmetry of the chiral torus knot structure, the observed polarization rotation behavior is found to be independent of the incident wave’s polarization state. Knots that possess such a unique and fundamentally important property have the potential for a wide range of applications in optical physics, chemistry, material science, and engineering.

This talk aims to review the recently emerged field of Mie-resonant dielectric metaphotonics employed for efficient spatial and temporal control of light via multipolar electric and magnetic resonances and bound states in the continuum to achieve high values of the Q factor, with applications of these metaphotonics concepts to nanolasers, quantum optics, topological photonics, and sensing.

Metasurfaces offer complete control of optical wavefront, such as phase, amplitude and polarization at the subwavelength scale, enabling a new class of artificial two-dimensional optics. Metasurfaces hold great potential in on-chip optoelectronic integration applications, which will significantly promote the development of miniaturized optoelectronic systems. In this presentation, i will review our group results on Metasurfaces integration in VCSEL and new results on vectorial holography and LiDARs.

Researches aiming at controlling optical diffraction by high-index nanostructured surfaces, also called optical metasurfaces nowadays, is 20-30 years old [1]. In this talk, I will focus on optical metasurfaces composed of arrayed resonant meta-atoms and emphasize two aspects: fundamental limitations (see arXiv:2011.00232) and appearance design.

Excitons in atomically thin semiconductors are sensitive to their electronic and photonic environments. Here we present our experimental and theoretical results on the fluctuation, diffusion, and annihilation of excitons near nanostructures. Our results have implications for exciton-based sensors, single-photon sources based on 2D materials, and efficient and high-power light-emitting devices.

Here, we utilize cathodoluminescence microscopy and electron-beam-induced deposition for high throughput characterization and control of plasmonic properties as part of the development of in situ near-field control of color centers and excitons in nanoscale materials.

We demonstrate how excitonic resonances in atomically thin semiconductors can be harnessed as an optical resonance to create mutable, flat optics. We show how excitons can enhance the focusing efficiency of a millimeter-scale, patterned WS2 zone plate lens, and demonstrate 33% modulation of the focusing efficiency by electrical gating.

Nature has always represented a fundamental source of inspiration to solve mankind's scientific challenges and engineering tasks. For instance, it has been shown that a hierarchical organization over multiple length scales allows enhanced quasi-static mechanical properties, while the relative orientation of adjacent chiral centers strongly affects the physical properties of a polymer, and internal heterogeneous architectures may result in shape changing systems, to cite a few examples. In this paper, we discuss how bio-inspiration may be used to enhance the potential of phononic crystals and acoustic metamaterials.

We achieve non-orientable mechanics in an orientable metamaterial by geometrical frustration. Non-orientable mechanics generates a movable domain wall, whose moving path can be controlled by the loading sequence. This gives the metamaterial a sequential memory and non-abelian property. A mechanical sequential logic gate is designed based on the proposed metamaterial.

The quantum Klein tunneling phenomenon of relativistic particles unimpededly crossing a higher potential barrier, was recently observed in graphene. In this work I present an exact classical analogue of this quantum effect in a mechanical metamaterial, which is not constrained to a graphene-like geometry, and supports the tunneling conditions via its effectively continuous constitutive parameters. The required parameters are obtained in a real-time feedback operation of the metamaterial through an embedded active control mechanism.

We validate the concept of large scale clamped metamaterials with surface seismic waves propagating in a tank filled with a soft soil (granular medium). When cylindrical inclusions are clamped to the bottom of the tank, any incident wave on the network of inclusions should be reflected in the low frequency regime according to homogenization theory for singularly perturbed problems. However, the singular perturbation theory which is based on the analysis of the spectral properties of the Navier operator for a non-dissipative isotropic periodic elastic linear medium will be affected by the fact that the medium is granular. Our experimental setup should be a proof of concept of a seismic shield at the meter scale.

A novel way based on metamaterial concept is presented here to control the flexural vibrations of a periodic piping system. A pipe supported on a periodic rack is assumed to be pipe on periodic elastic supports whose dispersion relation is derived using Bloch-Floquet theorem, which is successively validated with finite element (FE) model. The results show that both Bragg and resonance type bandgaps exist in the frequency spectra. Moreover, the lateral localized resonators (LLRs) and lateral distributed resonators (LDRs) are designed for controlling the pipe vibration. Though, the efficacy of LDRs is found to be less than the LLRs, the use of LDRs leads to economical solutions.

In this work, we use square and rectangular phononic crystals to construct topological phononic circuits. The phononic system is made of a periodic array of square steel bars which partitions acoustic waves in water over a range of ultrasonic frequencies ($sim 0.5$ MHz). An ultrasonic transducer is used to generate acoustic pulses which propagate along a domain wall, before encountering a nodal point, from which the acoustic signal partitions towards three exit ports. Numerical and experimental results are in good agreement.

In this talk, we present a system of acoustic metamaterials generated by incommensurate bilayers with a phason degree of freedom. The system presents dynamic energy transfer in adiabatic cycles across the crystal via pumping of topological edge modes without any outside intervention or assistance. The system is characterized experimentally by standard acoustic measurements, and via a finite element approach utilizing COMSOL Multiphysics. The experimental results and simulations confirm the energy transfer via topological pumping process. This study suggests possible applications of electron pumping in conventional insulators.

We establish synthetic magnetic fields for acoustic transport in networks of nanomechanical resonators by modulating optomechanical interactions. We show that the controlled breaking of time-reversal symmetry leads to chirality in such a metamaterial's eigenmodes, energy transport and thermodynamics.

This presentation introduces an asymmetric metaporous treatment for sound absorption, i.e., simultaneous cancellation of reflection and transmission, in a lined duct. The treatment is 3D printed and composed of folded and detuned quarter–wavelength resonators filled by air or by porous media. The asymmetry of the treatment, i.e., the use of pairs of detuned resonators, enables perfect sound absorption, the folding of the resonators enhance their subwavelength behavior, and the combination of multiple pairs of resonators leads to subwavelength broadband absorption. The treatment is optimized in the absence of air flow, 3D printed and tested experimentally in a duct test bench. The experimental results in the absence of air flow are found in good agreement with the theory and a mean absorption coefficient of 99% over a large and subwavelength frequency range is observed. The experimental impact of an air flow with Mach number comprised between 0 and 0.25 is also evaluated, showing a very limited deterioration of the absorption coefficient.

The emergence of edge localized modes at the interface between two one-dimensional hyperuniform materials of different geometrical representations is theoretically, numerically and experimentally reported in this work. Being rather disordered and degenerate, hypeuniform materials suppress the acoustic scattering in the long wavelength regime, while counterintuitively possessing a wide band gap. Air-filled acoustic waveguides with rigid diaphragms acting as scatterers are used to do these hyperuniform materials. We show the wide band gap and the emergence of the edge modes in such systems with correlated disorder.

Fully reconfigurable metasurfaces would unlock great potential for dynamic beam-steering and wave-forming technologies. However, given their subwavelength constituents, achieving reconfigurability requires ultrawide index tuning. Here, we describe efforts to reconfigure metasurfaces by tuning optical properties between insulating and metallic behavior using: 1) semiconductor heterostructure devices and 2) Vanadium Oxide phase transitions.

Dynamic tuning of metamaterials is a critical step towards achieving advanced functionality and improved operational bandwidth. We outline several approaches towards achieving dynamic tuning by incorporating metasurfaces with phase change media. We explore both thermal and electrochemical approaches for achieving dynamic tunability in both the near-infrared and visible regimes.

By combining some of the outstanding properties of hybrid perovskite films, high-refractive index, high optical gain and temperature-induced structural phase transitions with scalable nanoimprint fabrication and all-dielectric metasurface design, we demonstrate the first phase-change tunable vortex laser with bistability in the optical spectral range.

We show that Babinet complementary patterns of metamaterials may not exhibit the same frequency tuning range when integrated with liquid crystals due to anisotropy of local fields and strong orientational optical nonlinearity of liquid crystals.

We introduce a novel type of phase change metasurfaces based on antimony trisulphide (Sb2S3) nanocrystals and plasmonic resonators. An adjacent thin film of Sb2S3 nanocrystals to an aluminum metasurface provides non-volatile control of optical properties in the visible part of the spectrum.

We present two examples on active tuning the polarization state of light with metastructures. One is a freely-tunable polarization rotator for broadband terahertz waves, and the other is about dynamically switching the polarization with phase-change materials. The investigations provide some guidelines to dynamically control the polarization states at subwavelength scale.

We present an overview of our ongoing work on exploring how collections of couplers and multipliers (phase shifters and amplifiers) can provide wave-based platforms for analog computation in the form of solving integral and differential equations and matrix inversion

Integrated photonic architectures have the potential to revolutionize neural network computing. However, conventional 2D lithography strongly limits the size of integrated photonic neural networks due to fundamental scaling laws. We overcome this problem by integrating neural networks using 3D printed photonic waveguides.

Wave-based analog computing aims to provide a fast, energy-efficient, and massively parallel computation beyond the limitation of digital processors by engineering wave-material interaction. In this talk, we describe an inverse-design framework for tailoring the nonlocal responses of a single scatterer as a compact and robust alternative to designs based on periodicity and resonance. The precise control of a scatterer's nonlocality is achieved by solving a partial differential equation-constrained optimization problem, where we use the adjoint method for matrix-free computations of a Newton system. We demonstrate the performance of the proposed design by solving integro-differential equations.

Optical computing holds a significant position as a legitimate candidate to replace transistor-based computing as we near the end of silicon evolution. Here, for the first time, we unveil all-optical signal compression. The idea relies on wave-matter interaction in a careful inverse topology optimization of metamaterial structure. Inspired by digital image compression, we propose photonic signal compression based on multi-input multi-output metamaterial networks. The photonic metamaterial structure realizes the Haar wavelet transform for an array of beams as input signals and delivers an array of outputs with reduced entropy according to the Haar transform. Numerical demonstration of the photonic compressor is presented with inversely designed 4 × 4 network. Our photonic signal compressor may pave the way of replacing traditional digital signal and image processing devices with wave-based meta-structures.

We exploit multiple interconnected transmission lines in series or parallel to achieve high-speed routing and switching of TEM pulses. Multiple scenarios will be discussed such as series and parallel crossings, multiple-port excitation, and the influence of the polarity of the incident TEM pulses in the proposed switching/routing technique. This work may have the potential to be applied in high-speed computing processes using electromagnetic waves rather than electrical signals where switching/routing are key processes.

We derive a simple and efficient method for designing wave-shaping materials composed of dipole scatterers, taking into account multiple scattering effects and both magnetic and electric polarizabilities. As an application of our theory, we design aperiodic metasurfaces that re-structure the radiation from a dipole emitter.

Thermal detectors are uniquely capable of sensing incident radiation for any electromagnetic frequency; however, the response times of practical devices are typically on the millisecond scale. By integrating a plasmonic metasurface with an aluminium nitride pyroelectric thin film, we demonstrate spectrally selective, room-temperature pyroelectric detectors from 660–2,000 nm with a 700 ps response time. This design approach has the potential to realize large-area, inexpensive gigahertz pyroelectric detectors for wavelength-specific detection.
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Perfectly absorbing and electrically conducting metasurfaces made form semiconductors are used to create sensitive photoconductive detectors for far-infrared (THz) pulses.

We evaluate near-field thermophotovoltaic energy conversion systems in terms of their open-circuit voltage, and identify opportunities where photonic design can yield significant TPV performance enhancement. We introduce a simple, analytic theory that captures the physics of radiative heat exchange in a TPV system for the accurate evaluation of TPV performance metrics. We demonstrate that a natural consequence of operating in the near-field is considerable luminescence enhancement, and discuss its role in approaching thermodynamic limits in terms of open-circuit voltage.

Metasurfaces provide new avenues for directed light emission, but simulations remain challenging due to the incoherent and multi-directional nature of spontaneous emission. We demonstrate reciprocity-based numerical simulations of unidirectional light emission from phase-gradient quantum well metasurfaces. Our method and results open new venues for design and optimization of light-emitting metasurfaces.

While phased-array metasurfaces have been used extensively for wavefront shaping of coherent light, their capability to control spontaneous emission is an open question. Here, we demonstrate metalenses that emit focused beams and compare the focusing performance across different devices. The developed concepts open new possibilities for development of versatile light sources.

Topology can not only describe the geometry of real space but also be used to capture the geometric properties of spaces spanned by artificial parameters known as synthetic dimensions. In this talk, we will introduce two examples of novel topological phases realizable by combining real and synthetic dimensions. First, a four-dimensional higher-order Chern insulator is realized using a two-dimensional acoustic cavity lattice. Second, a three-dimensional higher-order weak Chern insulator is achieved in a two-dimensional elastic-wave lattice.

We investigate theoretically and experimentally an anomalous topological phase occurring in nonreciprocal unitary scattering networks, that can survive disorder levels with random fluctuations much larger than its band gap. We quantitatively prove the superior resilience of anomalous edge modes over the Chern ones, both for arbitrarily large phase delays disorder and drastic impedance fluctuations. Our research paves the way for fully protected microwave manipulation platforms with reconfigurable mechanisms.

Recent years have witnessed a lot of interest about topological metamaterials for their ability to guide waves around corners or other discontinuities with no reflection. Such metamaterials are typically made of lattices of coupled resonators, which imposes strict limits over their bandwidth. Here, we present a new type of topological metamaterial based on a dual lattice of transmission lines, which exhibits robust topological properties over broad bandwidths. Importantly, the proposed metamaterial is based on differential pairs of transmission lines, making it suitable for combination with discrete circuit components, like varactors or transistors. Therefore, the new metamaterial can form the basis of new types of microwave devices, like phased antenna arrays and traveling-wave amplifiers, with inherent topological propection and reduced sensitivity to structural imperfections.

Wave propagation in metamaterial structures, including active nonlinear hyperbolic planar ones, cylindrical wave concentrators and photonic crystals, with different structure scales, is analyzed. We introduce topological nonlinearity and magnetooptical control over nonlinear strongly localized bullet structures with phase singularities.

We report the design, simulation, and testing of 1D dimerized minimal surface metamaterials exhibiting topological states. By introducing a varying dimerization parameter to minimal surfaces, bands of the unit cell close and reopen undergoing topological transition. Interface modes are observed in a chain consisting of units with distinct topological phases.

We present a solution to break the time-reversal symmetry and achieve strong nonreciprocal responses and regimes of optical gain at the nanoscale. We theoretically demonstrate that by coupling a drift-current biased graphene sheet to a polar dielectric (silicon carbide) slab, it is possible to obtain regimes of loss compensation and plasmonic amplification wherein the graphene plasmons are pumped by the drifting electrons.

Optical communications and linear optics can be precisely described by the unique orthogonal modes obtained from singular value decomposition (SVD) of the coupling operator. This gives sum rules that generalize diffraction and clarify channel counting, and limit device complexity. Novel physical laws apply only to these SVD modes.

In this presentation, we discuss a general approach to determine fundamental limits on scattering, absorption, and focusing of power for electromagnetic systems. The technique consists of three parts: 1) modeling the physics of the problem using integral equations; 2) formulating an optimization problem with a constraint derived from relaxing the method-of-moments equation expressing conservation of power; and 3) using duality to solve (or determine a bound on) the optimization problem. This framework has been successfully applied to derive physical bounds on scattering parameters such as cross-sections and radiation (antenna) parameters such as Q-factor, radiation efficiency, gain, and capacity. Extensions to include bandwidth and multiple materials are also discussed.

We present a general framework, based on Lagrange duality, for computing physical bounds on nanophotonic devices. Complementing structural optimization or inverse design, the approach exploits a hierarchy of energy conservation constraints that provides systematic control over the spatial extent of local violations of physics and that, in the limit of point clusters, produces optimal devices. We discuss representative examples, including bounds on scattering cross sections, thermal radiation, and field transformations.

Broadband metalenses with wide field-of-views are potentially of immense practical importance. In this context, we show that the spectral and angular bandwidth of metasurface systems designed for wide-field-of-view and achromatic operation are not independent. Specifically, metalens devices with a wider field of view necessarily have smaller spectral bandwidths for achromatic operation as compared to devices with a smaller field of view. We describe the origin of this fundamental bandwidth bound and discuss potential strategies to approach and bypass these limitations.

A convex optimization framework over contrast current density is developed to calculate fundamental bounds on the performance of linear passive cloaks. The formulation uses the method of moments applied to the electric field integral equation while using extincted power as the optimized metric. The presented results show that high cloaking efficiency requires cloaks made of low-loss and high-contrast materials.

Information metamaterial builds up a bridge between the physical world and digital world, which can be used to control both electromagnetic waves and digital information. Starting from the basic concepts, we demonstrate digital coding metamaterials, field programmable metamaterials, intelligent metamaterials, adaptive metamaterials, and space-time coding metamaterials. Two system-level applications – intelligent sensing and wireless communications – have been presented.

The defining property of a topological system is that it exhibits some physical property that is highly robust to perturbations, namely, it is topologically protected. In recent years, it has been demonstrated that such phenomena are not confined to the domain of condensed matter physics (for example, in the quantum and spin Hall effects), but rather can be found in other systems such as photonics, ultracold atoms, acoustics, polaritonics, etc. In this talk I will present our experimental results on the effect of nonlinearity on topological photonic systems. First, I will show the observation of edge solitons, and the implications of nonlinearity upon them. Next, I will demonstrate how nonlinearity can act to quantize transport in photonic Thouless pumps, despite the absence of perfect band filling. Nonlinearity is a close cousin of interparticle interactions for bosonic systems, so we expect our results to be widely applicable beyond photonics.
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We investigate a two-dimensional D4-symmetric system with next-nearest neighbor coupling realized with the help of resonant electric circuits. Retrieving the topological invariant experimentally, we demonstrate the emergence of higher-order topology along with the corner-localized state. Our results elucidate the role of long-range interactions in the formation of topological phases.

We present two of our recent works on nonlinear photonic topological insulators: The first realization, in any physical system, in which the non-trivial topological phase of a Topological Insulator itself is brought about by the nonlinear self-action of a propagating wave packet, and the first observation of a nonlinear wave dynamics in a second-order photonic topological insulator.

We investigate the topological phase extraction in the one-dimensional array of qubits with density-dependent interaction using two methods. We show a direct connection between the topological phase and the number and structure of the eigenstates. We apply another method based on a time-evolution measurement of the two-photon mean chiral displacement.

Nodal links in momentum space are numerically demonstrated using a dielectric double diamond structure. We reveal the topological nature of the nodal links using our own theoretical method and show that the topological invariants are summarized into non-Abelian quaternion charges.
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See arxiv preprint https://arxiv.org/abs/2102.12546

The signal-to-noise ratio (SNR) is the main figure of merit that assesses the quality of magnetic resonance imaging (MRI). Improving the imaging quality oftentimes involves enhancing the magnetic field intensities of the constant homogenous field from the main coil, or the oscillating field from the radio frequency (RF) coil. Aside from these options, SNR also depends on the coupling between the imaging subject and the RF coil during the signal reception, which has not been extensively studied. In this talk, we will discuss a different route towards enhancing the SNR of MRI by improving this coupling during the signal reception. We will provide a theoretical design of an ultrathin metasurface with micrometer thickness and high flexibility. This metasurface is reconfigurable and can selectively enhance the SNR at a desired imaging region with any arbitrary shapes. Our design has shown that this metasurface can enhance SNR by up to 28 times in the region of interest. At the same time, the metasurface is designed to minimally disturb the excitation fields by less than 1.6%, thus maintaining the uniformity of the excitation, important to achieve a high-quality MR image with minimal artifacts.

The introduction of emerging technologies such as autonomous vehicles, broadband satellite Internet and 5G/6G cellular communication has motivated countless research efforts in millimeter-wave phased arrays, radar systems, and MIMO antennas. The biggest hurdle against the large scale deployment of these technologies is the cost of design, development and manufacturing of the complex antennas required, and overcoming this hurdle will cause an unprecedented impact on our everyday lives. The concept of Peripherally-Excited (PEX) Antenna Arrays is an attractive candidate to satisfy some of the requirements of the aforementioned technologies, at a reduced active component, manufacturing and deployment cost. In this paper, a practical realization of the PEX antenna array is presented for the first time, with experimental verification.

In this article, we design and demonstrate a multi-functional, digitally programmable metasurface at 0.3 THz exploiting electromagnetic-circuit co-design approach. The metasurface is fabricated using industry standard 65-nm CMOS process. Each metasurface tile consists of 12x12 periodic array of unit cells. We also demonstrate the scalability of this approach by chip tiling and create a larger aperture of 2x2 array. Each unit cell in the metasurface is an individually addressable and programmable multi-split-ring resonator consisting of eight metal-oxide-semiconductor field-effect transistors (MOSFET) at the capacitive gaps. Each unit cell can be programmed to control both amplitude and phase independently. We experimentally demonstrate multi-functional applications namely, high-speed beam modulation with switching ON/OFF ratio of ~25 dB at a maximum clock speed of 5 GHz, beamforming capability of +/- 30deg and spatial wavefront manipulation using binary-amplitude-only holography technique at 0.3 THz. The metasurface chip operates at near-zero DC power (240 uW) consumption.

Optical metasurfaces that enable manipulation of more than two types of optical properties can underpin next-generation optical applications such as high-density optical storage, holography, and anticounterfeiting. Here, we employ anisotropic gap-plasmon structures to demonstrate simultaneous control of phase, amplitude, and luminescence.

We present the theoretical and experimental investigation of a thermally tunable all-dielectric metasurface that sustains the non-radiating anapole source. For the experimental realization we use PVC tubes filled with water presenting high permittivity and tunable properties in microwaves. We measure the scattering parameters with the use of a rectangular waveguide.

We propose and demonstrate in full-wave simulation that by empowering multi-core chip packaging with programmable metasurfaces, we can improve on-chip propagation environment and overcome the caveat of current wireless interconnects.

Periodic boundary conditions are indispensable in the design of spatially periodic electromagnetic structures such as phased array antennas, photonic crystals and metamaterials/metasurfaces. In this talk, an analogous boundary condition will be presented for space-time periodic structures with spatially-discrete traveling-wave modulations (SDTWM).

We study the capabilities of time-modulated diffraction gratings as imaging devices. It is shown that a time-dependent but transversally homogeneous slab can be used to make a perfect image of an object in the far-field. It is also demonstrated that the size of the processing system does not limit the spatial resolution of the recovered image, consequently there is no physical limitation for the superresolution effect. We show therefore that timde-modulated gratings can be used to perfectly recover the image of an object in the far field, being therefore a promising approach to superresoloution imaging.

In this talk we introduce the temporal analogue of the Wood anomaly: temporal Wood anomalies rely on time-modulated surfaces to couple radiation to surface waves in the complete absence of spatial structure. We develop both analytical and numerical models incorporating the full response of a dispersive, time-modulated conductive surface to calculate the induced coupling of plane waves to surface modes, proposing temporal Wood anomalies as a novel, structureless path towards surface-wave excitation.

We study the interference phenomena produced in time-modulated metasurfaces when they are illuminated by multiple harmonics opening a new paradigm of coherent time-modulated metasurfaces. In particular, we obtain perfect absorption at multiple frequencies by inducing slow time modulation of a resistive sheet. Also, it will be shown that it is possible to fully tune the absorption by properly designing the modulation parameters.

We show efficient phase conjugation using a time-switched slab cavity. The temporal boundary conditions and the phase conjugation efficiency are derived. Energy balance and explorations on switching the cavity boundary will be discussed in the presentation.

The temperonic crystal, a periodic structure with a unit cell made of two slabs sustaining temperature wavelike oscillations on short timescales, is introduced. The complex-valued dispersion relation for the temperature scalar field is investigated for the case of a localized temperature pulse in graphene.

Two analytical methods are presented to retrieve the equivalent refractive index in a parallel plate waveguide loaded by non-homogeneous metasurfaces. The first one is based on the Abel transform and the second one on a Regularized Ray-Congruence Equation. These methods enable the design of new flat metalenses.

This work addresses the practical realization of perfect anomalous reflection through a metasurface consisting of a metallic patterning printed over a grounded slab. An exact solution for the homogenized penetrable impedance representing the metallic cladding is found, and the connection of this solution with the one obtained for a nondispersive impenetrable impedance boundary condition is discussed. It is shown that the two solutions can be related though an equivalent transmission network where transmission lines with different wavenumbers are associated to the incident and reflected waves.

A new approach for achieving frequency reconfigurability in wire antennas is proposed. In particular, we show that the antenna input impedance and its reflection coefficient can be tuned by properly engineering the geometrical and electromagnetic characteristics of a coating metasurface wrapped around. This mechanism is then exploited to design a reconfigurable dipole antenna coated by multi-layered metasurfaces loaded with varactor diodes. By tuning the capacitance of the varactors, the operative frequency band of the antenna can be dynamically and continuously shifted within a broad range of frequencies enabling wideband reconfigurability capabilities, while still preserving a stable omnidirectional radiation pattern.

In recent years, vortex beams have attracted considerable interests owing to the ability to enhance spectral efficiency and channel capacity of communication links. Here, we propose a vortex beam generator using a two-dimensional dynamic reflective metasurface in the microwave domain. Simulations and measurements are carried out at 9.5 GHz for the generation of classical and non-diffracting vortex beams. The spiral phase and ring-shaped magnitude distributions show that the vortex beams carry orbital angular momentum. The proposed dynamic metasurface paves the way to potential applications in smart device and wireless communications.

In this contribution, we discuss the possibility of exploiting the theory of composite vortices for manipulating the reflected beam by a single reflective metasurface. In particular, by designing a metasurface able to reflect both a vortex and a vortex-free component, we show that its scattering pattern can be tilted according to the amplitude ratio between the two components. This preliminary results confirm that composite vortex properties can be exploited for beam-shaping applications in different frequency ranges.

In this paper, a flat lens antenna using Gap Waveguide (GW) technology working in the millimeter waves band was designed. The metamaterial lens is fed using a Groove Gap Waveguide (GGW) horn antenna in order to achieve a plane wavefront at broadside. Both devices, metalens and GGW antenna achieve excellent radiation results when combined together. Due to metallic composition, the structure presents more robustness, low loss, and adaptability to a flat surface, able to be used in millimeter wave application.

A passive metasurface antenna with perfect aperture efficiency is presented. The metasurface consists of an inhomogeneous impedance sheet placed above a conductor-backed dielectric substrate. The metasurface antenna is fed by a line source placed within the substrate, which couples to the impedance sheet. The impedance sheet transforms the cylindrical wave of the line source into an aperture field with uniform amplitude and phase. Since the inhomogeneous impedance sheet is fully reactive and the aperture fields are uniform, the metasurface antenna has 100% aperture efficiency. The inhomogeneous impedance sheet is designed in three steps. First, an integral equation is constructed that relates the surface impedance to the desired total electric field along the aperture. The integral equation is solved via the Method of Moments to find the required impedance sheet. The resulting impedance is complex-valued since the metasurface reshapes the power density. Subsequently, an optimization strategy is used to remove the real part of the sheet impedance while still achieving the field transformation of the complex-valued sheet. The reactive sheet introduces surfaces by way of discontinuities, which shuttle power across the metasurface to reshape the power density profile. Finally, the inhomogeneous impedance sheet is realized through the patterning of a metallic cladding.

Fundamental aspects of quadratic materials will be presented along with strategies to enhance optical signals by engineering metal-oxides at the nanoscale. We aim at developing nonlinear and electro-optic photonics devices for a broad spectral range with either bottom-up or top-down fabrication. We will show a strong electro-optic response in assembled barium titanate nanostructures.

The generation, transport, and relaxation of plasmonically induced hot electrons have enabled intriguing ultrafast behavior in photonic metamaterials. We elucidate how to leverage hot carriers for externally triggered nonlinear optical properties for all-optical modulation, nonlinear optical generation, and signal detection.

Dielectric-plasmonic hybrid metasurfaces offer unprecedented possibilities for light manipulation. Here, we report a nonlinear chiral meta-mirror based on silicon split-ring resonators on top of a silver backplane for picosecond optical polarization switching of near-infrared light. The observed dramatic polarization modulation arises from two factors: (1) the strong chiro- and enantio-selective resonance in the hybrid meta-mirror, and (2) the subpicosecond carrier dynamics in α-Si. Our results show that dielectric-plasmonic hybrid metadevices can be used as high-speed and power-efficient polarization-state modulators.

We numerically demonstrate that it is possible to significantly boost third harmonic generation in the ultra-violet frequency range by pumping a chalcogenide-based metasurface in the transparency regime. The combination of high third order nonlinearity, strong field localization, and phase-locking yields a third harmonic signal at 320 nm whose intensity well exceeds the third harmonic signal intensity generated by a thin film of the same thickness, under identical pumping and tuning conditions. This effectively renders chalcogenides extremely useful in a frequency range that is usually overlooked.

We present the first realization and experimental demonstration of second harmonic generation (SHG) modulation by a single all dielectric nanoantenna optically induced by a continuous wave laser source. We prove that even with moderate temperature changes (few tens of degrees), the SHG emitted power by the nanoantenna can be dramatically modulated (up to 60%).

Light propagation in multimoded nonlinear media has found its technological applications in a variety of circumstances. Despite the complexity of the problem, recent thermodynamic studies on optical systems have revealed that, under weak nonlinearity, the thermal equilibrium modal power distribution follows a Rayleigh-Jeans statistics. Here, we will demonstrate that by employing a dispersion engineering method, one can achieve (quasi-)equilibrium solutions that differ from the standard Rayleigh-Jeans statistics. Our analysis relies on non-equilibrium kinetic theories, and can be verified directly through numerical simulations.

Deep insight into the basics of scattering theory and understanding the peculiar features of electromagnetic/light scattering is essential for modern technology. A broad spectrum of exceptional scattering phenomena attainable in suitably engineered structures has recently been predicted and demonstrated, including bound states in the continuum (BIC), exceptional points in PT-symmetrical non-Hermitian systems, coherent perfect absorption, virtual perfect absorption, anapole, cloaking and nontrivial lasing. Here, these unusual scattering phenomena are discussed with a focus on their applications. A unified description of such exotic scattering phenomena based on fundamental properties of the underline scattering matrix is provided. I also demonstrate that these insights provide a powerful approach to tailor unusual scattering regimes for various advanced applications.

This presentation discusses the scattering response of a Janus sphere: a composite object consisting of two attached hemispheres, one of PEC and the other of PMC. An electrically small Janus sphere is shown to behave extremely anisotropically, changing its character from a zero-backscattering object to dominantly backscattering when rotated 90 degrees.

Electromagnetic performances of small subwavelength structures are subject to different limitations, including Chu-Harrington bound of scattering cross-sections and antennae directivity. Achieving superscattering and superdirectivity performances beyond the limitations is a challenging and practically rewarding goal. Here we propose a wire bundle architecture, which consists of a dense array of vertically alighted metal dipoles. Being extremely low-loss configuration, tolerant to fabrication imperfections, this structure supports a variety of high quality modes with overlapping spectra. In particular, several modes with quality factors of few thousands were experimentally observed and engineered to interfere constructively over a wide frequency bands, making the structure to be a broadband superscatterer. The single-channel scattering limit was overcome by almost an order of magnitude. Another variation of the structure was shown to surpass Chu-Harrington and Geyi directivity limits on pathways to demonstrate a superdirective antenna prototype, opening a venue to novel type of compact electromagnetic devices for wireless communications.

The electromagnetic scattering from interconnections of high-permittivity dielectric thin wires with sizes smaller than (or almost equal to) the operating wavelength is investigated. A simple lumped element model for the polarization current intensities induced in the wires is proposed.

The bulk-boundary or bulk-edge correspondence is a principle relating surface confined states to the topological classification of the bulk. By marrying non-Hermitian ingredients in terms of gain or loss with media that violate reciprocity, an unconventional non-Bloch bulk-boundary correspondence leads to unusual localization of bulk states at boundaries—a phenomenon coined non-Hermitian skin effect. Through colorful examples in acoustics I show how topology and non-Hermiticity gives rise to a plethora of highly unusual wave characteristics.

In this work, we discuss the interaction between Helmholtz resonators, using the finite element method. We show that the coupling between two spheres gives rise to two resonant modes at low frequencies. One is symmetric and corresponds to a mono-polar breathing mode, as currently observed. The second one is antisymmetric and behaves as a dipole. By managing the two modes, we aim to create a multifunctional meta-surface operating at two different frequencies.

In this work, three-dimensional phononic crystals are developed for waveguiding and wave attenuation in a broad frequency range, the former is induced by combining two types of unit cells with different wave scattering features. The functionality is demonstrated numerically and validated experimentally on additively manufactured structures along straight, angle- and arbitrary-curved paths. This work opens new perspectives for the practical utilization of phononic crystals in ultrasonic sensors, medical devices, and energy harvesting.

In this work, we consider unidimensional waveguides with changes of cross section, and show that the Helmholtz equation reduces to the discrete Su-Schrieffer-Heeger model. This allows us to obtain topologically protected edge modes inside certain frequency gaps, with well-controlled properties. In addition, by adding Helmholtz resonators side loaded on each segment of waveguide, their frequencies can be lowered to subwavelength regimes.

In this talk, we will discuss through analytical and numerical analysis, validated by experiments, the feasibility of transposing to acoustics the photonic doping phenomenon, i.e., the ability to modify the effective properties of a medium by incorporating a dopant. We show that a one-dimensional Plate-type Acoustic Metamaterial (PAM) can be efficiently doped using a single doping impurity, a tuned Helmholtz resonator in this study. The influence of dopant localization and loss is studied.

The design of acoustic metasurface typically includes the characterization of an enormous amount of acoustic designs with different physical parameters, which demands huge computational resources. This is especially the case for modeling narrow cavities where thermoviscous loss has to be considered. In this communication, a deep learning-based acoustic metasurface absorber modeling approach is proposed to significantly reduce the characterization time while maintaining accuracy. Based on a CNN, the proposed network can model absorption spectrum in the timescale of milliseconds. 

<p> In the framework of the “smart electromagnetic (EM) environments” paradigm, this work presents an innovative strategy for the design of large EM smart skins to be used in future-generation communication systems. The proposed strategy is aimed at synthesizing an electrically large artificial surface to be installed, for example, on the wall of a building through the combination of simple and cheap modular tiles. The location and number of the tiles is optimized by means of a customized approach such that the strength of the EM field generated from a base station is increased in a given area, where the signal was not sufficient to guarantee the connection of the users terminals before the installation of the smart skin in the environment. During the talk, illustrative examples will be shown to provide a preliminary proof-of-concept of the effectiveness and potentialities of the proposed methodology and solutions.</p>

<p> It is expected that future mobile communication systems will exploit the possibilities of intelligent radio environments to enable the controllability, programmability, and optimization of the propagation channel. This technology will need reconfigurable and smart metasurfaces integrated into walls, ceilings, or facades. One challenge to be solved for development of this technology is to create a modelling tool for finite-sized metasurface panels that can be integrated into the models of the propagation channel. In this work, we study how to analytically characterize the far-field scattering properties of reflective metasurfaces mounted on a wall.</p>

Joints of conductors with rough surfaces exhibit nonlinear response to high power RF signals. We show that surface roughness of good conductors plays a pivotal role in coupling the diverse mechanisms of nonlinear distortions of high-power RF signals and illustrate this by examples joints of flat conductors with rough surfaces.

We propose a new application of metamaterials and metasurfaces in magnetic resonance imaging (MRI). In order to reduce inhomogeneity artifacts of images by making the distribution of RF magnetic fields as uniform as possible, dielectric pads are used in MRI with operational frequencies from 128 MHz. Pads mixed of ceramic powders and liquids with permittivity typically ranging from 100 to 300 are heavy and degrade with time. Here, we numerically and experimentally show that a lightweight metamaterial slab with an appropriate effective permittivity and a thin metasurface with electric response grant the same homogeneity improvement but without the above drawbacks.

We proposed and show in full wave simulation a reconfigurable reflective metasurface with sensing capabilities which may find application in wireless communication, wireless power transfer, and smart sensors.

Latency currently limits the most promising applications of electromagnetic imaging, including those built upon programmable metasurface hardware. The fundamental problem is that the separation of relevant and irrelevant information currently only happens at the very last stage. We introduce a “learned sensing” paradigm in which programmable meta-atoms are interpreted as trainable physical weights; together with the digital weights of the processing layer, the programmable meta-atoms are integrated into a hybrid analog-digital sensing pipeline empowered by machine learning. Thereby, the discrimination between relevant and irrelevant information can be made already during the measurement process, yielding a remarkably improved latency. We discuss our recent numerical and experimental investigations of this approach.

We extend the concept of the coherent perfect absorption (CPA) in the non-linear domain. Our system consists of a microwave resonator inductively coupled to a diode with lossy non-linearity. We find out that such non-linear CPA demonstrates, under specific conditions, a broad-band absorption. The latter is associated with the formation of an exceptional point in the zeroes of the scattering matrix.

Absorbing electromagnetic waves over a broadband spectrum has been a long challenging problem. Here, we propose a water-based metastructure that can efficiently absorb the impinging electromagnetic energy over a broad bandwidth in the low-frequency range, while being optically transparent. Analytical calculations and a numerical analysis confirm the broad absorption spectrum of the proposed structure, which resides above 95% from 4GHz (C band) to 120GHz (over M band) and over a wide angular range from normal to grazing incident angle. The proposed microwave absorber offers various opportunities for different classes of applications.

The difference between the number of left-handed and right-handed photons of the free field (electromagnetic helicity), and the screwiness of the static magnetization density in matter (magnetic helicity), are shown to be two different embodiments of the same physical quantity, the total helicity.

We provide a compact overview of the salient results from our recent studies on line-wave propagation in non-Hermitian metasurfaces.

Structural and material symmetries can be engineered to create unique electromagnetic effects including backscattering-immune propagation. In this work we investigate the scattering properties of a class of structures with combined rotational and dual symmetries, i.e., self-dual structures. We demonstrate how self-duality will be manifested through different forms of zero backscattering in periodic and non-periodic structures.

The paper introduce a system design of software defined materials based on the development of novel tunable ferroelectrics, drawn upon the inspiration from multidisciplinary effort ranging from metamaterials, machine learning and wireless sensor works.

This paper proposes non-Foster tank circuit that comprises both positive and negative R, L, C elements. It is shown that, apart from familiar effect of broadband dispersion cancellation, it is also possible to achieve amplification and self-oscillations rooted in negative reactive elements.

In this contribution, we present and discuss the concepts of virtual perfect matching of reactive loaded circuits and virtual perfect absorption in metasurface-bounded cavities. The anomalous scattering behaviours of the two cases are here analysed through a corresponding transmission line models, showing how it is possible to enable both phenomenon in realistic scenarios and deriving the operative limits for a given reactive load or surface impedance of the metasurface bounding the cavity, respectively. The presented study aims to highlight limits and connections of both virtual effects and derive the proper enabling complex frequency excitation.

Here we propose and study a programmable metasurface (PMS) with analog memory that can be used for smart beamforming applications as well as for proactive control of the radiowave propagation environment. The operation of such PMS as a reconfigurable reflectarray is studied analytically and numerically. The PMS comprises a chess-board-like array of metallic patches placed over a dielectric slab with metallic vias connecting the patches to the controlling network. The network includes memory capacitors. The tunability is achieved with varactor loads placed at the corners of the patches. The proposed design has excellent angular stability of the resonant frequency for TE and TM polarizations. Analytical expressions are derived for the MS surface impedance and reflection coefficient. The analytical results are verified with a number of numerical simulations.

This paper reports the design a tunable active high-pass filter, based on negative circuit elements. The device comprises ordinary inductance and capacitance juxtaposed with negative inductance and negative capacitance, generated by two independent Negative impedance Converters (NIC’s). The filter design model is proposed and numerically verified using a commercial circuit simulator, with stability taken in consideration.

Traveling-wave modulation has been extensively studied for its applications in parametric amplification, frequency conversion and non-reciprocity. It is often realized by applying staggered modulation signals to a set of discrete unit cells. This form of modulation will be referred to as spatially-discrete traveling-wave modulation (SDTWM). Recently, it has been shown that many of the frequency harmonics generated by SDTWM radiating structures are bound to the near field. These frequencies are confined by the space-time symmetry of SDTWM, and can be viewed as bound states in the continuum (BICs). In this paper, a SDTWM antenna design is proposed which leverages the localization of BICs to efficiently perform subharmonic frequency conversion.

This study presents a pure frequency converter metasurface composed of engineered transmissive time-modulated radiating meta-atoms. Such meta-atoms are formed by a temporal patch resonator, a static patch resonator and two phase shifters. We show for the first time, experimentally that a transmissive frequency converter metasurface possessing high frequency conversion ratio and controllable frequency bands and transmission magnitude can be realized based on temporal modulation and breaking the periodicity of the meta-atoms.

Materials with extreme constitutive and geometrical parameters enable light matter interactions at spatial, strength and temporal scales that cannot be achieved in other nanophotonic platforms. They empower control over thermal and quantum light emission processes which are the basis of many energy, space, communication and sensing applications. In our talk, we will review our latest ex perimental and theoretical efforts on the topic.

I will introduce quantum metasurfaces: a new interface for quantum light-matter interaction which enables generation of atom-photon entanglement and many-body photonics states suitable for quantum information processing. Initial implementations in various experimental systems will be discussed, such as atomic arrays and two-dimensional semiconductors.

Hybrid modes resulting from the strong coupling of two open cavity modes can support supernarrow lines in their scattering spectra associated with quasi bound states in the continuum (quasi-BIC). These modes are of great interest for sensor applications, as they allow the creation of compact systems with high sensitivity. However, classical quasi-BIC sensors are fundamentally limited by the shot noise limit that can be overcome in quantum sensors. In this work, we investigate a quantum analogue of the hybrid modes with infinitely narrow emission lines arising in a three-level quantum system. We demonstrate that the coupling of such a three-level V-type quantum system with an optical resonator can provide narrow emission spectra, providing sensing properties and overcoming the noise limitations of classical measurement systems.

Manipulating the polarization state of light is essential for integrated photonics and quantum information technology. By introducing geometrical-scaling-induced phase modulations, we report here the simultaneous generation of different types of polarization states with a single metasurface.

Using analytical solution of the nonlinear wave equation we simulate the transformation of the Stokes wave spectrum depending on the medium permittivity. The wavenumber of the spectral Raman band decreases when approaching to low values of both the real and the imaginary part of permittivity and its shape becomes asymmetrical.

Second harmonic generation from a cross polarized double resonant triangular Au-metamolecule is investigated both experimentally and numerically. We demonstrate the contribution of nonlocal response in near field distribution at second harmonic frequency to the second harmonic (SH) response in a double resonant triangular Au-metamolecule. Experimentally observed wavelength dependence of SHG efficiency is reasonably reproduced by a numerical estimation calculated based on overlapping integral of nonlinear polarization and field distribution at SHG frequency.

In this talk, we illustrate the consequences of dualities on the properties of metamaterials. We focus on tight-binding models which describe a bunch of coupled harmonic oscillators. Such models provide a relatively universal effective description of linear systems both in optics and mechanics. Our main results are to (i) systematically construct families of Hamiltonians endowed with a given duality, (ii) provide a universal description of Hamiltonians families near self-dual points, and (iii) identify a duality in a given family of Hamiltonians.

We report our recent results on three topological photonics platforms: coupled ring arrays, photonic crystal, and synthetic dimension. In coupled-ring array, we demonstrate how indistinguishable photon pairs and optical frequency combs can be robustly generated. In the photonic crystal, we show how the topological design principles can be used to create topological resonators with helical edge states, robust against bends. We strongly couple these states to quantum emitters and observe the Purcell effect. Finally, we discuss how synthetic dimensions can be generated in time-delayed fiber loops. We demonstrated how a synthetic magnetic field and an electric field can be created. In the end, we discuss, how the concept topology can be used to make on-chip tapers with very small footprints.

In this talk, I will discuss our invention of topological lasers and unique opportunities they offer in controlling degrees of freedom of photons such as their orbital angular momenta. I will also discuss how bound states in continuum cavities enable new surface emitting lasers that we call bound state in continuum surface emitting lasers (BICSELs).

In this talk, we discuss nonreciprocal surface plasmon propagation on graphene in the presence of drifting electrons. Specifically, we investigate how these nonreciprocal surface waves can be exploited to generate intense and asymmetric field hotspots on a terminated drift biased graphene structure. We then show that the extreme field confinement and enhancement at these nonreciprocal hotspots offers unique opportunities to strengthen nonlinear light-matter interactions, for example third-harmonic generation, by orders of magnitude.

We study the influence of graphene Kerr effect on valley-Hall topological modes of a graphene plasmonic crystal waveguide. By breaking the spatial-inversion symmetry, a gapless Dirac cone and topologically protected edge modes form inside the nontrivial bandgap. Using the giant Kerr coefficient of graphene, we demonstrate that an all-optical switch can be implemented in this topological system by controlling a signal propagation via a pump beam injected into the bulk modes of the metasurface.

Plasmonic nanocavitties are formed by two tightly-coupled nano-metallic structures with nanometre sized gaps between them. They have the ability to extremely confine and enhance light, and also to efficiently radiate to the far-field. Due to these properties, plasmonic nanocavities have been recently used to observe light-matter interactions at room temperature even with single molecules, such as surface enganced Raman spectroscopy (SERS) and strong coupling.

Hybrid modes of plasmon antennas and microcavities, and of metasurfaces and etalons, are of large interest for light matter interaction. We tackle questions like: how do antenna arrays perturb cavities, what are ultimate limits on hybrid Q’s and mode volumes, and how can you leverage collective effects towards ultrastrong coupling

In this report we show that a diffractive metasurface consisting of 4-fold rotation symmetric plasmonic nanostructures can exhibit asymmetric transmission. Generation of higher order diffractive waves supported by the periodic arrangement of nanostructures combined with the losses associated with the lattice modes contribute to asymmetry in transmission.

In this paper, we derive a third-order linear differential equation for describing polarization dynamics of a spherical plasmonic nanoparticle. We entitle such equation, being analogous to the Abraham-Lorentz equation, as the Rudenberg equation that was initially written in 1907 for elucidating the Hertzian dipole antenna in the receiving regime. Based on this equation, we study the case when the plasma frequency of the nanoparticle material varies in time. Under some assumptions, we find analytical solutions which describe the radiative decay of such time-varying nanoparticle.

We study the optical properties of an array of plasmonic hollow conical pillars (HCP) with subwavelength spacing supporting very high field enhancement. We study the LDOS modification of single emitters on the HCP by simultaneous mapping the position and decay rate of photoactivatable single-molecules with a novel super-resolved microscopy approach.

Plasmonic systems are advantageous for nonlinear optics as their ability to strongly confine and enhance the incident light can be exploited to boost the nonlinear interactions. In this contribution, we expand on the possibility of exploiting dielectric-loaded plasmonic film-coupled nanopatch antennas for an optimal second-harmonic generation.

In this talk, we discuss our recent progress in exploring time metamaterials characterized by abrupt switching in time of their electromagnetic properties. We discuss general energy considerations in the involved temporal scattering processes, with special emphasis on situations in which multiple waves are present in the materials, and the involved materials are non-Hermitian and/or frequency dispersive. We also discuss more complex scenarios in which the temporal switching is not abrupt, and the case of open resonators switched in time, enabling efficient phase conjugation and frequency conversion of the scattered fields.

Molding light scattering through artificially engineered materials has been the subject of intensive research so far. However, the majority of these studies have focused on the engineering of scattering in the spatial or wavevector domain, where, for instance, the scatterer has been designed to eliminate wave scattering in certain spatial directions. Different from these approaches, here we show that a complex time-periodic medium, namely a non-Hermitian photonic time crystal, offers a new degree of control over the scattering response in the frequency direction. Specifically, we show that the phase difference between real and imaginary parts of the temporal modulation can be controlled to induce spectral scattering predominantly in a specified frequency-direction. Such a unidirectional spectral scattering feature might find important applications, such as for optical isolation and cloaking of electrically large objects.

Tailored time variations can enable efficient control over signal flows, giving rise to exotic wave phenomena. In this work, we demonstrate how abrupt temporal switching of the coupling between two cavities can tailor the energy flow between them beyond the limitations of static scenarios, enabling unitary energy transfer. The proposed scheme is robust with respect to a wide range of non-idealities, with implications for classical and quantum phenomena, from computing to nanophotonic systems.

we will present a new concept of space-time power combiners which allow perfect power concentration of plane waves from multiple input directions to a single wave propagating into the desired output direction. Such functionality can be realized in metasurfaces with travelling-wave modulations of the surface impedance. The spatiotemporal modulation imparts different spatial and temporal momenta on the incident beams, such that their reflected beams are spatially collimated and their powers are incoherently summed. The proposed technique has very important applications in unidirectional guiding of electromagnetic signals among multiple routes, as well as in high-power laser technologies.

In this talk we present two different mechanisms for wave amplification, which rely on linear and chiral spatiotemporal modulation respectively. Via exact analytic models, we unveil the photonic transition from the stable to the unstable modulation regime, establishing the full potential of linear and chiral metamotion for wave amplification.

It is proposed the novel method of the spectrally selective detection of the spin waves. It is based on the measurement of the magneto-optical effects in magnetoplasmonic nanostructure and their dependance of the magnetization modulation. It is shown that the magnitude of the magneto-optical effects depends on the spatial phase shift between the spin wave and the plasmonic grating.

We show that optical magnetism, generally displayed by spatially modulated composite structures, can also occur in metamaterials with a permittivity rapidly modulated in time. Specifically, we analytically evaluate from first principles the effective dielectric and magnetic response of a temporal metamaterial. We identify and discuss the parameter regime where such temporal metamaterials can exhibit a strong effective diamagnetic response.