<title>Nonlinear optical effects and phase conjugation in photorefractive fibers</title>

Abstract

Self-channeling of a laser beam in photorefractive fiber- like crystals has been studied both experimentally and theoretically. Total internal reflections of strong fanning beams and their coupling with the pump beam result in the light intensity redistribution inside the crystal and in a photorefractive surface wave generation. A theoretical model of the photorefractive surface wave is presented considering the light energy flow from the pump beam to the scattered (fanning) light and backwards after the fanning beams reflections. Both anomalously fast photorefractive response time and its acceleration with increasing amplitude of the external ac electric field are experimentally demonstrated in a photorefractive Bi<SUB>12</SUB>TiO<SUB>20</SUB> fiber. The photorefractive surface wave can be used as the energy source for the signal beam amplification in two-wave mixing experiments. This technique solves the problem of the pump beam depletion and it allows the high-gain low-noise amplification of ultraweak signals as it is experimentally shown for a Bi<SUB>12</SUB>TiO<SUB>20</SUB> fiber. Improved two-wave mixing interaction in photorefractive fibers results in better parameters of the dynamic double phase conjugate mirror (DPCM) recorded by mutually incoherent pump beams. Novel configurations of the optical interferometric sensors using injection locking of semiconductor lasers with photorefractive DPCM are proposed and experimentally demonstrated.