Bistable resonator utilizing saturable photorefractive gain and loss

Abstract

We report the observation of bistability in a unidirectional ring resonator that employs photorefractive barium titanate for gain and also for saturated loss. One photorefractive crystal provides gain via two-beam coupling in a conventional unidirectional ring configuration.1 A second crystal is arranged to couple light out of the resonator using two-beam coupling, thereby producing loss. The orientations of the two crystals are chosen so that the magnitude of the small signal loss is greater than the magnitude of the small signal gain. Thus the oscillation in the ring cannot build up from noise since there is no net gain. However, the pump intensity for the gain medium is made larger than that for the loss medium. This means that the loss saturates at a lower signal level. Hence, at large intensities, gain can exceed net loss so oscillation can occur.