Multifunctional Metasurface Tuning by Liquid Crystals in Three Dimensions.

Optical metasurfaces present remarkable opportunities for manipulating wave propagation in unconventional ways, surpassing the capabilities of traditional optical devices. In this work, we introduce and demonstrate a multifunctional dynamic tuning of dielectric metasurfaces containing liquid crystals (LCs) through an effective three-dimensional (3D) control of the molecular orientation. We theoretically and experimentally study the spectral tuning of the electric and magnetic resonances of dielectric metasurfaces, which was enabled by rotating an external magnetic field in 3D.

Infrared all-dielectric Kerker metasurfaces.

The unidirectional scattering of electromagnetic waves in the backward and forward direction, termed Kerkers' first and second conditions, respectively, is a prominent feature of sub-wavelength particles, which also has been found recently in all-dielectric metasurfaces. Here we formulate the exact polarizability requirements necessary to achieve both Kerker conditions simultaneously with dipole terms only and demonstrate its equivalence to so-called "invisible metasurfaces". We further describe the perfect absorption mechanism in all-dielectric metasurfaces through development of an extended Kerker formalism.

Engineering scattering patterns with asymmetric dielectric nanorods.

By controlling interference of Mie resonance modes of various nanostructures, we can achieve a large number of nontrivial effects in nanophotonics. In this work, we propose a cylindrical structure in which the spectral overlap of the Mie-type modes can be controlled by drilling a hole parallel to the axis, thus changing unidirectional scattering. We further demonstrate that the scattering patterns can be tailored by rotating the structure to achieve almost arbitrary scattered wave direction.

Ultrathin tunable terahertz absorber based on MEMS-driven metamaterial.

The realization of high-performance tunable absorbers for terahertz frequencies is crucial for advancing applications such as single-pixel imaging and spectroscopy. Based on the strong position sensitivity of metamaterials' electromagnetic response, we combine meta-atoms that support strongly localized modes with suspended flat membranes that can be driven electrostatically. This design maximizes the tunability range for small mechanical displacements of the membranes.

Nonlinear coupling in graphene-coated nanowires.

We propose and analyze nonlinear coupler based on a pair of single mode graphene-coated nanowires. Nonlinear wave interactions in such structure are analyzed by the coupled mode equations derived from the unconjugated Lorentz reciprocity theorem. We show that the routing of plasmons in the proposed structure can be controlled by the input power due to the third order nonlinear response of graphene layer.

Strong terahertz absorption in all-dielectric Huygens' metasurfaces.

We propose an all dielectric metamaterial that acts as a perfect terahertz absorber without a ground plane. The unit cell consists of a dielectric cylinder embedded in a low index material. In order to achieve near-perfect terahertz absorption (99.

Second harmonic generation in graphene-coated nanowires.

We study second harmonic generation in a pair of graphene-coated nanowires. We show that the phase matching condition for harmonic generation can be engineered in a wide range of frequencies by tuning the spacing between graphene nanowires. We derive coupled mode equations describing the process of second harmonic generation using an unconjugated Lorentz reciprocity theorem.

Elastic metamaterials for tuning circular polarization of electromagnetic waves.

Electromagnetic resonators are integrated with advanced elastic material to develop a new type of tunable metamaterial. An electromagnetic-elastic metamaterial able to switch on and off its electromagnetic chiral response is experimentally demonstrated. Such tunability is attained by harnessing the unique buckling properties of auxetic elastic materials (buckliballs) with embedded electromagnetic resonators.

Electrically tunable terahertz metamaterials with embedded large-area transparent thin-film transistor arrays.

Engineering metamaterials with tunable resonances are of great importance for improving the functionality and flexibility of terahertz (THz) systems. An ongoing challenge in THz science and technology is to create large-area active metamaterials as building blocks to enable efficient and precise control of THz signals. Here, an active metamaterial device based on enhancement-mode transparent amorphous oxide thin-film transistor arrays for THz modulation is demonstrated.

Tunable Meta-Liquid Crystals.

Meta-liquid crystals, a novel form of tunable 3D metamaterials, are proposed and experimentally demonstrated in the terahertz frequency regime. A morphology change under a bias electric field and a strong modulation of the transmission are observed. In comparison to conventional liquid crystals, there is considerable freedom to prescribe the electromagnetic properties through the judicious design of the meta-atom geometry.

Optical Metacages.

We suggest a novel strategy for spectrally selective optical shielding of arbitrary shaped volumes by arranging specifically designed two- or three-layer nanowires around an area that needs to be protected. We show that such nanowire shields preserve their functionality for almost arbitrary geometry, and we term such structures optical metacages. We analyze several designs of such optical metacages made from either metallic or dielectric materials with experimentally measured parameters.

Superabsorption of light by nanoparticles.

Nanoparticles have a fundamental limit as to how much light they can absorb. This limit is based on the finite number of modes excited in the nanoparticle at a given wavelength and maximum absorption capacity per mode. The enhanced absorption can be achieved when each mode supported by the nanoparticle absorbs light up to the maximum capacity.

Superabsorption of light by multilayer nanowires.

We suggest a new strategy for tailoring and enhancing the absorption of light by multilayered nanowires. We use the multipole expansion method and experimental data for dielectric and plasmonic materials and demonstrate that the absorption for one of the polarizations can be substantially enhanced due to an overlap of different resonant modes in nanowires. We show that our approach can be employed for a design of multiband tunable optical absorption across a wide spectral range for both TE and TM polarizations.

All-dielectric multilayer cylindrical structures for invisibility cloaking.

We study optical response of all-dielectric multilayer structures and demonstrate that the total scattering of such structures can be suppressed leading to optimal invisibility cloaking. We use experimental material data and a genetic algorithm to reduce the total scattering by adjusting the material and thickness of various layers for several types of dielectric cores at telecommunication wavelengths. Our approach demonstrates 80-fold suppression of the total scattering cross-section by employing just a few dielectric layers.

Spontaneous chiral symmetry breaking in metamaterials.

Spontaneous chiral symmetry breaking underpins a variety of areas such as subatomic physics and biochemistry, and leads to an impressive range of fundamental phenomena. Here we show that this prominent effect is now available in artificial electromagnetic systems, enabled by the advent of magnetoelastic metamaterials where a mechanical degree of freedom leads to a rich variety of strong nonlinear effects such as bistability and self-oscillations. We report spontaneous symmetry breaking in torsional chiral magnetoelastic structures where two or more meta-molecules with opposite handedness are electromagnetically coupled, modifying the system stability.

Flexible helices for nonlinear metamaterials.

The successful fabrication and experimental verification of a novel metamaterial based on flexible metallic helices is reported. The helices undergo compression under the influence of incident radiation, demonstrating a nonlinear chiral electromagnetic response, associated with the power-dependent change in the helix pitch. This design is promising for application to power-dependent polarization rotation of propagating waves.

Cloaking and enhanced scattering of core-shell plasmonic nanowires.

We study scattering of light from multi-layer plasmonic nanowires and reveal that such structures can demonstrate both enhanced and suppressed scattering regimes. We employ the mode-expansion method and experimental data for material parameters and introduce an optimized core-shell nanowire design which exhibits simultaneously superscattering and cloaking properties at different wavelengths in the visible spectrum.

Self-focusing of femtosecond surface plasmon polaritons.

We study the propagation of femtosecond pulses in nonlinear metal-dielectric plasmonic waveguiding structures by employing the finite-difference time-domain numerical method. Self-focusing of plasmon pulses is observed for defocusing Kerr-like nonlinearity of the dielectric medium due to normal dispersion. We compare the nonlinear propagation of plasmon pulses along a single metal-dielectric interface with the propagation within a metal-dielectric-metal slot waveguide and observe that nonlinear effects are more pronounced for the single surface where longer propagation length may compensate for lower field confinement.

Metamaterials controlled with light.

We suggest and verify experimentally the concept of functional metamaterials whose properties are remotely controlled by illuminating the metamaterial with a pattern of visible light. In such metamaterials arbitrary gradients of the effective material parameters can be achieved simply by adjusting the profile of illumination. We fabricate such light-tunable microwave metamaterials and demonstrate their unique functionalities for reflection, shaping, and focusing of electromagnetic waves.

Nonlinear control of invisibility cloaking.

We introduce a new concept of the nonlinear control of invisibility cloaking. We study the scattering properties of multi-shell plasmonic nanoparticles with a nonlinear response of one of the shells, and demonstrate that the scattering cross-section of such particles can be controlled by a power of the incident electromagnetic radiation. More specifically, we can either increase or decrease the scattering cross-section by changing the intensity of the external field, as well as control the scattering efficiently and even reverse the radiation direction.

Metamaterials with conformational nonlinearity.

Within a decade of fruitful development, metamaterials became a prominent area of research, bridging theoretical and applied electrodynamics, electrical engineering and material science. Being man-made structures, metamaterials offer a particularly useful playground to develop interdisciplinary concepts. Here we demonstrate a novel principle in metamaterial assembly which integrates electromagnetic, mechanical, and thermal responses within their elements.

Discrete dissipative localized modes in nonlinear magnetic metamaterials.

We analyze the existence, stability, and propagation of dissipative discrete localized modes in one- and two-dimensional nonlinear lattices composed of weakly coupled split-ring resonators (SRRs) excited by an external electromagnetic field. We employ the near-field interaction approach for describing quasi-static electric and magnetic interaction between the resonators, and demonstrate the crucial importance of the electric coupling, which can completely reverse the sign of the overall interaction between the resonators. We derive the effective nonlinear model and analyze the properties of nonlinear localized modes excited in one-and two-dimensional lattices.

Magnetoelastic metamaterials.

The study of advanced artificial electromagnetic materials, known as metamaterials, provides a link from material science to theoretical and applied electrodynamics, as well as to electrical engineering. Being initially intended mainly to achieve negative refraction, the concept of metamaterials quickly covered a much broader range of applications, from microwaves to optics and even acoustics. In particular, nonlinear metamaterials established a new research direction giving rise to fruitful ideas for tunable and active artificial materials.