The article proposes two new methods for multiplexing-demultiplexing communication channels in the FSO system, based on singular optics approaches. The first makes use of computer generated vortex holograms installed in the transmitting and receiving modules of the systems, which make it possible to generate and separate communication channels formed by vortex beams with different topological charges. The second method, spatial singular multiplexing, is based on the property of singular beams to restore angular momentum when vortex beams propagate in a medium with physical disturbances. The method uses opaque screens installed in the transmitting block of the system, which diaphragm the vortex beams. As a result of this operation, the centers of the vortices in the receiving part of the system are displaced, which makes it possible to separate the beams that are differently blocked in the transmitting unit. Computer simulation data and experimental results are presented.

We examine light scattering in a birefringent material, namely uniaxial nematic liquid crystal possessing macroscopic orientation perturbations (variations of director in planar alignment). Our theoretical analysis and direct experiments proved that the polarisation state of the scattered speckle-field is uniform and elliptical (in a common case). The polarisation ellipse azimuth of scattered waves is mirror reflected to one of the directly transmitted waves relative to the optical axis. [GRAPHICS]

We report on a set of experiments directed to a problem of microparticles interaction with a disclination in a nematic liquid crystal matrix. The idea of the study consists in the visualization of the disclination by filling it with particles efficiently scattering light. A theta-cell possessing a topological defect of undetermined twist which can capture micro-sized objects was exploited. The results obtained for samples of different shape can be used as for the understanding of the nature of self-assembling clusters, as for the practical goal of increasing the visibility of a disclination being a dynamic object sensitive to temperature and other external factors and able to move the trapped particles.

We report on the effect of a strong and protracted advanced response in pulse transmission and reflection in a double-prism scheme. In distinction to the well-known activity on superluminal-like tunneling of an electromagnetic pulse through a gap of a double prism, we consider an optical pulse refracting to a gap and sliding therein. The formation of a multiperiod light jet running within the gap well before the incident pulse is shown with account of normal material dispersion and excitation of leaky modes in the gap. Conditions for the paradoxical appearance of the forerunning jet are revealed to have a geometrical nature with a specific relation between phase and group velocities involved. This deduction assigns the stated effect to the counterintuitive manifestation of causality with no reference to superluminal propagation.

The review exposes basic concepts and manifestations of the singular and structured light fields. The presentation is based on deep intrinsic relations between the singularities and the rotational phenomena in light; it involves essentially the dynamical aspects of light fields and their interactions with matter. Due to their topological nature, the singularities of each separate parameter (phase, polarization, energy flow, etc.) form coherent interrelated systems (singular networks), and the meaningful interconnections between the different singular networks are analysed. The main features of singular-light structures are introduced via generic examples of the optical vortex and circular vortex beams. The review describes approaches for generation and diagnostics of different singular networks and underlines the role of singularities in formation of optical field structures. The mechanical action of structured light fields on material objects is discussed on the base of the spin-orbital (canonical) decomposition of electromagnetic momentum, expressing the special roles of the spin (polarization) and spatial degrees of freedom. Experimental demonstrations spectacularly characterize the topological nature and the immanent rotational features of the light-field singularities. The review is based on the results obtained by its authors with a special attention to relevant works of other researchers.

Research Institute of Zhejiang University–Taizhou, Taizhou, China, Correlation Optics Department, College of Engineering, Chernivtsi National University, Chernivtsi, Ukraine, Physics Research Institute, Odessa I.I. Mechnikov National University, Odessa, Ukraine, DTU Fotonik, Department of Photonics Engineering, Roskilde, Denmark, Institute of Physics, National Academy of Sciences of Ukraine (NAN Ukraine), Kyiv, Ukraine, Heriot-Watt University Edinburgh, Edinburgh, United Kingdom

We report the results of an experimental study of polymer bulk material Polyamide-6 luminescence properties. A new effect of persistent time-delayed luminescence was revealed at room temperature. Detailed inspection of the effect has shown strong dependence on the microscopic crystalline structure of the polymer. Two morphological forms were recognized with the aid of X-ray Bragg reflection treating. The afterglow with the decay time exceeding 10 seconds was found to appear at about 150 K for the γ-form and is observed at room temperature for the α- form. The temporal dependence of time-delayed luminescence was found to satisfy hyperbolic Becquerel law, thus indicating the recombination origin of the effect. Also, emission realized with the excitation by third optical harmonics of a femtosecond Ti:Sapphire laser (267 nm) at room temperature was examined. The registered luminescence spectra were found quite different for these forms. While γ-form samples exhibit spectrum at the visible region, the α-form emits a pronounced luminescence output in the near UV (340 nm).

We report on the effects associated with photonic nanojet (PNJ) formation under illumination of a metallic spherical particle with a focused light beam with polarization singularity. Owing to radial polarization, the strongly focused beam generates the on-axis localized structure of intensity in the shadow area of the metal scatterer of different sizes, from the Rayleigh particle to microbeads. Significant amplification factor, small transverse size, and zero magnetic component on the axis and longitudinal polarization of the electric field are the distinctive features of such structures.

Wave propagation in metamaterials with different structure scales is analyzed with account of nonlinear effects. We introduce topological nonlinearity and magnetooptical control over nonlinear strongly localized bullet-like structures with phase singularities.

We report the experiments aimed at controlling the position of linear topological defect (disclination) in a so-called  -cell filled with a nematic liquid crystal sandwiched between circularly rubbed polyimide (Kapton) layer and photoaligning PVCN material oriented unidirectionally.To satisfy surface-alignment conditions, the director within this cell experiences a twist.The topological defect appears in a plane where the twist angle of the director becomes indeterminate (90º).In an achiral liquid crystal, orientation of the disclination coincides with the alignment occurring on the unidirectionally oriented substrate.The idea of this work is to control the alignment direction on the substrate by a polarized ultraviolet light.Photo-induced director reorientation on the substrate changes the twist angle in the bulk and so varies the azimuthal angle of the disclination.We monitor reorientation of the disclination as a function of light-polarization angle and irradiation dose.

Both transmission and reflection of a short light pulse are considered for a double prism system in the geometry of in-gap refraction with an account of material dispersion. Within a frame of linear optics and Snell refraction law, we revealed the effect of a ‘negative dispersion’ regime close to the total internal reflection. A narrow area of parameters (wave number and angle of incidence) in the close vicinity of the total internal reflection is found to possess specific properties for the refracted field. A resonance excitation of leaky waveguide modes enables to extract the refracted field from the gap efficiently and inspect various transmission regimes. Analytical consideration and simulations demonstrate an appearance of advanced pulse in the transmitted and reflected waveforms, with the temporal shape depending on a number of modes enclosed in a spectral width of an incident pulse as well as the existence of elongated precursor within a gap.

Over 30 years ago a simple laboratory tool for optical-vortex beams generation was reported as a synthesized ‘forked’ diffraction grating. We renew the issue, addressing specific properties of such a grating in the sense of geometrical transformation of the grating shape. Stretching or compressing the grating scale results in the astigmatic optical vortex appearance in the first diffraction order. In the case of the induced vortex topological charge higher than unity, the astigmatism forces the optical vortex to separate into a line of unity-charged vortices. The initial splitting occurs along an azimuth angle, depending on the topological charge of the vortex. We show the rotation of the pattern in the free space propagation in simulations and analytical consideration.

We report on the observation of time-delayed luminescence of bulk Polyamide-6 polymer material under the room temperature and liquid nitrogen temperature conditions. The excitation was taken from low power diode laser operating at the wavelength 407 nm. The afterglow duration amounts up to several seconds and the decay function was found to coincide with the Becquerel hyperbolic law. The conclusion that we have made with account of the results obtained is the charge-recombination origin of this effect.

The Bragg diffraction in synthetic opal as a 3D photonic crystals has been analyzed using the weak disorder model in various approximations. For a one-domain crystal, the photonic bandgap is calculated in the regime of reflection along the 〈111〉 axis. In the multidomain case, a considerable expansion of the photonic bandgap, the emergence of asymmetry, and the photon band shift to the short-wavelength region are demonstrated. The results are compared with experimental dependences.

Soft material templating is a promising approach for assembling and manipulating nanoparticles structures. Due to the high sensitivity of soft matter systems to external stimuli, such composite materials exploit the soft surrounding medium to move or to reconfigure nano-structures or nano-objects as well as to tune their own properties. The use of topological defects in anisotropic fluids has been recently reported. Here, arrays of defect lines are created in planar-periodic nematic liquid crystal cells, wherein the nematic director undergoes static twist deformations separated by topological defects. Trapping and manipulation of the nanoparticles in disclinations are demonstrated and investigated by confocal fluorescence microscopy exploiting quantum dots. Nanoparticles gathering is observed during electrically controlled switching from orientational topological walls to disclinations. The external field is also used to perform displacement and deformation of the nanoparticles arrays, as well as their dynamical assembling and disassembling. The reported results substantiate the opportunities offered by defects architectures in anisotropic fluids as a successful bottom-up approach that enables versatile assembling and remote control of nanoparticles.

Diffraction of a linearly polarized plane wave and two counterpropagating orthogonally polarized plane waves by a spherical particle is considered. The influence of the particle translation on the far-field complex amplitude of the scattered wave is discussed. The possibility is shown to select symmetric directions of observation, in which the phase shift of a scattered wave depends the only on particle coordinate. All conclusions are generic as based on a symmetry only. The results can be useful for a new direct-measurement particle position detector engineering with high sensitivity and speed of response.

We report the results of an experimental study of the temporal response of the artificial opal luminescence excited by UV pulses from a nitrogen laser at room temperature, liquid-nitrogen temperature, and in the intermediate range. While the response time does not exceed 15 ns at room temperature, the afterglow at liquid-nitrogen temperature was detected with a decay time of about 700 ms. We have revealed that the afterglow appears suddenly with just millisecondrange duration at a definite temperature of 130± 5 K. The temperature dependence of the afterglow is of importance for the explanation of surprising effects of the stimulated emission in a single nano-sized SiO2 globule and the second harmonic generation in the material at liquid-nitrogen temperature.