Quasi-phase matched broadband difference frequency generation in the mid-infrared region using total internal reflection in a tapered gallium arsenide (GaAs) slab

We developed an analytical model of a quasi-phase matched mid-infrared frequency converter which uses total internal reflection in an isotropic semi-conductor slab (GaAs) having tapered configuration. A computer-aided simulation has been performed by adopting Difference Frequency Generation (DFG) with ppp polarisation where the pump wave is of 4 μm and the signal bandwidth lies between 14 and 17 μm. The resultant 3 dB broadband output has a bandwidth of 523 nm centred at 15.423 μm and a peak conversion efficiency of 0.091% in a 30 mm long slab. Due consideration has been given to the effect of optical beam walk-off on the frequency conversion process, and the losses due to absorption, Goos-Hänchen shift and surface roughness. We also analyse the impacts of the variations in tapering angle, temperature, angle of the front face, beam walk-off tolerance and angle of refraction at the air – crystal interface inside the slab, on the performance of the frequency converter.