Mushegh Rafayelyan

Yerevan State University | YSU · Faculty of Physics

We report on free-space strategy for electromagnetic concealment of three-dimensional macroscopic objects in the optical domain owing to unique energy flow redirection capabilities enabled by optical phase singularities. We propose and implement the generation of a quasi-nodal volume based on optical vortex Fourier processing, which inhibits light...

The features of the light localization and absorption in 1D harmonic chirped photonic crystals (PCs) were investigated. It 7 was shown that although chirping leads to a loss of perfect periodicity, the integral over a wide spectral region light energy density 8 practically does not change. We investigate the peculiarities of the spectra of photonic...

Reservoir Computing is a class of Recurrent Neural Networks with internal weights fixed at random. Stability relates to the sensitivity of the network state to perturbations. It is an important property in Reservoir Computing as it directly impacts performance. In practice, it is desirable to stay in a stable regime, where the effect of perturbatio...

The race to heuristically solve nondeterministic polynomial-time (NP) problems through efficient methods is ongoing. Recently, optics was demonstrated as a promising tool to find the ground state of a spin-glass Ising Hamiltonian, which represents an archetypal NP problem. However, achieving completely programmable spin couplings in these large-sca...

The features of light absorption and localization in one-dimensional chirped photonic crystals (PCs) are studied. It is shown that although chirping leads to the loss of ideal periodicity, the integral over a wide spectral region light energy density practically does not change. We have shown that violation of the ideal periodic structure (chirping...

The race to heuristically solve non-deterministic polynomial-time (NP) problems through efficient methods is ongoing. Recently, optics was demonstrated as a promising tool to find the ground state of a spin-glass Ising Hamiltonian, which represents an archetypal NP problem. However, achieving completely programmable spin couplings in these large-sc...

Cholesteric liquid crystals (CLCs) with induced defects are one of the most prominent materials to realize compact, low-threshold and tunable coherent light sources. In this context, the investigation of optical properties of induced defect modes in such CLCs is of great interest. In particular, many studies have been devoted to the spectral contro...

In our paper, the magneto-optical properties of a dichroic cholesteric liquid crystal layer with large values of magneto-optical parameter g and low values of dielectric permittivity were investigated. The solutions of the dispersion equation and their peculiarities were investigated in detail. The specific properties of reflection, transmission, a...

Many developments in science and engineering depend on tackling complex optimizations on large scales. The challenge motivates an intense search for specific computing hardware that takes advantage of quantum features, nonlinear dynamics, or photonics. A paradigmatic optimization problem is to find low-energy states in classical spin systems with f...

Reservoir computing is a relatively recent computational paradigm that originates from a recurrent neural network and is known for its wide range of implementations using different physical technologies. Large reservoirs are very hard to obtain in conventional computers, as both the computation complexity and memory usage grow quadratically. We pro...

Reservoir Computing is a class of simple yet efficient Recurrent Neural Networks where internal weights are fixed at random and only a linear output layer is trained. In the large size limit, such random neural networks have a deep connection with kernel methods. Our contributions are threefold: a) We rigorously establish the recurrent kernel limit...

Many developments in science and engineering depend on tackling complex optimizations on large scales. The challenge motivates intense search for specific computing hardware that takes advantage from quantum features [1, 2], stochastic elements [3], nonlinear dissipative dynamics [4-8], in-memory operations [9, 10], or photonics [11-14]. A paradigm...

Reservoir computing is a relatively recent computational paradigm that originates from a recurrent neural network, and is known for its wide-range of implementations using different physical technologies. Large reservoirs are very hard to obtain in conventional computers as both the computation complexity and memory usage grows quadratically. We pr...

Reservoir Computing is a relatively recent computational framework based on a large Recurrent Neural Network with fixed weights. Many physical implementations of Reservoir Computing have been proposed to improve speed and energy efficiency. In this study, we report new advances in Optical Reservoir Computing using multiple light scattering to accel...

Reservoir Computing is a relatively recent computational framework based on a large Recurrent Neural Network with fixed weights. Many physical implementations of Reservoir Computing have been proposed to improve speed and energy efficiency. In this study, we report new advances in Optical Reservoir Computing using multiple light scattering to accel...

Oblique propagation of light through a planar layer of a cholesteric liquid crystal (CLC) is solved by Ambartsumian’s modified layer addition method. Two cases are considered, namely, the case when dielectric boundaries have a minimum influence on light transmission and the case when the CLC layer is in a vacuum. It is shown that in the first case...

DOI:https://doi.org/10.1103/PhysRevLett.121.029901

Reflective geometric phase flat optics made from chiral anisotropic media recently unveiled a promising route towards polychromatic beam shaping. However, these broadband benefits are strongly mitigated by the fact that flipping the incident helicity does not ensure geometric phase reversal. Here we overcome this fundamental limitation by a simple...

The realization of geometric phase optical device operating over a broad spectral range is usually confronted with intrinsic limitations depending of the physical process at play. Here we propose to use chiral nematic liquid crystal slabs with helical ordering that varies in three dimensions. Namely, gradient-pitch cholesterics endowed with in-plan...

A quasi-modal version of the recently introduced Laguerre-Gaussian modal q-plates [Rafayelyan and Brasselet, Opt. Lett. 42, 1966–1969 (2017)] is proposed and implemented using femtosecond direct laser writing of space-variant nanogratings in the bulk of silica glass. The corresponding design consists of linear azimuthal modulation of the optical ax...

We propose space-variant uniaxial flat optical elements designed to generate pure Laguerre-Gaussian modes with arbitrary azimuthal and radial indices l and p from an incident Gaussian beam. This is done via the combined use of the dynamic and the geometric phases. Optimal design protocol for the mode conversion efficiency is derived, and the corres...

We explore the spin-orbit nature of the optical torque exerted on chiral liquid-crystal microspheres exhibiting circular Bragg reflection. Experimental investigation relies on the direct optomechanical observation of spinning liquid-crystal droplets immersed in water and held in a circularly polarized laser levitator. More generally, we anticipate...

It is well-known that paraxial coherent electromagnetic fields can be completely characterized in terms of their radial and azimuthal spatial degrees of freedom in the transverse plane that add to the polarization degree of freedom and wavelength. In this work we address two main issues of paraxial beam shaping that are the modality and the polychr...

In the present paper, we investigate the polarization properties of the cholesteric liquid crystals (CLCs) with an isotropic/anisotropic defect inside them. Possibilities of amplification of the polarization plane rotation and stabilization of the light polarization azimuth by these systems are investigated in details.

We report on highly reflective spin-orbit geometric phase optical elements based on a helicity-preserving circular Bragg-reflection phenomenon. First, we present a dynamical geometric phase experiment using a flat chiral Bragg mirror. Then, we show that shaping such a geometric phase allows the efficient spin-orbit tailoring of light fields without...

We report on the experimental realization of flat mirrors enabling the broadband generation of optical vortices upon reflection. The effect is based on the geometric Berry phase associated with the circular Bragg reflection phenomenon from chiral uniaxial media. We show the reflective optical vortex generation from both diffractive and nondiffracti...

The model and algorithm for the cooling of the magnetized neutron stars are presented. The cooling evolution described by system of parabolic partial differential equations with non-linear coefficients is solved using Alternating Direction Implicit method. The difference scheme and the preliminary results of simulations are presented.

The properties of chiral photonic crystals with a pitch gradient were investigated both experimentally and theoretically. The liquid-crystalline cell was prepared by bringing two cholesteric liquid crystals (CLCs) with different pitches into contact. There are some essential features in the dynamics of diffusion between the two CLCs. The most impor...

We consider reflection of light from half-space of anisotropic metamaterial at arbitrary direction of optical axis in the plane of light incidence. We obtain conditions at which total reflection and refraction do not depend on the polarization of incident light and the reflection does not depend on also the angle of incidence. We also study the pos...

Light transmission through and reflection from a medium layer with dielectric and magnetic helicities are discussed. The axes of the dielectric permittivity tensor, \hat {\varepsilon }, and the magnetic permeability tensor, \hat {\mu }, as well as the medium helix axis are all parallel to each other and they are perpendicular to the boundary surfac...

The photonic density of states (PDS) of the eigen polarizations (EPs) in cholesteric liquid crystal (CLC) cells are calculated. The dependences of the PDS on the parameters characterizing absorption, gain and refractive index of the CLC layer surroundings were obtained. We investigated the possibility of connections between the PDS and the density...

The peculiarities of solutions of the wave dispersion equation in an unbounded indefinite medium for arbitrarily oriented optical axes are considered. All possible dispersion surfaces arising in such media are described, and the conditions of their existence are obtained. It is shown that only some specific pairs of surfaces are possible. The dispe...

In frame of this paper we have investigated reflection and transmission properties of light in chiral liquid-crystalline photonic structures with inhomogeneous pitch. We have experimentally confirmed and theoretically justified the existence of the phenomenon of nonreciprocity in the mentioned above systems. The liquid-crystalline cells through the...

At the present work we have studied the polarization and spectral properties of light in different cholesteric liquid-crystalline systems, particularly in the systems prepared from mixture of right and left-handed cholesterics and nematic liquid crystal. The following systems were also examined: a) system consisting of right and left handed cholest...

In the present paper, we investigate the polarization properties of the cholesteric liquid crystals (CLCs) with an isotropic/anisotropic defect inside them, and possibilities of amplification of the polarization plane rotation and stabilization of the light polarization azimuth by these systems are investigated.

We have both experimentally and theoretically considered some properties of chiral photonic crystals. A liquid-crystalline cell through the contact of two cholesteric liquid crystals with different pitches was prepared. The peculiarities of polarization plane rotation of light were discussed. One of the substrates was coated with cholesteric liquid...

Normal light transmission (reflection) through (from) a medium layer with a dielectric and magnetic helicity was discussed. The axes of dielectric permittivity tensor, , and magnetic permeability tensor,, as well as the medium helix axis are parallel each other and they are perpendicular to the boundary surfaces. The reflection and transmission mat...

We investigated light propagation in a homogeneous medium having double anisotropy (i.e. with anisotropy of both dielectric and magnetic permittivities) and an arbitrary orientation of its optical axis in the plane of incidence. We investigated wave surfaces for the considered medium. We showed that only some groups of surfaces can arise. We invest...

We investigate light wave propagation through a one-axis anisotropic medium layer with simultaneously non-unit dielectric and magnetic tensors. 4x4 - Delta▵(see manuscript) matrix is built. We consider the general case when the dielectric and magnetic permittivity tensor elements have both positive and negative sings. We obtained the dispersio...