Spatial coherence singularities and incoherent vortex solitons

We study spatially localized optical vortices created by self-trapping of partially incoherent light with a phase dislocation in a biased photorefractive crystal. In contrast to a decay of coherent self-trapped vortex beams due to the azimuthal modulational instability, the incoherent vortices are stabilized for large values of the spatial incoherence; this was confirmed by experiment. We analyze the spatial coherence properties of the incoherent optical vortices and reveal the existence of ringlike singularities in the spatial coherence function of a vortex field that can characterize the stable propagation of vortices through nonlinear media.