PHASE-CONJUGATE BISTABILITY AND MULTISTABILITY IN MOVING-GRATING OPERATED ORTHOGONALLY POLARIZED PUMP 4-WAVE-MIXING IN PHOTOREFRACTIVES

We establish possible regions of bistability (BIST), multistability (M UST), hysteresis, self-oscillation (SO) and enhancement features of th e phase-conjugate reflectivity (PCR) by use of moving-grating operatio n (MGO) in the orthogonally polarized pump four-wave mixing (OPP-FWM) geometry employing a photorefractive (PR) crystal (usually BaTiO3). Nu merical evaluation of such PCR features has been presented as a functi on of parameters such as coupling strength (of complex gL and real g0L values), frequency-shift (OMEGA) owing to grating motion, the PR phas e shift (phi(PR), and pump (r) and probe (q) intensity ratios. PCR res ults of this geometry are compared with those obtained from the regula r (i.e. parallel-polarized pump) four-wave mixing (REG-FWM) geometry a ssuming the same set of parameters in both geometries. We find that th e OPP geometry leads to a drastic PCR enhancement together with the ap pearance of a rich variety of multibranched solutions exhibiting BIST and MUST features of the PCR, particularly in the range 0.5 less-than- or-similar-to OMEGA less-than-or-similar-to 3 with value g0L approxima tely 10, r = 1 and q less-than-or-similar-to 0.1 that are practically realizable. Nevertheless, this geometry sometimes offers the possibili ty of a PCR jump (from one stable state to the other), suggesting hyst eresis caused by changing OMEGA only slightly. In the REG geometry, ho wever, the PCR enhancement is less prominent, and also the BIST/MUST f eatures rarely exist unless g0L becomes sufficiently large, say approx imately 20 or more.