Stable vortex rings due to parametric wave mixing

Summary form only given. Since the pioneering experimental results of optical vortex solitons have been in the centre of interest because of their fundamental importance in optics and other fields of physics, and because of their potential applications for all-optical information processing. Formally conventional vortex solitons exist on an infinite nonzero background, which in practice requires rather large beam sizes for vortex observation. A possible solution to this problem is the use of ring solitons-vortices imprinted in bright (i.e., localised) self-guided beams. Unfortunately, recent studies have shown that both for materials with purely quadratic or purely cubic (Kerr) nonlinearities ring solitons are always unstable. A solution to this problem, in turn, could be in using optical media with a cubic-quintic nonlinear response which however represents a very special material situation and also requires very high optical intensities. In this work we suggest a realistic physical model which can support stable ring solitons as a result of parametric wave mixing in optical media with both quadratic and cubic nonlinearities.