Spiral waves in a class of optical parametric oscillators

The formation of three-armed rotating spiral waves is shown to occur in a spatially extended nonlinear optical system with broken phase invariance. These new spatial structures are found in the mean-field model of a class of optical parametric oscillators (3→ω2ω+ω) in which the multistep process 2ω=ω+ω breaks the phase invariance of the down-conversion process. A parametrically-forced Ginzburg-Landau equation is derived to explain the existence of phase-armed spiral waves.