arXiv subjects

Mikhail V. Rybin

Publications and source records attributed to Mikhail V. Rybin.

At least 19 recordsLinked to original sources

arXiv2026

Robustness of bound states in the continuum in metasurface based on Ge$_2$Sb$_2$Te$_5$ versus structural imperfections

We study the impact of lithography imperfections on quasi-bound states in the continuum (quasi-BICs) supported by a one-dimensional metasurface of Ge$_2$Sb$_2$Te$_5$ (GST) bars with trapezoidal deviations from rectangular cross-sections. Several mechanisms of quality ($Q$) factor scaling, including the impact of material losses, dispersion, and geometric imperfections are established. We demonstrate that transition to identical isosceles trapezoids, despite preserving the required $C_2$ symmetry, reduces the $Q$ factor in the amorphous phase due to absorption changes accompanying the resonance shift. Further, the $Q$ factor remains robust for both GST phases under random element-to-element variations of the trapezoid angle, while analytical and numerical estimations in the absence of material losses show inverse-quadratic scaling of the Q factor with the disorder amplitude. We reveal that in the GST-based metasurface, the $Q$ factor is tolerant to geometric imperfections for insignificant dispersion near the BIC wavelength, but changes in case of substantial dispersion. The phase shifting and established robustness of BICs in GST can be useful for applications where stable moderate $Q$ factors are essential.

physics.optics↗

arXiv2025

Robustness of Bound States in the Continuum in Bilayer Structures against Symmetry Breaking

We investigate the robustness of bound states in the continuum (BICs) in a bilayer dielectric rod array against geometric and material perturbations. Our analysis focuses on both symmetry-protected and Fabry-Pérot BICs, examining their transformation into quasi-BICs under three structural modifications: (i) in-plane displacement of one layer, which breaks the C$_2$ symmetry of the system; (ii) introduction of material losses that break time-reversal symmetry; and (iii) variation in the interlayer distance, which preserves structural symmetry. In particular, we demonstrate that material losses inevitably induce radiation in Fabry-Pérot BICs via second-order perturbation processes, converting them into quasi-BICs, while symmetry-protected BICs remain non-radiative. We further show that, despite the inherent instability of BICs under symmetry-breaking effects, their resilience can be significantly enhanced through proper design. Both Fabry-Pérot and symmetry-protected BICs exhibit exponentially weak sensitivity to C$_2$-breaking perturbations as the interlayer distance increases. Finally, we show that additional FP-BICs emerge under oblique incidence, originating from the interference of two high-Q quasi-BICs near the symmetry-protected ones. Our findings pave the way for the development of BIC-based photonic devices with improved robustness against fabrication imperfections, environmental variations, and material losses.

physics.optics↗

arXiv2025

A High Responsivity Broadband Photodetector Based on a WSe2 NiO Nanowire Heterostructure with Engineered Nanophotonic Enhancement

Engineering nanoscale light matter interaction in mixed dimensional semiconductor heterostructures offers a pathway to mitigate the intrinsic gain bandwidth trade off in photodetectors. Here, we report a broadband, high responsivity 2D and 1D photodetector formed by integrating monolayer p type WSe2 with electrospun p type NiO nanowires. The device photoresponse spans 350 to 780 nm and is governed by a nanophotonic field confinement mechanism rather than bulk optical absorption. The high index NiO nanowire acts as a dielectric Mie type nanoresonator that supports geometry defined optical modes and produces antenna like near field concentration at the nanoscale WSe2 and NiO junction. This localized optical mode increases the local absorption cross section and enhances the photocarrier generation rate within the junction region, identified as the dominant active volume for photocurrent. A coupled optoelectronic model linking full wave electromagnetic simulations to carrier generation, recombination, and extraction accurately captures the measured responsivity spectrum and its power dependence using only two electronic fitting parameters. The device achieves responsivities of 627 A/W in the visible region, 227 A/W in the UV, and 167 A/W in the NIR, demonstrating broadband operation with ultrahigh gain. These results show that geometric resonance in mixed dimensional junctions is a powerful design principle for next generation high gain optoelectronic detectors.

physics.optics↗

arXiv2024

Metaphotonics with subwavelength dielectric resonators

The recently emerged Mie resonant metaphotonics (or Mietronics) provides novel opportunities for subwavelength optics. Mietronics employs resonances in isolated nanoparticles and structured surfaces. We present a brief summary of the key concepts underpinning this rapidly developing area of research, using the examples of isolated high-index dielectric subwavelength particles. We also discuss recent advances and future trends in designs of high-Q elements for efficient resonant spatial and temporal control of light.

physics.optics↗

arXiv2023

Retardaion-induced exceptional point

Exceptional points in an optical dimer of spheres, which have the same size and operate in the spectral region of the dipolar resonance, are considered. By choosing different materials of these spheres, we can offset the radiative loss and create a gain-loss contrast to achieve a parity-time (PT)-symmetric dimer. In this case, an exceptional point corresponds to the point where the PT symmetry is broken. At the same time, if we consider a symmetric dimer, where both spheres are made of the same material (which may have a purely real dielectric constant), exceptional points occurring due to the radiative loss non-Hermiticity can also be observed. We study the transition between the two regimes and demonstrate that the exceptional point emerges due to the retardative nature of the coupling between the spheres, which makes the equation for eigenfrequencies nonlinear and allows it to have nontrivial solutions even when there is no contrast between the spheres.

physics.optics↗

arXiv2023

Density of photonic states in aperiodic structures

Periodicity is usually assumed to be the necessary and sufficient condition for the formation of band gaps, i.e., energy bands with a suppressed density of states. Here, we check this premise by analyzing the band gap properties of three structures that differ in the degree of periodicity and ordering. We consider a photonic crystal, disordered lattice, and ordered but nonperiodic quasicrystalline structure. A real-space metric allows us to compare the degree of periodicity of these different structures. Using this metric, we reveal that the disordered lattice and the ordered quasicrystal can be attributed to the same group of material structures. We examine the density of their photonic states both theoretically and experimentally. The analysis reveals that despite their dramatically different degrees of periodicity, the photonic crystal and the quasicrystalline structure demonstrate an almost similar suppression of the density of states. Our results give new insight into the physical mechanisms resulting in the formation of band gaps.

physics.class-ph↗

arXiv2022

Interlaced wire medium with quasicrystal lattice

We propose a design of interlaced wire medium with quasicrystalline lattice based on five-fold rotation symmetry Penrose tiling. The transport properties of this structure are studied. We distinguish two transport regimes, namely, propagation regime related to the low-frequency interval and localization regime in the high-frequency interval. While the former is observed in structures both with and without translation symmetry property, the latter is exclusive for aperiodic structures only. We show that the localization regime is promising for many applications including engineering of effective multi-channel devices for telecommunication and imaging systems.

physics.app-ph↗

arXiv2021

Bound states in the continuum in periodic structures with structural disorder

We study the effect of structural disorder on the transition from the bound states in the continuum (BICs) to quasi-BICs by the example of the periodic photonic structure composed of two layers of parallel dielectric rods. We uncover the specificity in the robustness of the symmetry-protected and accidental BICs against various types of structural disorder. We analyze how the spatial mode localization induced by the structural disorder results in an effective reduction of the system length and limits the Q factor of quasi-BICs. Our results are essential for the practical implementation of BICs especially in natural and self-assembled photonic structures, where the structural disorder plays a crucial role.

physics.optics↗

arXiv2021

Experimental observation of intrinsic light localization in photonic icosahedral quasicrystals

One of the most intriguing problems of light transport in solids is the localization that has been observed in various disordered photonic structures1-11. The light localization in defect-free icosahedral quasicrystals has recently been predicted theoretically without experimental verification10. Here we report on the fabrication of submicron-size dielectric icosahedral quasicrystals and demonstrate the results of detailed studies of the photonic properties of these structures. Here, we present the first direct experimental observation of intrinsic light localization in defect-free quasicrystals. This result was obtained in time-resolved measurements at different laser wavelengths in the visible. We linked localization with the aperiodicity of the icosahedral structure, which led to uncompensated scattering of light from an individual structural element over the entire sphere, providing multiple scattering inside the sample and, as a result, the intrinsic localization of light.

physics.optics↗

arXiv2019

Disorder-immune photonics based on Mie-resonant dielectric metamaterials

When the feature size of photonic structures becomes comparable or even smaller than the wavelength of light, the fabrication imperfections inevitably introduce disorder that may eliminate many functionalities of subwavelength photonic devices. Here we suggest a novel concept to achieve a robust bandgap which can endure disorder beyond 30 as a result of the transition from photonic crystals to Mie-resonant metamaterials. By utilizing Mie-resonant metamaterials with high refractive index, we demonstrate photonic waveguides and cavities with strong robustness to position disorder, thus providing a novel approach to the bandgap-based nanophotonic devices with new properties and functionalities.

physics.app-ph↗

arXiv2019

Strong optical coupling combines isolated scatterers into dimer

We analyze the transition between different coupling regimes of two dielectric rods, which occurs at a critical distance between them. The hallmark of strong coupling regime is the peak splitting effect observed in spectra. Here we comprehensively evaluate the critical distance as a function of the rod permittivity using a number of different approaches. The scattering spectra of the two rods in dependence on the distance demonstrate the weak to strong coupling transition. We start the analysis by introducing a region of a tidal energy flux around a single isolated rod (the region is related to the near field) and demonstrate that its effective radius corresponds to the critical distance obtained from the scattering spectra. Next, we study the eigenfrequencies of the dimer as functions of distance by 'diagonalizing' the coupled multipole matrix. In order to find an analytical formula for the critical distance, we consider the problem under several approximations, which yield similar results.

physics.optics↗

arXiv2019

Unconventional light scattering from glassy photonic films and metasurfaces

The propagation of light through a random medium is an important problem in photonics. When the random fluctuations of the orientation for individual rods were introduced to the ideal woodpile photonic structure, a crossover from Laue diffraction to randomly scattered fields which is similar in appearance to speckle patterns was observed and investigated. Unexpected interplay between order and disorder was discovered from anisotropic glassy samples when orientational disorder was added only in one direction of square woodpile structure. It is found that the ordered sets of rods produced disordered patterns and vice versa the disordered sets of rods produced ordered patterns that continue to be bright and sharp with increasing disorder. To explain this effect, it was demonstrated theoretically and experimentally that the light scattering can be described purely in terms of the intersection points of the rods.

physics.optics↗

arXiv2018

All-dielectric active photonics driven by bound states in the continuum

Recently emerged dielectric resonators and metasurfaces offer a low-loss platform for efficient manipulation of electromagnetic waves from microwave to visible. Such flat meta-optics can focus electromagnetic waves, generate structured beams and vortices, enhance local fields for sensing as well as provide additional functionalities for advanced MRI machinery. Recent advances are associated with exotic optical modes called bound states in the continuum, which can give rise to extremely large quality factors and supercavity lasing. Here, we experimentally demonstrate subwavelength active supercavities with extremely high-Q resonances that could be reconfigured at an ultrafast time scale. We reveal that such supercavities enable all-optical switching and modulation of extremely sharp resonances, and thus could have numerous applications in lasing, mode multiplexing, and biosensing.

physics.optics↗

arXiv2017

Optical properties of honeycomb photonic structures

We study, theoretically and experimentally, optical properties of different types of honeycomb photonic structures, known also as `photonic graphene'. First, we employ the two-photon polymerization method to fabricate the honeycomb structures. In experiment, we observe a strong diffraction from a finite number of elements, thus providing a unique tool to define the exact number of scattering elements in the structure by a naked eye. Then, we study theoretically the transmission spectra of both honeycomb single layer and 2D structures of parallel dielectric circular rods. When the dielectric constant of the rod materials $\varepsilon$ is increasing, we reveal that a two-dimensional photonic graphene structure transforms into a metamaterial when the lowest TE${}_{01}$ Mie gap opens up below the lowest Bragg bandgap. We also observe two Dirac points in the band structure of 2D photonic graphene at the $K$ point of the Brillouin zone and demonstrate a manifestation of the Dirac lensing for the TM polarization. The performance of the Dirac lens is that the 2D photonic graphene layer converts a wave from point source into a beam with flat phase surfaces at the Dirac frequency for the TM polarization.

cond-mat.mes-hall↗

arXiv2017

Effect of photonic crystal stop-band on photoluminescence of $a$-Si$_{1-x}$C$_x$:H

Effects associated with the change in the local density of photonic states in a periodic structure based on alternating \textit{a}-Si$_{1-x}$C$_x$:H and \textit{a}-SiO$_2$ amorphous layers forming a one-dimensional (1D) photonic crystal have been analyzed. The use of \textit{a}-Si$_{1-x}$C$_x$:H as the emitting material made it possible to examine the transformation of the photoluminescence spectrum contour that is comparable in width with the photonic stop-band. It was experimentally demonstrated that the emission is enhanced and suppressed in the vicinity of the stop-band. The relative intensities of the luminescence peaks at different edges of the stop-band vary with the detuning of the stop-band position and photoluminescence peak of a single \textit{a}-Si$_{1-x}$C$_x$:H film. The Purcell effect in the system under consideration was theoretically described by the method in which the local density of photonic states is calculated in terms of a 1D model. %A good agreement was obtained between the experimentally measured and calculated spectra. It was shown that the specific part of local density of states substantially increases at the long-wavelength (low-frequency) edge of the stop-band of a 1D photonic crystal as a result of the predominant localization of the electric field of the light wave in the spatial regions of \textit{a}-Si$_{1-x}$C$_x$:H which have a higher relative permittivity as compared with \textit{a}-SiO$_2$.

cond-mat.mes-hall↗

arXiv2017

Inverse dispersion method for calculation of complex photonic band diagram and $\cal{PT}$-symmetry

We suggest an inverse dispersion method for calculating photonic band diagram for materials with arbitrary frequency-dependent dielectric functions. The method is able to calculate the complex wave vector for a given frequency by solving the eigenvalue problem with a non-Hermitian operator. The analogy with $\cal{PT}$-symmetric Hamiltonians reveals that the operator corresponds to the momentum as a physical quantity and the singularities at the band edges are related to the branch points and responses for the features on the band edges. The method is realized using plane wave expansion technique for two-dimensional periodical structure in the case of TE- and TM-polarization. We illustrate the applicability of the method by calculation of the photonic band diagrams of an infinite two-dimension square lattice composed of dielectric cylinders using the measured frequency dependent dielectric functions of different materials (amorphous hydrogenated carbon, silicon, and chalcogenide glass). We show that the method allows to distinguish unambiguously between Bragg and Mie gaps in the spectra.

physics.optics↗

arXiv2017

High-Q supercavity modes in subwavelength dielectric resonators

Recent progress in nanoscale optical physics is associated with the development of a new branch of nanophotonics exploring strong Mie resonances in dielectric nanoparticles with high refractive index. The high-index resonant dielectric nanostructures form building blocks for novel photonic metadevices with low losses and advanced functionalities. However, unlike extensively studied cavities in photonic crystals, such dielectric resonators demonstrate low quality factors (Q-factors). Here, we uncover a novel mechanism for achieving giant Q-factors of subwavelength nanoscale resonators by realizing the regime of bound states in the continuum. We reveal strong mode coupling and Fano resonances in high-index dielectric finite-length nanorods resulting in high-Q factors at the nanoscale. Thus, high-index dielectric resonators represent the simplest example of nanophotonic supercavities, expanding substantially the range of applications of all-dielectric resonant nanophotonics and meta-optics.

physics.optics↗

arXiv2017

Switchable invisibility of dielectric resonators

The study of invisibility of an infinite dielectric rod with high refractive index is based on the two-dimensional Mie scattering problem, and it suggests strong suppression of scattering due to the Fano interference between spectrally broad nonresonant waves and narrow Mie-resonant modes. However, when the dielectric rod has a finite extension, it becomes a resonator supporting the Fabry-Perot modes which introduce additional scattering and eventually destroy the invisibility. Here we reveal that for shorter rods with modest values of the aspect ratio r/L (where r and L are the radius and length of the rod, respectively), the lowest spectral window of the scattering suppression recovers completely, so that even a finite-size resonator may become invisible. We present a direct experimental verification of the concept of switchable invisibility at microwaves using a cylindrical finite-size resonator with high refractive index.

physics.optics↗