AC-enhancement of the photorefractive response in the sillenites leads to high values of the gain factor in the low-contrast region. Analytically and numerically we investigate the photorefractive response in the whole contrast range and apply the results obtained to describe a number of vectorial (polarization) coupling effects. We show that under certain liberal conditions (applicable, e.g., to experiments with BTO crystals) the vectorial coupled-wave equations possess additional conservation laws involving the polarization degrees of freedom. This allows to predict a number of new polarization effects. While the low-contrast region is optimum for beam amplification, the high-contrast range is appropriate for non-perturbed grating recording.
© 2003 Optical Society of America