Feedback-controlled photorefractive two-beam coupling

We show that a certain phase feedback between output and input changes dramatically the characteristics of photorefractive two-beam coupling. The diffraction efficiency of the dynamic phase grating, eta, reaches 1 or 0 (depending on the feedback sign) within a finite time for a wide range of experimental parameters. The spatial-temporal behavior of the wave amplitudes is strongly nonlinear and the grating fringes for eta=1 or 0 are bended but not tilted. The theory elucidates a number of empirical observations and reveals the great potential of active stabilization for applications.564R2541R254