Due to inherent complexity of some photorefractive effects, one must often resort to numerical methods to describe them with some degree of realism. This is especially true when we consider the nonlinear photorefractive effects involving complicated light fields, eg, photorefractive image amplification, phase conjugation, or surface photorefractive wave formation. 1 In particular, the amplification in cubic photorefractive crystals occurs in the presence of optical activity and pulsing linear birefringence, which is caused by an applied ac electric field. The amplification involves the interaction between light beams with complicated spatial variation of the amplitude and frequently it is accompanied by the strong fanning effect. The analytical model can be scarcely developed for this case. In the experiments with some photorefractive crystals, such as BaTiO3 and SBN the beam evolution inside the crystal was traced by observing it through the upper face of the sample. 2 For other crystals this technique is not acceptable because of the low light intensity and the high optical quality of the crystals, such as the cubic crystals of sillenite family. However, these crystals have a good potential as the low-noise, fast-response media for the photorefractive amplifiers and conjugators and the numerical simulation is especially important for successful analysis of the experimental data.

It has been proved that the beam propagation method BPM is a powerful tool for an analysis of the light propagation in a nonuniform, anisotropic, and nonlinear media. It was developed first in underwater acoustic and seismology and then adapted to optical problems. 3 The BPM has widely used in the investigation of optoelectronic devices for years and has been improved by various modifications. A comprehensive review can be found in Ref. 4. Because the simulation of the light propagation by BPM is almost always successful and for certain problems it is the only way to obtain results, the BPM is the method of choice to simulate numeri-