JPH0942976A - Optical fiber gyro - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a small size and a low cost and improve precision by producing a reference phase difference between rectangular wave signals, which alternately varies to two constant values with mutually opposite signs and an equal absolute value for every preset time, in a signal showing the intensity of interference light. SOLUTION: A phase modulator 8 to control the phase of light propagating an optical fiber loop 3 produces a reference phase difference Δβ in an intensity signal I for interference light by using a delta surrodyne waveform signal. The phase x of the intensity signal I for the interference light is x=Δθ+Δβ, where Δθ is a sagnac phase difference. The phase difference Δβ varies to constant values ΔβA, ΔβB with the same absolute value and difference signs for every time T/2. When the phase difference Δβ is at a low level, ΔβA=-π/2, the intensity signal I for the interference light is at a high level IA and, when the phase difference Δβ is at a high level, ΔβB=π/2, the signal I is at a low level IB. A difference Δ I=IA-IB between two intensity signals IA, IB for the interference light is obtained as a sine value for the sagnac phase difference Δθ.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro suitable for use as an angular velocity meter for aircraft, ships, automobiles, etc.

[0002]

2. Description of the Related Art An optical fiber gyro is widely used as an apparatus for measuring an angular velocity, and has an advantage that it is small and highly reliable. The optical fiber gyro is configured to measure the angular velocity by utilizing the Sagnac effect of light (also referred to as Sagnac effect). As the interferometric optical fiber gyro, there are, for example, a phase modulation system, a serrodyne modulation system and a digital modulation system, which will be described.

First, a phase modulation type optical fiber gyro will be described with reference to FIG. Fiber optic gyro device
A light emitter 1 such as a semiconductor laser or a light emitting diode, a light receiver 2 for converting detection 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. And a phase modulator 8 provided at one end of the optical fiber loop 3.

The light output from the light emitter 1 passes through the first coupler 5 and the polarizer 4, and is branched into two propagating lights by the second coupler 6 and propagates 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 from the outside, the optical fiber loop 3 is caused by the Sagnac effect.
A phase difference Δθ occurs between lights propagating in the opposite directions. Such a phase difference Δθ is called a Sagnac phase difference,
It is proportional to the angular velocity Ω and is expressed by the following equation.

[0006]

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. It represents the angular velocity about the central axis of the loop.

According to the phase modulation method, the light propagating clockwise in the optical fiber loop 3 and the light propagating counterclockwise are respectively phase-modulated by the phase modulator 8. The light E _C propagating clockwise in the optical fiber loop 3 and the light E _CC propagating counterclockwise are expressed as follows at both ends of the optical fiber loop 3.

[0009]

## EQU2 ## 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 frequency 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 generated by the phase modulator 8. It is a phase difference. The phase difference β ₀ of the light E _C propagating in the clockwise direction is generated by propagating in the clockwise direction in the optical fiber loop 3 and then phase-modulated at the exit of the optical fiber loop 3. The phase difference β _T of E _CC is generated in the light that propagates in the counterclockwise direction through the optical fiber loop 3 after being phase-modulated at the entrance of the optical fiber loop 3.

The two propagating lights E _C and E _CC are combined by the second coupler 6, and the interference light is detected by the photodetector 2 via the first coupler 5. The intensity I of the interference light detected by the light receiver 2 is represented by the following equation.

[0012]

## EQU3 ## I = 2E ₀ ² [1 + cos (Δθ + β _T −β ₀ )] = 2E ₀ ² [1 + cos (Δθ + Δβ)] = 2E ₀ ² (1 + cosx)

However, Δβ = β _T −β ₀ , x = Δθ + Δβ
It is. In the method without phase modulation (Δβ = 0), the intensity I of the interference light detected by the photodetector 2 is a function of the cosine value cosΔθ of the phase difference Δθ, so that the intensity I of the interference light is small when the input angular velocity Ω is small. Accurate phase difference Δ
θ cannot be obtained. In the phase modulation method (Δβ ≠ 0), since the operating point is in the region where the sine curve has a large gradient, an accurate phase difference Δθ can be obtained even when the input angular velocity Ω is small.

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

[0015]

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

Where β is a constant and τ is the time required for light to propagate through the optical fiber loop 3. 2 from this formula
The difference Δβ = β _T −β ₀ between the two phase differences β _T and β ₀ is calculated as follows.

[0017]

[Number 5] _{Δβ = β T -β 0 = 2βsin} (ω m · τ / 2) · cosω m t = zcosω m t

Here, z is called a phase modulation degree and is represented by the following equation.

[0019]

## EQU6 ## z = 2β sin ω _m τ / 2

The phase modulation degree z changes depending on the magnitude of the voltage signal supplied to the phase modulator 8. Phase difference Δβ is calculated by Equation 3
Substituting into the expression, the following expression is obtained.

[0021]

(7) I = 2E ₀ ² [1 + cos Δθ · {J ₀ (z) +
2Σ _{k = 1} J _2k (z) cos _2k · ω _mt } −2 sin Δ
θ · Σ _{k = 0} J _{2k + 1} (z) sin (2k + 1) ω _m t]

E _O is a constant relating to the intensity of light, ω _m is the angular frequency given by the phase modulator 8, z is the degree of phase modulation, and J ₀ , J ₁ , J ₂ , ... Are Bessel functions. , T is time.

Equation (7) is expressed as the following equation (8).

[0024]

## EQU8 ## I = I ₀ −I ₁ sin ω _m t + I ₂ cos 2ω
_{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). In addition, I ₀ is a DC component, I
₁ is called a 1st harmonic component, I ₂ is called a 2nd harmonic component, I ₃ is called a 3rd harmonic component, etc.

[0026]

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

In the phase modulation type optical fiber gyro device, the intensity I of the interference light received by the photodetector 2 is not limited to the term of cos Δθ but sin Δθ as shown in the equation (9).
Therefore, when the input angular velocity Ω is small and the value of the Sagnac phase difference Δθ is small, an accurate value can be obtained by extracting the term of sin Δθ and obtaining the Sagnac phase difference Δθ.

Referring again to FIG. The optical fiber gyro device further includes a current-voltage converter 7, a signal generator 11, a synchronous detector 12, and a signal processing unit 13. The current-voltage converter 7 converts the current signal output from the light receiver 2 into a voltage signal and outputs the voltage signal to the synchronous detection unit 12. Signal generator 11
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 omega _m are, 3ω _m, 4ω _m
And a frequency divider that generates a pulse signal of.

The synchronous detector 12 is supplied from the signal generator 11.
Angular frequency ω_m2ω_m3ω _m4ω_mSignal of
The voltage signal output from the current-voltage converter 7 is input.
First, from the intensity signal I of the interference light, the DC component I_ORemove
You. Next, the angular frequency ω_m2ω _m3ω_m4ω_mNo faith
Signal, the intensity signal I of the interference light is synchronously detected and
Minute I₁Second harmonic component I₂Third harmonic component I_ThreeAnd quadrupling
Minute I_Four, Etc. to obtain signal components such as.

In order to obtain the Sagnac phase difference Δθ using these signals, E ₀ , J are calculated from the equation (9).
₁ (z), J ₂ (z), J ₃ (z) and J ₄ (z) may be erased. For example, it may be J ₁ (z) = J ₂ (z). If the maximum value of the modulation degrees z satisfying J ₁ (z) = J ₂ (z) is the optimum modulation degree z ₀ , then z ₀ ≈2.63. Therefore, the phase modulation may be performed by the phase modulator 8 so that the modulation degree z≈2.63. As a result, the Sagnac phase difference Δθ is obtained using the two equations of the equation (9). This is calculated by the signal processing unit 13.

Next, a conventional serrodyne modulation type optical fiber gyro will be described with reference to FIG. The serrodyne modulation 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.

Serrodyne modulation optical fiber gyro
Then, in addition to the phase modulator 8, a serrodyne modulator 9 is further installed.
Have been killed. Propagate right through the optical fiber loop 3
Light E _CAnd light E that propagates to the left_CCIs due to the phase modulator 8
It is superimposed on the phase modulation and further serrodyne modulated. Light fa
The light propagating through the Iber Loop 3 is
It is represented by the formula of 10.

[0033]

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

Α ₀ and α _T are the phase differences generated by the serrodyne modulator 9 between the light propagating rightward and the light propagating counterclockwise in the optical fiber loop 3. Light receiver 2
The intensity I of the interference light detected by is expressed by the following equation.

[0035]

I = 2E ₀ ² [1 + cos (Δθ + β _T −β ₀ + α ₀ −α _T )] = 2E ₀ ² [1 + cos (Δθ + Δβ + Δα)]

Here, Δβ is a phase difference generated by the phase modulator 8, and Δα is a phase difference generated by the serrodyne modulator 9. Δα is called the serrodyne phase difference.

[0037]

## EQU12 ## Δβ = β _T −β ₀ Δα = α ₀ −α _T

As is clear from the comparison between the equations (3) and (11), in the serrodyne modulation method, the light intensity I of the interference light is obtained by substituting Δθ + Δα for Δθ in the equation (7). To be Therefore, the DC component, the 1st harmonic component, the 2nd harmonic component, the 3rd harmonic component, etc. of the current signal output by the photodetector 2 are represented by the following equations corresponding to the equation (9).

[0039]

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

FIG. 11 shows the phase difference signals α ₀ , α _T and the serrodyne phase difference Δ generated by the serrodyne modulation.
indicates α. As shown in FIG. 11A, the phase difference signals α ₀ , α
_T is a sawtooth wave having an amplitude of 2π and a period T _S. As shown in FIG. 11B, the serrodyne phase difference Δα is a rectangular wave whose values alternate between α _S and α _S −2π. alpha _S is proportional to the slope 2 [pi / T _S of the sawtooth wave is expressed by the following equation.

[0041]

## EQU14 ## α _S = 2πτ / T _S = 2πf _S τ

Here, T _S is the period of the serrodyne phase difference Δα, f _S (= 1 / T _S ) is the frequency of the serrodyne phase difference Δα, and τ is the time required for light to propagate through the optical fiber loop 3. .

In the serrodyne modulation method, sin (Δθ +
The propagation light is phase-modulated by the serrodyne modulator 9 so that Δα) = 0. Therefore, the serrodyne modulator 9
At the stable point by the feedback loop including
Δθ. At this time, the gradient 2 of the sawtooth wave shown in FIG.
π / T _S is proportional to the Sagnac phase difference Δθ (that is, the angular velocity Ω).

If Δα = α _S = 2πτ / T _S , Δθ = 2πτ / T _S , ignoring the positive and negative signs. Substituting this into the equation of Equation 1, the following equation is obtained.

[0045]

Ω = λcτ / DLT _S = λcτf _S / DL

Referring back to FIG. The optical fiber gyro further includes a signal generator 11, a synchronous detector 12, first and second integrators 15 and 16, a counter 17, and a reset circuit 1.
8 and 2π reference device 19.

The synchronous detector 12 receives the reference signal of the angular frequency ω _m output from the signal generator 11 and synchronously detects the first harmonic component I ₁ of the equation (13). Therefore, the synchronous detector 1
The second harmonic signal I ₁ is supplied to the first integrator 15 from 2. The second integrator 16 produces a ramp signal that increases with a slope proportional to the serrodyne phase difference Δα.

On the other hand, the 2π signal generated by the 2π reference unit 19 is supplied to the reset circuit 18. The reset circuit 18 generates a 2π reset signal and resets it when the value of the tilt signal of the integrator 16 increases to 2π. Thus, the second integrator 16 generates a serrodyne modulation signal as shown in FIG. 11A, and the serrodyne modulation signal is supplied to the serrodyne modulator 9.

As described above, in the serrodyne modulation method,
Phase modulation is performed so that sin (Δθ + Δα) = 0. At this time, the output signal I ₁ of the synchronous detector 12 becomes zero. Therefore, at this time, the counter 17 causes
The wave number of the serrodyne phase waveform as shown in (1) is counted to obtain the frequency f _S. From this frequency f _S , the angular velocity Ω can be obtained by the formula of Expression 15.

Next, a conventional optical fiber gyro of the digital modulation system will be described with reference to FIGS. In the digital modulation method, the light propagating through the optical fiber loop 3 is phase-modulated by the phase modulator 8, whereby the intensity signal I of the interference light is Δβ ₁ = + π / 2 and Δβ for each time τ.
A phase difference Δβ alternating with ₂ = −π / 2 is generated. Therefore, the intensity signal I of the interference light is expressed by the equation (3) by Δβ =
Substituting ± π / 2, it is expressed as follows.

[0051]

I ₁ = 2E ₀ ² {1 + cos (Δθ + Δβ ₁ )} = 2E ₀ ² {1 + cos (Δθ + π / 2)} = 2E ₀ ² (1-sin Δθ) I ₂ = 2E ₀ ² {1 + cos (Δθ + Δβ ₂ ) } = 2E ₀ ² {1 + cos (Δθ-π / 2)} = 2E ₀ ² (1 + sin Δθ)

From this, the difference ΔI in the intensity I of the interference light when the phase difference is Δβ ₁ = + π / 2 and Δβ ₂ = −π / 2.
= I ₁ −I ₂ is calculated.

[0053]

ΔI = I ₁ −I ₂ = 2E ₀ ² (1-sin Δθ) −2E ₀ ² (1 + sin Δθ) = −4E ₀ ² sin Δθ

Since the right side of this equation does not include the phase difference Δβ generated by the phase modulator 8, the Sagnac phase difference Δ
θ can be obtained. Thus, according to the digital modulation method, the phase modulator 8 generates the phase difference Δβ = ± π / 2 in the interference light I which changes every time τ, and the phase difference Δ
Light intensity I ₁ when β ₁ = + π / 2 and Δβ ₂ = −π /
The difference ΔI between the light intensities I ₂ at the time of ₂ is obtained, and from this, Δθ
Find the value of

The digital modulation method will be described in detail with reference to FIGS. According to the digital modulation method, the phase difference β _{0 of the} right-hand light Ecw is, for example, as shown in FIG. 13A.
The phase is modulated so as to become a periodic rectangular wave having a period of 2τ and an amplitude of π / 4 as shown in FIG. 3, and the phase difference β _{T of the} left-handed light Eccw becomes a rectangular wave as shown in FIG. 13B, for example. Phase modulated. The phase difference β _T of the left-handed light Eccw has the same rectangular wave as the waveform of the phase difference of the right-handed light Ecw, but is delayed by the time τ with respect to the phase difference of the right-handed light Ecw.

Thus, the difference between the phase difference β ₀ of the right-handed light Ecw and the phase difference β _T of the left-handed light Eccw, that is, the phase difference Δβ.
= Β ₀ −β _T is a rectangular wave that alternately changes to + π / 2 and −π / 2 for each time τ as shown in FIG. 13C.

FIG. 13D shows the phase x = Δθ + Δβ in the equation (3).
Represents the waveform of. When the angular velocity Ω does not work in the optical fiber gyro, Δθ = 0, so the waveform of the phase x in FIG. 13D matches the phase difference Δβ in FIG. 13C.

Next, referring to FIG. 14, using the formulas of the formula 3 or the formulas of the formula 16, the intensities I ₁ and Δβ ₂ of the interference light when the phase difference Δβ is Δβ ₁ = + π / _2. A method of obtaining the intensity I ₂ of the interference light when = −π / 2 will be described.

FIG. 14A is a graph of the equation (3), which is often used to express the relationship between the phase difference x and the light intensity I. In such a graph, the horizontal axis represents the phase x (= Δθ + Δβ), and the vertical axis represents the intensity I (x) of the interference light. 14B and 14C shown on the lower side of FIG. 14A, the horizontal axis (vertical axis direction of FIG. 14A) is time, and the vertical axis (horizontal axis direction of FIG. 14A) is phase x (=
Δθ + Δβ). FIG. 14 shown on the right side of FIG. 14A
In D and FIG. 14E, the horizontal axis (the horizontal axis direction of FIG. 14A) is time,
The vertical axis (vertical axis direction in FIG. 14A) is the intensity I of the interference light.

FIG. 14B shows the waveform of the phase x (= Δθ + Δβ) when the Sagnac phase difference Δθ = 0, and corresponds to the waveform of FIG. 13C. FIG. 14D shows the intensity I of the interference light in such a case. Similarly, FIG. 14C shows the Sagnac phase difference Δ.
Shows the waveform of the phase x (= Δθ + Δβ) when θ ≠ 0,
It corresponds to the waveform of FIG. 13D. FIG. 14E shows the intensity I of the interference light in such a case.

When the Sagnac phase difference Δθ = 0, even if the value of the phase x changes alternately between + π / 2 and −π / 2 as shown in FIG. 14B, the intensity I of the interference light is as shown in FIG. As shown in FIG. 14D, it becomes a constant value (excluding spike-shaped protrusions).
However, when the Sagnac phase difference Δθ ≠ 0,
As shown in FIG. 14C, the value of the phase x alternates with Δ every time τ.
It changes to θ−π / 2 and Δθ + π / 2, and the intensity I of the interference light at this time alternately changes every time τ (excluding the spike-shaped protrusion) as shown in FIG. 14E.

In FIG. 14D, the value of the intensity I of the interference light is the time τ.
The spike-shaped protrusions are provided for each of the interference light of the sine wave of FIG. 14A when the value of the phase x shown in the waveform of FIG. 14B changes between −π / 2 and + π / 2. This is because the strength I increases. Similarly, in FIG.
The value of has a spike-shaped protrusion at every time τ, because the value of the phase x shown in the waveform of FIG. 14C is Δθ−π / 2 and Δθ.
This is because the intensity I of the interference light of the sinusoidal wave in FIG. 14A increases when changing between + π / 2.

The high level of the rectangular wave in FIG. 14E indicates the intensity I ₂ of the interference light when the phase x = Δθ−π / 2, and the low level of the rectangular wave indicates the phase x = Δθ + π /.
It represents the intensity I ₁ of the interference light when it is 2. Therefore, FIG.
The difference between the high level and the low level of the rectangular wave corresponds to the deviation ΔI = I ₂ −I ₁ of the intensity of the interference light.

That is, the magnitude of the difference between the high level and the low level of the rectangular wave in FIG. 14E represents the right side of the equation (17). Thus, in the digital modulation method, the light intensity I of FIG.
14E is generated from the sine wave of FIG. 14E, and Δθ is obtained from the difference between the high level and the low level of the rectangular wave by the equation of Expression 17.

Referring again to FIG. The optical fiber gyro of this example further includes a timing signal generator 21, a phase modulation signal generator 22, an AD converter 23, and a signal processor 2.
And 4. The timing signal generator 21 generates a timing signal having a period τ and outputs it to the phase modulation signal generator 22.
And to the signal processing unit 24. Phase modulation signal generator 2
2 generates a phase modulator drive signal for generating the phase differences β ₀ , β _T , and Δβ as shown in FIGS. 13A, 13B, and 13C.

On the other hand, the A / D converter 23 inputs the voltage signal (shown in FIGS. 14D and 14E) from the current-voltage converter 7 and generates a digital signal indicating the intensity I of the interference light, The values I ₁ and I ₂ are supplied to the signal processor 24.
The signal processing unit 24 operates based on the timing signal from the timing signal generator 21, and the two values I ₁ , I 2
Alternately store ₂ and subtract equation (17). From the Sagnac phase difference Δθ thus obtained, the angular velocity Ω is calculated in accordance with the equation of Formula 1.

[0067]

In the optical fiber gyro device of the phase modulation type and the serrodyne modulation type, the input signal I of the synchronous detector 12 is not limited to the sine wave component as shown in the equations (9) and (13). However, the input signal I has a large value even when the input angular velocity Ω is zero due to the inclusion of a cosine wave component. Therefore, the synchronous detector 12
It becomes difficult to increase the AC gain of the above, and the noise of the synchronous detector 12 directly becomes an error source of the gyro signal.

In the conventional digital modulation type optical fiber gyro, the period of the rectangular wave signals β ₀ and β _T used for phase modulation is 2τ (τ is the time required for light to propagate through the optical fiber loop 3). . Therefore, when using the optical fiber loop 3 having a normal length, the frequency corresponding to the period 2τ is on the order of mega Hz, and all the circuits used are high frequency circuits. Therefore, it is necessary to take measures against electrical noise and the like, and there is a drawback that the cost is higher than that when a low frequency circuit is used.

In view of the above points, the present invention has an object to eliminate the drawbacks of the conventional optical fiber gyro of the phase modulation system, the serrodyne modulation system and the digital modulation system.

[0070]

According to the present invention, for example, as shown in FIG. 1, a light source, an optical fiber loop, first propagating light and second light propagating in the optical fiber loop in mutually opposite directions. A phase modulator that changes the phase with respect to the propagating light and a photodetector that detects the interference light of the first propagating light and the second propagating light, and the optical fiber loop is the center of the loop. In the optical fiber gyro configured so as to obtain the angular velocity Ω from the Sagnac phase difference Δθ generated in the intensity signal I of the interference light when rotating about the axis at the angular velocity Ω, the phase modulator modulates the interference light of the interference light by the phase modulator. _A reference phase difference Δβ of a rectangular wave signal, which alternately changes into two constant values Δβ _A and Δβ _B whose signs are opposite to each other and whose absolute values are equal to each other, is generated in the intensity signal I at each time T / 2, and the reference position To generate the phase difference Δβ, the above The control voltage signal supplied to the phase modulator is characterized in that it is a delta serrodyne waveform signal of a triangular wave in which the inclination is inverted between positive and negative and bent at every time T / 2.

According to the present invention, in the optical fiber gyro, the reference phase difference is Δβ _A , where n is a positive integer.
=-(2n-1) π / 2 and Δβ _B = + (2n-1) π
It is characterized by being / 2. In another example, the reference phase difference is Δβ _A = − [(2n−1) π / 2 + δ] where n is a positive integer and δ is an arbitrary constant that satisfies | δ | <π / 2.
And Δβ _B = + [(2n−1) π / 2 + δ].

According to the present invention, in the optical fiber gyro, the difference ΔI = I between the two values I _A and I _B of the intensity I of the interference light corresponding to the two reference phase differences Δβ _A and Δβ _B.
Characterized by calculating an input angular velocity Ω based on _A -I _B.

[0073] According to the present invention, in an optical fiber gyro, the difference signal to input intensity signal I of the interfering light output from the light receiver intensity of the interference light [Delta] I = I _A -I
It is characterized by having a signal processing section for generating a voltage signal V ₀ corresponding to _B and a delta serrodyne section for generating the delta serrodyne waveform signal.

According to the present invention, in the optical fiber gyro, the signal processing unit removes a DC component from the intensity signal I of the interference light and generates an alternating signal which alternately changes to ΔI / 2 every time T / 2. The present invention is characterized by including a DC remover to be generated, an AC amplifier for AC amplifying the output signal of the DC remover, and a synchronous detector for obtaining a DC voltage signal V ₀ from the output signal of the AC amplifier.

According to the present invention, in the optical fiber gyro, the delta serrodyne section integrates the reference voltage signal V ^* by alternately changing the positive and negative signs at every time T / 2 and integrating. Is generated.

According to the present invention, the light source, the optical fiber loop, and the serrodyne for generating the serrodyne phase difference Δα in the intensity signal of the interference light of the two propagating lights propagating in the optical fiber loop in mutually opposite directions. The modulator and the reference phase difference of the rectangular wave signal that alternately changes into two constant values Δβ _A and Δβ _B of the signal I of the intensity of the interference light and having the same absolute value at each time T / 2 and having the same absolute value. A phase modulator for generating Δβ, and a photodetector for detecting the interference light,
In the optical fiber gyro configured to obtain the angular velocity Ω from the Sagnac phase difference Δθ generated in the intensity signal I of the interference light when the optical fiber loop rotates around the central axis of the loop at the angular velocity Ω, The serrodyne phase difference Δα is feedback-controlled so that sin (Δθ + Δα) = 0, and the control voltage signal supplied to the phase modulator to generate the reference phase difference Δβ is
It is characterized in that it is a delta serrodyne waveform signal of a triangular wave in which the inclination is inverted to be positive and negative and bent at every time T / 2.

According to the present invention, the triangular phase waveform, that is, the delta serrodyne waveform signal is used to generate the reference phase difference Δβ in the intensity signal I of the interference light. The delta serrodyne waveform signal is a triangular wave that bends every half cycle T / 2.
The phase x of the interference light intensity signal I is x = Δθ + Δβ.
The reference phase difference Δβ changes to constant values Δβ _A and Δβ _B having the same absolute value and different signs for each half cycle T / 2.

According to one preferred embodiment of the present invention, the reference phase difference Δβ is a low level Δ in one cycle T where n is an integer.
β _A =-(2n-1) π / 2 and high level Δβ _B = +
It changes to (2n-1) π / 2. In such a case, the phase x of the intensity signal I of the interference light is x = Δθ + Δβ = Δθ + [± (2
n-1) π / 2]. The difference [Delta] I of the intensity signal I _B of the interference light in the intensity signal I _A and the second phase difference [Delta] [beta] _B of the interference light in the first phase difference [Delta] [beta] _A is [Delta] I = 2I ₀ sin
Δθ. Therefore, the Sagnac phase difference Δθ can be obtained from the difference ΔI.

According to a preferred example of the present invention, the reference phase difference Δβ is Δβ _A =-[(2n-, where n is an integer and δ is an arbitrary constant satisfying | δ | <π / 2. 1) π
/ 2 + δ] and Δβ _B = + [(2n-1) π / 2 + δ] alternately. That is, in this example, it is not necessary to control the reference phase difference Δβ to be exactly ± (2n−1) π / 2. In such a case, the phase x of the intensity signal I of the interference light is x =
Δθ + Δβ + δ = Δθ + {± [(2n-1) π / 2 +
δ]}. 2 when Sagnac phase difference Δθ = 0
The difference ΔI between the two interference light intensity signals I _A and I _B is ΔI = 0.

[0080]

1 shows an example of the configuration of an optical fiber gyro according to the present invention. The optical fiber gyro of this example is
A light emitter 1 as a light source, a light receiver 2 for converting received light into a current signal, an optical fiber loop 3, a polarizer 4, two couplers 5 and 6, and a current-voltage converter 7 for converting a current signal into a voltage signal. A phase modulator 8 for controlling the phase of light propagating through the optical fiber loop 3, and further, the signal processing unit 3
1, a delta serrodyne unit 33, an angular angular velocity calculation unit 34, and a reference clock 35.

First, an outline of the optical fiber gyro according to the present invention
Explain just in case. In the fiber optic gyro according to the present invention,
The phase modulator 8 converts the interference light intensity signal I into a reference phase difference.
Generate Δβ. The reference phase difference Δβ is a quadrature of the cycle T.
Waveform, and alternates every half cycle T / 2 Δβ = ± (2n
-1) Change to π / 2. For example, the first half cycle of one cycle T
T_B= High level Δβ at T / 2_B= + (2n-1) π
/ 2 and the latter half cycle T _A= Low level Δβ at T / 2_A
=-(2n-1) π / 2.

The period T of the reference phase difference Δβ is constant, and the period T is sufficiently longer than the time τ required for propagating light to propagate through the optical fiber loop 3. For example, it may be several ten times to several hundred times the time τ.

N is a positive integer, but in the following, n =
1 will be described. As the reference phase difference Δβ in the expression of Equation 3,
Substitute ± π / 2. Reference phase difference Δβ is low level Δβ
Let I _A be the intensity signal I of the interference light when _A = −π / 2,
Let I _B be the intensity signal I of the interference light when the reference phase difference Δβ is at a high level Δβ _B = + π / 2. A formula similar to the formula 16 is obtained. The constant 2E ₀ ² = I ₀ is set.

[0084]

Equation 18] I _A = I _{0 [1 + cos (Δθ + Δβ A} ) ] = I ₀ [1 + cos (Δθ-π / 2) ] _{= I 0 (1 + sinΔθ)} I B = I 0 _{[1 + cos (Δθ + Δβ B} ) ] = I ₀ [1 + cos (Δθ + π / 2)] = I ₀ (1-sin Δθ)

When the reference phase difference Δβ is the low level Δβ _A , the intensity signal I of the interference light becomes the high level I _A , and when the reference phase difference Δβ is the high level Δβ _B = + π / 2, the intensity signal of the interference light is generated. I becomes low level I _B. When the difference ΔI between the two intensity signals I _A and I _B of the interference light is calculated, a formula similar to the formula 17 is obtained.

[0086]

Equation 19] _{ΔI = I A -I B = I} 0 (1 + sinΔθ) -I 0 (1-sinΔθ) = 2I 0 sinΔθ ΔI / 2 = I 0 sinΔθ

Description will be made with reference to FIG. FIG. 2 is a view similar to FIG. That is, FIG. 2A is a graph of the equation (3) and is often used to represent the relationship between the phase difference x and the intensity I of the interference light. In such a graph, the horizontal axis represents the phase difference x (= Δθ
+ Δβ), and the vertical axis represents the intensity I (x) of the interference light. Figure 2A
2B and 2C shown on the lower side, the horizontal axis (vertical axis direction of FIG. 2A) is time, and the vertical axis (horizontal axis direction of FIG. 2A) is phase difference x.
(= Δθ + Δβ). FIG. 2 shown on the right side of FIG. 2A
In D and FIG. 2E, the horizontal axis (horizontal axis direction of FIG. 2A) is time, and the vertical axis (vertical axis direction of FIG. 2A) is interference light intensity I.

Circles A and B on the curve of FIG. 2A indicate operating points when the Sagnac phase difference Δθ = 0, and circles A ′ and B ′.
Indicates the operating point when the Sagnac phase difference Δθ ≠ 0.

FIG. 2B shows the waveform of the phase x (= Δθ + Δβ) when the Sagnac phase difference Δθ = 0, and FIG. 2C shows the phase x (= Δθ + Δβ) when the Sagnac phase difference Δθ ≠ 0.
3 shows the waveforms of FIG. 2D shows the intensity I of the interference light when the Sagnac phase difference Δθ = 0, and similarly, FIG. 2E shows the intensity I of the interference light when the Sagnac phase difference Δθ ≠ 0.

As shown in FIGS. 2B and 2D, when the Sagnac phase difference Δθ = 0, the phase x (= Δθ + Δβ =
Δβ) is −π / 2 and + π for each half cycle T / 2 as described above.
The intensity I of the interference light is as shown in FIG.
As shown in, the value is constant (excluding spike-shaped protrusions).

However, as shown in FIGS. 2C and 2E, when the Sagnac phase difference Δθ ≠ 0, the value of the phase x is Δθ−π / 2 for each half cycle T / 2 as shown in FIG. 2C.
And Δθ + π / 2, and the intensity I of the interference light at this time changes to a high level and a low level every half cycle T / 2 (excluding the spike-like protrusion), as shown in FIG. 2E.

The high level of the rectangular wave in FIG. 2E has a phase x = Δ.
The intensity I _A of the interference light when θ + Δβ _A = Δθ−π / 2 is expressed, and the low level of the rectangular wave is the phase x = Δθ + Δβ _B = Δ
The intensity I _B of the interference light at θ + π / 2 is shown. Therefore,
The difference between the high and low levels of the rectangular wave in FIG. 2E corresponds to the deviation ΔI = I _A -I _B. That is, the magnitude of the difference between the high level and the low level of the rectangular wave in FIG. 2E represents the right side of the equation (19).

In FIG. 2D, the value of the intensity I of the interference light is the time T /
2A has a spike-shaped protrusion portion when the value of the phase waveform x shown in FIG. 2B changes between x = −π / 2 and x = + π / 2. This is because the operating points move above A from A to B or from B to A, respectively, and the intensity I of the interference light increases. Similarly, in FIG. 2E, the value of the intensity I of the interference light has a spike-shaped protrusion at every time T / 2 because the value of the phase waveform x shown in FIG. 2C is x = Δθ−.
When changing between π / 2 and x = Δθ + π / 2, the operating points on the sine wave of FIG. 2A change from A ′ to B ′, respectively.
This is because the intensity I of the coherent light increases by moving to or from B ′ to A ′.

Referring back to FIG. The reference clock 35 is
Switching signal V whose sign is inverted every cycle T / 2_CGenerate a
The signal processing unit 31 and the delta serrodyne unit 33.
To supply. The signal processing unit 31 outputs the output of the current-voltage converter 7.
Signal V_IInput voltage signal V corresponding to amplitude ΔI / 2
₀Generate The input signal V of the signal processing unit 31 is shown in FIG. 4A. _I
Figure 4B shows the waveform of the intensity I of the interference light corresponding to
Signal V₀Shows a waveform of ΔI / 2 corresponding to. Such voltage
Signal V₀Is the delta serrodyne part 33 and angular velocity calculation
Is supplied to the section 34.

The angular angular velocity calculator 34 receives the voltage signal V ₀ and determines the Sagnac phase difference Δθ. Since the voltage signal V ₀ indicates the value of the amplitude ΔI / 2 as described above, the Sagnac phase difference Δθ can be obtained by using the equation (19).

From the Sagnac phase difference Δθ, the angular velocity Ω can be obtained by using the equation of Equation 1. In addition, the turning angle is obtained by integrating the angular velocity Ω. The details of the configuration of the angular angular velocity calculation unit 34 will not be described, but any unit having an inverse trigonometric function calculation function for obtaining the Sagnac phase difference Δθ by using the formula (19) may be used.

The delta serrodyne portion 33 generates a triangular wave signal bent at every time T / 2, that is, a delta serrodyne wave signal V _S. The phase modulator 8 controls the phase of the light propagating through the optical fiber loop 3 by the delta serrodyne wave signal V _S. As a result, a phase difference Δβ is generated in the intensity signal I of the interference light.

The configuration and operation of the signal processing unit 31 according to this example will be described with reference to FIGS. 3 and 4. As shown in FIG. 3, the signal processing unit 31 includes a DC remover 31-1, an AC amplifier 31-2, and a synchronous detector 31-3.

The signal processing section 31 inputs the output signal V _I of the current-voltage converter 7 shown in FIG. 4A as described above and outputs the output signal V ₀ corresponding to the rectangular wave signal ΔI / 2 shown in FIG. 4B. To generate. The output signal V _I of the current-voltage converter 7 corresponds to the intensity signal I of the interference light shown in FIG. 2D or 2E.

According to this example, the intensity signal I of the interference light is a rectangular wave signal having a period T and has a time T as shown in FIG. 4A.
High level and low level alternate every 2/2. That is,
In the first half cycle T _A = T / 2 of one cycle T, the high level I _{A is set} , and in the second half cycle T _B = T / 2, the low level I _B is set.

As is apparent from the equation (18), the intermediate value between the two values I _A and I _B of the intensity signal of the interference light is I ₀ . Therefore, as shown in FIG. 4B, by subtracting the constant I ₀ from the intensity signal I of the interference light, −− is obtained every time T / 2.
A rectangular wave signal ΔI / 2 that changes to ΔI / 2 and + ΔI / 2 is obtained.

The DC remover 31-1 removes the DC component I ₀ from the output signal V _I of the current-voltage converter 7. FIG. 4C shows the waveform of the output signal V _I 'from the DC remover 31-1. As shown in FIG. 2D or FIG. 2E, the waveform of the intensity signal I of the interference light output from the current-voltage signal converter 7 actually has a spike-like protrusion at the time of switching between the high level and the low level of the rectangular wave. Have. Therefore, the waveform of the output signal V _I 'from the DC remover 31-1 also actually has a spike-like protrusion corresponding to it. In the waveform of the output signal V _I ′ of the DC remover 31-1 shown in FIG. 4A, such spike-like protrusions are omitted for convenience of description.

When the rectangular wave signal V _I 'of FIG. 4C is synchronously detected, a value proportional to the amplitude ΔI / 2 can be obtained, but in this example, in order to achieve higher accuracy, it passes through the AC amplifier 31-2. Let FIG. 4D shows the output signal V of the AC amplifier 31-2.
The waveform of _I ″ is shown. The rectangular wave signal V _I ′ is AC-amplified by the AC amplifier 31-2, and the period T as shown in FIG.
Sinusoidal waveform V _I "is obtained. AC amplifier 31-2 has a band-pass filter, but thereby spiky protuberances rich high frequency is removed, a slight phase delay as shown in FIG. 4D T _F occurs.

The output signal V _I ″ of the AC amplifier 31-2 is supplied to the synchronous detector 31-3 and is synchronously detected by the switching signal V _C having the period T / 2. FIG. 4E shows the synchronous detector 3
The waveforms of the output signals V _I '"of 1-3 are shown.
1-3 may be, for example, a circuit having a function of inverting the polarity every time T / 2. The DC component V ₀ of such signal V _I ′ ″ is proportional to the amplitude ΔI / 2.

In this way, the signal processing unit 31 generates the DC voltage signal V ₀ proportional to the amplitude ΔI / 2 and supplies it to the angular angular velocity calculation unit 34. Although the signal processing unit 31 of this example is configured by the AC amplification method as described above, it may be configured by the conventional synchronous detector 12 as long as a required gain can be obtained.

The configuration and operation of the delta serrodyne portion 33 of this embodiment will be described with reference to FIGS. As shown in FIG. 5, the delta serrodyne unit 33 includes a switch 33-1.
And a delta serrodyne integrator 33-2.

The switch 33-1 has a configuration as shown in FIG. 6A.
Reference DC voltage signal V in the delta serrodyne section 33^*And base
Switching signal of cycle T / 2 supplied from the quasi clock 35
Issue V _CTherefore, as shown in FIG. 6B, alternately every time T / 2
-V^*Or + V^*Square wave signal ± V^*Generate

The delta serrodyne integrator 33-2 integrates the output signal ± V ^* of the switch 33-1 with time, and the result is shown in FIG. 6C.
, A triangular wave signal, that is, a delta serrodyne waveform signal is generated. The slope of the delta serrodyne waveform signal corresponds to the square wave signal ± V ^* .

Next, the relationship between the slope of the delta serrodyne waveform and the reference phase difference Δβ will be described. The reference phase difference Δβ of the first half cycle T _A = T / 2 of one cycle T is Δβ _A = − (2n−
1) The reference phase difference Δβ of π / 2 and the latter half period T _B = T / 2 is Δβ _B = + (2n−1) π / 2.

Let k be the voltage phase conversion coefficient of the phase modulator 8 and T _{I be} the integration time of the delta serrodyne integrator 33-2.
The slope of the delta serrodyne phase angle in the first half period T _A = T / 2 is dΔβ _A / dt, and the slope of the delta serrodyne phase angle in the second half period T _B = T / 2 is dΔβ _B / dt. These are represented as follows.

[0111]

D Δβ _A / dt = −kV ^* / T _I dΔβ _B / dt = + kV ^* / T _I

Delta serrodyne phase difference Δβ _A , Δβ
_B is obtained by multiplying the slope of the delta serrodyne phase angle by the time τ, and becomes τ is the time required for light to propagate through the optical fiber loop 3.

[0113]

Δβ _A = −kV ^* τ / T _I Δβ _B = + kV ^* τ / T _I

The right side of this equation and the reference phase difference Δβ = ± (2n
-1) If π / 2 is set equal, the following relationship holds.

[0115]

V ^* / T _I = (1 / kτ) (2n−1) π / 2

Another example of the present invention will be described with reference to FIG. In the above example, the reference phase difference Δβ is a value obtained by multiplying ± π / 2 by an odd number (2n−1). However, according to the present invention, the reference phase difference Δβ is not necessarily Δβ =
It is not necessary to satisfy ± (2n-1) π / 2.

In order to obtain a predetermined resolution, the phase x = Δ
θ + Δβ, that is, the operating point may be in a region where the gradient of the sine wave curve is sufficiently large. ± (2n− as the reference phase difference Δβ
1) An example using an "arbitrary phase" close to π / 2 will be described.

[0118]

[Expression 23] Δβ = ± [(2n−1) π / 2 + δ]

Δ is an arbitrary constant that satisfies | δ | <π / 2. Here, n = 1 for simplification. The intensity signal I of the interference light is expressed by the following equation as in the equation (18).

[0120]

Equation 24] I _A = I _{0 [1 + cos (Δθ + Δβ A} ) ] = I ₀ [1 + cos (Δθ-π / 2-δ) ] = I ₀ [1 + sin (Δθ-δ)] I _B = I ₀ [1 + cos ( Δθ + Δβ _B )] = I ₀ [1 + cos (Δθ + π / 2 + δ)] = I ₀ [1-sin (Δθ + δ)]

[0121]

Equation 25] _{ΔI = I A -I B = I} 0 [sin (Δθ-δ) + sin (Δθ + δ) ] _{= 2I 0 sinΔθcosδ ΔI / 2 =} I 0 sinΔθcosδ

FIG. 7 shows an example in which "arbitrary phase" is used as the reference phase difference Δβ. FIG. 7 is a diagram similar to FIG. 2, in which the circles A and B in FIG. 7A represent the case where the Sagnac phase difference Δθ = 0, and the circles A ′ and B ′ in FIG. 7A indicate the Sagnac phase difference Δθ ≠ 0. Represents the case. FIG. 7B shows the Sagnac phase difference Δ.
When θ = 0, it represents the phase x = Δβ = ± (π / 2 + δ), which is approximately equal to 2π / 3, for example. FIG. 7D shows the intensity signal I of the interference light in such a case. FIG. 7C shows the phase x = Δθ + Δβ = Δθ ± (π / 2 when the Sagnac phase difference Δθ ≠ 0.
+ E), and FIG. 7E shows the intensity signal I of the interference light in such a case.

Thus, the present invention can be applied as long as the operating points A'and B'of the phase x of the intensity signal I of the interference light are in the region where the gradient of the sine wave curve is sufficiently large. When the "arbitrary phase" to which δ is added is used, the gain of the signal system may be simply multiplied by 1 / cos δ. For example, the AC gain of the signal processing unit 31 may be increased by 1 / cos δ times.

Next, another example of the optical fiber gyro of the present invention will be described with reference to FIG. In this example, the delta serrodyne waveform signal of the present example is used as a phase modulation signal in the conventional serrodyne modulation type optical fiber gyro described with reference to FIG. Comparing the present example shown in FIG. 8 with the conventional example shown in FIG. 10, instead of the signal generator 11 and the synchronous detector 12, the reference clock 35 and the signal processing unit 31 are provided.
Are replaced, and a delta serrodyne part 33 is further provided.

The reference clock 35 and the signal processing section 31 of this example
The delta serrodyne portion 33 is the same as that described with reference to FIGS. The phase modulator 8 phase-modulates the light propagating through the optical fiber loop 3 by the delta serrodyne waveform signal as shown in FIG. 6C, and the serrodyne modulator 9 by the sawtooth serrodyne waveform signal as shown in FIG. 11A. Phase-modulates the light propagating through. Thereby, the reference phase difference Δβ and the serrodyne phase difference Δα are generated in the intensity signal I of the interference light, respectively. Therefore,
The following formulas are established instead of the formulas (18) and (19).

[0126]

I _A = I ₀ [1 + cos (Δθ + Δβ _A + Δα)] = I ₀ [1 + cos (Δθ−π / 2 + Δα)] = I ₀ [1 + sin (θ + Δα)] I _B = I ₀ [1 + cos (Δθ + Δβ _B + Δα] )] = I ₀ [1 + cos (Δθ + π / 2 + Δα)] = I ₀ [1-sin (Δθ + Δα)]

[0127]

Equation 27] _{ΔI = I A -I B = I} 0 [1 + sin (Δθ + Δα)] - I ₀ [1-sin (Δ θ + Δα ) ] _{= 2I 0 sin (Δθ + Δα} ) ΔI / 2 = I 0 sin (Δθ + Δα)

At the stable point of the serrodyne loop, sin (Δ
θ + Δα) = 0, and the input angular velocity Ω is obtained by the equation (15).

The optical fiber gyro of this example avoids the common drawbacks of the conventional optical fiber gyros of the phase modulation type and the serrodyne modulation type. As represented by the equation (9) or the equation (13), in the conventional phase modulation method and the serrodyne modulation method, since each harmonic component of the output signal I of the current-voltage converter includes a cosine function, the input angular velocity Ω is The output signal I becomes large even when it is zero. In the present example, the output signal I of the current-voltage converter 7 does not include a cosine function as represented by the equation of Expression 26, so that the signal processing unit 31 can easily increase the AC amplification gain. is there.

Although the embodiments of the present invention have been described above in detail, 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.

For example, the configuration example of the optical fiber gyro of the present invention is shown in FIG. 1 as a block diagram, but this is merely an example, and the signal processing unit 31 and the delta serrodyne unit 3 are shown.
3. The angular angular velocity calculation unit 34 and the like may be appropriately combined with a CPU, a storage device, an A / D converter, a D / A converter, and the like.

In the example shown in FIG. 1, the two couplers 5,
Although 6, the polarizer 4, the phase modulator 8 and the like have been described as separate elements, some of these elements may be replaced by a single integrated optical circuit.

[0133]

In the conventional phase modulation type optical fiber gyro, a synchronous detector for detecting the second and fourth harmonics and a harmonic cancel circuit having a relatively large AC gain are used for controlling the modulation degree. However, the optical fiber gyro of the present invention does not need them, and thus has an advantage that it can be downsized and reduced in cost.

The second aspect of the present invention described with reference to FIG. 8 in particular.
In the above example, in the optical fiber gyro of the conventional serrodyne modulation system, the above advantages can be obtained only by supplying the delta serrodyne wave signal of this example to the phase modulator 8.

A conventional digital modulation type optical fiber gyro is configured to generate a phase difference Δβ having 2τ (τ is the time required for light to propagate through the optical fiber loop 3) as one cycle. Although a modulation frequency on the order of MHz is required, the period T of the delta serrodyne wave signal can be set to several tens to several hundreds times τ in the optical fiber gyro according to the present invention, and therefore several KHz to several tens KHz. Since it is possible to use a modulation frequency in the low frequency region of the order of, there is an advantage that the manufacturing cost can be reduced.

In the conventional digital modulation type optical fiber gyro, the reference phase difference Δβ = ± π is added to the intensity signal I of the interference light.
Is generated, and an error occurs if the reference phase difference Δβ is not exactly equal to ± π / 2. Therefore, it is necessary to control and manage the reference phase difference Δβ = ± π / 2. The optical fiber gyro according to the present invention has a drawback that it is expensive, but the reference phase difference Δβ is Δβ = ± (2n−1) π /
The number may not be 2, for example, Δβ = ± (2n−1) π /
It has the advantage that it can be a wide range of values in the vicinity of 2.

According to the present invention, there is an advantage that a defect or a problem of the conventional phase modulation type, serrodyne modulation type and digital modulation type optical fiber gyros can be eliminated to provide an optical fiber gyro with higher accuracy.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between an intensity signal of interference light and a phase difference in the optical fiber gyro according to the present invention.

FIG. 3 is a diagram showing a configuration example of a signal processing unit of an optical fiber gyro according to the present invention.

FIG. 4 is a waveform diagram for explaining the operation of the signal processing unit of the optical fiber gyro according to the present invention.

FIG. 5 is a diagram showing a configuration example of a delta serrodyne portion of an optical fiber gyro according to the present invention.

FIG. 6 is a waveform diagram for explaining the operation of the delta serrodyne portion of the optical fiber gyro according to the present invention.

FIG. 7 is a diagram showing the relationship between the intensity signal of interference light and the phase difference in the optical fiber gyro according to the present invention.

FIG. 8 is an explanatory diagram showing a configuration of a second example of an optical fiber gyro (serodyne modulation system) according to the present invention.

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

FIG. 10 is an explanatory diagram showing a configuration example of a conventional optical fiber gyro (serodyne modulation system).

FIG. 11 is a waveform diagram for explaining the operation of a conventional optical fiber gyro (serodyne modulation method).

FIG. 12 is an explanatory diagram showing a configuration example of a conventional optical fiber gyro (digital modulation system).

FIG. 13 is a waveform diagram for explaining the operation of a conventional optical fiber gyro (digital modulation method).

FIG. 14 is a diagram showing a relationship between an intensity signal of interference light and a phase difference in a conventional optical fiber gyro (digital modulation method).

[Explanation of symbols]

 1 Light emitter 2 Light receiver 3 Optical fiber loop 4 Polarizer 5, 6 Coupler 7 Current-voltage converter 8 Phase modulator 9 Serrodyne modulator 11 Signal generator 12 Synchronous detector 13 Signal processing part 15, 16 Integrator 17 Counter 18 reset circuit 19 2π reference device 21 timing signal generator 22 phase modulation signal generation unit 23 A / D converter 24 signal processing unit 31 signal processing unit 33 delta serrodyne unit 34 angular angular velocity calculation unit 35 reference clock

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

Claims (8)

[Claims] 1. A light source, an optical fiber loop, and a phase modulator for changing the phase between first propagating light and second propagating light propagating in the optical fiber loop in opposite directions. A light receiver for detecting the interference light of the first propagation light and the second propagation light, and the intensity signal of the interference light when the optical fiber loop rotates around the central axis of the loop at an angular velocity Ω. In the optical fiber gyro configured so as to obtain the angular velocity Ω from the Sagnac phase difference Δθ generated in I, the signal I of the intensity of the interference light has the opposite sign every time T / 2 by the phase modulator. _A reference phase difference Δβ of a rectangular wave signal that alternately changes into two constant values Δβ _A and Δβ _B having the same absolute value is generated, and a control voltage supplied to the phase modulator to generate the reference phase difference Δβ. Signal ramps every time T / 2 An optical fiber gyro, wherein is a delta serrodyne waveform signal of a triangular wave in which the positive and negative are inverted and bent. 2. The optical fiber gyro according to claim 1, wherein the reference phase difference is Δβ _A = − (2, where n is a positive integer.
An optical fiber gyro, wherein n-1) π / 2 and Δβ _B = + (2n-1) π / 2. 3. The optical fiber gyro according to claim 1, wherein the reference phase difference is such that n is a positive integer and δ is | δ | <π / 2.
Δβ _A =-[(2n-1) π as an arbitrary constant satisfying
/ 2 + δ] and Δβ _B = + [(2n-1) π / 2 + δ]
An optical fiber gyro characterized by the following. 4. The optical fiber gyro according to claim 1, 2 or 3, wherein two values I _A , I _B of the intensity I of the interference light corresponding to the two reference phase differences Δβ _A , Δβ _B Difference ΔI = I _A −I
An optical fiber gyro characterized by calculating an input angular velocity Ω based on _B. 5. The optical fiber gyro according to claim 1, 2, 3 or 4, wherein the intensity signal I of the interference light output from the photodetector is input and a difference signal ΔI of the intensity of the interference light is input. = I _A -I _B An optical fiber gyro having a signal processing section for generating a voltage signal V ₀ and a delta serrodyne section for generating the delta serrodyne waveform signal. 6. The optical fiber gyro according to claim 5, wherein the signal processing unit removes a DC component from the intensity signal I of the interference light and alternately changes to ΔI / 2 every time T / 2. A direct current remover for generating a signal, an alternating current amplifier for alternating current amplification of the output signal of the direct current remover, and a synchronous detector for obtaining a direct current voltage signal V ₀ from the output signal of the alternating current amplifier. Fiber optic gyro to do. 7. The optical fiber gyro according to claim 5 or 6, wherein the delta serrodyne portion outputs a reference voltage signal V ^* at time T /
An optical fiber gyro characterized in that the delta serrodyne waveform signal is generated by alternately changing positive and negative signs for every two and integrating. 8. A light source, an optical fiber loop, and a serrodyne modulator for generating a serrodyne phase difference Δα in an intensity signal of interference light of two propagating lights propagating in opposite directions in the optical fiber loop. , The signal I of the intensity of the interference light
At every time T / 2, the sign is opposite and the absolute value is equal to 2
The optical fiber loop has a phase modulator for generating a reference phase difference Δβ of a rectangular wave signal that alternately changes to two constant values Δβ _A and Δβ _B , and a photodetector for detecting the interference light. In the optical fiber gyro configured to determine the angular velocity Ω from the Sagnac phase difference Δθ generated in the intensity signal I of the interference light when rotating around the central axis of the loop at the angular velocity Ω, the serrodyne phase difference Δα is sin (Δθ + Δα) = 0
The control voltage signal, which is feedback-controlled so that the reference phase difference Δβ is generated, is a delta of a triangular wave whose slope is inverted between positive and negative at every time T / 2. An optical fiber gyro characterized by a serrodyne waveform signal.