Abstract

There has been growing interest in the temporal properties of wave mixing processes in photorefractive crystals. Several years ago, temporal instabilities such as frequency detuning [1] and pulsations [2] were observed in self-pumped phase conjugation. Also, there has been considerable interest in the possibility of bistability associated with the multiple solutions of the four-wave mixing coupled wave equations [3]. Especially important was the result of Gauthier et al. [4] where it was shown that instabilities occur for strong nonlinear coupling. As a result, demands for large coupling constants for large energy transfer and high phase conjugate reflectivity may lead to very unstable output. The mechanism responsible for these instabilities was competition among various coupling mechanisms with different time constants [4]. Very recently, a ring oscillator with photorefractive gain and loss was demonstrated experimentally and theoretically for application to associative memories. This system was shown experimentally to exhibit bistability when an external signal beam was injected [5].

© 1990 Optical Society of America