Japan Aviation Electronics Industry, Limited

Aritaka Ohno

Ryuji Usui

Shinji Motohara

Takashi Nakahara

Masao Takahashi

Kiyohisa Terai

Kazuo Hotate

Ryoji Kaku

Eiichi Asami

Kinichi Sasaki

Kazuhiro Sakuma

Masakazu Harashima

Kanji Shitara

Taro Miyama

Totally six polarization-maintaining optical fibers having the same beat length are arranged at both ends of a single-mode optical fiber and both ends of a single-mode optical fiber coil, respectively. An angle between a principal axis of polarization in a first polarization-maintaining optical fiber and a plane of polarization of linearly polarized light from a light source is 45 degrees. The optical length of each of the six polarization-maintaining optical fibers is larger than a coherent length of the linearly polarized light from the light source. The total of the optical lengths of the six polarization-maintaining optical fibers into which polarization rotation in the process of passing through the single-mode optical fibers is factored is larger than the coherent length of the linearly polarized light from the light source.

Fiber optic gyroscope

A light sourceis 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&#xb0; from each other. The other ends of the optical fibers are connected to the opposite ends of a single mode fiber optic coil.

Fiber optic gyroscope having optical integrated circuit, depolarizer and fiber optic coil

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. An optical system of optical fiber from the light source to the optical integrated circuit except for the polarization maintaining optical fiber of its length L is formed by a single mode optical fiber, and the fiber optic coupler is formed by a single mode optical fiber.

A depolarizer is inserted between an optical branch unit and a polarization filter , a depolarizer and a polarization filter are inserted between an optical phase modulator and a quarter-wave plate , and a depolarizer and a polarization filter are inserted between the other branch end of the optical branch unit and a quarter-wave plate . The optical branch unit and the optical phase modulator 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.

Sagnac interferometer current sensor

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.

Fiber optic gyro

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. The depolarizer is so constructed that the difference between the difference in propagation time between perpendicularly intersecting polarized light components in the depolarizer and the difference in propagation time between perpendicularly intersecting polarized light components in the optical fiber coil is greater that the coherence time of light which passes through the loop.

In a fiber optic gyroscope in which light from a light source is split into two beams for supply to one and the other end of an optical fiber coil respectively, and the two beams having propagated through the optical fiber coil and emitted the one and the other end thereof are coupled together for supply to a photodetector, there are separately formed on an optical integrated circuit substrate two optical waveguide couplers, each comprising a trunk and a pair of branches extending therefrom. The pair of branches of a first one of the two optical waveguide couplers are connected to the light source and the photodetector, respectively, and the pair of branches of the second optical waveguide coupler are connected to the one and the other end of the optical fiber coil, respectively. The trunks of the first and second optical waveguide couplers are interconnected via a connecting optical fiber. The optical integrated circuit substrate is fixed to a reinforcing plate of a material which has a thermal expansion coefficient nearly equal to that of the optical integrated circuit substrate. The reinforcing plate is held on a support structure by flexible holding means.

Fiber optic gyroscope using optical waveguide couplers

An optical fiber coil winding machine in which first and second spindles are axially aligned but spaced apart and a take-up bobbin for winding thereon an optical fiber is held between opposed ends of the first and second spindles. First and second indexes are rotatably mounted about the first and second spindles, respectively, and first and second spinners are mounted about the first and second indexes in a manner to be movable in their axial direction. First and second supply bobbins having wound thereon an optical fiber are rotatably mounted on the first and second spinners, respectively.

Growing community of inventors

Tokyo, Japan

Aritaka Ohno