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We present a theory of resonant photorefractive wave coupling in cubic photorefractive crystals that are in general optically active. This theory includes the resonance enhancement of the photorefractive response in a constant applied electric field, the influence of photoelasticity, and the spatial inhomogeneity of the light intensity. In a unified manner, it allows one to describe the polarization and energy properties of two-wave coupling for the optical configurations relevant to experiment. Applications of the theory are given to photorefractive crystals of the sillenite family.

We propose a theory of the instability of the space-charge field induced in a semiconductor by the movement of light fringes against subharmonic generation. A crucial element of this theory is taking into account three-dimensional perturbations and higher spatial harmonics of the space-charge field. It is shown that, irrespective of fringe contrast and velocity, the strongest instability corresponds to the excitation of subharmonics that are not split in the transverse direction. The theory is applied to experimental data on subharmonic generation in sillenites.

We analyze analytically and numerically the mechanism for modulational instability of the resonance excitation of a space-charge field by a moving light pattern in a photorefractive sillenite crystal to explain the results of recent experiments with Bi12SiO20 crystals.

We study the simultaneous influence of optical activity, piezoelectric effect, and elasto-optic effect on two-wave mixing (TWM) under diffusion recording in photorefractive Bi12TiO20 and Bi12SiO20 crystals and find numerically the maximum of the TWM gain as a function of the orientation of the grating vector. Contrary to widespread belief, the grating orientation K∥[111] is the optimum orientation only if optical activity is negligibly small. Nonzero optical activity results in a strong dependence of the optimum grating orientation on the crystal thickness. The strongest deviation of the optimum from the [111] direction is achieved for ϱd=180°, where ϱ is the rotatory power and d is the crystal thickness. Our theory explains well prior results for crystals of moderate thickness and predicts new effects for thick (e.g., fiberlike) crystals.