JPH05272981A - Optical gyro - Google Patents

Abstract

PURPOSE:To obtain an optical gyro which can compensate change in light path due to change in temperature and pressure speedily. CONSTITUTION:This gyro is provided with light sources 21 and 22 and a frequency resonator 20 with a stable frequency, an optical system for introducing light from both directions to frequency resonators, detectors 23-27 for detecting light which is output from the frequency resonator 20, and controllers 33 and 34 for comparing the intensity of light which is entered from one direction with that of light which is irradiated and then performs negative feedback of the change to the light sources 21 and 22. It is constituted so that the frequency of light entering each direction is fixed to one constant point of a resonator characteristic slope.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an optical gyroscope using a light source and a frequency resonator (hereinafter simply referred to as an optical gyro).
Regarding

[0002]

2. Description of the Related Art An optical gyro is a device for detecting the acceleration of a rotating object. FIG. 4 is an explanatory view of the principle of the optical gyro. It is assumed that there is a ring 2 rotatable about a rotation axis 1. This ring shall be made of a material that transmits light. Now, when light is input from the point A, this light splits into a loop L1 and a loop L2 and travels in the ring 2. In the state where the rotary shaft 1 is not rotating, the light traveling through L1 and the light traveling through L2 reach the point A at the same time.

However, when the rotary shaft 1 rotates clockwise as shown in the figure, the optical path of L1 apparently becomes longer than the optical path of L2, and the light interference state at point A changes from that in the stationary state. From this changed state, the angular velocity (rotational acceleration of the circular motion) of the rotating object can be obtained. In other words, if the angular velocity of the circular motion of the object is ω, and the radius of the circular motion is r, then between the acceleration α and the angular velocity ω, α
Since there is a relationship of = rω ² , it is easy to obtain the acceleration from the angular velocity (which means the angle at which the radius vector rotates for 1 second).

FIG. 5 is a diagram showing a configuration example of a conventional optical fiber gyro. In the conventional optical fiber gyro, changes in the optical path length caused by temperature and pressure of the optical fiber are detected, and the temperature and pressure corresponding to the changes are applied to the optical fiber to control the optical path length to a constant value. is doing. Frequency f
The light emitted from the first light source 11 is a half mirror M1,
It is reflected by M2 and enters the acousto-optic device (AOM) 12.
A frequency of an oscillation frequency ΔfA is applied from the oscillator 13 to the AOM 12. Therefore, from AOM12,
Light of frequency f1 + ΔfA is output.

This light passes through the half mirror M4 and enters the fiber-ring resonator 20. The fiber-ring resonator 20 is composed of a fiber 20a and an optical coupler C1. It is assumed that the fiber resonator 20 is rotating at a certain angular velocity in the direction shown in the figure. The frequency f
The light of 1 + ΔfA is the light that escapes from the optical coupler C1 without entering the fiber 20a, the light that enters the fiber 20a through the optical coupler C1, makes one round, and re-emits from the optical coupler C1, and makes two rounds of the optical coupler C1. The light coming out of it, divided into three rounds, and so on.

These lights interfere at the exit of the optical coupler. The interference light is reflected by the half mirror M3 and enters the light intensity detector 14. The output of the light intensity detector 14 is represented by P (f1 + ΔfA + Δf) as a power fluctuation function P. This signal enters one input of the lock-in amplifier (LIA) 15. The output ΔfA of the oscillator 13 is input to the other input of the LIA 15 as a reference signal. And the LIA15
Drives a piezoelectric element (PZT) 16 by generating a DC component signal of a fluctuation function P according to the phase difference between both inputs. The PZT 16 applies a force to the fiber 20a according to the input voltage. At this time, the optical path length of the fiber 20a changes according to the force. When the optical path length changes, the frequency Δf changes according to the angular velocity. Light intensity detector 14 to LIA 15
The feedback signal to the signal acts so that the frequency Δf becomes zero.

In this steady state, the light intensity detector 17
Difference (corresponding to the input of f1) and the output of the light intensity detector 18 of the light of f1 that has passed through the fiber-ring resonator 20 (corresponding to the modulation output of f1).
This deviation output becomes a signal corresponding to the angular velocity. The angular velocity and acceleration can be calculated from this signal.

[0008]

In the above-mentioned conventional optical fiber gyro, a change in optical path length caused by a change in temperature or pressure of the optical fiber is detected, and the temperature or pressure corresponding to the change is detected in the optical fiber. Negative feedback is performed to control the optical path length to be constant. However, this method can correct changes in optical path length due to large temperature and pressure changes,
When the change in temperature and pressure is small, there is a problem that the change due to the addition of the angular velocity and the change due to the change in temperature and pressure cannot be clearly discriminated. In other words, the conventional method has a drawback in that it cannot detect the resolution because the signal change is detected by the light intensity, and the accuracy cannot be obtained because the environmental change such as temperature and pressure cannot be completely corrected. .. Also,
The space type resonator has the same drawback.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical gyro which can correct a change in an optical path due to a change in temperature or pressure at high speed and with high accuracy.

[0010]

According to the present invention for solving the above-mentioned problems, a light source having a stable frequency, a frequency resonator, an optical system for bidirectionally introducing light into the frequency resonator, and the frequency resonator are provided. A detector for detecting the light output from the device, and a controller for comparing the intensity of the light incident from one direction with the intensity of the emitted light and negatively feeding back the change to the light source,
It is characterized in that the frequency of light incident in each direction is fixed to a fixed point of the resonator characteristic slope.

[0011]

The change in the signal is detected not as the light intensity but as the change in the frequency. This makes it possible to provide an optical gyro that can improve the resolution and accuracy of signal changes and can quickly correct changes in the optical path due to changes in temperature and pressure.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The same parts as those in FIG. 5 are designated by the same reference numerals. In the figure, 21 and 22 are light sources with stable optical frequencies. Let the frequency of the light source 21 be f1 and the frequency of the light source 22 be f2. C1 to C6 are optical couplers. 23-27
Is a light intensity detector, 28 and 29 are analyzers, 30 is a half-wave plate, 31 is a deviation detection amplifier, and 32 is a signal generator. Reference numerals 33 and 34 are comparators, and 35 is a mixer (combiner).

The output light from the light source 21 is the optical couplers C3 and C2.
The light output from the light source 22 is connected to the optical coupler C1 via the optical couplers C5 and C6. Part of the optical coupler C3 is connected to the optical coupler C4 via the half-wave plate 30, and part of the optical coupler C5 is connected to the optical coupler C4. A part of the optical coupler C4 is connected to the light intensity detector 24.

A part of the optical coupler C2 is connected to the light intensity detector 23, and the output of the light intensity detector 23 is input to one input of the comparator 33. Further, a part of the optical coupler C2 enters the light intensity detector 26 via the analyzer 28, and the output of the light intensity detector 26 enters one input of the comparator 34.

Further, a part of the optical coupler C6 enters the light intensity detector 27 via the analyzer 29, and the output of the light intensity detector 27 is input to the other input of the comparator 33. A part of the optical coupler C6 enters the light intensity detector 25, and the output of the light intensity detector 25 enters the other input of the comparator 34.

The output of the light intensity detector 24 is the mixer 35.
And is multiplexed with the output of the signal generator 32 and the frequency is beat down. The output of the mixer 35 enters the deviation detection amplifier 31, and the deviation detection amplifier 31 outputs a frequency deviation signal corresponding to the angular velocity of the fiber-ring resonator 20. The operation of the apparatus configured as described above will be described below.

The light emitted from the light source 21 is an optical coupler C3.
Are divided into two, and one light is incident on the optical coupler C2 and the other light is incident on the optical coupler C4. The light incident on the optical coupler C2 is divided into two again, and one of them is converted into an electric signal corresponding to the light intensity by the light intensity detector 23 as a light intensity reference signal.

The other light split by the optical coupler C2 enters the optical coupler C1 of the fiber-ring resonator 20 and enters the fiber-ring resonator 20. This light is emitted from the fiber-ring resonator 20 under the influence of external acceleration, passes through the optical coupler C6, and enters the analyzer 29. Then, the analyzer 29 allows only the component of the light source 21 to pass therethrough, and the light intensity detector 27 detects the intensity of the passed light. The detection signal of the light intensity detector 27 and the reference signal (output of the light intensity detector 23) shown above are compared by the comparator 33.

Then, the comparator 33 controls the output frequency of the light source 21 so that the intensity ratio of these light intensity signals becomes a constant value. In the light source 21, the frequency of the light output is changed by changing the current value of the laser, for example. Similarly, for the light source 22, the intensity ratio of the output of the light intensity detector 25 and the output of the light intensity detector 26 becomes a constant value.
The output of the comparator 34 feedback-controls the frequency of the light source 22.

Here, consider the operation when the angular acceleration Δf from the outside acts on the fiber-ring resonator 20. It is assumed that the output frequencies of the light sources 21 and 22 are f1 and f2, respectively, when the acceleration is 0. The absorption characteristic of the fiber-ring resonator 20 is expressed as shown in FIG. In the figure, the horizontal axis is the frequency f and the vertical axis is the absorption rate P. The solid line in the figure shows the characteristics before changes in temperature and pressure, and the broken line shows the characteristics after change. When the acceleration Δf is applied, the light undergoes a frequency change due to the Sagnac effect, and A → A ′, respectively.
The intensity and frequency of the transmitted light change as B → B ′.

In this embodiment, the frequencies of the light sources 21 and 22 are changed so that the intensity of the transmitted light has a constant ratio with respect to the absorption characteristics. That is, the emission frequencies of the light sources 21 and 22 are controlled so that the frequencies f1 + Δf and f2 -Δf while passing through the fiber-ring resonator 20 become the frequencies f1 and f2 in a state where no acceleration is applied. This change in the light source frequency is heterodyne detected by the optical coupler C4 and the light intensity detector 24. This signal and the output (f1 -f2) of the signal generator 32 are combined by the mixer 35, beat down to remove the frequency components f1 and f2, and enter the deviation detection amplifier 31. The deviation detection amplifier 31 outputs only the change in acceleration due to the beat signal detection as a deviation signal (acceleration).

Next, consider a state in which the fiber-ring resonator 20 is subject to temperature changes, pressure changes, and the like. At this time, it is assumed that the optical path length of the resonator 20 is changed and the state shown by the broken line in FIG. 2 is obtained. Even when no acceleration is applied to the resonator 20, the absorption characteristic moves with respect to the frequency axis due to the temperature change and the like.

Therefore, when the light of a constant frequency is observed, it appears as a change in intensity (A ", B"). However, if the transmitted light intensity is controlled so as to have a constant ratio with respect to the absorption characteristics (control level in FIG. 2) as in the present embodiment, the fiber-ring resonance may occur even if the absolute value of the frequency changes. Frequency difference between the two directions of light entering the container 20 (f1 -f
2) can be maintained constant and there is no need to control the fiber-ring resonator as in the conventional example. Therefore, highly accurate acceleration detection can be performed.

FIG. 3 is a block diagram showing another embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals.
In this embodiment, spatial light is used instead of the fiber and the optical coupler. Therefore, beam splitters M10 to M15 as shown in the figure are installed in the middle of the optical path. The operation is the same as in FIG.

In the above-mentioned embodiments, the case where the fiber is used as the optical path is taken as an example. However, the present invention is not limited to this, and an optical waveguide or the like can be used. Further, although the optical heterodyne method is used as the method for detecting the optical frequency difference in the above-described embodiment, the present invention is not limited to this, and other detecting methods can be used.

Further, although the fiber-ring resonator is used as the resonator in the above-mentioned embodiment, a structure utilizing the transmission characteristic or the reflection characteristic of the space type resonator may be used. Further, when the light sources 21 and 22 used in the above-described embodiment are configured to modulate and output the light, noise correction of a light intensity detector or the like and synchronous detection at the time of intensity comparison before and after entering the resonator are performed. Can be easy.

Further, in the conventional example, the light path length of the resonator can be controlled by changing the temperature and pressure by detecting the change of the resonator by transmitting the light corresponding to the peak portion of the absorption characteristic of the ring resonator as shown in FIG. If you add a control method,
The effect of pressure change can also be corrected.

In the embodiment of FIG. 1, the control level is turned clockwise.
It was set counterclockwise, but it is not necessary to match them. Further, in the embodiment of FIG. 1, the counterclockwise rotation and the clockwise rotation are fixed to one absorption characteristic of the resonator, but the control point may be set to another absorption characteristic. Further, in the embodiment, two light sources 21 and 22 are used, but the same function can be obtained even if the light emitted from one light source is divided into two and one of them is frequency-modulated as in the conventional example. Be done.

[0029]

As described above in detail, according to the present invention, a control system for changing the frequency so as to fix the resonator characteristic slope to a fixed point by the respective lights of the reverse rotation of the optical resonator is provided. Since it is used, it is possible to clearly separate the fluctuation due to the change in the temperature and pressure of the gyro and the fluctuation due to the change in the angular velocity. Then, the above correction can be realized accurately and easily.

Further, since the frequency is detected by the optical heterodyne and the electric heterodyne, stable and highly accurate acceleration detection can be performed. As described above, according to the present invention, it is possible to provide an optical gyro that can quickly correct a change in the optical path due to a change in temperature or pressure.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing absorption characteristics of a fiber-ring resonator.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a diagram illustrating the principle of an optical gyro.

FIG. 5 is a diagram showing a configuration example of a conventional optical fiber gyro.

[Explanation of symbols]

 21,22 Light source 23-27 Light intensity detector 28,29 Analyzer 30 1/2 wavelength plate 31 Deviation detection amplifier 32 Signal generator 33,34 Comparator 35 Mixer C1-C6 Optical coupler

Claims (1)

[Claims] 1. A light source having a stable frequency, a frequency resonator, an optical system for bidirectionally introducing light into the frequency resonator, a detector for detecting light output from the frequency resonator, and a unidirectional Equipped with a controller that compares the intensity of the light incident from and the intensity of the emitted light and negatively feeds back the change to the light source, and fixes the frequency of the light incident in each direction at a fixed point of the resonator characteristic slope. An optical gyro characterized by being configured to.