CLOSED LOOP ALL FIBER OPTIC GYROSCOPE WITH DIFFERENTIAL FREQUENCY PROPAGATION

摘要

CLOSED LOOP ALL FIBER OPTIC GYROSCOPEWITH DIFFERENTIAL FREQUENCY PROPAGATIONAbstract of the DisclosureA gyroscope system includes a coherent lightsource that supplies counterpropagating waves to asensing loop through a pair of directional couplers. Thepolarizations of the waves are controlled so that theytraverse identical paths before recombining in one of thecouplers to form an interference pattern. Rotation ofthe sensing loop, a phase modulator and a frequencyshifter cause phase changes in the counter propagatingwaves. A detector monitors the interference pattern ofthe combined waves and provides a signal to the coherentdemodulator that controls the phase modulator. Theoutput of the coherent demodulator is input to a servoloop circuit that drives a voltage controlled oscillator.The output of the voltage controlled oscillator is anoscillatory signal having a frequency equal to the shiftin frequency that the counter propagating wavesexperience in traversing the frequency shifter. Thefeedback circuitry adjusts the frequency shift to nullthe phase difference between the counterpropagatingwaves. The frequency shift is linearly related to thefrequency of the signal output from the voltagecontrolled oscillator. Each cycle of the output of thevoltage controlled oscillator corresponds to a fixedangular increment of displacement of the sensing loop.The rotation rate of the sensing loop is a function ofthe frequency shift and transit time of the waves throughthe sensing loop. The gyroscope system determinesrotation rates and angular displacements over a widedynamic range by measuring the frequency and zerocrossings of the oscillatory output of the voltagecontrolled oscillator.