JP3314318B2 - Fiber optic gyro - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to, for example, aircraft, ships,
The present invention relates to an optical fiber gyro suitable for use as an gyro for an automobile or the like, and more particularly, to an optical fiber gyro of a phase modulation system and a serrodyne system.

[0002]

2. Description of the Related Art An optical fiber gyro is widely used as a device for measuring an angular velocity, and has advantages of being small in size and having high reliability. The optical fiber gyro measures an angular velocity using a Sagnac effect (also called a Sagnac effect) of light. In an interference type optical fiber gyro, light propagates in one long optical path composed of an optical fiber loop wound a plurality of times in directions opposite to each other, and an angular velocity is obtained from a phase difference appearing in the interference light between the two propagated lights. .

An example of a conventional optical fiber gyro apparatus will be described with reference to FIG. This optical fiber gyro device is a phase modulation type of an interference type optical fiber gyro.

An optical fiber gyro device includes a light emitting device 1 such as a semiconductor laser or a light emitting diode, a light receiving device 2 for converting detection light into a current, an optical fiber loop 3 formed by winding one optical fiber a plurality of times, and an optical fiber gyro. And an integrated circuit 4. The optical integrated circuit 4 has first and second Y-branches 5 and 6 for combining or branching light propagating through an optical fiber, and a phase modulator 8 provided on a branch of the second Y-branch 6.

The light emitting device 1 and the light receiving device 2 are connected to each branch of the first Y branch 5, and both ends of the optical fiber loop 3 are connected to each branch of the second Y branch 6. The light output from the light emitter 1 passes through the first Y-branch 5, is split into two propagating lights by the second Y-branch 6, and propagates in the optical fiber loop 3 in opposite directions. That is, one propagates clockwise through the optical fiber loop 3, and the other propagates counterclockwise.

The lights that have propagated in the optical fiber loop 3 in opposite directions are combined by the second Y branch 6 to generate interference light. Such interference light is detected by the light receiver 2 via the other branch of the first Y branch 5.

When an angular velocity Ω is applied to the optical fiber loop 3 from the outside, the optical fiber loop 3 is caused by the Sagnac effect.
A phase difference Δθ is generated between lights propagating in the opposite directions. Such a phase difference Δθ is proportional to the angular velocity Ω and is expressed by the following equation.

[0008]

Equation 1 Δθ = (2πDL / λc) Ω

Here, D 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 output from the light emitter 1, c is the speed of light, and Ω is the optical fiber loop 3. Represents the angular velocity around the central axis of the loop.

According to the phase modulation method, the light propagating clockwise and the light propagating counterclockwise in the optical fiber loop 3 are respectively phase-modulated by the phase modulator 8. Thereby, an accurate phase difference Δθ can be obtained even when the input angular velocity Ω is small. In the method without phase modulation, the intensity I of the interference light detected by the light receiver 2 includes the cosine value cos Δθ of the phase difference Δθ, and if the input angular velocity Ω is small, there is a disadvantage that an accurate phase difference Δθ cannot be obtained. Was.

The light E _C propagating clockwise and the light E _CC propagating counterclockwise in the optical fiber loop 3 are expressed as follows at both ends of the optical fiber loop 3.

[0012]

E _C = E ₀ sin (ωt−Δθ / 2 + β ₀ ) E _CC = E ₀ sin (ωt + Δθ / 2 + β _T )

Where E ₀ is the amplitude, ω is the angular velocity with respect to the frequency of the light, t is the time, Δθ / 2 is the phase difference caused by the Sagnac effect, and β ₀ and β _T are the positions generated by the phase modulator 8. It is a difference. The phase difference β ₀ of the light E _C propagating clockwise is the phase difference of the light phase-modulated at the exit of the optical fiber loop 3 after propagating clockwise through the optical fiber loop 3 and propagating counterclockwise. The phase difference β _T of the light E _{CC is} the phase difference of the light that has been phase-modulated at the entrance of the optical fiber loop 3 and has propagated counterclockwise through the optical fiber loop 3.

The two propagation lights E _C and E _CC are the second Y light.
The interference light combined by the branch 6 is detected by the light receiver 2 via the other branch of the first Y branch 5. The intensity I of the interference light detected by the light receiver 2 is represented by the following equation.

[0015]

Equation 3] I = 2E ₀ ² _{[1 + cos (Δθ + β T} -β 0) ]

The phase modulation is performed using a sine wave of the reference frequency of the angular velocity omega _m. In such a case, the phase differences β _T and β
₀ is represented by the following equation.

[0017]

## EQU4 ## β _T = β sin (ω _mt + ω _m · τ / 2) β ₀ = β sin (ω _mt −ω _m · τ / 2)

Here, β is a constant, and τ is the time required for light to propagate through the optical fiber loop 3. When the difference between the phase differences β _T and β ₀ is obtained from this equation, the following is obtained.

[0019]

Δβ = β _T −β ₀ = 2β sin (ω _m · τ /
2) · cosω _m t

By substituting this into the equation (3), the following equation is obtained.

[0021]

I = 2E ₀ ² [1 + cos Δθ · ｛J ₀ (x) +
2Σ _{k = 1} J _2k (x) cos2k · ω _m t｝ -2sinΔ
θ · Σ _{k = 0} J _{2k + 1} (x) sin (2k + 1) ω _mt ]

E _O is a constant relating to the intensity of light, ω _m is the angular frequency given by the phase modulator 8, x is the degree of phase modulation, and J ₀ , J ₁ , J ₂ ,. , T is time. The phase modulation degree x changes according to the magnitude of the voltage signal supplied to the phase modulator 8.

The degree of phase modulation x is represented by the following equation.

[0024]

X = 2β sinω _m τ / 2

Equation (6) is represented by the following equation (8).

[0026]

[Equation 8] _{I = I 0 -I 1 sinω m} t + I 2 cos2ω
_{m t-I 3 sin3ω m t} + I 4 cos4ω m t + ··
・

However, I ₀ , I ₁ , I ₂ , I ₃ , and I ₄ are represented by the following equation (9). Here, I ₀ is a DC component, and I _0
1 is called a first harmonic component, I ₂ is called a second harmonic component, I ₃ is called a third harmonic component, and the like.

[0028]

I ₀ = 2E ₀ ² ｛1 + J ₀ (x) cos Δθ｝ I ₁ = 4E ₀ ² J ₁ (x) sin Δθ I ₂ = 4E ₀ ² J ₂ (x) cos Δθ I ₃ = 4E ₀ ² J ₃ (X) sin Δθ I ₄ = 4E ₀ ² J ₄ (x) cos Δθ

In the optical fiber gyro device of the phase modulation system, the intensity I of the interference light received by the photodetector 2 is not only the term of cos Δθ but also sin Δθ as shown in the equation (8).
When the input angular velocity Ω is small and the value of the phase difference Δθ is small, an accurate value can be obtained by extracting the term of sin Δθ and obtaining the phase difference Δθ.

Referring again to FIG. The optical fiber gyro device further includes a driver 11 for supplying a drive signal to the light emitting device 1, a current-voltage converter 9, a synchronous detector 53, a signal generator 55, a phase modulation signal generator 57, an angular velocity / angle calculator 59, and a modulator. And a degree calculation unit 61. The angular velocity / angle calculation unit 5
9 and the modulation degree calculating section 61 may be constituted by a signal processing device (CPU) 65.

The driver 11 receives a DC power supply DC and supplies a driving current to the light emitting device 1. The current-voltage converter 9 converts the current signal output from the light receiver 2 into a voltage signal, and outputs the voltage signal to the synchronous detector 53. Signal generator 55 has the angular frequency 2 [omega _m and Baishu the signal generating unit and such a reference signal for generating a reference signal of the angular frequency ω _m, 3ω _m, and a frequency multiplier which generates a pulse signal of 4Omega _m .

The synchronous detector 53 is supplied from the signal generator 55.
Angular frequency ω_m, 2ω_m, 3ω _m, 4ω_mSignal and
The voltage output of the current-voltage converter 9 is input. First,
From the light intensity signal I shown in the equation or the equation (8), the DC component I
_OIs removed. Next, the angular frequency ω_m, 2ω_m, 3ω_m,
4ω_mThe signal I is synchronously detected by the signal of
Obtain wave component, second harmonic component, third harmonic component and fourth harmonic component
You. These are represented by the following equations.

[0033]

I ₁ = KJ ₁ (x) sin Δθ I ₂ = KJ ₂ (x) cos Δθ I ₃ = KJ ₃ (x) sin Δθ I ₄ = KJ ₄ (x) cos Δθ

K is a constant. Here, modulation depth control
Will be explained. The expression of Equation 10 is obtained by comparing the output signal of the synchronous detection unit 53 with
Is obtained. Therefore, using such a signal, the phase difference Δ
To find θ, K, J₁(X),
J_Two(X), J_Three(X), J _FourJust delete (x)
No. Thus, for example, J₁(X) = J_Two(X) or J_Three
(X) = J_Four(X) may be used.

FIG. 10 shows the Bessel function J₀(X), J
₁(X), J_Two(X), J_Three(X), J _FourShow (x)
You. J₁(X) = J_Two(X)
Large value is optimal modulation depth x₀Then x₀$ 2.63
You.

[0036]

X ₀ ≒ 2.63

Therefore, the phase modulation may be performed by the phase modulator 8 so that the modulation degree x ≒ 2.63. As a result, the phase difference Δθ is determined using two of the equations (10).

In the modulation degree control, the modulation degree x is changed to a desired value by changing the voltage signal applied to the phase modulator 8. The modulation degree calculator 61 generates a modulation degree signal indicating a desired modulation degree x, and generates a modulation signal generator 57
To supply.

However, it is generally difficult to fix the modulation x to a constant value, and the modulation x fluctuates. In the modulation degree control, various improvements have been made to maintain the modulation degree x at a constant value. Japanese Patent Application No. 61-18 filed by the same applicant as an example of modulation degree control.
No. 2,352. This will be described below.

In this example, the modulation factor x is set to the optimum modulation factor x ₀ =
In order to fix the ratio to 2.63, the deviation of the output signal ratio of the synchronous detection unit 53 is used, whereby the voltage supplied to the phase modulator 8 is adjusted.

The output signal I ₁ from the synchronous detector 53,
The first and second ratios D, I ₃ , I ₂ , I _4
1 (x) and D ₂ (x) are obtained. The ratio of these two is
From the equation of 0, the following is obtained.

[0042]

D ₁ (x) = I ₁ / I ₃ = 2KJ ₁ (x) sinΔθ /
2KJ ₃ (x) sin Δθ = J ₁ (x) / J ₃ (x) D ₂ (x) = I ₂ / I ₄ = 2KJ ₂ (x) cos Δθ /
2KJ ₄ (x) cos Δθ = J ₂ (x) / J ₄ (x)

In the vicinity of Δθ = 2m × π / 2, sin Δθ ≒
0, the reliability of the value of the first ratio D ₁ (x) decreases, and cos Δθ near Δθ = (2m + 1) × π / 2.
Since ≒ 0, the reliability of the value of the second ratio D ₂ (x) decreases. Therefore, in this example, when Δθ = around 2m × π / 2, that is, when Δθ = 2m × π / 2 ± π / 4, the second ratio D ₂ (x) is used, and Δθ = (2m + 1)
In the vicinity of × π / 2, that is, Δθ = (2m + 1) × π / 2
When in the range of ± π / 4, the first ratio D ₁ (x) is used.

When the phase difference Δθ is Δθ = 2m × π / 2 ± π / 4
Or Δθ = (2m + 1) × π / 2 ±
The phase difference Δθ used to determine whether or not it is in the range of π / 4 uses the phase difference signal Δθ output from the angular velocity / angle calculator 59.

The optimum modulation factor x ₀ = 2.
The ratios obtained by substituting 63 are used as a first optimum modulation ratio D ₁ (x ₀ ) and a second optimum modulation ratio D ₂ (x ₀ ), respectively. Degree ratio D
The deviation amounts of ₁ (x) and D ₂ (x) are represented by ΔD
₁ (x) and ΔD ₂ (x).

[0046]

ΔD ₁ (x) = D ₁ (x ₀ ) −D ₁ (x) ΔD ₂ (x) = D ₂ (x ₀ ) −D ₂ (x)

As described above, the modulation degree calculating section 61 calculates the equation (13).
Deviation ΔD of the modulation ratio represented by₁(X), ΔD
_TwoCalculate (x) and use it as the correction value Δx of the modulation factor x
The modulated signal is supplied to the modulation signal generator 57. Modulation signal generator 57
Is the deviation ΔD₁(X), ΔD _TwoIt ’s proportional to (x)
The drive voltage to the phase modulator 8 is increased or decreased. Modulation degree calculation
To supply the output of the section 61 to the modulation degree signal generation section 57.
Thus, a closed loop is formed. Deviation ΔD
₁(X) = 0 or ΔD_TwoWhen (x) = 0, the modulation factor x is
Equals the optimal modulation depth, ie x = x₀It is.

The angular velocity / angle calculation section 59 includes a synchronous detection section 5
The first and second harmonic signals N _1A , N _1B output from 3
Is used to calculate the phase difference Δθ by the following equation.

[0049]

Δθ = tan ⁻¹ (N _1A / N _1B )

The angular velocity Ω is obtained by substituting the thus obtained phase difference Δθ into the equation (1). Angular velocity / angle calculator 5
9 calculates the angle by integrating the angular velocity Ω.

A conventional cellodyne type optical fiber gyro will be described with reference to FIG. The cellodyne type optical fiber gyro is an improvement of the phase modulation type optical fiber gyro, and is configured to obtain a wider dynamic range than the phase modulation type optical fiber gyro.

In the optical fiber gyro of the serrodyne system, a serrodyne modulator 8 ′ is provided in addition to the phase modulator 8. The light E _C propagating clockwise and the light E _CC propagating counterclockwise in the optical fiber loop 3 are superposed on the phase modulation by the phase modulator 8 and further subjected to serrodyne modulation. The light propagating through the optical fiber loop 3 is expressed by the following equation 1 instead of the equation 2
5

[0053]

E _C = E ₀ sin (ωt−Δθ / 2 + β ₀ + α ₀ ) E _CC = E ₀ sin (ωt + Δθ / 2 + β _T + α _T )

Α ₀ and α _T are phase differences generated by the serrodyne modulator 8 ′ between the light propagating clockwise and the light propagating counterclockwise in the optical fiber loop 3.

FIG. 12 shows the phase difference signals α ₀ and α _T generated by the serrodyne modulation. As shown in FIG. 12A, the phase difference signals α ₀ and α _T are sawtooth waves having an amplitude of 2π and a period of T _S.

The two propagating lights E _C and E _CC are _equal to the second Y light.
The light is combined by the branch 6 to generate interference light. The intensity I of the interference light detected by the light receiver 2 is represented by the following equation.

[0057]

I = 2E ₀ ² [1 + cos (Δθ + β _T −β
₀ + _{α T -α 0)]} = 2E ₀ ² [1 + cos (Δθ + Δ
β + Δα)]

Here, Δβ is the phase difference generated by the phase modulator 8 and Δα is the phase difference generated by the phase modulator 8 ′. Δα is called the serrodyne phase difference.

[0059]

Δβ = β _T −β ₀ Δα = α _T −α ₀

FIG. 12B shows a waveform of the serrodyne phase difference Δα. The cellodyne phase difference Δα has alternate values α _S and α _S −
This is a rectangular wave that changes to 2π. α _S is represented by the following equation.

[0061]

[Equation 18] α _S = 2πτ / T _S

T _S is the period of the phase difference signal α ₀ , and τ is the time required for light to propagate through the optical fiber loop 3.

As is clear from the comparison between the equations (3) and (16), in the serrodyne method, the light intensity I of the interference light is obtained by substituting Δθ + Δα in place of Δθ in the equation (6). . Therefore, the DC component, the first harmonic component, the second harmonic component, the third harmonic component, and the like of the current signal output by the light receiver 2 are represented by the following equations corresponding to the equation (9).

[0064]

I ₀ = 2E ₀ ² ｛1 + J ₀ (x) cos (Δ
θ + Δα)｝ I ₁ = 4E ₀ ² J ₁ (x) sin (Δθ + Δα) I ₂ = 4E ₀ ² J ₂ (x) cos (Δθ + Δα) I ₃ = 4E ₀ ² J ₃ (x) sin (Δθ + Δα) I ₄ = 4E ₀ ² J ₄ (x) cos (Δθ + Δα)

Referring back to FIG. The optical fiber gyro further includes a synchronous detector 53, a signal generator 55, a modulation signal generator 57, a CPU 65, and a serrodyne modulation signal generator 67.
And

[0066] synchronous detector 53 inputs the reference signal of the angular velocity omega _m outputted from the signal generator 55 1 harmonic component I ₁
Is detected. Therefore, the first harmonic signal I ₁ is supplied from the synchronous detector 53 to the serrodyne modulation signal generator 67.

The serrodyne modulation signal generating section 67
(Δθ + Δα) = 0, that is, Δα = −Δθ
Then, a serrodyne modulation signal is generated. Δα = α
_{If S} = 2πτ / T _S , ignoring the sign, Δ
the θ = 2πτ / T _S. By substituting this into the equation of Equation 1, the following equation is obtained.

[0068]

[Number 20] _{Ω = λcτ / 2LRT S = λcτf} S / 2LR

Here, f _S is the frequency f _{S of the} serrodyne wave.
= 1 / T _S.

The serrodyne modulation signal is supplied to the serrodyne phase modulator 8 'and the CPU 65.

FIG. 13 shows the configuration of the CPU 65. CPU
Numeral 65 denotes an angular velocity / angle calculator 59 for calculating an angular velocity and an angle by inputting a serrodyne modulation signal, a modulation degree calculator 61 for calculating a modulation degree x, and a 2π controller 6 for 2π control.
And 3.

The angular velocity / angle calculator 59 calculates sin (Δθ +
Δα) = 0, the frequency f _S is obtained by counting the number of serrodyne waves shown in FIG.
The angular velocity Ω is obtained by the equation of 0. The modulation degree calculating section 61 calculates the above-described equation (12) and the equation (13) to generate a modulation degree signal or a modulation degree correction signal, and the modulation signal generation section 57
To supply.

The 2π control unit 63 is provided for correcting a 2π error in a cellodyne type optical fiber gyro. Although the amplitude of the serrodyne wave is 2π as shown in FIG. 12A, it actually deviates slightly from 2π. 2π
The error is an error generated when the amplitude of the serrodyne wave deviates from 2π. For details of the 2π control, see, for example, Japanese Patent Application No. 4-306975 filed by the same applicant as the present applicant.

The 2π error correction signal Δ2π generated by the 2π control section 63 is supplied to a serrodyne modulation signal generation section 67. The serrodyne modulation signal generating section 67 corrects the serrodyne modulation signal generated under the condition of sin (Δθ + Δα) = 0, that is, Δα = −Δθ, with the 2π error correction signal supplied from the 2π control section 63 as described above. I do.

[0075]

In the conventional optical fiber gyro apparatus, the synchronous detector 53 is provided with, for example, a second harmonic wave remover in order to remove the second harmonic component I ₂ from the light intensity signal I. I was Therefore, there is a disadvantage that the configuration of the synchronous detection unit 53 becomes complicated.

In the conventional optical fiber gyro apparatus, in the synchronous detection unit 53, the fourth harmonic component I from the light intensity signal I is obtained.
₄ in order to separate the has been performed synchronous detection by using a signal of four times the angular frequency 4Omega _m of the angular frequency omega _m of the reference signal. When such a high frequency is used, the noise level of the circuit increases, and it has been difficult to perform accurate modulation degree control.

In the conventional optical fiber gyro apparatus, when the absolute value of the input angular velocity Ω is small, the synchronous detection by the synchronous detection section 53 has a disadvantage that the accuracy of modulation degree control is reduced due to heat, noise or dark current.

Further, when the absolute value of the input angular velocity Ω is large, it is necessary to reduce the gain of the amplifier, thereby increasing the error, and there is a disadvantage that an accurate angular velocity Ω cannot be obtained.

In view of the foregoing, it is an object of the present invention to provide an optical fiber gyro that can accurately control the degree of modulation even when the value of the input angular velocity Ω is small.

[0080]

An optical fiber gyro according to the present invention comprises: a light emitter 1 as a light source; an amplitude modulator for amplitude-modulating light from the light emitter 1; an optical fiber loop 3;
A phase modulator 8 that phase-modulates the first propagation light and the second propagation light propagating in the opposite directions in the optical fiber loop 3 and an interference light of the first propagation light and the second propagation light. When the optical receiver 2 to be detected and the optical fiber loop 3 rotate at an angular velocity Ω around the central axis of the loop, the first
Synchronous detector 53 for obtaining a sagnac phase difference Δθ generated between the transmitted light and the second propagated light, and an angular velocity / angle for calculating the angular velocity Ω from the output obtained by the synchronous detector 53 In the optical fiber gyro having the calculation unit 59, the reference frequency f _Q used for amplitude modulation of light from the light emitter 1 is a plurality of reference frequencies f _Q1 , f
_Q2, include f _Q3 or the like, the reference frequency f _m of the signal and the intermediate frequency mf _Qi -nf the signal strength I of the interference light for signals of the plurality of reference frequencies and the phase modulation
_m (m, n, i is a positive integer) without to generate a signal, the synchronous detection unit 53 is so as to synchronously detect only the signal of the desired frequency of the signals of the mf _Qi -nf _m It is characterized by the following.

[0081]

[0082]

According to the present invention, in the above-mentioned optical fiber gyro, the amplitude modulation of the light from the light emitting device 1 has a period T =
This is done using a square wave of 1 / f _Qi .

According to the present invention, in the above-mentioned optical fiber gyro, the amplitude modulation of the light from the light emitting device 1 has a period T = 1.
This is done using a sine wave of / f _Qi .

[0085]

[0086]

[0087]

According to the present invention, in the above-mentioned optical fiber gyro, the serodyne phase modulator 8 ′ that performs the serrodyne phase modulation on the first propagation light and the second propagation light that propagate in the optical fiber loop 3 in opposite directions. Is established,
The sagnac phase difference Δθ is calculated by the serrodyne method, and the angular velocity Ω is further calculated.

[0089]

According to the present invention, light from the light emitter 1 is the reference frequency f _Q optical fiber loop 3 from being amplitude modulated by
Is propagated to The reference frequency f _Q includes a plurality of reference frequency f _Q1, f _Q2, the f _Q3 or the like, in the optical fiber gyro of the phase modulation schemes, such light is phase-modulated by the reference frequency f _m in the phase modulator 8. Therefore, the interference light received by the light receiver 2 has a large number of intermediate frequencies mf _Qi −n
f _m (where i, m, and n are positive integers). Thus, similarly to superheterodyne, a desired intermediate frequency component can be easily separated from the light intensity signal I. The desired harmonic components I ₁ , I ₂ ,
Sagnac phase difference Δθ from the I _4, it is possible to calculate the modulation factor compensation value Δx like.

According to the present example, the synchronous detection unit 53 is composed of the first AC component signal N _1A amplified by the first AC amplifier 53-2A having a large gain and the second AC amplifier having a small gain. The second harmonic component signal N _1B and the second harmonic component signal N ₂ amplified by 53-2B are output.

In the angular velocity / angle calculating section 59, when the absolute value of the input angular velocity Ω is small, the first first harmonic component signal N
_The phase difference Δθ is calculated from _1A and the second harmonic component signal N _2. When the absolute value of the input angular velocity Ω is large, the second 1
The phase difference Δθ is calculated based on the harmonic component signal N _1B and the second harmonic component signal N ₂ .

In the angular velocity / angle calculation section 59, when the absolute value of the input angular velocity Ω is small, the first first harmonic component signal N _1A
And a bias correction value ΔN _1BD , which is a deviation between the first and second harmonic component signals N _1B . Such a bias correction value ΔN _1BD
Thus, bias correction of the second first harmonic component signal N _1B is performed.

[0093]

[0094]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the concept of an optical fiber gyro according to the present invention will be described. The present invention is configured to amplitude-modulate the light from the light emitter 1. In this example, the light amplitude E is equal to the period T
Modulated so that it becomes a _Q rectangular wave.

FIG. 1A shows a waveform of the amplitude E of the amplitude-modulated light. The light amplitude E is equal to the period T _Q , and its value is alternately E
It is a rectangular wave that changes to ₀ (1 + ΔB) and E ₀ (1−ΔB). Therefore, as shown in FIG. 1B, if f (ω _Q ) is a function of a period T _Q and a rectangular wave that alternately changes to 0 and 1,
The light amplitude E (t) is expressed by the following equation (21).

[0096]

E (t) = E ₀ (1−ΔB) + 2E ₀ ΔB · f (ω _Q ) = E ₀ [(1−ΔB) + 2ΔB · f (ω _Q )]

When the square of the light amplitude E (t) is obtained from this equation, the following is obtained.

[0098]

E (t) ² = E ₀ ² [(1−ΔB) + 2ΔB · f
(Ω _Q)] ² = E ₀ ^{2 [(1-ΔB) 2 + 4ΔB} · f (ω
_Q )]

Note that f (ω _Q ) ² = f (ω _Q ). Substituting E (t) of equation (21) for E _{0 in} the equation derived in the above description of the prior art, and substituting E (t) ² of equation (22) for E ₀ ² This gives a similar equation. For example, the light E and left-handed propagating through the optical fiber loop 3 similar to the number 2 in the formula by substituting the right side of Expression 2 number 21 formula E in place of E ₀ (t) in the clockwise Is obtained, and E of Expression 3 and Expression 6 is obtained.
₀ intensity I of formula of formula and 6 having 3 By substituting the expression for E (t) ² of the right side of Equation 22 to the ^second place and similar interference light is obtained.

The following equation (23) is obtained similarly to the equation (8).

[0101]

## EQU23 ## I = I ₀ −I ₁ sinω _mt + I ₂ cos2
_{ω m t-I 3 sin3ω m} t + I 4 cos4ω m t + ·
・ ・

[0102] However, be obtained by substituting the right-hand side of _{I 0, I 1, I 2} , I 3, I 4 number 9 equations E ₀ ² instead of the number 22 of the formula E (t) ² .

[0103]

Equation 24] I ₀ = 2E ₀ ^{2 [(1-ΔB) 2 + 4ΔB} · f
(Omega _{Q)] {1 + J 0 (x)} cosΔθ} I 1 = 4E 0 2 ^{[(1-ΔB) 2 + 4ΔB} · f (ω Q) ]
_{J 1 (x) sinΔθ I 2} = 4E 0 2 ^{[(1-ΔB) 2 + 4ΔB} · f (ω Q) ]
_{J 2 (x) cosΔθ I 3} = 4E 0 2 ^{[(1-ΔB) 2 + 4ΔB} · f (ω Q) ]
J ₃ (x) sin Δθ I ₄ = 4E ₀ ² [(1−ΔB) ² + 4ΔB · f (ω _Q )]
J ₄ (x) cosΔθ

F (ω _Q ) is alternately 1 as shown in FIG. 1B.
Since it is a periodic function that repeats 0 and 0, it is expressed by the following equation when Fourier-expanded.

[0105]

F (ω)_Q) = (1/2) + (2 / π) sin
ω_Qt + (2 / 3π) sin3ω _Qt + ...

This is substituted into the equation (24), and the obtained I ₁ , I ₂ , I ₃ , I _4, etc. are substituted into the equation (23), and only the term including the basic component sinω _Q t is obtained. Taking out and placing them as L ₁ , L ₂ , L ₃ and L ₄ respectively gives the following.

[0107]

L ₁ = − (32 / π) E ₀ ² ΔB · J ₁ (x)
_{· SinΔθ · sinω Q t · sinω} m t L 2 = (32 / π) E 0 2 ΔB · J 2 (x) · cosΔθ
· Sin ω _Q t · cos 2ω _mt L ₃ =-(32 / π) E ₀ ² ΔB · J ₃ (x) · sin Δ
θ · sin ω _Q t · sin3ω _mt L ₄ = (32 / π) E ₀ ² ΔB · J ₄ (x) · cos Δθ
・ Sin ω _Q t ・ cos4ω _mt

Here, the following modification is made using the trigonometric function formula.

[0109]

[Equation 27] 2 · sin ω_Qt sin ω_mt = cos
(Ω_Q−ω_m) T-cos (ω_Q+ Ω_m) T2 · sin ω_Qt ・ cos2ω_mt = sin (ω_Q-2
ω_m) T + sin (ω _Q+ 2ω_m) T2 · sin ω_Qt ・ sin3ω_mt = cos (ω_Q-3
ω_m) T-cos (ω _Q+ 3ω_m) T2 · sin ω_Qt ・ cos4ω_mt = sin (ω_Q-4
ω_m) T + sin (ω _Q+ 4ω_m) T

[0110] By substituting this equation in the equation of the number 26, each _{cos (ω Q -ω m) t} , sin (ω Q -2ω m) t,
cos (ω _Q -3ω _m ) t, sin (ω _Q -4ω _m ) t
Is taken out and put as M ₁ , M ₂ , M ₃ , M ₄ , the following is obtained.

[0111]

M ₁ = − (16 / π) E ₀ ² ΔB · J ₁ (x) · sin Δθ · cos (ω _Q −ω _m ) t M ₂ = (16 / π) E ₀ ² ΔB · J ₂ (X) · cos Δθ · sin (ω _Q −2ω _m ) t M ₃ = − (16 / π) E ₀ ² ΔB · J ₃ (x) · sin Δθ · cos (ω _Q −3ω _m ) t M ₄ = ( 16 / π) E ₀ ² ΔB · J ₄ (x) · cos Δθ · sin (ω _Q -4ω _m ) t

Thus, according to this example, by modulating the light amplitude E so as to have the waveform shown in FIG.
The intensity I of the interference light represented by the equation is
₁ , M ₂ , M ₃ , and M ₄ .

The angular velocities ω _Q and ω _m can be expressed as follows using the frequencies.

[0114]

Ω _Q = 2πf _Q ω _m = 2πf _m

F _Q is f (ω in FIG. 1B used for amplitude modulation.
Frequency of _Q), f _m is the frequency to be used for phase modulation by the phase modulator 8. Wherein the frequency f _Q number 28, is expressed by f _m, as follows.

[0116]

M ₁ = − (16 / π) E ₀ ² ΔB · J ₁ (x)
· Sin Δθ · cos2π (f _Q- f _m ) t M ₂ = (16 / π) E ₀ ² ΔB · J ₂ (x) · cos Δθ
_{· Sin2π (f Q -2f m)} t M 3 = - (16 / π) E 0 2 ΔB · J 3 (x) · sinΔ
_{θ · cos2π (f Q -3f m} ) t M 4 = (16 / π) E 0 2 ΔB · J 4 (x) · cosΔθ
_{· Sin2π (f Q -4f m)} t

As described above, according to the present example, the equation (30)
The intermediate frequency (f_Q−f _m), (F_Q-2f
_m), (F_Q-3f_m), (F_Q-4f_m) Is obtained
You. Therefore, like superheterodyne,
The amplitude is obtained by detecting the inter-frequency component.
You. Let the amplitude of each intermediate frequency component be N₁, N_Two, N_Three, N_Four
In other words, it is expressed by the following equation.

[0118]

N ₁ = − (16 / π) E ₀ ² ΔB · J ₁ (x)
Sin Δθ N ₂ = (16 / π) E ₀ ² ΔB · J ₂ (x) · cos Δθ N ₃ = − (16 / π) E ₀ ² ΔB · J ₃ (x) · sin Δ
θ N ₄ = (16 / π) E ₀ ² ΔB · J ₄ (x) · cos Δθ

Next, from the equation (31), the sagnac phase difference Δθ
Ask for. For example, the absolute value of the ratio between the _first amplitude N ₁ and the second amplitude N ₂ is obtained.

[0120]

N ₁ / N ₂ = [J ₁ (x) / J ₂ (x)] · tanΔθ

To eliminate J ₁ (x) / J ₂ (x), the ratio N ₁ / N ₂ is multiplied by the known J ₂ (x) / J ₁ (x). Alternatively, as shown in the conventional example, J ₁ (x) =
The modulation factor x may be set to 2.63 so that J ₂ (x). Thus, a sagnac phase difference Δθ is obtained from the obtained value of tan Δθ.

In the above description, the basic component s of the equation (25)
inω_QFocusing on t, an intermediate frequency component was obtained. However
However, the equation of Equation 25 is a third harmonic component sin3ω_Qincluding t
No. Therefore, substituting equation (25) into equation (24) gives
I obtained by₁, I_Two, I_Three, I_FourEtc. of the number 23
Substituting into the equation, the third harmonic component sin3ω_Qterms containing t
can get. 3rd harmonic component sin3ω_QOnly the terms containing t
S ₁, S_Two, S_Three, S_FourAnd put next
become that way.

[0123]

S ₁ = − (32 / 3π) E ₀ ² ΔB · J
₁ (x) · sin Δθ · sin3ω _Q t · sinω _m t S ₂ = (32 / 3π) E ₀ ² ΔB · J ₂ (x) · cos Δ
θ · sin3ω _Q t · cos2ω _m t S ₃ = − (32 / 3π) E ₀ ² ΔB · J ₃ (x) · sin
Δθ · sin3ω _Q t · sin3ω _m t S ₄ = (32 / 3π) E ₀ ² ΔB · J ₄ (x) · cos Δ
θ · sin3ω _Q t · cos4ω _mt

[0124] intermediate frequency by a similar to the above calculation calculation _{(3f Q -f m), (} 3f Q -2f m), (3f Q -
3f _m ) and (3f _Q -4f _m ) are obtained. Also, considering the other terms of the equation (25), it is clear that a larger number of intermediate frequency components can be obtained.

In the above example, a rectangular wave was used for amplitude modulation of light as shown in FIG. 1A. However, a sine wave can be used instead of a square wave. In such a case, the light amplitude E (t) and its square are represented by the following expression instead of the expression of Expression 21 and the expression of Expression 22, for example.

[0126]

E (t) = E ₀ (1 + ΔB · sin ω _Q t) E (t) ² = E ₀ ² (1 + 2ΔB · sin ω _Q t + ΔB ²⁾
sin ² ω _Q t)

Similarly to the equation (24), the DC component I ₀ , the first harmonic component I ₁ , the second harmonic component I ₂ , the third harmonic component I ₃ , the fourth harmonic component I _{4 and the} like are expressed as follows. Is done.

[0128]

I ₀ = 2E ₀ ² [1 + 2ΔB · sin ω _Q t +
ΔB ² sin ² ω _Q t] _{{1 + J 0 (x)} cosΔθ} I 1 = 4E 0 2 _{[1 + 2ΔB · sinω Q t +} ΔB 2 si
n ² ω _Q t] J ₁ (x) sin Δθ I ₂ = 4E ₀ ² [1 + 2ΔB · sin ω _Q t + ΔB ² si
n ² ω _Q t] J ₂ (x) cos Δθ I ₃ = 4E ₀ ² [1 + ² ΔB · sin ω _Q t + ΔB ² si
n ² ω _Q t] _{J 3 (x) sinΔθ I 4} = 4E 0 2 _{[1 + 2ΔB · sinω Q t +} ΔB 2 si
n ² ω _Q t] J ₄ (x) cosΔθ

The thus obtained I ₀ , I ₁ , I ₂ ,
Substituting I ₃ , I _4, etc. into the equation of Equation 23 to obtain the basic component sin
Only the terms including ω _Q t are extracted, and L ₁ ,
When L ₂ , L ₃ and L ₄ are put, the following is obtained.

[0130]

L ₁ = −8E ₀ ² ΔBJ ₁ (x) · sin Δθ
· Sinω _Q t · sinω _m t L ₂ = 8E ₀ ² ΔBJ ₂ (x) · cosΔθ · sinω _Q
t · cos2ω _mt L ₃ = −8E ₀ ² ΔBJ ₃ (x) · sin Δθ · sin ω
_Q t · sin3ω _mt L ₄ = 8E ₀ ² ΔBJ ₄ (x) · cos Δθ · sin ω _Q
t · cos4ω _mt

Here, the expression of Expression 27 using the formula of the trigonometric function is substituted into the expression of Expression 36, and cos (ω _Q
−ω _m ) t, sin (ω _Q −2ω _m ) t, cos (ω _Q
The terms including −3ω _m ) t and sin (ω _Q −4ω _m ) t are extracted and put as M ₁ , M ₂ , M ₃ , and M ₄ as follows.

[0132]

M ₁ = −4E ₀ ² ΔB · J ₁ (x) · sin Δθ · cos (ω _Q −ω _m ) t M ₂ = 4E ₀ ² ΔB · J ₂ (x) · cos Δθ · sin (ω _Q −2ω _m ) t M ₃ = −4E ₀ ² ΔB · J ₃ (x) · sin Δθ · cos (ω _Q −3ω _m ) t M ₄ = 4E ₀ ² ΔB · J ₄ (x) · cos Δθ · sin (ω _Q -4ω _m ) t

Similarly, the intermediate frequency (f _Q -f _m )
_{(F Q -2f m), (} f Q -3f m), (f Q -4
f _m ) component is obtained. By detecting such an intermediate frequency component, its amplitude is obtained. Assuming that the amplitudes of the respective intermediate frequency components are N ₁ , N ₂ , N ₃ , and N ₄ , they are represented by the following equations.

[0134]

N ₁ = −4E ₀ ² ΔB · J ₁ (x) · sin Δθ N ₂ = 4E ₀ ² ΔB · J ₂ (x) · cos Δθ N ₃ = −4E ₀ ² ΔB · J ₃ (x) · sin Δθ N ₄ = 4E ₀ ² ΔB · J ₄ (x) · cos Δθ

For example, the first amplitude N ₁ and the second amplitude
By calculating the absolute value of the ratio of the amplitude N _2, Sagnac phase difference Δθ is determined.

Note that sin ² ω _Q t =
Substituting _{(1/2) (1-cos2ω Q} t), co
A term including s2ω _Q t is obtained. Such a term is represented by R ₁ ,
R ₂ , R ₃ , and R ₄ are represented by the following equations.

[0137]

R ₁ = 2E ₀ ² ΔB · J ₁ (x) · sin Δθ
_{· Cos2ω Q t · sinω m t} R 2 = -2E 0 2 ΔB · J 2 (x) · cosΔθ · cos
2ω _Q t · cos 2ω _m t R ₃ = 2E ₀ ² ΔB · J ₃ (x) · sin Δθ · cos2
ω _Q t · sin3ω _mt R ₄ = −2E ₀ ² ΔB · J ₄ (x) · cos Δθ · cos
2ω _Q t · cos4ω _mt

Here, the following modification is made using the trigonometric function formula.

[0139]

(40) 2 · cos2ω _Q t · sin ω _m t = sin
_{(2ω Q + ω m) t} -sin (2ω Q -ω m) t 2 · cos2ω Q t · cos2ω m t = cos (2ω Q
−2ω _m ) t + cos (2ω _Q + 2ω _m ) t 2 · cos 2ω _Q t · sin 3ω _m t = sin (2ω <sub>Q
+ 3ω m) t-sin (</sub> 2ω Q -3ω m) t 2 · cos2ω Q t · cos4ω m t = cos (2ω Q
−4ω _m ) t + cos (2ω _Q + 4ω _m ) t

Therefore, the intermediate frequency (2f_Q−f_m),
(2f_Q-2f_m), (2f_Q-3f _m), (2f_Q−
4f_mAnd the like.

In the above example, a single sine wave as shown by the equation (34) was used. However, instead of a single sine wave, a combination of a few sine waves may be used. In such a case, the amplitude E (t) of the light is expressed by the following equation, for example, instead of the equation of Equation 21 and the equation of Equation 34.

[0142]

E (t) = E ₀ (1 + ΔB ₁ · sin ω _Q1 t
+ ΔB ₂ · sin ω _Q2 t + ΔB ₃ · sin ω _Q3 t)

Hereinafter, by similar calculations, the intermediate frequencies (f _Q1 -f _m ), (f _Q2 -2f _m ), (f _Q3 -4f _m )
Are obtained.

Thus, according to this example, a number of intermediate frequencies
mf_Q-Nf_m(Where m and n are positive integers)
You. Further, a reference frequency f used for amplitude modulation_QAs
Number frequency f_Q1, F_Q2, F_Q3If you use, etc.
The intermediate frequency of the number mf_Qi-Nf _m(However, i, m, n are positive
Integer. ) Is obtained.

Therefore, like superheterodyne,
A desired frequency component can be easily separated and extracted from other frequency components.

Next, an example of an optical fiber gyro according to the present invention will be described with reference to FIG. The optical fiber gyro of this example is of a phase modulation type. The optical fiber gyro has a light emitter 1, a light receiver 2, an optical fiber loop 3, an optical integrated circuit 4, a current-voltage converter 9, and a light emitter driver 11. The optical integrated circuit 4 has two Y branches 5 and 6 and a phase modulator 8.

The light emitter 1 receives the drive signal output from the light emitter driver 11 and outputs light. Such light passes through the first Y-branch 5 of the optical integrated circuit 4 and is branched by the second Y-branch 6 and propagates in the optical fiber loop 3 in opposite directions. Light propagating clockwise in the optical fiber loop 3 is phase-modulated at the exit of the optical fiber loop 3, and light propagating counterclockwise through the optical fiber loop 3 is phase-modulated at the entrance of the optical fiber loop 3.

The two lights having propagated in the optical fiber loop 3 in opposite directions are combined by the second Y branch 6, and the interference light is received by the light receiver 2. The current signal from the light receiver 2 is converted into a voltage signal by the current / voltage converter 9. The voltage signal output from the current-voltage converter 9, that is, the signal indicating the light intensity, is represented by the equation (23).

The optical fiber gyro according to this embodiment further includes
Synchronous detector 53, signal generator 55, and modulated signal generator 57
And an angular velocity / angle calculator 59 and a modulation degree calculator 61. The angular velocity / angle calculation section 59 and the modulation degree calculation section 61 may be constituted by the CPU 65.

[0150] The signal generating unit 55 frequency for amplitude modulating the light from the light source by a signal light emitter driver 11 of the reference frequency f _m to phase modulation by the phase modulator 8 f _Q
Signal and the intermediate frequency mf _Q -nf _m (where, m, n is a positive integer.) To generate a signal. The synchronous detector 53 synchronously detects the voltage signal I output from the current-voltage converter 9 and modulates the modulated signal N ₁ (= N _1A , N ₁₎ represented by the equation (31).
_1B ), N ₂ and N ₄ are output.

The angular velocity / angle calculation section 59 includes a synchronous detection section 53
Modulation signal N supplied from₁(= N _1A, N_1B), N_TwoYo
Calculate the sagnac phase difference Δθ and further calculate the angular velocity Ω
And outputs it as a gyro output. The modulation factor calculation unit 61
Modulation signal N supplied from synchronous detection section 53_Two, N_FourThan
Calculates a correction value Δx of the modulation factor x and outputs the result to the modulation signal generator 5
7

[0152] Modulation signal generator 57 uses the signal of the reference frequency f _m supplied from the signal generator 55 generates a driving voltage supplied to the phase modulator 8. Modulation signal generator 57
Is a correction value Δ of the modulation factor x supplied from the modulation factor calculator 61.
The drive voltage supplied to the phase modulator 8 is corrected by x.

FIG. 3 shows a configuration example of the synchronous detection unit 53. same
The phase detector 53 calculates the light intensity I expressed by the equation (23).
Of the signals, for example, the intermediate frequency (f_Q−f_m), (F
_Q-2f_m), (F_Q-4f_m) Demodulate the components. Middle
Frequency (f_Q−f_m), (F _Q-2f_mThe component of) is Sani
Used to determine the jack phase difference Δθ, (f_Q−
f _m), (F_Q-4f_m) Is a correction value Δ of the modulation factor x.
Used to calculate x.

[0154] For example, the reference frequency f _m to be used for phase modulation by the phase modulator 8 to 625 kHz. _{Therefore, 2f m = 1250kHz, 4f m} = 2500kH
z. Further, the frequency f _Q used for the amplitude modulation is f _Q = 623 kHz, 1050 kHz.
z, 2480 kHz. At this time, the following intermediate frequency is obtained.

[0155]

Equation 42] _{f Q -f m = 623kHz-625kHz} = -2kHz f Q -2f m = 1050kHz-1250kHz = -2
_{00kHz f Q -4f m = 2480kHz-} 2500kHz = -2
0 kHz

The synchronous detector 53 includes filters 53-1A and 53-1A.
3-1B, 53-1C, 53-1D and AC amplifier 53-
2A, 53-2B, 53-2C, 53-2D and demodulator 5
3-3A, 53-3B, 53-3C, and 53-3D. Filters 53-1A, 53-1B, 53-1C,
53-1D may be, for example, a bandpass filter.

Filters 53-1A, 53-1B, 53-
1C and 53-1D receive the light intensity I signal supplied from the current-to-voltage converter 9 to remove unnecessary DC components I ₀ and harmonic components, and obtain a first harmonic represented by the equation (24). The component I ₁ , the second harmonic component I ₂ , and the fourth harmonic component I ₄ are extracted. The first and second filters 53-1A and 53-1B take out the first harmonic component I ₁ , and the third filter 53-1C takes 2
Removed harmonic component I _2, the fourth filter 53-1D retrieve fourth harmonic component I _4.

First and second filters 53-1A and 53-1
-1B, the first harmonic component I output by₁Are respectively
By the first and second amplifiers 53-2A and 53-2B
Amplified. The first amplifier 53-2A has a relatively large
Current gain, and the second amplifier 53-2B is relatively small.
Has a high AC gain. Thus, a relatively large AC
First harmonic component I amplified by_1AAnd relatively
2nd first harmonic component amplified by small AC gain
I_1BIs obtained. Such two first harmonic components I _1A, I_1B
The reason for the request will be described later.

The demodulators 53-3A, 53-3B, 53-3
C and 53-3D receive the signals of frequencies 2 kHz, 200 kHz and 20 kHz supplied from the signal generator 55 to demodulate the components of the intermediate frequencies 2 kHz, 200 kHz and 20 kHz, and the amplitude N _1A represented by the equation 31 ,
N _1B , N ₂ and N ₄ are output.

The first and second demodulators 53-3A, 53-
3B demodulates an intermediate frequency component having a frequency of 2 kHz from output signals I _1A and I _1B of the first and second amplifiers 53-2A and 53-2B, and outputs amplitude signals N _1A and N _1B . The third demodulator 53-3C outputs the output signal I of the third amplifier 53-2C.
_2. Demodulate the intermediate frequency component of frequency 200kHz from ₂ ,
And outputs an amplitude signal N _2, fourth demodulator 53-3D fourth
Frequency 20kH from the output signal I ₄ of the amplifier 53-2D of
demodulates the intermediate frequency component of z, it outputs an amplitude signal N _4.

The modulation signals N _1A , N _1B , N
Of the signals N ₂ and N ₄ , the signals N _1A , N _1B and N ₂ are supplied to an angular velocity / angle calculator 59 to calculate a Sagnac phase difference Δθ, and the signals N ₂ and N ₄ are supplied to a modulation calculator 61. Thus, the correction value Δx of the modulation factor x is calculated.

Referring to FIG. 4, the configuration and operation of the angular velocity / angle calculator 59 according to the present embodiment will be described. The angular velocity / angle calculation unit 59 of the present example includes two
A phase difference Δθ signal is calculated from the harmonic component signals N _1A and N _1B and one double harmonic component signal N ₂ .

In this example, the angular velocity / angle calculation section 59 has two
Harmonic component signal N_1A, N_1BTo digital signals.
First and second quantizing circuits, for example, an AD converter
59-1 and 59-2 and the second harmonic component signal N_TwoThe digital
A third quantization circuit for converting to a signal, for example, an AD converter
59-3 and a signal for selectively outputting one of the two input signals.
Signal switching calculator 59-4 and such a signal switching calculator 59
-4 and the output signal of the third quantization circuit 59-3
To calculate the phase difference Δθ signal by inputting ^-1Arithmetic unit
59-6. The angular velocity / angle calculator 59 further includes
Addition to bias corrector 59-7 for correcting bias
Device 59-5.

Therefore, the first and second AD converters 59-
1, 59-2 to obtain the first harmonic component signal N _1A, N_1BDigit of
Value N_1AD, N_1BDIs output, and the third AD converter 59 is output.
-3 from the second harmonic component signal N_TwoDigital value N of_2DIs output
Is done. Note that a digital signal is added to indicate
Letter D is attached.

Here, the function of the signal switching calculator 59-4 will be described. Two first harmonic component signals N _1AD , N
_In consideration of the accuracy of _1BD , generally, the first harmonic component signal N _1AD which is the output signal of the first AC amplifier having a large AC gain is high in accuracy and the output signal of the second AC amplifier having a small AC gain. Of the second harmonic component signal N _1BD is low in accuracy and includes a larger error.

When the input angular velocity Ω (phase difference Δθ) is small, the first harmonic component signal N _1AD with higher accuracy can be used. However, when the input angular velocity Ω (phase difference Δθ) increases, the first AC amplifier saturates, so that the second harmonic component signal N _1BD with lower accuracy must be used.

When the input angular velocity Ω (phase difference Δθ) is smaller than a predetermined value, the signal switching calculator 59-4 outputs the first signal obtained by the first AC amplifier having a large AC gain.
1 harmonic component signal N _1AD supplied to TAN ^-1 calculator 59-6 of, when the input angular velocity Omega (phase difference [Delta] [theta]) is greater than or equal to a predetermined value, the second AC amplifier AC gain is small Obtained second first harmonic component signal N _1BD
Is supplied to the TAN- ¹ computing unit 59-6.

The TAN ^-1 computing unit 59-6 comprises a first or second first harmonic component signal N _1AD or N _1BD and a second harmonic component signal N _2D.
Then, the phase difference Δθ is calculated. The phase difference Δθ is obtained by Expression 32. However, in this example, 1 of Expression 32
The harmonic component signal N ₁ uses a digital value N _1AD or N _1BD , and the second harmonic component signal N ₂ uses a digital value N _2D . Therefore, tan Δθ is obtained by eliminating J ₁ (x) / J ₂ (x) from the equation (32).

To eliminate J ₁ (x) / J ₂ (x), the known ratio J ₂ (x) / J
₁ (x), or a modulation factor x such that J ₁ (x) = J ₂ (x) as shown in the conventional example.
= 2.63. Thus, the obtained tanΔ
From the value of θ, the sagnac phase difference Δθ is determined.

Accordingly, the TAN ^-1 calculator 59-6 calculates the phase difference Δθ by the following equation.

[0171]

Δθ = Tan ⁻¹ (N _1AD / N _2D ) or Δθ = Tan ⁻¹ (N _1BD / N _2D )

Next, the bias correction function of the angular velocity / angle calculator 59 will be described. As described above, the second first harmonic component signal N _1BD has lower accuracy and includes a larger error than the first first harmonic component signal N _1AD . angular velocity/
The signal switching calculator 59-4 of the angle calculator 59 is the second 1
Calculating a bias correction value .DELTA.N _1BD for correcting the bias error of the harmonic component signal N _1BD. Such a bias correction value ΔN _1BD is expressed by the following equation.

[0173]

[ _Equation 44] ΔN _1BD = N _1AD −N _1BD

As described above, the input angular velocity Ω (phase difference Δ
θ) is large, the first AC amplifier 31-3 is saturated.
And the first first harmonic component signal N_1ACannot be obtained. Therefore,
The bias correction value ΔN is calculated by the equation (44)._1BDIs calculated
The first harmonic component signal N _1ADAnd the second 1st harmonic
Minute signal N_1BDIs obtained, that is, the input angular velocity
Ω (phase difference Δθ) is relatively small.

When the input angular velocity Ω (phase difference Δθ) is relatively small, that is, when the first harmonic component signal N _1AD and the second 1
When both the harmonic component signals N _1BD are obtained, the phase difference Δ is calculated using the first higher harmonic component signal N _1AD with higher accuracy, so that it is not necessary to correct the bias.
It is necessary to perform the bias correction when the phase difference Δ is calculated by using the second harmonic component signal N _1BD with lower accuracy, that is, the input angular velocity Ω (phase difference Δθ) is relatively large. It is time.

Accordingly, the bias correction value ΔN _1B calculated by the signal switching calculator 59-4 is applied to the bias corrector 5
9-7 and temporarily stored. When the output of the signal switching operation unit 59-4 is switched from the first 1 harmonic component signal N _1AD the second 1 harmonic component signal N _{1B D,} the bias correction value .DELTA.N _1BD the adder 59-5 Supplied to
Thereby, the second first harmonic component signal N _1BD output from the second quantization circuit 59-3 is corrected.

[0177]

[ _Equation 45] N _1BDS = N _1BD -ΔN _1BD

The bias correction value ΔN _1BD is equal to the second first harmonic component signal N output from the second quantization circuit 59-3.
_Since it represents the bias error included in _1BD , _Equation 45
The second harmonic component signal N after correction obtained by the equation
_1BDS is an accurate value that does not include a bias error.

Next, the configuration and function of the modulation factor calculator 61 will be described with reference to FIG. The modulation degree calculating section 61 of the present example is configured to calculate the equations (12) and (13) from the output signal from the synchronous detection section 53. Here, a case will be described in which the modulation factor calculation unit 61 calculates D ₂ (x) by the second expression of Expression 12, and calculates ΔD ₂ (x) by the second expression of Expression 13.

The modulation degree calculator 61 may include a divider 61-1, an adder 61-2, and an integrator 61-3. Divider 6
1-1 by the expression division of supplied from the synchronous detector 53 second harmonic component signal N ₂ and fourth harmonic component signal N ₄ Number Enter the 12, calculating the ratio D ₂ (x) I do.

The adder 61-2 calculates the equation (13) from the ratio D ₂ (x) supplied from the divider 61-1 and, for example, the optimum modulation ratio D ₂ (x ₀ ) set manually. , And outputs a deviation amount ΔD ₂ (x) of the modulation ratio. The integrator 61-3 receives the deviation amount ΔD ₂ (x) and receives the modulation degree correction value Δx
Is output. The integrator 61-3 calculates the deviation amount ΔD
_The modulation degree correction value Δx is obtained by an integration operation so that ₂ (x) becomes zero. This modulation factor correction value Δx is supplied to the modulation signal generator 57.

The case has been described where the modulation degree calculating section 61 calculates the second equation of the equation (12) and the second equation of the equation (13), but the modulation degree calculating section 61 calculates the first equation of the equation (12). It may be configured such that the first expression of the expression and Expression 13 can also be calculated.

Next, the configuration and function of the modulation signal generator 57 will be described with reference to FIG. The modulation signal generator 57 includes a reference voltage generator 57-1 such as a precision DC power supply and an adder 57.
-2, a modulator 57-3, and a waveform shaper 57-4. The adder 57-2 adds the modulation factor signal x output from the reference voltage generator 57-1 and the modulation factor correction value Δx supplied from the modulation factor calculator 61, and the corrected modulation factor signal x ′ = X-Δx.

[0184] Modulator 57-3 AC modulated by the corrected signal supplied angular frequency f _m from the modulation degree signal x 'signal generator 55. The waveform shaper 57-4 shapes the waveform of the rectangular AC signal supplied from the modulator 57-5, converts it into a sine wave signal, and supplies it to the phase modulator 8.

Next, referring to FIG. 7, signal generating section 55 of the present example will be described.
The configuration and function of will be described. The signal generator 55 includes a high-speed clock generator 55-1 and two frequency dividers 55-2A, 55-.
2B and three digital mixers 55-3A, 55-3
B, 55-3C. The digital mixer may be, for example, a digital IC such as a flip-flop.

The frequency f is set by the first frequency divider 55-2A.
_m, 2f _m, signal 4f _m is generated, the second frequency divider 5
Signal of the frequency f _Q is generated by 5-2b. These signals are supplied to three digital mixers 55-3A and 55-A.
3B, is supplied to 55-3C, intermediate frequency f _m -f _Q signal from the first digital mixer 55-3A is generated, the signal of the intermediate frequency f _m -2f _Q is than the second digital mixer 55-3B is generated, the signal of the intermediate frequency f _m -4f _Q is generated from the third digital mixer 55-3C.

[0187] In general, the signal generator 55 of the present embodiment can also be configured to obtain a plurality of intermediate frequency mf _Q -nf _m explained in the above-mentioned amplitude modulation. For example, the frequency by a first frequency divider 55-2A nf _m (n = 1,2,4,
..), a signal f _Q having a frequency mf _Q (m = 1, 2, 4,...) By the second frequency divider 55-2B, and n × m digital mixers the intermediate frequency mf _Q -nf _m may generate.

[0188] Further, in the case of amplitude modulation represented by the numerical formula 41, a number of intermediate frequency mf _Qi -nf _m (i is a positive integer.) Is required. In such a case, the frequency f
_What is necessary is just to prepare a frequency divider for generating a signal of _Qi (i is a positive integer).

The function of the filter 71 will be described again with reference to FIG. The signal output from the signal generator 55 may be a rectangular wave. The amplitude modulation of the light according to the invention may be done digitally by means of a square wave as described above, or it may be made analogously by means of a sine wave. When the amplitude modulation of light is performed by a sine wave, the signal of the reference frequency f _Q output from the signal generator 55 is shaped into a sine wave by the filter 71. Thus, the signal of the reference frequency f _Q passed through the filter 71 is supplied to the light emitting device driver 11.

Next, a second example of the optical fiber gyro according to the present invention will be described with reference to FIG. The optical fiber gyro of this example is of a cellodyne type. Comparing the cellodyne type optical fiber gyro of this example with the conventional optical fiber gyro shown in FIG. 11, the cellodyne type optical fiber gyro of this example is configured so that the light from the light emitter 1 is amplitude-modulated. Are different. Figure 1 shows the amplitude modulation of light.
And the same as described with reference to FIG.

Although the embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments and can adopt various other configurations without departing from the gist of the present invention. It will be easily understood.

[0192]

According to the present invention, as in the case of superheterodyne, by modulating the amplitude of the light from the light source, a number of intermediate frequency components are generated in the signal of the intensity I of the interference light, whereby the desired modulation component is obtained. Can be easily taken out, and there is an advantage that an accurate angular velocity can be detected with a simple configuration.

According to the present invention, as in the case of superheterodyne, a large number of intermediate frequency components are generated in the signal of the intensity I of the interference light by amplitude-modulating the light from the light source, thereby facilitating the desired modulation component. Therefore, there is an advantage that it is not necessary to provide a second harmonic wave component remover as in the related art.

According to the present invention, as in the case of superheterodyne, a large number of intermediate frequency components are generated in the signal of the intensity I of the interference light by amplitude-modulating the light of the light source, thereby facilitating the desired modulation component. Therefore, there is an advantage that an accurate angular velocity can be detected by applying to both optical fibers of the phase modulation system and the serrodyne system.

[Brief description of the drawings]

FIG. 1 is a waveform diagram showing an example of a rectangular wave used for amplitude modulation of light in an optical fiber gyro of the present invention.

FIG. 2 is a diagram showing an example of an optical fiber gyro (phase modulation system) according to the present invention.

FIG. 3 is a diagram illustrating a configuration example of a synchronous detection unit according to the present invention.

FIG. 4 is a diagram showing a configuration example of an angular velocity / angle calculation unit according to the present invention.

FIG. 5 is a diagram illustrating a configuration example of a modulation factor calculating unit according to the present invention.

FIG. 6 is a diagram illustrating a configuration example of a modulation signal generation unit according to the present invention.

FIG. 7 is a diagram illustrating a configuration example of a signal generation unit according to the present invention.

FIG. 8 is a diagram showing an example of an optical fiber gyro (serodyne method) according to the present invention.

FIG. 9 is a configuration diagram showing an example of a conventional optical fiber gyro (phase modulation system).

FIG. 10 is a diagram showing a graph of a Bessel function.

FIG. 11 is a diagram showing an example of a conventional optical fiber gyro (serodyne method).

FIG. 12 is an explanatory diagram illustrating a conventional serrodyne phase modulation.

FIG. 13 is a diagram illustrating a configuration example of a conventional optical fiber gyro (serodyne method) CPU.

[Explanation of symbols]

 Reference Signs List 1 light emitter 2 light receiver 3 optical fiber loop 4 optical integrated circuit 5, 6 Y branch 8, 8 'phase modulator 9 current-voltage converter 11 light emitter driver 53 synchronous detector 55 signal generator 57 modulated signal generator 59 angular velocity / angle calculation unit 61 modulation degree calculation unit 63 2π control unit 65 CPU 67 serrodyne modulation signal generation unit

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kanji Yamamoto 2-16-46 Minami Kamata, Ota-ku, Tokyo Inside Tokimec Co., Ltd. (56) References JP-A-3-118415 (JP, A) JP-A-5-18763 (JP, A) JP-A-9-94464 (JP, A) JP-A-60-60513 (JP, A) JP-A-7-294264 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G01C 19/64-19/72

Claims (4)

(57) [Claims] A light emitting device serving as a light source; an amplitude modulation means for amplitude modulating light from the light emitting device; an optical fiber loop;
First propagating in opposite directions in the optical fiber loop;
A phase modulator that modulates the phase of the propagating light and the second propagating light, a photodetector that detects interference light of the first propagating light and the second propagating light, and the optical fiber loop is arranged around a central axis of the loop. When rotating at an angular velocity Ω, a sagnac phase difference Δθ generated between the first propagating light and the second propagating light.
And an angular velocity for calculating the angular velocity Ω from the output obtained by the synchronous detection section.
An optical fiber gyro having an angle calculation unit, wherein a reference frequency f used for amplitude modulation of light from the light emitter is used.
_Q is a plurality of reference frequency f _Q1, f _Q2, include f _Q3 or the like, the signal strength I of the interference light by the signal of the reference frequency f _m for the phase modulation and the signal of the reference frequency of the plurality of A signal having an intermediate frequency mf _Qi −nf _m (m, n, and i are positive integers) is generated, and the synchronous detection unit is configured to generate the mf _Qi
Optical fiber gyro, characterized in that so as to synchronously detect only the signal of a desired frequency among -nf _m signal. 2. The optical fiber gyro according to claim 1, wherein the amplitude modulation of the light from the light emitting device is performed using a rectangular wave having a period T = 1 / f _Qi. . 3. The optical fiber gyro according to claim 1, wherein the amplitude modulation of the light from the light emitter is performed using a sine wave having a period T = 1 / f _Qi. . 4. The optical fiber gyro according to claim 1, wherein the first and second propagating lights propagating in opposite directions in the optical fiber loop are subjected to serrodyne phase modulation. An optical fiber gyro comprising a modulator, wherein the sagnac phase difference Δθ is calculated by a serrodyne method, and the angular velocity Ω is further calculated.