JP2000146596A - Resonance point following system and ring resonance- type optical fiber gyro using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the continuous following of resonance points by providing a means to transfer a resonance point to be followed sequentially to an adjacent resonance point without losing the continuity of control. SOLUTION: This gyro is provided with a laser light source 61, an optical fiber ring resonator 73, waveguide modulators 64 and 69, which are phase modulating means, and piezoelectric element-type phase modulators 65 and 70. The gyro comprises the digital serrodyne wave generators 21 and 31 to provide a phase difference to two light waves different by one round in the number of propagation through the optical fiber ring resonator 73 by digital serrodyne waves. By this, it is possible to continuously provide a phase difference to become a closed loop for the movements of a resonance point and to follow the resonance point. Therefore, it is possible to follow the movements of the resonance point due to changes in temperature even up to a region at which following is impossible before and to implement a practical ring resonance-type optical fiber gyro.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a sensor using an optical fiber ring resonator, and more particularly, to a measurement of a resonance frequency difference caused by rotation between two light waves propagating oppositely in the optical fiber ring resonator. The present invention relates to an optical fiber gyro.

[0002]

2. Description of the Related Art A ring resonance type optical fiber gyro is one of optical fiber gyros for detecting the rotational speed of a measurement object by utilizing the Sagnac effect generated by rotation. Optical fiber ring resonators used in the ring resonance type optical fiber gyro include a reflection type and a transmission type. Normal,
In the reflection type, as shown in FIG. 8A, a sensing loop (optical fiber loop) 120 and one optical fiber coupler 12 are provided.
1. When a laser beam is made incident from port 1 and the intensity of the emitted light is observed at port 2 and the characteristic with respect to the frequency of the incident light is acquired, a reflection type resonance characteristic as shown in FIG. 9A is obtained.

The transmission type is constituted by a sensing loop (optical fiber loop) 123 and two optical fiber couplers 124 and 125 as shown in FIG. When a laser beam is made incident from the port 1 and the intensity of the emitted light is observed at the port 2 and the characteristic with respect to the frequency of the incident light is acquired, a transmission resonance characteristic as shown in FIG. 9B is obtained.
The resonance characteristic has a minimum value at discrete frequencies, and this point is called a resonance point. This minimum value interval ν _FSR is called a free spectral range, and is given by ν _FSR = c / nL (1). Here, c is the speed of light, n is the refractive index of the optical fiber, and L is the sensing loop length.

[0004] Near the resonance point, it has a sharp resonance characteristic, and there is a finesse as a parameter representing this sharpness.
Defined by an expression. Finesse = ν _FSR / Δν = π (αR) ^1/2 / (1−αR) (2) where Δν is the full width at half maximum of the resonance characteristic shown in FIG.
R is the branching ratio of the optical fiber coupler, and α is the loss in the optical fiber loop. The finesse indicates how many times a light wave can circulate in an optical fiber. The larger the finesse, the higher the resolution of the gyro.

Hereinafter, a description will be given of a reflection type optical fiber ring resonator as an example. When the optical fiber ring resonator is at rest, the resonance frequency of the counterclockwise lightwave and the counterclockwise lightwave become equal as shown by the solid line 1) in FIGS. When the optical fiber ring resonator rotates at an angular velocity Ω, an apparent difference occurs in the optical path length between the clockwise and counterclockwise resonators due to the Sagnac effect. This is a non-reciprocal effect, which causes a difference in the resonance frequency, and the dashed line 2) in FIGS.
As shown in FIG. This frequency difference is expressed as in equation (3). Δν _S = (4S / λL) Ω (3) where S is the area surrounded by the optical fiber ring resonator, and λ
Is the oscillation wavelength of the laser. The angular velocity Ω is obtained by measuring the resonance frequency difference, and the output of the gyro can be obtained by observing the resonance point of one light wave as a reference and the resonance point of the other light wave.

However, a change in temperature changes the length of the resonator and greatly changes the resonance frequency. However, since this is a reciprocal effect of giving the same amount of movement to the left and right light waves, in order to compensate for this, a method of returning to the frequency of the laser light source based on one of the two left and right light waves is used. Has been adopted. Alternatively, a piezoelectric element (P) attached to an optical fiber ring resonator without returning to the laser frequency
ZT) may be used to control the length of the resonator to exactly match the resonance point.

FIG. 11 is a schematic diagram showing an example of a ring resonance type optical fiber gyro disclosed in Japanese Patent Application Laid-Open No. 03-170016 (US Pat. No. 5,237,387) and US Pat. No. 5,296,912. This is to measure the deviation of the resonance frequency of a light wave circling left and right using an optical fiber ring resonator. The light emitted from the laser light source is split into two beams by a beam splitter (BS). The bifurcated light passes through the lenses (L1) and (L2), is guided to the optical fiber, and enters the optical coupler (C1). Optical coupler (C
Light incident on the ring resonator according to 1) propagates in the loop clockwise and counterclockwise. The frequency of light that becomes a standing wave in the fiber loop causes resonance, and the light is confined in the ring resonator and cannot come out. This state is observed by the light receiver (D1) for clockwise light and by the light receiver (D2) for counterclockwise light. At rest, the resonance frequencies of the left and right light waves are equal, but when an angular velocity is input, the Sagnac effect causes a difference in the optical path length between right-handed light and left-handed light. Occurs. The difference between the resonance frequencies can be used as a gyro output. Needless to say, the same configuration can be obtained by using a transmission type optical fiber ring resonator.

In order to detect the resonance point, the right and left light waves include:
Before entering the ring resonator, the frequency f _{n is} calculated by the piezoelectric element type phase modulators (PZT2) and (PZT1), _{respectively.}
Modulated by a sine wave of f _m and are added. Frequency f _n and f _m may be the same frequency, but preferably used are different frequencies. The modulation by the sine wave gives a shift of the resonance frequency as an error signal having a sine wave frequency component. For clockwise light waves, a lock-in amplifier (LI
In A1), the counterclockwise light waves are synchronously detected by the lock-in amplifier (LIA2), and a shift in the resonance frequency is detected. The output of the lock-in amplifier (LIA1) is input to a laser frequency control circuit, and is controlled so that the frequency (f ₀ ) of the laser coincides with one resonance point based on clockwise light. Lock-in amplifier (LIA
In the output of 2), the shift between the resonance points of the two right and left light waves is obtained as a voltage value. If this is used as a gyro output, it will be an open loop output.

In order to widen the detection range, it is necessary to form a closed loop using a cellodyne wave. The serrodyne wave has a function of changing the amplitude of the light wave by an amount corresponding to the frequency of the serrodyne wave by setting its amplitude to a voltage value that gives a phase rotation of 2π to the light wave. A waveguide-type modulator in which an electro-optic modulator is arranged on a lithium niobate (LiNbO ₃ ) waveguide has a wide usable frequency band and can perform modulation by a cellodyne wave. The output of the lock-in amplifier (LIA2) is V
Fill in CO, varying the frequency f ₂ of the serrodyne wave generated by serrodyne wave generator 2). The serrodyne wave is input to the waveguide phase modulator (PM2), and is controlled so that the counterclockwise light wave coincides with the resonance point. This frequency is f ₀ + f ₂ . A gyro output can be obtained by counting the frequency of the serrodyne wave, but in order to increase the resolution, it is better that the serrodyne wave has a certain frequency at rest. Therefore serrodyne wave having a frequency f ₁ of the fixed than serrodyne wave generator 1) by using a waveguide-type phase modulator (PM1) is inputted to the clockwise light. The frequency of the clockwise light is f ₀ + f ₁ . The two frequency differences f ₂ -f _{1 result} in a gyro closed loop output.

A conventional serrodyne wave is a serrodyne wave generated in an analog manner. There is a problem that it is difficult to generate an analog cellodyne wave without distortion and that there is a flyback time. Therefore, in order to overcome these problems, a method using digitally generated digital cellodyne waves has been proposed. "Digital Serrodyne Resonant Fiber Optic Gyro (Michiko Harumoto,
Kazuo Hotate, IEICE Technical Report, May 1996) describes a cellodyne wave in the case of forming a closed loop, a conventional analog cellodyne wave, and a light wave as shown in FIG. It has been shown that by using a digitally generated stepped serrodyne wave having a propagation time (τ) in a horizontal width, the light intensity on the photodetector becomes equal to an ideal analog serrodyne wave. Further, in order to detect the resonance point, instead of adding modulated by sine wave of each frequency f _n and f _m in the left and right two light waves by the piezoelectric element type phase modulator, each one waveguide type modulator in the lateral two-beam In FIG. 1, there is shown means for performing modulation for switching two serrodyne waves having different frequencies at alternate frequencies.

A closed loop using a digital serrodyne wave can be realized by a digital control circuit as shown in FIG. One frame of the digital control circuit is a time (τ) for a light wave to propagate one round in an optical fiber loop.
It is. Output (v1) of lock-in amplifier (LIA)
Is converted to a digital value by an AD converter (AD), and the digital value (v2) is converted to a first adder (ADD).
Input to 1). The first adder adds the output (v2) of the AD converter and the previous value of the first adder, and inputs the result (v3) to the second adder (ADD2). The second adder adds the output (v3) of the first adder and the previous value of the second adder, and outputs the result (v4) to the DA converter (DA). The output of the DA converter passes through a power amplifier (A), and then enters a waveguide phase modulator (PM).
Is input to The first adder is a signed digital integrator for determining the height of one step of the digital serrodyne wave.

The number of bits from the AD converter to the DA converter and the correspondence between input and output bits are determined in consideration of control responsiveness and resolution per bit. Generally, the number of bits of the AD converter is smaller than the number of bits of the first adder.
SB). Generally, the number of bits of the first adder is larger than the number of bits of the second adder, and the bit correspondence between them is determined by the most significant bit (MS) of the second adder.
B) corresponds to the most significant bit (MSB) of the first adder or a lower bit. Input and output between the second adder and the DA converter are performed with the most significant bit (MSB) aligned, and the full scale is the phase difference 2π
Is the quantity corresponding to Assuming that the number of bits of the second adder is M, 2π corresponds to 2 ^M , and overflows for an addition result of 2 ^M or more. In the second adder, the increasing serrodyne wave which is added at a fixed step value becomes a digital serrodyne wave having a property of starting increasing from 2π or more and starting to increase again, which is a phase modulator ( PM).

The resonance characteristics with respect to the frequency shown in FIG.
As shown in FIG. 14, the phase difference can be similarly expressed with respect to the phase difference between light waves having different numbers of propagations in the ring resonator by one round. Here, N is an integer, and the point where the phase difference between the light waves different in the number of propagations by one round becomes an integral multiple of 2π is the resonance point. It shows that digital serrodyne waves function in the same way as analog serrodyne waves in terms of phase. Assuming that the incident angle frequency to the phase modulator is ω, the phase rotation around the resonator becomes φ by a frequency shift corresponding to the angular frequency Δω.
= Ωτ-2nπ (0 ≦ φ <2π) to φ + Δφ (Δφ =
Δωτ). Here, φ + Δφ is a phase rotation while light propagates one round through the resonator, and is a phase difference between two light waves of light reaching the photodetector, the number of times of propagation in the resonator being different by one round.

When the phase modulator is modulated by an analog serrodyne wave, the time required for passing through the phase modulator is τ.
FIG. 15A shows the phase rotations received by different m-turn light and (m + 1) -turn light, respectively. The difference between the phase rotations of the two lights is Δφ or Δφ− as shown in FIG.
Since it is 2π, the phase difference between the light that has arrived at the photodetector and the number of times that the light propagates through the resonator by one round is φ + Δφ or φ + Δ
It is either φ-2π. When the phase modulator is modulated by a digital serrodyne wave, if the width of the step is equal to the fiber loop propagation time (τ) of the light wave, the time passed through the phase modulator is τ different by τ. The phase rotations of the light and the (m + 1) -turn light are shown in FIG.
(A). The difference between the phase rotations of the two lights is shown in FIG.
As shown in (b), Δφ or Δφ−2π, of the light that has arrived at the photodetector at the same time, two lights whose propagation times in the fiber resonator are different by one turn are φ + Δφ or φ + Δφ−2.
It has a phase difference of π, and provides an output of the photodetector equal to that when a frequency shift corresponding to the angular frequency of Δω is applied to both analog and digital serrodyne waves.

The phase difference of φ + Δφ−2π occurs when the waveform is reset, but no mismatch occurs if the amplitude of the serrodyne wave is 2π. If the amplitude of the serrodyne wave deviates from 2π, an error signal appears at the cycle of the serrodyne wave. This amplitude error can be corrected by performing synchronous detection at the cycle of the serrodyne wave. In any case, in the conventional ring resonance type optical fiber gyro, the shift of the resonance point due to the temperature, which is a reciprocal effect, is followed by returning to the laser frequency or the piezoelectric element (PZT) attached to the optical fiber ring resonator. Was adopted.

[0016]

By the way, the reciprocal effect due to temperature is extremely large compared to the non-reciprocal effect due to rotation. The shift of the resonance point with temperature is several GHz per degree Celsius, which corresponds to several hundred times the free spectral range. On the other hand, the amount that can be compensated by the laser frequency or PZT is only about 20 GHz even when both are used together. Therefore, it can only cope with the temperature within a range of about 10 ° C. Therefore, when the environmental temperature changes by 10 ° C. or more, it is impossible to keep following the same resonance point.

Next, as shown in FIG. 9, the resonance frequencies exist at intervals of a free spectral range ν _FSR . Therefore, for example, a conventional ring resonance type optical fiber gyro that feeds back to a laser oscillation frequency or a piezoelectric element (PZT) attached to a fiber loop, performs feedback control when following a certain resonance point existing at the above-mentioned interval. If the amount becomes insufficient, the gyro function can be continued by instantly shifting the target of tracking to a resonance point in a region where tracking can be performed with a smaller control amount. However, it has been difficult to shift the resonance point to be tracked without losing control continuity.
For this reason, the ring resonance type optical fiber gyro must always assume that the frequency of the light wave coincides with the resonance point initially targeted for tracking, and must cope with the above-mentioned fixed or larger temperature change. Could not.

An object of the present invention is to sequentially return resonance points to be tracked without losing control continuity by feeding back laser light emitted from a ring resonator to a modulating means using digital serrodyne waves. An object of the present invention is to provide a resonance point tracking system that can shift to an adjacent resonance point and continuously follow the resonance point and can cope with a large fluctuation in the temperature environment. Another object of the present invention is to provide an optical fiber gyro using the above resonance point tracking system.

[0019]

In order to solve the above-mentioned problems, a resonance point tracking system according to the present invention provides a laser light source for outputting a laser beam of a predetermined frequency, and modulates the phase of the laser beam emitted from the laser light source. A first phase modulating means, a second phase modulating means for modulating the phase of the laser light emitted from the laser light source with a modulation signal of a predetermined frequency, or a frequency modulating means for frequency modulating the laser light source; An optical fiber ring resonator for introducing and propagating laser light phase-modulated by the second phase modulating means, a photodetector for detecting laser light emitted from the optical fiber ring resonator, and the photodetector A lock-in amplifier that receives the output of the detector and the modulation signal, and synchronously detects the frequency component of the modulation signal in the output of the photodetector;
The output of the lock-in amplifier is input and integrated to generate a step value, to output a digital serrodyne wave corresponding to 2π, and to apply the digital serrodyne wave to a modulation input of the first phase modulating means. Control means for performing two rounds of the number of times of propagation in the optical fiber ring resonator different from each other by one round, to give a phase difference that forms a closed loop with respect to the movement of the resonance point by the digital serrodyne wave,
At this time, utilizing the property that the digital serrodyne wave repeats the change of the waveform regularly with respect to the phase difference between two light waves having different number of propagations by one round, and giving 2π different binary phase difference, It is configured to follow either one of the two closest resonance points among the resonance points existing every 2π. In the above configuration, the function of the second phase modulating means can be shared by the first phase modulating means by adding a modulation signal of a predetermined frequency to the first phase modulating means.

According to another aspect of the present invention, there is provided an optical fiber gyro comprising: a laser light source for outputting a laser beam having a predetermined frequency; a branching unit for branching a laser beam emitted from the laser light source; First and third phase modulating means for phase-modulating the laser light of the first and second optical paths branched by the means, and the laser light of the first and second optical paths branched by the branching means, respectively. Second and fourth phase modulating means for modulating the phase with first and second modulating signals of a predetermined frequency, and clockwise rotating the laser light phase-modulated by the first and second phase modulating means. An optical fiber ring resonator for introducing and propagating the laser light phase-modulated by the third and fourth phase modulating means counterclockwise, respectively, and the optical fiber A first photodetector that detects clockwise laser light emitted from the ring resonator, a second photodetector that detects counterclockwise laser light emitted from the optical fiber ring resonator, A first lock-in amplifier that receives an output of a first photodetector and the first modulation signal, and synchronously detects a frequency component of the first modulation signal in an output of the first photodetector. And the output of the first lock-in amplifier is input and integrated to generate a step value.
And outputs a first digital serrodyne wave corresponding to
This is fed back to the modulation input of the first phase modulating means so that the angular velocity is given to the optical fiber ring resonator, or that the optical path length of the optical fiber ring resonator fluctuates due to a temperature change or the like. A first control means for controlling to follow this phase change, and an output of the second photodetector and the second modulation signal, and the output of the second photodetector. A second lock-in amplifier for synchronously detecting a frequency component of the second modulated signal;
And outputs a second digital serrodyne wave corresponding to 2π, which is fed back to the modulation input of the third phase modulating means. Thereby, when an angular velocity is given to the optical fiber ring resonator, or when the optical path length of the optical fiber ring resonator fluctuates due to a temperature change or the like,
A second control means for controlling so as to follow a phase change, wherein two light waves that are different in the number of times of propagation in the optical fiber ring resonator by one turn from the clockwise direction and one in the number of times by which the lightwave propagates counterclockwise in the ring resonator. The two light waves having different circumferences are given a phase difference that forms a closed loop with respect to the movement of the resonance point by the first and second digital serrodyne waves. By taking advantage of the property of periodically repeating the change of the waveform with respect to the phase difference of the light wave and giving a binary phase difference different by 2π, the nearest 2 resonance points among 2π are present.
One of the two resonance points, and taking the difference between the height of the first digital serrodyne wave at one step and the height of the second digital serrodyne wave at one step. It is configured to measure the movement of the nonreciprocal resonance point between the surrounding light and the right-handed light, and obtain a gyro output.

According to another aspect of the present invention, there is provided an optical fiber gyro comprising: a laser light source for outputting a laser beam having a predetermined frequency; a branching unit for branching a laser beam emitted from the laser light source; First and third phase modulating means for phase-modulating the laser light of the first and second optical paths branched by the branching means, respectively, and laser light of the first and second optical paths branched by the branching means Phase modulating means and fourth phase modulating means for respectively modulating the phase with first and second modulating signals having predetermined frequencies, and the laser light phase-modulated by the first and second phase modulating means. An optical fiber ring resonator for introducing and propagating the laser light phase-modulated by the third and fourth phase modulating means counterclockwise so as to be clockwise, and the optical fiber ring resonator. A first photodetector for detecting clockwise laser light emitted from the ring resonator, a second photodetector for detecting counterclockwise laser light emitted from the optical fiber ring resonator, A first lock-in amplifier that receives an output of a first photodetector and the first modulation signal, and synchronously detects a frequency component of the first modulation signal in an output of the first photodetector. A first step value generator, which is a digital integrator that receives an output of the first lock-in amplifier and integrates the integrated signal to generate a step height of a digital serrodyne wave, and the first step value generator; An adder for adding the output of the step value generator and the output of the second step value generator, and receiving the output of the adder to generate a first digital serrodyne wave corresponding to 2π; The first feedback signal is fed back to the modulation input of the first phase modulation means. A digital serrodyne wave generator, when an angular velocity is given to the optical fiber ring resonator, or when the optical path length of the optical fiber ring resonator fluctuates due to a temperature change or the like,
First control means for controlling to follow this phase change, input of the output of the second photodetector and the second modulation signal, and inputting the output of the second photodetector. A second lock-in amplifier for synchronously detecting the frequency component of the second modulation signal and an output of the second lock-in amplifier;
A second step value generator, which is a digital integrator for generating a step height of a digital serrodyne wave by integration, and an output of the second step value generator corresponding to 2π A second digital serrodyne wave generator that generates a second digital serrodyne wave and feeds back to the modulation input of the third phase modulating means, wherein the optical fiber ring resonator is given an angular velocity. When, or when the optical path length of the optical fiber ring resonator fluctuates due to a temperature change, the second control means for controlling to follow the phase change, and clockwise in the optical fiber ring resonator The first and second digital serodyne waves shift the resonance point to two light waves that differ in the number of propagation times by one round and two light waves that differ in the counterclockwise number of propagation times by one round. , A phase difference that forms a closed loop is given to the digital serrodyne wave. At this time, the characteristic that the digital serrodyne wave repeats the change of the waveform regularly with respect to the phase difference of the two light waves having different numbers of propagations by one round, By giving a phase difference of values, one of the two resonance points closest to 2π is tracked, and the output of the first step value generator is set to the left. The gyro output is configured to correspond to the non-reciprocal resonance point shift of the surrounding light and the clockwise light. In the above configuration, the functions of the second and fourth phase modulating units are respectively added to the first and third phase modulating units by adding a modulation signal of a predetermined frequency to the first and third phase modulating units. Can be combined.

[0022]

According to the above configuration, it is assumed that the resonator length greatly changes due to a temperature change, and as a result, the resonance frequency moves beyond the range that can be compensated by the laser frequency and feedback to the resonator length by the piezoelectric element (PZT). In addition, it is possible to continuously follow the resonance point without losing control continuity and to function as a gyro.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. A closed loop using a digital serrodyne wave can be realized by a digital control circuit as shown in FIG. One frame of the digital control circuit is a time (τ) for a light wave to propagate one round in an optical fiber loop. The output (v1) of the lock-in amplifier (LIA) is converted into a digital value by an AD converter (AD), and the digital value (v2) is input to a first adder (ADD1). The first adder adds the output (v2) of the AD converter and the previous value of the first adder, and inputs the result (v3) to the second adder (ADD2). The second adder outputs the output of the first adder (v3)
And the previous value of the second adder are added, and the result (v4) is output to the DA converter (DA). The output of the DA converter is input to the waveguide type phase modulator (PM) via the power amplifier (A). The first adder is a signed digital integrator for determining the height of one step of the digital serrodyne wave.

The number of bits from the AD converter to the DA converter and the correspondence between input and output bits are determined in consideration of control responsiveness and resolution per bit. Generally, the number of bits of the AD converter is smaller than the number of bits of the first adder.
SB). Generally, the number of bits of the first adder is larger than the number of bits of the second adder, and the bit correspondence between them is determined by the most significant bit (MS) of the second adder.
B) corresponds to the most significant bit (MSB) of the first adder or a lower bit. Input and output between the second adder and the DA converter are performed with the most significant bit (MSB) aligned, and the full scale is the phase difference 2π
Is the quantity corresponding to Assuming that the number of bits of the second adder is M, 2π corresponds to 2 ^M , and overflows for an addition result of 2 ^M or more. In the second adder, the increasing serrodyne wave which is added at a fixed step value becomes a digital serrodyne wave having a property of starting increasing from 2π or more and starting to increase again, which is a phase modulator ( PM).

The first adder has two different numbers of propagations for one round.
When an optical wave has a phase difference, it is an integrator for generating a phase difference that cancels the phase difference. The output (v3) of the first adder increases or decreases, and becomes a constant value at the phase difference that just cancels. , Which is the step value of the digital serrodyne wave. When a large phase difference occurs between two light waves having one round of propagation times different from each other, the first adder must generate a large step value to cancel the phase difference.
However, since the full scale of the second adder corresponds to a phase difference of 2π, a step value of 2π or more cannot be input to the second adder. Since the number of bits of the second adder is M, a step value of 2 ^M or more is reset to a value of 2 ^M -1 or less. When the most significant bit of the first adder is treated as a sign bit, the reset step value initially follows a certain resonance point and is an integer of 2π with respect to the step value generated to form a closed loop. A value that is twice as large, that is, −π or more and π or less. When the step value is greater than or equal to 0 and less than or equal to π, the digital serrodyne wave is of a rising type. When the step value is equal to or more than -π and equal to or less than 0, the digital serrodyne wave has a descending type. The fact that the step value is π is the same as that of −π, and the step value is the same waveform, that is, a rectangular wave. At the time when the step value is π, the waveform of the digital cellodyne wave changes from the rising form to the falling form, or from the falling form to the rising form.

This indicates that the waveform has a property of regularly repeating a change in waveform with respect to a phase difference between two light waves having different numbers of propagations for one round. If this property is used, a digital serrodyne wave with a step value of Δφ gives a phase difference of Δφ or Δφ−2π to two light waves whose propagation number is different by one round, and a resonance point whose frequency is different by one round. The following describes that the resonance point follows the resonance point even if the resonance point largely moves to 2π or more because the resonance point exists every 2π with respect to the phase difference between the two light waves.

A digital serrodyne wave having a height of Δφ in one step gives a phase difference of Δφ or Δφ−2π to two light waves whose propagation times differ by one round. If a phase difference Δφ _X in the positive direction occurs in the light wave whose number of times of propagation is different by one round due to disturbance such as temperature or input of angular velocity, the height of one step is set to perform the zero-point method and make a closed loop. Δφ _X
Using a rising digital serrodyne wave, the same amount of phase difference is negatively fed back to follow the resonance point.
The phase difference in the negative direction -Δφ
_{If X} occurs, and -Derutafai _X the height of one step step in order to offset to a closed loop this, using a digital serrodyne wave decreases top-down, and negative feedback phase difference of the same amount Follow the resonance point.

When a large phase difference is added to two light waves having one round of propagation times different from each other, the number of steps of the digital serrodyne wave becomes small, and when the amplitude exceeds 2π with a small number of steps, it is digitally reset. Number of propagation times 1
When a larger phase difference of π or more is applied to two light waves having different circumferences, the digital serrodyne wave, which has been rising, changes to a falling one. This means that the height of one step is Δ
φ _X −2π. The boundary between the rising waveform and the falling waveform is a rectangular waveform having an amplitude of π. The fact that the height of one step is π is the same as that of −π, and they have the same waveform. Further, if the phase difference between the light waves whose number of times of propagation is different by one turn increases, the descending waveform becomes an ascending waveform, and when the height of one step exceeds π, it becomes a descending waveform again. .

As described above, the height of the first step as a closed loop by performing the null method on the phase difference between the light waves having different numbers of propagations for one round is shown in FIG. This is because the analog serrodyne wave continuously increases the frequency, that is, continuously increases the phase rotation of the modulated light wave, whereas the phase rotation of the light wave due to the digital serrodyne wave is −
It is limited to 2π or more and 2π or less, and its value is different from that of the analog cellodyne wave by an integral multiple of 2π. This indicates that the resonance point that the analog serrodyne wave originally tracks is permanently targeted for tracking, while the digital serrodyne wave tracks the closest resonance point.

Next, when an ascending digital serrodyne wave having a height of Δφ at one step is used, the phase difference given to light waves having different numbers of rounds of propagation one cycle is either Δφ or Δφ-2π. . In the case where the height of one step is a digital Serrodyne wave having a descending shape of -Δφ, the phase difference given to the light wave whose number of times of propagation is different by one round is either -Δφ or -Δφ + 2π. In the binary time distribution, in the ascending type, the time for giving a phase difference of Δφ is ((number of steps) −1) × (optical fiber loop propagation time (τ)), and the time for giving a phase difference of Δφ−2π. Is the optical fiber loop propagation time (τ)
It is. The time for giving a phase difference of −Δφ in the descending form is ((number of steps) −1) × (optical fiber loop propagation time (τ)), and the time for giving a phase difference of −Δφ + 2π is the optical fiber loop propagation time. Time (τ). To summarize the above relationship, the phase difference generated by the digital serrodyne wave and the frequency of occurrence of those phase differences satisfy the relationship shown in FIG. .

FIG. 2 is a diagram for explaining a phase difference generated by a digital cellodyne wave for performing a zero-order method when a phase difference occurs between two light waves having one round of different number of propagation times. FIG. The phase difference generated by the digital serrodyne wave indicates which resonance point it follows. The region A in FIG. 2 corresponds to the resonance point of 2Nπ and 2Nπ.
The region following any one of the resonance points of (N + 1) π, and the region of B is the resonance point of 2 (N + 1) π and 2 (N +
2) An area that follows any of the resonance points of π. The region C is a region that follows either the resonance point of 2Nπ or the resonance point of 2 (N−1) π, and the region D is 2 (N−
1) A region that follows either the resonance point of π or the resonance point of 2 (N−2) π. Which resonance point follows is sequentially shifted according to the frequency of occurrence of the phase difference.

FIG. 3 is a diagram showing the ratio of resonance points that are tracked by digital serrodyne waves when a phase difference occurs between two light waves that differ in the number of propagations by one round. FIG. 3 illustrates the following resonance points and their time ratios. This relationship always follows the two resonance points by resetting the amplitude of the digital serrodyne wave to 2π. Even if a large phase difference occurs between two light waves having different numbers of rounds of propagation, a digital phase difference as shown in FIG. This shows that the resonance point to be tracked can be shifted and the tracking can be continued using the control circuit while maintaining the continuity of the control. In order to continue the following, the bit correspondence between the first adder (ADD1) and the second adder (ADD2) in FIG. 13 is such that the most significant bit (MSB) is aligned, and the first adder It is not necessary to provide a higher-order bit, but if a higher-order bit is provided, it is possible to measure the movement amount of the resonance point that was initially followed over a wide range.

By using this method to follow the resonance point of the ring resonator, even if the resonator length greatly changes due to temperature, the laser frequency and the laser frequency are adjusted so that the frequency of the light wave matches the fluctuating resonator length. Alternatively, it is not necessary to feed back to the piezoelectric element (PZT) attached to the optical fiber ring resonator, and it is possible to follow the resonance point only with the digital serrodyne wave. In addition, if this method is used to follow the resonance point of each of the left and right light waves with only the digital serrodyne wave, if there is no input of angular velocity to the optical fiber ring resonator, it will only follow the movement of the resonance point due to temperature. I do.
This is a reciprocal effect of giving a phase rotation equal to two right and left light waves. Therefore, the two resonance points that the left-handed light follows and the two resonance points that the right-handed light follows are always the same resonance point. At this time, the step value of the digital serrodyne wave generated for following the counterclockwise light is the same as the step value of the digital serrodyne wave generated for following the clockwise light.

When an angular velocity is input to the optical fiber ring resonator, the amount of shift of the resonance point is an amount obtained by adding both a non-reciprocal component due to the Sagnac effect and a component due to temperature. Since this is a reciprocal effect, the step value of the digital serrodyne wave generated to follow the counterclockwise light and the step value of the digital serrodyne wave generated to track the clockwise light Is a non-reciprocal component due to the Sagnac effect,
This can be used as a gyro output.

[0035]

FIG. 4 is a schematic block diagram showing an embodiment of a resonance point tracking system according to the present invention. Claims 1 and 2
It corresponds to. The laser light of a predetermined frequency emitted from the laser light source 1 passes through the lens (L) 2 and is guided to the optical fiber, where the waveguide type modulator (PM) 3 as the first phase modulation means and the second phase modulation The light enters the optical coupler (C) 6 via a piezoelectric element type phase modulator (PZT) 4 which is a means.

The light incident by the optical coupler (C) 6 is
The light propagates through the loop of the optical fiber ring resonator 7. The light emitted from the ring resonator is observed by the light receiver (D) 8. In order to detect the resonance point, the incident light is applied to a piezoelectric element type phase modulator (PZT) before entering the optical fiber ring resonator 7.
By 4, phase modulation by a sine wave of a frequency f _m from the oscillator 19 is applied. In order to detect the resonance point, instead of the modulation using the sine wave, a means may be used in which only the waveguide type modulator 3 is used and the two cellodine waves having different frequencies are switched at the alternate frequency. Further, the piezoelectric element type phase modulator (PZT) 4 can be connected to the input side of the waveguide type phase modulator (PM) 3.

The light wave is synchronously detected by a lock-in amplifier (LIA) 9 and a deviation from a resonance point is detected. The output of the lock-in amplifier (LIA) 9 is input to a control circuit (CC) 18 having a function equivalent to that of FIG. Control circuit (CC)
The output (ST) of the step value generator 11 in the digital signal generator 18 is converted into a digital serrodyne wave generator 12 as a step value.
And a digital cellodyne wave is generated. This digital serrodyne wave is converted to a DA converter (DA)
15. The power is input to the waveguide-type phase modulator (PM) 3 via the power amplifier (A) 16, and is controlled so that the light wave follows the resonance point.

The amplitude of the digital serrodyne wave (S) input to the waveguide type phase modulator (PM) 3 must be kept at a voltage value that gives a light wave a phase rotation of 2π. Therefore, the output of the step value generator 11 is input to the step value / frequency conversion means 17, generates a frequency equal to the digital serrodyne wave (S), and is input to the lock-in amplifier (LIA ′) 13. The lock-in amplifier (LIA ') 13 synchronously detects the amplitude error signal of the digital cellodyne wave (S) contained in the light.
The amplitude error signal synchronously detected by the lock-in amplifier (LIA ') 13 is integrated by the integrator 14 and is integrated by the DA converter (D
A) It is fed back to 15 reference voltages. As a result, the amplitude of the digital serrodyne wave (S) is controlled to be 2π.

FIG. 5 is a schematic block diagram showing an embodiment of an optical fiber gyro to which the resonance point tracking system according to the present invention is applied. This corresponds to claims 3 and 5. The laser light of a predetermined frequency emitted from the laser light source 21 is split into two beams by a beam splitter (BS) 22. 2
The branched laser beams are respectively transmitted to a lens (L2) 23,
(L1) 28, it is guided to the optical fiber, and the waveguide type modulator (PM2) 24 which is the first phase modulation means, the waveguide type modulator (PM1) 29 which is the third phase modulation means, (2) a piezoelectric element type phase modulator (PZT
2) 25, the fourth phase modulation means (PZT1) 30
, And enters the optical coupler (C1) 32. From the beam splitter 22 to the two waveguide modulators 24 and 29, it is preferable to use a multifunctional optical integrated chip.

The light incident from the optical coupler (C1) 32 propagates clockwise and counterclockwise in the loop of the optical fiber ring resonator 33. Receiver for clockwise light (D1)
At 34, the counterclockwise light is observed at the photodetector (D2) 35, respectively. In order to detect the resonance point, the two right and left light waves are applied to the piezoelectric element type phase modulators (PZT2) 25 and (PZT2) before entering the optical fiber ring resonator 33, respectively.
By 1) 30, phase modulation by a sine wave of frequency f _n and f _m from the oscillator is applied. In order to detect the resonance point, instead of modulating the two right and left light waves with sine waves, only the waveguide type modulators 24 and 29 are used, and two cellodine waves having different frequencies are switched at alternate frequencies. Means may be used. Frequency f _n and f _m may be the same frequency, but preferably used are different frequencies. Further, the piezoelectric element type phase modulator (PZT2) 25
And (PZT1) 30 are waveguide phase modulators (PM
2) It can be connected to the input side of 24 and (PM1) 29 respectively.

The clockwise lightwave is synchronously detected by the lock-in amplifier (LIA1) 45, and the deviation from the resonance point is
Lock-in amplifier (LIA2) for counterclockwise light waves
Synchronous detection is performed at 36, and a deviation from the resonance point is detected. The outputs of the lock-in amplifier (LIA1) 45 and the lock-in amplifier (LIA2) 36 are output to control circuits (CC1) 55 and (CC2) 5 having the same functions as those in FIG.
4 is input. The output (ST1) of the step value generator (1) 47 in the control circuit (CC1) 55 is input as a step value to the digital serrodyne wave generator (1) 48 to generate a digital serrodyne wave. . The digital serrodyne wave (S1) is input to the waveguide type phase modulator (PM1) 29 via the DA converter (DA) 51 and the power amplifier (A1) 52, so that the clockwise light wave follows the resonance point. Is controlled.

On the other hand, the output (ST2) of the step value generator 38 in the control circuit (CC2) 54 is input to a digital serrodyne wave generator (2) 39 using the output (ST2) as a step value. Generated. This digital serrodyne wave (S2) is converted to a DA converter (D
A) 42 and a power amplifier (A2) 43 are input to the waveguide type phase modulator (PM2) 24, and are controlled so that the counterclockwise light wave follows the resonance point. Output (ST1) of step value generator (1) 47 and step value generator (2)
The difference between the outputs (ST2) of 38 is a component necessary for performing a null method on the phase difference generated by the rotation to form a closed loop,
Gyro output.

The amplitude of the digital serrodyne wave (S1) input to the waveguide type phase modulator (PM1) 29 must be maintained at a voltage value that gives a light wave a phase rotation of 2π. Therefore, the output (ST1) of the step value generator (1) 47 is input to the step value / frequency conversion means (1) 53 to generate a frequency equal to the digital serrodyne wave (S1), and to generate the lock-in amplifier (LIA1 '). ) 49
Is input to Lock-in amplifier (LIA1 ') 49
Is the digital cellodyne wave (S
The amplitude error signal of 1) is synchronously detected. The amplitude error signal synchronously detected by the lock-in amplifier (LIA1 ') 49 is integrated by the integrator (1) 50 and fed back to the reference voltage of the DA converter (DA) 51. As a result, the amplitude of the digital serrodyne wave (S1) is controlled to be 2π.

On the other hand, the waveguide type phase modulator (PM2) 24
Of the digital serrodyne wave (S2) input to the optical wave must be kept at a voltage value that gives the light wave a phase rotation of 2π. Therefore, the step value generator (2) 38
Output (ST2) is a step value / frequency conversion means (2)
44, a frequency equal to the digital serrodyne wave (S2) is generated, and a lock-in amplifier (LIA2 ′) is generated.
) Input to 40. Lock-in amplifier (LIA2 ')
Reference numeral 40 synchronously detects the amplitude error signal of the digital cellodyne wave (S2) included in the counterclockwise light. The amplitude error signal synchronously detected by the lock-in amplifier (LIA2 ') 40 is integrated by the integrator (2) 41 and fed back to the reference voltage of the DA converter (DA) 42. As a result,
Similarly to (S1), control is performed so that the amplitude of the digital serrodyne wave (S2) becomes 2π.

FIG. 6 is a schematic block diagram showing another embodiment of the optical fiber gyro applied to the resonance point tracking system according to the present invention, wherein the components due to the reciprocal effect and the components due to the non-reciprocal effect in the two control circuits. Is configured to be shared. This corresponds to claims 4 and 5. Laser light of a predetermined frequency emitted from the laser light source 61 is split into two beams by a beam splitter (BS) 62. 2
The branched laser beams are respectively a lens (L2) 63,
After passing through (L1) 68 and being guided to the optical fiber, the waveguide type modulator (PM2) 64 as the first phase modulation means, the waveguide type modulator (PM1) 69 as the third phase modulation means, (2) a piezoelectric element type phase modulator (PZT
2) 65, an optical coupler (C1) 72 through a piezoelectric element type phase modulator (PZT1) 70 as a fourth phase modulating means.
Incident on. From the beam splitter 62 to the two waveguide modulators 64 and 69, a multifunctional optical integrated chip is preferably used.

The light incident from the optical coupler (C1) 72 propagates clockwise and counterclockwise in the loop of the optical fiber ring resonator 73. Receiver for clockwise light (D1)
At 76, the counterclockwise light is observed by the light receiver (D 2) 77. In order to detect the resonance point, the two right and left light waves are applied to the piezoelectric element type phase modulators (PZT2) 65 and (PZT2) before entering the optical fiber ring resonator 73, respectively.
By 1) 70, phase modulation by a sine wave of frequency f _n and f _m from the oscillator is applied. In order to detect the resonance point, modulation is performed by using only the waveguide type modulators 64 and 69 and switching between two serrodyne waves having different frequencies at alternate frequencies, instead of modulating the two right and left light waves with sine waves. Means may be used. Frequency f _n and f _m may be the same frequency, but preferably used are different frequencies. Further, the piezoelectric element type phase modulator (PZT2) 65
And (PZT1) 70 are waveguide-type phase modulators (PM
2) It can be connected to the input side of 64 and (PM1) 69 respectively.

The clockwise light wave is shifted from the resonance point synchronously detected by the lock-in amplifier (LIA1) 87, while the clockwise light wave is shifted from the lock-in amplifier (LIA1).
2) The deviation from the resonance point synchronously detected in 78 is detected. The outputs of the lock-in amplifier (LIA1) 87 and the lock-in amplifier (LIA2) 78 are respectively shown in FIG.
Control circuit (CC1) 98, (CC
2) Entered in 97. The output (ST2) of the step value generator (2) 80 in the control circuit (CC2) 97 and the output (ST1) of the step value generator (1) 89 in the control circuit (CC1) 98 are output by the adder 90. Is added. The result (ST3) is input as a step value to the digital serrodyne wave generator (1) 91, and a digital serrodyne wave is generated. This digital serrodyne wave (S
1) is a waveguide type phase modulator (PM1) 69 via a DA converter (DA) 94 and a power amplifier (A1) 95.
And is controlled so that the clockwise light wave follows the resonance point.

On the other hand, the output ST2 of the step value generator 80 in the control circuit (CC2) 97 is input to the digital serrodyne wave generator (2) 81 using the output ST2 as a step value, and a digital serrodyne wave is generated. You. This digital serrodyne wave (S2) is converted to a DA converter (DA) 8
4. The signal is input to the waveguide type phase modulator (PM2) 64 via the power amplifier (A2) 85, and is controlled so that the counterclockwise light wave follows the resonance point.

The control circuit (CC2) 97 generates a step value common to the left and right light waves. Therefore, this is a component necessary to follow the reciprocal movement of the resonance point due to the temperature. The control circuit (CC1) 98 generates a step value necessary to follow the movement of the resonance point due to both non-reciprocal effects and reciprocal effects. The output (ST1) of the step value generator (1) 89, which is the difference between them, is a component necessary for performing the zero method on the phase difference generated by rotation to form a closed loop, and becomes a gyro output. A piezoelectric element type modulator (PZT3) 74 attached to the optical fiber loop is driven at a low frequency by an oscillator 75, and is used to prevent the digital serrodyne wave from being biased to a specific waveform.

The digital serrodyne wave (S1) inputted to the waveguide type phase modulator (PM1) 69 must keep its amplitude at a voltage value that gives a light wave a phase rotation of 2π. Therefore, the output (ST3) of the adder 90 is input to the step value / frequency conversion means (1) 96 to generate a frequency equal to the digital serrodyne wave (S1).
The signal is input to the lock-in amplifier (LIA1 ') 92. The lock-in amplifier (LIA1 ') 92 synchronously detects the amplitude error signal of the digital cellodyne wave (S1) included in the clockwise light. Lock-in amplifier (LIA
1 ') The amplitude error signal synchronously detected at 92 is integrated by the integrator (1) 93 and fed back to the reference voltage of the DA converter (DA) 94. As a result, the amplitude of the digital serrodyne wave (S1) is controlled to be 2π.

On the other hand, a waveguide type phase modulator (PM2) 64
Of the digital serrodyne wave (S2) input to the optical wave must be kept at a voltage value that gives the light wave a phase rotation of 2π. Therefore, the step value generator (2) 80
Output (ST2) is a step value / frequency conversion means (2)
86, a frequency equal to the digital serrodyne wave (S2) is generated, and a lock-in amplifier (LIA2 ') is generated.
) 82. Lock-in amplifier (LIA2 ')
Reference numeral 82 synchronously detects the amplitude error signal of the digital cellodyne wave (S2) included in the counterclockwise light. The amplitude error signal synchronously detected by the lock-in amplifier (LIA2 ') 82 is integrated by the integrator (2) 83 and fed back to the reference voltage of the DA converter (DA) 84. As a result,
Similarly to (S1), control is performed so that the amplitude of the digital serrodyne wave (S2) becomes 2π.

FIG. 7 is a schematic block diagram showing another embodiment of the resonance point tracking system according to the present invention. This corresponds to claim 1. The difference from the embodiment of FIG.
In order to detect the resonance point, a piezoelectric element type phase modulator (PZ
T) not to be inserted into the output side of the waveguide type modulator 103, in which so as to frequency modulation by the modulation signal of the frequency f _m of the laser light from the laser light source 101 from an oscillator 118 instead. The components 102 to 117 have the same configuration and operation as the components corresponding to 2 to 18 in FIG.

[0053]

As described above, according to the present invention, it is impossible to follow the shift of the resonance point due to the temperature change by the feedback amount to the laser frequency or the resonator length change amount of the piezoelectric element (PZT). By shifting the resonance point to be tracked up to the region without losing the control continuity, it is possible to continuously track. Therefore,
A ring resonance type optical fiber gyro, which conventionally could only function in a narrow temperature range, can function in a practical temperature range. Further, since the configuration is not such that the frequency of the laser is controlled for following, a semiconductor laser can be used. In addition, there is an advantage other than the temperature resistance characteristic that a single light source can constitute a multi-axis gyro, and a ring resonance type optical fiber gyro that can be mounted on an aircraft or the like can be put into practical use.

[Brief description of the drawings]

FIG. 1 is a diagram showing the height of one step for performing a zero-order method and forming a closed loop when a phase difference occurs between two light waves that differ in the number of propagations by one round.

FIG. 2 is a diagram for explaining a phase difference generated by a digital cellodyne wave for performing a zero-order method on a two-wave wave having a different number of times of propagation by one round when the phase difference is generated. .

FIG. 3 is a diagram illustrating a ratio of resonance points that are tracked by a digital serrodyne wave when a phase difference occurs between two light waves that differ in the number of propagations by one round.

FIG. 4 is a schematic block diagram showing an embodiment of a resonance point tracking system according to the present invention.

FIG. 5 is a schematic block diagram showing an embodiment of an optical fiber gyro to which a resonance point tracking system according to the present invention is applied.

FIG. 6 is a schematic block diagram showing another embodiment of the optical fiber gyro to which the resonance point tracking system according to the present invention is applied.

FIG. 7 is a schematic block diagram showing another embodiment of the resonance point tracking system according to the present invention.

8A and 8B are configuration diagrams of an optical fiber ring resonator, wherein FIG. 8A shows a reflection type and FIG. 8B shows a transmission type.

FIG. 9 is a diagram showing the resonance output of the reflection type and transmission type optical fiber ring resonators with respect to the frequency of the incident light.

FIG. 10 is a diagram for explaining a principle of detecting an angular velocity of a ring resonance type optical fiber gyro.

FIG. 11 is a diagram illustrating a configuration of a conventional ring resonance type optical fiber gyro.

FIG. 12 is a diagram illustrating a digital serrodyne wave.

FIG. 13 is a diagram showing a control circuit for generating a digital serrodyne wave and forming a closed loop.

FIG. 14 is a diagram showing, in the resonance characteristics of the optical fiber ring resonator, the resonator output with respect to the phase difference between two light waves having different numbers of propagations for one round.

FIG. 15 is a diagram illustrating a phase difference between two light waves that differ in the number of times of propagation by one round and are caused by an analog cellodyne wave.

FIG. 16 is a diagram illustrating a phase difference between two light waves that differ in the number of propagations by one round and are caused by a digital serrodyne wave.

[Explanation of symbols]

1, 21, 61, 101 laser light source 22, 62 beam splitter 2, 23, 63, 68, 102 lens 3, 24, 64, 69, 103 waveguide type modulator 4, 25, 65, 70, 74: Piezoelectric element type phase modulator 6, 32, 72, 105 ... Optical coupler 7, 33, 73, 106 ... Optical fiber ring resonator 8, 34, 35, 76, 77, 107 ... Light receiver 9, 13, 36 , 40, 45, 49, 78, 82, 8
7, 92, 108, 112 ... lock-in amplifiers 10, 37, 46, 79, 88, 109 ... AD converters 11, 38, 47, 80, 89, 110 ... step value generators 12, 39, 48, 81, 91, 111 Digital Serrodyne Wave Generator 14, 41, 50, 83, 93, 113 Integrator 15, 42, 51, 84, 94, 114 DA Converter 16, 43, 52, 85, 95, 115 Power amplifier 17, 44, 53, 86, 96, 116 ... step value /
Frequency conversion means 90 Adder 18, 54, 55, 97, 98, 117 Control circuit 19, 75, 118 Oscillator 26 Optical fiber 56 Difference device 115 Amplifier

Claims (5)

[Claims] 1. A laser light source for outputting laser light of a predetermined frequency, first phase modulation means for phase-modulating the laser light emitted from the laser light source, and a laser light emitted from the laser light source for a predetermined frequency. Second phase modulating means for modulating the phase by the modulation signal, or frequency modulating means for modulating the frequency of the laser light source; and introducing and propagating the laser light phase-modulated by the first and second phase modulating means. Optical fiber ring resonator, and a photodetector that detects laser light emitted from the optical fiber ring resonator,
A lock-in amplifier that receives the output of the photodetector and the modulation signal, synchronously detects the frequency component of the modulation signal in the output of the photodetector, and inputs and integrates the output of the lock-in amplifier. Control means for generating a digital serrodyne wave corresponding to 2π, and using the digital serrodyne wave as a modulation input of the first phase modulating means. A phase difference that forms a closed loop with respect to the movement of the resonance point is given by the digital serrodyne wave to two light waves that are different in the number of times of propagation in the vessel, and the digital serrodyne wave has a propagation frequency of 1 The property of regularly repeating the change of the waveform with respect to the phase difference between two light waves having different circumferences, and 2π
A resonance point tracking system characterized in that it is configured to follow one of two nearest resonance points among resonance points existing at intervals of 2π by using different binary phase differences. 2. The apparatus according to claim 1, wherein a function of the second phase modulating means is also used by the first phase modulating means by applying a modulating signal of a predetermined frequency to the first phase modulating means. A resonance point tracking system according to claim 1. 3. A laser light source for outputting a laser beam of a predetermined frequency, a branching unit for branching a laser beam emitted from the laser light source, and laser beams on first and second optical paths branched by the branching unit. First and third phase modulating means for respectively phase modulating the laser light, and phase modulating the laser light of the first and second optical paths branched by the branching means with first and second modulation signals of a predetermined frequency, respectively. Second and fourth phase modulating means, and the third and fourth phase modulating means so that the laser light phase-modulated by the first and second phase modulating means is turned clockwise. An optical fiber ring resonator for introducing and propagating the laser light phase-modulated in the counterclockwise direction, and a first optical detector for detecting the clockwise laser light emitted from the optical fiber ring resonator. An output unit, a second photodetector for detecting counterclockwise laser light emitted from the optical fiber ring resonator, and an input of the output of the first photodetector and the first modulation signal. A first lock-in amplifier for synchronously detecting a frequency component of the first modulated signal in an output of the first photodetector, and an output of the first lock-in amplifier; A value is generated, a first digital serrodyne wave corresponding to 2π is output, and this is fed back to the modulation input of the first phase modulation means, whereby an angular velocity is given to the optical fiber ring resonator. When
Alternatively, when the optical path length of the optical fiber ring resonator fluctuates due to a temperature change or the like, a first control unit that controls so as to follow this phase change, an output of the second photodetector and the second control unit. A second lock-in amplifier for receiving a modulation signal and synchronously detecting a frequency component of the second modulation signal in an output of the second photodetector, and an output of the second lock-in amplifier. And integrate to generate a step value,
By outputting a second digital serrodyne wave corresponding to 2π and feeding it back to the modulation input of the third phase modulating means, when an angular velocity is given to the optical fiber ring resonator, or A second control means for controlling the optical path length of the optical fiber ring resonator to follow the phase change when the optical path length fluctuates due to a temperature change or the like; The two light waves that differ by one round and the two light waves that differ by one round in the number of times of propagation in the counterclockwise direction have phase differences that form a closed loop with respect to the movement of the resonance point by the first and second digital serrodyne waves, respectively. At this time, the property that the digital serrodyne wave regularly changes its waveform with respect to the phase difference between two light waves whose propagation number differs by one round, and
Utilizing giving 2π different binary phase difference, 2π
Of the two nearest resonance points among the resonance points that are present every other, and the height of one step of the first digital serrodyne wave and the step of the second digital serrodyne wave An optical fiber gyro characterized by measuring a non-reciprocal resonance point movement of left-handed light and right-handed light by taking a difference in height of one step to obtain a gyro output. 4. A laser light source for outputting a laser beam of a predetermined frequency, a branching unit for branching a laser beam emitted from the laser light source, and laser beams on first and second optical paths branched by the branching unit. First and third phase modulating means for respectively phase modulating the laser light, and phase modulating the laser light of the first and second optical paths branched by the branching means with first and second modulation signals of a predetermined frequency, respectively. Second and fourth phase modulating means, and the third and fourth phase modulating means so that the laser light phase-modulated by the first and second phase modulating means is turned clockwise. An optical fiber ring resonator for introducing and propagating the phase-modulated laser light in a counterclockwise direction, and a first light detection for detecting a clockwise laser light emitted from the optical fiber ring resonator vessel And a second photodetector for detecting counterclockwise laser light emitted from the optical fiber ring resonator, and inputting the output of the first photodetector and the first modulation signal, A first lock-in amplifier for synchronously detecting a frequency component of the first modulation signal in an output of the first photodetector; and an output of the first lock-in amplifier, which is integrated and integrated to obtain digital cellodyne. A first step value generator, which is a digital integrator for generating a step height of the wave, and an output of the first step value generator and a second step value generator.
And an adder for adding the output of the step value generator, and generating the first digital serrodyne wave corresponding to 2π by inputting the output of the adder, to the modulation input of the first phase modulation means. The first digital serrodyne wave generator is fed back. When an angular velocity is given to the optical fiber ring resonator, or when the optical path length of the optical fiber ring resonator fluctuates due to a temperature change or the like, this phase A first control unit for controlling to follow the change, an input of the output of the second photodetector and the second modulation signal, and an input of the second control signal during the output of the second photodetector. A second lock-in amplifier for synchronously detecting a frequency component of the modulated signal;
The second step value generator, which is a digital integrator for receiving and integrating the output of the lock-in amplifier to generate a step height of a digital serrodyne wave, and the second step value generator To generate a second digital serrodyne wave corresponding to 2π,
And a second digital serrodyne wave generator that feeds back to the modulation input of the phase modulation means of the optical fiber ring resonator, when the angular velocity is given to the optical fiber ring resonator, or the optical path of the optical fiber ring resonator A second control means for controlling to follow a phase change when the length fluctuates, wherein two light waves having different numbers of propagations by one turn in the clockwise direction propagating in the optical fiber ring resonator and a counterclockwise The two light waves that are different in the number of times of propagation and
And the second digital serrodyne wave gives a phase difference that forms a closed loop with respect to the movement of the resonance point. At this time, the digital serrodyne wave has a waveform difference with respect to the phase difference between two light waves having different propagation times. Utilizing the property of repeating the change regularly and giving a binary phase difference different by 2π, to follow any one of the two nearest resonance points among resonance points existing every 2π, An optical fiber gyro, wherein an output of the first step value generator is a gyro output corresponding to a shift of a non-reciprocal resonance point between left-handed light and right-handed light. 5. The function of said second and fourth phase modulating means respectively to said first and third phase modulating means by adding a modulating signal of a predetermined frequency to said first and third phase modulating means respectively. The optical fiber gyro according to claim 3, wherein the optical fiber gyro is used.