Mirrorless optical parametric oscillators with stitching faults: backward downconversion efficiency and coherence gain versus stochastic pump bandwidth

Parametric downconversion in submicronic periodically poled (PP) quadratic materials allows for the generation of signal and idler waves in opposite directions. The distributed feedback mechanism enables a backward mirror-less optical parametric oscillator (BMOPO), which has been experimentally realized using a periodically poled KTiOPO (PPKTP) crystal with 800 nm periodicity. In this paper we will consider the backward signal configuration, where the effect of coherence enhancement of the backward signal wave is especially pronounced for exact group velocity matching of the co-propagating pump and idler waves. Thanks to the high performance computing facility available at Nice University, we analyze the parametric down-conversion efficiency and the coherence gain of the backward signal versus the stochastic pump bandwidth in a large pump-bandwidth range. In any case, for an incoherent pump of broad spectral bandwidth we obtain a coherence gain of almost three orders of magnitude.