EIGENFREQUENCY PHASE SHIFT CONTROL LOOP FOR FIBER OPTIC GYROS

摘要

A fiber optic rotation sensor having a pair of light beams counterpropagating in a loop includes a phase modulator for modulating the waves at a first frequency, upon exiting the loop the waves are c ombined into a light intensity signal indicative of rotation rate and is sensed. A signal at the first frequency is quadrature phase shifted by a lower frequency signal and summed with the sensed rate signal, an amplifier amplifies the summed signals, the amplifier also inherently induces undesirable phase shifts by an equal amount in both the sensed rate signal and the quadrature signal. The quadrature signal is demodulated and used in feedback fashion to control the phase of a variable phase shifter which provides a signal at the first frequency whose phase is shifted by an amount equal to the undesirable phase shift of the sensed rate sig nal, the variable phase shifter signal and the sensed rate signal being provided to a demodulator to demodulate rotation rate i nformation from the sensed rate signal.