Abstract

A ring resonator containing a phase-conjugate mirror can act as a phase-conjugate optical gyroscope (PCOG).¹ The frequencies of the counterpropagating oscillations depend on the nonreciprocal, but not on the reciprocal, optical path length of the resonator; thus, the device is potentially useful for inertial sensing of rotational motion. A primary limitation of conventional ring-laser gyroscopes is frequency-locking behavior, wherein backscattering couples the counterpropagating laser oscillations. Our previous theoretical results² indicated that, for nonreciprocal phase shifts of ~π/10 rad, frequency locking occurs when the ratio of backscattered light to pump light exceeds ~10^-3. We describe our experimental investigation of the frequency-locking characteristics for the ring PCOG. A weak seed beam was injected into the oscillator along the same direction as the phase-conjugate output. The frequency difference between the counterpropagating waves was measured as a function of the seed intensity and the nonreciprocal phase shift. Measurements were made with both coherent and incoherent (with respect to the pump) seed light to simulate scatter contributed by the phase-conjugate and conventional mirrors, respectively. The experimental results are in good agreement with theory.

© 1990 Optical Society of America