JPH05223581A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To obtain a highly accurate angular velocity in a serrodyne-type optical fiber gyro. CONSTITUTION:An optical fiber gyro is provided with a phase modulator which propagates light from a light source to an optical fiber loop in opposite directions each other and phase-modulates two propagation lights by a fundamental frequency, a light detector which detects the two propagation lights after guiding them to a same waveguide path, a synchronous detector 26 which performs synchronization detection of the output of the light detector according to the fundamental frequency of the phase modulator. thus obtaining an angular velocity from the phase difference between propagation lights. Then, a DC filter which cuts off DC constituent from the output of the light detector, a higher harmonic filter which cuts off higher harmonic component from the output of the light detector, and a signal generator 28 which generates a same frequency signal as the higher harmonic component to be filtered off provided and the higher harmonic filter is constituted so that the higher harmonic component can be filtered off based on a reference signal from the signal generator 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an aircraft, a ship,
The present invention relates to an optical fiber gyro suitable for use as an angular velocity meter for automobiles and the like.

[0002]

2. Description of the Related Art Optical fiber gyros are configured to measure angular velocity by utilizing the Sagnac effect of light.
Practical application is progressing because it has the advantages of high reliability and miniaturization of the device. Among optical fiber gyros, there is a type called an interferometric optical fiber gyro, which allows two long optical paths consisting of an optical fiber loop wound a plurality of times to propagate light in opposite directions to each other. It is configured to obtain the angular velocity from the phase difference of the propagating light.

As the interferometric optical fiber gyro, a phase modulation system and a serrodyne system improved from the phase modulation system have been developed.

FIG. 2 shows an example of a phase difference modulation type optical fiber gyro. The optical fiber gyro is a semiconductor laser,
A light source 1 such as a light emitting diode, a light receiver 2 for converting incident light into an electric current, an optical fiber loop 3 formed by winding one optical fiber a plurality of times, a polarizer 4, and light propagating through the optical fiber are combined. Alternatively, it has couplers 5 and 6 that branch. The light beam output from the light source 1 is guided to the second coupler 6 via the first coupler 5 and the polarizer 4. The light beam is branched by the second coupler 6, and the two light beams thus branched propagate in the optical fiber loop 3 in opposite directions. That is, one propagates rightward in the optical fiber loop 3 and the other propagates counterclockwise.

When the angular velocity Ω is applied to the optical fiber loop 3, the lights propagating in the optical fiber loop 3 in opposite directions generate a phase difference Δθ due to the Sagnac effect (Sagnac effect). Such phase difference Δθ
Is proportional to the angular velocity Ω and is expressed by the following equation.

[0006]

[Equation 1]

Where R is the loop diameter of the optical fiber loop 3, L is the length of the optical fiber loop 3, λ is the wavelength of the light beam output from the light source 1, and C is the speed of light.

Further, the phase difference modulation type optical fiber gyro includes a current / voltage converter 7, a phase modulator 8, a signal generator 9 and a synchronous detector 10. The current output from the light receiver 2 is converted into a voltage by the current / voltage converter 7 and output as a voltage. The phase modulator 8 is arranged at one end of the optical fiber loop 3 and is operated by the reference signal supplied from the signal generator 9. Lights propagating in the optical fiber loop 3 in opposite directions are phase-modulated by the phase modulator 8. If the angular frequency of the signal supplied from the signal generator 9 is ω _P , the output voltage V of the current / voltage converter 7 is

[0009]

[Number 2] I = K {1 + cosΔθ ( J 0 (x) -2J 2 (x) cos2ω P t + ‥‥) -sinΔθ (2J 1 (x) sinω P t- ‥‥)}

[0010] Where x is the degree of phase modulation, J ₀ ,
J ₁ , J ₂ , ... Are Bessel functions, K is a proportional constant, and t is time.

A signal having an angular frequency ω _P is supplied from the signal generator 9 to the synchronous detector 10, and the angular frequency component ω _P of the angular frequency nω _P component of the output voltage V is supplied by the reference signal.
Is detected synchronously and output 2KJ proportional to sin Δθ
₁ (x) sin Δθ is output. In this way, Δθ is obtained, and the angular velocity Ω is obtained from the equation (1).

FIG. 3 shows an example of a serrodyne type optical fiber gyro. The serrodyne system is developed so as to obtain a wider dynamic range than the phase modulation system, and the serrodyne modulator 16 is arranged at one end of the optical fiber loop 3 in addition to the phase modulator 8. .. The serrodyne modulator 16 has a sawtooth waveform (serodyne wave) for the light propagating in the optical fiber loop 3 in opposite directions.
Are superimposed and phase-modulated.

The optical fiber gyro further includes a synchronous detector 1
A first integrator 11 that integrates the phase difference Δθ output by 0, a second integrator 12 that further integrates the output of the integrator 11, and a 2π reference device 15 that generates a 2π reference signal,
The 2π reference signal from the 2π reference device 15 and the second integrator 12
And a reset circuit 14 for generating a reset signal by generating a reset signal and generating the output of the serrodyne wave (sawtooth wave) from the output of the second integrator 12 by the reset signal.
The counter 13 that counts the wave number of the serrodyne wave and outputs an angular velocity signal.

The operation of this serrodyne system will be described. FIG. 4A shows a phase-modulated wave of light that is phase-modulated by the serrodyne modulator 16. The phase-modulated wave of counterclockwise light is represented by a solid line as θ (t), and the phase-modulated wave of clockwise light is represented as θ. It is represented by a broken line as (t−τ). Since the serrodyne modulator 16 is arranged at one end of the optical fiber loop 3, the light propagating counterclockwise in the optical fiber loop 3 and the light propagating clockwise in the optical fiber loop 3 are phase-modulated at different timings. FIG. 4B shows a phase difference θ (t) −θ (t−τ) between lights propagating in two directions, counterclockwise and clockwise, where the positive phase difference θ _S is

[0015]

[Equation 3]

It is represented by Here, T _S is the period of the serrodyne wave, and τ is the time difference between the light propagating in the two directions of the counterclockwise and clockwise directions, which is determined by the length of the optical fiber loop 3.

The output voltage V of the current / voltage converter 7 has a value obtained by replacing Δθ with Δθ + θ _S in the equation (2). Therefore, sin (Δθ + θ) is output from the synchronous detector 10.
2 kJ ₁ proportional to _{S) (x) sin (Δθ} + θ S) is outputted.

The output is integrated by the two integrators 11 and 12 and fed back to the serrodyne modulator 16. In the serrodyne modulator 16, based on the signal from the integrator 12, sin (Δθ + θ _S ) = 0,
That is, the phase modulation is performed so that the phase difference becomes θ _S = −Δθ. Substituting the equations of equation 2 and equation 3 into this equation θ _S = −Δθ,

[0019]

[Equation 4]

Here, f _S is the frequency f _{S of the} serrodyne wave
= 1 / T _S. Thus, the serrodyne modulator 16 performs serrodyne modulation based on the signal fed back from the integrator 12, and the counter 13 counts the frequency of the serrodyne wave. From the frequency thus counted, the angular velocity Ω can be obtained by the equation (4).

In this method, the DC component K of the output voltage V of the current / voltage converter 7 expressed by the equation (2) is used.
(1 + J ₀ ) and harmonic components such as the second harmonic component 2KJ ₂ account for a large proportion, and the basic component 2KJ ₁ (x) required to calculate the angular velocity Ω is small, so high accuracy is obtained when the input angular velocity value is small. Has the drawback that it cannot be obtained.

FIG. 5 shows an example of an optical fiber gyro according to the patent application No. 3-132991 proposed by the same applicant as the present applicant. The purpose of this example is to eliminate the drawbacks of the serrodyne type optical fiber gyro shown in FIG. 3 and improve it. From the output voltage V of the current / voltage converter 7, the direct current component (1 + J ₀ ) and The harmonic component of the second harmonic component is removed, and the necessary basic component can be obtained with high accuracy.

This optical fiber gyro includes a direct current remover 17 and a second harmonic remover 18 on the output side of the current / voltage converter 7, as is apparent from comparison with the optical fiber gyro shown in FIG. Since the direct current component (1 + J ₀ ) is removed from the output voltage V of the current / voltage converter 7 by the direct current remover 17 and the second harmonic wave component 2J ₂ is removed by the second harmonic wave remover 18, the input angular velocity is small. Even in this case, the gain can be increased. The DC remover 17 may be composed of, for example, a high pass filter.

FIG. 6 shows an example of the structure of the second harmonic wave remover 18.
The second harmonic remover 18 includes a subtracter 21, a phase detector 22, compensation amplifiers 23 and 27, a voltage control phase shifter 24, and a multiplier 2.
5, including a synchronous detector 26 and a signal generator 28. The signal generator 28 is configured to generate a signal having a frequency 2ω _{P which} is twice the frequency ω _P of the signal generated by the signal generator 9. The output voltage V of the current / voltage converter 7 is supplied from the input terminal 17a to the second harmonic wave remover 18 via the direct current remover 17, and the output of the second harmonic wave remover 18 is output terminal 1
It is supplied to the synchronous detector 10 from 7b.

The phase detector 22, the compensation amplifier 23, the voltage control phase shifter 24 and the multiplier 25 constitute a first closed loop, and the output from the multiplier 25 should be removed in the first loop. It is controlled so as to have the same phase as the second harmonic component. That is, the phase difference detector 22 compares the double wave component of the voltage supplied via the input terminal 17a with the output from the multiplier 25, and outputs the voltage representing the phase difference. In the compensation amplifier 23, the output voltage from the phase difference detector 22 is amplified with an appropriate amplification factor and output to the voltage control phase shifter 24 as the control voltage V _C. In the voltage controlled phase shifter 24, the frequency 2ω _{P of the} signal generated by the signal generator 28 is
A signal is generated which has the same frequency as and which is phase-shifted by an amount proportional to the control voltage V _C.
Is output to. The multiplier 25 multiplies the signal from the voltage controlled phase shifter 24 and the signal from the compensation amplifier 27, and the resulting signal is output to the subtractor 21.

On the other hand, the synchronous detector 26, the compensation amplifier 27,
The multiplier 25 and the subtractor 21 form a second closed loop. In the second loop, the output from the multiplier 25 is controlled to have the same phase as the second harmonic component to be removed, and thus the multiplier 25 generates an output having the same phase as the second harmonic component. The resulting output is supplied to the subtractor 21 and the second harmonic component is removed. That is, in the synchronous detector 26, the subtractor 2
The output from 1 is synchronously detected by the signal of the frequency 2ω _P from the signal generator 28, and a signal having the same phase as the second harmonic component is generated. In the compensation amplifier 27, the output voltage from the synchronous detector 26 is amplified with an appropriate amplification factor and output to the multiplier 25. The multiplier 25 multiplies the signal having the same phase as the second harmonic component output from the voltage controlled phase shifter 24 by the signal having the same phase as the second harmonic component output from the compensation amplifier 27. .. In the subtractor 21, the DC component supplied via the input terminal 17a is removed, but the signal from the multiplier 25 is subtracted from the input signal containing the second harmonic component,
The resulting signal is output from the output terminal 17b.

Thus, the light receiver 2 and the current / voltage converter 7
By removing the direct current wave component and the second harmonic wave component from the output voltage from, the desired fundamental wave component can be extracted with high accuracy. Since the angular velocity is obtained from such a fundamental wave component, it is possible to obtain a sufficiently accurate measurement value even when the value of the input angular velocity is small.

[0028]

In the example shown in FIG. 5, the phase difference detector 22 forming the first loop is a current / voltage converter supplied via the DC remover 17 and the input terminal 17a. The output from 7 is used as a reference voltage and compared with the output voltage from the multiplier 25 to generate a signal representing the phase difference.

However, the output voltage V from the current / voltage converter 7 contains various noises. Such noise is due to, for example, the phase-modulated wave shown in FIG. 4A being a serrodyne wave (sawtooth wave). There is a reset time (this is called flyback time) required for the amplitude of the serrodyne wave to fall from 2π to 0, and the amplitude of the serrodyne wave is not 2π (this is 2π.
Error. There are things to do. This causes the above-mentioned noise.

Therefore, when the output voltage V from the current / voltage converter 7 is used as a reference signal, there is a drawback that a highly accurate output cannot be obtained from the phase difference detector 22.

In view of the above point, the present invention provides a current / voltage converter 7 in a serrodyne optical fiber gyro.
It is an object of the present invention to improve the accuracy of the output signal from the phase difference detector 22 included in the second harmonic wave remover 18 provided on the output side of.

[0032]

The optical fiber gyroscope of the present invention divides the light from the light source 1, the optical fiber loop 3, and the light from the light source 1 into the first propagating light and the second propagating light. Optical distributors 5 and 6 for propagating in the optical fiber loop 3 in mutually opposite directions, a phase modulator 8 for phase-modulating the first propagating light and the second propagating light at a fundamental frequency, and propagating in the optical fiber loop 3. The photodetector 2 that guides the first propagating light and the second propagating light to the same waveguide and then detects them, and the synchronization that synchronously detects the output of the photodetector 2 by the fundamental frequency of the phase modulator 8. In the optical fiber gyro having the detector 10 and obtaining the angular velocity from the phase difference between the first propagating light and the second propagating light, a direct current remover 17 for removing a direct current component from the output of the photodetector 2; , High to remove harmonic components from the output of photodetector 2 A wave remover 18, a signal generator 28 for generating the same frequency of the signal and the harmonic component to be removed
And the harmonic remover 18 is configured to remove the harmonic component based on the reference signal from the signal generator 28.

[0033]

According to the present invention, as the reference signal supplied to the phase difference detector 22 included in the second harmonic remover 18, the current
Not the output voltage V from the voltage converter 7, but the signal generator 2
The signal from 8 is being used. Therefore, the phase difference signal from the phase difference detector 22 does not include an error due to the noise included in the output voltage V from the current / voltage converter 7, and thus a more accurate phase difference signal can be obtained. it can.

[0034]

Embodiments of the present invention will be described below with reference to FIG. In FIG. 1, corresponding parts in FIGS. 2 to 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 shows the structure of the second harmonic wave remover 18 used in the serrodyne type optical fiber gyro of this example. The second harmonic remover 18 includes a subtractor 21 and a phase detector 2
2. Compensation amplifiers 23 and 27, a voltage control phase shifter 24, a multiplier 25, a synchronous detector 26, and a signal generator 28 that generates a signal of frequency 2ω _P.

As is clear from comparison between FIG. 1 and FIG. 6, in this example, the reference signal supplied to the phase difference detector 22 uses the signal generated by the signal generator 28, and the input terminal The output voltage V from the current / voltage converter 7 supplied via 17a is not used. Therefore,
As in the example shown in FIG. 6, the occurrence of an error due to noise included in the output voltage V from the current / voltage converter 7 is eliminated.

A signal having a frequency of 2ω _P is generated by the signal generator 28, and the signal is supplied to the phase difference detector 22 as a reference signal. In the phase difference detector 22, the output voltage from the multiplier 25 is compared with the reference signal to obtain the phase difference. Such a phase difference is obtained as a more accurate value as compared with the case where the output voltage V from the current / voltage converter 7 is used as the reference signal as described above.

That is, even if the output voltage V from the current / voltage converter 7 has an error due to the flyback time or a 2π error, the phase difference signal from the phase difference detector 22 produces such an error. It does not include the exact one. Therefore, in the serrodyne optical fiber gyro, the influence of the error due to the flyback time and the 2π error can be minimized, and thus a more accurate angular velocity can be obtained.

The present example is different from the conventional example only in that the reference signal input to the phase difference detector 22 is supplied from the signal generator 28, and other configurations are shown in FIGS. It may be the same as the example shown.

Although the embodiments of the present invention have been described in detail above, those skilled in the art will understand that the present invention is not limited to the above-mentioned embodiments and various other configurations can be adopted without departing from the gist of the present invention. Easy to understand.

[0041]

According to the present invention, the second-harmonic remover 18 for eliminating the second-harmonic component on the output side of the current / voltage converter 7 is provided.
In the optical fiber gyro of the serrodyne system provided with, there is an advantage that the phase difference signal from the phase difference detector 22 forming the second harmonic wave remover 18 can be obtained as a more accurate value.

According to the present invention, in the serrodyne type optical fiber gyro, the signal from which the second harmonic component is removed, which is output by the second harmonic remover 18, is supplied to the synchronous detector 10 as a more accurate signal. Therefore, there is an advantage that a more accurate angular velocity can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a second harmonic wave remover of an optical fiber gyro according to the present invention.

FIG. 2 is a diagram showing an example of a conventional optical fiber gyro.

FIG. 3 is a diagram showing an example of a conventional optical fiber gyro.

FIG. 4 is an explanatory diagram illustrating a function of a serrodyne modulator.

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

FIG. 6 is a diagram showing a configuration example of a conventional second harmonic wave remover.

[Explanation of symbols]

 1 light source 2 light receiver 3 fiber loop 4 polarizer 5, 6 coupler 7 current-voltage converter 8 phase modulator 9 signal generator 10 synchronous detector 11, 12 integrator 13 counter 14 reset circuit 15 2π reference 16 serrodyne modulator 17 DC remover 17a Input terminal 17b Output terminal 18 Double wave remover 22 Phase difference detector 23 Compensation amplifier 24 Voltage control phase shifter 25 Multiplier 26 Synchronous detector 27 Compensation amplifier 28 Signal generator

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[Procedure amendment]

[Submission date] April 6, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

[Number 2] I = K {1 + cosΔθ ( J 0 (x) -2J 2 (x) cos2ω P t + ‥‥) -sinΔθ (2J 1 (x) cosω P t- ‥‥)}

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

[0015]

[Equation 3]

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0019

[Correction method] Change

[Correction content]

[0019]

[Equation 4]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takeshi Hojo 2-16-46 Minami Kamata, Ota-ku, Tokyo Within Tokimec Co., Ltd.

Claims (1)

[Claims] 1. A light source, an optical fiber loop, and light distribution for distributing the light from the light source into a first propagating light and a second propagating light and propagating both of them in opposite directions to the optical fiber loop. And a phase modulator that phase-modulates the first propagating light and the second propagating light at a fundamental frequency, and the first propagating light and the second propagating light propagating in the optical fiber loop are guided by the same conductor. A first photodetector that guides the light to the waveguide and then detects it; and a synchronous detector that synchronously detects the output of the photodetector at the fundamental frequency of the phase modulator.
In a fiber optic gyro that obtains an angular velocity from the phase difference between the propagating light and the second propagating light, a DC remover that removes a DC component from the output of the photodetector and a harmonic component from the output of the photodetector A harmonic remover for removing and a signal generator for generating the same frequency signal as the harmonic component to be removed are provided, and the harmonic remover is a harmonic wave generator based on the reference signal from the signal generator. An optical fiber gyro characterized in that it is configured to remove components.