JPH06117863A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To obtain an optical fiber gyro which does not cause any bias fluctuation even when the duty ratio of a reference signal is deviated. CONSTITUTION:This gyro is provided with a DC remover 17 which removes a DC component from the output of a photoreceptor 2, double wave remover 18 which removes a double-wave component from the output of the photoreceptor 2, and a phase shifter 11 which inputs the outputs of a signal generator 9 and the remover 18 and outputs a reference signal inputted from the generator 9 to a synchronous detector 10 after shifting the phase of the reference signal. The shifter 11 is constituted so that the shifter 11 can eliminate a quadruple wave component from the output of the detector 10 by shifting the phase of the reference signal.

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 Generally, an optical fiber gyro is configured to measure an angular velocity by utilizing the Sagnac effect of light, and has an advantage that it has high reliability and can downsize the device, and thus is not put to practical use. It is progressing. Among the 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 propagating light.

FIG. 3 shows an interferometer type optical fiber gyro.
A conventional example of a phase modulation type optical fiber gyro is shown. The optical fiber gyro is a light source 1 such as a semiconductor laser or a light emitting diode, a light receiver 2 for converting incident light into an electric current, and an optical fiber loop 3 formed by winding one optical fiber a plurality of times.
And a coupler 5 and 6 for combining or splitting light propagating through a polarizer 4 and an optical fiber. The light output from the light source 1 is guided to the second coupler 6 via the first coupler 5 and the polarizer 4. The light is split by the second coupler 6, and the two split lights thus 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 produce a phase difference Δφ due to the Sagnac effect (Sagnac effect). Such phase difference Δφ
Is proportional to the angular velocity Ω and is represented by the following equation.

[0005]

[Equation 1]

Here, R is the loop radius of the optical fiber loop 3, L is the length of the optical fiber loop 3, λ is the wavelength of the light output from the light source 1, and c is the speed of light.

Further, such a phase 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 current-voltage converter 7
The output voltage I of

[0008]

## EQU2 ## I = K [1 + cos Δφ {J ₀ (z) -2J ₂ (z) cos 2ω _P t + ...} -sin Δφ {2J ₁ (z) cosω _P t -...}] Where z is the degree of phase modulation, J ₀ , J ₁ , J ₂ ,
Is a Bessel function, 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 of the angular frequency nω _P of the output voltage I is supplied by the reference signal.
Synchronous detection of _P, output 2KJ proportional to sin Δφ
₁ (z) sin Δφ is output. In this way, Δφ is obtained, and the angular velocity Ω is obtained from the equation (1).

However, in such a conventional optical fiber gyro, if the input angular velocity is small,
The 2KJ ₁ (z) sin Δφ detected in Equation 2 is very small. For this reason, in order to detect this signal with high accuracy, it is necessary to increase the overall signal gain before synchronous detection, but the overall signal is mainly the harmonics of the direct current component (1 + J ₀ ) and the second harmonic component 2J _2. Since they are occupied by the components, there is a problem that the entire dynamic range is limited by these signal components.

Therefore, patent applications proposed by the present applicants (Japanese Patent Application No. 3-132991 and Japanese Patent Application No. 4-2991).
No. 6756) optical fiber gyro is provided with a DC remover 17 and a second harmonic remover 18 on the output side of the current-voltage converter 7. From the output voltage I of the current-voltage converter 7, the DC component (1 + J ₀ ) is removed by the DC remover 17, and the second harmonic component 2J ₂ is removed by the second harmonic remover 18, so the input angular velocity is small. Even in this case, the gain can be increased. The signal passed through the DC remover 17 and the second harmonic remover 18 is supplied to the synchronous detector 10.

[0012]

The synchronous detector 10 used in the phase modulation method as described above has two types called a one-phase type and a two-phase type. The type configuration is shown in FIG.

In FIG. 4, reference numeral 18a denotes a second harmonic wave remover 18
Is a mixer, and 25 is a phase shifter. The phase shifter 25 has a phase shift amount θ.
A reference signal e ₂ for synchronous detection with an amplitude of 1 is generated at.
If e ₁ is the input signal and e ₃ is the synchronous detection output, e ₃ =
It becomes e ₁ and e ₂ . Here, consider a case where the duty ratio of the reference signal is not ideally 1: 1 but deviated by Δ. This state is shown in FIG. In FIG. 5, T is a period and T = 2
π / ω _P. When the _equation 2 is synchronously detected with the reference signal as shown in FIG. 5, if the direct current component is D ₀ , the fundamental component is D ₁ , the second harmonic component is D ₂ , ...

[0014]

[Formula 3] D ₀ = K · {1 + cos Δφ · J ₀ (z)} · 2Δ D ₁ = K · sin Δφ · 2J ₁ (z) · 4 cos (Δ / 2) · sin (θ + Δ / 2) D ₂ = K・ Cos Δφ ・ 2J ₂ (z) ・ 2sin Δ ・ cos (2θ + Δ) D ₃ = K ・ sin Δφ ・ 2J ₃ (z) ・ (4/3) cos (3Δ / 2) ・ sin (3θ + 3Δ / 2) D ₄ = K・ Cos Δφ ・ 2J ₄ (z) ・ sin 2Δ ・ cos (4θ + 2Δ)

[0015] If the output voltage I expressed by the equation 2 is subjected to the synchronous detection by removing the direct current component and removing the second harmonic component, D ₀ and D _{2 in the equation} 3 become zero. Therefore,
FIG. 6 shows the result of calculating D ₁ and D ₄ of Equation 3. FIG. 6 shows the components of the synchronous detection output when the reference phase θ is swept with z = 1.84 and Δ = 10 degrees. Δ = 10
The degree corresponds to a duty ratio of about 47:53. Further, the phase difference Δφ was set to 1 degree.

From FIG. 6, it is clear that when the duty ratio of the reference signal of the synchronous detector is deviated, a bias is generated in the output signal, and the bias fluctuates at a cycle four times that of the reference signal. Actually, the bias is D ₄ + D ₆ +
However, since D _{6 and} above are much smaller than D ₄ , 4
The harmonic component is dominant.

That is, when the duty ratio of the reference signal is slightly deviated, a bias is generated in the gyro signal, and the fluctuation of the duty ratio causes the bias to fluctuate, resulting in an unstable gyro output. become.
To eliminate this point, it is ideal that the duty ratio is 1: 1. However, it is extremely difficult to produce a signal that strictly satisfies this condition, and there is a disadvantage that a stable gyro signal cannot be obtained. An object of the present invention is to provide an optical fiber gyro that does not fluctuate in bias even when the duty ratio of the reference signal is deviated when the one-phase synchronous detector is used in view of the above point.

[0018]

An optical fiber gyroscope according to the present invention is, for example, as shown in FIG. 1, a light source 1, an optical fiber loop 3, and the light from the light source 1 into a first propagating light and a second propagating light. And a phase modulator 8 for phase-modulating the first propagating light and the second propagating light at a fundamental frequency, and the fundamental frequency A signal generator 9 for generating
The first propagating light and the second propagating light propagating through the optical fiber loop 3
The light propagating to the same waveguide and then detecting it, a current-voltage converter 7 for converting the current output from this light-receiver 2 into a voltage, and this current-voltage converter 7 And a synchronous detector 10 for synchronously detecting the voltage output from the signal generator 9 using the signal from the signal generator 9 as a reference signal, and detecting the phase difference between the first propagating light and the second propagating light, In the optical fiber gyro that obtains the rotational angular velocity from the amount of phase deviation at that time, a DC remover 17 that removes the DC component from the output of the photodetector 2 and a double wave remover that removes the double component from the output of the photodetector 2 18 and the output from the signal generator 9 and the output from the second-harmonic remover 18 are input, and the phase of the reference signal input from the signal generator 9 is shifted to the synchronous detector 10. The phase shifter 11 for outputting Vessel 11 is intended to fourth harmonic component of the output of the synchronous detector 10 by shifting the phase of the reference signal was set to zero.

[0019]

[Function] When the bias is stable, it means that the fluctuation of the duty ratio is small. However, if the fluctuation has a certain value, the point that the bias is stable means that the bias itself is not easily influenced by the fluctuation. You can think of it as a small point. Then, the reference phase at which the bias of the most dominant fourth harmonic component becomes zero can be obtained from Equation 3. That is,

[0020]

## EQU00004 ## cos (4.theta. + 2.DELTA.) = 0. Therefore,

## EQU00005 ## .theta. = (2n + 1) .pi. / 8-.DELTA. / 2 (n = 0, 1, 2, ... 7). In this case, if the phases of the reference signals are matched, a stable gyro output without bias fluctuation can be obtained even if the duty ratio is deviated.

That is, according to the present invention, when the one-phase synchronous detector is used to obtain the gyro signal of the optical fiber gyro, even if the duty ratio of the reference signal is deviated, the bias due to the fluctuation of the duty ratio is applied. Since the phase of the reference signal is matched to the point where there is no fluctuation, a stable output signal can be obtained.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical fiber gyro of the present invention will be described below with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. The optical fiber gyro shown in FIG. 1 is a light source 1 such as a semiconductor laser or 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, and a polarizer. 4 and couplers 5 and 6 that combine or split the light propagating through the optical fiber.
The light output from the light source 1 is the first coupler 5 and the polarizer 4
Is guided to the second coupler 6 through which the light is branched, and the two lights thus branched propagate through 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 produce a phase difference Δφ due to the Sagnac effect (Sagnac effect). Such phase difference Δφ
Is proportional to the angular velocity Ω and is expressed by the equation (1).

Furthermore, such a phase modulation type optical fiber gyro has 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.

In the present embodiment, the output voltage of the current-voltage converter 7 is supplied to the synchronous detector 10 via the DC remover 17 and the double wave remover 18, and the signal generator 9 is also provided.
The reference signal is supplied to the synchronous detector 10 via the phase shifter 11, and the output signal of the second harmonic wave remover 18 is supplied to the phase shifter 11 in this example.

An example of the structure of the phase shifter 11 is shown in FIG. In FIG. 2, 18a is an input terminal to which a signal from the second harmonic remover 18 is supplied, 12 is a bandpass filter having a center frequency of 4ω _P , 13 is a synchronous detector, 14 is a lowpass filter, and 15 is a compensation amplifier. Reference numeral 16 is a phase shifter, and 9a is an input terminal to which the reference signal from the signal generator 9 is supplied. The synchronous detector 13, the low-pass filter 14, the compensation amplifier 15, and the phase shifter 16 form a closed loop, and are controlled so that the output from the low-pass filter 14 becomes zero. That is, the bandpass filter 12 detects the quadruple component of the second-harmonic remover 18 and synchronously detects it, and the compensation amplifier 15 adjusts the voltage to an appropriate voltage. The output of the phase shifter 16 serves as a reference signal for the synchronous detector 10 and the synchronous detector 13.

The DC remover 17 and the second harmonic remover 18 are patent applications proposed by the present applicant (Japanese Patent Application No. 3-132).
No. 991 and Japanese Patent Application No. 4-26756) may be used for the optical fiber gyro. Double wave remover 18
May be further configured by a notch filter or the like. In this example, the others are configured similarly to the conventional one.

Since the present embodiment is constructed as described above, even if the duty ratio of the output from the phase shifter 16 is deviated, the phase of the reference signal becomes zero at the point where the bias output by the fourth harmonic component becomes zero. Always controlled. That is, the relational expression of Expression 5 is satisfied, and therefore Expression 6 is obtained, and by adjusting the phase of the reference signal to this phase, a stable gyro signal without bias fluctuation can be obtained even if the duty ratio is deviated. .

That is, according to this example, even if the duty ratio of the reference signal is deviated when the one-phase type synchronous detector is used to obtain the gyro signal of the optical fiber gyro, the fluctuation of the duty ratio causes Since the phase of the reference signal is matched to the point where there is no bias fluctuation, a stable output signal can be obtained.

Further, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other structures can be adopted without departing from the gist of the present invention.

[0031]

According to the present invention, the DC remover, the second harmonic remover, and the phase shifter for setting the phase of the signal from the signal generator to the equation 6 are provided. A stable gyro signal can be obtained even when the duty ratio of the signal phase is deviated, and as a result, a highly accurate optical fiber gyro can be obtained.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram showing an example of a phase shifter.

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

FIG. 4 is a configuration diagram of a synchronous detector.

FIG. 5 is a diagram showing an example of a reference signal.

FIG. 6 is a diagram used for explaining the present invention.

[Explanation of symbols]

 1 Light source 2 Light receiver 3 Optical fiber loop 4 Polarizer 5,6 Coupler 7 Current-voltage converter 8 Phase modulator 9 Signal generator 10,13 Synchronous detector 11 Phase shifter 14 Low-pass filter 16 Phase shifter 17 DC removal Container 18 2nd harmonic remover

Front page continued (72) Inventor Takeshi Hojo 2-16-46 Minami Kamata, Ota-ku, Tokyo Within Tokimec Co., Ltd. Within

Claims (1)

[Claims] 1. A light source, an optical fiber loop, and a coupler that distributes the light from the light source into a first propagating light and a second propagating light and propagates the both in opposite directions to the optical fiber loop. A phase modulator that phase-modulates the first propagating light and the second propagating light at a fundamental frequency, a signal generator that generates the fundamental frequency, a first propagating light that propagates through the optical fiber loop, and A light receiver that guides the two propagating lights to the same waveguide and then detects the light, a current-voltage converter that converts the current output from the light receiver into a voltage, and a voltage from the current-voltage converter. A synchronous detector that synchronously detects the output from the signal generator using the signal from the signal generator as a reference signal, detects the phase difference between the first propagating light and the second propagating light, and shifts the phase at that time. In the optical fiber gyro that calculates the rotational angular velocity from the amount, A DC remover 17 for removing a DC component from the output of the light receiver 2, and double wave remover 18 for removing the second harmonic component from the output of the light receiver 2, and output from the signal generator 9,
A phase shifter 11 is provided, which receives the output from the second-harmonic remover 18, shifts the phase of the reference signal input from the signal generator 9 to the synchronous detector 10, and outputs the phase-shifted reference signal. An optical fiber gyro 11 is characterized in that the fourth harmonic component of the output of the synchronous detector 10 is made zero by shifting the phase of the reference signal.