Optical vortex solitons in parametric wave mixing

We analyze two-component spatial optical vortex solitons supported by param etric wave mixing processes in a nonlinear bulk medium. We study two distin ct cases of such localized waves, namely, parametric vortex solitons due to phase-matched second-harmonic generation in an optical medium a with compe ting quadratic and cubic nonlinear response, and vortex solitons in the pre sence of third-harmonic generation in a cubic medium. We find, analytically and numerically, the structure of two-component vortex solitons, and also investigate modulational instability of their plane-wave background. In par ticular, we predict and analyze in detail nor el types of vortex solitons, a " halo-vortex,'' consisting of a two-component vortex core surrounded by a bright ring of its harmonic held, and a "ring-vortex" soliton which is a vortex in a harmonic field that guides a ring-like localized mode of the fu ndamental-frequency field.