JPS6217613A - Optical-fiber gyroscope - Google Patents

Abstract

PURPOSE:To attempt improvement of accuracy of measurement of an optical- fiber gyroscope, by correcting a detected value of a detecting apparatus according to an amplitude of A.C. element of interference light. CONSTITUTION:A beam of interference light of both laser light beams subjected to a phase difference due to an angular velocity OMEGA, after propagation in the mutually opposite directions inside an optical fiber 12 comes into a photo/ electricity convertor 14. This beam of interference light is converted into an electric signal by a photo/electricity convertor 15 and amplified by a variable- gain amplifying circuit 16, and later its amplitude of modified frequency is detected by a detecting unit 17. Here, a peak value of output of the amplifier 16 is detected by a gain controlling circuit 18 and when the gain of the circuit 16 is controlled in such a way that this value becomes always to represent the specified value, if any fluctuation might take place on the peak values in the output of the convertor, it can be cancelled.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical fiber and a gyro that are mounted on a moving body such as an aircraft and are used to measure the angular velocity of the moving body.

Conventional technology Optical fibers are used as gyros to detect the angular velocity of moving bodies such as aircraft, and utilize the Sagnac effect, which creates a difference in propagation velocity between light propagating in one direction and the opposite direction in a space where angular velocity acts. Gyro is used.

As shown in FIG. 3, this optical fiber gyro includes a laser light source 1, an optical fiber 2 disposed in an action space with an angular velocity Ω, an optical phase modulator 3, a half mirror 4, and an optical fiber.
It includes an electric converter 5 and a detector 6.

The laser light emitted from the laser light source 1 is transmitted to the half mirror 4.
It is divided into two parts. One of the two divided laser beams propagates clockwise within the optical fiber 2, is phase-modulated by the phase modulator 3, is reflected by the half mirror 4, and enters the optical/electrical converter 5. The other light split by the half mirror 4 is phase modulated by the phase modulator 3, propagates counterclockwise within the optical fiber 2, passes through the half mirror 4, and enters the optical/electrical converter 4. .

Therefore, the interference waves of the two laser beams propagating in opposite directions in the optical fiber 2 and having a phase difference due to the angular velocity Ω are incident on the optical/electrical converter 4. This interference light is converted into an electrical signal by an optical/electrical converter 5, and the amplitude of the modulation frequency fm is detected by a detector 6. The amplitude a of the AC component
is a = AJ+ (2m sinπfwy) si
nΔφ・・・・・・(1) Δφ=(4πlaΩ)/(Cλ)・・・(2) However, m: Modulation index A; Constant τ determined by light intensity and interference efficiency; Propagation time of laser light C; length of optical fiber; diameter C of optical fiber; speed of light in vacuum λ; wavelength of light in vacuum JI; Bessel linear function.

In this way, from the amplitude a of the frequency fm in the interference wave, (1)
SinΔφ can be detected based on the equation, and from this, Ω can be detected based on equation (2).

Problems to be Solved by the Invention In the conventional optical fiber gyro described above, the constant A in equation (1), which is determined from the light intensity and interference efficiency, depends on the output fluctuation of the laser light source 1 and the polarization plane within the optical fiber 2. There is a problem in that the interference efficiency fluctuates due to fluctuations in the angular velocity, resulting in a detection error in the angular velocity.

If you try to prevent various fluctuations to reduce measurement errors,
This requires feedback control of the output of the laser light source and temperature stabilization of the optical fiber portion within the propagation path, which poses a problem in that the entire device becomes expensive.

Means for Solving the Constituent Problems of the Invention The optical fiber of the present invention which solves the problems of the above-mentioned prior art.
The gyro is configured to improve measurement accuracy with a simple and inexpensive configuration by including means for correcting the detection value of the detection means based on the amplitude of the alternating current component of the interference light.

Hereinafter, the operation of the present invention will be explained in detail together with examples.

Embodiment FIG. 1 is a block diagram showing the configuration of an optical fiber gyro according to an embodiment of the present invention.

This optical fiber gyro includes a laser light source 11, an optical fiber 12 arranged in an action space with an angular velocity Ω, an optical phase modulator 13, a half mirror 14, and an optical/electrical converter 15.
, a variable gain amplifier 16 , a detector 17 , and a gain control circuit 18 .

The process until the laser light emitted from the laser light source 11 enters the optical/electrical converter 15 as interference light is the same as in the case of the conventional device described above.

That is, the laser beam emitted from the laser light source 11 is split into two by the half mirror 14, one of which propagates clockwise within the optical fiber 12, is phase modulated by the phase modulator 13, and is reflected by the half mirror 14. and enters the photo/electrical converter 15. The other laser beam is phase modulated by a phase modulator 13, propagates counterclockwise within the optical fiber 12, passes through a half mirror 14, and enters an optical/electrical converter 14.

The optical/electrical converter 14 receives interference light of both laser beams, which propagate in opposite directions in the optical fiber 12 and have a phase difference due to the angular velocity Ω.

This interference light is converted into an electrical signal by an optical/electrical converter 15, amplified by a variable gain amplifier 16, and then the amplitude of the modulation frequency fm is detected by a detector 17.

The output of the photo/electrical converter 15 is A cos (m cos (ytfm (tr/
2) )Xsin (πfmτ/2)+Δφ)+B...
・(3) becomes. However, B is a DC component, and like A, it is a constant determined by light intensity and interference efficiency.

Note that the above equations (1) and (2) correspond to the Bessel expansion of the AC component in (3) 2 above.

(3) The second constant A is m sin (πfmr/2)
>n, it can be determined from the peak value of the AC component.

Therefore, if the peak value of the output of the variable gain amplifier 16 is detected by the gain control circuit 18 and the gain of the variable gain amplifier 16 is controlled so that the peak value of the output of the variable gain amplifier 16 is always kept at a predetermined value. Even if the output A fluctuates, the fluctuation can be canceled out.

As illustrated in FIG. 2, the gain control circuit 18 compares this peak value with a reference value to a peak value detection section consisting of a full-wave rectifier circuit 18a and a subtracter 18b, and generates an error signal. It consists of a subtracter 18C that supplies the variable gain control circuit 16.

Above, we have illustrated the configuration in which the detection result of the detector 17 is corrected by keeping the output of the variable gain amplifier circuit constant.
The angular velocity is immediately detected from the modulation frequency component of the output of the optical/electrical converter 15, and the AC amplitude value of the output of the optical/electrical converter 15 is detected, and the detected value of the angular velocity is corrected based on this. It can also be configured.

Effects of the Invention As explained in detail above, the optical fiber gyro of the present invention is equipped with means for correcting the detection value of the detection means based on the amplitude of the alternating current component of the interference light, so it has an easy-to-use and inexpensive structure. The effect is that measurement accuracy can be improved under these conditions.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an optical fiber gyro according to an embodiment of the present invention, and FIG. 2 is a gain control circuit 1 of FIG.
FIG. 3 is a block diagram illustrating the configuration of a conventional device. 11... Laser light source, 12... Optical fiber, 13... Phase modulator, 14... Half mirror 215... Optical/electrical converter, 16... Variable gain control circuit. 17...Detector, 18...Gain control circuit.

Claims (1)

[Claims] An optical path formed in a space where angular velocity acts, a part of which includes an optical fiber, for propagating laser light in one direction and the opposite direction, and a phase modulating phase for the laser light propagating in this optical path. a modulation means; an optical means for causing interference between the laser beams propagated in both directions within the optical path; a detection means for detecting the amplitude of the modulation frequency component among the alternating current components of the interference light; and an amplitude of the alternating frequency component of the interference wave. An optical fiber gyro comprising: means for correcting a detection value of the detection means based on the detection means.