JPH0323844B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 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 azimuth data by integrating it.

Among these types of gyroscopes, optical fiber gyroscopes 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, and they have no moving parts. Furthermore, it is superior to conventional gyroscopes in terms of minimum detectable angular velocity (sensitivity), drift, measurable range (dynamic range), and scale factor stability. Therefore, it has been attracting attention and being developed in recent years.

Examples of such fiber optic tires include, for example, gear range gear. G. , Bukalo J. A. Others, ``Optical Fiber Sensor Technology,'' International Institute of Quantum Electronics (Giallorenzi TG, Bucaro J.
A.et al “Optical Fiber Sensor Technology”,
IEEE J. of Quantum Electronics) QE−18,
No. 4, pp626-662 (1982) and Kurashiyo and I. P. Culshawand IPGiles “Fiber Optic” Journal of Physics Electronics Science Instruments
Gyroscopes”J.Phys.E:Sci Instrument) 16 pp5
−15, (1983), Tsubokawa, Otsuka, “Optical Fiber Gyroscope” Laser Research, 11 , No. 12, pp889−
902 (1983) and others.

(a) Principle of optical fiber coil The principle of optical fiber coil will now be explained with reference to FIG. 8.

The light from the light receiving element 10 is sent to the beam splitter 1
The optical fiber loop is made by winding the single mode optical fiber 18 many times in a coil shape, that is, the input is input to both ends of the sensor coil 20. Propagate light. At that time, if 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 strength E _cw of the light propagated clockwise and the light propagated counterclockwise in the sensor coil 20,
_Eccw is expressed as follows.

E _cw = E _r sin (ωt + Δθ/2) E _ccw = E _L sin (ωt − Δθ/2) However, E _r , E _L : Amplitude of counterclockwise light and clockwise light ω : Angular frequency of light t : Time Δθ: Phase difference due to the sannyac effect The counterclockwise light and clockwise light with such a phase difference Δθ are combined by the beam splitter 12,
The light is incident on the light receiving element 26. The phase difference Δθ can be determined from the detection intensity of the light receiving element 26.
The phase difference Δθ can be expressed as follows.

Δθ＝4πLa／cλΩ ……(1) 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 sanyatsuk effect.

There are various methods of detecting the phase difference Δθ.
Various things have been proposed.

Most simply, when the sum of the counterclockwise light and the clockwise light is square-law detected using a light receiving element, the output I becomes I∝{1+cos(Δθ)}...(2).

Since Δθ is included in cos, this has the disadvantage of poor sensitivity when Δθ is close to 0.

Therefore, an optical mechanism has been proposed in which the phase of either the counterclockwise or clockwise light is shifted by 90 degrees and square-law detection is performed. In this case, the output I takes the form I∝{1+sin(Δθ)} (3), so 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 equal.

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

(b) Phase modulation type optical fiber irons Therefore, many optical fiber irons that attempt to detect Δθ using a dynamic mechanism have been proposed. For example, a phase modulation method, a frequency modulation method, etc. are used. Among them, the phase modulation optical fiber iron is the most superior in terms of minimum detectable angular velocity.

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

This phase modulation type optical fiber iron will be explained with reference to FIG. 9.

The coherent light from the light emitting element 10 is split into two by a beam splitter 12 and coupled to both ends of an optical fiber 18 . The optical fiber 18
is divided into a portion wound to constitute a sensor coil 20 and a portion 24 wound around a phase modulation element 22 such as a piezo element driven at an angular frequency ω _n . The light coupled from both ends of the optical fiber is
It propagates clockwise and counterclockwise within the optical fiber sensor coil 20, exits from the opposite end, is combined by the beam splitter 12, and is sent to the light receiving element 2.
6.

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. When the length of the optical fiber sensor coil is L, the refractive index of the fiber core is n, and the speed of light is c, the time τ required for light to pass through the sensor coil is τ=nL/c (4).

As mentioned above, the modulation signal has an angular frequency ω _n
Suppose that it is a sine wave. The phase difference φ of the modulation signal when the light emitted from the light emitting element at the same time is divided into clockwise light and counterclockwise light, each undergoing phase modulation.
φ=ω _n τ =nLω _n /c =2πf _n nL/c (5) However, ω _n =2πf _n .

Due to the sannyac effect, the clockwise light and the counterclockwise light have a phase difference of ±Δθ/2, but the phase is further modulated by the phase modulation element. If the amplitude of the phase modulation element is b, the electric field strengths E _cw and E _ccw of the clockwise and counterclockwise lights are E _cw = E _r sin (ωt + Δθ/2 + bsin (ω _n t + φ)}...(6) E _ccw = E _L sin {ωt−Δθ/2+bsin(ω _n t)} ...(7).

The clockwise light and counterclockwise light having the electric field strength as described above are combined by the beam splitter 12 and square-law detected by the light receiving element 26, so the output S(Δθ, t) of the light receiving element is E _cw and _Eccw squared.

S (Δθ, t) = {E _cw + E _ccw } ² ...(8) Calculating this, S (Δθ, t) = E _r E _L cos {Δθ−2bsin (φ/
2) cos(ω _n t+φ/2)}+D.C.+{2ω or more}……(
9) However, DC means direct current generation.

{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, DC is omitted and S(Δθ, t) is expanded into a series using the Betzel function. First, equation (9) is expressed as follows.

S(Δθ, t)=E _r E _L [cosΔθcos{2bsinφ/2cos(
ω _n t+φ/2)}−sinΔθsin{2bsinφ/2cos(ω _n
t+φ/2)}...(10) On the other hand, from the generating function expansion of the Betzel function, If we set t=e ⁱ 〓, it can be expressed as e ^Ixsin 〓= _∞ 〓 ^n=-∞ J _o (x) e ⁿⁱ 〓 ...(12). From the expansion of the real and imaginary parts of equation (12), we can obtain the series expansion of the cos and sin parts of equation (10). Divide S (Δθ, t) into these parts and write S (Δθ, t) = (S _c cos Δθ + S _s sin Δθ) E _r E _L ...(13), then the conversion of θ → θ + π/2 is written as After that, J _-o (x)=(-) ⁿ J _o (x) ...(14) However, using the property that n is a positive integer, ξ=2bsinφ/2 ...(15) Writing the above S _c and S _s , S _c = J _p (ξ) + 2 _∞ 〓 ⁿ⁼¹ (−) ⁿ J _2o (ξ) cos2nω _n t
...(16) S _s =2 _∞ 〓 ⁿ⁼⁰ (-) ⁿ J _2o+1 (ξ)cos(2n+1)ω _n t
...(17) becomes. Therefore, once again, S(Δθ, t) is expressed as follows.

S (Δθ, t) = 1/2 (E _r ² + E _L ² ) + (component over 2ωt) + E _r E _L J _p (ξ) cosΔθ + E _r E _L 2 _∞ 〓 ⁿ⁼¹ (-1) ⁿ J _2o (ξ)cos2nω _n t・cosΔθ +E _r E _L 2 _∞ 〓 〓 ⁿ⁼⁰ (−1) ⁿ J _2o+1 (ξ)cos(2n+1)ω _n t・sinΔθ
……(10)′ = DC component + 2E _r E _L J ₁ (ξ) cosω _n t・sinΔθ−2E _r E _L J
₂ (ξ) cos2ω _n t·cosΔθ+higher-order component...(10)'' This is the sum of the series of the fundamental wave of the modulation signal ω _n and the high-frequency signal.

By using an appropriate filter, it is possible to extract the fundamental wave ω _n or a harmonic signal of any order. No matter which signal is adopted, cosΔθ or sinΔθ
You can know the size of

In that case, the Betzell function J _o (ξ) of that order
The amplitude b of modulation by the phase modulation element, the modulation angular frequency ω _n , and the sensor coil transit time τ should be set so that the value of ω n is large.

The highest sensitivity can be expected from the first-order term (n=0) in equation (17), that is, the second term on the right side of equation (10).This is the fundamental wave component.This fundamental wave component If P(Δθ, t), then P(Δθ, t)=2E _r E _L J ₁ (ξ)cosω _n t・sinΔθ
...(18).

Therefore, when synchronous detection is performed at the modulation angular frequency ω _n of the piezoelectric vibrating element, the output Vo obtained by the detection is Vo=CsinΔθ (19) where C: constant. That is, in the phase modulation type optical fiber iron, the amount Δθ proportional to the rotational angular velocity can be detected from the amplitude of the modulation angular frequency ω _n component of the piezoelectric vibrating element.

Problems to be Solved by the Invention However, as can be seen from the above equation, in the case of phase modulation type optical fiber coils, as Δθ approaches ±π/2, the change in Vo with respect to the change in Δθ becomes smaller. This makes measurement difficult in practice.

As described above, the conventional phase modulation type optical fiber coil has a problem of a narrow dynamic range.

Therefore, methods for expanding the dynamic range of phase modulation type optical fiber irons have been studied, and some of these methods have already been published. To give one example,
The paper is below.

(1) H. C. Refbl, PH. Gramdoji, H. Jie. Ade Hete "Double closed loop hybrid gyroscope using digital phase lamp" No. 3
International Conference on Circular Fiber Sensors (HCLefevre,
PH.Graindorge, HJArdity, Double Clesed
−Loop Hybride Fiber Gyroscope Using
Digital Phase Ramp, Third International
Conference on Optical Fiber Sensors)
1985, PDS7-1 to PDS7-5 (2) B. Yay. Kim and H. J.A. BYKim and HJshaw, All-optical fiber sensor with linear scale factor using phase-day technology.
fiber−optic gyroscope with linear scale
factor using phase detection SPIE Fiber
Opticand Laser Sensors) Vol.478 1984
PP.142-148 Although the methods disclosed in the above-mentioned documents are theoretically successful in expanding the dynamic range, they actually have the following problems. In other words, the dynamic range required in practice is, for example, from 10 ^-3 deg/sec to 1000 deg/sec and 10 ⁶
There are more than that. 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 we try to cover a wide dynamic range of ¹⁰⁶ , for example, if the power supply voltage is 10V, then at least 10 ^-5 V =
It may output 10μV, which is extremely difficult in practice.

Therefore, the present invention aims to provide a practically necessary dynamic range to a phase modulation type optical fiber coil, which has a narrow dynamic range in principle despite being the best in terms of minimum detectable angular velocity and drift. It is something.

Means for Solving the Problems According to the present invention, a light emitting element;
An optical fiber including a sensor coil portion wound in a coil shape many times, into which light from the light emitting element is branched and coupled to both ends, and the light propagated in both directions through the sensor coil is output from both ends; and a light-receiving element that receives light propagated in both directions, and measures rotational angular velocity from a phase difference between the two directions of light generated when the sensor coil rotates. A sawtooth wave driving pulse is applied to the first phase modulator such that the voltage representing the phase difference from the light receiving element becomes substantially zero. A zero-position method servo circuit that supplies the modulator and outputs the output of the light receiving element as a phase difference signal when the phase difference is small, and outputs the voltage of the zero-position method servo circuit as a phase difference signal when the phase difference is large. An optical fiber gyro is provided, characterized in that it is equipped with a changeover switch for outputting the output.

Function In the above-mentioned optical fiber coil,
By providing the zero-order servo circuit, the phase difference due to the rotation received by the sensor coil can be obtained not from the output of the light receiving element itself but from the control voltage of the zero-order servo circuit. Therefore, according to 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,
On the other hand, when the phase difference is large, by outputting the voltage of the zero range method servo circuit as a phase difference signal,
It is possible to obtain stable output over a wide dynamic range and perform accurate measurements over a wide range.

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

FIG. 1 is a diagram showing the configuration of one embodiment of a phase modulation type optical fiber coil embodying the present invention. In the illustrated phase modulation type optical fiber iron, a light source such as a light receiving element 32 is provided,
It is driven by a power source (not shown) to generate a light beam. In addition, as a light source, He-Ne laser,
Semiconductor lasers, superluminescent diodes, 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 3
4 is for branching the light to the light receiving element 36. The light passing through the beam splitter 34 is coupled to one end of a single mode optical fiber 38,
The light emitted from the other end is transmitted to the beam splitter 4.
Enter 0. The beam splitter 34 splits the light into two and couples them to both ends of the optical fiber 42.

Optical fiber 42 is coiled a number of 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 ω _n . 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 LiNbO ₃ is considered to be effective. From the viewpoint of modulation efficiency, it is desirable to use a waveguide type element. For example, as shown in FIG. 3, an optical waveguide 54 is formed on the surface of the LiNbO ₃ substrate 52.
is provided, and a pair of electrodes 56 are embedded so as to sandwich the optical waveguide 54 therebetween. In this case, an optical waveguide 54 is inserted into one end of the optical fiber 42, and a sawtooth wave is applied between a pair of electrodes 56.

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 received via the single mode optical fiber 38 and the beam splitter 34. incident on element 36.

The electrical output of the light receiving element is connected to the input of a synchronous detector 60 via an amplifier 58. This synchronous detector 60, like the piezoelectric vibrating element 46 described above, is connected to an AC excitation power source 50 for phase modulation, and is adapted to receive an alternating current having an angular frequency ω _n . The output of the synchronous detector 60 is connected to one input terminal of a switch 64 via an A/D converter 62.

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, and an integration circuit 68 that receives the output. That is, the subtraction circuit 66 and the integration circuit 68 constitute a differential integrator. The output of the integrating circuit 68 is connected to a voltage controlled oscillation circuit 70,
It is connected to the respective inputs of the A/D converter 72 and the voltage determination circuit 74. The voltage controlled oscillation circuit 70 generates a signal with a frequency f proportional to the input voltage V _f and outputs it to the waveform shaping circuit 76 . The waveform shaping circuit 76 that receives the signal of frequency f is
Generating a sawtooth wave with a constant peak value _V0 , a period T of 1/f, and the same polarity as the input voltage _Vf ,
is applied to the phase modulator 48. 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 constitute a zero-order servo circuit for the optical fiber 42. On the other hand, the digital output of the A/D converter 72 is connected to the other input terminal of the switch 64.

Then, the voltage determination circuit 74 compares the analog output voltage of the integrating circuit 68 with a predetermined reference voltage.
When the analog output voltage of the integrating circuit 68 is greater than a predetermined reference voltage, the voltage controlled oscillation circuit 70 is put into operation, and the switch 64 turns on the A/D converter 7.
Switch 64 is switched so that the digital output of 2 is output as a phase difference signal, and on the other hand, the switch 64 is
When the analog output voltage of the A/D converter 62 is smaller than a predetermined reference voltage, the switch 64 is set so that the voltage controlled oscillation circuit 70 is put in an inoperable state and the switch 64 outputs the digital output of the A/D converter 62 as a phase difference signal. It works like switching.

In the phase modulation type optical fiber iron as described above, when the phase modulator 48 does not operate,
It operates in the same way as a conventional phase modulation type optical fiber coil. On the other hand, when the phase modulator 48 operates, the phase modulation by the phase modulators 46 and 48 is
It acts on light propagating in both directions through the optical fiber 42.

The operating principle of the optical fiber pilot using the zero-position method when the phase modulator 48 operates is described in the above-mentioned document.
Detailed in (1). Now, assuming that the phase shift caused by the phase modulator 46 is ω _n and the phase shift caused by the phase modulator 48 is φ, the ω _n component of the output of the light receiving element 36 can be expressed as follows.

S(Δθ)=2E _r E _L J ₁ (2bsinφ/2) cosω _n
t・sin{φ−Δθ}……(20) However, b: modulation degree, φ=nL/c・_ω nHere, φ is a function that changes with the slope of the sawtooth wave, so the first The output voltage V ₁ of the synchronous detector 60 in the figure is: V ₁ =C・sin(aτ+Δθ)...(21) where C: constant τ: time required for light to propagate through the sensor coil (see equation (4)) ) Δθ: Phase difference due to sannyac effect a=Vo/T (slope of sawtooth wave) V ₀ : Peak voltage of sawtooth wave T: Period of sawtooth wave. Therefore, by feedback-controlling the slope a of the sawtooth wave by the servo circuit so that V ₁ =0 is always maintained, that is, a = -Δθ/τ, the slope a can be changed from the slope a to Δθ (=-aτ ) can be obtained. Then, as mentioned above, the peak voltage Vo of the sawtooth wave
is constant, so its slope a is proportional to the frequency from the relationship a=V ₀ /T=V ₀ f (however, f=1/T), and the driving frequency of the phase modulator 48, that is, the voltage In principle, it is possible to obtain it from the oscillation frequency of the controlled oscillation circuit.

Now, simplifying V ₁ = A・sin (aτ + Δθ), V
= sin(aτ+Δθ), we will consider the responsiveness of the feedback control and the practical voltage representing Δθ.

The relationship between V and aτ+Δθ when V=sin(aτ+Δθ) is shown in FIG. Therefore, when finding the conditions under which V 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. i.e. Fiber Optic Gyro (FOG)
The output V of the optical system is first amplified by an amplifier A with a gain of -A, and the output -AV is then amplified by an integrator C.
The output voltage V _f is input to the voltage-controlled sawtooth wave generator VCO.

When we trace this signal processing and analyze V=aτ+Δθ, a becomes a=V ₀ /T= as described above.
V ₀ f, and f has the relationship f=cV _f (where c is the proportionality constant between voltage and frequency),
Furthermore, the V _f can be expressed as follows.

V _f =−A∫ ^t ₀ Vdt Therefore, V can be expressed as follows.

V=-τV ₀ cA∫ ^t ₀ Vdt+Δθ ...(22) Differentiating this equation with respect to t gives dv/dt+τV ₀ cA=0, that is, V=Δθ(1-e ^- 〓 ^cAV0t ) ...(23) becomes. The time constant of the above equation (23) is 1/τcAV ₀ , and the relationship between V and Δθ is as shown in FIG.
Therefore, by choosing c, A, and V ₀ ,
At the output V of the integrating circuit 68 with sufficient responsiveness,
Δθ can be expressed.

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 V _f =-(1/RC)∫ ^t ₀ Vdt, C=0.1μF=10 ^-7 F, R=
When 1KΩ=10 ³ Ω, V _f =−10 ⁴ ×∫ ^t ₀ Vdt The phase modulation type optical fiber coil constructed as above operates as follows.

A light beam from the light emitting device 32 driven by a power source passes through a beam splitter 34 and a single mode optical fiber 38 to a beam splitter 40.
The optical fiber 42 is branched into two parts and connected to both ends of the optical fiber 42.

The light beam input to the optical fiber 42 has a phase difference at the part of the sensor coil 44 undergoing rotation, and a piezoelectric vibrating element driven by a sinusoidal alternating current with an angular frequency ω _n from an alternating current excitation power source 50. 46
and the portions coupled to the electro-optic effect phase modulator 48 are phase-shifted.

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, are combined by the beam splitter 40, and are further combined into a single mode light beam. The light enters the light receiving element 36 via the fiber 38 and the beam splitter 34.

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

At this time, when the output voltage V _f of the integrating circuit 68 is smaller than the reference level, the voltage determining circuit 74
The output of the A/D converter 62 is outputted via the switch 64, and the voltage controlled oscillation circuit 70 is placed in a non-operating state. Therefore, at this time, phase modulation by the phase modulator 48 is not performed.

On the other hand, when the output voltage V _f of the integrating circuit 68 is larger than the reference level or becomes larger, the voltage determination circuit 74 outputs the output of the A/D converter 72 via the switch 64, and also outputs the output of the A/D converter 72 via the switch 64. The circuit 70 is placed 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 output from the integrating circuit 68, and the A/
It is converted by a D converter 72 and output.

As mentioned above, the reason why the output of the synchronous detector 60 and the output of the integrating circuit 68 are A/D converted separately is that the analog voltage of the synchronous detector 60 and the integral The analog voltage of the circuit 70 represents a different phase difference Δθ. Specifically, even if the analog voltage of the integrating circuit 70 is small, it represents a large phase difference Δθ.
For example, from 10 ^-3 deg/sec to 1000 deg/sec
If you want to ensure a total of 10 ⁶ dynamic cleanses,
When the phase modulator 48 does not operate and operates in the same manner as a conventional phase modulation type optical fiber gyro,
Covering the range from 10 ^-3 deg/sec to 1 deg/sec,
When the phase modulator 48 operates to measure using the zero position method, it covers the range from 1 deg/sec to 1000 deg/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 of low rotational angular velocity and high rotational angular velocity, and uses them by switching. Therefore, it is relatively easy to obtain stable output.

[Brief explanation of the drawing]

Fig. 1 is an optical system diagram illustrating the principle of the optical fiber coil according to the present invention, and Fig. 2 is a waveform diagram of the sawtooth wave applied to the phase modulator in the phase modulation type optical fiber coil of Fig. 1. 3 is a schematic perspective view illustrating an example of an electro-optic phase modulator used in the phase modulation method optical fiber gyro shown in FIG. 5 is a graph showing the relationship between the output voltage of the light receiving element and the phase difference in the optical fiber gyro; FIG. 5 is a system diagram of the zero position method servo system in the phase modulation type optical fiber gyro shown in FIG. 1; FIG. 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 type optical fiber iron shown in FIG. FIG. 8 is a basic configuration diagram illustrating the principle of an optical fiber gyro.
FIG. 9 is a basic configuration diagram illustrating the principle of a phase modulation optical fiber pilot. [Main reference numbers], 10... 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 vibrating element, 48... Electro-optic effect phase modulator, 50...Sine wave AC excitation power supply, 52...LiNbO ₃ substrate, 54... Optical waveguide,
56... Electrode, 58... Amplifier, 60... Synchronous detector, 62, 72... A/D converter, 64... Switch, 66... Subtractor, 68... Integrating circuit, 7
0... Voltage controlled oscillation circuit, 74... Voltage determination circuit, 76... Waveform shaping circuit.

Claims (1)

[Scope of Claims] 1. A device comprising a light emitting element and a sensor coil portion wound in a coil shape many times, and in which light from the light emitting element is branched and coupled to both ends, and light propagated in both directions through the sensor coil is split. An optical fiber coil is equipped with an optical fiber that outputs from both ends and a light receiving element that receives light in both directions propagated through the optical fiber, and measures the rotational angular velocity from the 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 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 a wave driving pulse 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 the voltage of a phase servo circuit 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 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. Optical fiber gyroscope according to scope 1. 3. The optical fiber gyroscope according to claim 1 or 2, wherein the first phase modulator is a phase modulator that utilizes an electro-optic effect. 4. The zero-level 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 sawtooth waveform that receives the output of the voltage controlled oscillation circuit. 4. The optical fiber gyroscope according to any one of claims 1 to 3, further comprising a waveform shaping circuit that outputs the waveform to the first phase modulator. 5. The optical fiber gyro according to any one of claims 1 to 4, further comprising an A/D converter that converts the phase difference signal into a digital signal.