By means of systematic simulations we demonstrate generation of a variety of ring-shaped optical vortices (OVs) from a two-dimensional input with embedded vorticity, in a dissipative medium modeled by the cubic-quintic complex Ginzburg-Landau equation with an inhomogeneous effective diffusion (spatial-filtering) term, which is anisotropic in the transverse plane and periodically modulated in the longitudinal direction. We show the generation of stable square-and gear-shaped OVs, as well as tilted oval-shaped vortex rings, and string-shaped bound states built of a central fundamental soliton and two vortex satellites, or of three fundamental solitons. Their shape can be adjusted by tuning the strength and 2 modulation period of the inhomogeneous diffusion. Stability domains of the generated OVs are identified by varying the vorticity of the input and parameters of the inhomogeneous diffusion. The results suggest a method to generate new types of ring-shaped OVs with applications to the work with structured light.
IntroductionIn the course of the past three decades, a great deal of interest was drawn to theoretical and experimental studies of the existence, stability, and excitation of localized patterns in optical and matter-wave media [1][2][3][4][5][6][7][8][9][10][11][12][13]. This work has produced many findings for temporal, spatial, and spatiotemporal solitons in both conservative and dissipative media, which offer applications to all-optical switching, pattern recognition, parallel data processing, and for guiding light by light. In particular, the cubic-quintic complex Ginzburg-Landau (CGL) equation [14,15] is a generic nonlinear model that predicts the generation of a plethora of temporal, spatial, and spatiotemporal patterns due to the simultaneous balance of gain and loss, and of self-focusing nonlinearity and either diffraction or dispersion (or both of them). The cubic-quintic CGL equation is an adequate model in diverse fields, such as superconductivity and superfluidity, fluid dynamics, reaction-diffusion phenomena, nonlinear photonics, matter waves (Bose-Einstein condensates), quantum field