Dark-ring cavity solitons in lasers

This paper demonstrates theoretically an alternative way for exciting cavity solitons (CSs) in lasers based on the injection of a resonant bichromatic signal into the laser cavity operating above lasing threshold. Differently from the previously suggested laser CSs, the ones presented here are based on the development of two dynamically equivalent laser field phases differing by π. Hence the reported CSs belong to the class of dark-ring cavity solitons, in which a bright spot with a definite phase is surrounded by an oppositely phased, spatially uniform light distribution, both phases being separated by a dark ring. These phases appear when the laser emission frequency locks halfway between the two injected signal components. This phase selection can be understood as a result of the competition between a (phase sensitive) resonant, degenerate four-wave mixing process, in which two injected photons (one of each signal component) are converted into two equal laser photons, and the usual (phase insensitive) stimulated emission process of free running lasers.