A phase-nulling detection is useful for obtaining a good linearity and scalefactor stabilization in a fiber gyro. We utilize optical heterodyne technique followed by a electronic phase-nulling detection, which provides electric signal frequency proportional to the rotation rate. To reduce the output drift, the optical system of the gyro has little pathlength difference and no frequency difference in the fiber loop between counterpropagating waves. Reduction of the output noise that is due to

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... backward Rayleigh scattering in the fiber is achieved by direct frequency modulation of a single-mode laser diode, the optical source. The constructed experimental gyro shows a short-time resolution of about 5deg/h rotation rate for an integration time of 1sec, and a good linearity even in fast rotation.