Backward optical parametric efficiency in quasi-phase-matched GaN waveguide presenting stitching faults.

We model a backward mirrorless optical parametric oscillator in a fragmented GaN waveguide consisting of a sequence of submicronic periodically poled elements separated by uniformly polarized connection sections representing stitching errors. We find that the generated coherent phase of the backscattered wave locks the phases of the forward propagating waves in such a way that the dynamics is nonintuitivelly as efficient as for a uniform quasi-phase-matched waveguide. The best coherence transfer to the backward wave, obtained for perfect group-velocity matching of the forward propagating waves, requires a nanoscale poled periodicity, which is achieved in GaN through epitaxy.