Abstract: An optical fiber coil in a fiber optic gyro is formed by a single mode optical fiber and two polarization retaining optical fibers of the same length connected respectively to both ends of the single mode optical fiber. The polarization retaining optical fibers and an optical fiber coupler are connected, and clockwise and counterclockwise light beams are distributed and supplied by the optical fiber coupler to the optical fiber coil, and the two light beams having returned to the optical fiber coupler are thereby caused to interfere with each other. The lengths of the X-axis and Y-axis components of light are displaced apart in phase to such an extent as not to interfere with each other, by the birefringent property induced in the coil of the single optical fiber and the birefringent property of the polarization retaining optical fibers themselves.

Abstract: Light from a light source is linearly polarized by a polarizer and is then split by an optical splitter/coupler into two parts which are simultaneously coupled, as right-handed light and left-handed light, into both ends of an optical fiber coil. The right-handed light and left-handed light emitted from the ends of the optical fiber coil are combined by the optical splitter/coupler into interference light, which is extracted after passing through the polarizer and is converted into an electric signal corresponding to its intensity. The phase difference between the right-handed light and the left-handed light, corresponding to an angular rate applied to the optical fiber coil, is detected from the electric signal. A depolarizer is inserted in series at an arbitrary position in a loop from one end of the optical splitter/coupler to the other end thereof via the optical fiber coil.