CONTROLLED BACKSCATTER IN RING LASER GYROSCOPES.
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abstract
A theoretical investigation of ring laser gyroscopes (RLGs) indicates that fundamental and practical improvements in sensitivity can be accomplished by introducing a controlled coupling between the counterpropagating fields of the ring cavity. The modes could be coupled, for example, by extracting some transmitted light from one cavity mode and injecting this light into the counterpropagating mode. This controlled coupled can lead to both dead band reduction in active (lasing medium in the ring cavity) RLGs and, under some conditions, enhanced quantum-limited sensitivities of passive (single-laser source outside the ring cavity) and correlated emission RLGs. In the absence of coupling, the difference in the frequencies of the two countercurrent fields in an active RLG is proportional to the rotation rate of the ring. Mirror backscatter couples these fields so that they tend to lock to a single frequency for small rotation rates. This dead band can be eliminated by introducing a controlled coupling of proper amplitude and phase which effectively cancels the coupling due to mirror backscatter. Thus the extraction-injection coupling mentioned above is a no-moving-parts alternative to mechanical dithering for dead band reduction.
