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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-scale optical Ising simulators remains an open challenge. Here, by exploiting the knowledge of the transmission matrix of a random medium, we experimentally demonstrate the possibility of controlling the couplings of a fully connected Ising spin system. By further tailoring the input wavefront we showcase the possibility of modifying the Ising Hamiltonian both by accounting for an external magnetic field and by controlling the number of degenerate ground states and their properties and probabilities. Our results represent a relevant step toward the realisation of fully-programmable Ising machines on thin optical platforms, capable of solving complex spin-glass Hamiltonians on a large scale., 13 pages, 9 figures

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 scattering from objects placed inside. The proof of concept is made by numerical simulations and the experimental implementation is carried out in the visible domain by using geometric phase vortex phase masks. Optical cloaking demonstration is made by using stainless steel sphere as the object to be concealed. The geometric phase nature of the vortex masks confers polarization independent features to the device and makes it possible to implement in a reflection mode.

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, nonlinear dynamics, or photonics. A paradigmatic optimization problem is finding low-energy states in classical spin systems with fully-random interactions. To date no alternative computing platform can address such spin-glass problems on a large scale. Here we propose and realize an optical scalable spin-glass simulator based on spatial light modulation and multiple light scattering. By tailoring optical transmission through a disordered medium, we optically accelerate the computation of the ground state of large spin networks with all-to-all random couplings. Scaling of the operation time with the problem size demonstrates optical advantage over conventional computing. Our results point out optical vector-matrix multiplication as a tool for spin-glass problems and provide a general route towards large-scale computing that exploits speed, parallelism and coherence of light., 9 pages, 4 figures

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 propose an optical scheme performing reservoir computing over very large networks potentially being able to host several millions of fully connected photonic nodes thanks to its intrinsic properties of parallelism and scalability. Our experimental studies confirm that, in contrast to conventional computers, the computation time of our optical scheme is only linearly dependent on the number of photonic nodes of the network, which is due to electronic overheads, while the optical part of computation remains fully parallel and independent of the reservoir size. To demonstrate the scalability of our optical scheme, we perform for the first time predictions on large spatiotemporal chaotic datasets obtained from the Kuramoto-Sivashinsky equation using optical reservoirs with up to 50 000 optical nodes. Our results are extremely challenging for conventional von Neumann machines, and they significantly advance the state of the art of unconventional reservoir computing approaches, in general., 9 pages, 7 figures, abstract is modified according to the published version

There have been a number of rapid advances in the prediction of the dynamics of chaotic systems using a technique known as Reservoir Computing. These techniques are mostly not effective for large networks, as the complexity of the task increases quadratically both in time and memory. We report new advances in Optical Reservoir Computing using multiple light scattering to accelerate the recursive computation of the reservoir states. Different approaches to information encoding based on phase or amplitude spatial light modulations are compared. We demonstrate the scalability and the good prediction performance of our approach using the Kuramoto-Sivashinsky equation as an example of a spatiotemporally chaotic system.

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...

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 control of the defect modes depending on their thickness, optical properties, distribution along the CLC, etc. In this paper, we investigate the lasing possibilities of a dye-doped polymer layer embedded in a wedge-shaped CLC. We show that multimode laser generation is possible due to the observed multiple defect modes in the PBG that enlarges the application range of the system. Furthermore, our simulations based on a Berreman 4 × 4 matrix approach for a wide range of CLC thickness show both periodic and continuous generation of defect modes along particular spectral lines inside the PBG. Such a robust spectral behaviour of induced defect modes is unique, and, to our knowledge, is not observed in similar CLC-based structures.

This corrects the article DOI: 10.1103/PhysRevLett.120.213903.

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-plane space-variant angular positioning of the supramolecular helix. By doing so, we show that the recently introduced Bragg-Berry mirrors [Opt. Lett. {\bf 41}, 3972-3975 (2016)] can be endowed with ultra-broadband spectral range. Experimental demonstration is made in the case of ultra-broadband optical vortex generation in the visible domain. These results offer practical solution to the polychromatic management of the orbital angular momentum of light combining the circular Bragg reflection of chiral media with the Berry phase., Comment: 11 pages, 13 figures

International audience; 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 and robust add-on whose advantages are emphasized in the context of spin-to-orbital angular momentum mapping.

International audience; 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 that the total angular momentum transfer per photon may depart from the commonly assumed spin-only ±2¯ h contribution, when the topological features of the illuminated microsphere are taken into account.

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 possibilities and conditions for using the considered system as beam splitter, omnidirectional reflector, phase retarder, and so on.

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 dispersion equation for the boundary problem is obtained, as well as the dependence of dispersion curves on the orientation of optical axis is investigated. The nonreciprocity of the wave refraction is shown.

International audience; 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 nondiffractive paraxial light beams using spatially patterned chiral liquid crystal films. The intrinsic spectrally broadband character of spin-orbit generation of optical phase singularities is demonstrated over the full visible domain. Our results do not rely on any birefringent retardation requirement and, consequently, foster the development of a novel generation of robust optical elements for spin-orbit photonic technologies.

International audience; 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 the need to fulfill any condition on birefringent phase retardation, in contrast to the case of transmission spin orbit optical elements. This is illustrated by optical vortex generation from chiral liquid crystal droplets in the Bragg regime that unveils spin orbit consequences of the droplet's curvature. Our results thus introduce a novel class of geometric phase elements " Bragg Berry " optical elements.

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.

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 matrices are constructed, and the character of the eigen polarizations (EPs) of the reflected and transmitted waves are investigated. Particularly, it is shown that a certain transmission region can rise between the diffraction and mirror reflection regions, in certain conditions. A superluminal light propagation is observed in the transmission band, in certain conditions.

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., Comment: 6 pages, 4 figures, accepted to the European Physical Journal Web of Conferences as a contribution of the International Conference Mathematical Modeling and Computational Physics 2015 (High Tatra Mountains, Slovakia, July 13 - July 17, 2015, http://web.tuke.sk/mmcp/mmcp2015/)

International audience; 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 axis orientation and polynomial radial modulation of the retardance profile. Experimental demonstration is made for Laguerre-Gaussian modes with azimuthal indices l =(1, 2, 3) and radial index p = 0. Such quasi-modal q-plates overcome previous limitations regarding the robustness of modality against the handedness of the incident circular polarization state.

International audience; 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 corresponding characteristics are given for −6≤l≤6 and 0≤p≤5. The obtained “modal q-plates” may find many applications whenever the radial degree of freedom of a light field is at play.

We investigate light wave propagation through a one-axis anisotropic medium layer with simultaneously non-unit dielectric and magnetic tensors. 4x4 - Δ u ( 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 dispersion equation and then built dispersion surfaces for a homogeneous anisotropic uniaxial material when the material is negative or positive (both with respect to the wave vector and Pointing's vector orientation of the refracted wave; the sign of the material is accordingly defined below.) Electromagnetic plane waves propagating inside the medium can exhibit dispersion surfaces in the form of ellipsoids of revolution, hyperboloids of one sheet, or hyperboloids of two sheets. The conditions of negative refraction with respect to the wave vector and Pointing's vector orientation are considered. We found wave nonreciprocity for the oblique incidence on the considered system and we showed that such a system can work as an alloptical diode.

Yerevan State University, Faculty of Physics, 1 Alex Manoogian Street, 0025 Yerevan, ArmeniaAbstract. The properties of chiral photonic crystals with a pitch gradient were investigated bothexperimentally and theoretically. The liquid-crystalline cell was prepared by bringing two cho-lesteric liquid crystals (CLCs) with different pitches into contact. There are some essential fea-tures in the dynamics of diffusion between the two CLCs. The most important feature is the factthat establishing the final equilibrium pitch (for the temperatures below 17°C) takes a long time—roughly 3monthsor more—which, in turn, allows us to investigate the nonstandard change inthe reflection spectra during the diffusion. The two reflection curves do not directly actually getcloser and merge into one peak, as usual, but the left one gradually gets smaller and almostvanishes, and the right one expands. For this reason, a theoretical model of a pitch changewas developed and it was seen that this model does not coincide with the classical ideas ofthe pitch change. It was also assumed that due to the “freezing” effect during the diffusionprocess, one could have fixed the intermediate states of the pitch gradient.

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 of the light energy accumulated in the medium and showed that these characteristics have analogous spectra and, besides, the influences of the problem parameters on these characteristics also are analogous. It was shown that the decrement of the refractive index of the CLC layer surroundings leads to a sharp increase of the maximum PDS and, consequently, leads to a sharp decrement of the laser excitation threshold. We showed that the subject system can work as a low threshold laser or a multi-position trigger.

Light transmission through and reflection from a medium layer with dielectric and magnetic helicities are discussed. The axes of the dielectric permittivity tensor, , and the magnetic permeability tensor, , as well as the medium helix axis are all parallel to each other and they are perpendicular to the boundary surfaces. The possibilities of formation of some new types of photonic bandgaps (PBGs) are presented for large anisotropies of the medium?namely, direct and indirect nonselective PBGs (with respect to the incident light polarization, in contrast to the usual direct PBGs, which are selective with respect to the polarization of the incident light). It is shown that a transmission region can arise among the three types of PBGs, in certain conditions, of course. In this paper we generalize the concept of nihility for structurally chiral media, such as cholesteric liquid crystals (CLCs) and we identify two types of CLC nihilities. It is shown that, for certain characteristic parameters of the medium, superluminal light propagation is possible in the transmission band. The influence of the anisotropy of the medium on the reflection spectra is considered and it is shown that one can tune the width, number and frequency range of PBGs of this layer, at essentially large limits, tuning the parameters of the layer. The case of oblique light incidence on the CLC layer is also discussed.

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 investigated the conditions for total independent of polarization reflection and the conditions for total transmission, as well as possibilities of the subject system of serving as: an omnidirectional reflector, a beam splitter and a phase retarder.

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 accelerate the recursive computation of the reservoir states. Two different spatial light modulation technologies, namely, phase or binary amplitude modulations, are compared. Phase modulation is a promising direction already employed in other photonic implementations of Reservoir Computing. Additionally, we report a Digital-Micromirror-based Reservoir Computing at up to 640 Hz, more than double the previously reported frequency using a remotely controlled optical device developed by LightOn, and present new binarization strategies to improve the performance of binarized Reservoir Computing.