JP2002131022A - Optical fiber sensing system and measuring method for wavelength of laser light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber sensing system and a measuring method for wavelength of laser light capable of measuring with high accuracy and high multiplexing. SOLUTION: An optical fiber sensing system 101 is composed of an excitation light source 111, an optical circulator 115, a wavelength measuring instrument 117, an optical fiber 119, more than one optical coupler C1, C2,... and more than one FBG laser sensor LS101, LS102,.... Each FBG laser sensor LS101, LS102,... is branch-connected to the fiber 119 by the coupler C1, C2,.... Each FBG laser sensor LS101, LS102,... have parallel relation to each other. Then, occurrences of multiple reflected lights between each FBG laser sensor LS101, LS102,... are suppressed and a S/N ratio is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber sensor system and a method for measuring the wavelength of laser light.

[0002]

2. Description of the Related Art An optical fiber sensor has high reliability with respect to electromagnetic induction because a sensor section is not powered.
Further, according to the optical fiber sensor, long-distance and large-scale multi-point measurement can be performed since optical transmission with small loss is used.

In recent years, while various optical fiber sensors have been put into practical use, WDM (Wavelength-Divisio) for optical communication has been developed.
n FBG (Fiber Bragg Grating) developed as a Multiplexing (Wavelength Division Multiplexing) device has attracted attention as a sensor device because of its wavelength selectivity. Research and development are being actively pursued.

References: Alan D. Kersey et al., "Fiber
Grating Sensors ", JOURNAL OF LIGHTWAVE TECHNOLOGY, V
OL.15, NO.8, AUGUST 1997, pp1442-1461.

An optical fiber sensor system configured using an FBG sensor detects a physical quantity to be measured (such as three-dimensional distortion information of an object to be measured) from a shift amount of an FBG reflection wavelength. This optical fiber sensor system is classified into the following two from the viewpoint of the operation method.

A first optical fiber sensor system is shown in FIG.
As shown in FIG. 1, the optical system includes a broadband light source 1, an optical circulator 5, a wavelength measuring device 7, an optical fiber 9, and a plurality of FBG sensors S1, S2, S3,. The light (wavelength width Δλ) emitted from the broadband light source 1 is transmitted along a plurality of F
Are incident on the BG sensors S1, S2, S3,... The reflected light from each of the FBG sensors S1, S2, S3,... Is guided to the wavelength measuring device 7 via the optical circulator 5, where the peak wavelength of the reflected light is measured. In this manner, the strain amount of the measured object at the place where each of the FBG sensors S1, S2, S3,... Is arranged is detected.

A second optical fiber sensor system is shown in FIG.
As shown in the figure, tunable laser (wavelength variable light source) 1
1, an optical circulator 5, a power meter 17, an optical fiber 9, and a plurality of FBG sensors S1, S2, S3,.
・ ・ It is composed of A plurality of FBG sensors S1, S arranged along the optical fiber 9 and in series with each other
2, S3,..., The wavelength-swept light is given from the tunable laser 11. Each FBG sensor S1, S
, S3,...
Through the optical power meter 17. The wavelength of the reflected light is calculated from the arrival time of the reflected light, and from this calculation result, the amount of distortion of the measured object at the location where each of the FBG sensors S1, S2, S3,.

An FBG laser sensor as an application example of the FBG sensor is also being developed. FIG. 7 shows an example of a conventional optical fiber sensor system having an FBG laser sensor.
Shown in This optical fiber sensor system includes an excitation light source 2
1, optical circulator 5, wavelength measuring device 7, optical fiber 9, and a plurality of FBG laser sensors LS1, LS2,
...

The FBG laser sensors LS1 and LS2 are a pair of FBGs 31 and 32 and an ED inserted between them.
F (Er-Doped Fiber) 33
It is composed of The FBG laser sensor is 1.48
When excitation light in the μm band or the 0.98 μm band is incident, laser oscillation occurs at the reflection wavelength of the FBG. And the FBG laser sensor is
It is expected to be a new strain detection sensor with improved wavelength resolution and optical power efficiency compared to sensors.

[0010]

SUMMARY OF THE INVENTION However, the FBG
According to the conventional optical fiber sensor system including the sensor, the wavelength resolution is limited by the reflection band (about 0.1 nm) of the FBG.

In the case of the optical fiber sensor system using the broadband light source 1 shown in FIG. 5, although the advantages are obtained in that the configuration is simple and the mounting is easy, the optical power efficiency is high for the FBG sensors S1, S2,.・ Because it decreases in inverse proportion to the dynamic range of
.. Are not suitable for large-scale strain measurement of a measured object that requires a long distance to the BG sensors S1, S2, S3,. When WDM is used for optical transmission, the dynamic range for all channels is limited by the resolution of the wavelength measurement device 7, and thus it is difficult to perform large multiplex measurement.

On the other hand, the tunable laser 1 shown in FIG.
In the case of the optical fiber sensor system using No. 1, performance for long-distance transmission of light is improved. However,
It is necessary to accurately grasp the propagation time of light. In addition, when performing high-accuracy measurement, the measurement time becomes long according to the wavelength sweep time of the laser beam and the time resolution of the measurement system.

Further, as a problem common to the conventional optical fiber sensor systems shown in FIGS.
It is difficult to apply me-Division Multiplexing (time division multiplexing). This is the FBG shown in FIG.
This also corresponds to an optical fiber sensor system equipped with a laser sensor, and it was necessary to solve such a problem in order to realize a large-scale optical fiber sensor system.

The present invention has been made in view of the above problems, and has as its object to provide an optical fiber sensor system capable of high-accuracy measurement and large-scale multiplex measurement, and a method of measuring the wavelength of laser light. Is to do.

[0015]

In order to solve the above problems, an optical fiber sensor system according to the present invention is provided. The optical fiber sensor system includes a first optical transmission path for transmitting pumping light, optical branching units arranged at a plurality of locations in the first optical transmission path, and connected to each optical branching unit to receive the pumping light and distort the optical fiber. A plurality of fiber grating type laser sensors for oscillating and outputting laser light having a wavelength corresponding to the amount are provided. According to such a configuration, multiple reflection of laser light between laser sensors is prevented. The provision of the oscillation wavelength detector for measuring the wavelength of the laser light output from each laser sensor as described in claim 2 enables the measurement of the wavelength of the laser light having a small error.

Further, it is preferable that a second optical transmission path connected to each laser sensor and guiding the laser light output from each laser sensor to the oscillation wavelength detector is provided. By providing the second optical transmission path, the transmission path of the excitation light and the laser light is completely separated, so that the laser light wavelength measurement can be performed with high accuracy. If the first optical transmission line and the second optical transmission line are selected according to the wavelengths of the excitation light and the laser light, respectively, long-distance transmission of the excitation light and the laser light becomes possible.

According to a fourth aspect of the present invention, a pulsed excitation light generating section for generating a pulsed excitation light and a laser light group including the pulsed laser light output from each laser sensor are received.
By providing a laser beam separation unit for separating each pulse laser beam from the laser beam group, TDM transmission of the excitation light and the laser beam becomes possible.

In the optical fiber sensor system according to the present invention, the transmission of the pulsed excitation light is delayed so that the pulsed excitation light is sequentially supplied to each laser sensor with a predetermined time difference. It is characterized by having an excitation light transmission delay unit. For example, even when the interval between the branching portions is short, the provision of the pumping light transmission delay portion makes it possible to cause a stepwise difference in the arrival timing of the pumping light to each laser sensor. That is,
TDM transmission can be performed even when the interval between the branch portions is short.

The optical fiber sensor system according to any one of claims 6 to 12 has a characteristic oscillation wavelength detector.

An oscillation wavelength detector according to a sixth aspect of the present invention comprises: an interferometer for receiving laser light output from each laser sensor;
A modulator that applies optical path difference modulation to the interferometer, an optical / electrical converter that converts the interference light obtained from the laser beam by the interferometer into an electrical interference signal, and a basic that removes the fundamental wavelength component from the interference signal It has a wavelength component removing unit, a fringe measuring unit that performs fringe measurement on the interference signal from which the fundamental wavelength component has been removed, and a wavelength calculating unit that calculates the wavelength of the laser beam according to the number of fringes obtained by the fringe measuring unit. It is characterized by: According to such a configuration, it is possible to measure the wavelength of the laser beam with high accuracy. It is preferable that the fringe measurement unit has a differentiation processing unit that differentiates the interference signal. By performing fringe measurement on the interference signal and a differential signal obtained by differentiating the interference signal, the resolution of laser wavelength measurement can be doubled. Further, by providing a fringe measurement unit for fringe-measuring the ²ⁿ component of the interference signal, the resolution of laser wavelength measurement can be increased to ²ⁿ times.

An oscillation wavelength detector according to a ninth aspect includes an interferometer that receives laser light output from each laser sensor;
A modulator that applies optical path difference modulation to the interferometer, an optical / electrical converter that converts the interference light obtained from the laser beam by the interferometer into an electrical interference signal, and a basic that removes the fundamental wavelength component from the interference signal A wavelength component removing unit, a frequency analyzing unit that performs frequency analysis on the interference signal from which the fundamental wavelength component has been removed, and a wavelength calculating unit that calculates the wavelength of the laser beam from the analysis result obtained by the frequency analyzing unit. It is characterized by. In addition, it is preferable that the frequency analysis unit includes a fast Fourier transform unit. According to this configuration, WDM channel separation and laser beam wavelength detection can be performed simultaneously.

An oscillation wavelength detector according to claim 11 is an interferometer that receives laser light output from each laser sensor, a modulator that applies optical path difference modulation to the interferometer, and the interferometer detects the laser light from the laser light. An optical / electrical converter for converting the obtained interference light into an electrical interference signal, a fundamental wavelength component remover for removing the fundamental wavelength component from the interference signal, and an interference signal and a fundamental wavelength component from which the fundamental wavelength component has been removed. A calculation unit for performing a calculation using the primary differential signal of the removed interference signal and a secondary differential signal of the interference signal from which the fundamental wavelength component has been removed, and the wavelength of the laser beam from the calculation result obtained in the calculation unit And a wavelength calculating unit for calculating the wavelength. According to this configuration, the need for fringe measurement is eliminated, and a measurement result with a smaller error can be obtained.

According to a twelfth aspect of the present invention, an oscillation wavelength detector includes an interferometer that receives laser light output from each laser sensor, a modulator that performs optical path difference modulation on the interferometer, and an interferometer that detects the laser light. An optical / electrical converter for converting the obtained interference light into an electrical interference signal, a fundamental wavelength component remover for removing the fundamental wavelength component from the interference signal, and an acos operation on the interference signal from which the fundamental wavelength component has been removed And execute
It is characterized by having an acos operation unit for performing phase demodulation and a wavelength calculation unit for calculating the wavelength of laser light from the operation result obtained in the acos operation unit. According to this configuration, the resolution of the wavelength measurement of the laser light is further improved.

According to the thirteenth to sixteenth aspects, there is provided a method for measuring the wavelength of laser light output from a fiber grating type laser sensor.

According to a thirteenth aspect of the present invention, there is provided a method for measuring a laser beam, comprising the steps of: generating an interference beam from the laser beam using an interferometer to which optical path difference modulation is applied; and converting the interference beam into an electrical interference signal. Optical / electrical conversion step, a fundamental wavelength component removing step of removing the fundamental wavelength component from the interference signal, a fringe measuring step of performing fringe measurement on the interference signal from which the fundamental wavelength component has been removed, and a fringe measuring step. A wavelength calculating step of calculating the wavelength of the laser beam according to the number of fringes. According to this measuring method, the wavelength of the laser beam can be measured with high accuracy.

According to a fourteenth aspect of the present invention, there is provided a method for measuring a wavelength of a laser beam, comprising the steps of: generating an interference beam from the laser beam using an interferometer to which optical path difference modulation is applied; An optical / electrical conversion step of converting, a fundamental wavelength component removing step of removing the fundamental wavelength component from the interference signal,
It is characterized by including a frequency analysis step of performing a frequency analysis on the interference signal from which the fundamental wavelength component has been removed, and a wavelength calculation step of calculating the wavelength of the laser beam from the analysis result obtained in the frequency analysis step. According to this measurement method, WDM channel separation and laser beam wavelength detection can be performed simultaneously.

According to a fifteenth aspect of the present invention, there is provided a method for measuring the wavelength of a laser beam, comprising the steps of: generating an interference beam from the laser beam using an interferometer to which optical path difference modulation is applied; An optical / electrical conversion step of converting, a fundamental wavelength component removing step of removing the fundamental wavelength component from the interference signal,
An operation step of executing an operation using an interference signal from which the fundamental wavelength component has been removed, a first derivative signal of the interference signal from which the fundamental wavelength component has been removed, and a second derivative signal of the interference signal from which the fundamental wavelength component has been removed; And a wavelength calculating step of calculating the wavelength of the laser beam from the calculation result obtained in the calculating step. According to this measuring method, the need for fringe measurement is eliminated, and a measurement result with a smaller error can be obtained.

According to another aspect of the present invention, there is provided a method for measuring the wavelength of a laser beam, comprising the steps of: generating an interference beam from the laser beam using an interferometer to which optical path difference modulation is applied; An optical / electrical conversion step of converting, a fundamental wavelength component removing step of removing the fundamental wavelength component from the interference signal,
An acos operation for performing an acos operation on the interference signal from which the fundamental wavelength component has been removed and performing phase demodulation;
a wavelength calculating step of calculating the wavelength of the laser beam from the calculation result obtained in the os calculating step. According to this measuring method, the resolution of the wavelength measurement of the laser beam is further improved.

[0029]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
Preferred embodiments of an optical fiber sensor system and a laser beam wavelength measuring method according to the present invention will be described in detail. In the following description and the accompanying drawings, components having substantially the same functions and configurations are denoted by the same reference numerals, and redundant description is omitted.

[First Embodiment] FIG. 1 shows an optical fiber sensor system 101 according to a first embodiment of the present invention.
Shown in The optical fiber sensor system 101 includes an excitation light source 111, an optical circulator 115, and a wavelength measurement device 1.
17, an optical fiber 119, a plurality of optical couplers C1, C2,
, And a plurality of FBG laser sensors LS101,
LS102,...

Each of the FBG laser sensors LS101, LS1
Are branched and connected to the optical fiber 119 by optical couplers C1, C2,. Each of the FBG laser sensors LS101, LS102,.
... are in a parallel relationship with each other.

The excitation light source 111 outputs excitation light in the 1.48 μm band. This excitation light is transmitted to optical couplers C1, C2,.
Are guided to each channel, that is, to each FBG laser sensor LS101, LS102,. The pump light is selected in consideration of the transmission loss in the transmission line (optical fiber 119). For example, when a 1.3 μm single mode fiber is used as a transmission line,
It is preferable to select the 1.48 μm band instead of the 0.98 μm band.

Each FBG laser sensor LS101, LS1
.. Are composed of an FBG 121, an EDF 123, and a mirror 125. Each of the FBG laser sensors LS101, LS102,... Has a sensing mechanism in which a distortion amount proportional to an external signal is applied to the FBG121. Note that the external signal referred to here is
Each of the laser sensors LS101, LS102,... Is provided with a physical quantity (strain of the measured object,
Or the temperature of the measured object).

Each FBG laser sensor LS101, LS1
02,... Indicate that F
Laser oscillation occurs at the reflection wavelength of BG121.

The wavelength measuring device 117 receives the laser beam output from each of the FBG laser sensors LS101, LS102,... Via the optical circulator 115 and measures the wavelength. An external signal is detected from the measurement result.

In the optical fiber sensor system 101 according to the first embodiment, general wavelength separation means (wavelength filters and the like) required for separating WDM signals are provided.
It is incorporated between the optical circulator 115 and the wavelength measuring device 117 (not shown).

The operation of the optical fiber sensor system 101 according to the first embodiment configured as described above will be described.

Each FBG laser sensor LS101, LS1
When the FBG 121 belonging to 02,... Receives a distortion amount of δε by an external signal, a wavelength shift given by Expression 1 occurs in the pump light.

[0039]

(Equation 1)

Here, λ represents the basic reflection wavelength, and δλ represents the shift amount of the reflection wavelength. For example, when the pumping light in the 1.55 μm band is used, the strain of 1% which is a practical limit value is F
When applied to the BG 121, a wavelength shift of about 12 nm occurs in the excitation light.

EDF between FBG 121 and mirror 125
The pumping light is sent to the EDF 123 and the oscillation conditions (Er doping density, pumping light power, resonator length, F
When the reflectance of the BG 121, the reflectance of the mirror 125, and the like are satisfied, laser oscillation occurs at the reflection wavelength of the FBG 121.

The wavelength measuring device 117 calculates each FB from the oscillation wavelength spectrum obtained through the optical circulator 115.
The oscillation wavelength in each of the G laser sensors LS101, LS102,... Is measured. Then, a measured physical quantity is obtained from the measurement result.

As described above, according to the optical fiber sensor system 101 according to the first embodiment, each of the FBG laser sensors LS101, LS102,. 119 and are independent of each other. Therefore, each F
The generation of multiple reflected light between the BG laser sensors LS101, LS102,... Is suppressed, and the S / N ratio is improved.

Further, according to the optical fiber sensor system 101 according to the first embodiment, it is possible to arrange a plurality of FBG laser sensors that oscillate at the same wavelength. Therefore, it is easy to construct a TDM system as in the third embodiment described later.

[Second Embodiment] FIG. 2 shows an optical fiber sensor system 201 according to a second embodiment of the present invention.
Shown in The optical fiber sensor system 201 includes an excitation light source 211, a wavelength measurement device 117, an optical fiber 119 for transmitting excitation light, an optical fiber 219 for transmitting oscillation light, and a plurality of optical couplers C1, C2,..., C11, C12. , ...
.. and a plurality of FBG laser sensors LS201, LS
.., 202.

Each FBG laser sensor LS201, LS2
.. Are connected to the optical fiber 119 by optical couplers C1, C2,.
Are connected to the optical fiber 219 by 2,.
Then, each FBG laser sensor LS201, LS20
Are in a mutually parallel relationship. That is, F
The BG laser sensors LS201, LS202,.
The optical fiber 119 and the optical fiber 219 form a ladder shape.

Each FBG laser sensor LS201, LS2
02,... Are composed of a pair of FBGs 221 and 222 and an Er-Yb (erbium-ytterbium) -doped fiber 223 inserted between them. F
Each of the BGs 221 and 222 may be a narrow band FBG that receives a distortion amount proportional to an external signal, or one may be a narrow band FBG and the other may be a fixed wide band FBG.
Here, the narrow band FBG is an FB that receives distortion in a narrow band.
G, and the fixed broadband FBG is an FBG that is not distorted in a wide band. And the latter functions as a half mirror.

The excitation light source 211 outputs excitation light in the 1 μm band.

The optical fiber 119 for transmitting the pump light is 1 μm
Optical fiber 21 for transmission of oscillation light
Reference numeral 9 denotes a 1.55 μm band transmission fiber.

The operation of the optical fiber sensor system 201 according to the second embodiment configured as described above will be described.

First, the pumping light source 211 outputs 1 μm band pumping light suitable for the Er-Yb doped fiber 223.

The FBG laser sensors LS201, LS202,
.. Indicate that the FBG2
Laser oscillation occurs at the reflection wavelengths 21 and 222. Here, the amount of distortion proportional to the external signal is applied to each of the FBG laser sensors LS201, 202,.
When it is added to 222, a wavelength shift occurs in the laser light.

Each of the oscillated laser sensors LS201, LS20
The laser light output from 2,... Reaches the wavelength measuring device 117 via the optical fiber 219 for transmitting the sensor signal. The wavelength measuring device 117 calculates each of the FBG laser sensors LS201, LS202,.
Measure the oscillation wavelength at. Then, a measured physical quantity is obtained from the measurement result.

As described above, according to the optical fiber sensor system 201 according to the second embodiment, as in the optical fiber sensor system 101 according to the first embodiment, generation of multiple reflected light is suppressed. , S / N ratio is improved.

Further, since the optical fiber 119 for transmitting the pumping light and the optical fiber 219 for transmitting the oscillating light are provided, the transmission loss of the pumping light and the oscillating light is reduced, and the scale of the multi-point measurement is further expanded. Becomes possible.

Further, in the optical fiber sensor system 201 according to the second embodiment, an Er-Yb-doped fiber 223 is employed as a resonator constituting each of the FBG laser sensors LS201, LS202,. Therefore, the gain of each resonator increases. For this reason, the oscillation power of each of the FBG laser sensors LS201, LS202,... Increases, and single-mode oscillation becomes easy.

[Third Embodiment] An optical fiber sensor system 301 according to a third embodiment of the present invention is shown in FIG.
Shown in The optical fiber sensor system 301 includes an excitation light source 311, an optical circulator 115, and a wavelength measurement device 1.
17, an optical switch (pulse pumping light generator) 313, a time division demultiplexer 315, a plurality of delay optical fibers 319-1,
319-2,..., A plurality of optical couplers C1, C2,.
.. and a plurality of FBG laser sensors LS301, LS
., 302.

Each of the FBG laser sensors LS301, LS3
Are connected to the delay optical fibers 319-1, 319-2,... By optical couplers C1, C2,. Then, the FBG laser sensor LS301,
LS302,... Are in a mutually parallel relationship.

The delay optical fibers 319-1, 319-2,
Have a function of delaying the light to be transmitted. In the optical fiber sensor system 301, the optical transmission between the optical couplers C1, C2,.

The optical switch 313 performs a switching operation when a trigger signal 317 is input. The light emitted from the excitation light source 311 is converted by the optical switch 313 into pulse light having a predetermined pulse width and frequency. This pulse light is applied to each FBG laser sensor LS30
, LS302,... Are sequentially input.

Each FB to which pulsed light is input as excitation light
The G laser sensors LS301, LS302,... Perform pulse oscillation. The pulse light output from the optical switch 313 passes through each of the delay optical fibers 319-1, 319-2,.
, LS302,... Are sequentially input with a predetermined time difference. Therefore, each FBG laser sensor L
The oscillation light output from S301, LS302,... Forms a pulse train.

The oscillated light is guided to the time division demultiplexer 315 via the optical circulator 115. The time-division separation device 315 time-division-divides the oscillation light composed of the pulse train in synchronization with the trigger signal 317. The wavelength of the oscillation light that has been time-division separated is measured by the wavelength measurement device 117. Then, a measured physical quantity is obtained from the measurement result.

As described above, according to the optical fiber sensor system 301 according to the third embodiment, the optical fiber sensor system 101 according to the first and second embodiments,
The same effect as 201 is obtained, and TDM transmission of pump light and oscillation light is realized.

The arrangement of the FBG laser sensors LS301, LS302,... In the optical fiber sensor system 301 according to the third embodiment is the same as that of the FBG laser in the optical fiber sensor system 101 according to the first embodiment. The sensors LS101, LS102,.
, Or the other arrangement of the FBG laser sensors LS201, LS202,... In the optical fiber sensor system 201 according to the second embodiment.

[Fourth Embodiment] An optical fiber sensor system 401 according to a fourth embodiment of the present invention is shown in FIG.
Shown in The optical fiber sensor system 401 has the first
Optical sensor system 101 according to the embodiment
, A wavelength measuring device 117 as an oscillation wavelength detecting unit
Are receiving interferometer 411, optical / electrical converter 413, analog / digital converter 415, and demodulation processor 4
17 is replaced with a configuration.

The reception interferometer 411 is a FRM (Faraday
Michelson with Rotator Mirror (419)
n) Interferometer. According to the receiving interferometer 411,
The occurrence of polarization fading is prevented. A piezoelectric element 421 is attached to the arm of the receiving interferometer 411, and a triangular wave (including a sawtooth wave) is generated for the oscillation light output from each FBG laser sensor (not shown).
Is applied.

The interference signal obtained by the receiving interferometer 411 is converted into an electric signal by the optical / electrical converter 413, further converted into a digital signal by the analog / digital converter 415, and sent to the demodulation processing device (general-purpose computer) 417. It is captured. Here, the receiving interferometer 41
1 is multiplied by the interference signal for the fundamental wavelength to remove the fundamental wavelength component. Then, the demodulation processing device 417 performs fringe measurement in the optical path difference modulation cycle of the reception interferometer 411, and calculates the oscillation light wavelength of each FBG laser sensor from the obtained fringe number.

Next, the operation of the optical fiber sensor system 401 according to the fourth embodiment, in particular, the operation of the oscillation wavelength detector will be described in detail.

A triangular wave modulation is applied to the optical path difference of the receiving interferometer 411 by the piezoelectric element 421. The optical path difference is
This corresponds to the difference between the lengths (optical paths) of the two arms of the receiving interferometer 411. The length of one arm is changed by the piezoelectric element 421 and the length of the other arm is fixed, thereby modulating the optical path difference. This is called a push-zero operation. In addition, push-pull (push-pull) that applies opposite-phase modulation to each of the two arms
-pull) operation also modulates the optical path difference. In this case, twice the modulation is added to the optical path difference compared to the push-zero operation.

When the light of the oscillation wavelength λ ₀ + λ _FBG is output from the FBG laser sensor and made incident on the receiving interferometer 411, the interference signal obtained by the receiving interferometer 411 is expressed by the following equation (2).

[0071]

(Equation 2)

Here, A and B are constants depending on the amount of incident light, n is the effective refractive index of the fiber core (about 1.468),
_dΔ is the optical path difference modulation amount in the sampling cycle of the analog / digital converter 415, t is the sampling time of the analog / digital converter 415, and ψ is the initial phase. Ω ₀ and ω _λ represent the angular frequency with respect to the fundamental wavelength and the angular frequency with respect to the wavelength shift amount, respectively.

The oscillation light of the FBG laser sensor is λ ₀ to
Includes components of 1.55 μm, λ _FBG <12 nm. Therefore, ω _λ <0.01 × ω ₀ holds. In order to accurately measure an interference signal obtained from the oscillation light of the FBG laser sensor, it is necessary to remove a signal having a fundamental wavelength of 1.55 μm. Therefore, an interference signal obtained from the fundamental frequency is prepared in advance, and the ω ₀ component is removed by multiplying the two as shown in Expression 3. This ensures a sufficient dynamic range. Note that in Equation 3, for convenience, omitting the DC term, by reversing the sign of omega _lambda.

[0074]

(Equation 3)

Here, I _S and I _R represent an interference signal obtained from the oscillation light of the FBG laser sensor and a reference interference signal prepared in advance, respectively. ψ
_S and ψ _R are these initial phases, and ψ ₊ = _{Ｓ S} +
ψ _R, ψ _- a = ψ _S -ψ _R. The second term on the right-hand side of the third row of Equation 3 is removed by an appropriate low-pass filter,
The formula on the fourth line is obtained.

Instead of I _R , an interference signal I _R ′ obtained from the output light of a reference sensor (a sensor in which the wavelength of the output light shifts by an external temperature change) may be used. This makes it possible to compensate for an error due to a slight change in temperature applied to the FBG laser sensor as shown in Expression 4. Note that, in Equation 4, similarly to Equation 3, D
The C term is omitted, and the sign of ω _λ is inverted.

[0077]

(Equation 4)

Here, I _S ′ and I _R ′ are FBGs, respectively.
4 shows an interference signal obtained from the oscillation light of the laser sensor and an interference signal obtained from the oscillation light of the reference (temperature compensation) FBG laser sensor. ω _λ and ω _T represent a wavelength shift amount due to a measured physical quantity and a wavelength shift amount due to a temperature change, respectively.

Using the equation (3) or (4), the optical path difference modulation
Oscillation wavelength λ from the number of fringes in the period_FBGCalculate
You. One cycle of the optical path difference modulation by the triangular wave is t₀As this
Counts the center cross point of the interference signal in one cycle
And the oscillation wavelength λ _FBGIs calculated. What
In Equation 5, fringe in one cycle of optical path difference modulation
The number is represented by m.

[0080]

(Equation 5)

By adding the following auxiliary processing, the resolution of fringe measurement is further improved.

(1) The differential component of the interference signal has a phase of π / 2.
Therefore, the fringe measurement of both the interference signal and its differential signal (Equation 6) results in a measurement interval of π / 2.
Becomes That is, the resolution of the finally obtained oscillation wavelength λ _FBG is doubled.

[0083]

(Equation 6)

(2) When the fringe measurement is performed on the 2 ⁿ component of the interference signal, the fringe measurement interval becomes π / 2 ⁿ based on the double angle formula (Equation 7). That is, the resolution of the oscillation wavelength lambda _{FB G} finally obtained is improved to 2 ⁿ times.

[0085]

(Equation 7)

As described above, according to the optical fiber sensor system 401 according to the fourth embodiment, similarly to the optical fiber sensor system 301 according to the third embodiment, TDM transmission of pump light and oscillation light is performed. Is realized.

Here, the analog / digital converter 4
The digital processing of the interference wave taken into the demodulation processing device 417 from No. 15 has been described using Expressions 3 to 7. Instead, the oscillation wavelength λ _{FBG of the} FBG laser sensor is obtained using the following three methods. Is also possible.

First, there is a method of obtaining the oscillation wavelength λ _FBG by analyzing the frequency of the interference signal represented by the equation 3 or 4 using FFT (Fast Fourier Transform) and detecting the peak frequency. .

According to the first method, it is not necessary to separate the WDM-transmitted interference signal by the demultiplexing coupler.
WDM separation is performed simultaneously with signal demodulation.

In the second method, as shown in Expression 8, the first derivative and second derivative are performed on the interference signal represented by Expression 3 or 4, and three components including the interference signal before differentiation are obtained from the three components. The _{purpose is} to obtain the oscillation wavelength λ _FBG .

[0091]

(Equation 8)

When demodulation is performed using the second method, the fringe measurement is omitted, so that an error due to a fringe count error is prevented from being included in the oscillation wavelength λ _FBG . Further, according to the second method, compared to the first method of measuring the peak frequency using FFT,
The oscillation wavelength λ _FBG can be obtained with high resolution.

The third method is to apply an acos (arc cosine) process to the interference signal represented by Expression 3 or 4 as shown in Expression 9 and to perform a connection (unwrapping) of the phase 2π. Is used to calculate the phase change. Unwrapping is a technique used to determine the value of φ when, for example, cos φ = 1 is obtained. That is, if cos φ = 1 is obtained, the value of φ is 0
Or 2π to determine if
The value of φ is determined with reference to the value immediately before osφ = 1. Here, the oscillation wavelength λ _FBG is obtained by performing an inverse calculation from the total phase change amount in the period of the optical path difference modulation.

[0094]

(Equation 9)

According to the third method, the oscillation wavelength λ can be obtained at a higher resolution than in the case where fringe measurement is performed.
_FBG can be obtained.

Incidentally, the receiving interferometer 41 provided in the optical fiber sensor system 401 according to the fourth embodiment.
1 is preferably a Michelson interferometer with an FRM 419 as described above, but may be replaced with a normal Michelson interferometer with a mirror or a Mach-Zehnder interferometer. However, it is necessary to adopt a polarization diversity system, adjust retardation, and the like so that polarization fading does not occur.

The optical fiber sensor system 401 according to the fourth embodiment includes an analog / digital converter 415, and the interference waveform data obtained here is digitally processed by a demodulation processor 417. However, this function can be realized by an analog circuit.

Although the receiving interferometer 411 is described as performing optical path difference modulation by the piezoelectric element 421, a magnetostrictive material may be employed instead of the piezoelectric element 421.

The optical fiber sensor system 401 according to the fourth embodiment is compatible with both TDM transmission and WDM transmission, and has an effect that the demodulation processing time is short in any transmission method. .

Although the preferred embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to such embodiments. It is clear that a person skilled in the art can conceive various changes or modifications within the scope of the technical idea described in the claims, and those modifications naturally fall within the technical scope of the present invention. It is understood to belong.

For example, in the optical fiber sensor system 101 according to the first embodiment, each of the FBG laser sensors LS101, LS102,.
However, it is also possible to adopt FBG or FRM instead.

In the optical fiber sensor system 101 according to the first embodiment, each FBG laser sensor LS
, 101, LS102,... Are equipped with the EDF 123, but other rare earth doped fibers can be employed instead. Similarly, in the optical fiber sensor system 201 according to the second embodiment, each FB
G laser sensors LS201, LS202,.
Although the r-Yb-doped fiber 223 is provided, another rare-earth-doped fiber may be employed instead. However, it is necessary to adjust the band of the excitation light according to the rare-earth doped fiber.

In the optical fiber sensor systems 101, 201 and 301 according to the first, second and third embodiments,
It is preferable to arrange a wavelength filter in a stage preceding the wavelength measuring device 117. As a result, the S /
The N ratio is further improved.

[0104]

As described above, according to the optical fiber sensor system and the method for measuring the wavelength of laser light according to the present invention, high precision measurement and large multiplex measurement can be performed. Also, the measurement time is greatly reduced as compared with the conventional case.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an optical fiber sensor system according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an optical fiber sensor system according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of an optical fiber sensor system according to a third embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an optical fiber sensor system according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a conventional optical fiber sensor system (part 1).

FIG. 6 is a block diagram showing a configuration of a conventional optical fiber sensor system (part 2).

FIG. 7 is a block diagram showing a configuration of a conventional optical fiber sensor system (part 3).

[Explanation of symbols]

 101: Optical fiber sensor system 111: Pump light source 115: Optical circulator 117: Wavelength measuring device 119: Optical fiber 121: FBG 123: EDF 125: Mirror 201: Optical fiber sensor system 219: Optical fiber 211: Pump light source 221, 222: FBG 223: Er-Yb doped fiber 301: Optical fiber sensor system 311: Excitation light source 313: Optical switch 315: Time division demultiplexer 317: Trigger signal 319-1, 319-2: Delayed optical fiber 401: Optical fiber sensor system 411 : Receiving interferometer 413: Optical / electrical converter 415: Analog / Digital converter 417: Demodulation processor 421: Piezoelectric element 423: Optical path difference modulation signal C1, C2: Optical coupler C11, C12: Optical coupler LS101, LS102 : FBG laser sensor LS201, LS202: FBG laser sensor LS301, LS302: FBG laser sensor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA65 DD00 DD04 DD06 EE01 FF48 FF51 GG04 GG08 GG22 JJ01 LL00 LL02 LL11 LL22 LL42 NN02 QQ03 QQ13 QQ16 QQ33 2F073 AA22 AB12 BB06 BC04 CC09 CD05 DD02

Claims (16)

[Claims] A first optical transmission path for transmitting pumping light; an optical branching unit disposed at a plurality of locations on the first optical transmission path;
A plurality of fiber grating type laser sensors connected to each of said optical branching units and receiving said pumping light and oscillating and outputting laser light having a wavelength corresponding to the amount of distortion. system. 2. The optical fiber sensor system according to claim 1, further comprising an oscillation wavelength detector for measuring a wavelength of the laser light output from each of the laser sensors. 3. The apparatus according to claim 2, further comprising a second optical transmission path connected to each of said laser sensors and for guiding a laser beam output from each of said laser sensors to said oscillation wavelength detector. 2. The optical fiber sensor system according to claim 1. 4. A pulse pumping light generator for generating the pulsed pumping light, and a laser beam group including pulsed laser beams output from each of the laser sensors; And a laser beam separating section for separating a laser beam.
Or the optical fiber sensor system according to 3. 5. An excitation light transmission delay unit for delaying transmission of the pulsed excitation light so that the pulsed excitation light is sequentially supplied to each of the laser sensors with a predetermined time difference. The optical fiber sensor system according to claim 4, wherein: 6. An interferometer for receiving laser light output from each of the laser sensors, a modulating unit for performing optical path difference modulation on the interferometer, and the laser light by the interferometer. An optical / electrical converter for converting the interference light obtained from the signal into an electrical interference signal, a fundamental wavelength component remover for removing a fundamental wavelength component from the interference signal, and a fringe for the interference signal from which the fundamental wavelength component has been removed. 5. The apparatus according to claim 2, further comprising: a fringe measuring unit that performs measurement; and a wavelength calculating unit that calculates a wavelength of the laser light according to the number of fringes obtained by the fringe measuring unit. Or the optical fiber sensor system according to 5. 7. The optical fiber sensor system according to claim 6, wherein the fringe measurement unit has a differentiation processing unit that differentiates the interference signal. 8. The optical fiber sensor system according to claim 6, wherein the fringe measuring unit measures a fringe of a ²ⁿ component of the interference signal. 9. An interferometer for receiving a laser beam output from each of the laser sensors, a modulator for performing optical path difference modulation on the interferometer, and the laser beam by the interferometer. An optical / electrical conversion unit for converting the interference light obtained from the optical signal into an electrical interference signal, a fundamental wavelength component removing unit for removing a fundamental wavelength component from the interference signal, and an interference signal for the interference signal from which the fundamental wavelength component has been removed. 4. The apparatus according to claim 2, further comprising: a frequency analysis unit that performs frequency analysis; and a wavelength calculation unit that calculates a wavelength of the laser light from an analysis result obtained by the frequency analysis unit.
The optical fiber sensor system according to 4, or 5. 10. The optical fiber sensor system according to claim 9, wherein said frequency analysis unit comprises a fast Fourier transform unit. 11. An interferometer for receiving a laser beam output from each of the laser sensors, a modulating unit for performing optical path difference modulation on the interferometer, and the laser beam by the interferometer. An optical / electrical converter for converting the interference light obtained from the signal into an electrical interference signal, a fundamental wavelength component remover for removing a fundamental wavelength component from the interference signal, A calculation unit for performing a calculation using a first-order differential signal of the interference signal from which the wavelength component has been removed and a second-order differential signal of the interference signal from which the fundamental wavelength component has been removed; and a calculation obtained by the calculation unit 6. The optical fiber sensor system according to claim 2, further comprising: a wavelength calculator for calculating a wavelength of the laser beam from a result. 12. An interferometer for receiving a laser beam output from each of the laser sensors, a modulator for performing optical path difference modulation on the interferometer, and the laser beam by the interferometer. An optical / electrical conversion unit for converting the interference light obtained from the signal into an electrical interference signal, a fundamental wavelength component removing unit for removing a fundamental wavelength component from the interference signal, An acos operation unit for executing acos operation and performing phase demodulation by using
6. The optical fiber sensor system according to claim 2, further comprising: a wavelength calculating unit configured to calculate a wavelength of the laser beam from a calculation result obtained in the cos calculating unit. 13. A method for measuring the wavelength of laser light output from a fiber grating type laser sensor, comprising:
An interference light generation step of generating interference light from the laser light by an interferometer to which optical path difference modulation has been added, a light / electric conversion step of converting the interference light into an electric interference signal, and a fundamental wavelength from the interference signal. A fundamental wavelength component removing step of removing a component, a fringe measuring step of performing fringe measurement on the interference signal from which the fundamental wavelength component has been removed, and a wavelength of the laser beam according to the number of fringes obtained in the fringe measuring step. A wavelength calculating step of calculating the wavelength of the laser beam. 14. A method for measuring the wavelength of laser light output from a fiber grating type laser sensor, comprising:
An interference light generation step of generating interference light from the laser light by an interferometer to which optical path difference modulation has been added, a light / electric conversion step of converting the interference light into an electric interference signal, and a fundamental wavelength from the interference signal. A fundamental wavelength component removing step of removing a component, a frequency analyzing step of performing a frequency analysis on the interference signal from which the fundamental wavelength component has been removed, and calculating a wavelength of the laser beam from an analysis result obtained in the frequency analyzing step. Wavelength calculating step of performing
A method for measuring the wavelength of laser light. 15. A method for measuring the wavelength of laser light output from a fiber grating type laser sensor, comprising:
An interference light generation step of generating interference light from the laser light by an interferometer to which optical path difference modulation has been added, a light / electric conversion step of converting the interference light into an electric interference signal, and a fundamental wavelength from the interference signal. A fundamental wavelength component removing step of removing components, the interference signal from which the fundamental wavelength component has been removed, a first-order differential signal of the interference signal from which the fundamental wavelength component has been removed, and the interference signal from which the fundamental wavelength component has been removed. A calculation step of performing a calculation using a secondary differential signal; and a wavelength calculation step of calculating a wavelength of the laser light from a calculation result obtained in the calculation step. Measuring method. 16. A method for measuring the wavelength of laser light output from a fiber grating type laser sensor, comprising:
An interference light generation step of generating interference light from the laser light by an interferometer to which optical path difference modulation has been added, a light / electric conversion step of converting the interference light into an electric interference signal, and a fundamental wavelength from the interference signal. A fundamental wavelength component removing step of removing a component, an acos computing step of performing an acos computation on the interference signal from which the fundamental wavelength component has been removed, and performing a phase demodulation, and a computation result obtained in the acos computation step. A wavelength calculating step of calculating a wavelength of the laser light.