Abstract

Degenerate four-wave mixing oscillators are phase-bistable cavities. In such systems, above the oscillation threshold, two equivalent states, of equal intensities but opposite phases are generated. This phase bistability extends over the whole range of stable emission, unlike the intensity bistability (in, e.g. a saturable absorber cavity) that exits in a limited range of injection. When the cavity Fresnel number is large different patches of the beam transverse section can have different phases and a pattern forms. Basic patterns here are phase fronts (or domain walls), which are 1D structures separating regions with opposite phase that manifest as dark lines (as the phase jumps by π across the wall), phase domains, labyrinths, rolls, hexagons, and phase solitons [1]. This behaviour contrasts with that of phase-invariant optical cavities (like in the laser or in a nondegenerate photorefractive oscillator). As no preferred phase exists the basic pattern is the optical vortex (a phase singularity at which the field intensity is null and around which the field phase rotates by 2π) [1].

© 2011 IEEE