- A mutually pumped phase-conjugate mirror based on a bidirectional ring oscillator in a single photorefractive crystal has been studied theoretically and experimentally. This system has a significantly increased operating range and a lower threshold coupling strength compared with other types of mutually pumped conjugators. High-quality mutual phase conjugation without cross talk has been demonstrated in experiments in a single barium titanate crystal. Both stable and unstable regimes of operation have been observed. A theoretical model of this conjugator based on a six-wave mixing process in the photorefractive material has been developed. Good agreement between theory and experiment has been achieved. 1994 Optical Society of America.