Optical vortices crystals: Spontaneous generation in nonlinear semiconductor microcavities

Broad-area, vertical-cavity surface-emitting lasers were shown to switch their emission mode from the regular single or multilobed light fields to exhibit complex arrays of 'dark beams.' Examination of these dark spot arrays revealed that they consist of multiple, closely packed optical vortices: optical fields that have phase singularities and show increase complexity as the injection current level is raised. Contrary to their complex appearance, most of these light distributions are not the result of a multimode (multiple-frequency) operation but exhibit single-frequency characteristics. The dark beam patterns can be described as emanating from a spontaneous process of transverse mode locking of nearly degenerate modes, assisted by the laser nonlinearity. Surprisingly, these patterns show high resemblance to patterns generated in other nonlinear scenarios that are completely different both in scale and in mechanism.