Single cell Brillouin enhanced four-wave mixing with focusing geometry

Abstract

Brillouin enhanced four-wave mixing (BEFWM) is a judicious combination of SBS and FWM processes. In the traditional BEFWM experiments, two cells are used: one generates SBS, the other provides four-wave mixing. We demonstrated the generation of a phase conjugate signal by single cell BEFWM with focusing geometry. A single cell containing the optical nonlinear medium was used simultaneously for conventional SBS and FWM. Experiments were performed by using either CS2 or TiCl4 as the nonlinear medium; both have large Brillouin gain but differ greatly in their nonlinear indices of refraction. Thus the mechanism for four-wave mixing is shown to be Brillouin nonlinearity. In this experiment, the phase matching condition was satisfied and the frequency of the phase conjugate signal was not shifted from that of the master input beam. The operating regime of the experiment was far below the threshold of instability, which accounts for the low reflectivity that we observed. This single cell configuration is more compact and the optical alignment is easier than in the conventional BEFWM, in which two nonlinear cells are used.