MODULATION TRANSFER-FUNCTION OF PHOTOREFRACTIVE PHASE CONJUGATORS FOR2 MUTUALLY COHERENT INPUT BEAMS

We investigate theoretically and experimentally the modulation transfe r function of a photorefractive phase conjugator for two mutually cohe rent input beams. The two coherent beams are incident on a crystal and undergo stimulated photorefractive backscattering in different region s, in which the phase conjugations are generated. Then the four waves present in the crystal interact. Due to the unreciprocal energy coupli ng between different spatial-frequency waves and the directional depen dence of the two-wave mixing gain, the output modulation exhibits two values corresponding to one input modulation. The output modulation de pends on the input beam ratio, on the backscattering coefficient of th e imperfection on the surface of the crystal, and on the crossing angl e of the two input beams. (C) 1998 Elsevier Science B.V.