Optical vortex solitons in parametric wave mixing

We analyze two-component spatial optical vortex solitons supported by parametric wave mixing processes in a nonlinear bulk medium. We study two distinct cases of such localized waves, namely, parametric vortex solitons due to phase-matched second-harmonic generation in an optical medium a with competing quadratic and cubic nonlinear response, and vortex solitons in the presence 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 particular, 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 fundamental-frequency field.