JPH09318366A - Wavelength monitor and optical fiber gyroscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength monitor for monitoring the wavelength of light from a light source and an optical fiber gyroscope therewith. SOLUTION: A wavelength monitor detects the wavelength of light from a light source 11 having a light intensity distribution almost symmetrical centering around the center wavelength λ0 . The wavelength monitor contains two filters 13A and 13B to pass light with a wavelength width (d) which has as center wavelength a wavelength λ0 ±Δλ symmetrical with the center wavelength λ0 of light from the light source 11 and the quantity of the light passing through the two filters 13A and 13B is compared to detect changes in the wavelength of the light from the light source 11. The light source of an optical fiber gyroscope is provided with the wavelength monitor and a signal of the wavelength monitor is fed back to the light source to keep the wavelength of the light source light constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength monitor device for detecting fluctuations in the wavelength of light from a light source and an optical fiber gyro equipped with the wavelength monitor device.

[0002]

2. Description of the Related Art As an optical fiber gyro which measures an angular velocity by utilizing the Sagnac effect of light, an interference type and a resonance type are known. The interference type optical fiber gyro typically propagates light in a direction opposite to each other through one long optical path composed of an optical fiber loop, combines the two propagating lights to generate interference light, and the interference light is generated. The angular velocity is obtained from the phase difference included in.

A phase modulation type optical fiber gyro of the conventional interference type will be described with reference to FIG. The optical fiber gyro combines a light source 101, a light receiver 102 for converting incident light into current, an optical fiber loop 103 formed by winding one optical fiber a plurality of times, a polarizer 104, and light propagating through the optical fiber. Or, couplers 105 and 106 are provided. The optical fiber gyro further includes a current / voltage converter 107, a phase modulator 108, a signal generator 109, and a synchronous detector 110.

The light output from the light source 101 passes through the first coupler 105 and the polarizer 104,
6 and is split into two lights by the second coupler 106. The two split light beams propagate through the optical fiber loop 103 in opposite directions. That is, one propagates clockwise through the optical fiber loop 103 and the other propagates counterclockwise.

When an angular velocity Ω is applied to the optical fiber loop 103, the optical fiber loop 10
3, a phase difference Δφ occurs between the lights propagating in opposite directions. This phase difference Δφ is proportional to the angular velocity Ω and is expressed by the following equation.

[0006]

## EQU1 ## Δφ = (2πLD / λC) Ω

Where Ω is the angular velocity around the central axis of the optical fiber loop 103, D is the loop diameter of the optical fiber loop 103, L is the length of the optical fiber loop 103, and λ is the wavelength of the light beam output from the light source 101. , C represent the speed of light.

The signal generator 109 generates a reference signal having an angular frequency of ω _P and supplies it to the phase modulator 108 and the synchronous detector 110. The phase modulator 108 is the signal generator 1
The phase frequencies of the light propagating in directions opposite to each other in the optical fiber loop 103 are modulated by the angular frequency supplied from the optical fiber 09 in the optical fiber loop 103 by the reference signal of ω _P.

The phase modulator 108 is connected to the optical fiber loop 10.
3, light propagating clockwise in the optical fiber loop 103 is phase-modulated at the exit of the optical fiber loop 103, and light propagating counterclockwise is phase-modulated at the entrance of the optical fiber loop 103. You.

The lights that have propagated in the opposite directions through the optical fiber loop 103 are combined by a second coupler 106,
Interference light is generated. Such interference light is detected by the light receiver 102 via the polarizer 104 and the first coupler 105. The current signal output by the light receiver 102 is converted into a voltage signal V by the current / voltage converter 107. The voltage signal V is represented as follows.

[0011]

V = K [1 + cosΔφ · ｛J ₀ (z) −2J
₂ (z) cos2ω _P t + ··｝ −sinΔφ · ｛2J
₁ (z) cosω _P t -...}]

Here, z is the phase modulation degree, J ₀ , J ₁ , J
_2, ... are Bessel functions, K is a proportionality constant, t is time.

The synchronous detector 110 synchronously detects the voltage signal V based on the reference signal having the angular frequency ω _P supplied from the signal generator 109. As a result, the angular frequency component ω _P among the angular frequency nω _P components included in the output voltage V is synchronously detected, and the output 2KJ ₁ (z) si proportional to sinΔφ
nΔφ is output. Thus, the Sagnac phase difference Δφ
Is obtained, and the angular velocity Ω is obtained from the equation (1).

A cellodyne type optical fiber gyro is known as an improvement of the phase modulation type optical fiber gyro. In the serrodyne method, as shown in FIG.
8 'is provided. For details of the cellodyne type optical fiber gyro, refer to Japanese Patent Application No. 4-306975 filed by the same applicant as the present applicant.

Light propagating clockwise in the optical fiber loop 103 is serrodyne-modulated by a serrodyne phase modulator 108 'at the entrance of the optical fiber loop 103, and phase-modulated by the phase modulator 108 at the exit of the optical fiber loop 103. You. The light propagating counterclockwise in the optical fiber loop 103 is phase-modulated by the phase modulator 108 at the entrance of the optical fiber loop 103, and
At the exit of 03, serrodyne modulation is performed by the serrodyne phase modulator 108 '.

As the light source 101, a semiconductor light emitting device such as a light emitting diode (LED) or a super luminescent diode (SLD) is used. Also, a rare earth element-doped optical fiber may be used as the light source 101. In this case, erbium Er, neodymium Nd, praseodymium Pr or the like is used as the rare earth element to be added.

In the high precision optical fiber gyro, the light source 1
It is necessary that the wavelength λ of 01 is constant and stable.
Super Luminescent Diode (SLD) is
Typically, it emits infrared rays having a wavelength λ = 0.830 μm. However, the wavelength λ of the light source 101 changes due to various causes. These causes include ambient temperature changes and aging changes. Therefore, in order to remove the error, the light source 1 is always used.
01 wavelengths need to be monitored.

Conventionally, the following method is known as a method for measuring the wavelength of the light source 101.

(1) Method Using Diffraction Grating The light whose wavelength is to be measured is diffracted by the diffraction grating and the diffracted light is detected by the light receiver. The diffracted light satisfies the Bragg equation. Therefore, if the grating spacing of the diffraction grating is known, the wavelength λ can be obtained from the Bragg equation.

(2) Method of using absorption cell An appropriate liquid or gas is put into the absorption cell and the light whose wavelength is to be measured is transmitted. Since a substance absorbs light having a specific wavelength, the wavelength of the absorbed light can be examined from the absorption spectrum.

[0021]

Although the method using a diffraction grating is widely used, it has a drawback that the device is complicated and large and stable measurement cannot be performed. Further, the method using the absorption cell has a drawback that it is difficult to find a substance suitable for the light whose wavelength is to be measured, and is not suitable for measuring the wavelength of a light source having a wide wavelength λ.

While conventional methods are suitable for measuring unknown wavelengths, they are not suitable for monitoring light of known wavelength, such as the wavelength of light from a light source. In particular, it is unsuitable for use in monitoring wavelength fluctuations of light sources used in fiber optic gyros.

In view of the above problems, an object of the present invention is to provide a wavelength monitor device for detecting a wavelength variation of a light source with a simple device.

In view of the above problems, an object of the present invention is to provide an optical fiber gyro provided with a wavelength monitor device for monitoring the wavelength of light from a light source.

[0025]

According to the present invention, for example, as shown in FIG. 1, a variation in the wavelength of light from a light source having a substantially symmetrical light intensity distribution around a central wavelength λ ₀ is detected. In the wavelength monitor device for this purpose, two filters are provided which transmit light having a wavelength width d with the central wavelength λ ₀ ± Δλ, which is symmetrical to the central wavelength λ ₀ of the light from the light source, as transmitted. The variation of the wavelength of the light from the light source is detected by comparing the light amounts of the above-described light.

According to the present invention, in the wavelength monitor, the light from the light source is branched into two lights, and the two filters are arranged along the optical paths of the two lights from the branches. Is characterized by. Alternatively, the two filters are exchangeably arranged along the optical path of the light from the light source.

According to the present invention, in the wavelength monitor, the light transmitted through the two filters is received by the photodetector, the current signal from the photodetector is converted into a voltage signal, and the light quantities are compared. The comparison of the amounts of light transmitted through the two filters is performed by subtracting the voltage signal.

According to the present invention, it includes a light source, a light receiver, two couplers for combining and splitting light, and an optical fiber loop,
Light from the light source is split into two lights by a second coupler, the two lights propagate in opposite directions in the optical fiber loop, and are combined by the second coupler to generate interference light. In the optical fiber gyro configured such that the interference light is received by the light receiver via the first coupler, a wavelength monitor device for detecting a variation in wavelength of light from the light source is provided. The light source is connected to one end of the first coupler, and the wavelength monitor device is connected to the other end of the first coupler.

According to the present invention, in the optical fiber gyro, when the wavelength monitor detects a variation in the wavelength of the light from the light source, a control signal is supplied to the light source so that the wavelength of the light from the light source is always constant. Is configured to be retained. Further, when the wavelength monitor detects a variation in the wavelength of the light from the light source, it corrects the gyro signal according to the variation in the detected wavelength.

According to the present invention, in the optical fiber gyro, the light from the light source has a substantially symmetrical light intensity distribution around the center wavelength λ _0, and the wavelength monitor device has the center wavelength of the light from the light source. includes two filters that transmit light of wavelength width d and a symmetrical wavelength lambda ₀ ± [Delta] [lambda] with the center wavelength lambda _0, by comparing the amount of light transmitted through the two filters of the light from the light source It is characterized in that it is configured to detect a variation in wavelength.

According to the present invention, in the optical fiber gyro, the light from the light source is branched into two lights, and the two filters are arranged along the optical paths of the two lights from the branches. Alternatively, the two filters are exchangeably arranged along the optical path of the light from the light source. The light transmitted through the two filters is received by a light receiver, the current signal from the light receiver is converted into a voltage signal, and the light amounts are compared.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a wavelength monitor device for detecting a wavelength variation of a light source according to the present invention will be described with reference to FIGS. As shown in FIG. 1, according to this example, the wavelength monitoring device includes a branch 12 for branching the light from the light source 11, two filters 13A and 13B, two light receivers 14A and 14B, and two current-voltage converters. Vessels 15A, 15B
And subtracter 16.

The light from the light source 11 is equally divided into two lights by the branch 12, and the first light is divided into the first filter 13 by the first light.
The light is guided to A and the second light is guided to the second filter 13B. The light transmitted through the first filter 13A is received by the first light receiver 14A, and the light transmitted through the second filter 13B is received by the second light receiver 14B. First
And the output voltage signals I _A and I _B of the second photodetectors 14A and 14B are respectively the first and second current-voltage converters 1
5A, the converted voltage signal V _A, to V _B by 15B. The subtractor 16 has two current-voltage converters 15A and 15B.
Of the output voltage signals V _A and V _B are subtracted. The output signal ΔV of the subtractor 16 is expressed as follows.

[0034]

[Formula 3] ΔV = V _A −V _B

The curve C in FIG. 2A shows the intensity distribution of the wavelength of the light from the light source 11 in the normal state, the horizontal axis is the wavelength λ, and the vertical axis is the light intensity. The distribution of light intensity forms a normal distribution curve that is symmetrical about the center wavelength λ ₀ . The curve C ′ in FIG. 2B shows the intensity distribution of the wavelength of the light from the light source 11 in the state where the wavelength has changed due to the influence of temperature or the like. The distribution of light intensity forms a normal distribution curve, which is symmetrical about the center wavelength λ ₀ '.

The first filter 13A transmits light having a center wavelength λ _A and a wavelength range d, and the second filter 13B transmits light having a center wavelength λ _B and a wavelength range d. Filter 13
The center wavelengths λ _A and λ _B of A and 13B are wavelengths outside the center wavelength λ _{0 of the} light source light in the normal state by ± Δλ on both sides.

[0037]

[Formula 4] λ _A = λ ₀ + Δλ λ _B = λ ₀ −Δλ

When the light source 11 is in a normal state, as shown in FIG.
The light corresponding to the area P _A indicated by the diagonal line in FIG.
The light passes through 3A and is received by the first light receiver 14A. Light corresponding to the shaded area P _B in FIG. 2A passes through the second filter 13B and is received by the second light receiver 14B.

The central wavelength λ _A of the filters 13A and 13B,
Since λ _B is located symmetrically on both sides of the central wavelength λ ₀ of the source light, the shaded area P _A and area P _B in FIG. 2A are equal. The amount of light received by the first light receiver 14A and the amount of light received by the second light receiver 14B are equal. Therefore, the output voltage signals V _A and V _B of the two current-voltage converters 15A and 15B are equal. At this time, the output signal ΔV of the subtractor 16 becomes zero.

[0040]

[Number 5] ΔV = V _A -V _B = 0

When the wavelength of the light source is changed by the influence of temperature or the like, the central wavelength of the light from the light source 11 is λ _0.
To λ ₀ ′, the light intensity curve moves entirely to the right by λ ₀ ′ −λ ₀ . Light corresponding to the shaded area P _A ′ in FIG. 2B passes through the first filter 13A, and light corresponding to the shaded area P _B ′ in FIG. 2B is applied to the second filter 1.
Penetrates 3B. Center wavelength λ _A of the first filter 13A
Is Δλ on the right side of the central wavelength λ ₀ 'of the light from the light source 11.
The second filter 13B has a wavelength outside _A , and the second filter 13B has a wavelength outside the center wavelength λ _B and Δλ _B to the left of the center wavelength λ ₀ ′ of the light from the light source 11.

[0042]

[Formula 6] λ _A = λ ₀ ′ + Δλ _A λ _B = λ ₀ ′ −Δλ _B

Since Δλ _A ≠ Δλ _B , the shaded areas P _A 'and P _B ' in FIG. 2B are different from each other. For example, light source 1
When the central wavelength of the light from 1 increases, the light intensity curve moves to the right as a whole, the first area P _A ′ on the right side increases and the second area P _B ′ on the left side decreases. On the contrary, when the central wavelength of the light from the light source 11 becomes smaller, the light intensity curve moves to the left side as a whole, the first area P _A 'on the right side decreases and the second area P _B ' on the left side increases. To do.

Therefore, the output current signals I _A , I _{B of the} two photodetectors 14A, 14B or the two current-voltage converters 15A,
The output voltage signal V _A of 15B, by detecting the increase and decrease of V _B, or the wavelength of light becomes or less increased from the light source 11 is seen. In this case, the output signal ΔV of the subtractor 16 is not zero.

[0045]

[Formula 7] ΔV = V _A −V _B ≠ 0

According to this example, the output signal ΔV of the subtractor 16
Is zero, the wavelength of the light from the light source 11 is in a normal state, and when the output signal ΔV of the subtractor 16 is not zero, the wavelength of the light from the light source 11 is not in a normal state and is displaced. You can see that More specifically, the subtractor 16
Is positive, the wavelength of the light from the light source 11 is larger than in the normal state, and the output signal Δ of the subtractor 16 is
It can be seen that when V is negative, the wavelength of the light from the light source 11 is smaller than in the normal state.

A second example of the wavelength monitor device according to the present invention will be described with reference to FIG. According to this example, the wavelength monitor device includes two filters 13A and 13B arranged along the optical path of light from the light source 11, one light receiver 14, one current-voltage converter 15, a register 17, and a subtractor 18. Have and.

The two filters 13A and 13B are arranged so that they can be alternately arranged in the optical path of the light from the light source 11. The two filters 13A and 13B are shown in FIG.
And a configuration similar to that used in the first example described with reference to FIG. That is, the first filter 13A transmits light having a center wavelength λ _A and a wavelength range d, and the second filter 13B transmits light having a center wavelength λ _B and a wavelength range d.

First, the first filter 13A is arranged. The light transmitted through the first filter 13A is received by the photodetector 14, the current signal I _A from the photodetector 14 is converted into the voltage signal V _A by the current-voltage converter 15, and stored in the register 17. At this time, the register 17 stores the signal corresponding to the first area P _A or P _A ′ shown in FIG.

Next, instead of the first filter 13A, the second filter 13A is used.
The filter 13B is placed. Similarly, the light transmitted through the second filter 13B is received by the light receiver 14,
The current signal I _B from the light receiver 14 is converted into a voltage signal V _B by the current-voltage converter 15 and stored in the register 17. At this time, the second value shown in FIG.
The signal corresponding to the area P _B or P _B 'of

The subtractor 18 outputs the output voltage signal V from the current-voltage converter 15 when the first filter 13A is arranged.
_A is compared with the output voltage signal V _B from the current-voltage converter 15 when the second filter 13B is arranged, that is,
The difference ΔV between the two is calculated.

When the wavelength of the light from the light source 11 is normal, the difference ΔV between the two is zero as shown in the equation (5), but when the wavelength of the light from the light source 11 is not normal, the equation (7) is used. As described above, the difference ΔV between the two does not become zero.

The first example of the wavelength monitor device of the present invention shown in FIG. 1 will be compared with the second example shown in FIG. In the first example, the light transmitted through the two filters 13A and 13B is simultaneously detected by the two light receivers 14A and 14B. Therefore, when the wavelength of the light from the light source 11 changes, the subtractor 16
The output signal at changes accordingly. That is, the light source 11
The change in the wavelength of the light from can be detected in real time. However, it requires branch 12 and also requires two receivers and two current-voltage converters.

On the other hand, in the second example, the branch 12 is not necessary, and the number of photodetectors and current / voltage converters may be one each. However, it is necessary to exchange the two filters 13A and 13B, and a mechanism therefor is required. In addition, the register 17 stores two signals, and the stored two signals are stored.
Two signals need to be calculated. Therefore, the light source 1 is actually
The time when the wavelength of the light from 1 changes and the time when the output from the subtractor 18 changes are different.

An example of the optical fiber gyro according to the present invention will be described with reference to FIG. The optical fiber gyro of this example is
A light source 101, a wavelength monitor device 111 for monitoring the wavelength of light from the light source 101, and a light receiver 10 for converting incident light into a current.
An optical fiber loop 103 formed by winding two and one optical fibers a plurality of times, a polarizer 104, couplers 105 and 106 for combining or splitting light propagating through the optical fiber, and further a current / voltage converter 107. It has a phase modulator 108, a signal generator 109, and a synchronous detector 110.

The optical fiber gyro of this example is different from the conventional optical fiber gyro shown in FIG. 5 in that a wavelength monitor device 111 is additionally provided, and the other configurations are the same. Good. According to this example, the wavelength monitoring device 111 has one end of the first coupler 105, that is,
It is provided at the end opposite to the light source 101.

The wavelength monitor device 111 is the first one shown in FIG.
Or the second example shown in FIG. 3 (excluding the light source 11). The light from the light source 101 is branched by the first coupler 105, one of which is guided to the polarizer 104 and the other of which is guided to the wavelength monitor device 111.

The output signal of the wavelength monitor device 111 is fed back to the light source 101 via a control circuit (not shown). In this way, when the wavelength λ of the light from the light source 101 changes, the control signal is fed back to the light source 101, so that the wavelength λ of the light from the light source 101 can always be kept constant.

Further, the value of the wavelength λ of the light from the light source 101 used in the equation of Equation 1 is corrected by the output signal of the wavelength monitor device 111, thereby correcting the gyro signal (Ω) and eliminating the error. can do.

Although the embodiments of the present invention have been described above in detail, those skilled in the art will understand that the present invention is not limited to the above-mentioned embodiments and various other configurations can be adopted without departing from the gist of the present invention. Easy to understand.

[0061]

According to the wavelength monitor device of the present invention, there is an advantage that the wavelength variation of the light source can be detected by a device having a simple structure.

According to the optical fiber gyro of the present invention, the wavelength monitor of the light source is provided to observe the fluctuation of the wavelength, and when the wavelength fluctuates, the control signal is supplied to the light source. Therefore, the wavelength of the light source is constant. It is possible to provide a high-accuracy gyro signal that is maintained at.

According to the optical fiber gyro of the present invention, the wavelength monitor is provided in the light source to observe the fluctuation of the wavelength, and the gyro signal can be corrected according to the fluctuation of the wavelength, so that a highly accurate gyro signal is provided. There is an advantage that can be.

[Brief description of drawings]

FIG. 1 is a diagram showing a first example of a wavelength monitor device of the present invention.

FIG. 2 is an explanatory diagram for explaining the operation of the wavelength monitor device of the present invention.

FIG. 3 is a diagram showing a second example of the wavelength monitor device of the present invention.

FIG. 4 is a diagram showing an example of an optical fiber gyro of the present invention.

FIG. 5 is a diagram showing an example of a conventional optical fiber gyro.

[Explanation of symbols]

 11 light source 12 branch 13A, 13B filter 14, 14A, 14B light receiver 15, 15A, 15B current-voltage converter 16 subtractor 17 register 18 subtractor 101 light source 102 light receiver 103 optical fiber loop 104 polarizer 105, 106 coupler 107 current Voltage converter 108, 108 'Phase modulator 109 Signal generator 110 Synchronous detector 111 Wavelength monitor device

Claims (12)

[Claims] In the wavelength monitoring apparatus for detecting variations in wavelength of the light from 1. A center wavelength lambda light source having a substantially symmetrical light intensity distribution centered on _0, the central wavelength lambda ₀ of the light from the light source Fluctuations in the wavelength of the light from the light source are provided by providing two filters that have a symmetrical wavelength λ ₀ ± Δλ as the central wavelength and transmit light with a wavelength width d, and compare the amounts of light transmitted through the two filters. A wavelength monitoring device configured to detect the. 2. The wavelength monitor device according to claim 1, wherein the light from the light source is branched into two lights, and the two filters are arranged along an optical path of the two lights from the branch. A wavelength monitoring device characterized in that 3. The wavelength monitor device according to claim 1, wherein the two filters are arranged so as to be exchangeable with each other along an optical path of light from the light source. 4. The wavelength monitor device according to claim 1, 2 or 3, wherein the light transmitted through the two filters is received by a photoreceiver, and a current signal from the photoreceiver is converted into a voltage signal to obtain the light quantity. Are compared with each other. 5. The wavelength monitor device according to claim 4, wherein the comparison of the light amounts of the light transmitted through the two filters is performed by subtracting the voltage signal. 6. A light source, a light receiver, two couplers for synthesizing and splitting light, and an optical fiber loop, wherein the light from the light source is split into two lights by a second coupler, and the two lights are The optical fiber loops propagate in opposite directions and are combined by the second coupler to generate interference light, and the interference light is received by the light receiver via the first coupler. The optical fiber gyro is provided with a wavelength monitor device for detecting a variation in wavelength of light from the light source, the light source is connected to one end of the first coupler, and the other end of the first coupler is connected to the other end. An optical fiber gyro, to which the above wavelength monitor device is connected. 7. The optical fiber gyro according to claim 6, wherein the wavelength monitor device supplies a control signal to the light source when the wavelength monitor detects variation in the wavelength of the light from the light source, and the wavelength of the light from the light source is always constant. An optical fiber gyro characterized by being configured to be held constant. 8. The optical fiber gyro according to claim 6 or 7, wherein when the wavelength monitor detects a variation in the wavelength of light from the light source, the gyro signal is corrected according to the variation in the detected wavelength. An optical fiber gyro characterized by being configured as follows. 9. The optical fiber gyro according to claim 6, 7 or 8, wherein the light from said light source has a light intensity distribution substantially symmetrical with respect to a central wavelength λ ₀ , and said wavelength monitor device comprises said light source. symmetrical wavelength lambda ₀ in the central wavelength lambda ₀ of the light from the
It is configured to include two filters having a central wavelength of ± Δλ and transmitting a light having a wavelength width d, and detecting variations in the wavelength of the light from the light source by comparing the light amounts of the light transmitted through the two filters. An optical fiber gyro characterized by being used. 10. The optical fiber gyro according to claim 9, wherein the light from the light source is branched into two lights, and the two filters are arranged along optical paths of the two lights from the branches. An optical fiber gyro characterized by the fact that 11. The optical fiber gyro according to claim 9, wherein the two filters are exchangeably arranged along an optical path of light from the light source. 12. The optical fiber gyro according to claim 8, 9, 10 or 11, wherein the light transmitted through the two filters is received by a light receiver, and a current signal from the light receiver is converted into a voltage signal. An optical fiber gyro characterized in that the amounts of light are compared.