Abstract: A light source 10 is connected sequentially through a single mode optical fiber and a coupler to one end of a polarization maintaining optical fiber, the other end of which is connected to an optical waveguide of an optical integrated circuit having a branching optical waveguide which has a polarizing function with the polarization axis of the optical fiber being coincident with the direction of the TE mode in the optical waveguide. One end of each of polarization maintaining optical fibers are connected to two other ends of the optical waveguide with the polarization axis of the optical fibers being coincident with the direction of the TE mode in the optical waveguide. The other ends of the optical fibers are connected to one end of each of polarization maintaining optical fibers with their polarization axis displaced by an angle of 45° from each other. The other ends of the optical fibers are connected to the opposite ends of a single mode fiber optic coil.

Abstract: A light source 10 is connected sequentially through a single mode optical fiber and a coupler to one end of a polarization maintaining optical fiber, the other end of which is connected to an optical waveguide of an optical integrated circuit having a branching optical waveguide which has a polarizing function with the polarization axis of the optical fiber being coincident with the direction of the TE mode in the optical waveguide. One end of each of polarization maintaining optical fibers are connected to two other ends of the optical waveguide with the polarization axis of the optical fibers being coincident with the direction of the TE mode in the optical waveguide. The other ends of the optical fibers are connected to one end of each of polarization maintaining optical fibers with their polarization axis displaced by an angle of 45° from each other. The other ends of the optical fibers are connected to the opposite ends of a single mode fiber optic coil.

Abstract: In a fiber optic gyroscope comprising a light source, a fiber optic coupler, an optical integrated circuit having a function of a polarizer and a branching optical waveguide, and a fiber optic coil, and detecting an angular velocity applied to the fiber optic coil about the axis thereof, a polarization maintaining optical fiber having its length L is connected to an input/output end of the optical integrated circuit nearer the light source in an optical system of optical fiber from the light source to the optical integrated circuit, the polarization maintaining optical fiber of its length L resulting in a difference in group delay time between the orthogonal two polarization modes and the difference at least exceeding a coherence length of light from the light source.

Abstract: A depolarizer 11 is inserted between an optical branch unit 2 and a polarization filter 3, a depolarizer 12 and a polarization filter 14 are inserted between an optical phase modulator 5 and a quarter-wave plate 16, and a depolarizer 13 and a polarization filter 15 are inserted between the other branch end of the optical branch unit 4 and a quarter-wave plate 17. The optical branch unit 2 and the optical phase modulator 5 are formed by single mode optical fibers, and single mode optical fibers are used to connect between optical elements, thus providing an arrangement which is inexpensive as a whole.

Abstract: In a fiber optic gyroscope comprising a light source, a fiber optic coupler, an optical integrated circuit having a function of a polarizer and a branching optical waveguide, and a fiber optic coil, and detecting an angular velocity applied to the fiber optic coil about the axis thereof, a polarization maintaining optical fiber having its length L is connected to an input/output end of the optical integrated circuit nearer the light source in an optical system of optical fiber from the light source to the optical integrated circuit, the polarization maintaining optical fiber of its length L resulting in a difference in group delay time between the orthogonal two polarization modes and the difference at least exceeding a coherence length of light from the light source.

Abstract: A depolarizer 11 is inserted between an optical branch unit 2 and a polarization filter 3, a depolarizer 12 and a polarization filter 14 are inserted between an optical phase modulator 5 and a quarter-wave plate 16, and a depolarizer 13 and a polarization filter 15 are inserted between the other branch end of the optical branch unit 4 and a quarter-wave plate 17. The optical branch unit 2 and the optical phase modulator 5 are formed by single mode optical fibers, and single mode optical fibers are used to connect between optical elements, thus providing an arrangement which is inexpensive as a whole.

Abstract: Clockwise and counterclockwise light beams, which have a Sagnac phase difference caused by an angular rate in an optical fiber coil, are combined into interference light, which is converted by a photodetector into an electrical signal. A sine component and a cosine component of the Sagnac phase difference .increment..PHI..sub.s in the output of the photodetector are detected by first and second synchronous detectors, respectively, and the sine component is used as the fiber optic gyro output and it is provided to a correcting signal generator to produce a correcting signal. The detected cosine component is added by an adder to the correcting signal, and the added output is compared by a differential amplifier with a reference voltage and the resulting error signal is produced.

Abstract: A cylindrical bobbin having flanges at both ends thereof is formed as a unitary structure, using a material of thermal conductivity nearly equal to or lower than that of an optical fiber coil, and the optical fiber coil is wound on a housing portion defined between the flanges. An annular member is mounted on the bobbin to cover the housing portion on the outside of the optical fiber coil, forming an annular case for housing the optical fiber coil, together with the bobbin. The annular member is also made of a material which has a thermal conductivity nearly equal to or lower than that of the optical fiber coil.