New results on ring dark solitons

Summary form only given. Ring dark solitons correspond to phase domains with radial symmetry and minimum size, surrounded by a domain wall where the field intensity vanishes, and are where the phase difference between field inside and outside the ring is /spl Delta//spl phi//spl ap//spl pi/. Such localised states usually exist in physical systems described by a real order parameter, where two values of the phases are preferred. A representative optical system showing this property is the degenerate optical parametric oscillator. These solutions have been extensively investigated recently. We report here the influence that several factors have on their existence and stability conditions.