Numerical calculation of the two-wave mixing gain factor for arbitrary
orientation of the holographic grating vector using the coupled wave
theory developed for optically active electro-optic crystal enabling p
ump-beam depletion is presented. Two-dimensional angular dependencies
of the gain factor are measured in Bi12TiO20 photorefractive crystal u
nder an alternating external electric field using the fanning effect.
It is found experimentally that the angular distribution of fanning li
ght is independent of the polarization state of the pump beam. This fa
ct could not be explained by the existing theory.