Abstract

We describe a new type of fiber-optic gyro which utilizes the phase reversal of the conjugation process, and we report some preliminary experimental results. Polarization scrambling is a well-known source of signal fading and noise in fiberoptic gyros. Polarization-preserving fibers and couplers must be used to decouple the two states of polarization and hence improve the sensitivity.¹ In the phase conjugate fiber-optic gyro, a scalar phase conjugator is employed to restore the severely scrambled waves to their original state of polarization. This eliminates the signal fading and noise due to polarization scrambling. Consider a fiber loop which contains a phase conjugate reflector at the end. The net phase shift of light completing a round trip is proportional to the rotation rate and can be used for rotation sensing. In addition, if the phase conjugate reflector is scalar², the polarization state will not change on reflection. Such a scalar phase conjugator will produce a true time-reversed version of the incident wave and will undo all the reciprocal changes (e.g., polarization scrambling, modal aberration, temperature fluctuation) when the light propagates backward from the phase conjugator to the input coupling. Since the polarization scrambling and modal aberration of the multimode fibers can be corrected by scalar phase conjugation, even multimode fibers can be used in this new type of gyro. We have demonstrated the correction, by scalar phase conjugation, of polarization scrambling and modal aberration, in single and multimode fibers. We have also measured the conjugate phase shift introduced by rotation.

© 1985 Optical Society of America