JPS5913908A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To detect and correct drift mobility and to detect an angle of rotation precisely by inverting an optical fiber part which is coiled at necessary intervals of time. CONSTITUTION:Two outgoing light beams 104 and 105 are emitted toward a photodetector 5 and a light source 1 according to their phase difference. The oscillation frequency of an oscillator 6 is so controlled that the output signal level of the photodetector 6 has a specific value corresponding to some phase difference, and a rotating angular speed is found from the extent of a frequency shift from the oscillation frequency in a statinary state. The optical fiber 4 is inverted by an in version driving mechanism 7 at some determined time intervals, and a correcting circuit 8 finds the drift mobility from detected values before and after the inversion and corrects it to eliminate the influence of the drift, detecting the rotating angular speed precisely.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber gyro that optically detects rotational angular velocity using a ring interferometer.

A ring interferometer with a long optical fiber as its optical path acts as a rotation meter for inertial space, and can constitute an optical gyroscope. Compared to conventional mechanical gyroscopes that use rotation with a rotor, they have the advantage of not causing errors due to wear of the rotating parts, and can provide long-life and highly reliable products. Its practical application is desired. The detection principle is Sagnac (Sag
Known as the nac) effect, it is based on the fact that a difference in propagation time occurs between two lights propagating in opposite directions in an optical fiber, which is proportional to the speed of movement of the optical fiber. However, the difference in propagation time caused by the Sagnac effect,
Since the phase difference caused by this is very small, it is necessary to use a fairly long optical fiber and to measure the phase difference with high precision. Various methods have already been proposed for detecting rotational angular velocity from such a weak phase difference. However, in reality, a large error called a drift error occurs in which the zero point of the phase difference changes due to the effects of light source output fluctuations, wavelength changes, and optical fiber transmission loss changes, so all methods are still insufficient. Accuracy has not been achieved.

Furthermore, since the optical fiber gyro is a so-called rate gyro and can only detect rotational angular velocity, in order to know the direction, it is necessary to calculate the detected rotational angular velocity efft. Therefore, if there is a drift as described above, the calculated orientation will deviate from the correct orientation over time, and there is a drawback that it can only be used for short-term measurements.

There was no known detection method.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical fiber gyro that can detect the amount of drift and, by correcting the drift amount, can accurately detect the rotational angular velocity.

According to the present invention, there is provided a light source, a photodetector, a coiled optical fiber, and a portion of the output light of the light source is incident on both ends of the optical fiber and emitted from both ends of the optical fiber. an optical branching and combining circuit that superimposes two lights and outputs an optical signal with an intensity corresponding to the phase difference to the photodetector; An optical fiber gyro is obtained which is characterized in that it is equipped with means for alternately inverting the optical fiber by 180° at appropriate times.

This optical fiber gyro has the following features: When a coiled optical fiber is reversed, the detected rotation direction is reversed for the Sagnac effect, but does not change for the drift component, and that drift usually changes slowly. The rotational angular velocity can be detected with high accuracy by completely inverting the coiled optical fiber part at a required time interval, detecting the amount of drift, and correcting it.

Next, the present invention will be explained in detail with reference to the drawings.

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

The light source 1 is a single wavelength laser light source, and its output light 10
1 enters the semi-transparent mirror 2, and the component 102 transmitted through the inner core semi-transparent mirror 2 is frequency-shifted by the oscillation frequency using the output of the oscillator 6 in the acousto-optic modulator 3, and then is emitted from the end face 41. The light is input into the fiber 4. On the other hand, the component 103 reflected by the semi-transparent mirror 2 enters the optical fiber 4 from the other end face 42 as it is. Both end faces 41.4
The two lights incident from 2 propagate through the coiled optical fiber 4 and are emitted from opposite end faces 42 and 41, respectively. These two emitted lights 104 and 105, one of which remains unchanged, the other of which is frequency shifted by the acousto-optic modulator 3, and then both enter the semi-transparent mirror 2. In the semi-transparent mirror 2, these two lights are superimposed and emitted to the photodetector 5 side and the light source 1 side according to the phase difference. With this configuration, when the oscillation frequency of the oscillator 6 is controlled so that the output signal strength of the photodetector 5 becomes a predetermined value corresponding to a certain phase difference,
The amount of frequency change from the oscillation frequency in a stationary state and the rotational angular velocity can be determined. Although the value includes a drift error, the optical fiber 4 is quickly reversed at a predetermined time interval by the reversing drive mechanism 7,
In the correction step j168, the amount of drift is determined from the detected values before and after the reversal, and the amount of drift is corrected, thereby making it possible to eliminate the influence of drift in this fiber optic gyro and detecting the rotational angular velocity with high accuracy.

In the first embodiment described above, one of the signals separated by the semitransparent mirror 2 is detected by the photodetector 5 as a phase detection method, but the other signal that returns to the light source 1 side is branched and detected. Alternatively, a configuration in which both signals are detected and the oscillation frequency is controlled so that the ratio of their outputs is constant may be used, as in the first embodiment, to correct the drift (f) and accurately control the rotational angular velocity. can be detected.

FIG. 2 is a block diagram conceptually showing the configuration of an optical fiber gyro according to a second embodiment of the present invention.

In this configuration, an optical phase modulator 9 is used in place of the acousto-optic modulator 3 of the first embodiment, and weak phase modulation is performed on the optical signal by the output signal of the oscillator 61. By extracting the modulated frequency component contained in the output signal of and synchronously detecting it with the synchronous detector 10, an output approximately proportional to the rotational angular velocity can be obtained. Even in this configuration, by inverting the coiled optical fiber 4, the correction circuit 8 can correct the drift as in the second embodiment.

Note that even when using a detection method other than the above embodiments,
By inverting the coiled optical fiber, drift can be similarly corrected and the rotational angular velocity can be detected with high accuracy.

In addition, each of the above embodiments has a configuration in which the amount of drift is determined and corrected, but when calculating the change in direction by integrating the detected value of rotational angular velocity, simply reverse the sign of the detected value of rotational angular velocity at the same time as reversal. By doing this, it is possible to determine the exact change in direction when all the lights are off during the drift.

Note that the time interval for reversing can be arbitrarily set within a range that is faster than the change in drift, and it is also possible to perform control so that the rotation angular velocity is completely reversed during times when the rotational angular velocity is high, and reversal is performed during times when the rotational angular velocity is low. Yes, this is possible, and in this case, errors caused by inversion can be reduced. Further, the portion to be inverted may be the entire detection system or only the optical fiber.

In each of the above embodiments, a single wavelength light source such as a semiconductor laser or a gas laser can be used as the light source, and a photodiode or avalanche photodiode can be used as the photodetector. - In addition to a semi-transparent mirror, various types of optical directional couplers can be used as the tip branching and combining circuit.

As detailed above, according to the present invention, in an optical fiber gyro that utilizes the Sagnac effect, the temperature of the light source, optical fiber, etc. can be adjusted by inverting the coiled part of the optical fiber at required time intervals. An optical fiber gyro can be obtained that can detect and correct the drift caused by the change in characteristics due to , and can accurately detect the entire rotational angular velocity.

[Brief explanation of the drawing]

1 and 2 are the first and second embodiments of the present invention, respectively.
1 is a block diagram conceptually showing the configuration of an optical fiber gyro according to an embodiment of the present invention. 1... Light source, 2... Semi-transparent mirror, 3...
Acousto-optic modulator, 4... Optical fiber, 5... Photodetector, 6, 61... Oscillator, 7... Inversion drive mechanism, 8... Correction circuit. Plan 1 Figure

Claims (1)

[Claims] A light source, a photodetector, a coiled optical fiber,
The output light of the light source is divided into two parts and input from both ends of the optical fiber, and the two lights emitted from both ends of the optical fiber are completely superposed, and an optical signal with an intensity corresponding to the phase difference thereof is sent to the photodetector. An optical fiber gyro comprising: a light branching/combining circuit for outputting light to the coiled optical fiber;