Kelvin-Helmholtz instability in nonlinear optics

Paraxial propagation of a quasi-monochromatic light wave with two circular polarizations in a defocusing Kerr medium with anomalous dispersion inside a waveguide of annular cross-section was considered. In the phase-separated mode, the dynamics is similar to a flow of immiscible fluids. For some initial conditions with relative gliding of the fluids along the interface, the Kelvin-Helmholtz instability in its ``quantum'' variant is developed. Numerical simulations of the corresponding coupled nonlinear Schr\"odinger equations have shown formation of specific structures at the nonlinear stage of the instability. Similar structures have been known in the theory of binary Bose-Einstein condensates, but for optics they were presented for the first time.