Heterodyne fiber-optic gyroscope using orthogonally polarized two-frequency beams.

A new type of heterodyne fiber-optic gyroscope using orthogonally polarized light components with different frequencies is described. Each counterpropagating beam consists of the orthogonal components transmitted in the principal axes of a polarization-maintaining fiber coil. A pair of beat signals containing Sagnac phase shifts with opposite signs can be produced by selectively superimposing the counterpropagating components. Detection of the difference between the two beat signals allows a doubling of the Sagnac phase shift free from noise sources raised from differences in frequency and path. In a preliminary experiment, a long-term stability of 5 degrees /h was attained.