Constant frequency digital closed-loop optical fiber gyro

摘要

An improved fiber-optic inertial sensor of the Sagnac interferometer type is provided with the capablility of precise linear measurement of sensed motion. The sensor uses closed-loop synchronous demodulation of sensed signals representative of angular motion in a manner that permits operation over a wide dynamic range in inertial rate along with null stability and a high degree of noise rejection. The improved inertial sensor comprises a multi-turn sensing coil of optical fiber; an optical pulse source supplying optical pulses to both ends of the sensing coil so that the pulses are proagated in opposite directions through the coil; a phase modulator for introducing a non-reciprocal phase difference between the counter-propagating optical pulses, the relative phase difference between the pulses remaining fixed when the coil is stationary but changing when the coil is moved; and a circuit responsive to changes in the relative phase difference for (1) producing an output signal reresenting the magnitude and direction of the change and (2) adjusting the phase of the optical pulses supplied to the sensing coil to at least partially null out any change in the relative phase difference.