We investigate theoretically and experimentally the operation of a nonlinea
r system, feedback controlled photorefractive beam coupling. It is shown th
at the feedback equations used earlier if (+/- pi /2 phase shift between th
e diffracted and transmitted beam components) are satisfactory only during
a relatively short initial stage of development. We have generalized these
equations by taking into account the inertia inherent in any real feedback
loop. The initial feedback equations ensure the permanent operation of the
nonlinear system and lead to a variety of periodic and quasiperiodic regime
s. We investigate the distinctive features of these regimes and transitions
between them for moderately thick crystals. Good qualitative agreement bet
ween theory and experimental data is obtained for LiNbO3 crystals.