<p> We discuss how selective spatiotemporal variation of different material parameters can provide us with higher degrees of freedom and richer functionality and dimensionalities in manipulating wave interaction with such platforms. Several scenarios are presented and potential applications of such metastructures are mentioned.</p>

In this paper some perspectives on Huygens’ metasurfaces for antenna beamforming are described. Both paired, as well as, single metasurface approaches are described for beamshaping of elementary feeding sources in close proximity. Such metasurfaces are capable of controlling the far-zone radiation patterns of these feeding sources, including the shape of the beams and their sidelobe levels.

This paper presents a validation of the accuracy of the homogenized impedance model for the description of periodically modulated patch-type metasurfaces. The validation is done through comparison of predicted propagation and attenuation constant and current distribution with results from a full wave solver.

In order to efficiently analyze planar photonic devices, we propose a discontinuous Galerkin time domain (DGTD) method with a generalized dispersive material (GDM) model. By integrating the GDM model into a full-wave DGTD formulation, we develop a general framework that includes a universal model for the analysis of arbitrary dispersive materials. As an example application, we utilize the new DGTD-GDM solver to analyze the response of a thin pixelized metasurface. The metasurface’s optical responses are computed and compared to results obtained using CST, which provides validation of the efficiency improvement as well as accuracy of the proposed algorithm.

Omega bianisotropic metasurfaces (OBMS) are capable of producing perfect wide angle anomalous refraction, a feat previously impossible with Huygens' metasurfaces (HMS). Using a geometrical optics model, it is shown that an HMS with an anti-reflective coating can produce the same perfectly refracted field as the OBMS. A realistic design for such a coating is presented for use with a Fabry-Perot HMS. Full-wave calculations not only validate this combination as a new approach for attaining perfect anomalous refraction, but also demonstrate improved angular response.

The frequency and incidence-angle dependence of a metagrating consisting of an array of dielectric-loaded slots in a thick perfectly conducting screen is investigated using an analytical method based on a rectangular waveguide model. This model makes experimental validation much simpler than attempting to approximate an infinitely extended array for measurements. In this paper, we study the effect of air gaps in the dielectric loading on the positions and amplitudes of transmission resonances.

We have implemented a method to retrieve the dispersion relation and the effective material constitutive parameters of a densely arranged periodic structure by solving an eigenvalue problem associated with the multimodal transfer matrix of the corresponding unit cell. The material parameters and the dispersion relation of a metasurface made of glide-symmetric square patches are here obtained with this method.

A metamaterial-inspired solution to the RF blackout problem that occurs when plasma shrouds form around high-speed vehicles traveling through the atmosphere is reported. Antenna simulations demonstrate significant transmissions into free space beyond the ENG plasma layer facilitated by the pass-band formed by matching a tunable MNG metasurface to it.

The amount of time that waves spend inside random media is an issue of funda- mental and practical importance. In canonical disordered systems where Anderson localization of waves takes place, this problem has been studied via the time delay. We experimentally and theoretically study the time delay in 1D random media with the possibility that waves perform Lévy flights, which leads to anomalous localization. We show that a wide class of disorder–Lévy disorder–leads to strong random fluctuations of the delay time; nevertheless, the tail of the distribution and the average of the delay time are insensitive to Lévy flights. Our results reveal a universal character of wave propagation that goes beyond standard Brownian wave-diffusion.

In lossless transmission lines terminated on purely reactive loads reflections cannot be avoided, due to the significative impedance mismatch between the real characteristic impedance of the transmission line and the imaginary impedance of the load. Several techniques have been proposed to achieve matching, and all of them are based on the introduction of a resistive lumped element at the end of the line to obtain the power dissipation required to achieve zero reflection. In this contribution, we show a way to achieve the perfect matching condition for purely reactive loads by exploiting the properties of complex frequency excitation, i.e. a signal having a peculiar temporal shape. The proposed solution does not involve dissipation, since the load is purely reactive and energy is stored in the load as long as the complex frequency excitation condition is satisfied, giving rise to an interesting singularity in the transient regime, also known as virtual absorption. Then, the stored energy leaks out the load as soon as the applied excitation varies or stops.

In this paper, double imaging by a periodic bi-fold transformation medium is presented. It is shown that a periodic array of axisymmetric isovolumetric coordinate transformation metamaterials has a double imaging with different angles of sight ±θ due to peculiar refractions on the surface of the medium. The condition for the double imaging is presented and the double imaging operations are confirmed based on ray tracing and full-wave simulations.

Anapole resonances in high-index dielectric nanoparticles arise from the destructive interference between electric and toroidal dipole moments. So far, this mode interference has been solely observed using normal incidence free-space radiation. Here we show that anapole resonances can also arise in silicon disks being excited by an in-plane oriented waveguide. We provide both far-field and near-field measurements at telecom wavelengths which, in good agreement with numerical simulations, show the expected signatures of an anapole resonance. This work paves the way towards the use of the anapole resonances in on-chip silicon photonics.

A small dielectric object with positive permittivity may resonate when the free-space wavelength is large in comparison with the object dimensions if the permittivity is sufficiently high. We show that these resonances are described by the magnetoquasistatic approximation of the Maxwell’s equations.

The field of topological photonics started ten years ago with the first photonic topological insulator realized in a gyromagnetic photonic crystal. While the field is progressing enormously, the development in the gyromagnetic topological photonic crystals is quite limited. Here I will introduce some new configurations in gyromagnetic topological photonic crystals.

We will show that the transmission line network is a versatile platform that can demonstrate new physics notions including topological effects due to orbital angular momentum, the effect of disorder on topological states and new topological phases due to non-Abelian band topologies.

We propose a scheme to realize a higher-order Chern insulator in an electrical circuit. By utilizing basic circuit elements synthesizing complex hoppings between sites of the lattice, we observe multiple topological phases of the three-dimensional circuit array, including higher-order Chern number and crystalline topological phase. In addition to nonreciprocal propagation of topological chiral hinge states, we find that these chiral states do not flow into the hinge opposite to the excitation, opening interesting opportunities for multiplexing.

Put your abstract hereWe discuss nonreciprocal hotspots for photonic applications, which are not subject to the same trade-off as reciprocal cavities, thereby providing unique and exciting opportunities. In particular, we demonstrate how these hotspots provide extremely large and broadband LDOS and second-harmonic generation enhancements.

In this work, we discuss the application of terminated one-way plasmonic waveguides in enhancing nonlinear effects by orders of magnitude over broad bandwidths. We first theoretically demonstrate that remarkable levels of electric field enhancement (field hot-spots) can be achieved when the propagation path of one-way magneto-plasmons is suitably terminated. Then, by investigating the nonlinear, nonlocal, non-Hermitian and dispersive behavior of a relevant example of terminated plasmonic waveguide, we show that the presence of these giant broadband field hot-spots leads to a significant boosting of nonlinear interactions, exemplified by an improvement of several orders of magnitude in the third-harmonic-generation efficiency

We demonstrate that broadband slow light can be achieved over the entire topological bandgap by periodically loading a protected unidirectional edge state with low-Q resonances. As a result of the broadband slow light, the dispersion folds around the Brillouin zone multiple times. We discuss implementations and limitations in (non)reciprocal systems.

A conceptually novel approach to generation of single photons with engineered wavefronts and polarizations is presented, which entails nonradiative coupling of quantum emitters to cylindrically diverging surface plasmon polaritons that are subsequently outcoupled by design metasurfaces into collimated streams of photons in a desired polarization state.

We use aluminum gratings to design emitters with predefined spectral response in the infrared. We create a reference library to investigate the relationship between the grating design parameters and their spectral properties. Next, we develop a search algorithm based on minimization of errors to select gratings from this library corresponding to emission peaks with desired spectral attributes. Finally, we discuss an approach for designing hybrid structures using these gratings to generate a few predefined target spectra.

The transverse magneto-optical effect in transmission is addressed in plasmonic nanostructures with three different kinds of spatial symmetry breaking. The features of the transverse magnetophotonic effect in transmission in each of the asymmetric magnetoplasmonic nanostructures are reported.

The enhancement of light-matter interaction is usually achieved through resonant mechanisms, affected by a trade-off between the field enhancement factor and bandwidth. Several plasmonic devices, featuring geometrical singularities, have been proposed for efficient light harvesting over a wide part of the visible spectrum, therefore overcoming the fundamental competition between bandwidth and field enhancement in small footprints. In this work, we propose an analytical approach for the analysis of such configurations, based on a field modal expansion. We pinpoint the existence of an accumulation point in the spectrum of the plasmonic operator governing the electromagnetic scattering process and investigate the time-dynamics of two coupled parallel infinite cylinders. Finally, based on the obtained insight, we place the sensitivity to fabrication disorder of such singular structures in the context of the Chu limit.

Creation of compact and efficient light sources is one of the fast-developing directions in nanophotonics. Here, we study hybrid nanosystem representing plasmonic nanosponge (Au) which pores are filled by high refractive index semiconductor (Si). We show experimentally that system possess broadband white light emission under irradiation by femtosecond laser pulses. Numerical studies demonstrate that in the case of three-photon excitation such system provides broadband enhancement in the region of photoluminescence. We believe hybrid metal-dielectric nanosponges can be used as universal white-light source for sensing, lab on a chip devices, etc.

We study the parametric dependence of the temperature distribution in plasmon-assisted photocatalysts. Our results provide a better understanding of thermal effects in conventional photocatalytic experiments and other applications that rely on heat generation from a large number of particles.

We present a method capable of manipulating and controlling the propagation of surface plasmons using plasmonic structures composed only of metals. As an example of our technique, we design, evaluate and demonstrate a plano-convex lens with the ability to focus the incident surface plasmons onto a single focal spot.

This talk will describe recent advances in compound metaoptics: devices based on multiple metasurfaces arranged along an axis. The additional degrees of freedom afforded by compound metaoptics enable electromagnetic responses that are difficult or impossible to achieve with a single metasurface. Analysis methods will be presented that rigorously account for and exploit the interactions between tightly coupled metasurfaces and metasurface elements. In addition, several metaoptic devices will be described exhibiting a wide range of wavefront and spectral control functions. These will include broadband, multiband, and multifunctional polarization converters; multiband metasurface-based reflectarray antennas; paired metasurfaces that exhibit reflectionless and lossless transformation of a wavefront's amplitude and phase distributions; and tightly coupled metasurface stacks that allow extreme mode conversion and aperture synthesis.

Virtual perfect absorption is the effect in which the reflection from a reactive lossless load is canceled due to appropriate shaping of the impinging signal or time-modulation of the load, resulting in transfer of the signal to the load in the form of stored energy. As a result, the load appears lossy, although it does not contain any lossy elements. Here, we present a simple circuit based on a time-modulated inductor and capacitor that exhibits a real effective impedance, either positive or negative, thereby providing virtual loss or gain. We also show how the same circuit can also realize time-varying positive/negative effective impedances. Quite importantly, the required modulation is adiabatic, making it easier to realize than other approaches. We expect that these results will be useful in the design of parity-time symmetric systems and photonics topological insulators.

We report a design of single-layer metasurface with multifunctional control of electromagnetic waves at different frequencies in the microwave range. The metasurface performs three main functionalities as a total absorption and polarization conversions in the reflection and transmission regimes while being fully transparent away from the resonance frequencies. The proposed multifunctional metasurface exhibits a great performance and might be a good candidate for the microwave filtering and antenna applications.

A general method to convert between azimuthally-invariant TM0n cylindrical waveguide modes using metasurfaces is presented. Mode conversion is achieved by a metasurface comprising cascaded electric impedance sheets that vary radially. The metasurface is described by a modal scattering matrix that relates the incident and reflected modes on both sides of the metasurface. The sheets’ impedance profiles of the metasurface are optimized to realize stipulated modal scattering matrix entries. As an example, a mode splitter that divides the power of an incident TM01 mode evenly between TM01 and TM02 modes is reported at 10 GHz. The performance of the mode splitter is verified using a commercial electromagnetic field solver.

In this work we show that there is a tradeoff between the maximum absorbed power and the angular dependence for a metasurface absorber. Using spherical nanoparticles supporting embedded eigenstates, we present a metasurface that minimizes the angular dependence of the absorption peak and simultaneously realizes an ultra-narrow absorption linewidth

We study Bode-Fano bounds on the maximum attainable solar power absorption, over the whole solar spectrum, for ultrathin solar cells made of different materials and with antireflection coatings of arbitrary complexity.

We show that combining PT-symmetry and chirality in the same metamaterial system one can achieve a variety of novel propagation and scattering effects. These include mixed PT-related phases, multiple exceptional points, asymmetric reflection and transmission, asymmetric transmitted wave ellipticity and optical activity, and others. The appearance of all these uncommon features can be highly controlled by either the system chirality or, dynamically, by the angle of incidence, resulting to a variety of possibilities in all applications targeting electromagnetic wave polarization control.

Optical techniques to check the chiral response of either chemical (bio)molecules or artificial nanostructures usually relies upon free-space illumination and detection. Here, we propose chiral characterization via light-waves in an integrated approach. The viability of this approach is numerically tested using a metallic nano-helix as a chiral probe.

For many small scatterers $alpha_{ee} alpha{mm} = alpha_{me}alpha_{em}$. However, it is possible to find others that strongly violate this rule. By using a multiple expansion on the electromotive force of an equivalent circuit equation obtained via the complex Poynting’s theorem, here we demonstrate that the rule is only valid when the expansion can be truncated at the dipole moments.

We report a design of an optical metasurface that selectively absorbs impinging electromagnetic waves in the desired wavelength while being fully transparent away from the resonance range. The proposed absorber consists of three-dimensional helical resonators that enable full control of light absorption due to the manipulation of the induced electric and magnetic dipole moments at the resonance. Full-wave simulations confirm the effectiveness of the proposed concept in the mid-infrared spectral range.

In this paper, a Geometrical Optics (GO) solution for electromagnetic scattering from a periodic multilayer anisotropic slab is presented. An approach based on the Transfer Matrix Method (TMM) is used to determine effective slab reflection and transmission coefficients. Numerical results for various scattering problems showing excellent agreement with reference solutions are provided.

Metamaterial waveguides are known to provide additional degrees of freedom in dispersion engineering, thus enabling a finer control over the spectral response of microwave and optical components. In our presentation, we will review how similar concepts can be applied to the field of waveguide quantum electrodynamics (QED), including the generation of nonclassical light states, multi-qubit entanglement generation, and engineering many-body physics.

We discuss the electrodynamics of slowly rotating metamaterials as observed in their rest frame of reference, and present a corresponding first order polarizability theory. A formulation governing the response of an arbitrary array of scatterers to excitation under rotation is provided and used to explore the rotation footprint properties. The metamaterial sensitivity to rotation can be intimately related to two century-old problems in number theory: the no-three-in-line problem, and the Heilbronn triangle problem. New arrays, base on Erd˝os solution to the former, are proposed.

A methodology to investigate 3D Anderson localization of light in large-scale clusters made from high index dielectric spheres is proposed. First, sets of cylindrical slabs with a larger diameter are constructed consisting of dense arrangements of micron-sized GaAs spheres. Second, the full-wave optical problem is solved by means of a T-matrix approach upon illuminating the sample with a Gaussian beam. Light transmission indicates that only classical diffusion occurs and strong localization effects observed in some experiments should be attributed to absorption. The proposed method is an excellent tool to tweak the multipolar response from the spheres to drive the system into a regime where localization is observed, thus providing clear indications for future experiments.

We investigate the quantum optical behavior of quantum emitters coupled to a Weyl-like photonic environment. For the single emitter case, we report on the formation of a photon-atom bound state featuring a tunable power-law confinement. When two emitters are considered, the emergent bound state can mediate robust long-range coherent interactions.

We introduce a method of bandwidth enhancement on metasurfaces based on a more insightful analytical approach of LC resonances. In obtaining L and C parameters, we use surface impedance model considering not only a single frequency matching but also its first frequency derivative. We show that broadband anomalous reflection can be obtain with simple geometries involving dipole and inverse dipole structures. We verified our method using experiment in millimeter-wave frequencies and show that the broadband metasurface achieves a significant increase of bandwidth (more than 80\% increase) compared to a single frequency design, with minimum -3dB power is maintained in the desired reflection and maximum -10dB for all other diffraction orders.

Using structures of subwavelength metallic capped helices with both negative electric and magnetic couplings, we demonstrate a broadband negative mode index metasurface. Numerical and experimental results are presented for the structure with negative dispersion bandwidth of 44% compared to the resonant frequency of individual capped helices. Optimisation of such structures in terms of their size, element geometry and operational passband width is demonstrated.

A relation between a metamaterial (MTM) liner for a circular waveguide and its equivalent surface impedance is made to allow for the replacement of the MTM liner with a metasurface. The equivalent surface impedance is found for a representative MTM-lined waveguide design and below-cutoff backward-wave propagation is predicted.

The problem of perfectly transforming an incident cylindrical wave into a reflected plane wave using a reflective metasurface is considered. The metasurface is a subwavelength-patterned metallic cladding that is placed above a ground plane. The subwavelength features of the textured metallic cladding are homogenized and represented as a purely reactive impedance sheet. The homogenization allows the mutual coupling between elements to be modeled efficiently and accurately. An integral equation is constructed which relates the surface impedance to the desired total electric field in the aperture. The integral equation is solved via the method of moments to find the required sheet impedance of the patterned metallic cladding. The resulting impedance is, in general, complex indicating the need for lossy and/or active elements, which is generally undesired. Here, we use an optimization strategy to remove the real part of the sheet impedance, while still achieving the field transformation of the complex sheet. In other words, a purely reactive sheet is maintained with no need for loss and/or gain. Hence, we show that shaping of amplitude and phase in the radiative near field can be achieved using a single, fully passive, electric impedance sheet.

In this talk, we present our recent results on single-sheet metasurfaces which act as retroreflectors when illuminated from both sides by two coherent plane waves. We call these sheets ``coherent retroreflectors''. In particular, we discuss an application of these metasurfaces for realization of a bound state in a waveguide.

We explore meta-structures supporting comb-like resonances with skyrmion features, highly desirable for compact, stable, and robust information processing. The skyrmion combs are originated from inherently localized plasmon resonances. The demonstrated topological properties open exciting avenues towards dynamic data storage, near-field communications with simultaneous ultra-compact and topologically robust features.

Ballistic metamaterials, metal-dielectric composites with the unit cell size smaller than electron mean free path, represent a new class of composite media with many unique properties, such as hyperbolic response above the plasma frequency. The electromagnetic response of these ballistic metamaterials is controlled by the surface scattering of the free electrons at the metal-dielectric interface.

A pronounced self-induced nonreciprocal transmission is demonstrated due to the enhanced Kerr nonlinear effect in compact epsilon-near-zero media photonically doped with gain and loss defects. The obtained nonlinear parity-time symmetric metamaterial system can achieve almost unitary transmission contrast by operating close to the exceptional point.

By using parametrically modulated metasurfaces, we propose and demonstrate an extremely flexible approach for manipulating electromagnetic waves. We show that the metasurfaces with periodically changing parameters can control scattered waves both in frequency and spatial domain.

We introduce van der Waals metamaterials to rapidly prototype and screen their quantum counterparts. These layered metamaterials are designed to reshape the flow of ultrasound to mimic electron motion. In particular, we show how to construct analogs of all stacking configurations of bilayer and trilayer graphene through the use of interlayer membranes that emulate van der Waals interactions. By changing the membrane's density and thickness, we can also reach coupling regimes far beyond that of naturally occurring graphene. We anticipate that van der Waals metamaterials can be used to explore, extend, and inform future electronic devices. Furthermore, they allow the transfer of useful electronic behavior to acoustic systems, such as flat bands in magic-angle twisted bilayer graphene, which may aid the development of super-resolution ultrasound imagers.
Media link(s):

See Phys. Rev. B 101, 121103R (2020)

https://doi.org/10.1103/PhysRevB.101.121103

Building on a recently developed linear response optimization framework, we here demonstrate that the spectra of nonlinear active mechanical and electric circuits can be designed similarly to those of linear passive network.

In this work, we will present our recent research on the obtaining of the dispersion relation (both the phase shift and the attenuation constant) of the periodic structure from the multi-modal transfer matrix of the unit cell, taking also advantage of the possible higher symmetries that may exist in the unit cell. The non-trivial extension to 2-D periodic structures will also be discussed and complemented with several numerical examples of application.

Metasurface antennas are artificially engineered surfaces designed to generate a given radiation pattern from excitation specifications. The radiation analysis of electromagnetic surfaces can be rigorously carried out in an integral equation formalism with the Method of Moments (MoM). Recently, a technique based on the MoM has been proposed for the direct synthesis of metasurface antennas. We explain how relying on the integral-equation approach in the design phase allows a good control of the radiation, beyond the capabilities of holographic techniques; we also highlight the way in which the method deals with the non-linear relation between surface impedance and radiation patterns.

In this work a metasurface able to provide anomalous refraction of a plane wave has been proposed. Unlike other designs, our structure is made of just one type of geometry, what makes the design very simple. Besides, since each element is very transparent in a wide range of frequency, at least in the range 0-6 GHz, the whole metasurface is frequency stable. We have found that the simulated structure provide anomalous refraction from 3 to 4 GHz.

<p> A single metasurface is designed which can convert a traveling-wave antenna’s feed wave into a collection of radiation patterns. Multiple holographic patterns are jointly optimized to create a series of steered beams through a switched-feed architecture.</p>

This paper presents a technique based on combination of Integral Equations (IEs) and Generalized Sheet Transition Conditions (GSTCs) with bianisotropic susceptibility tensors to compute the wave scattering by an arbitrarily-shaped cylindrical metasurface cavity containing impenetrable scatterers. Moreover, it applies this technique to a newly introduced form of cloaking, redirection cloaking that seems more realistic than transformation-electromagnetics cloaking, showing that adequately synthesized gain-less and loss-less susceptibilities can effectively cloak an impenetrable object of arbitrary shape.

Equivalent-circuit models of Fano-like resonances have typically included multiple resonators. In this work, it is demonstrated that Fano-like resonances can be realized with one parallel-LC resonator, along with a phase shift, for example as provided by a transmission-line section. An application of this model is provided by investigating a plane wave normally incident on a simple transversely periodic LC-based metasurface, which is modelled using a multiconductor transmission-line with an embedded LC resonator. Investigation of the model reveals that the bandwidth of the resulting Fano-like resonance may be controlled with the ratio of the L and C values.

In this contribution we study the feasibility of a novel approach to design artificial materials based devices. In particular, the scattering matrices method originally introduced for analysis problems is conveniently turned into a tool for synthesis and design. In particular, two design strategies are proposed and commented. A first assessment regarding PBG based devices is performed through the design of a waveguide having enhanced performances.

We introduce a quantum mechanics inspired approach for the characterization of space-time non-separable waves, such as the Flying Doughnut pulse. We apply techniques analogous to quantum state tomography to quantify the type and degree of non-separability and provide quantitative predictions of the pulse propagation dynamics.

The excitation fields D&H cannot be directly measured and have gauge freedom. This opens possibilities concerning axionic responses including: (1) a scenario which due to topological reasons is impossible using D&H, (2) allowing periodic lattices with nonzero total charge and (3) an evaporated black hole breaking charge conservation.

Allowing the polarizations and the fields to have delta functions in the transition layer between free space and spatially dispersive continua, while noting that physically realizable constitutive parameters of spatially dispersive continua must remain finite everywhere, a unique set of a deterministic number of interface boundary conditions can be derived from Maxwell's differential equations.

We extend the notion of critical coupling to high-Q lossless resonators based on tailoring the temporal profile of the excitation wave. Utilizing coupled-mode theory, we demonstrate an effect analogous to critical coupling by mimicking loss with non-monochromatic excitations at complex frequencies. Remarkably, we show that this approach enables unitary excitation efficiency in open systems, even in the limit of extreme quality factors in the regime of quasi-bound states in the continuum.

We show that relativistic quantum gases behave as left-handed materials at low frequencies by computing their effective responses. Collective plasmon excitations are obtained for both relativistic electron gas (REG) and relativistic Bose gas (RBG). For both, we found a pure photonic mode that propagates with speed of light with no energy dissipated. For such modes, the effective refractive index is n =-1. In addition, the longitudinal dispersion relation for the RBG shows a local minimum gap energy in the condensate phase, analogous to the roton excitation in Helium superfluid

We unveil a previously overlooked wave propagation regime in magnetized plasmonic materials with comparable plasma and cyclotron frequencies, which enables giant broadband nonreciprocal effects. These findings may pave the way for superior nonreciprocal components, in terms of bandwidth of operation and compactness, in particular at THz frequencies. As a relevant example, we consider Indium Antimonide (InSb) to theoretically demonstrate a subwavelength broadband isolator under moderate magnetic bias at room temperature.

We derive general bounds to optical superresolution, i.e., maximum intensity for electromagnetic waves from arbitrary wavefront-shaping devices that break the diffraction “limit.” We use inverse design to discover metasurfaces operating close to our bounds.

This paper will review recent research in photonic topological insulators and chiral metasurfaces, including isolated states and unidirectional propagation, diffusive transport, and applications such as for integrated photonics, scattering control, and antennas, as well as phononic analogs for acoustic applications.

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 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.  

Interest in realizing reflection-free waveguides recently boomed following discovery of photonic topological insulators, wherein spin-polarized modes are allowed only in opposite directions. Here, we show that guided TEM modes, like in ordinary slot line waveguide, have similar properties, provided that they are properly isolated from all other modes.

We propose a new understanding of metal and dielectric by considering them as two limiting cases of a periodic metal-dielectric layered metamaterial. A metal can continuously transform into a dielectric by varying the metal filling ratio form 1 to 0. We further demonstrate a topological invariant in this continuous transition and find an abrupt phase transition when the metal filling ratio is half, which classifying the metamaterials into metallic state and dielectric state. This classification extends our previous understanding of metal and dielectric. Finally, we also study the edge state between metallic state and dielectric state, which offers the surface plasmon polariton (SPP) at a metal/dielectric interface a new physical meaning: the limiting case of a topological edge state.

Previous proposals for one-way topological edge modes have relied mostly on magnetic materials or independently time-modulating a large number of elements independently. We propose a structure that supports these unique edge modes with a uniform driving field over the entirety of the lattice, compatible with dielectric photonic platforms.

A major goal in nanophotonics is to achieve efficient and robust control of light on the subwavelength nanoscale. We utilise the spatial symmetry of a plasmonic metasurface to realise two types of modes: pseudospin dependent modes and topological valley modes. We study the optical response of the systems in the far-field and highlight how it is necessary to include retardation and radiative effects to appropriately model the band structures. Furthermore, we excite edge states locally in the near-field to reveal the nature of the directionality of the modes. From this we show the importance of source position, as well as source polarization, in exciting purely unidirectional modes.

Artificially-engineered Floquet topological insulators (TIs) based on spatio-temporal modulation of Hermitian potentials has been attracting a lot of attention in recent years thanks to their ability to transport electromagnetic energy in a certain direction without backscattering while at the same time not requiring an external magnetic field as in TIs based on the quantum hall effect (QHE). Prior Floquet TIs were limited to narrow operation bandwidths and remain very challenging to implement in practice due to the difficulty in generating and distributing multi-phased modulation signals across an electrically large lattice with accurate phase synchronization, thus weakening their argument against QHE TIs and prohibiting their use in real applications. In this paper, we address these critical problem by developing a new Floquet TI with a wide topologically protected bandgap from DC up to GHz frequencies by leveraging infinitesimal meta-molecules based on quasi-electrostatic wave propagation in switched capacitor networks. For the first time, we present the implementation of a floquet TI on a chip, thus opening the door to numerous applications of TIs in wireless communications and integrated photonics.

Detection of faint fluxes of photons at terahertz frequencies is crucial for various applications including biosensing, medical diagnosis, chemical detection, atmospheric studies, space explorations, high-data-rate communication, and security screening. Heterodyne terahertz spectrometers based on cryogenically cooled superconducting mixers have so far been the only instruments that can provide high spectral resolution and near-quantum-limited sensitivity levels. The operation temperature, bandwidth constraints, and complexity of these terahertz spectrometers have restricted their use to mostly astronomy and atmospheric studies, limiting the overall impact and wide-spread use of terahertz technologies. Here we introduce a spectrometry scheme that uses plasmonic photomixing for terahertz-to-radio frequency downconversion to offer quantum-level sensitivities at room temperature for the first time. Frequency downconversion is achieved by mixing terahertz radiation and a heterodyning optical beam with a terahertz beat frequency in a plasmonics-enhanced semiconductor active region. We demonstrate spectrometer sensitivities down to 3 times the quantum-limit at room temperature. Our presented spectrometry scheme can be applicable to resolve both the high-resolution spectra of gas molecules and mid-resolution spectra of condensed phase samples over a total operable bandwidth of 0.1-5 THz. As an example, we use the presented spectrometer to resolve the spectral information of ammonia, which has a number of narrowband absorption peaks over the 0.1-5 THz frequency range. With a versatile design capable of broadband spectrometry, this plasmonic photomixer has broad applicability to quantum optics, chemical sensing, biological studies, medical diagnosis, high data-rate communication, as well as astronomy and atmospheric studies.

We demonstrate experimentally that Tamm plasmons can be supported by a dielectric mirror interfaced with a metasurface, a discontinuous thin metal film periodically patterned on the sub-wavelength scale. Not only do Tamm plasmons survive the nano-patterning of the metal film, but they also become sensitive to external perturbations, as a result. In particular, by depositing a nematic liquid crystal on the outer side of the metasurface we were able to red-shift a Tamm plasmon by 35 nm, while electrical switching of the liquid crystal enabled us to tune the wavelength of this notoriously inert excitation within 10 nm.

Nanoscale photothermal effects enable important applications in cancer therapy, imaging and catalysis. These effects also induce substantial changes in the optical response experienced by the probing light, thus suggesting their application in all-optical modulation. Here, we demonstrate the ability of graphene, thin metal films, and graphene/metal hybrid systems to undergo photothermal optical modulation with depths as large as >70% over a wide spectral range extending from the visible to the terahertz frequency domains.

Following the excitation of metallic nanoparticles by ultrashort light pulses, the system subcomponents, such as electron gas, lattice and environment, return to equilibrium by means of complex dynamic relaxation processes. Here, we report a direct measurement of the dynamic electronic response of gold nanoparticles, by means of time-resolved Photoemission Spectroscopy.

Entangled two-photon states are key resources in quantum information science. However, state-of-the-art optical techniques cannot generate them efficiently. We demonstrate that atomically thin plasmonic nanostructures provide a novel platform for substantially enhancing photon-pair production from quantum emitters. We further discover that competing photonic and plasmonic emission mechanisms have unique spectral profiles emerging from an intricate interplay between Fano and Lorentzian resonances, which may serve as experimental fingerprints to unravel the Purcell effect two-quanta generation pathways.

We derive non-perturbative closed form expressions of decay rate and frequency shift of plasmon modes in terms of their quasistatic spatial distribution, by studying the dynamics of the expectation values of the plasmon creation and annihilation operators.

The nonlocal dynamics of the electrons in a plasmonic structure are commonly described using the hydrodynamic Drude model (HDM) based on the fluid equations. Here, we re-write the fluid equations with the Madelung formalism as a nonlinear Schr¨odinger equation to provide a more natural bridge between quantum mechanics and plasmonics. We then apply this formalism to a system composed of two overlapping nanowires and compare it with classical electrodynamics to ensure that the local approximation holds, identifying in the process the corrections needed.

In this work, we present three different metamaterial based spectro-polarimetric systems. Their principles of operation and their performances are briefly discussed. A more detailed analysis of the three systems and the results of the experimental characterization of the first concept will be presented at the conference.

We reveal that dielectric metasurfaces can perform tailored non-conservative transformations optimized for monitoring of small deviations around arbitrarily chosen linear, circular, or elliptical polarizations. We demonstrate that such metasurfaces can convert the anchor polarization to horizontal linear polarization with attenuated power, while they map the small deviations to vertical linear polarization with nearly full power, delivering amplified vertical-to-horizontal polarization ratios for sensitive and convenient single-shot detection.

The inverse-design of metamaterials often requires full-wave evaluation of an enormous number of different candidate designs, which can be extremely time consuming and, in many cases of practical interest, even intractable. By introducing deep learning at an early stage in the design process, a generalized network can be paired with multiobjective optimization to rapidly solve a variety of complex electromagnetic metamaterial design problems.

In this work we propose a solution for the creation of a nanojet focusing component based on a combination of two dielectric materials capable of managing the position of the focused beam in the near zone. We demonstrate that the double-material design of the elements of metagratings can be used to change its diffraction properties improving the diffraction efficiency and diffraction uniformity

Three dimensional metasurface structures hold the potential for better performing devices and interesting new properties. However, at optical frequencies it is very difficult to fabricate truly three dimensional designs. One of the most promising techniques is Membrane Projection Lithography (MPL), which can allow for dielectric and metallic inclusions to be deposited on the side wall of a cavity. However, the design process is difficult due to the large search space afforded by these 3D structures and the many coupling environments that arise between neighboring unit cells. Fortunately, advanced optimization techniques have been developed that allow for the space to be fully explored in an efficient manner for optimal designs.

A colloidal metamaterial is realized by dispersing submicron-sized high-refractive-index dielectric resonators in a nematic liquid crystal medium. Darkfield hyperspectral imaging reveals that when the NLC molecules reorient on application of an ac electric field a doughnut-shaped scattering pattern is obtained, indicating the occurrence of Fano resonance. The theoretical simulation based on the ‘Multi-pole Fano interference model’ confirms the experimental findings. With increasing voltage, the value of Fano parameter q decreases and approaches unity corresponding to an ideal Fano shape.

EM enhancement is typically a lensing-type of effect by which a wide input beam couples to spatially localized resonant modes as for example Mie plasmons, void plasmons or Mie modes at high refractive index particles. Accordingly, EM enhancement is inherently a sub-wavelength phenomenon. Here, we explore a different paradigm for EM enhancement that is based on EM energy being collected over large time intervals by means of an ultra-slow-light waveguide.

A number of ideas have been explored by the metamaterials community on how to achieve far-field optical super-resolution in imaging. A practical solution is closer than we anticipated. We demonstrate metrology and optical imaging with deeply subwavelength resolution in different modalities based on the use of artificial intelligence and light topologically structured by metasurfaces.

I give an overview of the field of epsilon-near-zero (ENZ) optics. I discuss some of the salient features of wave interaction in this platform, and present some of its potential applications.

We experimentally demonstrate that the large optical nonlinearity of epsilon-near-zero materials can be used to manipulate light beams in time and in space domains. We specifically discuss wavelength conversion due to time refraction and real-time image processing with THz refresh rate using a subwavelength-thick epsilon-near-zero thin film.

We look at the underlying cause of the intensity-dependent refractive index in heavily doped epsilon-near-zero semiconductors and highlight the effects of absorption and band non-parabolicity in the model. A figure of merit is proposed to evaluate new candidate materials for nonlinear applications.

Epsilon Near Zero (ENZ) materials exhibit many different fascinating phenomena. In this talk I will survey some of the fundamentals of ENZ modes and experimental results in light-matter interaction and nonlinear optical phenomena using semiconductors as ENZ materials.

Layered Metal/Insulator/Metal cavities sustain Epsilon-Near-Zero (ENZ) resonances that can be tuned across the visible range. We discuss the effects of lateral patterning of such cavities, and the properties of multilayer stacks. The latter show ENZ bands formed by mode coupling that can be described with the Kronig-Penney model.

In this study, we obtained epsilon-near-zero metamaterial at visible range by designing and fabricating a metal–dielectric multilayer anisotropic hyperbolic metamaterial. To do this, we experimentally characterize and extract the permittivity from the TMM (transfer matrix method). Later, we show by optically pumping with fs pulses at a proper wavelength the ENZ point of the structure alters, in comparison to the linear case. The change in the effective permittivity happens in the order of unity, leading to ultrafast light induced refractive index change.

High-impedance surfaces are metamaterial constructs that enable the design of low-profile antennas, electromagnetic absorbers, beamforming and anti-radar systems. In our talk, we will discuss how continuous epsilon-near-zero (ENZ) media enables high-impedance surfaces that do not require from nanofabrication, do not suffer from spatial dispersion, their geometry is not limited by the size of the unit-cell, and are able to recover subwavelength near-field details. As an example, here we theoretically and experimentally demonstrate how a silicon carbide substrate enhances the absorption on a titanium thin film.

We experimentally demonstrate and theoretically confirm that metasurfaces consisting of arrays of randomly distributed spintronic-plasmonic antennas (slits or rods) fabricated with Ni81Fe19/Au multilayers exhibit Giant Magneto Resistance (GMR) and show spintronic modulation of their optical and mid-infrared response, using very weak magnetic fields.
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We experimentally demonstrate and theoretically confirm that metasurfaces consisting of arrays of randomly distributed plasmonic antennas (slits or rods) fabricated with Ni81Fe19/Au multilayers exhibit GMR and show spintronic modulation of their optical and mid infrared response, using very weak magnetic fields

Reflection amplifiers can be used to amplify an incident electromagnetic wave impinging onto a metasurface upon reflection without compromising stability. Here, a reflection amplifier based on a negative-impedance converter is proposed and its stability properties examined. The stability highly depends on the loading impedance and can be achieved by using a shunt resonator, which limits the bandwidth of the amplifier to fit the bandwidth of the load.

In this contribution, the fundamental bounds that apply to low-scattering antennas are discussed and the use of non-linear cloaking metasurfaces is proposed to overcome them. Different power-dependent mantle cloak designs, which are able to dynamically transforming their effective geometry depending on the power level of the impinging field, are introduced. Their effectiveness is assessed in several antenna and array scenarios. This innovative approach may find applications in all those radiating systems in which a considerable difference between transmitted and received power levels is present.

We describe a cloaking strategy for the 3D Helmholtz equation that uses multipolar sources located at the vertices of an imaginary Platonic solid to construct a silent region which shields any object inside from an incoming wave. The source amplitudes can be conveniently determined using the symmetry of the configuration.

This paper presents the design of a phase conjugating metasurface operating at 10 GHz. The designed metasurface achieves phase conjugation, by heterodyning (mixing) an incident RF signal with a pump (modulation) signal at twice the frequency of the incident RF signal. Frequency mixing is achieved through the use of fast switching Schottky diodes. The unit cell of the metasurface is composed of a subwavelength metallic patch that is aperture coupled to the heterodyning circuit. Metasurfaces offer a low-profile alternative to retrodirective antenna arrays. Such metasurfaces could play a key role in far-field wireless power transfer systems.

Recent work have shown light confinement can occur during propagation through a twisted coreless photonic crystal fiber (a chiral fiber). In the absence of a twist, the modal profile is assumed known from Bloch theory and assumed not to be confined. By use of asymptotic techniques applied to the field propagation equation, we provide a theoretical framework in support of observed confinement. While we do this for a particular periodic index profile, recent experiments suggest this to be a robust effect. In this work, we also explore the problem both in the linear and the nonlinear regime. We show that an increase in twist rate will result in more confined modes and indications that nonlinearity plays a secondary role on confinement.

Atom arrays are an exciting new type of quantum light-matter interface. One-dimensional ordered arrays can be used as atomic waveguides. Their guided modes mediate tunable, long-range interactions between impurity atoms coupled to the chain. The waveguides are intrinsically quantum and display strong nonlinearities, allowing for the exploration of many-body physics between photons and the realization of single-photon switches and transistors.

Achieving topologically protected robust transport in optical systems has recently been of great interest. Most studied topological photonic structures can be understood by solving the eigenvalue problem of Maxwell’s equations for static linear systems. Here, we extend topological phases into dynamically driven nonlinear photonic systems. Floquet topological phases in both 1D and 2D will be discussed.

We study the band structure of transverse electric waves in 2D high contrast honeycomb media. Using analytical ideas, together with numerical simulations, we obtain detailed local information, such as the existence of Dirac points, as well as global behavior of the dispersion surfaces over the full Brillouin zone.

We theoretically explore the dynamics of spatial solitons in nonlinear/interacting bosonic topological insulators. We employ a time-reversal broken Lieb-lattice analog of a Chern insulator and find that in the presence of a saturable nonlinearity, solitons bifurcate from a band of non-zero Chern number into the topological band gap with vortex-like structure on a sub-lattice. I will also discuss some further explorations of nonlinear bifurcations in other topological models and properties of continuum mathematical models if time allows.

We present an adaptive, higher-order finite element approach for the simulation of optical phenomena on layered heterostructures: We present a homogenization theory of such plasmonic crystals and introduce a heterogeneous multiscale method based on the analytic homogenization result. We conclude with a spectral analysis quantitatively describing Lorentz resonances in the effective permittivity tensor.

The loss mechanisms of slow waves guided by media interfaces are discussed by examples of surface plasmon polaritons and spin waves. It is shown that plasmons and spin waves with propagation constants kn have anomalously high losses ~kn3, which are directly related to vortices of the wave power flow.

The paper presents the perspective of the author on the novel paradigm of spacetime metamaterials. It presents this emergent field as an extension of relativity physics and modulated-device engineering, and discusses the unprecedented opportunities that such metamaterials offer in terms of the simultaneous control of the spatial and temporal spectra of waves.

In this talk we identify a new mechanism for pulse amplification: the compression of lines of force that are nevertheless conserved in number. 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. Analytic approximations are also presented.

In this talk, we describe excitation of time-varying dipolar particles (time-modulated meta-atoms) by external time-varying fields from a nonstationary and causal perspective. For a time-harmonic excitation, we introduce a complex-valued function, called temporal complex polarizability, and use this function to study a classical electron through the equation of motion whose damping coefficient and natural frequency are changing in time. We theoretically derive the temporal complex permittivity corresponding to time-varying media formed by time-modulated meta-atoms and explicitly show the differences with the conventional macroscopic Drude-Lorentz model.

We propose a highly efficient magnet-free ring circulator constituted of a nonreciprocal time-varying phase shifter. Such a circulator introduces strong nonreciprocity between its isolated ports and possesses a simple architecture.

We use 5-30 keV cathodoluminescence spectroscopy to measure plasmonic scattering wavefronts using holography, determine the density of states and band structure of topological Si photonic crystals, unravel the near-field state transfer of diamond NV centers, and probe optical near fields that control quantum electron wavepackets in space and time.

Metasurface motifs and plasmonic oligomers can have diffraction patterns rich in features in intensity, polarization and phase, leveraging strong multiple scattering, near-field hybridization of resonances, and the coupling of photon spin, angular momentum, and multipoles. Here we demonstrate the utility of these diffraction patterns for metrology, asking how to optimally encode and extract near-field information in far field radiation patterns.

We investigate the interaction between fast electrons and confined optical excitations which are allowed to experience quantum fluctuations. In particular, we explore the effects that the quantum nature of light induces on the electron wave function and the possibility of retrieving its second-order correlation function through the intensities of the peaks in the electron energy spectrum.

We propose a mechanism to produce high-resolution spatial focusing at telecommunication wavelengths by using high-refractive index nanoparticles. We are able to generate photonic nanojets by carefully engineering truncated nanospheres placed on an optical fibre achieving a focal spot with high transverse resolution of less than 0.25λ.

The significant suppression of photobleaching can be observed in a system of a J-aggregated organic choromophore and a plasmonic nanostructure in strong coupling regime. In the present work, we show that this suppression is connected with the temperature of the environment, namely, the ratio of the interaction energy between the near field of the plasmonic nanostructure and the dipole moment of J-aggregated molecule and the energy of thermal fluctuations in the molecule. We also demonstrate the existence of an optimal value of red detuning between the plasmon resonance frequency and the frequency of exciton in J-aggregate for which the photobleaching suppression is the largest. These results reveal the role of strong coupling between a plasmonic nanostructure near field and a molecular dipole moment in the photobleaching suppression.

Using a multipolar decomposition of a system’s plasmonic modes, we show that in plasmonic structures beyond the quasi-static limit, an emitter radiates energy much more efficiently than a plane wave couples energy into the antenna. These results significantly impact our understanding and interpretation of the light-matter dynamics.

In this contribution, we review some of our recent efforts in the investigation of unusual properties of plasmonic and dielectric metasurfaces. We first outline the fundamentals of a surface impedance homogenization approach, which has resulted to be suitable for effectively describing the macroscopic response of metasurfaces made by spheroidal atoms for both normal and oblique incidences. Then, we will describe some of our findings about the unconventional applications of these structures at microwave and optical frequencies.

With recent developments in additive manufacturing techniques, a vast design space of free-form photonic devices is opening up. To make use of this, we present a new approach to inverse design in nanophotonics by fusing it with structural topology optimization.

We present a theoretical and experimental study of a nanostructured guided-mode resonant (GMR) spectral filter operating in the long-wave infrared (LWIR) wavelength range. The component is made of III-V semiconductors: heavily n-doped InAsSb for the grating and GaSb for the waveguide of the GMR resonator.

A smooth helix, widely used as an element of metamaterials and metasurfaces, is studied in an external field under half-wave resonance conditions. The axial and tangential components of the electric force acting on the charges in the helix from the side of the incident wave have been calculated. It is shown that the moment of force, having an axial direction, arises simultaneously with the force directed along the axis of the helix. The action of these factors can lead to the simultaneous stretching and unwinding of the helix in the field of the external wave. The results can be used when considering equilibrium and retention the helix shape, including as an element of metamaterials. The possibilities of tailoring the helix shape by external wave are also considered.

It is well-known that a non-Foster capacitance can be achieved by negative inversion of ordinary positive capacitor with the virtue of Negative Impedance Converter. Here, we propose an alternative way, based on appropriately modulated time-varying reactive element. The correctness of the basic idea is verified by circuit-theory simulation of time-varying-based non-Foster negative capacitor.

In this presentation, we outline a novel architecture to enable intelligent, reconfigurable multibeam antennas for future device-to-device wireless communications. Two-dimensional metamaterials – metasurfaces – have been proposed for high-throughput microwave/millimeter and sub-millimeter band communications. Metasurfaces have emerged as versatile photonic tools for controlling wave fronts and performing nearly-instantaneous operations on the angular spectrum of propagating electromagnetic waves. Our aim is to implement the signal processing and control associated with the formation and tracking of the communication beams within the smart, programmable metasurface layers. Offsetting a part of such processing from the silicon to the quasi-optical metasurface layers shall result in reduction of the computational overheads, which is required when dealing with the evergrowing throughput needs for future telecommunications.

We predict a strong enhancement of quantum photon-pair generation through spontaneous parametric down-conversion in a quadratically nonlinear metasurface with a one-dimensional periodicity. Our metasurface supports bound states in the continuum at the emission wavelengths. We establish the experimental conditions for tailoring of the bi-photon spatial and frequency spectra associated with quantum entanglement.

This work proposes a reconfigurable holographic leaky-wave antenna that offers independent and dynamic control over (i) the radiation angle (including broadside) and (ii) the radiation rate at the fixed operation frequency of 5 GHz. This is achieved by leveraging the theory of binary holography and utilizing a tunable Huygens’ metasurface as a reconfigurable holographic surface. We present a route to the physical realization of the proposed reconfigurable leaky-wave antenna and numerically verify its versatile scanning properties via full-wave simulations.

This work proposes a reconfigurable leaky-wave antenna that can independently control (i) the radiation angle (including broadside), (ii) leakage constant, and (iii) phase constant of a guided mode at the fixed operation frequency of 5 GHz. This is achieved by incorporating a tunable omega-bianisotropic Huygens' metasurface in the design of a leaky-wave antenna. In particular, the tunable Huygens’ metasurface is synthesized by cascading four reconfigurable impedance layers to dynamically control the constitutive parameters of the Huygens' metasurface, thereby eliminating unwanted Floquet modes and the open-stopband effect. The versatile scanning capability of the proposed reconfigurable leaky-wave antenna is numerically studied based on full-wave simulations.

We propose a photonic limiter operating at exceptional point degeneracies (EPD). At low-power radiation it demonstrates an EPD-based high transmittance. At high-power radiation the transmittance is abruptly suppressed, due to a self-induced lift of EPD.

Reconfigurable meta-devices have the potential to disrupt conventional optical elements by offering both the exotic performances of metamaterials and a pathway to all-optical or electrical tuning. To this end, phase change chalcogenide materials represent one of the most promising platforms for realizing truly disruptive optical performances. However, it remains a challenge to design meta-devices that fully exploit the range in permittivity that these phase change materials offer. To this end, multi-objective optimization algorithms are perfectly suited to maximizing the performances of reconfigurable meta-devices.

We review our recent progress on three-dimensional (3D) chiral mechanical metamaterials in the linear elastic regime. This includes ultrasound experiments on acoustical activity with transient nanometer-precision displacement-detection, the mapping of this behavior (as well as of the static behavior) onto effective-medium descriptions beyond Cauchy elasticity, the possibility of isotropic acoustical activity in rationally designed 3D chiral quasi-crystalline mechanical metamaterials, and early work on the possibility of using 3D chiral mechanical metamaterials for high-frequency gravitational-wave detection.

This work introduces an active scatterer in a mechanical meta-layer that exploits piezoelectric sensor-actuator-pairs controlled by digital circuits. We experimentally demonstrate abilities of the mechanical Willis meta-layer, in beams and plates, for independently engineering transmission and reflection coefficients of flexural waves in both amplitude and phase and nonreciprocal wave propagations.

This work puts forward the design, fabrication and experimental characterization of a lightweight three-dimensional micro-lattice-based elastic metamaterial. Alongside being equipped with wide tailorable bandgaps in all directions of propagation, the material also possesses the second order functionality of exhibiting a negative Poisson's ratio

In this study, a new elastic metamaterial featuring multiple local resonators has been developed with negative effective mass and/or negative effective modulus. An illustrative example is presented to show the corresponding influence of the multiple local resonances. The current method opens a novel route to design elastic metamaterials by fully exploring the effect of multiple local resonances on the double negative behaviour featuring negative phase velocity, as well as the single negative behaviour featuring wave attenuation.

– Mechanically actuated a phononic metamaterial underwater is proposed for the active control of the transmission of sound waves and demonstrated through numerical simulation and experiments. The phononic crystal consists of passive asymmetric scatterers with the active mechanical control system of the rotation of the individual scatterer. The rotation of the individual scattering elements of the phononic crystal is able to provide the modification of the equifrequency contour resulting in a different mode of propagation of the ultrasonic waves. The tunability of the phononic crystal allows for dynamic switching between an acoustically conducting state to an insulating state of the phononic device. Furthermore, it can be used as an active acoustic filter or lens.

In this work, we review our recent research on advanced cloaking metasurfaces used to cover monopole antennas. Cloaking devices based on passive metasurfaces have demonstrated a dramatic enhancement of the antenna functionalities, thanks to the additional the degrees of freedom available in the design. Integrating electronic circuits and enabling time modulation in cloaking metasurfaces can further lead to more advanced functionalities, making the covered antennas ever more intelligent. In this framework, our vision is to extensively use reconfigurable metasurfaces to make the antennas cognitive and adaptive, enabling sensing capabilities of the surrounding electromagnetic environment, and dynamic changing of their properties (e.g. operation frequency, visibility/invisibility, polarization, radiation pattern shape, power level, etc.) accordingly.

In this paper, we will report recent results that are aimed at characterizing the path-loss of reconfigurable intelligent meta-surfaces by using theory and experiments.

An innovative approach for the design of future-generation communication systems is proposed aimed at synthesizing a user-defined field distribution in a given domain by opportunistically exploiting the complex scattering environment in which both primary source and receiving terminals operate.

This work is aimed at presenting an overview on how the time-modulation strategy has been applied to the design and control of antenna systems, until its recent consideration in time-modulated EM surfaces.

Topological concepts have found several applications in different branches of physics. As a notable example at microwave frequencies, in this contribution, we focus on the topological properties of phase singularity points of vortex modes, which can be generated by using higher order modes of patch antennas. In particular, we report our recent results on the possibilities offered by structured fields, i.e. the collinear superposition of vortex modes with different topological charges, for designing radiating systems with novel or enhanced functionalities.

This talk describes the concept, theory, and experimental demonstration of phased-array antennas able to exhibit exciting nonreciprocal functionalities, including (i) an independent control of their transmission and reception patterns at the same operation frequency; and (ii) the ability of transmit and receive waves with opposite polarization states. The approach is based on combining time-modulated resonators with high-Q radiating elements and then exploiting the Aharonov-Bohm effect to manipulate the phase of the transmitted and received waves in a nonreciprocal manner. This technique can be applied to develop efficient nonreciprocal phased-array antennas across the electromagnetic spectrum and find broad applications in wireless communication system as well as in polarimetric radars and sensors.

An extension of the basic concept of a self-oscillating non-Foster cross-dipole to a self-oscillating Huygens radiator has been developed theoretically and studied numerically. A proof-of-concept prototype has been built. The preliminary results have demonstrated self-oscillations with nearly-perfect admittance matching over a tuning bandwidth of 1:1.35.

This work focuses on introducing a novel application of topological insulators in the form of self matched antennas. Self-matching is a property of the topological antenna that leads it to be resistant to any reflection caused by the impedance mismatch at the truncation of the metasurface topological structure with free space. This behavior can be attributed to the spin-momentum locking property of topological insulators and removes the need for any matching networks or flaring ends to promote a gradual impedance mismatch. The proposed implementation provides a 30\% bandwidth with a return loss ranging between -15 to -22 dB in the operating bandwidth and a radiation efficiency of over 98.4%.

Optical force can stably bind multiple microparticles into an optical matter. However, we discovered that the Lorentz force alone can bind only a small number of particles and the optical cluster always becomes unstable when the particle number or the dielectric constant of the particles increases beyond a certain critical point. The instability can be explained as the consequence of an open system always possesses exceptional points.

<p> We review and explore sensor applications based on electromagnetic systems operating near an exceptional point of degeneracy (EPD). The EPD is defined as the point at which the system eigenmodes coalesce in both their eigenvalues and eigenvectors varying a system parameter. Sensors based on EPDs show sensitivity proportional to δ^1/m, where δ is a perturbation of a system parameter and m is the order of the EPD. EPDs manifest in PT-symmetric systems or periodic systems that can be periodic in either time or space. We review all the methods to obtain EPD based sensors, and we focus on two classes of ultra-sensitive EPD systems: i) periodic linear time-varying single oscillators, and ii) optical gyroscopes based on a modified coupled resonators optical waveguide (CROW) exhibiting 4th order EPD.</p>

We show that a wave scattered wave from a time-modulated target, encircling quasi-adiabatically an exceptional point in a parameter space, can be robust to variations of the incident field and local operational details of the driving. This insensitivity is abruptly suppressed for scattering dwell times smaller than a critical value.

Exceptional points (EPs) are degeneracies of non-Hermitian Hamiltonians where both eigenvalues and corresponding eigenvectors coalesce. Over the past five years, EPs in open wave systems with gain, loss, or both, have been intensely explored due to their topological properties and enhanced sensitivity. In this classical domain (the number of energy quanta is much larger than one), the non-unitary dynamics of a system are accurately described by an effective, non-Hermitian Hamiltonian. In contrast, the dynamics of a minimal quantum system, inevitably coupled to the environment, are described by a Lindblad equation for its density matrix. I will review the challenges for realizing a quantum system that undergoes the non- unitary, coherent time evolution generated by a non-Hermitian Hamiltonian, or more generally, parity-time symmetric quantum systems. I will then show how these challenges can be overcome in multiple platforms comprising ultracold atoms, integrated or table-top quantum photonics, and superconducting qubits.

We propose a parity-time symmetric accelerometer that involves a micromechanical spring-mass coupled to a photonic circuit which is tuned at exceptional-point degeneracy. Spring-mass response to acceleration leads to square-root circuit’s resonance detuning, enhancing the probe of ultra-small accelerations. Our design provides a pathway towards new generation of hypersensitive accelerometers/vibrometers.

Spectral degeneracies, known as exceptional points, in open quantum systems exhibit rich physics and promise new advances in controlling wave transport and enhancing lightmatter interactions. In this talk, we will discuss exceptional points emerging from asymmetric coupling between the modes of a physical system, and present two examples on how such chiral exceptional points lead to enhanced sensor’s response [1]-[2], and to quantum processes that stem solely from their presence in a nonlinear photonic system [3].

Frequency synchronization of two coupled lasers with initially detuned frequencies is investigated using a second-order nonlinear oscillator model. It is shown that the two lasers have a better tendency to synchronize when their interaction is of dissipative nature. In this case, the onset of synchronization is found to be at an exceptional point singularity.

We propose several dynamic optical platforms based on gate-tunable biasing and integration of indium-tin-oxide and doped-semiconductors into all-dielectric/plasmonic metasurfaces. Besides the widely-utilized gap-plasmon and Mie-type resonances to enhance the light-matter interaction, we focus on the excitation of guided-mode and Fabry-Pérot-type resonances with relatively higher quality-factors. This helps to achieve highly-efficient tunable reflective and transmissive metasurfaces in near-infrared regime.

Achieving perfect absorption (PA) in a complex scattering enclosure recently attracted much attention thanks to its large potential for applications in analog signal processing, energy transfer, precision sensing, secure communication and random lasing. Current schemes rely on shaping multiple incident wave fronts to achieve coherent PA. Here, we introduce an alternative route by tweaking the randomness of the medium itself. In our experiment, we use a programmable metasurface to reconfigure the boundary conditions of a chaotic cavity. We systematically analyze achievability and sensitivity of the PA condition. Our scheme can also be applied to other types of wave phenomena, e.g. in photonic or phononic systems.

Dielectric nonlinear optical metasurfaces show an unprecedented potential to realize optical applications like nonlinear vortex beam generation or multiplexed holography. Therefore, all-dielectric metasurfaces have been used to realize a plethora of nonlinear optical experiments, like wave mixing or efficient higher harmonic generation. Here, we present a nonlinear silicon metasurface for third harmonic wavefront control.

The properties of multitone wave packets and products of their nonlinear mixing are discussed. An average power is obtained for wave packets with a finite number Nc of carriers and their mixing products. Distinctive features of nonlinear products generated by wave packets are illustrated for harmonic signals with Gaussian envelopes.

We demonstrate that a waveguide resonance of free-standing dielectric photonic crystal nanomembrane with the four-fold rotational symmetry allows the circularly-polarized third harmonic generation in vacuum ultraviolet region at 157 nm with sufficient intensity for VUV spectroscopy.

We demonstrate the fabrication of nano-structures from lithium niobate thin films and investigate their optical resonances in the visible and near-infrared region. The large electro-optic coefficient of LiNbO3 offers a platform for active tuning of transmission properties in deeply subwavelength films.

We give an overview of our work on shifting of frequencies using linear, time-dependent structures. We discuss both the three-dimensional and the two-dimensional case and indicate the differences in the performance of the structures.

We use GaAs-based metasurface operating at its magnetic quadrupole resonance to switch the -1 diffraction order. We design suppression of radiation in the diffraction direction and tune it with 2.5 ps modulation time using optical pumping.

We experimentally observe frequency conversion via electromagnetic wave interaction with a high quality-factor resonance in an array of resonators whose refractive indices are varied on an ultrafast timescale. Further, we describe the observations using coupled mode theory.

Time-variant semiconductor resonators have attracted interest for non-reciprocity and applications in frequency conversion and the photon acceleration regime. Here, we control the nonlinear response of time-variant metasurfaces by changing the pulse chirp of the incident fundamental, with both the magnitude and sign of the chirp affecting the third harmonic generation spectrum.

We overcome material absorption of high harmonics generated from a silicon crystal by generating them from a periodic array of thin one-dimensional crystalline silicon ridge waveguides. Adding vacuum gaps between the ridges avoids the high absorption loss of the bulk and results in a ~ 100-fold increase of the extraction depth. Looking ahead, our results enable bright on-chip coherent short-wavelength sources and may extend the usable spectral range of traditional nonlinear crystals to their absorption windows.

we study the directionality of the second harmonic (SH) signal emitted by a dielectric metasurface made of AlGaAs nanodisks embedded into a liquid crystal matrix. Notably, we numerically demonstrate the modulation of the SH total power and the emission pattern signal coming from the proposed metasurface as a function of the liquid crystal orientation.

Pump-probe measurements are performed on amorphous Ge based micro-resonator metasurfaces which exhibit strong photonic resonant modes in the mid infrared. We observe a 51% (0.31 OD) change in transmittance signal modulation depth with subpicosecond modulation speed. This is obtained with pump fluences P < 204 uJ=cm^2.

The possibility of controlling the spectrum of the generated third harmonic for high quality-factor resonant metasurfaces is examined. The ultrafast dynamics for both fundamental wavelength and third harmonic generation is observed in all-dielectric metasurfaces with pump-probe technique.

In this work we propose a high-quality factor semiconductor nanoparticles array made of rectangular silicon nanobricks. Our optimized metasurface can dramatically boost third harmonic generation, with a complex polarization dependence in the different diffraction orders.

We provide a compact summary of our recent results and ongoing research on digital metasurfaces based on spatio-temporal coding. Examples of field manipulations include harmonic beam steering and/or shaping and programmable nonreciprocal effects. Possible applications range from wireless communications to radars and imaging.

Dynamical modulation of the optical properties of thin films promises to open new avenues for wave control. We present two new opportunities enabled by time-modulation for surface-wave control: (1) Luminal amplification, namely the broadband generalisation of parametric amplification, and (2) Temporal Wood anomalies, namely the generalization of the Wood anomaly used in grating couplers to the time domain, enabling perfect coupling of radiation to surface waves while circumventing the need for surface structuring and near-field coupling schemes.

Electromagnetic time dependent media are materials whose constitutive relations vary in time. Most models assume a constant permittivity and permeability, to model loss it is natural to consider complex constitutive relations. We show this is unphysical, presenting the correct boundary conditions necessary for wave propagation in a time dependent media.

In this contribution, we propose a magnet-less non-reciprocal isolating system based on time-varying metasurfaces. The system consists of a conventional frequency selective device placed between two time-varying metasurfaces, one for frequency up-conversion and one for down-conversion by the same amount. The overall reciprocity of the system is broken by exploiting the different scattering response from the embedded device when illuminated from opposite directions, since the two time-varying metasurfaces impart an opposite frequency conversion for the two directions of illumination. Note that the transmitted fields are always at the same frequency as for the incident one, since the metasurfaces cancel the frequency conversion of each other. This strategy can be successfully exploited for conceiving a new family of non-reciprocal isolating systems, based upon well studies conventional electromagnetic devices.

Space-time modulated structures have attracted substantial attention in the metamaterials community in recent years. Most physical realizations of space-time modulated systems consist of discrete unit cells that can be independently modulated. While these physical structures are often analyzed as continuously modulated media, consideration of the spatial discretization yields a more accurate model. Additionally, a finite unit cell size enables phenomena which do not arise in the continuum limit. In this paper, a relation between the fields in each unit cell (pixel) of a free-space N-path system is derived. The relation is incorporated into a method of moments solver to compute the scattered field from a space-time modulated metasurface.

A reflective, dual-polarized, spatiotemporally modulated metasurface is reported at X-band frequencies. Each column of subwavelength unit cells on the experimental metasurface can be independently, temporally modulated. Here, we consider a space-time modulation where the time modulation of adjacent columns is staggered to realize a discretized traveling-wave modulation. We propose an analytical model of such a metasurface with discretized spatial modulation. It is shown that at certain incident angles, the metasurface can perform retroreflective subharmonic frequency translation: Doppler-like frequency translation to a higher-order frequency harmonic in retroreflection. By changing the temporal modulation waveform on each column, the retroreflected frequency harmonic can be controlled.

Conventionally, nonreciprocity in time-varying systems is achieved by exploiting both temporal and spatial modulations. In this paper, we introduce a concept of magnetless bianisotropic time-modulated systems that support nonreciprocal wave propagation at the fundamental frequency and use only uniform, solely temporal material modulations.

Metasurfaces have been crucial for the development of THz technology. The recently proposed “metageometries”, which consist in convoluted unit cell geometries, have been demonstrated to improve largely the performance of metasensors based on metaatoms. Here we present results that extend the reach of metageometries in two different lines of technological importance. A labyrinth metasensor for the detection of fungi and a zigzag half-wave plate with excellent performance, both operating at THz and with an extremely compact profile.

Modulated metasurfaces (MTSs) have sprung up in the last decade as an attractive solution for wave guidance and radiation. More precisely, modulated MTS antennas stand out for providing an unprecedented control of the aperture fields with low-profile and lightweight structures. In this class of antennas, a surface-wave (SW) is gradually radiated, owing to its interaction with a modulated impedance boundary condition (IBC). This IBC is typically implemented in the microwave regime by several thousands of sub-wavelength patches printed on a grounded slab. However, dielectric losses may hinder the use of standard printed circuit board (PCB) technology at higher frequencies. In this paper, we will address this issue by introducing a new class of metal-only modulated MTS, which can be easily fabricated by additive manufacturing or micro-machining for millimeter-wave and sub-THz applications.

The transmission spectra of trun cated rectangular arrays of tilted subwavelength slots measured with quasi optical systems are far richer in terms of resonances than the customary circular and square subwavelength hole arrays measured at optics We provide a comprehensive experimental st udy of such asymmetric arrays combined with Method of Moments analysis to understand the underlying physics and to provide design guidelines.

We propose and experimentally demonstrate a concept of an ultra-thin spatial phase modulator (SPM) for correcting THz wavefronts. It exploits a combination of spatially addressable metasurfaces and an optically thin low-voltage liquid crystal cell. Our metadevice allows ‘imprinting’ 2D phase profile of any spatial complexity with a sub-wavelength spatial resolution, and can be readily fabricated using the well-established LC-device technology and high-resolution photolithography technique.

In this contribution, we present our recent progress on mm-wave metasurface based antennas. We review synthesis and simulation techniques that enable highly efficient metasurfaces for the operation at W-band frequencies (75-110 GHz) and higher. Additionally, we present the design and characterization of a W-band switched beam antenna. We use high resolution near-field scanning to determine the phase focal point of the metasurface as well as the transmission efficiency. Switched beam functionality is demonstrated using far-field measurements with a bistatic system.

In this paper, we present the implementation of a new surface wave lens for beam-forming applications. The Flat Optics theory and a double-layered configuration are employed to create a plane wave with modifiable direction in the entire azimuth range. By using metallic pins, we implement a radially-dependent refraction index that, combined with a cylindrical reflector, results in a flat and symmetric system ideal for the excitation of reconfigurable antennas.

Holey higher-order topological insulators are capable to sustain deeply confined corner states below 1/50 of the wavelength. Remarkable resilience of these surface confined acoustic states against defects and topologically-protected sound in three different frequency regimes are observed, which push forward exciting applications for robust acoustic imaging beyond the diffraction limit.

The vibrational waves in a one-dimensional composite system containing double-negative acoustic metamaterials were studied. The transmission of sound waves of multilayer systems was numerically clarified. A method for calculating the transmission rate in these systems was also described.

Eaton lens namely, omnidirectional retroreflector, enables light to reflect back to source-driven zone as an optical device used by transformation optics. However, in physical space, the requirement of a singularity accompanied by an extremely large refractive index struggles to make the realization. By making use of the transmuted index profile and considering flexural waves on a thin plate with hemispherical geometric curvature regarding thickness variations being scraped out, the inflexible demand of refractive index at the singularity point can be alleviated and also it gives rise to better efficiency compared to metamaterial scheme due to the curvature frame with smoothness in form factor.

Scattering of elastic waves off a single and double array of cylindrical scatters is considered for arbitrary polarizations. Analysis of the scattering problem is investigated via Lippmann Schwinger Integral Equation formalism; analytical expressions for the scattering amplitudes are used in order to analyze the resonances width. For the single array it is shown that the resonance width has a minimum which arises from elastic dipole interference that of which doesn't occur in similar photonic or acoustic structures. For the double array it is demonstrated that one can tune the width of the resonances to zero, forming a standing wave of mixed polarizations, a Bound State in the Continuum (BSC). These spectral states require more restrictive conditions on the parameters of the theory due to the polarization mixing and different dispersion between both polarizations.
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https://arxiv.org/abs/1906.00955

The Structural, magnetic and transport behavior of La1-xCaxMnO3+ (x=0.48, 0.50, 0.52 and 0.55 and =0.015) compositions close to charge ordering, was studied through XRD, resistivity, DC magnetization and AC susceptibility measurements. With time and thermal cycling (T<300 K) there is an irreversible transformation of the low-temperature phase from a partially ferromagnetic and metallic to one that is less ferromagnetic and highly resistive. For instance, an increase of resistivity can be observed by thermal cycling, where no effect is obtained for lower Ca concentration. The time changes in the magnetization are logarithmic in general and activation energies are consistent with those expected for electron transfer between Mn ions. The data suggest that oxygen non-stoichiometry results in mechanical strains in this two-phase system, leading to the development of irreversible metastable states, which relax towards the more stable charge-ordered and antiferromagnetic microdomains at the nano-meter size. This behavior is interpreted in terms of strains induced charge localization at the interface between FM/AFM domains in the antiferromagnetic matrix. Charge, orbital ordering and phase separation play a prominent role in the appearance of such properties, since they can be modified in a spectacular manner by external factor, making the different physical properties metastable. Here we describe two factors that deeply modify those properties, viz. the doping concentration and the thermal cycling. The metastable state is recovered by the high temperature annealing. We also measure the magnetic relaxation in the metastable state and also the revival of the metastable state (in a relaxed sample) due to high temperature (800 ) thermal treatment.

The PLA and 3D-printable copper-based semiconductor filament were selected to fabricate the substrate and resistive pattern, which had the characteristics of low density, and broadband absorbing. Foremost, such a complex perforated structure can be fully fabricated by Fused Deposition Modeling 3D printing.

The technologies for the numerical analysis of the electrodynamic characteristics of systems consisting of composites, meta-surfaces, and metamaterials are considered. The developed methods, algorithms and programs allow to effectively model the interaction of electromagnetic radiation with structurally inhomogeneous materials with complex structural and material composition, including multiscale, nonlinearity, anisotropy.

<p> We propose a Fabry-Perot type optical cavity resonator based on a Mie resonances, consisting double dielectric cylinder array on low – index substrate. Single dielectric cylinder arrays have high reflectance at a particular period. Our Fabry-Perot cavity structure has a high transmittance and high quality factor of about 10^5.</p>

In this paper, we present our numerical investigation results of the enhanced electromagnetic propagation when an antireflective metasurface superstrate is placed atop of the material under test for non-destructive testing applications. The simple metasurface design can effectively manipulate the transmission/reflection coefficients of the incident EM waves. The resultant enhanced propagation is numerically demonstrated for various MUT's properties, which provides a strong evidence for practical NDT applications.

An innovative sensing mechanism based on the variations in the sensor radiation diagram in correspondence of changes in the refractive index of the surrounding material is illustrated.

We study the model of a complementary metamaterial element embedded in a waveguide wall as a collection of dipole and quadrupole moments. In the analytic model of a metasurface, the elements are often characterized as electric and magnetic point dipoles, with their higher-order moments ignored. In this study, we present the retrieval of the quadrupole moments of a metamaterial element etched into the top wall of a parallel-plate waveguide and demonstrate that considering the quadrupole moments of the element, in addition to its dipole moments, can improve the accuracy of the analytic model of a metamaterial element.

Inspired by many interesting electromagnetic devices designed from transformation optics, here we illustrate how to derive the time-domain electromagnetic concentrator model. Then we present the theoretical analysis and time-domain finite element method for solving the model. Numerical results are presented to illustrate the concentrator's behavior.

We propose that gravitational meta-atoms (or unit cells) with gravitomagnetic moments could exhibit gravitomagnetic permeability, analogous to the magnetic permeability of materials comprised of atoms with magnetic moments. In this paper, GEM field approximations to general relativity are used to derive the gravitomagnetic dipole moment of gravitational systems.

We clarify the mechanism for the phenomenon of parallel conductors at the light line. By analyzing them with a circuit model including retardation, the singularity at the light line is clarified. Using this singularity, we can excite the light line mode specifically and form a beam with a sharp directivity.

Electromagnetic interference (EMI) pollution world and seriously affects the operation safety of various electronic devices electronic systems and telecommunications. The undesirable heat emissions and electromagnetic radiation result in degrade the performance of electronic components as well as its harmful effects on human health. Therefore there is a critical need for developing effective and practical EMI shielding materials with a low-cost and scalable solution fabrication process. Recently colloidal nanocrystal (NC) thin films have attracted great attention in a wide variety of applications since the overall properties of the NC thin films strongly depend on the surface chemistry of NC. Herein, we introduce NC-based EMI shielding materials through ligand-exchanged, conductive silver (Ag) NCs. The ligand exchange process with optimum condition enables the stabilization of NC in the form of colloidal, allowing their bottom-up multi-layered films. Ag NC films treated with short and compact inorganic ligands successfully provide highly conductive thin films with markedly different EMI shielding properties. By controlling nanocracks in Ag NC film, we monitored the structural states and dramatically change EMI shielding properties. Resultant Ag NC films showed excellent EMI shielding effectiveness greater than 40 dB in a frequency range from 8 MHz to 12 GHz. This strategy provides new opportunities to construct scalable and high-performance EMI shielding materials for advanced flexible applications.

Equivalent circuit of a non-Foster negative capacitor, based on an SCS voltage inversion negative converter with one-pole and two-pole amplifier model, has been developed. The circuit was loaded with an external RC network of series or parallel type, and the stability of the whole system is investigated. It was found that there is always a trade-off between operating bandwidth and the range of external capacities and resistances that assure stable operation.

Two easily scalable manufacturing techniques to realize conformal metasurface antennas embedded in a structural laminate are presented. Given the finite size of the manufactured samples, a numerically simulated ‘reference’ wave was used in the design process to further improve the electromagnetic performance of these antennas.

Interaction of a plane electromagnetic wave with structures comprising two co-located in one plane periodic gratings from infinite and finite on length conductors was investigated. It is established that combining grids into one structure leads to its full transparency at fixed frequencies. Variation in the size of gaps between the ends of conductors leads to changes in frequency corresponding to the maximum transmission coefficient. This effect can be used to create frequency selective structures with a tunable transmission coefficient.

In this work, a planar transmission line loaded with square shaped split ring resonator (SRR) metamaterials works around 150 GHz is modeled and validated by means of full-wave electromagnetic simulations. The transmission characteristics of such a transmission line is reported. The SRR loaded coplanar waveguide (CPW) structure exhibits stop band characteristics in response to the resonance of the inductively coupled SRR rings excited by the magnetic fluxes through the rings. A parametric analysis of the rings and arrays of SRRs carried out to predict the behavior of the meta cells loaded transmission line. Since these metamaterials are much smaller than the feeding signal wavelength, these metamaterials loaded transmission lines are potentially useful to optimize size and quality factor of millimeter-wave circuit components and radiating elements.

This study presents a novel azimuthal 6 channels retrodirective metagrating (MG). The designed MG adopts the planar hexagonal unitcell to ensure the retrodirective channels at every 60° interval in the azimuth direction. The efficiency of the MG can be adjusted by varying the length and height of the unitcell, resulting in a low profile design. The characteristics of MG at elevation angles of theta_i= 50° were confirmed from the HFSS full wave simulation and experiment.

We compare structural, chemical, and optical properties of monocrystalline and polycrystalline plasmonic antennas fabricated by electron and ion beam lithography. The antennas fabricated by electron lithography are superior to those fabricated by ion beam lithography. No significant effect of the crystallinity is observed.

In this work, we demonstrate a single-step laser-assisted fabrication of thin plasmonic nanocomposite thin films. The common processes taking place in Ag:Au:TiO2 thin nanocomposite films under UV laser irradiation are discussed. We describe the main nanostructure formation mechanisms, as well as their effect on the optical properties of the films. The obtained results pave the way for the implementation of such materials in modern photonics and optoelectronics devices, photocatalytic systems, sensing, and SERS due to their unique and well-controlled optical properties.

We present a model for exciton-plasmon coupling based on energy exchange between emitters and localized surface plasmons in metal-dielectric structures. Plasmonic correlations between emitters give rise to a collective state exchanging its energy with a resonant plasmon mode. By accurately defining the plasmon mode volume, we relate the QE-plasmon coupling to collective energy transfer rate. For QEs distributed in extended region enclosing a plasmonic structure, the ensemble QE-plasmon coupling saturates to a universal value independent of system size and shape.

Photovoltage excited by circular polarized light is demonstrated on a periodic arch structure engraved in a Au film. In order to determine the character of the voltage it is essential to know the sense of circular polarization.

in this paper we demonstrate experimentally by near-field imaging the propagation of a diffraction-free Bessel-type beam in a guided wave configuration generated by means of a metasurface-based axicon lens integrated on a silicon waveguide. Full wave simulations are in excellent agreement with near field measurements.

We discuss the design and fabrication of plasmonic filters that can be integrated with infrared photodetectors to create highly compact instruments for space applications. The filters are designed for the wavelengths 3-5 micrometers and simultaneously perform wavelength and polarization filtering.

<p> We present an approach based on effective medium theory in the Burgerman-Bergman approximation for modeling of optical properties of nanocomposites based on TiO2 and SiO2 films with Ag nanoparticles. The importance of volume fraction of metal phase for spectral characteristics of such nanocomposite is demonstrated and confirmed. The increase of this parameter leads to the redshift of the spectral peak and an increase of the reflection amplitude. The numerical calculations demonstrate a good agreement with the experimental data for laser-obtained TiO2- and SiO2-based nanocomposite films with Ag nanoparticles.</p>

Plasmonic metamaterial are characterized with plasmonic modes, of which field can be resonantly enhanced at particular wavelengths. This gives room to enhance nonlinear process such as second harmonic generation (SHG). Here we report SHG spectroscopy for double resonant (DR) plasmonic single nanoantenna array with resonances for cross polarized excitation at pump and emission wavelength. In addition, using finite element method (FEM), we numerically demonstrate how the type of mode generated at each resonant wavelength determines the efficiency of the generated SHG signal at double resonance. The experimental data can be explained in terms of the SH intensity wavelength dependence of double resonant and single resonant plasmonic metasurfaces. Our finding paves a way to design and fabricate double resonant nonlinear medium with single nanoantenna constituent for efficient nonlinear response.

The PC nanostructures with magnetic layer of gradient thickness are proposed. Two designs of magnetic PC nanostructures are discussed. The smooth magnetic layer provides gradual tuning of the IFE, and the perforated magnetic layer allows spatially localized emergence of the IFE in the spots of several microns.

We study electromagnetic field enhancement of plasmonic resonator array and the applications for enhancing emission and enhanced photodetection. By varying the dimension of the star-shape resonators, emission enhancements in the semiconductor quantum dots can be monitored and an enhancement factor of ~6 times has been demonstrated. By adjusting the resonance mode of the resonator array integrated with a mid-infrared semiconductor photodiode, the room temperate specific detectivity of greater than 1010 Jones can be achieved.

Put your abstract hWe proposed the narrow band graphene metamaterial-based infrared tunable absorber. Proposed absorber structure is numerically investigated over the 1.5μm to 1.6μm wavelength range. The proposed absorber structure is tunable for the wide range of the chemical potential that can be controlled with external biasing. It offers the perfect absorption in the multiple narrowband regions. The absorber work as metamaterial because it is observed the negative refractive index response at resonating frequency.ere

We propose a simple design approach based on metal-masked titanium dioxide nanopillars, which can realize strong Mie resonance in metasurfaces and enables light confinement within itself over the range of visible wavelengths. By selecting the appropriate period and diameter of individual titanium dioxide nanopillars, the coincidence of resonance peak positions derived from excited electric and magnetic dipoles can be achived.

Acoustic coding metasurface consisting of identical asymmetric acoustic unit (AAU) is proposed. The AAU is tunable in transmission coefficient and reflection phase asymmetry, functioning as coding elements 0/1 when patterned in regular/inverse form. We demonstrate efficient projection of complex acoustic images and achieve controllable encryption and decryption of acoustic images.

We will report on the Valley Acoustoelectric Effect (VAE), which represents an extension of the Acoustoelectric Effect and arises in two-dimensional metamaterials, like transition metal dichalcogenide (TMD) monolayers. This effect consists in the emergence of a drag Hall electric and a spin currents due to the propagation of surface acoustic waves along the sample, exposed to external polarized light.

We show experimentally and numerically how antenna impedance measurements provide knowledge of the local photon density of states, as well as of Förster resonant energy transfer, the non-radiative energy exchange between two dipoles. We further generalize this to the full complex electromagnetic Green tensor, which completely characterizes an electromagnetic environment and its effect on cooperative phenomena.

In simple fluids, such as water, invariance under parity and time-reversal symmetry imposes that the rotation of constituent ‘atoms’ is determined by the flow and that viscous stresses damp motion. Mechanically excited hydrodynamic surface waves propagate isotropically. Activation of the rotational degrees of freedom of a fluid by spinning its atomic building blocks breaks these constraints and has thus been the subject of fundamental theoretical interest across classical and quantum fluids. I will discuss the creation of a cohesive two-dimensional chiral liquid consisting of millions of spinning colloidal magnets and study its flows. We find a new mechanism for chiral surface wave propagation which we dub viscous ‘edge-pumping’. We further find the presence of chiral instabilities with no counterpart in conventional fluids. Spectral measurements of the chiral surface dynamics suggest the presence of Hall viscosity, an experimentally elusive property of chiral fluids with analogs in plasmas and quantum, fluids. Precise measurements and comparison with theory demonstrate excellent agreement with a minimal chiral hydrodynamic model, paving the way for the exploration of chiral hydrodynamics in experiment.

We present a method to design autonomous active metamaterials that can create arbitrary physical interactions on a single, reprogrammable platform, including non-local, non-linear, time-dependent or non-Newtonian couplings. The underlying principle includes application of external forces to a regular mechanical lattice, and processing them in real-time through closed-loop controllers that are pre-programmed to create desired couplings between the metamaterial sites. As an example, we demonstrate that a lattice constrained to out-of-plane vibration can be programmed to exhibit an analogy either of the quantum spin Hall effect, or the quantum Hall effect, thereby enabling a versatile unconventional guiding of mechanical waves.

An important issue in the field of elastic metamaterials is that their dynamic properties, such as the band gap frequencies, are typically fixed once the structure has been designed and fabricated. To overcome this limitation, many efforts have been made to conceive materials with adaptive elastic properties based on piezoelectric materials, temperature and magneto-based techniques, actuated polymers via electromagnetic waves, as well as the application of an external mechanical load. In the present research we present an alternative approach based on light-responsive polymers. We show the possibility to reversibly change the material parameters in specific regions of the unit cells of these structures through external light stimuli, leading to the tunability of their transmission spectrum.

Metamaterial with bandgap tunability is an emerging area in manipulating elastic wave transmission characteristics for next generation phononic devices. Although several attempts are made employing multi-fields such as magnetic, electric and thermal etc., mechanical deformation based tunable bandgap is a major interest. However, achieving tunability in terms of broadening or terminating the bandgap in single-phase locally resonant acoustic metamaterial (LRAM) remains as challenging tasks. In this work, we explore the bandgap of a single-phase star shaped structure with applied deformation. Initially, a quasi-static analysis of unit cell has been performed to find the static displacement field under prescribed deformation. Further, a linearized elastodynamics is adopted for wave analysis of the predeformed periodic unit cell, and we apply Bloch-Floquet boundary condition. Subsequently, utilizing finite element based framework, an eigenvalue problem is formulated. Accordingly, dispersion responses are predicted and bandgaps are extracted for specified external mechanical deformation. In particular, the development of bandgap under equibiaxial tensile deformation is addressed, and underlying local resonances (dipole, quadrupole and monopole) are explained through vibration mode shapes.

A new chiral elastic meta-beam is proposed to attenuate the propagation of flexural waves. A chiral and achiral meta-beam is designed and their band structures are numerically calculated. Transmission loss is considered for verification. This approach will pave the way for the design of chiral meta-structures for attenuation of vibrations.

We study a temporal photonic crystal with square profile of permittivity and permeability. The continuity of the D(t) and B(t) fields across the time discontinuities facilitates the Konig-Penney methodology, leading to an analytic photonic band structure (PBS). It is periodic in frequency and exhibits k-bands separated by k-gaps, but for equal modulations the PBS is composed of straight lines without k-gaps. The field D(t) displays the Bloch-Floquet behavior. We also study the Zak phase associated with the PBS.

In this talk, we show the topological transport in a SOI valley photonic crystal slab. The topological robust transport at telecommunication wavelength is observed and topological photonic routing is achieved. We also proposed valley photonic systems combining layer or frequency degree of freedoms with valley degree freedom. These valley photonic systems enrich the topological nontrivial phases and offers more methods on light manipulation.

We provide a novel perspective on surfaces states arising from the corrugated termination of a photonic crystal that would otherwise not support any surface states. Through theoretical and experimental investigations, we associate the photonic crystals surface states with metasurface bound states which selectively interact and hybridize with the band structure of the bulk photonic crystal.

Traditionally, the analysis of electromagnetic bandgap structures designed with multiconductor transmission-line metamaterial techniques has been limited to geometrical changes in the host transmission lines, or variation in the loading components. This work investigates adjusting the modal properties of the host transmission lines, thereby forming a set of universal design considerations which may be applied regardless of the layout of the physical structure.

The Chu bound imposes constraints on the radiation characteristics of small antennas, namely, directivity and directivity-bandwidth product. We consider effective time modulation of a small antenna structure as a means to broaden these radiation characteristics, beyond what expected for passive, linear, time-invariant antenna systems.

In this contribution, we expand the possibility offered by structured fields at microwave frequencies by exploiting phase singularity points of vortex modes for designing a single radiating structure exhibiting orthogonal radiation patterns pointing in different directions. This kind of structure, being able to radiate two orthogonal polarizations with low-coupling levels, can be exploited in compact multi-antenna systems for antenna diversity or MIMO applications.

<p> A recently proposed concept of a self-oscillating non-Foster antenna array is modified for the case of a single loop. The idea was tested by simulations of a model of small loop integrated with a Linvill floating INIC and operating in 50 MHz RF band. Obtained results revealed efficient self-oscillations with a 1:2 tuning bandwidth and the suppression of harmonics better than 20 dB. This antenna might find application in future active metasurfaces.</p>

In this talk we introduce a concept of antenna body modulation. We show approximated theoretical formulas for effective resistance and reactance at the carrying frequency and discuss how antenna body modulation can affect them. Finally, we show how radiation resistance can be decreased keeping the reactance unchanged in the limit of small modulations.

Recently, circuit loaded metasurfaces exhibiting different responses depending on the waveform of the incoming waves have been proposed. Here, we extend this approach presenting two different antenna applications. As a first example, we report an open-ended waveguide antenna capped with a band-pass filtering iris loaded with a lumped element circuit. Thanks to its peculiar frequency- and time-domain selectivity response the antenna exhibits different radiating patterns depending on the waveform of the transmitted/received signal. The same circuit is also exploited to design a mantle cloak able to hide an antenna to a pulsed radar system while keeping its radiation characteristics unaffected for a continuous-wave signal.

Top down nanofabrication approaches lack the fidelity coupled with throughput to create the sub 100 nanometer unit cell, sub 10 nanometer feature size, meta atoms required to create metamaterials operating within the optical regime. We present a novel fabrication methodology enabling the fabrication of highly purified meta atoms with yields sufficient to create effective materials.

With the rapid progress in the field of metasurfaces and their use in miniature integrated devices arise the quest for cheap mass-production of efficient metasurfaces. We suggest a novel way to design and fabricate all-dielectric Huygens metasurfaces using photo-annealing of As2S3 chalcogenide glass. Our method has potential advantages for the low-cost production of metasurfaces-based compact devices

We present the design, fabrication, and characterization of multifunctional 2.5D metastructures using adjoint optimization. Our technique considers complex interactions among meta-atoms and offers significantly improved performance compared to conventional unit-cellbased techniques.

We show the development of a 100 keV electron-beam lithography liftoff fabrication process for a plasmonic metasurface designed to resonate at 15 µm. Such a metasurface may prove useful in enhancing mid-IR absorption spectroscopy, e.g. for CO2 detection. Helium ion beam microscopy and Fourier transform infrared spectroscopy show evidence of the expected resonance, but which has been shifted outside of the measurable range due to variations in exposure and thickness.

Bidirectional Transmittance Distribution Function (BTDF) measurements of an out-of-plane (OOP) metasurface beamsteerer were carried out at 6 μm for four different polarization states. These are compared to ideal models of the metasurface beamsteerer to compare and contrast behaviors in ideal and measured results.

A wall-first variant of membrane projection lithography (MPL) is introduced which yields three-dimensional meta-films; mm-scale structures with micron-scale periodicity and 3D nm-scale unit cell structure. These meta-films combine aspects of photonic crystals, metamaterials and plasmonic nano antennas in their infrared scattering behavior. We present the fabrication approach, and modeling/IR characterization results.

We introduce a novel concept of Multi-Input Multi-Output (MIMO) metasurface processor with asymmetric Optical Transfer Function (OTF) which can perform spatial firstorder derivation on two orthogonal distinct input signals for both TM and TE polarizations. Two distinct input signals, regardless of their polarization, simultaneously illuminate the metasurface computer and the resulting differentiated signals are separated from each other via appropriate Spatial Low Pass Filters (SLPF). Our simulations confirm the claim of a 2×2 MIMO optical differentiator processor. The proposed metasurface computer is away from the restrictions such as lack of computing speed, large size of bulky or two additional sub-blocks, supporting only a single input, and constant polarization mode. Our proposed scheme pave the way for real-time massive parallel signal processing by single metasurface.

Optical signal processing (OSP) has recently received renewed interest as digital computers are approaching the processing limits dictated by Moore’s law. Here, inspired by digital filters, we propose a new type of OSP metamaterials based on discretization of optical waves in space and subsequent implementation of the desired mathematical operation on the discretized wave. A first order differentiator (subtractor) metasurface in transmission mode is designed as a proof of concept. Compared to other techniques, our approach is characterized by modularity, adaptivity to different forms of operations, broader bandwidth and lower loss.

We present our recent work on tuning the polarization states (PSs) of light passively or actively with both 2D/3D metastructures. It is shown that the PSs are manipulated by a time-retardation metasurface, dispersion-free metastructures and phase-changed hybrid materials. The investigations provide some guidelines to control the PSs at subwavelength scale.

We demonstrate equivalence between 3D bulk optics and certain 2D metasurfaces, where phase delay arises from trains of Lorentzian resonances in the effective sheet conductivities, instead of propagating phase accumulation. We show perfectly achromatic sheet versions of prisms and lenses with arbitrary spectral bandwidth and dual reflection/transmission operation.

Analytical models for plasmonic structures are desirable in lieu of full-wave simulations. Though these models cannot be derived for all complex structures, an exact model for nanoloop antennas has been recently developed. This paper presents a demonstration of the theory in the design of directive and reconfigurable loaded nanoloop antennas.

We propose a gold – based nanostructured design for achieving enhanced absorption in ultrathin black phosphorus (BP) layers in the 3 – 5 μm wavelength range. By suitably tuning the design parameters, we are able to excite strongly localized modes in BP layers of thicknesses ranging from 5 to 50 nm at a wavelength of 4 μm. We test the efficiency of these absorbers by computing their absorption enhancement factor and comparing it against the conventional 4n2 limit. For a BP layer thickness of 5 nm, we are able to achieve an enhancement of 561 at a wavelength of 4 μm, which is significantly greater than the conventional value of 4n2 equal to 34 for an isolated textured BP layer.

Embedding Ge-quantum dot emitters in Mie resonators leads to an enhancement of their luminescence efficiency due to the Purcell effect. To increase this effect, collective Mie resonances in extended Mie-resonator chains are investigated leading to a partial cancellation of radiation losses and experimentally observed Q-factors of up to 500. The corresponding modes and their field localization are theoretically analysed and traced back to a combination of individual oscillating dipoles.

Large scale elastic metamaterials as an innovative passive isolation strategy for seismic waves has recently attracted increasing interest in the scientific community. In this work, we investigate the feasibility of an innovative design based on hierarchical organization of the unit cell, i.e. a structure having a self-similar geometry repeated at different scale levels. Results show how the introduction of hierarchy allows the conception of unit cells exhibiting reduced size while attaining good isolation efficiency at frequencies of interest for earthquake engineering.

We demonstrate experimentally and numerically that metamaterials can be used to control water wave propagation and resonance properties of a closed cavity. Experimental data show the capability of water-wave metamaterials to provide a robust anisotropic medium for water wave propagation.

We show, experimentally and numerically, that the wake of a ship becomes highly asymmetrical when the bathymetry is varying periodically. This bathymetry forms a metamaterial modifying the properties of the waves (wavenumber, speed) depending on the direction toward which they propagates.

We propose a passive wave splitter, created purely by geometry, to engineer three-way beam splitting for flexural waves in thin plates. We do so by considering a square perforation within a cell that is then extended periodically upon a square lattice. To achieve splitting and transport around a sharp bend we use accidental, and not symmetry-induced, Dirac cones, upon rotation of the square perforation in the periodic cell. The theory is developed and full scattering finite element simulations demonstrate the effectiveness of the proposed designs. Such elastic plate systems have potential applications ranging from ultrasonics to geophysics.

The phenomenon, known as a complete band gap in photonic crystals consisting of periodically arranged man-made nano structures, caused a huge sensation in photonics. Inspired by the physical methodology, we extend it to large-scale wave propagation for seismic waves. In particular, we exploit the elastodynamic Navier equation in the medium for seismic phononic crystals to induce complete band gaps of body (P) and shear (S) waves. We also show a technique that uses weak formulations to analyze band structures. Estimation of evanescent modes by complex-valued wave vectors yields propagation length, then we redesign bulky phononic crystals to be as thin as possible.

The amplitude and the period of the rectangular distribution are derived from the matching between the ansatz and the exact solution of the equation in a periodic and anharmonic mass-spring system. These results could be employed for the analysis and modeling of seismic metamaterials in composite foundations.

An approach for conceptual development for vibroacoustic metamaterial structures for realization in aerospace applications is presented. Vibration reduction in the frequency range up to 500 Hz has been evaluated for a composite launcher interstage, designed as a vibroacousitc metamaterial structure based on the local resonance effect. Aspects as numerical design, relevant design parameters and manufacturing requirements addressed in this paper.

<p> We present advances for flexural-gravity, by coupling bending in thin-plates to linearized water-waves. First, we show that scattering of flexural-gravity waves results in non-vanishing scattering cross-section in the zero-frequency limit and propose ways for cloaking. Second, we demonstrate the existence of exceptional points and asymmetric scattering in PT-symmetric floating structures.</p>

Optical metasurfaces are thin large-area structures with aperiodic subwavelength patterns, designed for focusing light and a variety of other wave transformation. Because of their irregularity and large scale, they are one of the most challenging tasks for computational design. This talk will present ways to harness the full computational power of modern large-scale optimization in order to design metasurfaces with thousands or millions of free parameters. We exploit various methods of domain-decomposition approximations, supercomputer-scale topology optimization, laptop-scale “surrogate” models based on Chebyshev interpolation or new active-learning neural networks, and other techniques to attack challenging problems: achromatic lenses that simultaneously handle many wavelengths and angles, “deep” images, hyperspectral imaging, and active structures.

<p> In this talk we focus on the 2 dimensional Dirac-Weyl equation with a sign-change mass along a curved edge. We construct explicit quasi-traveling wave solutions to this equation for circular edges and slowly varying straight edges. We prove such solutions are asymptotically stable with an energy estimate. We also provide many numerical simulations to demonstrate our constructions and estimates independently.</p>

We describe a generalized normal modal expansion (GENOME) for electromagnetic problems based on eigenpermittivity modes. We demonstrate that our method is significantly faster, more accurate and robust than other scattering and modal methods. As a demonstration, we study the Green's tensor of various complex scatterers and study quantum photonic phenomena like the Purcell effect and FRET enhanced by the scatterers.

This talk focuses on time-domain simulation of dispersive optical materials. Our approach is based on the second-order formulation of Maxwell's equations, and uses auxiliary differential equations to evolve the wave polarization vectors for a generalized dispersion material model, with material parameters determined to fit the frequency domain material response.

A two-dimensional periodic array of ferrite rods with an external magnetic field applied to them is studied. The formidable nature of this problem motivates a discrete reduction through an expansion in terms of exponentially localized Wannier modes. The topological nature of the problem prevents a direct application of the Wannier functions, so a perturbative approach is developed to find a suitable basis. The discrete model produces states which have nontrivial topological Chern invariants. Edge modes are found that propagate unidirectionally and do not backscatter at lattice defects.

Topological insulator-inspired devices have shown promise for a host of applications requiring precise manipulation of waves. I will present recent progress on mathematical questions related to design of practical T.I.-based devices. First, I will present an exact numerical method for computing edge states in the presence of defects which eliminates ``spurious'' edge states at the boundary of the computational domain. Then, I will present an analytical proof that one-dimensional structures which support defect states (bound states created by defects in an otherwise periodic structure) which are truncated sufficiently far from the defect will support resonances with explicitly computable life-times (joint work with Jianfeng Lu, Jeremy Marzuola, and Kyle Thicke).

<p> We show that Lagrangian duality can be used to identify the smallest possible mode volume of any dielectric resonator, knowing only the available material refractive index. This technique can identify bounds subject to two constraints that had not been feasible to incorporate into any previous bound approach: minimum feature size (without which the bounds would trivially converge to 0) and multi-frequency operation. We use inverse design to discover 2D structures approaching their respective bounds, showing that they are tight or nearly so.</p>

At this conference, I will provide a brief introduction to the methods to analyze and fundamentally understand glide-symmetric structures and I will introduce a few examples of their potential for practical applications in the microwave regime with special emphasis on radar, spectroscopy and satellite and ground communications.

Gap waveguide technology was first proposed ten years ago. Most of the designs are based on the use of the bed of nails as periodic structure to create the required parallel plate stop band. In addition, the manufacturing is typically made by milling. In this presentation, alternative options for designing antennas in the Ka band with a simplified manufacturing gap waveguide technology will be shown.

Two compact antennas in Ridge Gap Waveguide (RGW) technology, working at 60 GHz, with a high-purity circular polarization (CP) within a broad bandwidth are manufactured and measured. A great broadband matching with reflection coefficient magnitude and CP is achieved. The maximum gain in both designs is 5.49 and 11.12 dB respectively.

<p> In this paper, we show how metasurface cloaks can be used for decoupling and cloaking of interleaved planar phased arrays operating at neighboring frequencies. Accordingly: (a) the two arrays occupy one quarter of the area they would occupy in the case of being separated traditionally and (b) The arrays operate independently, and beam scanning can be achieved with frequency diversity. In this regard, the arrays act as if they were isolated and do not sense the presence of each other.</p>

The study of invisibility cloak with metamaterials has attracted great interests since 2006. In this article, we review the transformation-based electromagnetic cloaking models and the corresponding mathematical results we obtained in recent years.

We present an extremely compact quad-band filter which consists of four split-ring resonators (SRRs) placed concentrically one inside the other. Switchable version of this filter is achieved by switching-off either single or multiple SRRs using PIN diodes which are placed on the vertical branches of SRRs. In that way different triple-band, dual-band and single-band configurations from the initial quad-band topology. Measured performances of the proposed multi-state filter are in very good agreement with simulations.

In this paper a periodic array of metal patches with glide symmetry is studied. It was found that it is a broadband uniaxial dielectric-magnetic medium with giant anisotropic factors. The transverse components of permittivity and permeability tensors are much bigger than the axial ones. Simple but accurate formulas have been provided for them.

Multiscale homogenization method is developed for irrational metamaterials in the quasiperiodic (cut-and-projection) setting. We project partial differential operators acting on periodic functions in higher-dimensional space onto operators acting on quasiperiodic functions in the physical space. The method allows us to replace heterogeneous quasiperiodic structures by homogeneous media with anisotropic permittivity and permeability tensors, obtained from solving annex problems in higher dimensional space.

To compute the electric dipole moment, there are two classical ways: from the charge density or from the current density. Although both ways are equivalent for the case of a local source, they are different when the current density touches the boundary of the integration volume, as may happen for some unit cells of periodic structures. In this paper, we study what is the best choice in order to get the macroscopic polarization of a periodic metamaterial.

We propose an approach based on neural networks to enable fast retrieval of effective material properties, avoiding the need of costly numerical fitting procedures. The key to our approach is an automated approach to subdivide the parameter space into subspaces, where the parameter retrieval problem is unique and can thus be learned effectively with neural networks.

We identify the range of complex permittivities of isotropic composite materials made from two isotropic components by deriving corresponding bounds and identifying microstructures attaining these bounds. As a consequence, we obtain the range of absorption in such materials.

For homogenizing metamaterials, nonlocal constitutive relations are obtained while approximating the general response function up to order 2N. Dispersion relations are discussed and the corresponding interface conditions that support the constitutive relations are derived with a weak formulation. Details are given for the sixth order term of the approximation.

<p> Nonlinear optical processes have been traditionally studied in molecular systems where one tunes the laser frequencies to the molecular energy levels for resonance enhancements. With metasurfaces one can do the reverse, namely for fixed laser frequencies the ‘system’ is tuned to be resonant with the laser frequencies. The resonant local field enhancements in such systems, typically connected to surface plasmons, enable the design of nanoscale nonlinear optical components, which, in turn, can be integrated into novel nanophotonic devices. Various approaches to surface optimization will be reviewed.</p>

We experimentally demonstrate dielectric metasurfaces that support spatially tailored dark modes (quasi-Bound States in the Continuum) and mold optical wavefronts only at narrowband Fano resonances, while leaving the rest of the spectrum unaffected.

Recently it was shown that nonlinear metasurfaces can be used to generate broadband THz radiation. Here I will discuss different generation mechanisms, their selection rules, and show that complete spatiotemporal control over the polarization and phase of the THz waves is obtained, allowing a new class of functional THz emitters.

<p> We combine computational electrodynamics for propagating plasmon-polaritons with quantum approach for quantum emitters and develop a microscopic physical model of exciton-plasmon nanomaterials. We scrutinize optical properties of exciton-plasmon systems under strong coupling conditions by coupling Maxwell’s equations to nonlinear hydrodynamic model for metal and Liouville-von Neumann equations describing quantum emitters. The model is used to describe second harmonic generation in periodic arrays of nanoholes coupled to quantum emitters. It is shown that both the Coulomb interaction of conduction electrons and the convective term contribute on equal footing to the nonlinear response of metal. We also demonstrate that the energy conversion efficiency in the second harmonic process is the highest when the system is pumped at the localized surface plasmon resonance. When quantum emitters are placed on a surface of an array the lineshape of the second harmonic exhibits three peaks corresponding to second harmonics of the plasmon mode and upper and lower polaritonic states.</p>

<p> Metasurfaces are ideally suited for nonlinear optical processes due to their relaxation of the phase-matching condition. This opens the possibility to generate and alter the wavefront of nonlinear harmonic generation beams. However, the short propagation distance through the metasurface limits the conversion efficiency. Here, we discuss concepts of tailoring the spatial phase together with high efficiency of harmonic signals generated by silicon metasurfaces.</p>

We demonstrate a plasmonic metasurface operating near the telecommunications C band exhibiting a record-high quality factor exceeding 2000. Motivated by this demonstration, we will also present numerical predictions suggesting that such nonlinear metasurfaces could soon answer the existing demand for miniaturized and/or flat nonlinear components.

We present a novel type of ferroelectric nanomaterial based on barium titanate nanoparticles. Nanoparticle films of nanoscale thickness are deposited with large-scale uniformity, while support second order optical nonlinearities and electro-optic responses in the near infrared.

We present a general approach to determine physical bounds on electromagnetic systems such as scattering and absorption by metamaterials. The technique is based on numerical modelling combined with optimization over the induced sources. Solving a (convex) dual problem guarantees strict easy-to-calculate bounds. Numerical examples for maximum absorbed, scattered, and extincted power, directional scattering, and Purcell factor are used to illustrate the approach.

In this talk, we discuss our recent efforts on deriving and elucidating bandwidth limits for some important classes of metamaterial devices. Particular attention is devoted to achromatic broadband metalenses, which are currently attracting substantial interest. We also discuss whether and how these bandwidth bounds may be relaxed or surpassed.

In this contribution, we discuss two different strategies aimed at tailoring the electric and magnetic response of an all-dielectric metasurface. Specifically, we investigate the possibilities enabled by two different families of core-shell meta-atoms: concentric all-dielectric spheres and homogenous spheres covered by a reactive layer. The analysis of the scattering properties of these two classes of particles reveals intriguing effects that can be used for the design of innovative metasurfaces exploiting the entire multipolar response of their meta-atoms. Several examples are considered and investigated both analytically and numerically.

We report on the derivation of a spectral element method the originality of which comes from the use of modified Legendre polynomials. The method is easy to implement and it behaves much better for plasmonic structures than the widely used Fourier Modal Method .

<p> We develop an analytical framework to derive upper bounds to single-frequency electromagnetic response. It unifies previous theories on optical scattering bounds and reveals new insight for optimal nanophotonic design, with applications including far-field scattering, near-field local-density-of-states engineering, and the design of perfect absorbers.</p>

<p> We investigate lattice resonances (LRs) in metasurfaces (MSs), composed of silicon nano-cylinders. It is revealed that LRs can be detected through concentration of fields at specific locations in the gaps between nano-cylinders. Formation of LRs appears to significantly modify the resonance responses of MSs, transforming elementary responses into collective phenomena. Their contribution in red-shifting of resonances at increasing the lattice constants and in phenomena, associated with Rayleigh anomalies, are discussed. It is demonstrated that the coincidence of electric and magnetic resonances at the presence of LRs is not imperative for realizing the Kerker’s effects.</p>

Ability to concentrate the electrical field into the sub-wavelength volumes is the key benefit sought and to a certain degree found within the discipline of plasmonics. This ability is restricted only by the ohmic loss in the noble metals and as of recently in the infrared region metals are beginning to face a challenge from the emerging alternative media: phononic (i.e. relying on surface phonon polaritons) and photonic (i.e. relying on high refractive index) all-dielectric structures and highly doped semiconductors, all of them having smaller intrinsic loss than metals. In this work we perform comparison of the degree of enhancement and its spectral selectivity for different media and confirm that while one can obtain sharper resonant features with all-dielectric structures, the magnitude of the field enhancement is invariably higher with metals like gold and copper primarily due to higher density of electrons there. In the end, depending on application, metals and dielectrics have their own unique advantages.

A quantum mechanical model is used to study EELS from crystalline noble metal films, which show intrinsic features associated with their crystallographic orientation.

Two-dimensional semiconductors are ideal light sources for on-chip integration. To overcome the diffraction-limited spatial resolution, near-field handling of the emission would be essential. We present fully near-field luminescence study of two-dimensional semiconductors, with a surface plasmon interference device used for the excitation and scanning near-field optical microscopy for the collection.

We demonstrate the design and fabrication of a square cavity metasurface QWIP with high signal-to-noise ratio, which serves as the basis for detectors made from a patchwork of square cavities that absorb across the full spectral range of the quantum well. Absorption behavior follows previous metasurface absorber reports, indicating this process and device structure can be a roadmap for developing next-generation detectors.

Ultra-thin noble metal nanodisks facilitate high entanglement between distant quantum emitters (QEs). The ultra-thin noble metal nanodisk supports localized plasmon resonances; when these modes are excited and high coupling values between a pair of QEs are observed. We present that the entanglement time of the QEs surpasses the relaxation time of the individual QEs interacting with the metallic disk and reach the steady state faster than the case the QE are placed in free-space.

We study the thermo-optical nonlinearity of a single metal nanoparticle and many-nanoparticle composite under continuous-wave illumination. This study is an important step towards a better understanding of the role of thermal effects in single-nanoparticle systems and in multiple-nanoparticle systems under intense illumination.

We study analytically frequency conversion in subwavelength nanoparticles usingtransformation optics from a singular geometry of touching plasmonic wires. We obtain analyticsolutions of the near field, and unlike previous studies of these structures, we complement itwith a solution of the far field properties. Our investigation revealed that apart from the mode-matching condition, the phase-matching condition plays a major role even for subwavelengthstructures. In addition, unexpectedly, a new and highly influential component was discovered.We further focus on three wave mixing process and show a superiority to the degenerate (secondharmonic) case, SH is dominant for near and far field. This investigation enables optimizing thefrequency conversion process

Topological and spatio-temporal plasmonic metasurfaces enable novel effects based on “one-way” light modes. Topological plasmonic metasurfaces host spin-dependent edge states, and can also realize higher-order topological states (corner modes). Spatio-temporal modulation of the electromagnetic parameters enables broadband nonreciprocal amplification, as well as relativistic effects such as the Fresnel drag of light, even if there is no real motion of the medium.

Drift-biased graphene enables strong nonreciprocal light-matter interactions. In this work, we show that applying two longitudinal DC bias orthogonal to each other permits to greatly manipulate the isofrequency contour of the surface in a nonreciprocal manner, allowing to dynamically steer and canalize one-way plasmons towards desired directions in the plane. Through a dedicated Green’s function formalism that takes graphene’s intrinsic nonlocality into account, we demonstrate that simply controlling two bias of just a few volts enables unprecedented flexibility to synthesize a large variety of nonreciprocal and broadband electromagnetic responses over a unique physical surface. Our findings may open intriguing applications in dynamic sub-diffractive imaging and sensing systems as well as in the routing and processing of surface plasmons.

We create 1D and 2D robotic mechanical metamaterials wherein we use local control loops to break reciprocity at the level of the interactions between the unit cells to probe a wide range of non-Hermitian phenomena, ranging from the non-Hermitian skin effect, to non-Hermitian topological bulk-edge correspondence and odd-elasticity.

Optical spin-orbit coupling describes how spin angular momentum of light (associated with circular polarisation of an electromagnetic wave) influences a propagation of light beam and its orbital angular momentum. The spin-orbit coupling in evanescent waves results in complex topological field structures analogous to prototypical condensed matter phenomena, such as quantum spin-Hall effect, skyrmions, merons, and others. In this talk, we will overview spin-orbit coupling, its topological manifestations and applications.

We study the emergence of nonreciprocal and topologically nontrivial phonon transport in nano-optomechanical networks, where on-chip mechanical resonators are coupled through radiation pressure. We reveal the emergence of nanomechanical circulation, helical quantum Hall states, and chiral thermal transport in phononic networks in which both time-reversal symmetry and Hermiticity are broken at will.

In this talk, we describe a series of acoustic experiments using a monomode waveguide containing a finite number of cylindrical scatterers, to investigate the possibility to engineer robust scattering signatures by leveraging topological waves. We ask three kinds of questions: (i) can topology force the transmission of a given two-port system to have a given filtering response ?; (ii) to what extent and under which conditions can this response be robust to geometrical disorder ?; and (iii) can the disorder itself be a driving mechanism to force a system to perform a definite, non-random filtering operation ? Exploring these questions theoretically and experimentally, we demonstrate a rich class of physical transmission phenomena tied to topology, including symmetry-protected Lorentzian and Fano transmission spectra, as well as disorder-induced Lorentzian filters relying on randomly-drawn geometries.

In this work, we propose the use of metasurfaces to create multiphysics devices for simultaneous control of electromagnetic and acoustic waves. Using an analytical model based on surface impedances, we introduce power flow-conformal metasurfaces that perform the same functionality for electromagnetic and acoustic waves. Moreover, we also explore possibilities to realize different functionalities for electromagnetics and acoustics within the same platform. We numerically simulate realistic topologies for practical implementations and confirm the viability of the proposed platforms.

We report a method to design 2D acoustic materials with prescribed scattering properties. We target information in reciprocal space to construct materials the structure factor of which, i.e. the scattering pattern in the Born approximation, exactly matches the scattering properties for a set of wavelengths. In this work the material is made of a distribution of rigid cylinders embedded in air. As an example, we show 2 dimensional (2D) stealth acoustic materials showing omnidirectional and broadband back-scattering suppression. The scattering intensity is described in terms of single as well as multiple scattering formalism, showing excellent agreement with each other.

Materials with zero permittivity can fully suppress the radiation loss and enable the formation of embedded eigenstates. Here, we investigate how the spatial dispersion caused by the electron-electron interactions in a metal affects the light localization. Surprisingly, it is found that the nonlocality strongly relaxes the requirements for the observation of trapped light.

In this contribution, we propose the design in time-domain of two key components in electromagnetic theory, the Fabry-Perot cavity and the matching slab. Starting from the well-known reflection and transmission properties of a temporal medium discontinuity, we extend here the study to the case of the general case of multiple discontinuities, evaluating analytically the general reflection and transmission coefficients for a temporal metamaterial slab, i.e. a uniform homogeneous medium that is present in space for a limited time. It is found that the scattering response from this temporal device may be tuned to act as a temporal Fabry-Perot cavity and matching network by selecting the application time that acts like the electrical thickness for spatial slabs. Several novel devices based on temporal discontinuities can be derived by the presented concept of the temporal slab, such as temporal dielectric mirrors, broadband temporal matching networks, and temporal anomalous refraction.

Photonic neural networks provide a pathway to realize energy-efficient and fast neural networks (NN) while benefitting from extreme parallelism. At the heart of optical NN’s lies a nonlinear activation function, which is challenging to realize in an all-optical form. Epsilon-Near-Zero materials (ENZ) offer a unique blend of high speed and large index changes, enabling a new avenue for photonic neural networks. Here we present a theoretical framework describing the intensity-dependent nonlinearity of commonly used ENZ materials, which would enable theoretical modeling and testing of a range of non-linear activation functions.

Non-Hermitian systems with judiciously designed loss and gain distributions have been shown to enable novel wave effects compared to their Hermitian counterparts. While this concept was recently extended to the temporal domain through time-varying material properties, a systematic investigation of dynamical open structures with time-varying radiation properties is still lacking, especially in the context of optical scattering. Here, we show that the radiation characteristics of a scattering system can be engineered in new ways using time-modulated epsilon-near-zero materials, leading to unique opportunities to overcome some of the limits and bounds of time-invariant system. Specifically, we demonstrate that such temporal modulations can enable novel wave effects, including unidirectional frequency transitions and bound states in the continuum that can be externally excited by broadband light sources.

We present extensions of the metagrating (MG) synthesis approach to tackle a wide variety of problems in configurations other than the typical free-space diffraction engineering scenarios. It is shown that an adapted semianalytical methodology allows the design of sparse constellations of subwavelength scatterers facilitating mode conversion and seamless bending in waveguides, directive sparse antenna arrays, and formation of near-field subwavelength hot spots. These results reveal the merits of MG-inspired devices for a broad range of applications.

In this paper, a design of a linear-to-circular polarization converter based on an anisotropic metasurface is presented. The proposed design is comprised of a thin polyimide layer with two dipoles arrays printed on either side and shifted appropriately and placed on top of a metal grounded substrate. This enables the conversion of a linearly polarised (LP) incident wave to a circular polarised (CP) reflected wave. Results demonstrate that the proposed anisotropic metasurface provides good angular stability. Left hand Circular polarization (LHCP) conversion for the proposed structure is realized over frequency range 9.5 GHz to 15 GHz with 3-dB-AR BW of more than of 46% for φ=0° and 37% for φ=90°.

This study presents metasurfaces designed to selectively transmit electromagnetic waves even at the same frequency depending on their waveforms or pulse widths. In particular, we demonstrate such waveform-selective metasurfaces operating at several frequency bands, which leads to providing an additional selectivity of scattering control by frequency combination.

WepresentageneratorofNon-IntegerCylindricalBesselBeams(NIC-BBs),which may find applications in communication systems, polarimetric instrumentation and particle routing. This device consists of a pair of cascaded phase-plate metasurfaces illuminated by a uniform circularly polarized wave, where the first metasurface provides the required phase dis- tribution while the second provides the required polarization distribution. It is accompanied by a powerful design procedure, which involves a unique metaparticle shape with fast axis rotated according to the geometric phase principle and Stokes parameter synthesis.

Bessel beams have attracted considerable interests due to their intriguing non-diffracting and self-healing properties. Here, an electronically-engineered metamirror is designed for the flexible control of Bessel beams over a broad frequency band ranging from 9 GHz to 12 GHz. Several configurations are presented to illustrate the non-diffracting characteristics of Bessel beams. Besides, the self-healing property is verified by placing a metallic obstacle in the propagation path of the Bessel beam. Owing to the flexible manipulation capabilities, wide-bandwidth and high-efficiency properties of the reconfigurable metamirror, the proposed Bessel beam generation device opens the door to potential applications such as focusing and wireless power transmission.

We report on the first experimental realization of charge-2 Dirac point in the visible region by engineering hybrid super-modes in a 1-D optical superlattice system with two synthetic dimensions.Utilizing reflection and transmission measurements, we show the approach to manipulating two spawned Weyl points with identical charge and associated end modes.

In this work, the design of a dielectric hollow-core waveguide mode-converter is reported. We demonstrate that this structure can find application as high-power mode converter in Dielectric Laser Accelerators (DLAs).

The bi-anisotropic metawaveguide (BMW) is a versatile platform for realizing quantum Hall, quantum spin Hall and quantum valley Hall effects for electromagnetic waves. We utilize these photonic topological insulators (PTI) to realize a chaotic graph system whose statistical properties fall into the universality class of the Gaussian symplectic ensemble (GSE). The bonds of the graph are built with quantum spin Hall (QSH) BMW waveguides. The built-in two-fold degeneracy and time-reversal invariance make QSH-BMW systems an excellent platform to simulate the symplectic ensemble, which was first noted to describe the statistical properties of spin-1/2 time-reversal invariant chaotic systems. The spectral level spacing distribution of the PTI network eigenmodes is found to be in agreement with the predictions from the Gaussian symplectic ensemble expected for chaotic systems with such symmetry.

One-dimensional photonic crystals whose dielectric constant varies with time harmonically have been considered. The transmission spectra have been investigated using the perturbation method and the transfer matrix method. It has been found that the time variation of the dielectric constant amplifies the incident wave resonantly.

A rod-type silicon photonic crystal structure has been designed and numerically analyzed for the first time in a sensing application. Light-matter interaction is maximized by strong light localization in the air region, cavity Q-factor is enhanced with Fano-like resonance, and an ultra-high sensitivity up to 1039 nm/RIU is observed.

We describe the design, fabrication and characterization of woodpile photonic crystal waveguides. In particular, we fabricated hollow core waveguides in two different materials (alumina and silicon) and operating in two distinct frequency regimes (18 and 96 GHz).

We discuss the physics and applications of all-optically manipulated Photonic Metasurfaces. Flexible polymeric membranes were fabricated using electron beam lithography, subsequently suspended in a microfluidic chamber and manipulated using Holographic Optical Tweezers. Here we argue that thanks to their exceptional intrinsic stability, optically controlled photonic membranes are the ideal platform for a wide range of optomechanical and biophotonic applications.

<p> In recent years a wide interest has been spurred by the inverse design of artificial materials for nano-biophotonic applications. In particular, the extreme optical properties of artificial hyperbolic dispersion nanomaterials allowed to access new physical effects and mechanisms. The unbound isofrequency surfaces of hyperbolic metamaterials and metasurfaces allow to access virtually infinite photonic density of states, ultrahigh confinement of electromagnetic fields and anomalous wave propagation. Here, we will present the physics of different hyperbolic dispersion material geometries and how they allow to control light-matter interaction at the single nanometer scale, including within living systems.</p>

The reduction of wavelengths at UH-field MRI, results in head coils B1+ field inhomogeneities. This has been effectively targeted, but challenges remain. Here, we present a new approach based on Hilbert-fractal-inspired dipoles, able to improve the B1+ field in each temporal lobe maintaining patients’ comfort and the remaining field intact.

Recently, a great deal of research efforts has been focused to realize subwavelength photonics devices for magnetic resonance imaging (MRI), one of the cornerstone diagnostic techniques in life science. We show that the excitations of magnetic localized surface plasmons (MLSPs), surface waves hosted by a subwavelength negative magnetic permeability sphere, can yield a strong enhancement of the MRI scanner performance. In addition, we demonstrate that MLSPs can be mimicked by substituting the metamaterial (MM) negative magnetic sphere with a homogeneous high-permittivity one of the same radius. Our approach overcomes several limits of the standard MM approach (generally based on effective medium theories) avoiding complex 3D fabrication procedures and removing the spatial MM inhomogeneities whose presence is detrimental in subwavelength photonics applications. Considering that RF high-dielectric homogeneous materials are available in nature, their MLSPs mimicking holds great potential in those applications based on the RF signals manipulation.

Elastic metamaterials with spatiotemporally modulated material properties have received attention as a means to increase the degree of control over propagating mechanical waves in unbounded elastic media. We investigate standing elastic waves in finite structures with time- and space-dependent material properties and implications for the creation of nonreciprocal vibrational systems.

We demonstrate controllable frequency conversion using time-varying acoustic metamaterials. Using digitally virtualized resonating atoms as building blocks, we construct acoustic metamaterials with arbitrary time-varying response, in either resonance strength, gain/loss parameter or resonating frequency. The high efficiency on frequency conversion is experimentally demonstrated by tailor-made time-varying response function. Its application with material gain and loss being alternating in time is also investigated.

We consider the scattering of acoustic waves on a set of equidistant resistive sheets. We show that at the Bragg frequency, the transmission presents an anomalously high peak. Using the transfer matrix formalism, we show that this effect occurs when the two eigenvalues of the transfer matrix coalesce, i.e. at an exceptional point. Exploiting this algebraic condition, it is possible to obtain similar anomalous transmission peaks in more general periodic media such as phononic or photonic crystals. In this context, a peak will be observed at some bandgap edges, depending on the symmetry of the wave function.

A method for the fundamental design of phononic lenses for transcranial ultrasound irradiation to break blood clots using holographic techniques is described. This lens is a generalized kind of Fresnel zone plates. Multi-layer FZPs as metamaterials devices are proposed and three-layer FZP shows the higher performance than that of single one.

We show how the equivalence between a waveguide operating near cutoff and the dispersion of compressibility can lead to ideal illumination in an acoustic source. The near-zero behavior makes the source robust to disorder, which is shown using a statistical description of the radiation patterns of randomly generated geometries.

We review the exceptional variety of functionalities accessible by design in nanomechanical photonic metamaterials, wherein dynamic reconfiguration of sub-wavelength structure by external stimuli can yield extreme and unusual electro-, magneto-, thermo-, acousto- and nonlinear optical response characteristics.

We report on design, fabrication and characterization of an optomechanical chiral dielectric metasurface capable of dynamic control of near-infrared light polarization. We show MHz polarization modulation and 350 kHz light polarimetry using the membrane fundamental drum mechanical mode.

This paper reports retardation modulation using Au nanograting driven in out-of-plane direction by electrostatic force. By optimizing the thicknesses of sacrificial Si layer, the maximum deformation was decreased to be 61 nm, which is only 6% of the previous research. Retardation modulation of of 3.4 degree at 715 nm was measured.

The building blocks of nanomechanical photonic metamaterials are perturbed by collisions with atoms of ambient atmospheric gas and by phonons in the crystal lattice of the constituent materials. Between collisions movements are ballistic, becoming diffusive (Brownian) at longer time scales. We show how one may distinguish between these regimes using ultrafast hyperspectral SEM nanomotion imaging and discuss their manifestation in the time-dependent optical properties of the metasurfaces.

Here we numerically demonstrate the possibility to shape a wave front in the terahertz range using a self-complementary metasurface (SCMS) with spatial modulation. A circularly polarized incident wave passing through a SCMS causes two transmitted waves, a co- and cross-polarized. The co-polarized wave, in theory, has a complex transmission coefficient of 1/2 and keeps the same front shape as the incident wave, even if the metasurface is nonuniform. On the contrary, the cross-polarized wave obtains a phase, which can be locally controlled by geometric parameters of unit cells. We apply a phase holographic method to modify the shape of the cross-polarized wave in a desirable way while keeping the co-polarized wave unchanged.

We have recently suggested a cavity, defined by two silicon-disk arrays supporting helicity-preserving modes, that allows for enhanced sensing of idealized dual and chiral molecules within the cavity. Here, we simplify this cavity design, aiming at making it robust for experimental realizations. Furthermore, we investigate the influence of the concentration of real chiral molecules, which are usually not dual.

I demonstrate how noise can be turned into a resource for optical sensing when using a resonator with Kerr nonlinearity. The proposed sensor displays a measurement rate that increases monotonically with the noise strength, and a sensitivity that is optimum for a particular value of the noise strength.

We proposed an optical hydrogen sensor composed of Mg, Ag and Pd nano-blocks which can detect hydrogen more sensitively compare with conventional methods. This sensor utilizes the properties of Mg and Pd when absorbing hydrogen: metallic Mg becomes dielectric material, MgHx. Pd lattice expands with changing its optical properties. When the material change with hydrogen concentration, the far-field distributions of sensor change significantly at specific scattering angles, 36 and 324 degrees.

A slow-wave periodic artificial transmission line implemented by means of dumbbell-shaped defect ground structures (DB-DGS) is applied to the implementation of a phase variation permittivity sensor. Due to the dispersion characteristic of these lines, the sensitivity of the phase with the dielectric constant of the material under test (MUT) can be improved, as compared to the one of conventional lines. This sensitivity improvement is demonstrated in this work through full-wave electromagnetic simulations.

We show in this paper that electroinductive-wave (EIW) transmission lines can be applied to the implementation of differential-mode microfluidic sensors with high sensitivity. The sensor is based on EIW lines equipped with microfluidic channels for dielectric characterization of liquid samples. Deionized (DI) water is used as reference (REF) liquid, whereas solutions of isopropanol in DI water are used as liquid under test (LUT).

Mode mixing due to disorder and non-linear mode coupling dramatically affects the light propagation in multimode systems. Our analysis establishes a connection with the theory of spin networks and reveals the existence of optical phase transitions between a paramagnetic, ferromagnetic and spin-glass phases.

We show that the nonlinear mixing of thermally generated photons in a resonant system can be used to overcome the fundamental blackbody limit on thermal emission, and to introduce nontrivial statistics and biphoton intensity correlations at two distinct frequencies in the emission spectrum. These effects can be observed by heating a properly designed photonic system without using any external signal.

Controlling optical spins and pseudospins carried by electromagnetic guided waves can find many applications in the fields of spintronics and valleytronics, supporting efficient information transport using these degrees of freedom. In this work, we explore the general opportunities offered by metasurfaces to route optical momentum, spin and helicity by coupling to guided surface waves. We show how tailoring anisotropy and bianisotropy yields extreme directionality when coupled to the spin of localized sources. In-plane circularly polarized excitations are particularly important in this context when considering 2D excitonic materials. They offer specific challenges when coupled to metasurfaces, addressed here with suitably engineered nonlocality and nonreciprocity.

First, we discover circularly polarized thermal radiation from a dimer of coupled nanoantennas held at unequal temperatures (nonequilibrium). The handedness of light can be flipped by interchanging the antenna temperatures. Second, we reveal that a nonreciprocal planar slab can exhibit nonzero thermal photon spin and heat flux in its vicinity, despite being at thermal equilibrium with the environment.

We reveal nonlocal and quantum finite-size effects in hybrid systems consisting of graphene and few-atomic-layer noble metals, based on a quantum description that captures the crystallographic orientation of these materials as well as their band structure.

We present broadband metamaterial absorber using split ring resonator and thin wire. The C-shape single split ring resonator and thin wire are placed on a graphene sheet to improve the absorption of the absorber. The thickness of metamaterial and height of substrate material is changed to observe its effect on absorption.

The MoS2 precursor solution was formulated by a sulfur-dissolving method. 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 effect of the topology to the properties of a material has been a subject of interest for engineers, physicists and mathematicians around the globe for many years. In particular, the interest is focused towards determining how the arrangement of the fundamental building blocks of a complex system affects its properties. Here, we examine a new state of matter, the so-called hyperuniform disordered, that adopts properties form both the periodic and the random topologies and its effect on several research fields.

We design sub-wavelength passive non-reciprocal optical devices using recently discovered magnetic Weyl semimetals. These passive bulk topological materials do not require any external magnetic field and exhibit anomalous Hall effect which results in giant magnetooptical effects. The designed isolators have dimensions that are reduced by three orders of magnitude compared to conventional magneto-optical configurations. Our results indicate that the magnetic Weyl semimetals may open up new avenues in photonics for the design of various nonreciprocal components.

In this work, we use electromagnetic-dual metasurfaces to make photonic topological insulators with amorphous and non-periodic patterns. We demonstrate robust pseudospin edge modes at the interface as well as, for the first time, robust localized cavity modes in the interior of the PTI. The newly discovered cavity modes are associated with topological defects in real-space.

This study introduces a highly efficient magnet-free isolator based on signal interference in time-modulated loops. The proposed isolator offers strong nonreciprocity. It also possesses a low profile architecture in comparison to other recently proposed space-time-modulated isolators. This is due to the fact that the it is not governed by unidirectional progressive coupling between the input signal and the space-time modulation signal where a long structure is required.

We introduce a ‘perfect’ Faraday-rotation metasurface. This metasurface provides arbitrary-angle, reflectionless and absorptionless nonreciprocal polarization rotation. Moreover,we show, using the surface susceptibility model, that such a metasurface involves a simultaneously electric and magnetic response, which may be realized with transistor-loaded straight and looped wires. This metasurface may potentially accommodate arbitrary incident and refraction angles.

Due to immunity to disorder and structural imperfections, topologically-protected plasmonic modes have recently attracted increasing attention. Here, we introduce two different mechanisms to construct valley-Hall domain-wall interface waveguides in graphene plasmonic crystal to mimic the quantum valley-Hall effect. In the first case, we break the in-plane spatial inversion symmetry of a single-layer graphene plasmonic crystal waveguide to achieve valley-Hall topological characteristics, whereas in the second case, we break the out-of-plane spatial inversion symmetry of a bi-layer graphene plasmonic crystal waveguide to implement the analog quantum valley-Hall effect. A molecular sensor based on this valley-Hall topological transport phenomenon is also be presented.

A photonic topological insulators features waveguiding insensitive to structural imperfections and environmental fluctuations. This has been used to achieve topological insulator lasers based on the waveguide mode and a configuration of gain and loss distribution. Here, we demonstrate a topologically protected mode extended over the bulk of a two-dimensional kagome lattice with rhombus geometry by means of a synthetic imaginary gauge fields via auxiliary rings. This shows a phase-locked broad-area topological lasers in two-dimensional lattices.

I discuss recent progress to deriving bounds to electromagnetic response, from single-frequency to broad-band response across near- and far-field scattering regimes. We develop brightness-theorem analogs for wave physics, with ramifications for metasurface design and partially coherent optics. We use quadratic constraints to identify maximum response possible for any material in a given allowable volume. And we identify optimal materials to achieve record levels of near-field radiative heat transfer.

<p> Coupled arrays of nonlinear circuits with linear inter-cell coupling and nonlinear intra-cell coupling, nonlinear variants of the Su-Schrieffer-Heeger (SSH) model, have been observed to exhibit novel phenomena such as self-induced topologically protected states, see e.g. Hadad et al, ACS Photonics (2017) and Nature Electronics 1 (2018) 178-182. We present an analytical and numerical study of a closely related class of Lagrangian systems. We focus on the regime of excitations whose wavelengths are long compared with the lattice constant, and described by continuum nonlinear partial differential equations. We study (1) the bifurcation of weakly nonlinear coherent structures, such as solitons, from linear regime plane-wave like states, and (2) coherent structures, without amplitude restrictions, by global dynamical systems methods.</p>

Fundamental limits on scattering metrics such as absorption, extinction, and Purcell's factor are formulated by separating a scattering structure into controllable and uncontrollable regions. We present each bound as a special case of a general methodology based on the method of moments and convex optimization.

Engineering photonic resonators for high-efficiency performance has recently become an avenue for extensive research and development. In this direction, we present that optical Bound states in the continuum can enhance nonlinear response in cavities with spatial variation of gain-loss. We report an enhancement of 3 orders of magnitude in the SHG efficiency in a specially designed AlGaAs nanowire. The formation of high-Q modes via avoided resonance crossing at both the fundamental and second harmonic wavelengths boosts the second harmonic generation (SHG).

We introduce a metasurface design that supports chiral surface waves having two transverse spins, one due to out-of-plane field rotation, intrinsic to any surface wave, and the other is due to in-plane field rotation which is imposed by the design. Both spins follow spin-momentum locking resulting in unidirectional wave propagation.

We present a combination of T-matrix methods with lattice summation techniques. With this computational method bi-periodic, layered metamaterials can be efficiently simulated. Throughout, we use modes of well-defined helicity as a basis set and, thus, enables the use of chiral materials. Exemplary applications of the method are presented.