Heterodyne Fiber-Optic Gyroscope Using Orthogonal Polarizations With Different Frequencies

A heterodyne detection scheme used in a fiber-optic gyroscope (FOG) provides a stable scale factor and a wide dynamic range in a phase output. 1) The output, however, is open to the influence on environmental fluctuations, since the output contains a bias phase caused by a frequency difference between two counterpropagating beams in a fiber coil. In order to overcome this, the heterodyne FOG has been improved by using a reference beam different in frequency from that of the counterpropagating beams of an identical frequency,213) or by shifting the frequency in one of the counterpropagating beams after emerging from the fiber coi1.4) However, these approaches lead to alternative problems such as Rayleigh backscattering or a phase fluctuation caused by a frequency shifter (AOM). In this paper, we present a novel approach capable of canceling inherently the noise sources appeared in the conventional heterodyne FOGs.