Patent ID: 7505139

Claim:
A method of modulating the phase difference between a pair of optical waves that exit a Sagnac interferometer after having counter-propagated through a common optical path, including an optical fiber and a phase modulator, and impinges upon a detector that produces a detector output signal responsive to the combined optical power of said pair of optical waves and is indicative of the total phase difference between the pair of optical waves, and wherein the total phase difference includes (i) the Sagnac phase difference, and (ii) a phase-difference modulation induced by said phase modulator in response to a command signal, and wherein said phase modulator is capable of imparting phase modulation substantially equally to said counter-propagating waves passing therethrough, the method comprising the steps of: driving said phase modulator with a command signal [S] that causes said phase-difference modulation between said pair of optical waves to have (i) a bias phase-difference modulation component [J] having a selected bias modulation amplitude and waveform, (ii) a rotation-rate feedback phase-difference component [K] that is equal in magnitude to, and opposite in sign of, the Sagnac phase difference, so that the sum of the two is controlled to be substantially zero, and (iii) a calibration feedback phase-difference modulation component; [Z]; and deriving a rotation-rate feedback phase-difference component signal [R] as a function of, (i) said detector output signal [D], and (ii) a bias modulation signal [B], where said rotation-rate feedback phase-difference component signal [R] is a signal processing counterpart of said rotation-rate feedback phase-difference component [K], and deriving a calibration signal [G] corresponding to a selected phase difference as a function of, (i) said detector output signal [D], (ii) said bias modulation signal [B], and (iii) a calibration feedback phase-difference modulation component signal [Y], where said calibration-feedback-phase-difference-modulation-component signal [Y] is a signal processing counterpart of said calibration feedback phase-difference modulation component [Z] ; deriving said calibration feedback phase-difference modulation component signal [Y] by modulating said calibration signal [G] in part to restrict the command signal [S] to a given range of values, and deriving said command signal [S] as a function of, (i) said rotation rate feedback phase difference component signal [R], (ii) said calibration feedback phase-difference modulation component signal [Y], and (iii) said bias modulation signal [B].