Rotation detection by optical heterodyne fiber gyro with frequency output

A fiber gyro with optical heterodyne detection is proposed. The experimental setup has been constructed and tested. Both the frequency difference in the fiber and the path-length difference between counterpropagating waves are eliminated to reduce output drift. An electronic circuit for phase-nulling detection has been constructed, which gives an electronic frequency output in proportion to the rotation rate. Direct frequency modulation of a single-mode laser diode has been adopted to reduce the noise that is due to the backward Rayleigh scattering. A short time resolution of the rotation rate of about 5 deg/h for an integration time of 1 sec. (0.0014 deg/sec) has been achieved with good linearity, for an integration time of 1 sec.