Observation of a novel large-signal four-photon instability in optical wave mixing

Experiments of four-photon frequency conversion in a birefringent optical fiber reveal, besides the usual small-signal parametric modulational instability, a novel large-signal instability. The main observed physical signatures of this instability are the peak stimulated conversion at signal detunings outside the parametric gain bandwidth and a signal power threshold. The transition between the two instability domains is controlled by the wavelength separation between pump and probe beams.