Construction of special multi-mode annular optical vortex

Multiple-charged optical vortex solitons (OVSs) are generated in a thermal nonlinear medium with saturation. The respective soliton constants are found to be linearly proportional to the topological charges. The linear stability analysis and the numerical simulations indicate a rich variety of instability scenaria depending on the type of perturbation. The saturation of the nonlinearity is shown to be able to slow down the decay of multiple charged dark beams at an intermediate evolution stage and to prevent their ultimate decay into charge-one OVSs. This concept is experimentally verified by the experimental observation of a partial decay of a triple- charged optical vortex beam.

Radially polarized hollow Gaussian beam with on-axis spiral optical vortex

The observation of confinement and guiding of light induced by an optical vortex soliton (OVS) in a cubic-quintic (defocusing-focusing) medium is reported. The waveguide effect induced by the bright region of the vortex beam, is mainly due to the defocusing nonlinearity that allows the guiding of a probe beam propagating inside of the OVS dark region. The experimental results are corroborated by numerical simulations based on the cubic-quintic nonlinear Schrödinger equation, showing excellent agreement.

When a spatially-inhomogeneous few-cycle vortex laser interacting with quantum wells, besides the general odd-order harmonics occur, unusual "even-order" ones can be found, which are clarified to possess even orders, however their topological charge numbers are not consistent with those predicted from the vortex transformation criterion (i.e., topological charge number should be directly proportional to its harmonic order for any a harmonic). The origin is the broader spectral width of odd-order harmonics tails at the positions of even-order harmonics due to the short-duration pulse excitation, whose contribution overwhelms the spatial-inhomogeneity degree.

Self-trapping of light beams in nonlinear self-focusing Kerr media has been explored intensively during the last three decades. The self trapped beams, often in the form of spatial solitons, evolve from nonlinear changes in the refractive index (δn) of the material proportional to the intensity distribution of the light, when the confining effect of the refractive index exactly compensates for the defocusing effect of diffraction. Motivated by experimental results of self-focusing of light beams [1] in the presence of the optical Kerr effect, a theoretical solution for the resulting spatial solitons was found [2,3]. This was followed by demonstrations of self-trapping in vapors [4], liquids [5], and finally, in the last few years, spatial solitons in solid (glass) media [6]. However, the index changes needed for optical-Kerr spatial solitons require high intensities, often exceeding 1 MWatt/cm2. Several other materials, such as slightly-absorbing liquids, exhibit Kerr-like thermal nonlinearities at much lower power densities (Watts/cm2), typically with a negative δn. These materials enabled the observations of dark spatial solitons [7] (narrow dark “notches”) and optical vortex solitons [8,9] (dark solitons were also observed using optical-Kerr nonlinearities in ZnSe [10] at GWatt/cm2 power densities). The most distinct properties of all these Kerr-like solitons are (i) a strong intensity dependence and the existence of a power threshold, and (ii) stability of bright solitons only in a single transverse dimension (consequently, bright Kerr-type solitons can be observed only in a planar waveguide, otherwise the soliton becomes unstable and cannot be observed).KeywordsDark SolitonInput BeamBright SolitonSpatial SolitonPhotorefractive CrystalThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The interactions between electromagnetic (EM) waves and Kerr nonlinear media result in various appealing phenomena, including self-focusing, optical vortex soliton, etc. However, existing numerical methods for resolving Kerr nonlinearities demand multiple iterations or solutions to a huge number of cubic equations in each time advance, thus hardly achieving the optimal trade-off between accuracy and efficiency. In this article, an explicit non-iterative discontinuous Galerkin time-domain (DGTD) method is proposed for transient EM analysis involving Kerr media. The proposed method can be seamlessly integrated into the widely adopted Runge-Kutta-DGTD (RK-DGTD) method. The essence is the deliberate evaluation of the incremental electric field intensity, during which the only approximation required is to replace the current electric field intensity with that at the previous intermediate time instant of the RK scheme, so that implicit or iterative time stepping can be avoided. In addition, in regions with strong nonlinear effects or fine geometry, the computational burden is exacerbated by local fine meshes and the resultant tiny time-step size. Therefore, the local time-stepping (LTS) technique is further introduced to improve computational efficiency. Numerical results demonstrate that the proposed method can achieve high accuracy similar to those of Newton’s iterative method and direct method with the cubic formula, and consume roughly the same short execution time as that of the conventional explicit non-iterative method.

We introduce the concept of soliton clusters--multisoliton bound states in a homogeneous bulk optical medium--and reveal a key physical mechanism for their stabilization associated with a staircaselike phase distribution that induces a net angular momentum and leads to cluster rotation. The ringlike soliton clusters provide a nontrivial generalization of the concepts of two-soliton spiraling, optical vortex solitons, and necklace-type optical beams.

Nonlinear optical processes of spatially structured light such as optical vortices and vector optical fields have exhibited many interesting physical effects and found a variety of important applications from classical to quantum regimes. However, high-harmonic generation of a vector optical field with a space-varying polarization state is still a challenge. Here we present a solution to realize third-harmonic generation of spatially structured light including vector optical fields in a nonlinear Sagnac interferometer containing only one carefully designed quasi-periodically poled potassium titanyl phosphate, for the first time, to our knowledge. The experimental results well confirm our theoretical predictions. Our results will enable to manipulate spatially structured light or photons carrying higher orbital angular momentum at new wavelengths. Our scheme has potential applications such as in optical skyrmions and may open up new opportunities to produce spatially structured entangled photons for quantum communication and computation.

An optical vortex appears as a black circular spot surrounded by bright illumination in the transverse cross-section of a light beam. This phenomenon is attributed to the phase of the beam, which twists like a spiral stair-case, along the optical axis. In fact, this field is a well known mode in both waveguide and scattering theory, and is given in cylindrical coordinates. As will be shown, there are simple methods of producing such linear waves. In self-defocusing nonlinear refractive media, the refractive index is greatest where the intensity is zero, e. g., in the center of an optical vortex.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This study investigates the wave structures and qualitative assessment of a two-dimensional vector nonlinear Schrödinger equation (2D VNLSE) that occurs in Bose–Einstein condensates (BECs) and nonlinear optics. We convert the vector PDE form into two linked scalar PDEs to yield optical vortex structures of the governing model. We create different optical soliton solutions using the Kudryashov and the sine-Gordon expansion methods. We present their 3D, 2D, and density maps to allow for a comprehensive and understandable representation of their underlying physical patterns. Furthermore, we assess the system’s qualitative behavior by analyzing its obvious characteristics, such as modulation instability, sensitivity, bifurcation, and chaos detection, and we give accompanying illustrations to support our conclusions. This study’s accomplishment allows researchers to examine the dynamics and growth of optical solitons and vortices in nonlinear systems in greater detail, which opens up important possibilities with broad significance in many scientific and technological fields.

Investigated in this paper is the interaction of light and the nanospheres composed by a dielectric core with a gold-shell cladding that causes the optical vortices inside the core and the whirlpools around the shell. Different radius ratios, dimensions and the dielectric functions of nanospheres were studied using the finite-difference time-domain method. It was found that optical vortices were most likely to occur in the regions of increased absorption cross section and reduced scattering cross section. Two optical vortices of the opposite polarity, each centered in one of the particles of a dimer are created by a nanoshell dimer. The surrounding media of a nanoshell with different dielectric functions can be used to affect the energy flows generated by core-shell nanospheres.

Formation of optical vortices with topological charge [formula omitted] and [formula omitted] by use of the S-waveplate

The formation of optical vortices in optical fibres is studied. Speckle patterns of optical fibres produced due to the interference of guided modes and optical vortices are simulated. The spatial statistical characteristics of speckle structures are obtained. It is shown that speckle structures, formed by the radiation of optical vortices rotating in the same direction, have the characteristic azimuthal angular dimensions of spots that are considerably larger than their axial size, whereas speckle patterns, formed by vortices rotating in the opposite directions, do not virtually differ from speckles produced due to the interference of usual guided modes. A method is proposed to distinguish speckles produced by optical vortices rotating in the same direction from speckles formed by usual guided modes with the predominant excitation of modes with comparatively small azimuthal indices. A comparison with experimental data is performed.

We study theoretically the non-phase-matched degenerate four-wave mixing of type &omega;_s = 2&omega;₁ &omega;&omega;₂ , involving beams carrying two-dimensional spatial phase dislocations in the form of singly-charged optical vortices (OVs). Accompanying third-order nonlinear processes in the non-resonant nonlinear medium (NLM), which are accounted for, are self- and cross-phase modulation. In the case of pump OV beams with identical topological charges the model predicts the generation of signal beams carrying OVs of the same charge. If the pump beams carry OVs with opposite charges, the generated signals are predicted to carry triply charged vortices which, in the case of a nonnegligible initial free-space propagation from the plane of vortex generation to the NLM, decay inside the NLM into three singly-charged vortices with highly overlapping cores.

Optical intensity distributions in the focal region play an important role in many optical systems. In this paper, the tunable focusing properties of linearly polarized hyperbolic-cosine-Gaussian beams with sine-azimuthal variation wavefront were investigated by adding a spiral optical vortex. It was found that the focal patterns can be altered very considerably by changing the charge number of the optical vortex under a different phase parameter that indicates the phase change frequency upon increasing the azimuthal angle. The symmetry of focal patterns also changes remarkably upon increasing the charge number. And some novel focal patterns may appear, including a multiple-peak array, wheel focal pattern, or swallow-tailed focal pattern.