JPS61283812A - Optical fiber gyroscope having wide dynamic range - Google Patents

Abstract

PURPOSE:To make it possible to obtain stable output over a wide dynamic range, by providing a zero method servo circuit and outputting a phase difference signal corresponding to phase difference generated in a sensor coil. CONSTITUTION:An optical fiber gyroscope is constituted of a light emitting element 32, a light receiving element 36, an optical fiber 42 having parts respectively connected to a sensor coil 44 and phase modulators 46, 48 and a zero method servo circuit consisting of a substraction circuit 66, an integrating circuit 68, a voltage control oscillation circuit 70 and a wave form shaping circuit 76. By this constitution, phase difference due to rotation received by the sensor coil 44 can be determined from the control voltage of the zero method servo circuit but not from the output itself of the light receiving element 36. Therefore, corresponding to the phase difference generated in the sensor coil 44, the output of the light receiving element 36 can be outputted as a phase difference signal when the phase difference is small and the voltage of the zero method servo circuit can be outputted as the phase difference signal when the phase difference is large.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical fiber gyro, and more specifically to a phase modulation type optical fiber gyro.

BACKGROUND OF THE INVENTION Currently, gyros are used as angular velocity sensors for navigation and attitude control of aircraft, flying objects, automobiles, robots, and the like. By using this gyro, you can obtain not only angular velocity but also data such as orientation by integrating it.

Among such gyros, optical fiber gyros can be used in any environment without shielding problems because the light and the optical fiber through which the light propagates are not easily affected by magnetic fields or electric fields. It is superior to conventional gyros in terms of minimum detectable angular velocity (sensitivity), drift, measurable range (dynamic range), and scale factor stability. Because of this, it has attracted attention and development in recent years.

Examples of such fiber optic gyros are, for example, Gearo Range Tee, G0, Bucaloge, and Nie.

Other "Optical Fiber Sensor Technology" IEE Journal of Quantum Electronics (Giallor)
enzi T, G, Bucaro J, A, et
al”0pticalFiber 5ensor
Technology”, 1888 J,
of Quantum electronics)
QB-18, Na4. pp626-662 (1982
) and Tarasho and I.P. Gilles, "Optical Fiber Gyroscope" Journal of Physics Electronics Science Instruments (Culshaw
nd 1. P, G11es “Fiber 0ptic
Gyroscopes”J, Phys, B: Sci I
nstrum, ) 16 pp5-15. (198
3), Yo Tsubo, Otsuka "Optical Fiber Gyroscope" Laser Research, 11. No, 12. pp889-902
(1983) and others.

(a) Principle of the optical fiber gyro The principle of the optical fiber gyro will now be explained with reference to FIG.

The light from the light emitting element 10 is split by the beam splitter 12, and the single mode optical fiber 1 is coiled many times.
Optical fiber loop wound with 8 or sensor coil 2
0 manually, rotate the sensor coil clockwise (CW) to both ends of 0.
) and counterclockwise (CCW). At this time, when the sensor coil 20 is rotating at an angular velocity Ω, a phase difference Δθ occurs between the clockwise light and the counterclockwise light, and the angular velocity Ω is detected by measuring Δθ.

The electric field strengths Ecw and Eccw of the light that propagated clockwise and the light that propagated counterclockwise in the sensor coil 20 are expressed as follows.

However, Er, Et: Amplitude of counterclockwise light and clockwise light ω: Angular frequency of light t: Time Δθ: Phase difference due to Sagnac effect. are combined by the beam splitter 12 and incident on the light receiving element 26. From the detection intensity of the light receiving element 26, the phase difference Δθ
can be known. The phase and difference Δθ can be expressed as follows.

A However, L: fiber length of sensor coil a: radius of sensor coil C: Speed of light in vacuum □ λ: wavelength of light Ω: rotational angular velocity This is called the Sagnac effect.

There are various methods of detecting the phase difference Δθ, and various methods have been proposed.

Most simply, when the sum of the counterclockwise light and the clockwise light is squared using a light-receiving element, the output I is in the form: IO: (1+cos(Δθ))−−−−(2).

This has the disadvantage that since Δθ exists in the COS, sensitivity is poor when Δθ is close to 0.

Therefore, the phase of either counterclockwise or clockwise light is 90
An optical mechanism has been proposed in which the beam is shifted by 0.0 degrees and square-law detection is performed. In this case, the output ■ is I OC(1+5in(Δ
θ)) Because it takes the form of (3), the sensitivity is good when Δθ is close to 0.

However, in order to separate one of the lights, three new beam splitters are required to separate the optical paths. Furthermore, the lengths of the separated optical paths must always be made equal.

Improving the sensitivity when Δθ is close to 0 using a static optical detection mechanism as described above has the above-mentioned difficulties.

(c) Phase modulation optical fiber gyro Many optical fiber gyros that use a dynamic mechanism to detect Δθ have also been proposed. For example, a phase modulation method, a frequency modulation method, etc. are used. Among them, the phase modulation optical fiber gyro is the most superior in terms of minimum detectable angular velocity.

A phase modulation type optical fiber gyro is a type in which a phase modulation element is provided at one end of an optical fiber sensor coil, and a phase difference Δθ is determined by measuring the magnitude of a modulation signal.

The phase modulation optical fiber gyro will be explained with reference to FIG. 9. The coherent light from the light emitting element 10 is transmitted to the beam splitter 12
The optical fiber 18 is divided into two parts and coupled to both ends of the optical fiber 18. The optical fiber 18 is divided into a portion wound to constitute a sensor coil 2G and a portion 24 wound around a phase modulation element 22 such as a piezo element driven at an angular frequency ω. ing. The light coupled from both ends of the optical fiber propagates clockwise and counterclockwise within the sensor coil 20 of the optical fiber, exits from the opposite end, is combined by the beam splitter 12, and is sent to the light receiving element. 26.

When the phase modulation element is installed at an asymmetric position with respect to the sensor coil, the light emitted from the light emitting element at the same time passes through the sensor coil and the phase modulation element winding part in clockwise and counterclockwise directions, but the light is not modulated. Since the times are different, when the output is square-law detected by the light receiving element, a modulated signal appears in the output. Since Δθ is included in the amplitude of the modulation signal, Δθ can be determined by knowing the magnitude of the modulation signal.

For example, assume that a phase modulator is provided near the input end of counterclockwise light. Assuming that the length of the optical fiber sensor coil is n1, the refractive index of the fiber core is C, and the speed of light is C, the time τ required for light to pass through the sensor coil is τ=nL/c (4).

Assume that the modulation signal is a sine wave with an angular frequency ω, as described above. When the light emitted from the light-emitting element at the same time is split into clockwise light and counterclockwise light and each undergoes phase modulation, the phase difference φ of the modulation signal is φ=ω, τ = nLω/C = 2πf, nL/ c * 6 ・(5) However, ω
,=2πf.

becomes.

Due to the Sagnac effect, clockwise light and counterclockwise light are ±Δθ
Although it has a phase difference of /2, the phase is further modulated by the phase modulation element. If the amplitude of the phase modulation element is b,
The electric field strengths Ecw and Eccw of the clockwise light and counterclockwise light are as follows.

Clockwise light and counterclockwise light having the above electric field strength are
They are combined by the beam splitter 12 and square-law detected by the light receiving element 26, so the output of the light receiving element S(Δθ, 1>
is proportional to the sum of Ecw and Ecew squared.

S(Δθ, t) = (EC, + Ecc,)”
...(8) Calculating this, ...(9) However, D, C, mean DC components.

(2ω or more) means a term with a frequency twice the angular frequency of light. Note that this is 0 because it is not applied to the detector.

becomes. Thus, because of the phase difference φ provided by the phase modulation element, Δθ can be obtained in relation to the amplitude of the modulation signal.

Therefore, we omit D, C, and expand S(Δθ, 1) into a series using the Bessel function. First, equation (9) is expressed as follows.

S(Δθ, 1) ...α1 On the other hand, it can be expressed as from the generating function expansion of the Bessel function. From the expansion of the real and imaginary parts of equation (12), the series expansion of the cos and sin parts of the α1 equation can be obtained. Divide S(Δθ, 1) into these parts, S(Δθ, 1) = (SccosΔθ+5ssinΔθ)E, E, −
If we write -(13), after converting θ→θ+π/2, we get
J-, (x) = (-)” J n(x) ・
...(14) However, using the property that n is a positive integer, and writing the above Sc and S, Sc= J, (ξ) +2Σ(-)"J2. (ξ) cos 2 n oU,t
...(16) S,=2Σ(-)"J2.,,,(ξ)cos(2n+
1) a+, th meeting 0...(17) becomes. Therefore, once again, S(Δθ, 1) is expressed as follows.

S (Δθ, 1) = W (Er"+EL") + (components of 2ω or more) + E
rE L J o (ξ)cosΔθ+E, Et2E
(-1)”J2g(ξ)cos2nω, t・cosΔθ
ns+1 +E, Et2Σ(-1) ” J 2-1 (ξ)co
s(2n+1) ω+mj”sjnΔθr1−〇...αQ.

=DC component +2E, ELJI(ξ)cos a+, t -5in
Δ θ2ErErJa(ξ) cos 2ω, t-CO3
Δθ + higher order component °°°αQ”
This is the series sum of the fundamental wave of the modulation signal ω1 and the high frequency signal.

By using an appropriate filter, it is possible to extract the fundamental wave ω or a harmonic signal of any order.

No matter which signal is adopted, the magnitude of COS Δθ or sin Δθ can be known.

In that case, the amplitude b of modulation by the phase modulation element, the modulation angular frequency ω1, and the sensor coil transit time τ should be set so that the value of the Bessel function J, , (ξ) of that order becomes large.

The highest sensitivity can be expected from the first-order term (
n, = 0), that is, the second term on the right side of the αQ'' equation.

This is the fundamental wave component. This fundamental wave component is P(Δθ
, 1), then P(Δθ, 1) = 2E, ELJ, (ξ)cos ω, t-5inΔθ
...(18).

Therefore, when synchronous detection is performed at the modulation angular frequency ωm of the piezoelectric vibrating element, the output Vo obtained by the detection is Vo = C5inΔ
θ --- (19) However, C: becomes a constant. That is, in the phase modulation type optical fiber gyro, the modulation angular frequency ω of the piezoelectric vibration element.

An amount Δθ proportional to the rotational angular velocity can be detected from the amplitude of the component.

Problems to be Solved by the Invention However, in the phase modulation type optical fiber gyro, as can be seen from the above equation, when Δθ approaches ±π/2, the change in Vo with respect to the change in Δθ becomes small, making it difficult to measure in practice.

In this way, the conventional phase modulation type optical fiber gyro
There was a problem with the dynamic range being narrow.

Therefore, a method for expanding the dynamic range of a phase modulation type optical fiber gyro has been researched, and some of the methods have already been published.One example is the paper below.

(1) H.C., Lefpur, P.H., Gramdoge, H.J., Adehete, “Double Closed Loop Hybrid Gyroscope Using Digital Phase Lamp” 3rd Eye 7 Fiber Sensor International Conference VIA ()1. c, Lefevre, P.H.

Graindorge, H.J., Ardity,
Louble C1osed-LoopHybri
d Fiber Gyroscope Usin
g Digital Phase Ramp, Th
1st International Conference
nce on Optical Fiber 5en
sors ) 1985 PDS7-1~PDS7
-5 (2) B, Y, Kim and H, J, Shaw "All-optical fiber gyro with linear scale factor using phase detection" SPI Optical fiber and laser sensor If (B, Y,
Kim and HoJ, shaw, All-fi
ber-optic gyroscope with 1
inear 5cale factor using
phase detection, 5PIB Fib
er 0pticand La5er 5ensors
II) Vol, 478 1984 PP, 142-1
48 The methods disclosed in the above-mentioned documents are theoretically successful in expanding the dynamic range, but
In reality, there are the following problems. In other words, the practically required dynamic range is, for example, IQ-3d.
eg/sec to 11000 de/sec and 10
There are also more than 6. On the other hand, all of the various devices disclosed in the above-mentioned documents obtain the output as an analog signal, or take out the output as a voltage or current for signal processing. However, if an attempt is made to cover a dynamic range as wide as 106, for example, when the power supply voltage is 10V, an output of at least 10-'V = 10μ may be required, which is extremely difficult in practice.

Therefore, the present invention provides a phase modulation type optical fiber gyro which is superior in terms of minimum detectable angular velocity and drift, but whose dynamic range is narrow in principle.
The objective is to provide the dynamic range necessary for practical use.

A means for solving the problem, that is, according to the present invention, includes a light emitting element and a sensor coil portion wound in a coil shape many times, and light from the light emitting element is branched and coupled to both ends. It is equipped with an optical fiber that outputs light propagated in both directions through the sensor coil from both ends, and a light receiving element that receives the light propagated in both directions, and detects the position between the light generated in both directions when the sensor coil rotates. An optical fiber gyro that measures rotational angular velocity from the phase difference includes a first phase modulator provided near the end of the sensor coil, and a first phase modulator that receives the output of the light receiving element and calculates the phase difference from the light receiving element. a zeroing method servo circuit that supplies the first phase modulator with a sawtooth wave driving pulse such that the voltage represented is substantially zero; and when the phase difference is small, the output of the light receiving element is used as a phase difference signal. An optical fiber gyro is provided, characterized in that it is equipped with a changeover switch that outputs the voltage of the null method servo circuit as a phase difference signal when the phase difference is large.

- In the optical fiber gyro described above, by providing a zero-order servo circuit, the rotation received by the sensor coil is generated not from the output of the light-receiving element itself, but from the control voltage of the zero-order servo circuit. A phase difference can be obtained.

Therefore, depending on the phase difference generated in the sensor coil, when the phase difference is small, the output of the light receiving element is output as a phase difference signal, while when the phase difference is large, the voltage of the zero position method servo circuit is output as a phase difference signal. By outputting as follows, stable output can be obtained over a wide dynamic range, and accurate measurements can be performed over a wide range.

Embodiments Hereinafter, an optical fiber gyro embodying the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of a phase modulation optical fiber gyro according to the present invention. In the illustrated phase modulation type optical fiber gyro, the light emitting element 32
A light source such as a light source is provided and driven by a power source (not shown) to generate a light beam. In addition, as a light source, He
-Ne laser, semiconductor laser, superluminescent diode, etc. can be used. The light beam generated by the light emitting element 32 is sent to a beam splitter 34 such as a half mirror. This beam splitter 34 is for splitting light to a light receiving element 36. The light passing through the beam splitter 34 is coupled to one end of the single mode optical fiber 38, and the light emitted from the other end is input to the beam splitter 40. The beam splitter 34 splits the light into two and couples them to both ends of the optical fiber 42.

Optical fiber 42 is wound into a coil many times to form an optical fiber sensor, and includes a sensor coil 44 and portions coupled to phase modulators 46 and 48, respectively.

One phase modulator 46 is composed of, for example, a piezoelectric vibrating element, is connected to an AC excitation power source 50 for phase modulation, and is configured to be driven by a sinusoidal AC wave having an angular frequency ω1. In this case, the optical fiber 42 is wound around the piezoelectric vibrating element 46, for example.

The other phase modulator 48 is intended to be driven with a sawtooth wave as shown in FIG. However, phase modulation using a sawtooth wave is difficult to achieve using a method that utilizes the resonance of a piezoelectric vibrator. For this reason, a method using an electro-optic crystal such as LiNb0a is considered to be effective. From the viewpoint of modulation efficiency, it is desirable to use a waveguide type element. For example, the third
As shown in the figure, the surface of the LiNb()+ substrate 52 is exposed to light.
A waveguide 54 is provided, and a pair of electrodes 56 are embedded so as to sandwich the optical waveguide 54. In this case, the optical waveguide 54 is inserted into one end of the optical fiber 42, and a sawtooth wave is applied between the pair of electrodes 560.

The light beams propagated clockwise and counterclockwise through the optical fiber 42 are output from both ends of the optical fiber 42, are combined by the beam splitter 40, and are sent to the light receiving element 36 via the single mode optical fiber 38 and the beam splitter 34.
incident on .

The electrical output of the light receiving element is connected to the input of a synchronous detector 60 via an amplifier 58. Like the piezoelectric vibrating element 46 described above, this synchronous detector 6 is connected to an AC excitation power source 50 for phase modulation, and receives alternating current at an angular frequency ω. The output of the synchronous detector 60 is then sent to a switch 64 via an A/D converter 62.
is connected to one input terminal of the

Further, the circuit that supplies the sawtooth wave to the phase modulator 48 includes a subtraction circuit 66 that receives the analog output of the synchronous detector 60;
It has an integrating circuit 68 that receives the output thereof. That is, what are the subtraction circuit 66 and the integration circuit 68?

It constitutes a differential integrator. The output of the integrating circuit 68 is connected to the respective inputs of a voltage controlled oscillation circuit 70, an A/D converter 72, and a voltage determination circuit 74. This voltage controlled oscillation circuit 70 receives an input voltage ■.

The waveform shaping circuit 76 generates a signal with a frequency f proportional to
Output to. The waveform shaping circuit 76 that receives the signal of frequency f has a peak value ■. is constant, the period T is 1/f, and the polarity is the same as that of the input voltage (2). A sawtooth wave is generated and applied to the phase modulator 481. Such voltage controlled oscillator circuits and waveform shaping circuits are well known in the art, so their explanation will be omitted. In particular, the waveform shaping circuit that generates the sawtooth wave under the above conditions can be realized by a so-called constant amplitude sawtooth wave generation circuit.

Thus, the subtraction circuit 66, the integration circuit 68, the voltage controlled oscillation circuit 70, and the waveform shaping circuit 76 are connected to the optical fiber 4.
2, a zero-order method servo circuit is constructed.

On the other hand, the digital output of the A/D converter 72 is
It is connected to the other input terminal of 4.

Then, the voltage determination circuit 74 compares the analog output voltage of the integrating circuit 68 with a predetermined reference voltage, and when the analog output voltage of the integrating circuit 68 is larger than the predetermined reference voltage, puts the voltage controlled oscillation circuit 70 into an operating state. Switch 6 as you put it on
4 switches the switch 64 so that the digital output of the A/D converter 72 is output as a phase difference signal, and on the other hand, when the analog output voltage of the integrating circuit 68 is smaller than a predetermined reference voltage, the voltage controlled oscillation circuit 70 is disabled. When placed in the operating state, the switch 64 is operated so as to output the digital output of the A/D converter 62 as a phase difference signal.

In addition to the phase modulation type optical fiber gyro as described above, when the phase modulator 48 does not operate, it operates in the same manner as a conventional phase modulation type optical fiber gyro. On the other hand, when the phase modulator 48 operates, phase modulation by the phase modulators 46 and 48 is applied to light propagating in both directions in the optical fiber 42.

The operating principle of the optical fiber gyro using the zero position method when the phase modulator 48 operates is detailed in the above-mentioned document (1). Now, the phase shift caused by the phase modulator 46 is ω,
If the phase shift caused by the phase modulator 4B is φ, then
The ωy component of the output of the light receiving element 36 can be expressed as follows.

ψ S (Δθ) = 2ErEtJ + (2bsin −) cos
ω, t, φ, ′? Since it is a function that changes with the slope of the knee wave, the output voltage of the synchronous detector 60 in FIG.
, is V+=C-5in(a r+Δθ') ---(21
) where C: constant τ: time required for light to propagate through the sensor coil (see equation (4)) Δθ: phase difference a=V due to Sagnac effect. /T (slope of sawtooth wave) ■. :Peak voltage of sawtooth wave T: Can be expressed as period of sawtooth wave. Therefore, by feedback-controlling the slope a of the sawtooth wave by the servo circuit so that 1=0 is always maintained, that is, Δθ τ, the slope a can be changed from the slope a to Δθ
(=-aτ) can be obtained.

And, as mentioned above, the peak voltage of the sawtooth wave■. is constant, so its gradient a is a=Vo/'r=V
From the relationship of <where f=1/T), it is proportional to the frequency, and can be determined in principle from the drive frequency of the phase modulator 48, that is, the oscillation frequency of the voltage controlled oscillation circuit.

Now, by simplifying V, = A - 5 in (a r + Δθ) and setting V = sin (af + Δθ), we will consider the responsiveness of the feedback control and the practical voltage representing Δθ.

The relationship between ■ and at+Δθ in V=sin(ar+Δθ) is shown in FIG. Therefore, when finding the conditions under which ■ becomes zero, assuming that (aτ+Δθ) is sufficiently small compared to 1, it can be expressed as V=aτ+Δθ.

On the other hand, if the zero-order method servo circuit in the circuit of FIG. 1 is extracted and illustrated, it will be as shown in FIG. 5. In other words, the output ■ of the optical system of the fiber optic gyro (FOG) is
First, it is amplified by amplifier A to gain -, and its output -AV
is then input to an integrator C for integration, and its output voltage , is input to a voltage controlled sawtooth wave generator CO.

When we trace this signal processing and analyze V=aτ+Δθ, a becomes a=Vo/T”V o f as described above.
, and its f has the relationship f=cVr (where C is a proportionality constant between voltage and frequency), and further, its {circle around (2)} can be expressed as follows.

Therefore, ■ can be expressed as follows.

Differentiating such an expression with respect to t yields, that is, . The time constant of the above equation (23) is 1/τc A V
.

Therefore, the relationship between ■ and Δθ is as shown in FIG.

Therefore, by selecting c, A, Vo,
Δθ can be expressed by the output (■) of the integrating circuit 68 with sufficient responsiveness.

Furthermore, the characteristic of equation (22) described above can be easily realized. For example, it can be realized by an integrating circuit as shown in FIG. In that case, it can be expressed as, C=0.1μF=10-7FJR=
When IKΩ=103Ω, the phase modulation type optical fiber gyro configured as above operates as follows.

The light beam from the light emitting element 32 driven by the power source is
Beam splitter 34, single mode optical fiber 38
The beam is split into two by a beam splitter 40 and coupled to both ends of an optical fiber 42.

The light beam inputted into the optical fiber 42 has a phase difference at the sensor coil 44 which is being rotated, and the piezoelectric vibrating element 46 is driven by a sinusoidal alternating current with an angular frequency ω1 from an alternating current excitation power source 50. and electro-optic effect phase modulator 4
8, respectively, and are phase modulated.

The clockwise light beam and the counterclockwise light beam, which have a phase difference and are phase-modulated in the optical fiber 42, are output from both ends of the optical fiber 42 and are outputted from the beam splitter 4.
0, and furthermore, single mode optical fiber 3
The light enters the light receiving element 36 via the beam splitter 34 and the beam splitter 34.

The output of the light receiving element 36 is synchronously detected by a synchronous detector 60 at ω power.

At this time, when the output voltage (2) of the integrating circuit 68 is smaller than the reference level, the voltage determination circuit 74
2 is outputted via the switch 64, and the voltage controlled oscillation circuit 70 is placed in a non-operating state. Therefore, this signal is not phase modulated by the phase modulator 48.

On the other hand, when the output voltage (2) of the integrating circuit 68 is larger than the reference level or becomes larger, the voltage judgment circuit 74
outputs the output of the A/D converter 72 via the switch 64, and puts the voltage controlled oscillation circuit 70 into operation. Therefore, at this time, phase modulation is performed by the phase modulator 48, measurement is performed by the zero-position method, and a voltage signal representing the phase difference Δθ at that time is outputted from the integrating circuit 68.
/D converter 72 and output.

As described above, the output of the synchronous detector 60 and the integrating circuit 68
The reason for A/D conversion of the output of . Specifically, even if the analog voltage of the integrating circuit 70 is small, it represents a large phase difference Δθ. For example, 110-3 de/sec to 11
When securing a total dynamic range of 106 de/sec to 000 de/sec, when the phase modulator 48 does not operate and operates in the same manner as a conventional phase modulation type optical fiber gyro, the dynamic range from 110-3 de/sec to l de
g/sec, and when the phase modulator 48 operates and measures by the zero-position method, ldeg/sec.
to cover the range from c to 11000 de/sec.

In the above embodiments, the phase modulator using sawtooth waves is not limited to one that utilizes an electro-optic effect, and any element may be used as long as it is capable of phase modulation using sawtooth waves.

Effects of the Invention As is clear from the above explanation, the optical fiber gyro according to the present invention extracts signals in a manner that is easy to handle and switches between regions with a small rotational angular velocity and a region with a large rotational angular velocity. Therefore, it is relatively easy to obtain stable output.

[Brief explanation of drawings]

FIG. 1 is an optical system diagram illustrating the principle of the optical fiber gyro according to the present invention, and FIG. 2 is a waveform of the sawtooth wave applied to the phase modulator in the phase modulation type optical fiber gyro of FIG. 3 is a schematic perspective view illustrating an example of an electro-optic phase modulator used in the phase modulation type optical fiber gyro of FIG. 1, and FIG. 5 is a graph showing the relationship between the output voltage of the light receiving element and the phase difference in the phase modulation type optical fiber gyro; FIG. Yes, Figure 6 shows the first
FIG. 7 is a graph showing the relationship between the phase difference Δθ and the sawtooth wave control voltage when a sawtooth wave is applied to the phase modulator in the phase modulation optical fiber gyro shown in FIG. FIG. 8 is a basic configuration diagram explaining the principle of an optical fiber gyro. FIG. 9 is a basic configuration diagram explaining the principle of a phase modulation type optical fiber gyro. [Main reference numbers] lO...Light emitting element 12...Beam splitter 14
．． 16...Coupling lens 18...Optical fiber 20...
Sensor coil 22... Phase modulation element 26... Light receiving element 32... Light source 34.40... Beam splitter 36... Light receiving element 38... Single mode optical fiber 42... Optical fiber 44... Sensor coil 46... Piezoelectric Vibration element 48...Electro-optic effect phase modulator 50...Sine wave AC excitation power supply 52...LiNbC)+substrate 54...Optical waveguide 56
... Electrode 58 ... Amplifier 60 ... Synchronous detector 62.72 ... Δ/D converter 64 ... Switch 66 ... Subtractor 68 ... Integrating circuit 70
...Voltage control oscillation circuit 74...Voltage judgment circuit 76.
・Waveform shaping circuit patent applicant Tatsu Todoroki, Director of the Agency of Industrial Science and Technology Figure 1 32: Light source / 5: > TLT5 Round Cross τCAV.

Claims (5)

[Claims] (1) Includes a light emitting element and a sensor coil portion wound in a coil shape many times, and light from the light emitting element is branched and coupled to both ends, and light propagated in both directions through the sensor coil is output from both ends. The optical fiber gyro includes an optical fiber and a light-receiving element that receives light in both directions propagated through the optical fiber, and measures a rotational angular velocity from a phase difference between the lights in both directions generated when the sensor coil rotates. A first phase modulator provided near an end of the sensor coil, and a sawtooth wave drive that receives the output of the light receiving element so that a voltage representing a phase difference from the light receiving element becomes substantially zero. a zero-position method servo circuit that supplies pulses to the first phase modulator; and a zero-position method servo circuit that outputs the output of the light receiving element as a phase difference signal when the phase difference is small; An optical fiber gyro characterized by comprising a changeover switch that outputs a circuit voltage as a phase difference signal. (2) The sensor coil further includes a second phase modulator provided near an end of the sensor coil, and a synchronous detector that synchronously detects the output of the light receiving element at the driving frequency of the first phase modulator. The patent is characterized in that the voltage controlled oscillator circuit receives the output of the synchronous detector, and the changeover switch outputs the output of the synchronous detector as a phase difference signal when the phase difference is small. An optical fiber gyro according to claim (1). (3) The optical fiber gyro according to claim 1 or 2, wherein the first phase modulator is a phase modulator that utilizes an electro-optic effect. (4) The zero method servo circuit includes a differential integrator that receives the output of the light receiving element, a voltage controlled oscillation circuit that receives the output of the differential integrator, and a voltage controlled oscillation circuit that receives the output of the voltage controlled oscillation circuit. Claims 1 to 3 further include a waveform shaping circuit that outputs a sawtooth wave to the first phase modulator. fiber optic gyro. (5) A/D that converts the phase difference signal into a digital signal
An optical fiber gyro according to any one of claims (1) to (4), characterized in that a converter is provided.