Large-dynamic-range fiber optic gyroscope

A method of operating a fiber optic gyroscope having a source of optical radiation, a fiber coil, and a photodetector all optically coupled to a modulator, the method comprising:

• energizing said source to generate a beam of optical radiation, said modulator arranged to divide said beam into two counter-propagating beams circulating around said fiber coil, said modulator recombining said counter-propagating beams after circulating completely around said fiber coil, said photodetector arranged to intercept said recombined beams, said photodetector generating a photodetector voltage that is proportional to an optical power of said recombined beams interfering on said photodetector;
• supplying a modulator control voltage to said modulator that changes a relative phase between said interfering beams;
• adjusting continuously said modulator control voltage to maintain a target photodetector voltage, said target photodetector voltage corresponding to a selected relative phase when said gyroscope is not rotating, thereby maintaining closed-loop operation on one interference fringe of said gyroscope as said gyroscope rotates;
• interrupting said adjusting-continuously step when said modulator control voltage reaches a threshold voltage;
• setting said modulator control voltage to a voltage that corresponds to said selected relative phase when said gyroscope is not rotating;
• and
• resuming said adjusting-continuously step, thereby resuming closed-loop operation on another interference fringe of said gyroscope.