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. Here, we present the first experimental demonstration of nonlinear wavefront shaping with three-dimensional (3D) NPCs formed by ultrafast-light-induced ferroelectric domain inversion approach. Compared with those previously used low-dimensional structures, 3D NPCs provide all spatial degrees of freedom for the compensation of phase mismatch in nonlinear interactions and thereby constitute an unprecedented system for the generation and control of coherent light at new frequencies.
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. Here we report on spatial solitons in bulk NLCs with no lateral anchoring, where the application of an external magnetic field effectively controls the direction of propagation and the angular steering of the self-trapped wavepackets. Our results entail a completely new approach to the routing of self-localized beams and light-induced waveguides in three dimensions, without the usual limitations imposed by transverse boundary conditions.
Singularities, i.e. places of discontinuity of physical parameters are extremely general objects appearing in both stationary and wave processes. They commonly occur in purely coherent, highly ...directional electromagnetic waves, such as laser beams, determining additional spatial or 'topological' properties of the beams independently of their propagational dynamics. For instance, a helicoidal structure of the wavefront curved around a line of undefined phase, so-called phase singularity, adds an orbital degree of freedom to electromagnetic waves. The phase singularities are typical to all types of scalar and one-component vectorial waves where the wave field can be defined only by intensity and phase distributions in space and time. The situation becomes more complex when the electromagnetic wave, as a vectorial object, depends in a different way on coordinates in its field components. This leads to a nonuniform field pattern containing singular points of an undefined instantaneous orientation of the electromagnetic field. In contrast to the phase singularities in a scalar wave, the points of instantaneous field (IF) singularities can be completely isolated by surrounding fields in 3D space at any fixed moment of time. Here we present a systematic description of the IF singularities of the electromagnetic waves in a paraxial approximation. Based on the IF distributions around the singularities, we provide a general qualitative classification of the wave beams. We also detail some of the common types of singularities where the transverse components of electric and magnetic fields have a form of the field sources and show the compensation mechanism of such vectorial field distributions by the longitudinal field components.
We show that focusing a laser light onto the boundary between antiparallel ferroelectric domains leads to the non-collinear generation of two second harmonic (SH) beams. The beams are emitted in a ...plane normal to the domain boundaries at the angles that satisfy the Cerenkov-type phase matching condition. Moreover, these beam disappear when the laser light is focused on a homogenous part of a single domain. We utilize this effect for 3-dimensional visualization of fine details of the ferroelectric domain pattern with a submicron accuracy.
Abstract
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. Those small rods are spatially arranged in such a way that, according to effective medium theory, the refractive index of this internal structure is constant in the radial direction and linearly changes following azimuthal angle. Numerical results demonstrated that a nanostructured vortex phase mask with a thickness of 19 μm can convert Gaussian beams into fundamental optical vortices over 290 nm wavelength bandwidth from 1275 to 1565 nm. This has been confirmed in experiments using three diode laser sources operating at 1310, 1550, and 1565 nm. The generation of vortex beams is verified through their uniform doughnut-like intensity distributions, clear astigmatic transformation patterns, and spiral as well as fork-like interferograms. This new flat-surface component can be directly mounted to an optical fiber tip for simplifying vortex generator systems as well as easier manipulation of the generated OVB in three-dimensional space.
We suggest a novel approach in all-optical trapping employing a photophoretic force for manipulation of absorbing particles in open air. We demonstrate experimentally the robust three-dimensional ...guiding, over the distances of a few millimeters, of agglomerates of carbon nanoparticles with the size spanned from 100 nm to 10 microm, as well as their acceleration up to velocities of 1 cm/sec. We achieve stable positioning and guiding of particles as well as simultaneous trapping of a large number of particles in a dual-beam optical trap created by two counter-propagating and co-rotating optical vortex beams.
Abstract
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. Along these lines, we provide a consistent thermodynamic methodology for both controlling and maximizing the unidirectional power flow in the topological edge states. This can be achieved by either employing cross-phase interactions between two subsystems or by exploiting self-heating effects in disordered or Floquet topological lattices. Our results indicate that photonic topological systems can in fact support robust photon transport processes even under the extreme complexity introduced by nonlinearity, an important feature for contemporary topological applications in photonics.
PDF
