Multimode fiber gyro using a mutually pumped conjugator

Abstract

Phase-conjugate fiber-optic gyros (PCFOGs) use phase conjugation to compensate for reciprocal phase changes due to thermal and mechanical effects on the fiber, while at the same time allowing for measurement of the nonreciprocal phase shift produced by rotation. Where the best standard fiber-optic gyros require polarization preserving fibers and couplers to avoid polarization scrambling that is a source of noise and signal fading, the PCFOG can avoid this problem by using polarization preserving phase conjugation. This has the advantage of allowing for use of inexpensive non-polarization preserving and even multimode fibers and components. We previously demonstrated rotation sensing with a PCFOG using multimode fiber and a self-pumped phase-conjugate mirror. However, to form a grating in the self-pumped conjugator, the two inputs to the conjugator (the two counterpropagating outputs from the fiber) must be coherent to within the response time of the conjugator. As a result, this configuration cannot use the preferred technique of fast phase modulation for biasing. We have solved this problem by constructing a PCFOG using a mutually pumped conjugator that does not require coherence between its two inputs.