JPH10132578A - Optical fiber gyroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber gyroscope structured for amplitude modulation of light from a light source, and to provide the optical fiber gyroscope with the light source possessed of excellent temperature characteristics. SOLUTION: The light from a light source is amplitude modulated with a reference frequency fQ then propagates through an optical film loop 3. The lights propagating in opposite directions are phase modulated with a reference frequency fm , then undergoing serodyne modulation in the case of serrodyne modulation mode. Hence many intermediate frequencies mfQ-nfm are included in a signal indicating an interference light intensity I, and as the case of superheterodyne mode, desired intermediate frequency components are demodulated by the interference light intensity signal. Based on the desired intermediate frequency components obtained in this way, a Sagnac phase difference Δθ and the like are calculated. A rare earth element dope optical fiber type of a light source is adopted as the light source including a rare earth element dope optical fiber 1A and an excitation light source 1B. The excitation light from the excitation light source 1B is intensity modulated, thereby amplitude modulating the light from the light source.

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 for detecting an angular velocity by utilizing a Sagnac effect of light (also referred to as a Sagnac effect).
The present invention relates to an optical fiber gyro using superheterodyne amplitude modulation.

[0002]

2. Description of the Related Art An optical fiber gyro is configured to detect an angular velocity using a Sagnac effect of light.
It has an optical fiber coil or optical fiber loop, typically consisting of a single long optical fiber wound many times, which propagates light in opposite directions.

[0003] When an angular velocity Ω of an external force is applied to an optical fiber loop, a phase difference Δθ (hereinafter, referred to as a Sagnac phase difference) occurs between lights propagating in the optical fiber loop in directions opposite to each other due to a Sagnac effect. The sagnac phase difference Δθ is proportional to the angular velocity Ω and is expressed by the following equation.

[0004]

Equation 1 Δθ = (2πDL / λc) Ω

Where D is the loop diameter of the optical fiber loop, L is the length of the optical fiber loop, λ is the wavelength of light propagating through the optical fiber loop, c is the speed of light, and Ω is the center axis of the loop of the optical fiber loop. Represents the angular velocity around.

[0006] Resonant type and interference type optical fiber gyros are known. The interference-type optical fiber gyro is configured to combine two propagating lights propagating in opposite directions through an optical fiber loop to generate an interference light, and obtain an angular velocity Ω from a Sagnac phase difference Δθ appearing in the interference light. ing. As the interference type, a phase modulation method and a serrodyne method are known.

In the phase modulation method, two propagating lights propagating in the optical fiber loop in opposite directions are phase-modulated. Therefore, the intensity of the interference light is expressed as follows.

[0008]

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

Here, ω _m is an angular frequency given by phase modulation, and t is time. I ₀ , I ₁ , I ₂ , I ₃ ,
I ₄ represents a DC component, a first harmonic component, a second harmonic component,
It is called a harmonic component, a fourth harmonic component or the like, and is represented by the following equation (3).

[0010]

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

E ₀ is a constant relating to the light intensity, x is the degree of phase modulation, and J ₀ , J ₁ , J ₂ ,... Are Bessel functions. The phase modulation degree x changes according to the magnitude of the voltage signal supplied to the phase modulator.

[0012] The interference light is received by an appropriate light receiver to obtain a current signal, and this current signal is converted into a voltage signal. This voltage signal is expressed by the equation of Equation 2 and the equation of Equation 3. From this voltage signal, the first harmonic component I ₁ or the second harmonic component I ₂ is detected by an appropriate synchronous detector, and sin Δθ or cos Δθ is obtained therefrom, and the Sagnac phase difference Δ
θ is required.

In a phase modulation type optical fiber gyro,
The intensity I of the interference light is given by cos Δ
Since not only the term of θ but also the term of sin Δθ, when the input angular velocity Ω is small and the value of the sagnac phase difference Δθ is small, the term of the sin Δθ is taken out and the sagnac phase difference Δ
If θ is obtained, an accurate value can be obtained.

The cellodyne type optical fiber gyro is an improvement of the phase modulation type optical fiber gyro, and can obtain a wider dynamic range than the phase modulation type optical fiber gyro. An example of a cellodyne type optical fiber gyro is disclosed in Japanese Patent Application No. 4-306975 filed by the same applicant as the present applicant. See the same application for details.

In an optical fiber gyro of the serrodyne system, two propagating lights propagating in the optical fiber loop in opposite directions are phase-modulated by a phase modulation system, and further superimposed thereon, and are subjected to serrodyne modulation. The intensity I of the interference light is represented by the equation (2), but the DC component I ₀ , the first harmonic component I ₁ , the second harmonic component I ₂ , the third harmonic component I _3, etc. are replaced by the equation Is represented by the following equation:

[0016]

Equation 4] ^{_{I 0 = 2E 0 2 {1}} + J 0 (x) cos (Δθ + Δα)} I 1 = 4E 0 2 · J 1 (x) sin (Δθ + Δα) I 2 = 4E 0 2 · J 2 (x) cos _{(Δθ + Δα) I 3 =} 4E 0 2 · J 3 (x) sin (Δθ + Δα) I 4 = 4E 0 2 · J 4 (x) cos (Δθ + Δα)

Δα is called a serrodyne phase difference, and is generated in the interference light by serrodyne modulation. Serrodyne modulation is performed by a kind of closed loop control,
The value of the serrodyne phase difference Δα is controlled so that n (Δθ + Δα) = 0.

Therefore, at the stable point of this closed loop control, Δ
α = −Δθ. By calculating the value of the serrodyne phase difference Δα at this time, the angular velocity Ω is obtained from the equation (1).

A method for determining the value of the serrodyne phase difference Δα will be described with reference to FIG. FIG. 3A shows a case in which a cellodyne modulation propagates an optical fiber loop in opposite directions to each other.
7 shows waveforms of the phase differences α ₀ and α _T generated in two propagating lights. As shown in the figure, these phase differences α ₀ and α _T have a sawtooth waveform (serodyne waveform), and the time difference τ
(Τ is the time required for the propagating light to propagate through the optical fiber loop.) This serrodyne waveform linearly increases from a minimum value 0 to a maximum value 2π within one cycle T _S (T _S is called a serodyne cycle).

When the serrodyne cycle T _S is large, the slope of the serrodyne waveform is small, and when the serrodine cycle T _S is small, the slope of the serrodyne waveform is large. The serrodyne period T _S can be controlled by a voltage signal applied to the serrodyne modulator.

FIG. 3B is a waveform of the serrodyne phase difference Δα appearing in the interference light. The serrodyne phase difference Δα is expressed as a difference α _T −α ₀ between the phase differences α ₀ and α _T occurring in the two propagating lights, and forms a rectangular wave. This square wave has one period T _S
, Two values, α _S and α _S -2π, are taken alternately, and the larger value α _S is the serrodyne phase difference Δα. This value α _S is proportional to the slope of the serrodyne waveform and is expressed as follows.

[0022]

Δα = α _S = 2πτ / T _S = 2πτf _S

Therefore, in order to obtain the serrodyne phase difference Δα, the period T _{S of the} serrodyne waveform or the frequency f _S = 1/1
It suffices if T _S is obtained. This is obtained by detecting a voltage signal applied to the serrodyne modulator.

Therefore, in the serrodyne method, at a stable point of the closed loop control, the serrodyne period T _S is obtained from the voltage signal applied to the serrodyne modulator, the serrodyne phase difference Δα is obtained by the equation (5), and the sagnac phase difference Δθ is obtained. Is required.

An example of a conventional optical fiber gyro will be described with reference to FIG. This example is disclosed in Japanese Patent Application Laid-Open No. Hei 4-98117. For details, refer to the publication.
The optical fiber gyro of the present embodiment is a rare earth element doped optical fiber type light source 101, a light receiver 102, and an optical fiber loop 1.
03, a polarizer 104, first and second couplers, and a phase modulator 108. In the case of the serrodyne method, a serrodyne modulator 108 'is further provided in addition to the phase modulator 108.

According to this embodiment, the light source 101 includes the rare-earth element doped optical fiber 101A, the excitation light source 101B, the optical isolator 101C, and the dichroic mirror 101D. The rare earth element doped optical fiber 101A may be an erbium doped optical fiber (EDF). As the excitation light source 101D, a semiconductor laser (LD) may be used.

Excitation light from the excitation light source 101B is deflected by the dichroic mirror 101D and guided to the rare earth element doped optical fiber 101A. The rare-earth element-doped optical fiber 101A emits light by the excitation light. Light from the rare earth element doped optical fiber 101A is guided to the first coupler 105 via the dichroic mirror 101D and the optical isolator 101C.

The light guided to the first coupler 105 is guided to the second coupler 106 via the polarizer 104 and split into two lights, and the two lights pass through the optical fiber loop 103 in opposite directions. Propagate. The two lights that have propagated through the optical fiber loop 103 in opposite directions are phase-modulated by the phase modulator 108, and in the case of the serrodyne method, are further serrodyne-modulated by the serrodyne modulator 108 '.

The two lights thus phase-modulated and further subjected to serrodyne modulation are combined by the second coupler 106 to generate interference light. This interference light is applied to the polarizer 104.
Is again guided to the second coupler 105 via the
02 is received.

The optical fiber gyro further includes a current-voltage converter 107, a signal generator 109, and a synchronous detector 110. The current-voltage converter 107 converts the current signal from the light receiver 102 into a voltage signal. The signal generator 109 outputs the reference frequency f _m (= ω _m / 2π) and its harmonic frequency nf _m (n
= 1, 2,...) And the phase modulator 10
8 ′ and the synchronous detector 110.

The synchronous detector 110 has a reference frequency nf _m (n
= 1, 2,...), A desired harmonic component represented by the equation (3) (phase modulation scheme) or the equation (4) (serodyne scheme) is detected. Equation 3 in the phase modulation method
The sagnac phase difference Δθ is obtained from the following equation. The serrodyne method, so that the sin (Δθ + Δα) = 0 , to adjust the voltage signal supplied to the serrodyne modulator 108 ', at the control point obtains the serrodyne frequency f _S, the number from the serrodyne frequency f _S at that time 5 The sagnac phase difference Δθ is obtained by the following equation.

As an improved example of the interference type optical fiber gyro, there is an example using a superheterodyne type amplitude modulation, which is disclosed in Japanese Patent Application No. Hei 6-86879 (T9
400047). This application shows an example of both a phase modulation system using amplitude modulation of a superheterodyne system and a serrodyne system. For details, refer to the application.

An example of a phase modulation type optical fiber gyro using superheterodyne type amplitude modulation disclosed in Japanese Patent Application No. 6-86879 (T9400047) will be described with reference to FIG.

The optical fiber gyro of this embodiment has a light source 1 and a light emitting device driver 11, a light receiver 2, an optical fiber loop 3, an optical integrated circuit 4, and a current / voltage converter 9 as light sources. The optical integrated circuit 4 includes two couplers 5 and 6 and a phase modulator 8
And The light emitting device driver 11 receives a DC voltage signal and a signal of the reference frequency f _Q to generate an amplitude modulation voltage signal, and supplies the voltage signal to the light emitting device 1. Therefore, the light emitter 1 has the reference frequency f
_The light source light amplitude-modulated by _Q is output.

The light thus amplitude-modulated passes through a first coupler 5 and is split into two lights by a second coupler 6. The two split lights are separated by a phase modulator 8 into a reference frequency f.
Phase modulated by _m .

The interference light is represented by the formulas (2) and (3).
But the constant E included in the coefficient of the equation (3)₀ Is constant
It is a function E (t) representing amplitude modulation, not a value. This swing
The function E (t) representing the width modulation is represented by various intermediate frequencies (nf_Q
-Mf_m)). Therefore, the desired intermediate circumference
By detecting the wave number component, the desired harmonic component can be obtained.
I ₁, I_Two, I_ThreeEtc. are obtained, and the sagnac phase difference Δθ is
Desired.

The optical fiber gyro further includes a synchronous detector 53, a signal generator 55, a modulation signal generator 57, an angular velocity /
It has an angle calculation fiber 59, a modulation degree calculation unit 61 and a filter 71, the details of which will be described later with reference to FIG.

An example of a cellodyne modulation type optical fiber gyro using super heterodyne type amplitude modulation disclosed in Japanese Patent Application No. 6-86879 (T9400047) will be described with reference to FIG.

The optical fiber gyro of this embodiment has a light emitting device 1 and a light emitting device driver 11 as light sources, a light receiving device 2, an optical fiber loop 3, an optical integrated circuit 4, and a current-voltage converter 9. The optical integrated circuit 4 includes two couplers 5 and 6 and a phase modulator 8
And The light emitting device driver 11 receives the DC voltage signal and the signal of the reference frequency f _Q to generate an amplitude modulation voltage signal, and supplies it to the light emitting device 1. Therefore the light emitting device 1 outputs the source light that is amplitude modulated by the reference frequency f _Q.

The light thus amplitude-modulated passes through a first coupler 5 and is split into two lights by a second coupler 6. The two split lights are separated by a phase modulator 8 into a reference frequency f.
_The signal is phase-modulated by _m and further serrodyne-modulated by the serrodyne modulator 8 '.

The interference light is represented by the equation (2) and the equation (4). The constant E ₀ included in the coefficient of the equation (4) is not constant but a function E (t) representing amplitude modulation. The function E (t) representing this amplitude modulation is represented by various intermediate frequencies (nf _Q −m
f _m ). Accordingly, by detecting a desired intermediate frequency component from this, desired harmonic components I ₁ and I _1
2 , I _{3 and the} like are obtained, and the sagnac phase difference Δθ is obtained.

The optical fiber gyro further includes a synchronous detector 53, a signal generator 55, a modulation signal generator 57, a CPU 6
5. It has a serrodyne modulation signal generator 67 and a filter 71. The CPU 65 has an angular velocity / angle calculator 59, a modulation factor calculator 61, and a 2π controller 63, as shown in FIG. Details of these components will be described later with reference to FIGS.

[0043]

As shown in FIGS. 5 and 6, in a conventional optical fiber gyro of the type in which light from a light source is amplitude-modulated, a light emitting diode (LE) is used as a light emitting device 1.
D) or super luminescent diode (SL)
D) and other semiconductor light emitting devices have been used. The semiconductor light emitting device has a wide spectrum width (short coherent length) and has an advantage that gyro output errors can be reduced, but has a disadvantage that the wavelength of the light source changes with temperature. Typically, the rate of temperature change of the wavelength λ of the light source is about 300 ppm / ° C.

Further, this type of light source has a drawback that the light quantity that can be coupled to the optical fiber is relatively small and cannot be used for a high-precision optical fiber gyro.

In the example shown in FIG. 4, a rare earth element-doped optical fiber type light source is used as a light source in an ordinary phase modulation type or serrodyne type optical fiber gyro. The rare-earth element-doped optical fiber type light source has an advantage that it is relatively less affected by a change in temperature and can be easily coupled to the end of the optical fiber gyro on the sensor side.

In view of the above, the present invention provides a light emitting diode (LED) or a semiconductor light emitting element such as a super luminescent diode (SLD) as a light source in an optical fiber gyro of a type for modulating the amplitude of light from a light source. An object of the present invention is to provide an optical fiber gyro that does not need to be performed.

In view of the above, an object of the present invention is to use a rare earth element-doped optical fiber type light source as a light source in an optical fiber gyro of a type that modulates the amplitude of light from a light source.

[0048]

According to the present invention, there is provided a light source, an optical fiber loop, and a phase modulator for phase modulating first and second propagating lights propagating in opposite directions in the optical fiber loop. A light receiver for detecting interference light of the first and second propagation lights, a synchronous detector for synchronously detecting a desired frequency component from a signal of the intensity I of the interference light detected by the light receiver; An angular velocity / angle calculator for calculating a sagnac phase difference Δθ appearing in the interference light from the signal obtained by the synchronous detector, and further calculating an angular velocity Ω, by amplitude-modulating the light from the light source. A desired intermediate frequency component is generated in the signal of the intensity I of the interference light, and the desired intermediate frequency component is detected by the synchronous detection unit, so that the angular velocity / angle calculation unit causes the sagnac phase difference Δθ and the angular In an optical fiber gyro configured to calculate the speed Ω, the light source includes a rare earth element-doped optical fiber and a pumping light source, and the intensity of the pumping light from the pumping light source is modulated by intensity modulation. It is configured to amplitude modulate light.

According to the present invention, in the optical fiber gyro, the desired intermediate frequency generated in the signal of the intensity I of the interference light is a reference frequency f _{Q of} a signal used for amplitude modulation of light from the light source. and by the reference frequency f _m of the signal used to phase modulation by the phase modulator, mf _Q -nf _m (where m, n are positive integers.) represented by.

According to the present invention, in the optical fiber gyro, the reference frequency f used for amplitude modulation of the light of the light source is used.
_Q includes a plurality of reference frequencies f _Q1 , f _Q2 , f _Q3 , f _Q4, etc., and is determined by a signal of the plurality of reference frequencies and a signal of a reference frequency f _m used for phase modulation by the phase modulator. It desired intermediate frequency mf the signal intensity I of the interference light _Qi -nf _m (i is a positive integer.) is configured to generate. The amplitude modulation of the light from the light source is performed by modulating the intensity of the excitation light from the excitation light source using a rectangular wave having a period T = 1 / f _Q. Further, the amplitude modulation of the light from the light source is performed by changing the excitation light from the excitation light source to a period T.
This is done by intensity modulation using a sine wave of = 1 / f _Q.

According to the present invention, the signal of the reference frequency f _Q used for amplitude modulating the light of the light source and the reference frequency f _Q used for phase modulating by the phase modulator are used.
_m and an intermediate frequency mf _Q −nf _m used for detecting the desired intermediate frequency by the synchronous detector.
And a signal generating unit for generating the signals of the above.

According to the present invention, in the optical fiber gyro, a first AC amplifier for amplifying the light intensity signal I with a relatively large AC gain and a second AC amplifier for amplifying the light intensity signal I with a relatively small AC gain. An AC amplifier, a first synchronous detector for synchronously detecting the output of the first AC amplifier to generate a first first harmonic component signal N _1A , and a synchronous detector for detecting the output of the second AC amplifier A second synchronous detector for generating a second first harmonic component signal N _1B, and a third synchronous detector for synchronously detecting the light intensity signal I to generate a second harmonic component signal N _2. A signal switch for outputting the first first harmonic component signal N _1A when the input angular velocity Ω is low and outputting the second first harmonic component signal N _1B when the input angular velocity Ω is high. When the input angular velocity Ω is low, the first first harmonic component No. N _1A and the second harmonic component signal N ₂
And calculates the phase difference Δθ from the second first harmonic component signal N _1B and the second harmonic component signal N ₂ when the input angular velocity Ω is large. I have.

According to the present invention, in the optical fiber gyro, a bias for supplying a bias correction value ΔN _1B which is a deviation between the first first harmonic component signal N _1A and the second first harmonic component signal N _1B. A correction device and an adder for subtracting the bias correction value ΔN _1B from the second harmonic component signal N _1B . The bias correction device sets the bias correction value ΔN _1B when the input angular velocity Ω is small. is supplied to the adder is configured to correct the second 1 harmonic component signal N _1B. Further, a serrodyne modulator for serrodyne-modulating the first propagation light and the second propagation light propagating in opposite directions in the optical fiber loop is provided, and the sagnac phase difference Δθ is calculated by a serrodyne method, and the angular velocity is further calculated. It is configured to calculate Ω.

[0054]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the optical fiber gyro according to the present invention will be described with reference to FIG. The optical fiber gyro of this embodiment is a phase modulation type optical fiber gyro using amplitude modulation.

According to the present embodiment, a rare earth element doped optical fiber type light source device is used as the light source device. As shown, the rare earth element doped optical fiber type light source device includes a rare earth element doped optical fiber 1A, an excitation light source 1B, an optical isolator 1C, and a dichroic mirror 1D.

The optical fiber gyro of this embodiment is different from the embodiment shown in FIG. 5 in that a rare earth element-doped optical fiber type light source device is used instead of the light emitter 1 and the light emitter driver 11. Other configurations may be the same.

Erbium Er, neodymium Nd, praseodymium Pr and the like are known as rare earth elements added (doped) to the rare earth element doped optical fiber 1A. As the excitation light source 1D, a semiconductor laser (LD) may be used.
In the case of an erbium-doped optical fiber (EDF), the wavelength λ ₁ of the excitation light source 1B is λ ₁ = 1.48 μm or 0.98
μm, and the wavelength λ ₂ of the generated light source light is λ ₂ = 1.
55 μm.

The optical isolator 1C functions to prevent light of the same wavelength from propagating in the opposite direction. This prevents unnecessary light, for example, reflected light from propagating in the same path in the opposite direction and propagating to the rare-earth element-doped optical fiber 1A. Thereby, the light emitting state of the rare-earth element doped optical fiber 1A is stabilized. Optical isolator 1C
Alternatively or together with a suitable optical filter may be provided. The optical filter allows only light of a predetermined range of wavelengths to pass, and blocks light of a different wavelength from passing therethrough.

The excitation light from the excitation light source 1B is deflected by the dichroic mirror 1D and guided to the rare earth element doped optical fiber 1A. The rare-earth element-doped optical fiber 1A emits light by the excitation light. The light generated by the rare-earth element-doped optical fiber 1A is a dichroic mirror 1D
And output via the optical isolator 1C.

The optical fiber gyro of the present embodiment has a light receiving device 2, an optical fiber loop 3, an optical integrated circuit 4, and a current / voltage converter 9 in addition to a rare earth element doped optical fiber type light source device.
And The optical integrated circuit 4 has two Y branches 5 and 6 and a phase modulator 8.

The light from the rare earth element-doped optical fiber type light source passes through the first Y branch 5 of the optical integrated circuit 4 and passes through the second Y branch.
The light is branched by the branch 6 and propagates through the optical fiber loop 3 in opposite directions. Light propagating clockwise in the optical fiber loop 3 is phase-modulated at the exit of the optical fiber loop 3, and light propagating counterclockwise through the optical fiber loop 3 is phase-modulated at the entrance of the optical fiber loop 3.

The two lights that have propagated in the optical fiber loop 3 in opposite directions are combined by the second Y branch 6 to generate interference light. The interference light is received by the light receiver 2 via the first branch 5. The current signal from the light receiver 2 is converted into a voltage signal by the current / voltage converter 9.

According to this example, the light from the rare earth element doped optical fiber type light source is amplitude-modulated by the reference frequency f _Q. Excitation light source 1B inputs a voltage signal of the DC voltage DC and the reference frequency f _Q. DC voltage is the reference frequency f _Q
Is amplitude modulated. Excitation light source 1B outputs the excitation light is amplitude-modulated by the reference frequency f _Q, a rare earth element doped optical fiber 1A generates source light that is amplitude modulated by the reference frequency f _Q.

[0064] Thus the amplitude modulated light propagates through the optical fiber loop 3, is further phase-modulated by the reference frequency f _m by the phase modulator 8.

The light intensity signal I output by the current-voltage converter 9 is represented by the equations (2) and (3). The coefficients in the equations (3) are not constants, but are amplitudes. Includes a function E (t) representing modulation.

[0066]

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

The amplitude modulation function E (t) is generally a rectangular wave or a sine wave including the reference frequency f _Q. After all, receiver 2
The intensity signal I of the interfering light received by the light source or the light output by the current-to-voltage converter 9 has a large number of intermediate frequencies mf
_Q -nf _m (where m, n is a positive integer.) It obtained as comprising component.

For example, suppose m = 1 and n = 1, 2, 3, 4,
As the four intermediate frequency _{(f Q -f m), (} f Q -2
f _m), think about the _{(f Q -3f m), (} f Q -4f m). The amplitudes of these intermediate frequency components are represented by N ₁ , N ₂ , N
₃ and N ₄ are represented by the following equations.

[0069]

Equation 7] ^{_{N 1 = -KE 0 2 · J}} 1 (x) · sinΔθ N 2 = KE 0 2 · J 2 (x) · cosΔθ N 3 = -KE 0 2 · J 3 (x) · sinΔθ N 4 _{^{= KE 0 2 · J 4 (}} x) · cosΔθ

K is a constant determined by the function E (t).

More generally, a number of reference frequencies f _Qi (where i is a positive integer) can be used as the reference frequency f _Q. In this case, the intermediate frequency is mf _Qi −nf
_m (where m, n, and i are positive integers). For example, the reference frequency f _m to be used for phase modulation by the phase modulator 8 to 625 kHz. Therefore, 2f _m = 125
0kHz, 4f _m = 2500kHz, to become. Also, the reference frequency f _Q used for the amplitude modulation corresponding thereto is
f _Q = 623 kHz, 1050 kHz, 2480 kHz
z. At this time, the following intermediate frequency is obtained.

[0072]

[Equation 8] _{f Q -f m = 623kHz-625kHz} = -
_{2kHz f Q -2f m = 1050kHz-} 1250kHz = -2
_{00kHz f Q -4f m = 2480kHz-} 2500kHz = -2
0 kHz

Thus, similarly to the superheterodyne method, a desired intermediate frequency component can be easily separated from the intensity signal I of the interference light. The sagnac phase difference Δθ can be calculated from the amplitudes N ₁ , N ₂ , N ₃ and N _{4 of} the desired intermediate frequency components obtained thereby. This will be described later.

The optical fiber gyro of this embodiment further includes a synchronous detector 53, a signal generator 55, a modulation signal generator 57, an angular velocity / angle calculator 59, a modulation degree calculator 61, a filter 7
And 1. The angular velocity / angle calculation section 59 and the modulation degree calculation section 61 may be constituted by the CPU 65.

[0075] The signal generating section 55 is desired intermediate frequency for signal and synchronous detection of the reference frequency f _Q to be supplied to the signal and pumping light source 1B of the reference frequency f _m to be supplied to the phase modulator 8 mf _Q -nf _m (where, m, n is a positive integer.) to generate a signal.

The synchronous detector 53 synchronously detects the voltage signal I output from the current-to-voltage converter 9 and selects a desired _{one of} the modulated signals N ₁ , N ₂ , N ₃ and N ₄ expressed by the equation (6). Output the modulated signal. For example, three intermediate frequencies (f _Q
−f _m ), (f _Q −2f _m ), and (f _Q −4f _m ) components are demodulated.

The first and second intermediate frequencies (f_Q−
f_m), (F_Q-2f_mComponent N)₁, N _TwoIs Sagnac
Used to determine the phase difference Δθ.
Inter-frequency (f_Q−f_m), (F_Q-4f_mComponent N)₁
N_FourIs used to calculate the correction value Δx of the modulation factor x.
You.

The synchronous detector 53 outputs the first intermediate frequency (f
Two values as components N _{1 Q} -f _m), i.e., when the absolute value of the first 1 harmonic component signal N _1A and the input angular velocity Ω to be used when the absolute value of the input angular velocity Ω is small is large The second used first harmonic component signal N _1B is calculated. The first first harmonic component signal N _1A is amplified by a first AC amplifier having a large gain, and the second first harmonic component signal N _1B is amplified by a second AC amplifier having a small gain. is there.

The angular velocity / angle calculating section 59 includes a synchronous detecting section 53
Modulation signal N supplied from₁(= N _1A, N_1B), N_TwoYo
Calculate the sagnac phase difference Δθ and further calculate the angular velocity Ω
And outputs it as a gyro output.

In order to obtain the sagnac phase difference Δθ, the same calculation as in the case of an ordinary phase modulation type optical fiber gyro is performed. For example, two intermediate frequencies (f _Q −f
_{m), (f Q -2f m} ) amplitude N ₁ components, the ratio of N ₂ N ₁
/ A N ₂ seek.

[0081]

N ₁ / N ₂ = − [J ₁ (x) / J ₂ (x)] tan Δθ

From the ratio N ₁ / N ₂ , the coefficient J ₁ (x) / J
₂ Eliminating (x) gives tan Δθ. For example, this ratio N ₁ / N ₂ of the known [J ₁ (x) /
J ₂ (x)] or the reciprocal of the value of
_The modulation factor x is set to x = 2 so that ₁ (x) = J ₂ (x).
63 may be used. When the sagnac phase difference Δθ is obtained in this manner, the angular velocity Ω can be obtained by the equation (1).

According to the present embodiment, the angular velocity / angle calculator 59
Uses the first or second first harmonic component signals N _1A and N _1B to determine the sagnac phase difference Δθ. When the absolute value of the input angular velocity Ω is small, the first first harmonic component signal N
_The phase difference Δθ is calculated from _1A and the second harmonic component signal N _2. When the absolute value of the input angular velocity Ω is large, the second 1
The phase difference Δθ is calculated based on the harmonic component signal N _1B and the second harmonic component signal N ₂ .

As described above, when the absolute value of the input angular velocity Ω is large, the second first harmonic component signal N _1B is used to calculate the sagnac phase difference Δθ. _{Since 1B} has a larger error than the first harmonic component signal N _1A , it is necessary to correct it. The angular velocity / angle calculator 59 calculates a bias correction value ΔN _1BD which is a deviation between the first first harmonic component signal N _1A and the second first harmonic component signal N _1B . By the bias correction value ΔN _1BD , the second 1
The bias correction of the harmonic component signal N _1B is performed.

The modulation degree calculating section 61 is provided to execute more accurate modulation degree control. The modulation degree control is to obtain a desired phase modulation degree x by changing a voltage signal supplied to the phase modulator 8, that is, a modulation degree signal. However, in general, it is difficult to fix the modulation factor x to a desired value, and various control systems for maintaining the modulation factor x at a constant value have been devised.

In this example, the modulation degree calculating section 61 calculates a correction value Δx of the modulation degree x from the modulation signals N ₂ and N ₄ supplied from the synchronous detection section 53 and supplies it to the modulation signal generation section 57. The modulation factor control for obtaining the desired modulation factor x is disclosed in, for example, Japanese Patent Application No. 61-182352 filed by the same applicant as the present applicant.

The modulation signal generator 57 corrects the modulation signal x with the modulation correction value Δx and supplies it to the phase modulator 8. Thereby, a desired modulation factor x can be obtained. Finally, the filter 71 will be described. As described above, the function E (t) of amplitude modulation is generally equal to the reference frequency f _Q
Is a rectangular wave or a sine wave. On the other hand, the signal generator 55
Reference frequency f _Q generated by has a rectangular wave. Therefore, when the function E (t) is a sine wave, the filter 71 shapes the reference frequency f _Q into a sine wave.

A second example of the optical fiber gyro according to the present invention will be described with reference to FIG. The optical fiber gyro of the present embodiment is a cellodyne type optical fiber gyro using amplitude modulation.

According to this embodiment, a rare earth element doped optical fiber type light source device is used as the light source device. The rare earth element doped optical fiber type light source device has a rare earth element doped optical fiber 1A, an excitation light source 1B, an optical isolator 1C, and a dichroic mirror 1D. The light source device of this embodiment may have the same configuration as the light source device used in the second example of the optical fiber gyro according to the present invention shown in FIG.

The optical fiber gyro of this embodiment is different from the embodiment shown in FIG. 6 in that a rare earth element doped optical fiber type light source device is used instead of the light emitting device 1 and the light emitting device driver 11. Other configurations may be the same.

The optical fiber gyro of this embodiment has a light receiver 2, an optical fiber loop 3, an optical integrated circuit 4, and a current-voltage converter 9 in addition to the rare earth element doped optical fiber type light source device. The optical integrated circuit 4 has two Y branches 5 and 6, a phase modulator 8, and a serrodyne phase modulator 8 '.

[0092] According to the present embodiment, the light from the rare-earth element doped optical fiber type light source is amplitude modulated by the reference frequency f _Q. Excitation light source 1B inputs a voltage signal of the DC voltage DC and the reference frequency f _Q. DC voltage is the reference frequency f _Q
Is amplitude modulated. Excitation light source 1B outputs the excitation light is amplitude-modulated by the reference frequency f _Q, a rare earth element doped optical fiber 1A generates source light that is amplitude modulated by the reference frequency f _Q.

[0093] Thus, in this way the amplitude modulated light propagates through the optical fiber loop 3, it is phase-modulated by the reference frequency f _m by the phase modulator 8, further Serrodyne modulated by serrodyne phase modulator 8 '.

In the case of this example, the intensity signal I of the interference light received by the light receiver 2 or the light output by the current-to-voltage converter 9 is represented by the amplitude modulation function E (t) as in the equation (6).
including.

[0095]

## EQU10 ## I ₀ = 2E ₀ ² E (t) ² ｛1 + J ₀ (x) c
os (Δθ + Δα)｝ I ₁ = 4E ₀ ² E (t) ² · J ₁ (x) sin (Δθ + Δ
α) I ₂ = 4E ₀ ² E (t) ² · J ₂ (x) cos (Δθ + Δ
α) I ₃ = 4E ₀ ² E (t) ² · J ₃ (x) sin (Δθ + Δ
α) I ₄ = 4E ₀ ² E (t) ² · J ₄ (x) cos (Δθ + Δ
α)

Δα is a cellodyne phase difference. Amplitude modulation function E (t) is a square wave or sine wave generally includes a reference frequency f _Q. Eventually, the intensity signal I of the light output by the interference light or the current to voltage converter 9 is received by the light receiving unit 2, a number of intermediate frequency mf _Q -nf _m (where m,
n is a positive integer. )).

For example, m = 1, n = 1, 2, 3, 4
As the four intermediate frequency _{(f Q -f m), (} f Q -2
f _m), think about the _{(f Q -3f m), (} f Q -4f m). The amplitudes of these intermediate frequency components are represented by N ₁ , N ₂ , N
₃ and N ₄ are represented by the following equations.

[0098]

Equation 11] ^{_{N 1 = -KE 0 2 · J}} 1 (x) · sin (Δθ + Δα) N 2 = KE 0 2 · J 2 (x) · cos (Δθ + Δα) N 3 = -KE 0 2 · J 3 ( x) · sin (Δθ + Δα ) N 4 = KE 0 2 · J 4 (x) · cos (Δθ + Δα)

K is a constant determined by the function E (t).

The optical fiber gyro of this embodiment further comprises a synchronous detection section 53, a signal generation section 55, a modulation signal generation section 57,
PU65, serrodyne modulation signal generator 67, and filter 7
One. The configuration and operation of the synchronous detection unit 53, the signal generation unit 55, and the modulation signal generation unit 57 are the same as those in the example of FIG.

The serrodyne modulation signal generator 67 converts the two lights propagating in the optical fiber loop 3 in opposite directions to each other.
The phase difference α _T , α _{0 of the} serrodyne waveform as shown in FIG. 3A
To generate a serrodyne modulated signal. According to the control loop of the serrodyne modulation, sin (Δθ + Δ
The serrodyne modulation signal is adjusted so that α) = 0. Therefore, at the control point, the amplitude signal N1 of the _first intermediate frequency component supplied from the synchronous detection unit 53 becomes zero.

Thus, when the amplitude signal N _{1 of} the first intermediate frequency component becomes zero, ie, sin (Δθ + Δ
α) = 0, the cellodyne frequency f _S is obtained,
It is supplied to the CPU 65.

The configuration of the CPU 65 will be described with reference to FIG.
You. In this example, the CPU 65 modulates with the angular velocity / angle calculation unit 59.
It has a degree calculation unit 61 and a 2π control unit 63. Angular velocity / angle
The degree calculation section 59 is provided by the serrodyne modulation signal generation section 67.
The supplied serodyne frequency f _SEquation 5
The Gnack phase difference Δθ is obtained, and the angular velocity Ω is calculated by the equation (1).
Ask for. The modulation degree calculation unit 61 uses the phase modulation method shown in FIG.
With the same configuration and operation as in the case of the optical fiber gyro
May be.

The 2π control section 63 is provided for correcting a 2π error in a cellodyne type optical fiber gyro. The sawtooth waveform used for serrodyne modulation changes from zero to 2π during one period T _S as shown in FIG. 3A, but it is generally difficult to make the maximum value exactly 2π. An error that occurs when the maximum value deviates from 2π is called a 2π error. The correction of the 2π error is called 2π control. The details of the 2π control are described in Japanese Patent Application No. Hei 4-3069 filed by the same applicant as the present applicant.
See No. 75.

The 2π error correction signal Δ2π generated by the 2π control section 63 is supplied to a serrodyne modulation signal generation section 67. The serrodyne modulation signal generator 67 modifies the serrodyne modulation signal with the 2π error correction signal Δ2π.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to these examples, and various modifications can be made within the scope of the invention described in the claims. It will be understood by those skilled in the art.

In the above example, an example in which the optical integrated circuit 4 including the two couplers 5 and 6 and the phase modulators 8 and 8 'is used has been described. However, unlike the example shown in FIG. 4, the optical integrated circuit 4 is not used, and the two couplers 5, 6 and the phase modulator 8,
8 'may be configured as an independent part.

[0108]

According to the present invention, since the rare earth element doped optical fiber type light source is used in the optical fiber gyro of the type in which the light source light is amplitude modulated, the excitation light of the rare earth element doped optical fiber is amplitude modulated. Accordingly, there is an advantage that the light source light can be amplitude-modulated.

According to the present invention, a rare-earth element-doped optical fiber type light source is used in an optical fiber gyro of the type in which the light source light is amplitude-modulated. This has the advantage that errors caused by temperature changes are reduced.

According to the present invention, a rare earth element-doped optical fiber type light source is used in an optical fiber gyro of the type in which the light source light is amplitude-modulated. This has the advantage that the coupling with the optical fiber on the measuring section side is good and the loss of light can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of an optical fiber gyro (phase modulation system) according to the present invention.

FIG. 2 is a diagram showing a second example of the optical fiber gyro (serodyne method) according to the present invention.

FIG. 3 is a waveform diagram for explaining serrodyne modulation.

FIG. 4 is a diagram showing a first example of a conventional optical fiber gyro.

FIG. 5 is a diagram showing a second example of a conventional optical fiber gyro (phase modulation system).

FIG. 6 shows a conventional optical fiber gyro (serodyne method).
It is a figure showing the 3rd example of.

FIG. 7 is a diagram illustrating a configuration example of a conventional CPU.

[Explanation of symbols]

 Reference Signs List 1A Rare earth element doped optical fiber 1B Excitation light source 1C Optical isolator 1D Dichroic mirror 2 Optical receiver 3 Optical fiber loop 4 Optical integrated circuit 5, 6 Coupler 8, 8 'Phase modulator 9 Current voltage converter 53 Synchronous detector 55 Synchronous detector 55 Signal generation Unit 57 Modulation signal generation unit 59 Angular velocity / angle calculation unit 61 Modulation degree calculation unit 65 CPU 67 Serrodyne modulation signal generation unit 71 Filter 101 Light source 102 Receiver 103 Optical fiber loop 104 Polarizer 105, 106 Coupler 107 Current-voltage converter 108, 108 'phase modulator 109 signal generator 110 synchronous detector

Claims (9)

[Claims] 1. A light source, an optical fiber loop, and first and second light beams propagating in opposite directions in the optical fiber loop.
A phase modulator that modulates the phase of the propagating light, a photodetector that detects the interference light of the first and second propagation lights, and a desired frequency based on the signal of the intensity I of the interference light detected by the photodetector. A synchronous detector for synchronously detecting the component, and an angular velocity / angle calculator for calculating a sagnac phase difference Δθ appearing in the interference light from the signal obtained by the synchronous detector and further calculating an angular velocity Ω. A desired intermediate frequency component is generated in the signal of the intensity I of the interference light by amplitude-modulating the light from the light source, and the desired intermediate frequency component is detected by the synchronous detection unit. An arithmetic unit configured to calculate the sagnac phase difference Δθ and the angular velocity Ω, wherein the light source includes a rare earth element-doped optical fiber and a pumping light source; An optical fiber gyro configured to amplitude-modulate light from the light source by intensity-modulating excitation light from the source. 2. The optical fiber gyro according to claim 1, wherein the desired intermediate frequency generated in the signal of the intensity I of the interference light is a reference frequency of a signal used for amplitude modulation of light from the light source. By f _Q and the reference frequency f _{m of the} signal used for phase modulation by the phase modulator, m
f _Q -nf _m (where m, n are positive integers.) optical fiber gyro characterized by being represented by. 3. The optical fiber gyro according to claim 2, wherein the reference frequency f _Q used for amplitude modulation of the light of the light source includes a plurality of reference frequencies f _Q1 , f _Q2 , f _Q3 , f _Q4 , and the like. a plurality of reference frequency signal and the phase modulator desired intermediate frequency by the signal of the reference frequency f _m to be used for phase modulation of a signal intensity I of the interference light by mf _Qi -
An optical fiber gyro configured to generate nf _m (i is a positive integer). 4. The optical fiber gyro according to claim 2, wherein the amplitude modulation of the light from the light source is performed by intensity modulation of the excitation light from the excitation light source using a rectangular wave having a period T = 1 / f _Q. An optical fiber gyro characterized by being performed by: 5. The optical fiber gyro according to claim 2, wherein the amplitude modulation of the light of the light source is performed by intensity modulation of the excitation light from the excitation light source using a sine wave having a period T = 1 / f _Q. An optical fiber gyro characterized by being performed by: 6. The fiber optic gyro of claim 1, 2, 3, 4 or 5, wherein, phase modulated by the signal and the phase modulator of the reference frequency f _Q used to amplitude modulate the light of the light source characterized in that the signal and the synchronous detector reference frequency f _m that use was equipped with signal generator for generating a signal of intermediate frequency mf _Q -nf _m used to detecting the desired intermediate frequency for Optical fiber gyro. 7. The optical fiber gyro according to claim 1, wherein the first AC amplifier amplifies the light intensity signal I with a relatively large AC gain, and the light intensity signal. A second AC amplifier for amplifying I with a relatively small AC gain, and a first synchronous detector for synchronously detecting the output of the first AC amplifier to generate a first first harmonic component signal N _1A. , The second
A second synchronous detector that synchronously detects the output of the AC amplifier to generate a second first harmonic component signal N _1B, and generates a second harmonic component signal N ₂ by synchronously detecting the light intensity signal I. A third synchronous detector that outputs the first first harmonic component signal N _1A when the input angular velocity Ω is low and outputs the second first harmonic component signal N _1B when the input angular velocity Ω is high A signal switching device that performs the above-described first operation when the input angular velocity Ω is small.
The above-described phase difference Δθ is calculated from the first harmonic component signal N _1A and the second harmonic component signal N _{2. When} the input angular velocity Ω is large, the second first harmonic component signal N _1B and the second harmonic component are obtained. An optical fiber gyro configured to calculate the phase difference Δθ from the signal N ₂ . 8. The optical fiber gyro according to claim 7, wherein a bias correction value ΔN _1B that is a deviation between the first first harmonic component signal N _1A and the second first harmonic component signal N _1B is supplied. A bias corrector that performs the correction, and an adder that subtracts the bias correction value ΔN _1B from the second first harmonic component signal N _1B .
The bias corrector supplies the bias correction value ΔN _1B to the adder when the input angular velocity Ω is small, and
An optical fiber gyro configured to correct the first harmonic component signal N _1B of the optical fiber gyro. 9. The optical fiber gyro according to claim 1, further comprising a first propagating light and a second propagating light propagating in opposite directions in the optical fiber loop. An optical fiber gyro which is provided with a serrodyne modulator for performing the serrodyne modulation, and calculates the sagnac phase difference Δθ by the serrodyne method, and further calculates the angular velocity Ω.