ACOUSTOOPTICALLY INDUCED UNIDIRECTIONAL OPERATION OF A RING LASER - A FEEDBACK MECHANISM

A second mechanism for acousto-optically induced unidirectional operation of a ring laser has been identified and demonstrated experimentally. The mechanism involves feeding back the diffracted wave, thus restoring it to its original frequency and direction via a second diffraction from the travelling-wave acousto-optic modulator. Since the feedback resonance condition is different for the two counter-propagating waves of the ring laser, they experience a loss difference which results in unidirectional operation. Via this method a very large loss difference can be achieved with negligible insertion loss.