Hitachi Cable, Inc.

Hitachi, Ltd.

Other

Hitachi Metals, Ltd.

Tatsuya Kumagai

Hiroshi Kajioka

Hisao Sonobe

Shigeru Oho

Munehiro Akiyama

Junichi Makino

Wataru Ohnuki

Yasuhiro Gunji

Shinji Komatsuzaki

Hisao Iitsuka

Yuuetsu Takuma

Toshihide Tokunaga

Toshiyuki Tetsu

Kohdo Yamada

Osamu Kobayashi

Keiji Abe

An optical ingredient-measuring apparatus is provided for measuring a concentration of an optically rotative substance. The apparatus includes a sensor main body which detects a phase difference between linear polarized light beams that propagate through an optical fiber loop in opposite directions, a circular polarized input component interposed in the middle of the optical fiber loop having first and second converters that convert the linear polarized light propagating through the optical fiber loop into left-hand and right-hand circular polarized light, and a concentration detector, installed in the sensor main body, which calculates the concentration of the substance in the sample based on the detected phase difference.

Sagnac optical ingredient-measuring apparatus with circular polarizers in parallel

An optical fiber vibration sensor includes a light source, an optical receiver, an optical dividing/coupling portion, a signal processing unit, and a fiber loop portion made of an optical fiber. A part of an optical fiber composing the fiber loop portion is installed inside a housing of a main body of the optical fiber vibration sensor as an optical fiber for delay and another part of the optical fiber composing the fiber loop portion is installed outside the housing as a vibration detecting optical fiber.

Optical fiber vibration sensor

A phase modulated light is propagated through an optical fiber sensing loop, from which a propagated light is obtained. The propagated light is converted to an electric signal, from which a fundamental wave component and even number harmonic wave components of a phase modulating signal for the phase modulated signal are detected. In accordance with the changes of the fundamental and even number harmonic wave components, fault is detected. On the other hand, the electric signal may be integrated to provide an integrated signal. In accordance with the comparison between the integrated signal and a fault reference voltage, the fault may be detected.

Method for detecting fault of optical fiber gyro and apparatus for

A photodetector generates an electric signal by receiving a light signal which is obtained by coupling lights having propagated through an optical fiber sensing loop in clock-wise and counter clock-wise directions, and modulated in a phase modulator. The electric signal is detected in a synchronous detection circuit to generate a fundamental wave component of the phase modulation signal, a duplicate harmonic wave component, a quadruple harmonic wave component, and an orthogonal component which is obtained in accordance with a phase shift of the quadruple harmonic wave component by one quarter period.

Phase adjustable optical fiber gyro using both even order harmonics and

A signal processing circuit of an optical fiber gyro comprises a memory for storing data measured in the signal processing circuit in accordance with angular velocities applied to an optical fiber sensing loop at preparatory stage, and the applied angular velocities. In operation, the memory is accessed in accordance with data obtained in the signal processing circuit at an operation stage, so that an angular velocity is read from the memory without complicated calculation.

Optical fiber gyro with memory storing data measured under application

In an optical fiber gyro for detecting a rotation angular velocity by Sagnac phase difference of light signals propagated through an optical fiber sensing loop, no polarizer is used, and a light source having a difference in attenuation or amplification factor between two orthogonally polarized lights is used. Alternatively, a light source is optically coupled to an optical coupler for supplying two divided light signals to the sensing loop and receiving the two light signals propagated through sensing loop by an optical fiber of a predetermined length which is set to meet a relation in which a distance difference determined by the predetermined length and a phase difference of two orthogonally polarized lights propagated through the optical fiber is greater than an interference distance of the light source.

Optical fiber gyro

The light emitted from a laser diode is divided into two lights and the divided lights are introduced into a sensing loop such that the lights propagate through the sensing loop clockwise and counterclockwise. These lights are combined by a light receiving device and then a signal processing circuit calculates an angular velocity .OMEGA.'. The temperature near the laser diode is detected to obtain a correction value Kt, a current supplied to the laser diode is detected to obtain a correction value Ki and a corrected angular velocity .OMEGA. is obtained by calculating the product of the angular velocity with the correction values Ki and Kt, i.e., .OMEGA.=.OMEGA.'*Ki*Kt.

Fiber-optic gyroscope having angular velocity correction

An interference sensor passes radiation from a source and a polariser to a loop of optical fiber so that radiation beams circulate in opposite directions around the loop and interfere. The loop contains an optical phase modulator which imposes an optical modulator on the radiation beams circulating on the loop. A converter detects the interfering and modulated beams and generates an interference signal which is then processed by an analyser. The interference in the loop is dependent on rotation of the loop and therefore analysis of the interference signal permits that rotation to be measured. In the present invention, the interference signal is (i) sampled at a frequency different from that of the optical modulation, or (ii) electronically modulated in the analyser at a frequency different from that of the optical modulation, or (iii) optically modulated in the loop at a second optical modulation frequency. The analysis in the analyser may be in the frequency domain (i.e. consideration being given to the frequency of the interference signal) or in the time domain (i.e. independent of frequency).

Interference sensor and method utilizing extracted alliasing frequency

In an optical fiber gyroscope, the sensitivity thereof is optimized with a phase bias afforded by utilizing the phase characteristics of an optical branching/coupling unit. Further, the fluctuation of the intensity of a light source and the error and secular change of the phase characteristics of the optical branching/coupling unit are compensated by an electronic circuit. Moreover, an optical fiber loop is located in a heat insulation casing so as not to be affected by an ambient temperature change, thereby to prevent the drift of the optical fiber gyroscope attributed to an temperature change. Thus, the optical fiber gyroscope of high measurement accuracy is provided.

An improved optical branching/coupling unit for an optical fiber

A polarized wave preserving fiber has a core at its center, cladding, an oval jacket, and a support member in order to improve transmitting property of the polarized single mode by adjusting the refractive index distribution and the ellipticity of the oval jacket.

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Hitachi, Japan

Tatsuya Kumagai