Mikhail V. Rybin

Switching from Visibility to Invisibility via Fano Resonances: Theory and Experiment

Subwavelength structures demonstrate many unusual optical properties which can be employed for engineering of a new generation of functional metadevices, as well as controlled scattering of light and invisibility cloaking. Here we demonstrate that the suppression of light scattering for any direction of observation can be achieved for a uniform dielectric object with high refractive index, in a sharp contrast to the cloaking with multilayered plasmonic structures suggested previously. Our finding is based on the novel physics of cascades of Fano resonances observed in the Mie scattering from a homogeneous dielectric rod. We observe this effect experimentally at microwaves by employing high temperature-dependent dielectric permittivity of a glass cylinder with heated water. Our results open a new avenue in analyzing the optical response of high-index dielectric nanoparticles and the physics of cloaking.

Phase diagram for the transition from photonic crystals to dielectric metamaterials.

Photonic crystals and dielectric metamaterials represent two different classes of artificial media but are often composed of similar structural elements. The question is how to distinguish these two types of periodic structures when their parameters, such as permittivity and lattice constant, vary continuously. Here we discuss transition between photonic crystals and dielectric metamaterials and introduce the concept of a phase diagram, based on the physics of Mie and Bragg resonances. We show that a periodic photonic structure transforms into a metamaterial when the Mie gap opens up below the lowest Bragg bandgap where the homogenization approach can be justified and the effective permeability becomes negative. Our theoretical approach is confirmed by microwave experiments for a metacrystal composed of tubes filled with heated water. This analysis yields deep insight into the properties of periodic structures, and provides a useful tool for designing different classes of electromagnetic materials with variable parameters.

Fano interference governs wave transport in disordered systems

Light localization in disordered systems and Bragg scattering in regular periodic structures are considered traditionally as two entirely opposite phenomena: disorder leads to degradation of coherent Bragg scattering whereas Anderson localization is suppressed by periodicity. Here we reveal a non-trivial link between these two phenomena, through the Fano interference between Bragg scattering and disorder-induced scattering, that triggers both localization and de-localization in random systems. We find unexpected transmission enhancement and spectrum inversion when the Bragg stop-bands are transformed into the Bragg pass-bands solely owing to disorder. Fano resonances are always associated with coherent scattering in regular systems, but our discovery of disorder-induced Fano resonances may provide novel insights into many features of the transport phenomena of photons, phonons, and electrons. Owning to ergodicity, the Fano resonance is a fingerprint feature for any realization of the structure with a certain degree of disorder.

Fano resonances in antennas: General control over radiation patterns

The concepts of many optical devices are based on fundamental physical phenomena such as resonances. One of the commonly used devices is an electromagnetic antenna that converts localized energy into freely propagating radiation and vise versa, offering unique capabilities for controlling electromagnetic radiation. Here we propose a concept for controlling the intensity and directionality of electromagnetic wave scattering in radio-frequency and optical antennas based on the physics of Fano resonances. We develop an analytical theory of spatial Fano resonances in antennas that describes switching of the radiation pattern between the forward and backward directions, and we confirm our theory with both numerical calculations and microwave experiments. Our approach bridges the concepts of conventional radio antennas and photonic nanoantennas, and it provides a paradigm for the design of wireless optical devices with various functionalities and architectures.

Mie scattering as a cascade of Fano resonances

We reveal that the resonant Mie scattering by high-index dielectric nanoparticles can be presented through cascades of Fano resonances. We employ the exact solution of Maxwells equations and demonstrate that the Lorenz-Mie coefficients of the Mie problem can be expressed generically as infinite series of Fano functions as they describe interference between the background radiation originated from an incident wave and narrow-spectrum Mie scattering modes that lead to Fano resonances.

Light‐Induced Tuning and Reconfiguration of Nanophotonic Structures

Interaction of light pulses of various durations and intensities with nanoscale photonic structures plays an important role in many applications of nanophotonics for high-density data storage, ultra-fast data processing, surface coloring and sensing. A design of optically tunable and reconfigurable structures made from different materials is based on many important physical effects and advances in material science, and it employs the resonant character of light interaction with nanostructures and strong field confinement at the nanoscale. Here we review the recent progress in physics of tunable and reconfigurable nanophotonic structures of different types. We start from low laser intensities that produce weak reversible changes in nanostructures, and then move to the discussion of non-reversible changes in photonic structures. We focus on three platforms based on metallic, dielectric and hybrid resonant photonic structures such as nanoantennas, nanoparticle oligomers and nanostructured metasurfaces. Main challenges and key advantages of each of the approaches focusing on applications in advanced photonic technologies are also discussed.

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.

Inverted yablonovite fabricated by the direct laser writing method and its photonic structure

Three-dimensional photonic crystals with an inverted yablonovite structure have been fabricated by the direct laser writing method based on the two-photon polymerization of a photosensitive material. The correspondence of the structure of the samples to the inverted yablonovite lattice has been confirmed by scanning electron microscopy. The photonic band structure of inverted yablonovite, as well as a number of related photonic materials with an fcc lattice, has been calculated. It has been found that the photonic properties of opal and yablonovite are opposite: the complete photonic band gap appears in inverted opal and direct yablonovite and is absent in direct opal and inverted yablonovite. A method for the fabrication of ideal three-dimensional photonic structures having the complete photonic band gap in the infrared and visible spectral ranges has been discussed.

Two-dimensional light diffraction from thin opal films

This paper reports on experimental and theoretical investigations of light diffraction from thin films of synthetic opal. The diffraction patterns have been studied visually and recorded in different scattering geometries with the films illuminated with white unpolarized light. The diffraction pattern obtained with the film illuminated with a light beam along the [111] axis, which is normal to the film surface, has C6 symmetry and consists of six strong reflections arranged symmetrically with respect to the incident beam. This pattern becomes substantially more complicated when the film is illuminated by white light at an arbitrary angle to the [111] axis. An experimental study of the spectral response and angular relations of the diffraction patterns has established a fairly full pattern of transformation of diffraction reflections obtained under variation of the angle of light incidence on an opal film. The remarkably good matching of experimental and calculated data provides compelling evidence for light diffraction from thin opal films being two-dimensional.

Experimental study of the photonic band structure of synthetic opals at a low dielectric contrast

This paper reports on a comprehensive study of optical transmissivity spectra of synthetic opals as a function of the four major parameters of the observed photonic stop bands, namely, light beam orientation relative to the opal fcc lattice, light polarization, opal-filler dielectric permittivity contrast, and sample thickness. The measurements were performed under low opal-filler dielectric contrast conditions for the principal high-symmetry directions of the twinned fcc lattice of the opals. The experimentally determined dependence of the energy positions of photonic stop bands on the direction of the light wave vector is fitted well by the calculated dispersion relation of Bragg wavelengths in diffraction of light from the (hkl) fcc plane system.