Broadband optical vortex beam generation using flat-surface nanostructured gradient index vortex phase masks.

We developed a new kind of compact flat-surface nanostructured gradient index vortex phase mask, for the effective generation of optical vortex beams in broadband infrared wavelength range. A low-cost nanotechnological material method was employed for this work. The binary structure component consists of 17,557 nano-sized rods made of two lead-bismuth-gallium silicate glasses which were developed in-house.

Nonlinear generation of an optical bottle beam in domain-engineered ferroelectric crystals.

Nonlinear wavefront shaping in periodically poled ferroelectric crystals has received great attention because it offers a convenient way to generate a structured light beam at new frequencies. In contrast to structurally uniform beams like Laguerre-Gaussian or Hermite-Gaussian modes, here we demonstrate the possibility to generate a spatially varied optical bottle beam via a frequency doubling process in a domain-engineered SrBaNbO (SBN) crystal. The nonlinear holography method was employed to design the modulation pattern of the second-order nonlinear coefficient χ, and the femtosecond laser poling was used to imprint the χ pattern into the SBN crystal via ferroelectric domain inversion.

Asymmetric wavefront shaping with nonreciprocal 3D nonlinear detour phase hologram.

Asymmetric control of light with nonlinear material is of great significance in the design of novel micro-photonic components, such as asymmetric imaging devices and nonreciprocal directional optical filters. However, the use of nonlinear photonic crystals for asymmetric optical transmission, to the best of our knowledge, is still an untouched area of research. Herein we propose the 3D nonlinear detour phase holography for realizing asymmetric SH wavefront shaping by taking advantage of the dependence of the SH phase on the propagation direction of the excitation beam.

Ferroelectric domain engineering with femtosecond pulses of different wavelengths.

Direct femtosecond laser writing of ferroelectric domain structures has been an indispensable technique for engineering the second-order optical nonlinearity of materials in three dimensions. It utilizes localized thermoelectric field motivated by nonlinear absorption at the position of laser focus to manipulate domains. However, the impact of laser wavelengths, which is pivotal in nonlinear absorption, on the inverted domains is still sketchy.

Transmission of an optical vortex beam in antiresonant fibers generated in an all-fiber system.

We report an experimental study on transmission of orbital angular momentum mode in antiresonant fibers generated with a dedicated all-fiber optical vortex phase mask. The vortex generator can convert Gaussian beam into vortex beams with topological charge l = 1. Generated vortex beam is directly butt-coupled into the antiresonant fiber and propagates over distance of 150 cm.

Effect of spatial variation of the duty cycle in transverse second-harmonic generation.

Transverse second-harmonic generation, in which the emission angles of the second harmonic are determined by the spatial modulation of the quadratic nonlinearity, has important applications in nonlinear optical imaging, holography, and beam shaping. Here we study the role of the local duty cycle of the nonlinearity on the light intensity distribution in transverse second-harmonic generation, taking the generation of perfect vortices in periodically poled ferroelectric crystal as an example. We show, theoretically and experimentally, that spatial variations of the nonlinearity modulation must be accompanied by the corresponding changes of the width of inverted ferroelectric domains, to ensure uniformity of the light intensity distribution in the generated second harmonic.

Thermal control of the topological edge flow in nonlinear photonic lattices.

The chaotic evolution resulting from the interplay between topology and nonlinearity in photonic systems generally forbids the sustainability of optical currents. Here, we systematically explore the nonlinear evolution dynamics in topological photonic lattices within the framework of optical thermodynamics. By considering an archetypical two-dimensional Haldane photonic lattice, we discover several prethermal states beyond the topological phase transition point and a stable global equilibrium response, associated with a specific optical temperature and chemical potential.

Quasi-phase matched second harmonic generation in a PMN-38PT crystal.

We used an all-optical poling method to fabricate quadratic nonlinearity gratings in a tetragonal 0.62Pb(MgNb)O-0.38PbTiO (PMN-38PT) crystal.

Near-infrared photobiomodulation of blood reversibly inhibits platelet reactivity and reduces hemolysis.

Photobiomodulation (PBM) in the red/near-infrared (R/NIR) spectral range has become widely recognized due to its anti-inflammatory and cytoprotective potential. We aimed to assess the effects of blood PBM on platelets function and hemolysis in an in vitro setting. Porcine blood samples were separated into four aliquots for this study, one of which served as a control, while the other three were subjected to three different NIR PBM dosages.

Scalar and vector supermode solitons owing to competing nonlocal nonlinearities.

We investigate scalar and vector multi-hump spatial solitons resulting from competing Kerr-like nonlinear responses excited in a nonlocal medium by either one or two (mutually incoherent) light beams. Two-color vector supermode solitons are more amenable to control but exhibit an intriguing form of spontaneous symmetry breaking in propagation.

Nonlinear detour phase holography.

Nonlinear photonic crystals are capable of highly efficient nonlinear wavefront manipulation, providing a promising platform for compact and large-scale integrated nonlinear devices. However, the current nonlinear encoding methods for nonlinear photonic crystals inherently require a number of disordered and complex microstructures, which are quite challenging in a real fabrication process. Herein we propose and experimentally demonstrate a nonlinear detour phase method for nonlinear wavefront manipulation in nonlinear photonic crystals.

Formation and stability of vortex solitons in nematic liquid crystals.

We study the propagation dynamics of bright optical vortex solitons in nematic liquid crystals with a nonlocal reorientational nonlinear response. We investigate the role of optical birefringence on the stability of these solitons. In agreement with recent experimental observations, we show that the birefringence-induced astigmatism can eventually destabilize these vortex solitons.

Numerical analysis of optical vortices generation with nanostructured phase masks.

We study the theoretical formation of optical vortices using a nanostructured gradient index phase mask. We consider structures composed of spatially distributed thermally matched glass nanorods with high and low refractive indices. Influence of effective refractive profile distribution, refractive index contrast of component glasses and charge value on the quality of generation of vortices are discussed.

Nonlinear wavefront shaping with optically induced three-dimensional nonlinear photonic crystals.

Generation of coherent light with desirable amplitude and phase profiles throughout the optical spectrum is a key issue in optical technologies. Nonlinear wavefront shaping offers an exceptional way to achieve this goal by converting an incident light beam into the beam (or beams) of different frequency with spatially modulated amplitude and phase. The realization of such frequency conversion and shaping processes critically depends on the matching of phase velocities of interacting waves, for which nonlinear photonic crystals (NPCs) with spatially modulated quadratic nonlinearity have shown great potential.

Anomalous interaction of spatial solitons in nematic liquid crystals.

We study experimentally the interaction of mutually incoherent bright spatial solitons in dye-doped nematic liquid crystals (LCs). The dye-induced light absorption results in a complex nonlinear optical response of the LC having spatially nonlocal focusing and defocusing contributions. The competition between both nonlinearities leads to the separation-dependent soliton interaction with repulsion of distant and attraction of closely placed solitons.

Nonlinear propagation and quasi self-confinement of light in plasmonic resonant media.

We study nonlinear propagation of light in colloidal suspension of metallic nanoparticles, in the regime of particles surface plasmon resonance. We show that the propagation exhibits features typical for purely defocusing media and the observed spatial confinement is not a real self-trapping, as for solitons, but rather than is caused by the phase modulation of the beam via nonlocal defocusing nonlinearity. We also show that the light-induced refractive index change in the suspension leads to stabilization of structured light beams.

Broadband enhancement of Čerenkov second harmonic generation in a sunflower spiral nonlinear photonic crystal.

We present an experimental study on the Čerenkov second harmonic emission in a novel sunflower spiral array of ferroelectric domains in LiNbO crystal. The spiral patterns offer a diffusive, circularly symmetric distribution of reciprocal lattice vectors, thereby enabling enhanced emission of the Čerenkov beam in a broad spectral range. Instead of the traditional electric field poling, the sunflower spiral patterns are fabricated here by using our pioneering method of ferroelectric domain engineering with ultrafast light.

Breather solutions of a fourth-order nonlinear Schrödinger equation in the degenerate, soliton, and rogue wave limits.

We present one- and two-breather solutions of the fourth-order nonlinear Schrödinger equation. With several parameters to play with, the solution may take a variety of forms. We consider most of these cases including the general form and limiting cases when the modulation frequencies are 0 or coincide.

Formation of optical vortices with all-glass nanostructured gradient index masks.

We report the development of microscopic size gradient index vortex masks using the modified stack-and-draw technique. The vortex mask has a form of flat surface all-glass plate. Its functionality is determined by an internal nanostructure composed of two types of soft glass nanorods.

Semi-analytical approach to supermode spatial solitons formation in nematic liquid crystals.

We study light propagation in nematic liquid crystals in the context of spatial optical solitons formation. We propose a simple analytical model with multiplicative nonlinearity, which represents (qualitatively) the liquid crystal response by comprising the competition between focusing (reorientational) and defocusing (thermal) nonlocal nonlinearities. We show that at sufficiently high input power the interplay between both nonlinearities leads to the formations of two-peak solitons, which represent supermodes of the self-induced extended waveguide structure.

Breather-to-soliton transformation rules in the hierarchy of nonlinear Schrödinger equations.

We study the exact first-order soliton and breather solutions of the integrable nonlinear Schrödinger equations hierarchy up to fifth order. We reveal the underlying physical mechanism which transforms a breather into a soliton. Furthermore, we show how the dynamics of the Akhmediev breathers which exist on a constant background as a result of modulation instability, is connected with solitons on a zero background.

Magnetic routing of light-induced waveguides.

Among photofunctional materials that can be employed to control the propagation of light by modifying their properties, soft dielectrics such as nematic liquid crystals (NLCs) stand out for their large all-optical response. Through reorientation, the molecular distribution of NLCs can be modified by the electric field of light, permitting functional operations and supporting self-localized light beams or spatial optical solitons. To date, the generation and routing of such solitons have been limited by the boundary conditions employed to tailor the properties of NLCs in planar cells or capillaries.

Enhanced fourth harmonic generation via nonlinear Čerenkov interaction in periodically poled lithium niobate crystal.

We introduce a custom-cut periodically poled ferroelectric crystal for the phase matching of multistep cascading frequency conversion processes. Our approach involves combination of collinear second harmonic generation and transverse sum frequency mixing via the total internal reflection of the fundamental and collinear second harmonic beams. As a proof of concept we demonstrate multiple frequency generation with an enhanced fourth harmonic signal in a one-dimensional periodically poled LiNbO crystal.

Quasi-phase matching via femtosecond laser-induced domain inversion in lithium niobate waveguides.

We demonstrate an all-optical fabrication method of quasi-phase matching structures in lithium niobate (LiNbO) waveguides using a tightly focused femtosecond near-infrared laser beam (wavelength of 800 nm). In contrast to other all-optical schemes that utilize a periodic lowering of the nonlinear coefficient χ by material modification, here the illumination of femtosecond pulses directly reverses the sign of χ through the process of ferroelectric domain inversion. The resulting quasi-phase matching structures, therefore, lead to more efficient nonlinear interactions.