Stimulated Raman amplification in Ga As/Al As intermixed superlattices

We show the effectiveness of a χ(3)-quasi-phase-matched structure made of a GaAs/AlAs inter- mixed superlattice in stimulated Raman amplification for an enhancement in the output efficiency of anti-Stokes waves, where the efficiency is originally extremely small due to a phase mismatch for the anti-Stokes waves (although the output efficiency of Stokes waves is sufficiently large because of no such phase mismatch). We demonstrate that our quasi-phase matched structure enhances the anti-Stokes output efficiency up to the order of 10^3 when compared with that without the quasi-phase matched structure, particularly at a small pump intensity. Here, the effects of four- wave mixing, self- and cross-phase modulations are included in addition to Raman amplification with linear optical losses. In this efficiency enhancement, we see that the output efficiency of the anti-Stokes waves is boosted via simultaneous four-wave mixing. Moreover, we show how much the effects of the self- and cross-phase-modulations degrade this efficiency enhancement. With all those effects taken into account, we show that there is an optimal superlattice length that pro- vides the highest efficiency. In addition, we analyze the efficiency degradation due to two-photon absorption, and point out that in order to keep the highest efficiency at the optimal length, the Stokes, anti-Stokes, and pump wavelengths should be set larger than the half-bandgap wavelength of the intermixed superlattice.