JPS63217216A - Optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To obtain a device which corrects a mechanical shift in fiber position and has small drift by splitting two light beams propagated in an optical fiber in opposite directions and observing the quantities and intensity values of light which does not interfere and light which interferes to vary by the phase difference. CONSTITUTION:The projection light beam from a light source 1 is split by a polarized light demultiplexer 2 into 1st and 2nd light beams 1 and 2 which have different planes of polarization, which are propagated in the optical fiber loop 4 in the opposite directions to obtain 3rd and 4th light beams 3 and 4, which are multiplexed by a demultiplexer 2. One frequency shifter 3 is arranged between them to shift the frequency of the passing beam 1. Then the multiplexed light beam (5) is split by an optical demultiplexer 5 and the light beam (6) which does not interfere is made incident on a photodetector 6 to detect its light quantity. A polarized light optical demultiplexer 7 extracts a specific polarized wave component and makes it incident on a photodetector 8 as a light beam (7)' to detect its light intensity.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is directed to improving a gyro configured using optical fiber, and more specifically, to reducing the drift of a frequency modulation type optical fiber gyro. It is something that will take place.

2. Description of the Related Art Rotation sensors that detect angular velocity are required for position detection and attitude control of various moving objects such as aircraft and ships, and mechanical gyros have been mainly used. However, mechanical gyros have problems such as a long start-up time due to the need to rotate the rotor at high speed, drift due to bearing friction, and difficulty in extending the life of the gyro.

Therefore, in recent years, gyros other than mechanical gyros have been developed with the aim of putting them into practical use.

The optical fiber gyro according to the present invention is one such device, and since it has no mechanically moving parts, it has short start-up time and long life, and is being researched.

The basic principle of angular velocity detection with this optical fiber gyro is that, as shown in Figure 6, when light propagates in opposite directions through a ring-shaped optical path, the CW light (light waves propagating clockwise) and CCW light (light waves propagating counterclockwise) is based on the Sagnac effect, which states that when the entire optical path is rotating, the time required for each rotation varies depending on the angular velocity. In other words, if the optical path is rotating clockwise, the exit of the ring-shaped optical path appears to approach the CCW light.
On the other hand, for CW light, it appears to be moving away. Therefore, even if the optical path is the same, it can be observed that the optical path length of each light until it reaches the exit differs depending on the magnitude of the angular velocity. When two lights propagated through optical paths with different optical path lengths are superimposed, they interfere with each other, and the intensity changes depending on the difference in the two optical path lengths, that is, the phase difference. An optical fiber gyro measures changes in angular velocity as changes in light intensity in this way.

Its basic configuration is as shown in FIG. 7(a), in which the light emitted from the same light source 701 is split into two by a beam splitter 702, and an optical fiber loop is constructed by winding a long single mode fiber many times. 704 in opposite directions,
The two emitted light waves are combined and interfered again, and the light intensity is detected by a light receiver 708.

The light waves reaching the photoreceiver 708 have a time difference, that is, a phase difference, due to the 5agnac effect, and thereby the amount of light changes as shown in FIG. 7(b). The principle of the optical fiber gyro is to detect the change in the amount of light p and conversely obtain the angular velocity ω.

With this basic configuration of an optical fiber gyro, there are problems in that the change in light intensity with respect to angular velocity is not linear and the sensitivity is low at low angular velocities, so various improvements have been made and research is underway with the aim of practical application. is in progress.

(Prior Art) In order to put this fiber gyro into practical use, it is essential to adopt a method of increasing sensitivity, and two methods are used, which can be roughly divided into a frequency change method and a phase modulation method.

In the phase modulation method, high resolution and low drift can be achieved relatively easily, but it has the disadvantage that a wide dynamic range cannot be achieved, so it has not yet been put into practical use.

Although a wide dynamic range can be obtained relatively easily with the frequency change method, it has the disadvantage that it is difficult to reduce drift.

The basic idea of this frequency variation method is to use an acousto-optic device (AOM) etc. to change the frequencies, or wavelengths, of light propagating in opposite directions through an optical fiber loop, thereby creating a ring shape. This is a zero-position method in which a phase difference is created equivalently in the optical path to cancel out the phase difference caused by the Sagnac effect.

In Figure 8, Auch Fiber-Optic
Gyro With Polarization Pre
serving Fiber″Sywp, Gyro.

A configuration example of this frequency variation method according to Tech pp, 2.1-2.15 (1983) is shown. The light emitted from the light source 1 such as a laser shown in FIG. 8 is transmitted to a beam splitter 51. The 0-divided light passes through the constant polarization fiber +02, which is a mode filter, and is split into two by the beam splitter 21, and is divided into light that propagates clockwise in the fiber loop 4 and light that propagates counterclockwise. Each acousto-optic device (AOM)
30.31. It propagates through the fiber loop 4 in the opposite direction, and is combined again by the beam splitter 21 to form the fixed polarization fiber 1.
02. The light passes through the beam splitter 51 and reaches the light receiver 8 . The acousto-optic elements 30 are connected alternately in a time-sharing manner through oscillators 209 and 210 driven at frequencies f, , f, and a switch 213, respectively. The controller 206 controls the V for driving the acousto-optic element 31 so that the light amount signal detected by the light receiver 8 does not change in synchronization with the switch 213.
The oscillation frequency f of CO207 is controlled.

The output signal F is the ft and fh output from the signal generator 220.
The mixer 221 generates a signal with a frequency that is the difference between a signal with an average frequency of , and a signal with a frequency f output by the VCO 207 .

In such an optical fiber gyro, E, J, Po
5t “Sagnac Effect Rev, of
Modern Phys, vol.

Due to the Sagnac effect described in 39-2 p., 475-493 (1967), when this entire system rotates at an angular velocity ω, the light propagating clockwise in the optical fiber loop 4 and the light propagating counterclockwise. However, when they reach the light receiver 8, a phase difference ψ3 occurs between them.

Here, λ is the wavelength, C is the speed of light, R is the radius of the fiber loop, and L is the length of the fiber loop.

In the configuration example shown in FIG.
By connecting, the frequency of light is changed to (f-fI) or (
f−fh>, which is expressed as Δf. This causes a phase difference ψ between the clockwise light and the counterclockwise light on the light receiver 8.

However, n is the refractive index of the fiber core. The light receiver 8 obtains the interference light intensity between the two lights, and its output ■ is given by (ae l +cos (ψ3+ψ4-)).The controller 206 controls the acousto-optic element 30 to When driven at a frequency of The VCO 207 is controlled to set the receiver 8.
When the amount of light at is large when the acousto-optic element 30 is driven at the frequency fl, the driving frequency f of the acousto-optic element 31 is increased, and in the opposite case, the driving frequency f of the acousto-optic element 31 is decreased.
Controls the set voltage to 07. With such a servo system having a closed loop, the frequency and angular velocity for driving the acousto-optic elements 30 and 31 satisfy the following relationship.

At this time, the frequency F of the signal output from the mixer 221 changes linearly with respect to the angular velocity, that is, a gyro is configured as a rotation sensor.

(Problems with the Prior Art) One of the problems with the gyro is that the diameter of the optical fiber serving as the sensing loop is small, particularly the diameter of the core serving as the optical path is as small as 6 to 10 microns. In an optical fiber, light cannot propagate unless the light beam is precisely focused on this core. Therefore, if for some reason a relative deviation occurs between the position of the core of the optical fiber and the position of the light spot image obtained by reflecting the light beam with a lens, the amount of light propagating through the optical fiber will change. In a basic optical fiber gyro system, this appears as a drift in measured values. For this reason, there was a drawback that high performance could not be obtained. This will be further explained as follows.

(1) As the magnitude of the deviation between the position of the light spot and the position of the core as shown in FIG. 9 increases, the amount of light guided into the optical fiber decreases as shown in FIG. 10.

(2) Therefore, the amount of light obtained by propagating through the fiber and combining and interfering changes even if the angular velocity does not change.

(3) The detector cannot distinguish between a change in light amount due to a change in angular velocity and a change in light amount caused by positional deviation, resulting in a drift in the measured value.

In the frequency change method gyro shown in FIG. 8, a change in the amount of light synchronized with modulation of the drive frequency of the acousto-optic element causes a drift in the measured value. This drift generating mechanism will be explained in detail with respect to the gyro shown in FIG.

In this gyro configuration, light passing through the acousto-optic element is diffracted in the direction of an angle determined by its driving frequency, and the light is imaged by a lens to form a spot image on the fiber end face. In this gyro, the measured value of the angular velocity is obtained at the driving frequency of the acousto-optic element using the null method in which the phase difference between the CW light and the CCW light is set to zero. In order to detect that this phase difference is zero and set the drive frequency, the drive frequency of the acousto-optic element is FM modulated in a rectangular waveform. Therefore, the position of the spot image also changes accordingly.

Therefore, the amount of light entering the photodetector changes in synchronization with this FM modulation.

Figure 11(a) shows the relationship between the phase difference given by the acousto-optic element and the amount of detected light when the movement of this spot image is negligibly small and the amount of light detected by the photodetector changes only due to the phase difference. It shows. However, in reality, the movement of the spot image is not small as shown in Figure 1(a), and the relationship between the phase difference given by the acousto-optic element and the amount of detected light is as shown in Figure 0(b). The change in light amount caused by the movement of the spot image is superimposed on the change in light amount caused by the movement of the spot image. The slope of the change in light amount due to the movement of this spot image changes depending on a slight change in the position of the fiber end. Therefore, when frequency modulation is applied around the point where the phase difference is zero, a change in the light amount signal appears in synchronization with the modulation. Since this signal is used to detect how far the phase difference deviates from zero, changes in this light amount signal affect the measured value as a drift. Therefore, even a slight shift in the position of the fiber due to a temperature change, for example, will cause a drift in the measured value. In addition to this mechanical variation of the fiber position, the temperature of the acousto-optic element,
The position of the light spot image also changes due to variations in the wavelength of the laser beam, which similarly causes a drift. In reality, it is difficult to reduce these changes, so high performance cannot be obtained, which has been an obstacle to practical application. For example, if (f h - f t) = 100, the sound velocity of the acousto-optic element is 3600 ■/sec, and the focal length of the imaging lens is 5
．． In a typical configuration example of an optical fiber gyro with 3n+*, each 1 micron change in fiber position causes 0.
It is calculated that a drift of about 3"/sec occurs. In a real system, it is quite difficult to fix the position of the fiber end with fluctuations of less than 0.1 micron, so It was difficult to suppress the drift to a magnitude of about 1.0 sec. In an inertial navigation system, it is necessary to reduce the drift to 10 ''/sec. This is not possible in reality, and optical gyroscopes cannot be applied.

In other words, the reason why the frequency-changing optical fiber gyro had a wide dynamic range and high resolution could not be put into practical use because the cause of the above drift was not sufficiently clarified, and no countermeasures were taken. First, it did not have the ability to be stably measured.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems of the prior art, and provides a high-performance optical fiber gyro with less drift by correcting mechanical fluctuations in the fiber position. The purpose is to provide the following.

(Point of focus for solving the gap) In other words, mechanical fluctuations in the fiber position affect the intensity of the light that is combined and interfered, resulting in drift. We focused on the point that if the intensity of the light to be combined and interfered is kept constant, the amount of light detected by the photodetector will change only due to the phase difference, and no drift will occur.

Therefore, we installed a new detector and configured an optical system that allows this detector to observe changes in the amount of light propagated through the optical fiber.

In order to be able to observe changes in the amount of light propagated through the optical fiber, it is necessary to prevent two lights propagated in opposite directions through the optical fiber loop from interfering with each other.

As a method to prevent interference after being propagated through a fiber loop and combined, two linearly polarized lights whose polarization planes are orthogonal to each other are combined, and the light intensity is affected by the phase difference between the two lights. I took advantage of the fact that it wasn't. In other words, a polarized light demultiplexer is used to combine the lights that have propagated in opposite directions through the optical fiber loop, and in the combined light, the two lights that have propagated in opposite directions through the optical fiber loop have their polarizations. The wavefronts are configured to be orthogonal to each other.

The light combined in this way has a constant light intensity regardless of the phase difference, so if it is split with a light splitter that does not change the polarization state and guided to a photodetector, it can be connected to an optical fiber. The amount of light that propagated can be observed.

With the above configuration, it is possible to use the newly installed detector to detect changes in the amount of light propagated through the optical fiber due to the influence of disturbances, etc., and use the output of this detector to detect changes in the amount of light propagated through the optical fiber. By controlling the drive power of the element or the output of the laser beam, the brightness of the optical spot image on the end face of the optical fiber can be changed, so that the amount of light propagated through the optical fiber can be kept at a constant value.

Furthermore, it is necessary to combine two linearly polarized lights whose planes of polarization are orthogonal to each other and to interfere with each other to extract light whose light intensity changes depending on the phase difference. To achieve this, if we extract only the polarized components of two linearly polarized lights whose polarization planes are orthogonal to each other as linearly polarized lights, these lights will interfere with each other, and their light intensity will vary according to their phase difference. We took advantage of the fact that . In other words, two lights propagating in opposite directions through an optical fiber loop are combined by a polarization splitter, and one of the lights split by a light splitter that does not change the polarization state is passed through a polarization element. By guiding the light to a detector, it is possible to observe interference light in which the phase difference caused by the Sagnac effect is converted into light intensity.

In other words, the main point of the present invention is to improve the configuration of the optical system,
After propagating through a fiber loop and combining, two lights that propagated in opposite directions are kept from interfering with each other, and the light is split into two to observe the intensity of the light that does not interfere with one of the lights. The optical system is designed so that the other split light interferes with the other split light in the same way as before, changing it according to the phase difference, and then leads it to a conventional detector to observe the light intensity. This is due to the placement of the .

With this invention, a signal indicating changes in the amount of light propagated through the optical fiber due to the influence of disturbance etc. can be obtained from the newly installed detector, and this can be used to control the driving power of the acousto-optic element or the output of the laser light. By changing the brightness of the light spot image on the end face of the optical fiber, the amount of light propagating through the optical fiber can be made constant. By realizing this, the amount of light detected by the other photodetector can be changed only by the phase difference between the two lights propagating in opposite directions through the optical fiber. As a result, a signal that is not affected by disturbances such as minute fluctuations in the position of the optical fiber and changes only depending on the angular velocity to be measured can be obtained, so a highly accurate optical fiber gyro with little drift can be constructed.

(Means for solving the problem) The optical gyroscope according to the present invention emits light! (1); an optical fiber loop (4) that propagates first and second light beams entering from both ends in opposite directions and exits from both ends as third and fourth light beams; The light beam emitted from the light source is divided into first and second light beams with different polarization planes and emitted toward both ends of the optical fiber loop. polarized light demultiplexing means (2) that combines the third and fourth light beams and outputs a fifth light beam; and a polarized light demultiplexing means (2) that is provided between the optical fiber loop and the polarized light demultiplexing means and passes through the polarized light demultiplexing means. a frequency shifter (3) that shifts the frequency of the beam; and a fifth light beam output from the polarized light splitting means, which is divided into two, and one of the light beams obtained by dividing into two is converted into a sixth light beam. polarization and light demultiplexing means (which extracts a specific polarization component from the other and outputs it as a seventh light beam);
5, 7) and the sixth beam from the polarization and light demultiplexing means.
A first light receiver (6) that detects the light intensity of the zero light beam, and a second light receiver (8) that detects the light intensity of the seventh light beam from the polarization and light splitting means. It is characterized by:

According to this aspect, the polarization and optical demultiplexing means includes an optical demultiplexer (5) that divides the fifth optical beam into a sixth optical beam and a seventh optical beam; It is characterized by comprising a polarization optical demultiplexer (7) that receives the seventh light beam from the optical demultiplexer and outputs a light wave of a specific polarization component thereof.

(Operation) The operation of the above configuration will be explained with reference to FIG. In the figure, a light beam emitted from a light source 1 is split into two by a polarized light demultiplexer 2, which is a polarized light splitting means, according to the polarization component of the light, resulting in two linearly polarized light beams. ■
becomes. These two light beams (■) enter from both ends of the optical fiber loop 4 and propagate in opposite directions.

Since at least one frequency shifter 3 is disposed between the polarization light demultiplexer 2 and the end face of the fiber 4, the frequency of the light beam (3) passing through it is shifted.

As a result, one of the light beams (■) among the lights propagating through the optical fiber loop 4 has its frequency shifted before propagating through the optical fiber loop 4, and the other light beam (■) propagates through the optical fiber loop 4. The frequency is shifted from When two lights of different frequencies propagate through an optical path of the same length, the optical path lengths appear to be different, so the phase difference between the two lights changes depending on the transition frequency.

The third light beam ■ and the fourth light beam ■ that have propagated through the optical fiber loop 4 and reached the polarization splitter 2 pass through the frequency shifter 3 once each, so their frequencies are the same. They are shifted and are the same, but because they are propagating through the optical fiber at different frequencies, that is, because they are propagating at different wavelengths, their apparent principal optical path lengths are different and their phases are different.

The polarized light demultiplexer 2 separates the third light beam ■ and the fourth light beam ■
is divided into two parts according to their respective polarization states,
It emits two light beams that are superimposed on each other. The two obtained light beams, the light from the third light beam (2) and the light from the fourth light beam (2), do not interfere with each other because their planes of polarization are orthogonal to each other.

The fifth light beam (■), which is one of the obtained light beams, is obtained by combining the third light beam (■) and the fourth light beam (■), each of which has become a linearly polarized light whose polarization planes are orthogonal to each other. It has been obtained.

In addition, as the fifth light beam (■), the third light beam is
Either of the two light beams generated by combining the light beam (■) and the fourth light beam (■) can be taken, but the optical path of the fifth light beam (■) is emitted from the light source l and the polarized light is separated. It is better to match the optical path of the light beam up to the wave splitter 2, because by matching the optical path, the light propagating in either direction through the optical fiber loop 4 will have opposite optical paths at the polarization splitter 2. Since the polarized light is guided to the optical demultiplexer 5 through one degree each, it cancels out the phase difference caused by the difference in the characteristics of the optical path of the polarized optical demultiplexer 2, which is advantageous in suppressing the drift caused by this. This is because.

In the configuration shown in FIG. 1, the polarization and light demultiplexing means consists of a light demultiplexer 5 and a polarized light demultiplexer 7.

The optical demultiplexer 6 splits the fifth optical beam (2) and generates a sixth optical beam (2) and a seventh optical beam (2). The optical demultiplexer 5 splits the light propagated through the optical fiber loop 4 into orthogonal linearly polarized lights depending on the propagation direction, so that both the fifth and sixth light beams obtained are light beams. The lights propagating in opposite directions through the fiber loop 4 do not interfere with each other, and the light intensity does not change due to the phase difference.

Since the first light receiver 6 is placed at a position where this sixth light beam (2) is incident, it is not affected by the phase relationship between the two lights that have propagated through the optical fiber loop 4 in opposite directions. A signal proportional to the sum of the amount of light propagated can be obtained. The polarized light splitter 7 is placed at a position through which the seventh light beam (1) passes, and selects and outputs a specific polarized component of the linearly polarized light whose polarization planes are orthogonal to each other. For this reason, the obtained seventh
The light beam ■゛ has the same plane of polarization and is a combination of two lights with different phases, so they interfere with each other,
The light intensity changes depending on the phase difference between the two. Therefore, the light intensity of the seventh light beam
After passing through the optical fiber loop 4, the amount of light changes depending on the amount of light that has propagated through the optical fiber loop 4 and the phase relationship of the light that has propagated in opposite directions. The second photoreceiver 8 is placed at a position to observe this as described above, and the phase difference generated by the frequency shifter 3 and the Sag
It is possible to detect the amount of light that changes according to the sum of the phase difference generated according to the angular velocity due to the NAC effect.

(Effect of the invention) By adopting such a configuration, the first light receiver 6 can obtain a signal that changes the amount of light propagated through the optical fiber loop 4 according to the magnitude, and the second light receiver 8 can obtain a signal that changes depending on the magnitude of the light amount propagated through the optical fiber loop 4. It changes depending on the phase difference between the two lights propagating in opposite directions through the optical fiber loop 4, that is, the sum of the phase difference generated by the frequency shifter 3 and the phase difference generated according to the angular velocity by the Sagnac effect. A signal is obtained.

Therefore, if the amount of light propagating through the optical fiber loop 4 changes, it can be detected, so the amount of light propagating through the optical fiber loop 4 can be kept constant by controlling the amount of light R1, the loss of the frequency shifter 3, etc. It can be done. At this time, the change in loss in the propagation path of the laser beam is corrected, and the second photoreceiver 8 simply adjusts the phase difference generated by the frequency shifter 3 and Sagn without being affected by the change in propagation loss.
It is possible to obtain a signal that changes only according to the sum of the phase difference generated according to the angular velocity due to the ac effect.

In addition, by passing the two signals through an appropriate arithmetic unit that performs division, changes in loss in the propagation path of the laser beam can be similarly corrected, and the angular velocity can be changed simply by the phase difference generated by the frequency shifter 3 and the Sagnac effect. It is possible to obtain a signal that changes only in accordance with the sum of the phase difference generated accordingly.

This makes it possible to construct a highly accurate optical fiber gyro that does not cause drift due to changes in loss in the propagation path of the laser beam.

(Example) Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 2 is a diagram showing a schematic configuration of the first embodiment of the present invention. The light beam emitted from the laser light source IO passes through the optical isolator 100 and further passes through the polarizing beam splitter 70.
．． The light passes through a non-polarizing beam splitter 50, is focused by a lens +01, and is guided to a polarization constant fiber +02.

The optical isolator 100 used in this example utilizes the Faraday effect, and transmitted light becomes linearly polarized light regardless of the properties of the laser light source IO. Although this optical isolator 100 is not essential to the present invention, it is possible to change the direction of the polarization plane of the optical beam emitted from the optical isolator 100 to prevent the laser beam from returning to the laser beam filO and making the laser oscillation unstable. The polarizing beam is made to coincide with the eigenaxis direction of the splitter 70, and is efficiently transmitted through the polarizing beam splitter 70.

Further, the direction of the eigenaxis of the core of the polarization constant optical fiber 102 is made to match the direction of the incident polarization plane.

The light emitted from the constant polarization optical fiber 102 is transmitted to the lens 10
The light is collimated at step 3, becomes parallel light, and enters the polarizing beam splitter 20. The light emitted from the constant polarization optical fiber 102 becomes linear □□□ wave light because the polarization state of the light emitted from the optical isolator 100 is preserved. This lens +01. Constant polarization optical fiber 102 and lens +0
3 is not essential to the present invention, but its provision is advantageous in improving the SNR of the signal.

By setting the plane of polarization of the light incident on the polarizing beam splitter 20 at approximately 45° with respect to the eigenaxis of the polarizing beam splitter 20, the light is split into two light beams having approximately equal amounts of light.

The two divided light beams are each passed through an acousto-optic element 30.
．． 31 and condensed by lenses 104 and 105, the light is guided to the optical fiber loop 4. As a result, the frequency of each light beam is shifted by a frequency equal to the driving frequency of each acousto-optic element. 2 acousto-optic elements
This is because the drive frequency band and the desired band are different, so two acousto-optic elements are used to bring the difference in frequency to the desired band. For example, two acousto-optic elements are used. If the drive frequencies are made equal, the frequencies of the two light beams can be made the same. Needless to say, one element is sufficient as long as the frequency band to be driven matches the desired band.

After each of the two light beams propagates through the optical fiber loop 4 in opposite directions, they pass through the lens 104 or +05 and the acousto-optic element 30 or 31 again, enter the polarizing beam splitter 20, and are superimposed. In this embodiment, a constant polarization optical fiber is used as the optical fiber of the optical fiber loop 4, and by making the plane of polarization of the light incident from both coincide with one eigenaxis of the optical fiber, the optical fiber loop 4
The plane of polarization of the light propagating through the laser light source 10 is made to match the plane of polarization of the light coming from the laser light source 10, so that each light travels in the same optical path in opposite directions.

The light that passes through the acousto-optic element 30 and exits the polarization beam splitter 20 and the light that passes through the acousto-optic element 31 and exits the polarization beam splitter 20 are both linearly polarized lights, but their planes of polarization are orthogonal to each other. so they do not interfere with each other. These two lights are combined and the lens 103. Constant polarization optical fiber 102. The light passes through the lens +01 and enters the non-polarizing beam splitter 50.

One of the lights split by the non-polarizing beam splitter 50 is guided to the polarizing beam splitter 70, so the light receiver 60 is placed at a position where the other light can be received. Since the intensity of the light split by the non-polarizing beam splitter 50 does not change due to the phase difference between the two lights propagating in the opposite direction through the optical fiber loop 4, the amount of light propagating through the optical fiber loop by the optical receiver 60 can be You can know.

Further, the light receiver 80 is placed at a position where the polarizing beam splitter 70 can receive one of the two lights that has been split into two at a ratio according to the state of polarization of the light. This polarizing beam splitter 7
The light split by 0 is obtained by extracting and combining certain polarized components of two lights that propagated in opposite directions through an optical fiber loop, so they interfere with each other, and the light intensity changes depending on the phase difference. Therefore, the phase difference can be sensed by the light receiver 80. More specifically, with such an optical system, the phase difference of the light propagating in the opposite direction through the optical fiber loop 4 is adjusted to the polarizing beam splitter 20.
If the phase difference is zero when the light is superimposed at Become.

In the constant polarization optical fiber 102, this light propagates with different propagation constants for each polarization plane component in the direction of its two eigenaxes, and the polarization state of the light emitted to the lens 101 is different from the state of the polarization beam splitter 20. It's different. However, the amount of light observed by the light receiver 6 is different from that of the non-polarizing beam splitter 5.
Since it is light divided by 0, regardless of its polarization state,
That is, the 2 waves propagating in the opposite direction through the optical fiber loop 4
A signal proportional to the amount of light returning through the optical fiber 102 is obtained, regardless of the phase difference between the two lights.

On the other hand, the amount of light measured by the light receiver 8 is the light split by the polarizing beam splitter 70, and thus varies depending on the polarization state. That is, since the polarization state changes depending on the phase difference between the two lights propagating in opposite directions through the optical fiber loop 4, the sum of the phase difference caused by the angular velocity and the phase difference caused by the frequency shift value is calculated based on the Sagnac effect. The amount of light measured by the light receiver 8 varies depending on the size. Since the direction of the eigenaxis of the polarization beam splitter 70 and the eigenaxis direction of the constant polarization plane optical fiber 102 are made to match, the amount of light measured by the photoreceiver 8 is from the laser of the light combined by the polarization beam splitter 20. It is obtained for the component of polarization perpendicular to the light of . When the phase difference between the two beams combined by the polarizing beam splitter 20 is θ, the intensity of the light component of this component is proportional to 1−cos θ. Therefore, the amount of light measured by the photoreceiver 8 changes in a COS relationship with respect to the phase difference θ between the two lights propagating in opposite directions through the optical fiber loop 4, and thus a signal indicating the phase difference is obtained. be able to.

With the above optical system, a signal related to the amount of light that has propagated through the ring interferometer with the optical fiber loop 4 as the optical path is detected in the light receiver 6, and a light amount and phase difference of the light that has propagated in the opposite direction through the optical fiber loop 4 in the light receiver 8. It is possible to obtain a signal that varies according to the following. These signals are input manually to the control system 200. FIG. 3 shows an example of the configuration of this control system 200.

To explain its configuration and operation, the signals from the photoreceiver 6 and the photoreceiver 8 are transmitted to the amplifiers 201 and 201, respectively. The amplifier 202 amplifies the electrical signal to an appropriate level.

These signals are each sent to a demodulator 203 . The demodulator 204 converts it into a signal indicating the magnitude of a component synchronized with the oscillation pulse of the pulse oscillator 205, which sets the switching timing of the switch 2+3 that switches the drive frequency of the acousto-optic element 31.

After the signal from the optical receiver 8 is converted by the demodulator 203, it is connected to the controller 206 in the same manner as in the prior art, and is used to control the oscillation frequency of the VCO 207 that drives the acousto-optic element 30.

On the other hand, the signal from the photoreceiver 6 is converted by a demodulator 204 and then connected to a controller 211, and a modulator 212 .
It is used to control the driving power of the acousto-optic element 31 via the variable amplifier 214.

With this configuration, for example, when the acousto-optic element 31 is connected to the oscillator 209 that oscillates at a frequency of f+ by the switch 213, if the amount of light measured by the light receiver 6 becomes small, the controller 211 switches the variable amplifier 2+4. The gain of the acousto-optic element 3! can be increased in synchronization with this via the modulator 212, and along with this, the gain of the acousto-optic element 3! Since the driving power to the light beam increases and its diffraction efficiency increases, the amount of light detected by the light receiver 6 can be increased. That is, the light receiver 6
A servo system is constructed such that the output of is a constant value. When the output of the optical receiver 6 is a constant value, the output of the optical receiver 8 depends only on the phase difference between the lights propagating in the opposite directions through the optical fiber loop 4.

Since the controller 206 can control this phase difference by controlling the driving frequency of the acousto-optic element 30, the phase difference can be maintained at a constant value by controlling the output of the light receiver 8 to a constant value. be able to. In the conventional technology, even if the output of the light receiver 8 is set to a constant value, if the amount of light propagating through the optical fiber loop 4 fluctuates, this does not mean that the phase difference remains constant, and the phase difference changes as the amount of light changes. As a result, the influence of this change has appeared in the form of a drift in the measured output. With the configuration of this embodiment, it is possible to prevent fluctuations in the amount of light, so that the phase difference can be kept at a constant value in a true sense.

As a result, even if one end of the optical fiber loop 4 moves due to some reason such as temperature change and its relative position with the light spot embedded by the lens 105 shifts and the coupling efficiency changes, the diffraction of the acousto-optic element 31 Correct by increasing or decreasing efficiency,
As a result, it is possible to prevent drift in the gyro output.

Conversely, temperature fluctuations or changes in the driving frequency of the acousto-optic element will cause the position of the light spot to move, but this is similarly corrected so that no drift occurs in the output of the gyro.

In other words, with conventional optical fiber gyros, there is a limit to suppressing mechanical fluctuations in fiber holding, making it difficult to reduce drift, but this example corrects for these effects. A highly accurate optical fiber gyro without drift can be realized.

In this embodiment, a bulk element beam splitter is used as the optical demultiplexer, but it goes without saying that it can also be realized using a so-called fiber coupler.

Although the driving power of the acousto-optic element was controlled to keep the output of the light receiver 6 constant, the optical system of the present invention
For example, a similar effect can be obtained by controlling the driving power of the laser light source IO, and an element such as a fiber-type frequency shifter can be used as the frequency shifter instead of an acousto-optic element.

Next, another embodiment of the present invention will be described using FIG. 4.

The embodiment shown in FIG. 4 has a configuration in which the functions of the optical demultiplexer 5 and the polarized light demultiplexer 7 in FIG. 1 are combined in one polarized light demultiplexer 51. That is, the fifth light beam is made incident on the polarization light demultiplexer 51 and split into two, and the obtained sixth and seventh light beams are sent to the first light receiver 6 and the second light receiver, respectively. The arrangement is such that the light is guided to the light receiver 8. At this time, the sum of the signals obtained by the two light receivers 6 and 8 indicates the sum of the amounts of light propagated through the optical fiber loop 4, and each signal indicates that the fifth light beam is polarized by the polarization splitter 51. is changed, the phase difference between the lights that interfere with each other and propagate in opposite directions through the optical fiber loop 4, that is, the phase difference generated by the frequency shifter 3 and Sa
It changes according to the sum of the phase difference generated according to the angular velocity due to the gnac effect.

With this configuration, the same signal as the optical fiber gyro according to the first embodiment can be obtained by using an appropriate arithmetic circuit, so the optical fiber gyro is free from drift due to changes in loss in the propagation path of the laser beam. can be constructed with fewer optical elements.

Further, FIG. 5 shows the configuration of still another embodiment, in which the light incident on the polarized light splitter 7 which interferes with the light waves of different polarization planes of the seventh light beam in the configuration of FIG. 1 is shown. The first light receiver 6 is placed at the position where the two divided light beams pass through.
and a second light receiver 8.

That is, since the polarization characteristics of the seventh light beam are changed by the polarization beam splitter 7, the phase difference between the lights that interfere with each other and propagate in opposite directions through the optical fiber loop 4,
That is, the phase difference generated by the frequency shifter 3 and Sag
The amount of light observed by the first light receiver 6 and the second light receiver 8 changes depending on the sum of the phase difference generated according to the angular velocity due to the NAC effect. However, the first receiver 6
The sum of the amounts of light observed by the optical fiber loop 4 and the second light receiver 8 indicates the amount of light propagated through the optical fiber loop 4.

Therefore, it is also possible to suppress drift caused by changes in this characteristic over time. Further, by using an appropriate arithmetic circuit, a signal indicating the amount of light propagated through the optical fiber loop 4 can be obtained, similar to the optical fiber gyro according to the first configuration. Therefore, although the number of arithmetic circuits increases somewhat, the degree of freedom in arranging the optical system increases, which is useful for downsizing as necessary.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the basic configuration of the present invention. FIG. 2 is a diagram showing the configuration of the first embodiment of the present invention. FIG. 3 is a diagram showing the configuration of the control system in the above embodiment. FIG. 4 is a diagram showing the configuration of another embodiment of the present invention. FIG. 5 is a diagram showing the configuration of still another embodiment. Figure 6 shows Sagnac, which is the principle of the optical fiber gyro.
It is an explanatory diagram of an effect. Figures 7 (a) and (b) are diagrams showing the configuration of a basic optical fiber gyro and the relationship between its manual angular velocity and detector output. Figure 8 shows the configuration of a gyro based on the conventional frequency variation method. FIG. 9 is a diagram showing the diffraction by the acousto-optic element and the position of the spot image, and FIG. 1O is a diagram showing the influence of relative positional deviation on the light beam introduction efficiency of the optical fiber. are diagrams showing the detector output when zero phase difference is achieved by the frequency variation method; (a) is the ideal situation;
b) is a diagram showing a case where there is a change in introduction efficiency due to positional deviation. 1,! 0...Light source, 2,7...Polarized light demultiplexer, 20
, To... Polarization beam splitter, 3... Frequency thick, 30.31... Acousto-optic element, 4... Optical fiber loop, 5... Non-polarized optical demultiplexer, 50...
Non-polarizing beam splitter, 6, 60.8.80... Light receiver, +00... Optical isolator, 102-th◆mode filter, 101.1
03.104.105・φ・Lens, 200...Control system. Patent Applicant Toyota Central Research Institute Co., Ltd. Figure 3 Figure 4 Figure 5 Figure 6 Figure 8 Figure 8. )Kyoe Tori 221-・Miku size Fig. 9 Fig. 10 g Kaya Fig. 11 Light intensity

Claims (2)

[Claims] (1) a light source that emits light; an optical fiber loop that propagates first and second light beams incident from both ends in opposite directions and exits from both ends as third and fourth light beams; The light beam emitted from the light source is divided into first and second light beams having different polarization planes and output to both ends of the optical fiber loop, and the third and second light beams are emitted from both ends of the optical fiber loop and polarized light demultiplexing means for combining the four light beams and outputting a fifth light beam; and a polarized light demultiplexing means provided between the optical fiber loop and the polarized light demultiplexing means to transition the frequency of the light beam passing therethrough. A frequency shifter and a fifth light beam output from the polarized light splitting means are divided into two, one of the two divided light beams is emitted as a sixth light beam, and the other is polarized with a specific polarization. a polarization and light demultiplexing means for extracting a wave component and outputting it as a seventh light beam; a first light receiver for detecting the amount of light of the sixth light beam from the polarization and light demultiplexing means; An optical fiber gyro comprising: a second light receiver that detects the light intensity of the seventh light beam from the polarization and light splitting means. (2) The polarization and light demultiplexing means includes an optical demultiplexer that divides the fifth light beam into a sixth light beam and a seventh light beam, and a seventh light beam from the optical demultiplexer. 2. The optical fiber gyro according to claim 1, further comprising a polarization optical demultiplexer for inputting a light beam and outputting a light wave of a specific polarization component.