We present the results of numerical simulation of the feedback-controlled 2W-coupling in photorefractive crystals for nonlocal (typical for BaTiO<sub>3</sub>, SBN crystals) and resonant (DC-biased BSO, BTO and BGO crystals) photorefractive response. We demonstrate in all the cases the distinctive features of this coupling - 100% diffraction efficiency of the recorded dynamic gratings, periodic states instead of steady states, and generation of moving light fringes. The conditions for the achievement of periodic states and the apparent features of these states are shown to be essentially different from those known for the case of local response. A special stress is made on indication of the experimental conditions for detection of the periodic states in BaTiO<sub>3</sub> and BTO crystals.

© 2003 Optical Society of America

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