Kirill Koshelev

High- Q Supercavity Modes in Subwavelength Dielectric Resonators

We reveal that isolated subwavelength dielectric resonators support states with giant Q-factors similar to bound states in the continuum formed via destructive interference between strongly coupled eigenmodes and characterized by singularities of the Fano parameters.

Temperature-tunable semiconductor metamaterial

We propose a novel class of temperature-tunable semiconductor metamaterials that exhibit negative refraction in the terahertz spectral range. These metamaterials are based on doped semiconductor superlattices with ultrathin barriers of about 1 nm thickness. Due to the tunnel transparency of the barriers, layers of the superlattice cannot be considered as isolated and, therefore, the classical homogenization approach is inapplicable. We develop a theory of quantum homogenization which is based on the Kubo formula for conductivity. The proposed approach takes into account the wave functions of the carriers, their distribution function and energy spectrum. We show that the components of the dielectric tensor of the semiconductor metamaterial can be efficiently manipulated by external temperature and a topological transition from the dielectric to hyperbolic regime of metamaterial can be observed at room temperature. Using a GaAs/Al

Interplay between anisotropy and spatial dispersion in metamaterial waveguides

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Nonlinear Wavefront Control with All-Dielectric Metasurfaces

Ga

High-Q resonances with low azimuthal indices in all-dielectric high-index nanoparticles

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Effect of substrate on optical bound states in the continuum in 1D photonic structures

As superlattice slab as an example, we provide a numerical simulation of an experiment which shows that the topological transition can be observed in the reflection spectrum from the slab.

Transition from Optical Bound States in the Continuum to Leaky Resonances: Role of Substrate and Roughness

We analyze the spectrum of waveguide modes of an arbitrary uniaxial anisotropic metamaterial slab with nonlocal electromagnetic response whose permittivity tensor could be described within the Drude approximation. Spatial dispersion was introduced within the hydrodynamical model. By considering both anisotropy and spatial dispersion as perturbations, we distinguish their effect on the spectrum of the slab and analyze lifting of the degeneracy of eigenmodes at plasma frequency in detail. Spatial dispersion is shown to result in a break of the singularity in the density of optical states in the hyperbolic regime and in suppression of negative dispersion induced by anisotropy. We demonstrate that the interplay of spatial dispersion and anisotropy can bring light to a complete stop at certain frequencies.

Strong Mode Coupling and High-Q Supercavity Modes in Subwavelength Dielectric Resonators

Metasurfaces, two-dimensional lattices of nanoscale resonators, offer unique opportunities for functional flat optics and allow the control of the transmission, reflection, and polarization of a wavefront of light. Recently, all-dielectric metasurfaces reached remarkable efficiencies, often matching or out-performing conventional optical elements. The exploitation of the nonlinear optical response of metasurfaces offers a paradigm shift in nonlinear optics, and dielectric nonlinear metasurfaces are expected to enrich subwavelength photonics by enhancing substantially nonlinear response of natural materials combined with the efficient control of the phase of nonlinear waves. Here, we suggest a novel and rather general approach for engineering the wavefront of parametric waves of arbitrary complexity generated by a nonlinear metasurface. We design all-dielectric nonlinear metasurfaces, achieve a highly efficient wavefront control of a third-harmonic field, and demonstrate the generation of nonlinear beams at a designed angle and the generation of nonlinear focusing vortex beams. Our nonlinear metasurfaces produce phase gradients over a full 0-2π phase range with a 92% diffraction efficiency.

Asymmetric metasurfaces with high-

Recently, a novel class of high-Q optical resonators based on all-dielectric subwavelength nanoparticles with high refractive index has been proposed [M. V. Rybin, et al, arXiv:1706.02099, 2017]. Here we study a complex spectrum of such nanoscale resonators by means of the resonant-state expansion, treating the problem as a nonHermitian eigenproblem. We show that the high-Q features can be described within the mechanism of external coupling of open channels via the continuum. For ceramic resonators with permittivity ε = 40, we demonstrate that the quality factor of a trapped mode with a low azimuthal index could reach the value Q = 104 .

Q

Optical bound states in the continuum (BIC) are localized states with energy lying above the light line and having infinite lifetime. Any losses taking place in real systems result in transformation of the bound states into resonant states with finite lifetime. In this work, we analyze properties of BIC in CMOS-compatible one-dimensional photonic structure based on silicon-on-insulator wafer at telecommunication wavelengths, where the absorption of silicon is negligible. We reveal that a high-index substrate could destroy both off-Γ BIC and in-plane symmetry protected at-Γ BIC turning them into resonant states due to leakage into the diffraction channels opening in the substrate.