JPH0352005B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical fiber gyroscope, and more specifically, to an optical fiber gyroscope having high precision and a wide dynamic range.

BACKGROUND ART Currently, gyros are used in various fields, particularly as angular velocity sensors for navigation and attitude control of moving objects such as aircraft, flying objects, and automobiles. If you use this gyroscope,
Not only angular velocity, but also data such as orientation can be obtained 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. It is superior to conventional gyros in terms of minimum detectable angular velocity (sensitivity), drift, measurable range (dynamic range), and scale factor stability. has been attracting attention and development in recent years.

Examples of such fiber optic tires include, for example, gear range gear. G. Bookology.
A. Other "Optical Fiber Sensor Technology" Institute of Electronics (Giallorenzi TG, Bucaro JAet al.
“Optical Fiber Sensor Technology”, IEEE J.
of Quantum Electronics) QE−18, No.4pp626−
662 (1982) and Kurashijo and I. P. Culshaw and IPGiles "Optical Fiber Gyroscope" Journal of Physics Electronics Science Instruments
“Fiber Optic Gyroscopes”J.Phys.E:Sci
Instrum.) 16pp5-15, (1983), Tsubokawa, Otsuka, "Optical Fiber Gyroscope" Laser Research, 11 ,
No. 12, pp. 889-902 (1983), etc., for details.

(a) Principle of the optical fiber coil The principle of the optical fiber coil will now be explained with reference to FIG. 2.

Light beam splitter 12 from light emitting element 10
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, and the light is transmitted clockwise (CW) and counterclockwise (CCW) to the sensor coil 20. propagate. 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 is of the form 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 has the form A∝{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 made equal.

Improving the sensitivity when Δθ is close to 0 by using a static chemical 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.

The phase modulation type optical fiber coil will be explained with reference to FIG. 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 a direct current component.

{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 as a function of 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, It is. By setting 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 we can convert θ → θ + π/2. Then, J _-o (x)=(-) ⁿ J _o (x) ...(14) However, using the property that n is a positive integer, set ξ=2bsinφ/2 ...(15), and write the above S _{c If we} ^write _{S s} ^as _{_ _} ^{_ _} _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 ) + (2ωt
(components above) +E _r E _l J ₀ (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)a = 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)b This is the modulation signal It is the sum of the series of the fundamental wave of ω _n and the high frequency signal.

By using an appropriate filter, it is possible to extract the fundamental wave ω _n or a high frequency 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 equation 1 in (17).
This is the next term (n=0), that is, the second term on the right side of equation (10)b. This is the fundamental wave component. Letting this fundamental wave component be P(Δθ, t), P(Δθ, t) = 2E _r E _l J ₁ (ξ) cosω _n t·sinΔθ (18). In this way, an output proportional to sin Δθ is obtained, and Δθ can be found by finding the amplitude of the fundamental wave component.

Note that since sensitivity improves when J ₁ (ξ) is maximized, it is set to ξ = 1.8. At this time, the DC component J ₀ (ξ) is approximately 0.

The above is the basic configuration of a phase modulation type optical fiber pilot.

Problems to be solved by the invention The conventional optical fiber gyroscope has the above-mentioned problems (18).
As you can see from the formula, since Δθ is detected in the form of sinΔθ, linearity is poor and the detection range is limited to Δθ.
It was difficult to obtain a wide dynamic range because it was limited to a range that could be approximated to sinΔθ with extremely small errors.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an optical fiber gyroscope having a wide dynamic range without reducing the accuracy of the high-precision optical fiber gyroscope.

Means for Solving the Problems According to the present invention, a light emitting element;
an optical fiber that includes a sensor coil portion wound in a coil shape many times, and from which light from the light emitting element is branched and coupled to both ends, and the light that has propagated in the sensor coil in both directions is output from both ends; In an optical fiber gyroscope that measures rotational angular velocity from the phase difference between the two directions of light generated when the sensor coil rotates, the sensor coil is equipped with a light receiving element that receives light in both directions propagated by the sensor coil, and a light receiving element is provided near one end of the sensor coil. a first oscillator that excites the phase modulator at a first angular frequency ω _n ;
first and second synchronous detectors that receive the output of the light receiving element and extract frequency components that are the same as the first angular frequency ω _n and frequency components that are twice the first angular frequency ω n; first and second modulators each receiving the output as a modulation signal and electrically amplitude-modulating a signal of a second angular frequency ω ₁ having a phase different by 90 degrees as a modulated signal; an adder that adds the outputs of the modulators;
A phase comparator is provided which compares the output of the adder using the second angular frequency as a reference phase and outputs a phase difference between the clockwise light and the counterclockwise light which is proportional to the rotational angular velocity.

Operation The output of the phase modulation type optical fiber iron is as shown in the above equation (10)′, and when it is modified and shown, it becomes as follows.

S (Δθ) = 1/2 (E _r ² + E _l ² ) + E _r E _l {[J ₀ (ξ) +
∞ 〓 ⁿ⁼¹ J _2o (ξ)cos2nω _n t〕cosΔθ +∞ 〓 〓 ⁿ⁼¹ J _2o-1 (ξ)cos(2n−1)ω _n t・sinΔθ}…(10)
c Therefore, when the above-mentioned phase modulator is excited at the first angular frequency ω _n , the output of the light-receiving element is the above (10).
It becomes like expression c. Then, if we extract only n=1, that is, ω _n and 2ω _n components from the output S (Δθ), we get S (Δθ) = E _r E _l {J ₂ (ξ) cos2ω _n t] cos Δθ
+J ₁ (ξ)cosω _n t・sinΔθ}. Therefore, the DC component when synchronously detected at ω _n by the first synchronous detector is E _r E _l J ₁ (ξ)sinΔθ (19), and the DC component is synchronously detected at 2ω _n by the second synchronous detector. The DC component when synchronously detected is E _r E _l J ₂ (ξ) cosΔθ (20). Here, ξ is selected so that J ₁ (ξ) = J ₂ (ξ), and the components of equations (19) and (20) are shifted in phase by 90° from each other using the first and second modulators described above. By modulating the shifted carrier of angular frequency ω ₁ and adding the sum using an adder, E _r E _l J ₁ (ξ) {sinΔθcosω ₁ n+cosΔθ・sinω ₁ t}=
E _r E _l J ₁ (ξ)・sin(ω ₁ t+Δθ)…(21). Therefore, by comparing equation (21) with the reference phase using the phase comparator described above, Δθ can be determined. That is, an output proportional to Δθ, that is, the sannyac phase difference, can be obtained.

Embodiments Hereinafter, embodiments of the optical fiber sensor according to 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. This phase modulation type optical fiber coil has a minimum configuration that meets the basic requirements of an optical fiber coil. Regarding the minimum configuration, please refer to Izekiel S. and ARDT H. J.A. "Optical fiber rotation sensor" Springer-Verlag Berlin (Ezekil S. and Arditty
HJ “Fiber Optic Rotation Sensors”
Springer-Verlag Berlin.) 1982 has a detailed explanation.

In the illustrated phase modulation type optical fiber iron, a light source such as a light emitting element 32 is provided, and is driven by a power source (not shown) to generate a light beam. Note that as a light source, a He--Ne laser, a semiconductor laser, a superluminescent diode, etc. can be used. The light beam generated by the light emitting element 32 is sent to beam splitters 34 and 36, which are like half mirrors arranged in series. The beam splitter 34 is for splitting the light to the light receiving element 38, and the beam splitter 36
splits the light from the light source 32 into two and couples them to both ends of the optical fiber 40.

The optical fiber 40 is wound into a coil many times to form an optical fiber sensor, and includes a sensor coil 42 and a portion coupled to a phase modulator 44.

The phase modulator 44 is composed of, for example, a piezoelectric vibrating element, is connected to an AC excitation power source 46 for phase modulation, and is configured to be driven by a sinusoidal AC having an angular frequency ω _n . In this case, the optical fiber 40
is wound around the piezoelectric vibrating element 44, for example.

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

The electrical output of the light receiving element 38 has an angular frequency ω _n
and a bandpass filter 4 that passes the components of 2ω _n .
8 to the inputs of two synchronous detectors 50 and 52. One of the synchronous detectors 50, like the piezoelectric vibrating element 44 described above, is connected to an AC excitation power source 46 for phase modulation, and is configured to receive an AC having an angular frequency ω _n . The other synchronous detector 52 is connected to an AC excitation power source 46 for phase modulation.
It is connected to a double frequency multiplier 54 to receive the output of , and receives an alternating current with an angular frequency of 2ω _n .

The outputs of the synchronous detectors 50 and 52 are input to modulators 56 and 58, respectively. One of the modulators 56 receives a sine wave carrier signal of angular frequency ω ₁ from a vibrator 60 via a 90° phase shifter 62 and modulates it with the input signal from the synchronous detector 50 . Also, the local modulator 58 is connected to the oscillator 6
0 as is, and modulates the carrier of angular frequency ω ₁ with the input signal from the synchronous detector 52.

The outputs of these modulators 56 and 58 are
It is input to an analog adder 64, and its output is input to a phase comparator 66. The phase comparator 66
receives the angular frequency ω ₁ from the oscillator 60, compares it with the input, and outputs a signal representing the phase difference.

The phase modulation type optical fiber coil configured as described above operates as follows.

A light beam from a light emitting element 32 driven by a power source passes through a beam splitter 34 and is split into two by a beam splitter 36 and then connected to an optical fiber 40.
is connected to both ends of the

The light beam input to the optical fiber 40 has a phase difference at the part of the sensor coil 42 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 46. 46
is phase modulated in the portion coupled to the .

The clockwise light beam and the counterclockwise light beam, which have a phase difference and are phase-modulated in the optical fiber 40, are output from both ends of the optical fiber 40, are combined by the beam splitter 36, and are further combined by the beam splitter 36. 34 to the light receiving element 38
incident on .

The output of the light receiving element 38 is filtered by a bandpass filter 48 to output ω _n and 2ω _n components, and further filtered by synchronous detectors 50 and 52 to ω _n
and 2ω _n , respectively, and the output expressed by equations (19) and (20) above, i.e.
The sin Δθ and cos Δθ components are output to modulators 56 and 58, respectively.

The modulator 56 has an input sin Δθ component and an oscillator 60
The carrier of angular frequency ω ₁ which is phase-shifted by 90° and sent through the phase shifter 62 is modulated to obtain cosω ₁ t・
Outputs the sinΔθ component signal. In addition, the modulator 58
modulates the carrier of angular frequency ω ₁ sent from the oscillator 60 with the input cosΔθ component to obtain sinω ₁ t・
Outputs a cosΔθ component signal.

The adder 64 receiving the outputs of the modulators 56 and 58 adds the input signals, performs the calculation of equation (21) described above, and outputs a signal of the component of sin(ω ₁ t+Δθ). The phase comparator 66 receiving the output receives the angular frequency ω ₁ from the oscillator 60, and
With the angular frequency ω ₁ as the reference phase, sin(ω ₁ t + Δθ)
Compare and output Δθ.

Therefore, since the output can be obtained in the form of Δθ, Δθ can be obtained as is without approximating it to sinΔθ. Therefore, the dynamic range is not limited to the range in which Δθ can be approximated to sinΔθ,
It can have a wide range.

Effects of the Invention As is clear from the above explanation, the optical fiber coil according to the present invention can directly obtain Δθ without approximating it to sinΔθ.
It has a wide dynamic range without being limited to a range that can be approximated to sinΔθ. Therefore,
The optical fiber according to the invention can be used in a wide range of applications.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the optical system configuration of a phase modulation type optical fiber coil according to the present invention, FIG. 2 is a basic configuration diagram illustrating the principle of the optical fiber coil, and FIG. FIG. 2 is a basic configuration diagram illustrating the principle of a fiberglass iron. [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,
30... Phase modulator, 32... Light source, 34, 36
... Beam splitter, 38 ... Light receiving element, 40
...Optical fiber, 42...Sensor coil, 44...
...Piezoelectric vibrating element, 46...Sine wave AC excitation power supply,
48... Band pass filter, 50, 52... Synchronous detector, 54... Frequency multiplier, 56, 58...
... Modulator, 60 ... Oscillator, 62 ... Phase shifter, 6
4... Adder, 66... Phase comparator.

Claims (1)

[Scope of Claims] 1. A light-emitting element and a sensor coil portion which is wound in a coil shape many times, and the light from the light-emitting element is branched and coupled to both ends, and the light propagates in both directions through the sensor coil. 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. an optical phase modulator provided near one end of the sensor coil; a first oscillator that excites the phase modulator at a first angular frequency; and an optical phase modulator that excites the phase modulator at a first angular frequency; first and second synchronous detectors that extract the same frequency component and twice the frequency component, and receive the outputs of the first and second synchronous detectors as modulation signals, and have a phase difference of 90° from each other. first and second modulators that electrically amplitude modulate a signal at a second angular frequency as a modulated signal;
an adder that adds the outputs of the first and second modulators; and a clockwise light and a counterclockwise light that are proportional to the rotational angular velocity and compare the outputs of the adder with the second angular frequency as a reference phase. An optical fiber gyro comprising: a phase comparator that outputs a phase difference between the two. 2. The optical fiber optic according to claim 1, wherein the first and second angular frequencies are sinusoidal waves. 3. The first synchronous detector receives the output of the first oscillator and synchronously detects the output of the light receiving element, and the second synchronous detector doubles the output of the first oscillator. 3. The optical fiber gyroscope according to claim 1 or 2, wherein the output of the light receiving element is received via a frequency multiplier and synchronously detected. 4. The output of the light-receiving element is input to the first and second synchronous detectors via a bandpass filter that passes a frequency component having the same frequency as the first angular frequency and a frequency component twice that frequency. An optical fiber gyroscope according to any one of claims 1 to 3, characterized in that: