If the time-reversal symmetry of a ring phase conjugator is broken, the output of the device is no longer the phase conjugate of the input. For a TEM00 input wave, the output wave can be a higher-order resonator mode, although there is no resonator. Additionally, there will be a frequency shift between the input and output waves that varies discontinuously as the asymmetry in the ring is increased. Experiments using photorefractive BaTiO3 are in good agreement with theory and demonstrate the ability of the system to choose the combination of output mode and frequency that maximizes the mode gain.
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