JP2005030890A - Method and apparatus for measuring fiber bragg grating physical quantity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for measuring fiber Bragg grating physical quantity that are capable of measuring physical quantity precisely and reliably while being less affected by a change in ambient temperature. <P>SOLUTION: The fiber Bragg grating physical quantity measuring apparatus is provided with a wide-band light source 2 for generating a light spread in wavelength band; a wavelength-variable filter 3 for selectively extracting band light in a specified wavelength band from light; an optical pulsed device 4 for generating optical pulses from the band light; and an FBG (fiber Bragg grating) element 7 for sensing connected to the optical pulsed device 4 via an optical fiber 5 provided in a target whose physical quantity is measured. Further, it is constituted so that a wide-band light source 2 and a wavelength variable filter 3 are accommodated in a temperature adjustment section 1 for accommodating the operating ambient temperature of the wide-band light source 2 and the wavelength variable filter 3 in a specified range, the specified peak wavelength of the wide-band light source 2 is used as a reference wavelength value, and also it has a temperature compensation section 12 for suppressing the temperature dependency of the characteristics of the wavelength variable filter 3 by utilizing the difference between the setting instruction value of the wavelength variable filter 3 and the actually extracted wavelength value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fiber Bragg grating physical quantity measuring method and apparatus for measuring physical quantities such as temperature and mechanical strain using a fiber Bragg grating element.
[0002]
[Prior art]
Fiber Bragg Grating (hereinafter abbreviated as FBG) element was originally developed as a key component of optical wavelength division multiplexing, but in recent years it has been actively applied as a sensor, and various FBG elements have been developed. The optical fiber sensing system used has been developed. Many patent applications have been filed in Japan, and many sensor structures, signal processing methods, installation / laying methods, etc. have been proposed. The FBG element has many advantages common to optical sensing, and is expected as a technique that can overcome the disadvantages of conventional optical fiber distributed sensing, such as slow measurement / response and insufficient sensitivity.
[0003]
The physical quantity sensing principle using the FBG element is all based on the change of the reflection wavelength due to the change of the pitch of the Bragg diffraction grating formed in the optical fiber core. In addition to temperature, a sensor is provided with a mechanism for converting physical quantities such as strain, vibration, pressure, and water level into changes in the diffraction grating spacing.
[0004]
For example, in the case of a temperature sensor, the sensitivity of the FBG element is a very small wavelength change of about 0.01 nm per 1 ° C. For this reason, high wavelength resolution is required, and it is important to ensure the reproducibility and stability of the entire measurement system. However, even when looking at the equipment specifications of general optical spectrum analyzers, there are few that have the accuracy required to meet this, and a slight drift in the ambient temperature often becomes a problem.
[0005]
As a well-known FBG wavelength measuring device, there is a product of Micron Optec Inc. in the United States, and the WEB site http: // www. microoptics. com / mechsense. It is posted on htm. Again, it seems that the influence of temperature dependence on wavelength measurement is inevitable, and in order to correct this, it is described that a device called picoWave is added as a temperature compensated reflection source (http: // www) .. micronoptics.com/ffpi.htm), http: // www. microoptics. com / fbgis. htm states that “a calibration accuracy of 10 pm can be realized”.
[0006]
However, since the wavelength accuracy of 10 pm corresponds to 1 ° C. in terms of temperature, the high sensitivity of the FBG element is not utilized. In addition, because wavelength calibration is one point of wavelength information supplied by picoWave, correction for mechanical deviation and aging of the piezoelectric element used in the wavelength tunable filter of this device at the time of system start-up is still not possible. If the system has nonlinear temperature dependence, it cannot be handled.
[0007]
As described above, in the conventional system, the high sensitivity of the FBG element has an adverse effect, which may result in being extremely unstable with respect to the ambient temperature and failing to obtain reliability of measurement data.
[0008]
This is due to the fact that only the same quality optical parts are compensated for the problem that the temperature coefficient of the characteristics of optical parts becomes a problem for precise wavelength measurement. However, there is a problem that the temperature compensation effect is limited. Therefore, it is necessary to realize wavelength offset correction at system startup and compensation for nonlinear temperature dependence of the wavelength tunable filter within the normal system operating temperature range.
[0009]
A second problem is signal processing technology. In physical quantity measurement using an FBG element, multipoint measurement utilizing the characteristics of wavelength multiplexing transmission is often performed, but in addition to this, it is known that a multiplexing method in the time domain can also be applied (see Patent Document 1 below). ). That is, the light source is pulsed, and the relationship between the connection position of the sensor composed of the FBG element in the optical fiber transmission line and the propagation delay time of the pulse is used as position information.
[0010]
In this case, the light finally reaching the photodetector is often handled as a pulse train (pulse train) of light. In order to connect a large number of sensors, it is a conventional means to make the light pulse width smaller and closer to the time. In order to detect a weak high-speed pulse train, a multi-stage cascade amplifier having a relatively small gain is often used as a preamplifier of the photodetector in order to maintain a good frequency characteristic capable of high-speed response. Therefore, in order to finally obtain a signal to be processed, it is necessary to avoid the influence of the direct current offset so that the amplifier is not saturated, and AC coupling by a capacitor is used.
[0011]
Actually, all parameters such as the width, interval, period, and pulse height of the pulse train are not always constant, so the baseline (no signal level) of the pulse varies depending on the sensor state, and the exact optical pulse It becomes difficult to measure the power value and the voltage value.
[0012]
In this way, a system for measuring with a very large number of sensors can be constructed by combining two types of methods of wavelength multiplexing and time multiplexing. In this case, however, the baseline fluctuates due to AC coupling according to the state of the sensor. In some cases, depending on the case and the degree of the error, there is a possibility that a high-precision and high-reliability measurement of a multipoint sensor cannot be realized.
[0013]
[Patent Document 1]
JP 2002-352369 A
[0014]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a fiber Bragg grating physical quantity measuring method and apparatus that can perform physical quantity measurement with high accuracy and reliability with little influence of changes in ambient temperature.
[0015]
[Means for Solving the Problems]
The invention according to claim 1 is a broadband light source that generates light having a broad wavelength band, a wavelength tunable filter that selectively extracts light in a predetermined wavelength band from the light, and generates an optical pulse from the band light. And a sensing FBG element connected to the optical pulsing device via an optical fiber, the broadband light source and the wavelength tunable filter comprising the broadband light source and the wavelength. A wavelength adjustment value that is stored in a temperature adjustment unit that keeps the operating ambient temperature of the tunable filter within a predetermined range and that is actually extracted by using the specific peak wavelength of the broadband light source as a reference wavelength value. And a temperature compensation unit that suppresses the temperature dependence of the characteristics of the wavelength tunable filter by utilizing the difference between them.
[0016]
According to a second aspect of the present invention, the temperature compensation unit includes a temperature coefficient calculating unit that calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter using temperature as an input, a wavelength value of a reference wave of the broadband light source, and the wavelength tunable filter. A difference wavelength calculation unit for obtaining a difference wavelength between a wavelength value of the extracted wave with respect to the reference wave and a drift by estimating a temperature change from a reference temperature using the difference wavelength, the reference wavelength, and the temperature drift coefficient for each wavelength. A drift temperature calculation unit that calculates temperature; a drift wavelength calculation unit that calculates a wavelength drift value of the wavelength tunable filter for a specific wavelength band from the drift temperature to obtain a drift wavelength; and an observation wavelength reading value of the sensing FBG element And an observation wavelength calculation unit for obtaining a true observation wavelength from the drift wavelength.
[0017]
According to a third aspect of the present invention, the temperature compensation unit includes a temperature coefficient calculation unit that calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter using temperature as an input, a wavelength value of a reference wave of the broadband light source, and the wavelength tunable filter. A difference wavelength calculation unit for obtaining a difference wavelength between a wavelength value of the extracted wave with respect to the reference wave and a drift by estimating a temperature change from a reference temperature using the difference wavelength, the reference wavelength, and the temperature drift coefficient for each wavelength. A drift temperature calculation unit that calculates temperature; a drift wavelength calculation unit that calculates a wavelength drift value of the wavelength tunable filter for a specific wavelength band from the drift temperature to obtain a drift wavelength; and reads an observation wavelength of the sensing FBG element An observation wavelength determining unit that determines a true set wavelength value using the drift wavelength component in advance with respect to a set wavelength value. For example the Configurations.
[0018]
According to a fourth aspect of the present invention, there is provided the wavelength tunable filter according to the second or third aspect, wherein the differential wavelength obtained by the differential wavelength calculation unit is included in a conversion formula from an observation wavelength of the sensing FBG element to a physical quantity. An offset correction unit that corrects an offset wavelength component due to a mechanical shift at the time of startup is provided.
[0019]
According to a fifth aspect of the present invention, in the fourth aspect of the invention, the broadband light source is an ASE light source that generates light of a plurality of wavelength bands, and the difference wavelength calculation unit is a plurality of differences obtained from a plurality of reference wavelength values. The average value of the wavelength calculation values is adopted as the final difference wavelength.
[0020]
According to a sixth aspect of the present invention, there is provided a broadband light source that generates light having a broad wavelength band, a tunable filter that selectively extracts band light of a predetermined wavelength band from the light, and an optical pulse generated from the band light. An optical pulsing device, a sensing FBG element connected to the optical pulsing device via an optical fiber provided in a physical quantity measurement target, and a reference wavelength FBG element connected to the optical fiber, The broadband light source, the wavelength tunable filter, and the reference wavelength FBG element are accommodated in a temperature adjustment unit that keeps the operating ambient temperature of the broadband light source, the wavelength tunable filter, and the reference wavelength FBG element in a predetermined range, and the reference wavelength The wavelength variable by utilizing the difference between the setting instruction value of the wavelength variable filter and the actually extracted wavelength value using the peak wavelength of the FBG element for reference as the reference wavelength value A configuration that includes a temperature compensating unit for suppressing the temperature dependency of the filter.
[0021]
According to a seventh aspect of the present invention, in the sixth aspect of the invention, the temperature compensation unit includes: a temperature coefficient calculating unit that calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter using the temperature as an input; and the reference wavelength FBG element. Using a difference wavelength calculation unit for obtaining a difference wavelength between a wavelength value of a reference wave and a wavelength value of an extracted wave with respect to the reference wave of the wavelength tunable filter, and using the difference wavelength, the reference wavelength, and the temperature drift coefficient for each wavelength A drift temperature calculation unit that estimates a temperature change from a reference temperature and calculates a drift temperature; a drift wavelength calculation unit that calculates a wavelength drift value of the wavelength tunable filter for a specific wavelength band from the drift temperature and obtains a drift wavelength; and A configuration comprising an observation wavelength calculation unit for obtaining a true observation wavelength from the observation wavelength reading value of the sensing FBG element and the drift wavelength To.
[0022]
The invention according to claim 8 is the invention according to claim 6, wherein the temperature compensation unit includes: a temperature coefficient calculation unit that calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter by using temperature; and the reference wavelength FBG element. Using a difference wavelength calculation unit for obtaining a difference wavelength between a wavelength value of a reference wave and a wavelength value of an extracted wave with respect to the reference wave of the wavelength tunable filter, and using the difference wavelength, the reference wavelength, and the temperature drift coefficient for each wavelength A drift temperature calculation unit that estimates a temperature change from a reference temperature and calculates a drift temperature; a drift wavelength calculation unit that calculates a wavelength drift value of the wavelength tunable filter for a specific wavelength band from the drift temperature and obtains a drift wavelength; and True observation wave using the drift wavelength component in advance for the wavelength value set to read the observation wavelength of the sensing FBG element A structure in which and a monitoring wavelength determination unit for determining the set value.
[0023]
The invention according to claim 9 is the wavelength tunable filter according to the invention according to claim 7 or 8, wherein the difference wavelength obtained by the difference wavelength calculation unit is included in a conversion formula from an observation wavelength of the sensing FBG element to a physical quantity. An offset correction unit that corrects an offset wavelength component due to a mechanical shift at the time of startup is provided.
[0024]
The invention of claim 10 is the invention of claim 9, comprising a plurality of the reference wavelength FBG elements, wherein the difference wavelength calculation unit is an average value of a plurality of difference wavelength calculation values obtained from a plurality of reference wavelength values. Is adopted as the final difference wavelength.
[0025]
The invention according to claim 11 is the invention according to claim 1, wherein a wavelength region including a peak of a specific spectral region of the broadband light source or a wavelength band of reflected light of the sensing FBG device or the reference wavelength FBG device is the wavelength. As a means to find the wavelength position indicating the maximum light intensity in a specific region of the spectrum obtained by scanning with a variable filter, the spectral wavelength is fitted to an even-order polynomial function, and the peak wavelength from the point indicating the maximum value of the function Or it is set as the structure provided with the calculating means which calculates a center wavelength.
[0026]
According to a twelfth aspect of the present invention, in the first aspect of the invention, a wavelength region including a peak of a specific spectral region of the broadband light source or a wavelength band of reflected light of the sensing FBG element or the reference wavelength FBG element is the wavelength. As a means of obtaining the wavelength position indicating the maximum light intensity in a specific region of the spectrum obtained by scanning with a variable filter, the light intensity data of the spectrum data is naturally logarithmically converted and the second order coefficient is negative. A configuration is provided in which arithmetic means for calculating the peak wavelength or the center wavelength from the point indicating the maximum value of the obtained function is applied to the function.
[0027]
The invention according to claim 13 is the invention according to claim 1, wherein the wavelength region including a peak of a specific spectral region of the broadband light source or a wavelength band of reflected light of the sensing FBG device or the reference wavelength FBG device is the wavelength. Spectrum that is distribution data of light intensity by smoothing and differentiating linearly the light intensity data of spectrum data as a means for obtaining a wavelength position indicating the maximum light intensity in a specific region of the spectrum obtained by scanning with a variable filter. A differential processing means for converting from data to derivative data and a derivative data string in a region including the peak value of the spectrum data are fitted to a straight line or a polynomial function, and the peak wavelength from the point where the derivative value crosses zero Or it is set as the structure provided with the wavelength extraction means which extracts a center wavelength.
[0028]
A fourteenth aspect of the present invention is the optical detector according to the first or sixth aspect, wherein the light detection unit that converts and amplifies an optical pulse train in which a plurality of reflected pulses from the sensing FBG element are arranged in time, to the electric pulse; A signal processing unit that processes the amplified electric pulse train signal, and the signal processing unit includes an AC coupling portion by a capacitor and a baseline regeneration circuit connected after the AC coupling portion.
[0029]
A fifteenth aspect of the present invention is the light detection unit according to the first or sixth aspect, wherein the optical pulse train in which a plurality of reflected pulses from the sensing FBG element are temporally arranged is converted into an electric pulse and amplified, A signal processing unit that processes the amplified electrical pulse train signal, the signal processing unit using a wavelength scanning function of the wavelength tunable filter from a specific sensor FBG element that arrives at a specific time window of the pulse train. A wavelength calculation unit that obtains the center wavelength by measuring the wavelength spectrum of the optical pulse, and a wavelength scan similar to the wavelength scan for the specific FBG element for the sensor for the time window in which no pulse arrives in the pulse train, and then observed Obtained with respect to a baseline measurement unit that obtains a direct current component for each wavelength as a baseline spectrum and the FBG element for the specific sensor. A structure in which and a correction operation unit for obtaining the true wavelength spectrum from the wavelength spectrum by subtracting the baseline spectrum.
[0030]
A sixteenth aspect of the invention is the optical fiber according to the first aspect of the invention, comprising an optical detector for detecting the output light of the broadband light source, and performing optical transmission from the broadband light source to the photodetector; Ancillary parts are configured to be fixed by a fixing device so that the manner of shape change such as bending or twisting within an allowable range does not change with time.
[0031]
According to a seventeenth aspect of the present invention, in the first or sixth aspect of the invention, there is provided a central wavelength acquisition means for acquiring a central wavelength of a reflected wave of the sensing FBG element for physical quantity conversion, and a reflection characteristic of the sensing FBG element. Spectrum information acquisition means for acquiring the spectrum information to be shown, and comparing the acquired spectrum information with the spectrum information acquired in the initial operation of the sensing FBG element, A soundness diagnosis unit that determines the presence or absence of a shape change is provided.
[0032]
The invention of claim 18 is a fiber Bragg grating physical quantity measuring method, a broadband light source that generates light having a broad wavelength band, and a wavelength tunable filter that selectively extracts band light of a predetermined wavelength band from the light; A fiber Bragg grating physical quantity measuring device comprising: an optical pulsing device for generating an optical pulse from the band light; and a sensing FBG element connected to the optical pulsing device via an optical fiber provided in a physical quantity measuring object And adjusting the operating ambient temperature of the broadband light source and the wavelength tunable filter to fall within a predetermined range, and using the specific peak wavelength of the broadband light source as a reference wavelength value, A structure that suppresses the temperature dependence of the characteristics of the wavelength tunable filter by utilizing the difference from the wavelength value extracted by To.
[0033]
The invention of claim 19 is a fiber Bragg grating physical quantity measuring method, a broadband light source that generates light having a broad wavelength band, and a wavelength tunable filter that selectively extracts band light of a predetermined wavelength band from the light; , An optical pulsing device that generates an optical pulse from the band light, a sensing FBG element that is provided in a physical quantity measurement object and is connected to the optical pulsing device via an optical fiber, and a reference that is connected to the optical fiber In a fiber Bragg grating physical quantity measuring device comprising a wavelength FBG element, the operating ambient temperature of the broadband light source, the wavelength tunable filter, and the reference wavelength FBG element is adjusted to fall within a predetermined range, and the reference wavelength Using the peak wavelength of the FBG element for reference as the reference wavelength value, the setting instruction value of the wavelength tunable filter and the actual extracted value are extracted. That by utilizing a difference between the wavelength value and suppresses constituting the temperature dependency of the wavelength tunable filter.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS. (ASE temperature compensation framework)
As shown in FIG. 1, the fiber Bragg grating physical quantity measuring device of the present embodiment includes a broadband light source 2 and a wavelength tunable filter 3 provided in the temperature adjustment unit 1, and an optical pulsing device connected to the wavelength tunable filter 3. 4, a first photodetector 9, a second photodetector 10, a signal processing device 11 including a temperature compensation unit 12, a control unit 8, an optical fiber 5, and an optical splitter 6. A sensing FBG element 7 connected to the fiber 5 is provided.
[0035]
This measuring device is an optical fiber sensing system in which FBG elements 7 are connected by an optical fiber 5. A plurality of sensing FBG elements 7 are connected, and these are equipped with a mechanism for converting a physical quantity that is a necessary measurement target into expansion and contraction of the sensing FBG element 7, and are configured as various physical quantity sensors. .
[0036]
The temperature adjustment unit 1 controls the temperature of the broadband light source 2 and the wavelength tunable filter 3 that are generally considered to have particularly large temperature dependency of characteristics and performance. The temperature adjusting unit 1 is a thermostatic chamber or an electronic temperature controller that holds a broadband light source 2 and a wavelength tunable filter 3 in a box-like container and keeps the temperature within a predetermined range, or a normal air conditioner, etc. The room may be maintained at a temperature within a predetermined range.
[0037]
The light emitted from the broadband light source 2 is selectively extracted in the wavelength band designated by the control unit 8 by the wavelength tunable filter 3, and then the optical pulsing device 4 is operated by the signal given by the control unit 8 to generate pulsed light. To be. This pulsed light is often controlled by the control unit 8 so as to be sent out at a constant period.
[0038]
The sent pulse light propagates through the optical fiber 5 and is distributed to the branch line of the optical fiber 5 to which the sensing FBG element 7 is connected by the optical splitter 6. When a sensing FBG element 7 having reflection characteristics matching the wavelength band of the pulsed light is encountered, the light pulse is reflected there. The reflected light pulse returns to the first photodetector 9 and becomes an electric pulse by photoelectric conversion. This electric pulse is input to the signal processing device 11.
[0039]
Since the wavelength tunable filter 3 is a narrow-band wavelength filter, the signal processing device performs wavelength scanning in a stepped manner by the control unit 8 in a wavelength region in which the reflection wavelength band of the target sensing FBG element 7 is included. 11, the reflection spectrum information of the sensing FBG element 7 of interest can be obtained. The center wavelength is obtained from this spectrum, and the target physical quantity is finally obtained by substituting the wavelength value into a physical quantity conversion formula prepared in advance.
[0040]
When the FBG element 7 functions as a vibration sensor, the reflection wavelength band (spectrum) itself changes on the wavelength axis with time. In this case, the control unit 8 fixes the wavelength tunable filter 3 to an appropriate wavelength value, and the first photodetector 9 obtains light intensity time-series change data. Vibration data such as frequency, acceleration, and displacement can be obtained by performing FFT (Fast Fourier Transform) on the time series data.
[0041]
In the present embodiment, as shown in FIG. 1, the output of the broadband light source 2 that includes the second photodetector 10 and is filtered by the wavelength tunable filter 3 reaches through the optical fiber 5 and the optical branching device 6. I am doing so. The emission spectrum of the broadband light source 2 can be obtained by appropriately selecting the wavelength step and scanning range of the wavelength tunable filter 3 by the control unit 8.
[0042]
As the broadband light source 2, an SLD (Super Luminescence Diode) light source or an ASE (Amplified Spontaneous Emission Spontaneous Emission Light) light source or the like is generally used. Some peaks are seen. As an example, FIG. 2 shows a spectrum of a broadband ASE light source ASE-FL700x series manufactured by Fiber Lab Co., Ltd. having both C and L bands.
[0043]
In this example, it can be seen that there is a characteristic peak in the vicinity of 1560 nm although it is not sharp. Since this peak is related to the excitation / transition energy level depending on the doping material of the rare earth doped fiber used in the ASE light source device, it is not easily influenced by temperature. Therefore, when the ambient temperature of the broadband light source 2 is controlled in advance within a certain temperature range by the temperature adjusting unit 1, the previous peak wavelength can be used as a reference wavelength value that does not change.
[0044]
When the wavelength tunable filter 3 drifts with respect to the peak wavelength on the spectrum of the broadband light source 2 obtained by scanning the wavelength tunable filter 3, the difference between the observed peak wavelength and the reference wavelength value is the drift component of the wavelength tunable filter 3. Can be considered. From this result, the temperature compensator 12 is provided with a function of performing calculation / control for the measurement data or the operation of the control unit 8 so as to cancel out the drift amount.
[0045]
According to the fiber Bragg grating physical quantity measuring apparatus of the first embodiment of the present invention described above, the temperature drift of the characteristics of the broadband light source 2 and the wavelength tunable filter 3 is minimized and the remaining temperature drift is compensated. It is possible to perform physical quantity measurement with high accuracy and reliability with little influence of changes in ambient temperature.
[0046]
Next, a second embodiment of the present invention will be described with reference to FIGS. (ASE temperature compensation, table reference, wavelength dependence consideration (static))
In this embodiment, the reflection spectrum of the sensing FBG element 7 does not change within the observation time, that is, corresponds to a static physical quantity such as temperature or strain.
[0047]
In the fiber Bragg grating physical quantity measuring device of this embodiment, as shown in FIG. 3, the temperature compensation unit 12 calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter 3 by using the temperature as input, A difference wavelength calculation unit 14 for obtaining a difference wavelength between the wavelength value of the reference wave of the broadband light source 2 and the wavelength value of the extracted wave with respect to the reference wave of the wavelength tunable filter 3, and the difference wavelength, the reference wavelength, and the temperature drift for each wavelength A drift temperature calculation unit 15 that estimates a temperature change from a reference temperature using a coefficient and calculates a drift temperature, and calculates a wavelength drift value of the wavelength tunable filter 3 for a specific wavelength band of interest from the calculated drift temperature. The drift wavelength calculation unit 16 for obtaining the drift wavelength, the observation wavelength reading value of each sensing FBG element 7 and the drift wavelength Consisting observation wavelength calculating unit 17 for obtaining the Shin Luo observation wavelength.
[0048]
The temperature coefficient calculating unit 13 has a wavelength (nm) vs. a wavelength as shown in FIG. A function or numerical table showing the relationship of the temperature drift coefficient D (nm / ° C.) is provided. When a wavelength is given as an input, the temperature drift coefficient D of that wavelength is obtained and output.
[0049]
The characteristic peak of the broadband light source 2 described above is treated as a reference marker, and this central wavelength value is defined as “reference wavelength value λr”. When the peak wavelength value obtained from the data obtained by scanning the marker region with the wavelength tunable filter 3 is defined as “reference marker observed value λsm”, the difference wavelength calculation unit 14 obtains the following drift wavelength value (Δλ0). It is done.
Δλ0 = reference marker observation value λsm (nm) −reference wavelength value λr (nm)
When the wavelength tunable filter 3 is drifting, a difference appears between the value set by the control unit 8 and the wavelength value actually extracted and transmitted. This corresponds to the aforementioned Δλ0.
[0050]
The amount Δλ0 is a drift amount with respect to the reference wavelength value λr (nm), while the temperature drift coefficient D at the reference wavelength value λr (nm) is obtained from the above-described temperature coefficient calculation unit. From these two values, the temperature change occurring in the variable wavelength filter 3, that is, the converted drift temperature Tc can be estimated in reverse.
[0051]
The drift temperature calculation unit 15 is a means for obtaining the converted drift temperature Tc,
Tc = Δλ0 ÷ D
It is obtained by.
When this data is ready, the reflected wavelength measurement result λm of each sensing FBG element 7 can be corrected.
[0052]
The temperature coefficient calculation unit 13 obtains a unit drift coefficient D (nm / ° C.) with respect to the wavelength center value = λm of each target FBG element 7 obtained by physical quantity measurement.
Since the drift coefficient D is known and the drift temperature Tc is also known, the drift wavelength calculator 16 can determine the wavelength correction coefficient Coe (nm). That is,
Coe (nm) = Tc (° C.) × D (nm / ° C.)
The correction coefficient Coe obtained in this way corresponds to the wavelength correction amount for the FBG7 element. Accordingly, the wavelength calculation unit 17 can obtain the true wavelength λt (nm) by setting λm (nm) + Coe (nm).
[0053]
In the fiber Bragg grating physical quantity measuring device according to the second embodiment of the present invention described above, the temperature compensation of the observation wavelength by the sensing FBG element 7 is effectively performed, and the influence of the change in the ambient temperature is small and accurate. Highly reliable physical quantity measurement can be performed.
[0054]
Next, a third embodiment of the present invention will be described. (ASE temperature compensation, table reference, wavelength dependence consideration (dynamic))
In this embodiment, the FBG element 7 is used as a dynamic physical quantity, that is, a vibration sensor.
[0055]
In the fiber Bragg grating physical quantity measuring device of this embodiment, as shown in FIG. 3, the temperature compensation unit 12 calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter 3 by using the temperature as input, A difference wavelength calculation unit 14 for obtaining a difference wavelength between the wavelength value of the reference wave of the broadband light source 2 and the wavelength value of the extracted wave with respect to the reference wave of the wavelength tunable filter 3, and the difference wavelength, the reference wavelength, and the temperature drift for each wavelength A drift temperature calculation unit 15 that estimates a temperature change from a reference temperature using a coefficient and calculates a drift temperature, and calculates a wavelength drift value of the wavelength tunable filter 3 for a specific wavelength band of interest from the calculated drift temperature. Drift wavelength calculation unit 16 for obtaining a drift wavelength, and a wavelength set to read the observation wavelength of each sensing FBG element 7 Consisting observation wavelength determination unit 18 for determining the true set value using previously said drift wavelengths respect.
[0056]
In this embodiment, the wavelength tunable filter 3 is fixed to a constant wavelength value without scanning, and the signal obtained by the first photodetector 9 is observed as time series data. As a value to be set as a constant wavelength value, an appropriate value λs0 is determined in advance for each FBG element 7, but the Coe (nm) value obtained by the drift wavelength calculation unit 16 described above is determined. Perform drift correction by. That is, the wavelength determining unit 18 performs a calculation of the wavelength value λs (nm) = λs0 (nm) + Coe (nm) to be set for the wavelength tunable filter 3 to determine the wavelength value to be set for the wavelength tunable filter 3. .
[0057]
In the fiber Bragg grating physical quantity measuring device of the third embodiment, it is possible to determine the wavelength of light observed by the sensing FBG element before light reception and perform efficient physical quantity measurement.
[0058]
Next, a fourth embodiment of the present invention will be described. (ASE temperature compensation, initial offset correction at startup)
In the fiber Bragg grating physical quantity measuring device of the fourth embodiment, the wavelength value of the reference wave of the broadband light source 2 and the extracted wave of the wavelength tunable filter 3 with respect to the reference wave in the first to third embodiments. Due to a difference wavelength calculation unit 14 for obtaining a difference wavelength with respect to the wavelength value, and by including this difference wavelength in a conversion formula from the wavelength of each sensing FBG element 7 to a physical quantity, a mechanical shift at the start of the wavelength tunable filter 3 or the like And an offset correction unit having a function of correcting an offset wavelength component, and in particular, performs conversion coefficient temperature compensation at the time of system startup.
[0059]
When the temperature adjustment unit 1 is not a temperature control by a room temperature air conditioner, but a particularly precise temperature control, for example, a thermostatic device that houses the broadband light source 2 and the wavelength tunable filter 3, the fiber Bragg grating physical quantity measuring device is powered When a sufficient Δλ0 value obtained by the differential wavelength calculation unit 14 in FIG. 3 is significant when a sufficient warm-up time has elapsed after the introduction, this is due to a mechanical offset of the wavelength tunable filter 3 or a secular change. It is thought that it occurred. In this case, the influence of the offset of the wavelength tunable filter 3 can be reduced by controlling and calculating the Δλ0 value as an offset constant in all the set value operations and reading operations of the wavelength tunable filter 3. .
[0060]
Next, a fifth embodiment of the present invention will be described. (Handling of ASE wavelength center during offset correction)
In the fiber Bragg grating physical quantity measuring device of the fifth embodiment, in the fourth embodiment, by using an ASE light source composed of a plurality of bands as the broadband light source 2, a plurality of difference wavelength calculation units 14 An average value of a plurality of calculated difference wavelength values obtained from each reference wavelength value is adopted as a final difference wavelength.
[0061]
In the fourth embodiment, the differential wavelength calculator 14 determines the drift wavelength value Δλ0 from a single reference wavelength value. However, looking at the spectrum example of the ASE light source in FIG. 2, the region around 1600 nm or 1520-1530 nm has a characteristic shape in addition to the characteristic peak at 1560 nm. By doing so, a plurality of information can be used as the reference wavelength.
That is, three characteristic wavelengths in the spectrum are set as the reference wavelengths λr1 to λr3.
[0062]
Δλ01 = reference marker observation value λsm1 (nm) −reference wavelength value λr1 (nm)
Δλ02 = reference marker observed value λsm2 (nm) −reference wavelength value λr2 (nm)
Δλ03 = reference marker observation value λsm3 (nm) −reference wavelength value λr3 (nm)
By determining Δλ0 as an average value of Δλ01, Δλ02, and Δλ03, offset correction with higher accuracy can be performed.
[0063]
Next, a sixth embodiment of the present invention will be described. (FBG element temperature compensation framework)
As shown in FIG. 5, the fiber Bragg grating physical quantity measuring apparatus of the present embodiment includes a broadband light source 2, a wavelength tunable filter 3, a reference wavelength FBG element 19, and a wavelength tunable filter 3 provided in the temperature adjustment unit 1. The optical pulse generator 4 connected, the first optical detector 9, the signal processing device 11 including the temperature compensation unit 12, the control unit 8, the optical fiber 5, and the optical fiber via the optical branching device 6. 5 includes a sensing FBG element 7 connected to 5.
[0064]
Although the sixth embodiment has many parts in common with the configuration of the first embodiment (FIG. 1), the second photodetector 10 is not provided, and the temperature adjustment unit 1 includes a reference. The difference is that the wavelength FBG element 19 is provided.
[0065]
The temperature adjusting unit 1 keeps the operating ambient temperature of the wide-area light source 2, the wavelength tunable filter 3, and the reference wavelength FBG element 19 within a certain range. The temperature compensator 12 uses the peak wavelength of the reference wavelength FBG element 19 as a reference wavelength value, and utilizes the difference between the setting instruction value of the wavelength tunable filter 3 and the wavelength value that is actually extracted and transmitted. Suppresses the temperature dependence of.
[0066]
In the first to fifth embodiments, a value obtained by feature extraction from the spectrum of the broadband light source 2 is used as the reference wavelength. In the sixth embodiment, the reflected wavelength from the reference wavelength FBG element 19 is used. Reference as the reference wavelength. As described above, in the sixth embodiment, the light to be referred to is reflected light. However, in some cases, the light may be arranged and connected so that the transmitted light of the reference wavelength FBG element 19 is received.
[0067]
As for the reference wavelength FBG element 19, in the case of a so-called temperature compensated FBG element, the temperature adjustment unit 1 may be used even for a general air conditioner, but when high accuracy is required, The temperature adjustment unit 1 is preferably a constant temperature device.
[0068]
The fiber Bragg grating physical quantity measuring apparatus according to the sixth embodiment does not require a temperature-compensating photodetector (10), and is a simple apparatus that is less affected by changes in ambient temperature and has high accuracy and reliability. Measurement can be performed.
[0069]
Next, a seventh embodiment of the present invention will be described. (FBG temperature compensation: see table, wavelength dependence consideration (static))
This embodiment is a configuration provided with temperature compensation means (FIG. 3) for static measurement similar to that in the second embodiment in the configuration of FIG.
[0070]
That is, the temperature compensation unit 12 receives the temperature as a temperature coefficient calculation unit 13 that calculates the temperature drift coefficient for each wavelength of the wavelength tunable filter 3, the wavelength value of the reference wave of the reference wavelength FBG element 19, and the wavelength tunable filter 3. A drift that estimates a temperature change from a reference temperature using the difference wavelength calculation unit 14 that obtains a difference wavelength between a wavelength value of the extracted wave and the reference wave, and the difference wavelength, the reference wavelength, and the temperature drift coefficient for each wavelength. A temperature calculation unit 15; a drift wavelength calculation unit 16 that calculates a wavelength drift value of the wavelength tunable filter 3 for a specific wavelength band from the calculated drift temperature; an observation wavelength reading value of each sensing FBG element 7 and the drift wavelength; And an observation wavelength calculation unit 17 for obtaining a true observation wavelength from.
[0071]
The fiber Bragg grating physical quantity measuring device according to the seventh embodiment compensates the temperature of the observation wavelength of the sensing FBG element 7 by the wavelength value of the reference wave of the reference wavelength FBG element 19, and the influence of the change in the ambient temperature is affected. It is possible to perform physical quantity measurement with little and high accuracy and reliability.
[0072]
Next, an eighth embodiment of the present invention will be described. (FBG temperature compensation: table reference, wavelength dependence consideration (dynamic))
This embodiment is a configuration provided with temperature compensation means (FIG. 3) for dynamic measurement similar to that in the third embodiment in the configuration of FIG.
[0073]
That is, the temperature compensation unit 12 receives the temperature as a temperature coefficient calculation unit 13 that calculates the temperature drift coefficient for each wavelength of the wavelength tunable filter 3, the wavelength value of the reference wave of the reference wavelength FBG element 19, and the wavelength tunable filter 3. A drift that estimates a temperature change from a reference temperature using the difference wavelength calculation unit 14 that obtains a difference wavelength between a wavelength value of the extracted wave and the reference wave, and the difference wavelength, the reference wavelength, and the temperature drift coefficient for each wavelength. A temperature calculation unit 15; a drift wavelength calculation unit 16 that calculates a wavelength drift value of the wavelength tunable filter 3 for a specific wavelength band from the calculated drift temperature; and a wavelength that is set to read the wavelength of each sensing FBG element 7 An observation wavelength determining unit 18 that determines a true observation wavelength setting value using the drift wavelength for the value in advance.
[0074]
In the fiber Bragg grating physical quantity measuring device of the eighth embodiment, the wavelength value of the observation wave of the sensing FBG element 7 is calculated from the wavelength value of the reference wave of the reference wavelength FBG element 19 to change the ambient temperature. Therefore, it is possible to perform physical quantity measurement with high accuracy and reliability.
[0075]
Next, a ninth embodiment of the present invention will be described. (FBG temperature compensation, initial offset correction at startup)
This embodiment is a configuration provided with temperature compensation means for dynamic measurement similar to that in the fourth embodiment in the configuration of FIG.
[0076]
That is, the difference wavelength calculation unit 14 for obtaining a difference wavelength between the wavelength value of the reference wave of the reference wavelength FBG element 19 and the wavelength value of the extracted wave with respect to the reference wave of the wavelength tunable filter 3, and this difference wavelength for each sensing FBG. An offset correction unit having a function of correcting an offset wavelength component due to a mechanical shift at the time of starting the wavelength tunable filter 3 by being included in a conversion formula from the wavelength of the element 7 to a physical quantity, and in particular, a conversion coefficient at the time of starting the system Temperature compensation is performed.
[0077]
The fiber Bragg grating physical quantity measuring device according to the ninth embodiment can reduce the influence of the offset of the wavelength tunable filter 3 to perform the physical quantity measurement with high accuracy and reliability with little influence of changes in the ambient temperature. it can.
[0078]
Next, a tenth embodiment of the present invention will be described. (Handling of FBG wavelength center during offset correction)
As shown in FIG. 6, the fiber Bragg grating physical quantity measuring device of the present embodiment includes a broadband light source 2, a wavelength tunable filter 3, three reference wavelength FBG elements 19 provided in the temperature adjustment unit 1, and a wavelength tunable device. An optical pulsing device 4 connected to the filter 3, a first photodetector 9, a signal processing device 11 including a temperature compensation unit 12, a control unit 8, an optical fiber 5, and an optical branching unit 6 are used. A sensing FBG element 7 connected to the optical fiber 5 is provided.
[0079]
In the tenth embodiment, in the configuration of the sixth embodiment (FIG. 5), three (plural) reference wavelength FBG elements 19 are connected in series. The three reference wavelength FBG elements 19 have different reflection wavelengths. All are under a constant temperature condition and can be referred to as three standard wavelengths. The difference wavelength calculation unit 14 employs an average value of a plurality of difference wavelength calculation values obtained from a plurality of reference wavelength values as a final difference wavelength. That is, it functions as an offset correction unit similar to that described in the fifth embodiment.
[0080]
In the fiber Bragg grating physical quantity measuring apparatus according to the tenth embodiment, the wavelength of the measurement light is precisely corrected, and the physical quantity can be measured with high accuracy and reliability with little influence of changes in the ambient temperature.
[0081]
Next, an eleventh embodiment of the present invention will be described. (Broadband light source / FBG peak wavelength calculation (secondary))
The fiber Bragg grating physical quantity measuring device according to the present embodiment includes a peak in a specific spectral region of the broadband light source 2 or the reference wavelength FBG element 19 of the fiber Bragg grating physical quantity measuring device according to the first to tenth embodiments. As a means for obtaining the wavelength position indicating the maximum light intensity in a specific region of the spectrum obtained by scanning the wavelength region including the wavelength band of the reflected light with the wavelength tunable filter 3, the spectral data is fitted to an even-order polynomial function. And a calculation means for calculating the peak wavelength and the center wavelength from the point indicating the maximum value of the function.
[0082]
In the fiber Bragg grating physical quantity measuring apparatus of the eleventh embodiment, when measuring the spectrum of the broadband light source 2, the sensing FBG element 7, and the reference wavelength FBG element 19, the wavelength of reflected light or transmitted light, all The center wavelength is determined from the optical spectrum of the discrete data set obtained by scanning the wavelength of the wavelength tunable filter 3 and measuring the optical power for each wavelength.
[0083]
At this time, in particular, when a peak-like spectrum is obtained, it is obtained by extracting even-order polynomial approximation by extracting data of a region considered to contain a peak from the obtained discrete data set. The peak center can be obtained from the obtained function value. In the case of a peak that protrudes upward, the maximum value is reached, but particularly in the case of the reflected light peak, it protrudes downward, and in this case, the minimum value corresponds to the peak center value.
[0084]
In the fiber Bragg grating physical quantity measuring device according to the eleventh embodiment, the peak wavelength of the broadband light source 2, the sensing FBG element 7 or the reference wavelength FBG element 19 is accurately obtained, and the influence of the change in the ambient temperature is small. Physical quantity measurement with high accuracy and reliability can be performed.
[0085]
Next, a twelfth embodiment of the present invention will be described. (Peak wavelength calculation for broadband light source / FBG (LogE, quadratic, Gaussian fit))
The fiber Bragg grating physical quantity measuring device according to the present embodiment includes a peak of a specific spectral region of the broadband light source 2 in the devices according to the first to tenth embodiments, the sensing FBG element 7 or the reference wavelength FBG element 19. As a means for obtaining a wavelength position indicating the maximum light intensity in a specific region of the spectrum obtained by scanning the wavelength region including the wavelength band of the reflected light with the wavelength tunable filter 3, the light intensity data of the spectrum data is subjected to natural logarithmic conversion. In this configuration, a function is fitted to a quadratic expression having a negative second-order coefficient, and calculation means for calculating the peak wavelength and the center wavelength from the point indicating the maximum value of the obtained function is provided.
[0086]
In the twelfth embodiment, instead of the even-order polynomial approximation in the eleventh embodiment, the optical power value data of the partially extracted data set is taken as a natural logarithm and then converted into a quadratic expression. Approximate Gaussian function approximation by fitting function.
[0087]
In the fiber Bragg grating physical quantity measuring apparatus according to the twelfth embodiment, the peak wavelength of the broadband light source 2, the sensing FBG element 7, or the reference wavelength FBG element 19 is accurately obtained, and the influence of changes in ambient temperature is small. Physical quantity measurement with high accuracy and reliability can be performed.
[0088]
Next, a thirteenth embodiment of the present invention will be described. (Peak wavelength calculation for broadband light source and FBG (zero cross point of first derivative))
The fiber Bragg grating physical quantity measuring device according to the present embodiment includes a peak of a specific spectral region of the broadband light source 2 in the devices according to the first to tenth embodiments, the sensing FBG element 7 or the reference wavelength FBG element 19. As a means for obtaining a wavelength position indicating the maximum light intensity in a specific region of the spectrum obtained by scanning the wavelength region including the wavelength band of the reflected light with the wavelength tunable filter 3, the light intensity data of the spectrum data is first smoothed. Differentiating the spectral data, which is the distribution data of light intensity by differentiation, into differential data, and the derivative data string in the region including the peak value of the original spectrum data is fitted to a straight line or polynomial function. And a wavelength extracting means for extracting the peak wavelength and the center wavelength from the point where the derivative value crosses zero. It is formed.
[0089]
The smoothed first derivative is a filter calculation method for obtaining a first derivative value while performing smoothing by polynomial approximation on a section including before and after the data of interest, and is described in, for example, the following document.
[0090]
A. Savitzky, M.M. J. et al. E. Golay, “Smoothing and Differentiation of Data by Simulated Least Squares Procedures”, Analytical Chemistry, vol. 36, no. 8, pp. 1627-1639, 1964.
When even-order polynomial approximation of spectrum data in the eleventh embodiment is performed, polynomial approximation is used for sharp peak shapes with relatively narrow half-value widths, such as the spectra of the sensing FBG element 7 and the reference wavelength FBG element 19. Or the Gaussian function approximation is easy to apply, but the spectrum of the broadband light source 2 is a broad peak, or as described in the description of the fifth embodiment, it is not a clear peak but flat in the middle of the gradient. When the reference wavelength is determined from a shape in which the portion appears and immediately becomes a gradient state, function approximation is difficult.
[0091]
If the peak shape is exhibited even if it has spread, a smoothed first derivative value is obtained and the point at which the value crosses zero can be considered as the wavelength center. In the case of flatness, a section where the smoothed primary differential value is a value near zero is determined, and a reference wavelength for the flat portion of the original spectrum is set from the section. In order to find the zero cross point, a discrete data group before and after the actual zero cross point is extracted, a straight line or polynomial fit is performed on the data group, and the obtained function formula (Y: derivative, X: wavelength) ) Is used as the target wavelength value.
[0092]
In the fiber Bragg grating physical quantity measuring apparatus according to the thirteenth embodiment, the characteristics of the spectrum with fluctuations and the expanded range are extracted, the reference wavelength is obtained with good reproducibility, and the influence of the change in the ambient temperature is small and accurate. And reliable physical quantity measurement.
[0093]
Next, a fourteenth embodiment of the present invention will be described. (DC regeneration circuit (baseline lister))
In this embodiment, in a fiber Bragg grating physical quantity measuring device using a change in reflection wavelength accompanying a change in diffraction grating pitch due to the temperature or mechanical force of the FBG element, a plurality of reflected pulses from the sensing FBG element 7 are temporally transmitted. And a signal processing unit 11 for processing the amplified electrical pulse train signal, and an AC circuit by a capacitor in the internal circuit of the signal processing unit 11. This is a configuration including a coupling portion and a baseline regeneration circuit connected thereafter.
[0094]
A signal reaching the photodetector 9 from the sensing FBG element 7 through the optical fiber 5 becomes a pulse train. This is because the connection points of the sensing FBG elements 7 are different, and the reflected pulse is returned with a time difference as one optical pulse is sent out.
[0095]
In order to detect a weak optical signal at high speed, a multi-stage high gain amplification stage is prepared. AC (alternating current) coupling is used to avoid subsequent output saturation due to amplification of the direct current offset. The peak value of each pulse in the pulse train is acquired by an AD converter or the like directly or via an integrator with a time gate called a boxcar integrator. In this case, when the pulse train has a positive amplitude as shown in FIG. 7, the baseline sinks to a negative value depending on the peak value of the pulse train. Of course, when there is no signal, the base line is at a voltage zero level because of AC (alternating current) coupling.
[0096]
In general, the baseline shifts to such a level that the positive and negative voltage values × time cancel each other with respect to the zero level of the voltage in terms of time average. Therefore, the higher the pulse repetition frequency and the higher the pulse peak value, the larger the baseline shift. Therefore, when a time window corresponding to a specific pulse is set in this state and a peak value of a pulse arriving there is to be acquired, it is mistaken for a value smaller than the true pulse peak value.
[0097]
Further, when the reflected light of the sensing FBG element 7 is measured by wavelength scanning, the light transmission amount is large in the middle of the scanning step because it is near the spectrum center of the reflected light, and the peak value of the reflected optical pulse signal is also large. On the other hand, the beginning and end of the scanning step are regions where the optical power is reduced on both sides of the peak on the spectrum, so the time interval condition of the pulse train does not change, but the pulse peak value becomes small. Therefore, the average baseline value gradually shifts when the wavelength scanning process is performed in the wavelength scanning process in which the center wavelength (peak wavelength) region is expanded on both sides centering on the center wavelength (peak wavelength) region. It follows a change that is large and then returns to the original value.
[0098]
Therefore, the observed value obtained by AD conversion becomes a spectrum compressed in the Y-axis (optical power) direction, and the compression is not uniform. For this reason, even if the center of the optical spectrum obtained in this way is obtained, true information is no longer included therein.
[0099]
In the present embodiment, a baseline regeneration circuit is applied as means for preventing a change in the baseline. Although there are various circuit configurations for the baseline regeneration circuit, the basic configuration is shown in FIG. The baseline regeneration circuit configuration itself is well known as a circuit used for linear amplifiers for γ-ray and X-ray spectrometry, and fluctuations in the zero level of the baseline due to the arrival of random pulses in front of the AD converter It is used to stabilize
[0100]
In FIG. 8, a signal is input and output in the direction of the arrow. A switch 20 is provided in parallel to the ground on the AC-coupled output side. When there is no signal, the switch 20 is closed and the output is kept at the ground potential (zero level). The switch 20 is opened at the moment when the signal enters, and the output signal rises from the zero level. The switch 20 is closed again at the moment when there is no signal. In this way, the baseline is kept at zero level without depending on the amplitude and period of the signal.
[0101]
As an actual implementation circuit, a passive method or an active method using an active element can be considered, but since the time between the pulses and the valley of the pulse is the operation time of the baseline reproduction circuit in the pulse train, It is essential to adopt a circuit configuration that can operate at high speed.
[0102]
Although radiation measurement deals with random pulses, in the fiber Bragg grating physical quantity measuring device of the present invention, the time interval between pulses is constant, so the only parameter that changes is the peak value. Therefore, it is very easy to distinguish between when there is a signal and when there is no signal, pulse transmission dimming in the optical pulsing device 4 is known, and the connection position and length of the optical fiber 5 and the sensing FBG element 7 are also known. For example, the time parameters of the reflected pulse train are all known. By using this information, the conceptual opening / closing control operation of the switch 20 of FIG. 8 can be performed strictly, and therefore, baseline reproduction with high accuracy can be realized.
[0103]
In the fiber Bragg grating physical quantity measuring device according to the fourteenth embodiment, the optical pulse train returned from the sensing FBG element 7 is accurately signal-processed, and is less affected by changes in the ambient temperature and highly accurate and reliable. Physical quantity measurement can be performed.
[0104]
Next, a fifteenth embodiment of the present invention will be described. (DC regeneration correction by software) In this embodiment, in the fiber Bragg grating physical quantity measuring device using the change in the reflection wavelength due to the change in the diffraction grating pitch due to the temperature of the FBG element and the mechanical force, the FBG element 7 from the sensing FBG element 7 An optical detector 9 that converts and amplifies an optical pulse train in which a plurality of reflected pulses are arranged in time into electrical pulses, and a signal processing device 11 that processes the amplified electrical pulse train signal. A calculation unit that obtains a center wavelength by measuring a wavelength spectrum of an optical pulse from a specific sensing FBG element 7 that arrives at a specific time window of the pulse train by using the wavelength scanning function of the wavelength tunable filter 3, and a pulse in the pulse train A wavelength scan similar to the wavelength scan for the specific sensing FBG element 7 is performed for a time window in which the A baseline measurement unit that acquires a direct current component for each wavelength observed at the time as a baseline spectrum, and true by subtracting the baseline spectrum from the wavelength spectrum obtained for the specific sensing FBG element 7 And a correction calculation unit that obtains a wavelength spectrum.
[0105]
In this embodiment, the phenomenon in which the base line of the reflected light pulse fluctuates and changes due to wavelength scanning is dealt with by signal processing. Now, when wavelength scanning is performed on a specific sensing FBG element 7 of interest with respect to the pulse train shown in FIG. 9, a time window including the reflected light of the sensing FBG 7 is set.
[0106]
Actually, the peak value of the reflected light pulse from each sensing FBG element 7 is acquired while scanning the time window one after another for one step (one wavelength value) in the wavelength scanning. When scanning the time window in the example of FIG. 9, five time windows are required to acquire the data of the FBG element 7. In the present embodiment, a sixth time window is set at a time when there is no valid pulse in the pulse train, and in the example of FIG. 9, a timing after the last pulse. In this way, a baseline at each wavelength step can be acquired.
[0107]
FIG. 10 shows a spectrum a) obtained with respect to the sensing FBG element 7 when the wavelength scanning is completed, and a spectrum b) (actually a change characteristic of the baseline) with respect to the obtained baseline. From this, a true spectrum can be obtained by the calculation of a) -b).
[0108]
In the fiber Bragg grating physical quantity measuring device according to the fifteenth embodiment, the optical pulse train returned from the sensing FBG element 7 is accurately signal-processed, and is less affected by changes in ambient temperature and highly accurate and reliable. Physical quantity measurement can be performed.
[0109]
Next, a sixteenth embodiment of the present invention will be described. (Soft & Hard)
The fiber Bragg grating physical quantity measuring device of the present embodiment has both the configuration of the fourteenth embodiment and the configuration of the fifteenth embodiment. In the fourteenth and fifteenth embodiments, the configuration for compensating / correcting the fluctuation of the pulse baseline due to the electronic circuit or data processing / calculation has been shown. In particular, when a number of sensing FBG elements 7 include vibration sensors, the intensity of the reflected light itself constantly vibrates within one step of wavelength scanning, and the vibration frequency and readout timing are asynchronous. Therefore, there is a possibility that extra variation resulting from this is added to the AD converted value. Therefore, it is possible to perform correction by data processing / calculation for the remaining components that cannot be fully compensated by the electronic circuit, and measures by the electronic circuit that has the effect of suppressing the original event itself. Measurement can be realized.
[0110]
Next, a seventeenth embodiment of the present invention will be described. (ASE transmission fiber)
The fiber Bragg grating physical quantity measuring apparatus according to this embodiment has a configuration in which the output light of the broadband light source 2 in the first to fifth embodiments is detected and monitored by the photodetector 10 to perform temperature compensation. In this configuration, the optical fiber 5 that transmits light from 2 to the optical detector 10 and the incidental parts are fixed with a fixing device so that the manner of shape change such as bending or twisting within an allowable range does not change with time. .
[0111]
In an apparatus that monitors the spectrum shape of the broadband light source 2 and performs temperature compensation or offset correction of the wavelength tunable filter 3, the spectrum of the broadband light source 2 must not be distorted. When a 1.55 μm single mode fiber is used as the optical fiber 5, the transmission loss of broadband light greatly depends on the wavelength due to bending or distortion of the optical fiber 5, and as a result, the spectrum is distorted.
[0112]
When looking at the reflection wavelength by the sensing FBG element 7, the wavelength band to be used is extremely narrow, and the influence of the distortion of the entire spectrum is negligible. However, with respect to the above-mentioned reference wavelength, which is determined by extracting features from the entire spectrum of the broadband light source 2, it is a big problem that the spectrum itself changes over time.
[0113]
For this reason, in the system for measuring the spectrum of the emitted light from the broadband light source 2, it is necessary to keep the bending and strain of the optical fiber constant. FIG. 11 shown as an example has the same circuit configuration as FIG. 1, but encloses the optical fiber 5 and the optical branching device 6 with a one-dot chain line in the drawing. By fixing this portion with a fixing device, it is possible to maintain a stable spectral shape that does not change with time, thereby realizing highly accurate temperature compensation, offset correction, and the like.
[0114]
Next, an eighteenth embodiment of the present invention will be described. (Spectrum monitor)
In this embodiment, a reflected wave from a sensing FBG element 7 is used for physical quantity conversion in a fiber Bragg grating physical quantity measuring device that uses a change in reflection wavelength accompanying a change in diffraction grating pitch due to temperature or mechanical force of the FBG element. Means for obtaining the center wavelength of the FBG element 7, means for obtaining spectral information indicating the reflection characteristics of the FBG element 7 itself, spectrum information of the obtained specific FBG element, and spectrum obtained at the initial stage of system operation of the FBG element 7. This is a configuration including a soundness diagnosis unit having a function of determining the presence or absence of mechanical soundness or shape change of the FBG element 7 by comparing with information.
[0115]
As described above, for the specific sensing FBG element 7 of interest, data corresponding to the optical spectrum is acquired in advance by wavelength scanning, and then the center wavelength is set by the method shown in the eleventh to thirteenth embodiments. Ask. For the conversion between the measured physical quantity and the wavelength, the measured value of the central wavelength is sufficient, but the spectrum data includes the soundness data of the FBG element 7 itself. That is, if the FBG element 7 itself is subjected to abnormal strain or non-uniform strain, or if the transmission loss changes due to mechanical deformation or damage, the shape of the observed optical spectrum changes.
[0116]
By recording the spectrum information for each FBG element 7 acquired at the initial stage such as laying / starting operation of the measuring device, and determining whether the spectrum obtained during each measurement and the above-mentioned initial spectrum have changed, the FBG The soundness of the element 7 itself can be ensured, and the influence of changes in the ambient temperature is small, and physical quantity measurement with high accuracy and reliability can be performed.
[0117]
【The invention's effect】
According to the present invention, it is possible to provide a fiber Bragg grating physical quantity measuring method and apparatus capable of performing physical quantity measurement with high accuracy and reliability with little influence of changes in ambient temperature.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing the configuration of a fiber Bragg grating physical quantity measuring device according to a first embodiment of the present invention.
FIG. 2 is a curve diagram showing a spectrum of a broadband light source (ASE) provided in the fiber Bragg grating physical quantity measuring device according to the first embodiment of the present invention.
FIG. 3 is a circuit diagram showing a temperature compensation unit provided in the fiber Bragg grating physical quantity measuring device according to the second and third embodiments of the present invention.
FIG. 4 is a curve diagram illustrating the wavelength dependence of the temperature drift coefficient of the wavelength tunable filter and explaining the operation of the fiber Bragg grating physical quantity measuring device according to the second and third embodiments of the present invention.
FIG. 5 is a circuit diagram showing a configuration of a fiber Bragg grating physical quantity measuring device according to a sixth embodiment of the present invention;
FIG. 6 is a circuit diagram showing a configuration of a fiber Bragg grating physical quantity measuring device according to a tenth embodiment of the present invention.
FIG. 7 is a waveform diagram showing a pulse train that sinks by AC coupling in the fiber Bragg grating physical quantity measuring device according to the fourteenth embodiment of the present invention.
FIG. 8 is a diagram showing a pulse train baseline regeneration circuit in a fiber Bragg grating physical quantity measuring device according to a fourteenth embodiment of the present invention;
FIG. 9 is a waveform diagram for explaining baseline regeneration of a pulse train by data processing in the fiber Bragg grating physical quantity measuring device according to the fifteenth embodiment of the present invention;
FIGS. 10A and 10B illustrate pulse train baseline regeneration by data processing in the fiber Bragg grating physical quantity measuring device according to the fifteenth embodiment of the present invention, wherein a) is a curve diagram of an FBG signal, and b) is a baseline signal. Curve diagram.
FIG. 11 is a circuit diagram showing a configuration of a fiber Bragg grating physical quantity measuring device according to a seventeenth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Temperature control part, 2 ... Broadband light source, 3 ... Wavelength variable filter, 4 ... Optical pulse device, 5 ... Optical fiber, 6 ... Optical branching device, 7 ... Sensing FBG element, 8 ... Control part, 9th DESCRIPTION OF SYMBOLS 1 photo detector, 10 ... 2nd photo detector, 11 ... Signal processing apparatus, 12 ... Temperature compensation part, 13 ... Temperature coefficient calculation part, 14 ... Differential wavelength calculation part, 15 ... Drift temperature calculation part, 16 ... Drift wavelength Calculation part, 17 ... Observation wavelength calculation part, 18 ... Observation wavelength determination part, 19 ... Reference wavelength FBG element, 20 ... Switch.

Claims (19)

A broadband light source that generates light having a spread in a wavelength band, a wavelength tunable filter that selectively extracts band light of a predetermined wavelength band from the light, an optical pulsing device that generates an optical pulse from the band light, A sensing FBG element provided in a physical quantity measurement target and connected to the optical pulsing device via an optical fiber, and the broadband light source and the wavelength tunable filter have an operating ambient temperature of the broadband light source and the wavelength tunable filter. Housed in a temperature adjustment unit that falls within a predetermined range, using a specific peak wavelength of the broadband light source as a reference wavelength value, and using a difference between a setting instruction value of the wavelength tunable filter and an actually extracted wavelength value A fiber Bragg grating physical quantity measurement comprising: a temperature compensation unit that suppresses temperature dependence of the characteristics of the wavelength tunable filter Location. The temperature compensation unit includes a temperature coefficient calculation unit that calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter with temperature as an input, a wavelength value of a reference wave of the broadband light source, and an extraction wave of the wavelength tunable filter with respect to the reference wave Drift temperature calculation for estimating a temperature change from a reference temperature using the difference wavelength, the reference wavelength and the temperature drift coefficient for each wavelength, and calculating a drift temperature A drift wavelength calculation unit that calculates a wavelength drift value of the wavelength tunable filter for a specific wavelength band from the drift temperature and obtains a drift wavelength, an observation wavelength reading value of the sensing FBG element, and a true value from the drift wavelength The fiber Bragg gray according to claim 1, further comprising an observation wavelength calculation unit for obtaining an observation wavelength. Ingu physical quantity measuring apparatus. The temperature compensation unit includes a temperature coefficient calculation unit that calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter with temperature as an input, a wavelength value of a reference wave of the broadband light source, and an extraction wave of the wavelength tunable filter with respect to the reference wave Drift temperature calculation for estimating a temperature change from a reference temperature using the difference wavelength, the reference wavelength and the temperature drift coefficient for each wavelength, and calculating a drift temperature A wavelength value that is set to read an observation wavelength of the sensing FBG element, a drift wavelength calculation unit that calculates a wavelength drift value of the wavelength tunable filter for a specific wavelength band from the drift temperature, and obtains a drift wavelength An observation wavelength determining unit that determines a true set wavelength value by using the drift wavelength component in advance. Fiber according to claim 1, Bragg grating physical quantity measuring apparatus. An offset that corrects an offset wavelength component due to a mechanical shift at the time of activation of the wavelength tunable filter by including the difference wavelength obtained by the difference wavelength calculation unit in a conversion formula from an observation wavelength of the sensing FBG element to a physical quantity. The fiber Bragg grating physical quantity measuring device according to claim 2, further comprising a correction unit. The broadband light source is an ASE light source that generates light in a plurality of wavelength bands, and the difference wavelength calculation unit adopts an average value of a plurality of difference wavelength calculation values obtained from a plurality of reference wavelength values as a final difference wavelength. The fiber Bragg grating physical quantity measuring device according to claim 4, wherein: A broadband light source that generates light having a spread in a wavelength band, a wavelength tunable filter that selectively extracts band light of a predetermined wavelength band from the light, an optical pulsing device that generates an optical pulse from the band light, A sensing FBG element connected to the optical pulsing device via an optical fiber provided in a physical quantity measurement target; and a reference wavelength FBG element connected to the optical fiber, the broadband light source and the wavelength tunable filter And the reference wavelength FBG element is housed in a temperature adjusting unit that keeps the operating ambient temperature of the broadband light source, the wavelength tunable filter, and the reference wavelength FBG element in a predetermined range, and sets the peak wavelength of the reference wavelength FBG element. The temperature dependence of the wavelength tunable filter using the difference between the setting instruction value of the wavelength tunable filter and the actually extracted wavelength value as a reference wavelength value Fiber Bragg grating, characterized in that it comprises a suppressing temperature compensating unit of physical quantity measuring apparatus. The temperature compensation unit receives a temperature as a temperature coefficient calculation unit that calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter, a wavelength value of a reference wave of the reference wavelength FBG element, and the reference wave of the wavelength tunable filter A difference wavelength calculation unit that obtains a difference wavelength with respect to the wavelength value of the extracted wave with respect to the above, a temperature change from a reference temperature is estimated using the difference wavelength, the reference wavelength, and the temperature drift coefficient for each wavelength, and a drift temperature is calculated. A drift temperature calculating unit; a drift wavelength calculating unit for calculating a wavelength drift value of the wavelength tunable filter for a specific wavelength band from the drift temperature to obtain a drift wavelength; an observation wavelength reading value of the sensing FBG element; and the drift wavelength The fiber Bragg according to claim 6, further comprising an observation wavelength calculation unit for obtaining a true observation wavelength from Rating physical quantity measuring apparatus. The temperature compensation unit receives a temperature as a temperature coefficient calculation unit that calculates a temperature drift coefficient for each wavelength of the wavelength tunable filter, a wavelength value of a reference wave of the reference wavelength FBG element, and the reference wave of the wavelength tunable filter A difference wavelength calculation unit that obtains a difference wavelength with respect to the wavelength value of the extracted wave with respect to the above, a temperature change from a reference temperature is estimated using the difference wavelength, the reference wavelength, and the temperature drift coefficient for each wavelength, and a drift temperature is calculated. A drift temperature calculation unit, a drift wavelength calculation unit that calculates a wavelength drift value of the wavelength tunable filter for a specific wavelength band from the drift temperature and obtains a drift wavelength, and a reading wavelength of the sensing FBG element are set. An observation wavelength determining unit that determines a true observation wavelength setting value using the drift wavelength component in advance with respect to the wavelength value. Fiber Bragg grating physical quantity measuring apparatus according to claim 6, wherein a. An offset that corrects an offset wavelength component due to a mechanical shift at the time of activation of the wavelength tunable filter by including the difference wavelength obtained by the difference wavelength calculation unit in a conversion formula from an observation wavelength of the sensing FBG element to a physical quantity. The fiber Bragg grating physical quantity measuring device according to claim 7 or 8, further comprising a correction unit. A plurality of reference wavelength FBG elements are provided, and the difference wavelength calculation unit employs an average value of a plurality of difference wavelength calculation values obtained from a plurality of reference wavelength values as a final difference wavelength. The fiber Bragg grating physical quantity measuring device according to claim 9. A specific region of a spectrum obtained by scanning a wavelength region including a peak of a specific spectral region of the broadband light source or a reflected light wavelength band of the sensing FBG device or the reference wavelength FBG device with the wavelength tunable filter. As a means for obtaining the wavelength position indicating the maximum light intensity, it is provided with a calculation means for calculating the peak wavelength or the center wavelength from the point indicating the maximum value of the function by fitting the spectrum data to an even-order polynomial function. The fiber Bragg grating physical quantity measuring device according to claim 1, wherein: A specific region of a spectrum obtained by scanning a wavelength region including a peak of a specific spectral region of the broadband light source or a reflected light wavelength band of the sensing FBG device or the reference wavelength FBG device with the wavelength tunable filter. As a means of obtaining the wavelength position indicating the maximum light intensity in the spectrum, the light intensity data of the spectral data is subjected to natural logarithm conversion, and the function is fitted to a quadratic expression having a negative second-order coefficient. 2. The fiber Bragg grating physical quantity measuring device according to claim 1, further comprising an arithmetic means for calculating a peak wavelength or a center wavelength from the indicated point. A specific region of a spectrum obtained by scanning a wavelength region including a peak of a specific spectral region of the broadband light source or a reflected light wavelength band of the sensing FBG device or the reference wavelength FBG device with the wavelength tunable filter. A differential processing means for converting the spectral data, which is the distribution data of the light intensity, from the spectral data, which is the distribution data of the light intensity, into the change data of the differential coefficient, as a means for obtaining the wavelength position indicating the maximum light intensity in the light; And a wavelength extracting means for fitting the derivative data string of the region including the peak value of the spectrum data to a straight line or a polynomial function and extracting the peak wavelength or the center wavelength from the point where the derivative value crosses zero. The fiber Bragg grating physical quantity measuring apparatus according to claim 1. A light detection unit that converts and amplifies an optical pulse train in which a plurality of reflected pulses from the sensing FBG element are arranged in time into an electrical pulse; and a signal processing unit that processes the amplified electrical pulse train signal; The fiber Bragg grating physical quantity measuring device according to claim 1, wherein the signal processing unit includes an AC coupling portion using a capacitor and a baseline regeneration circuit connected after the AC coupling portion. A light detection unit that converts and amplifies an optical pulse train in which a plurality of reflected pulses from the sensing FBG element are arranged in time into an electrical pulse; and a signal processing unit that processes the amplified electrical pulse train signal; The signal processing unit uses a wavelength scanning function of the wavelength tunable filter to obtain a center wavelength by measuring a wavelength spectrum of a light pulse from a specific FBG element for a sensor that arrives at a specific time window of a pulse train, and Baseline for performing a wavelength scan similar to the wavelength scan for a specific sensor FBG element on a time window in which no pulse arrives in the pulse train, and acquiring a DC component for each wavelength observed at that time as a baseline spectrum The baseline spectrum is subtracted from the wavelength spectrum obtained for the measurement unit and the specific sensor FBG element. Fiber Bragg grating physical quantity measuring apparatus according to claim 1 or 6, characterized in that it comprises a correction arithmetic unit for obtaining the true wavelength spectrum by. An optical detector for detecting the output light of the broadband light source is provided, and the optical fiber for transmitting light from the broadband light source to the photodetector and the incidental parts have shapes such as bending and twisting within an allowable range. 2. The fiber Bragg grating physical quantity measuring device according to claim 1, wherein the fiber bragg grating physical quantity measuring device is fixed by a fixing device so that the manner of change does not change with time. Center wavelength acquisition means for acquiring the center wavelength of the reflected wave of the sensing FBG element for physical quantity conversion, spectrum information acquisition means for acquiring spectrum information indicating reflection characteristics of the sensing FBG element, and the acquired A health diagnosis unit that compares the spectrum information with the spectrum information acquired in the initial operation of the sensing FBG element to determine whether the sensing FBG element is mechanically sound or has a shape change; The fiber Bragg grating physical quantity measuring device according to claim 1 or 6, wherein: A broadband light source that generates light having a spread in a wavelength band, a wavelength tunable filter that selectively extracts band light of a predetermined wavelength band from the light, an optical pulsing device that generates an optical pulse from the band light, In a fiber Bragg grating physical quantity measuring device provided with a sensing FBG element provided in a physical quantity measurement target and connected to the optical pulse device via an optical fiber, the operating ambient temperature of the broadband light source and the wavelength tunable filter is predetermined. The wavelength is adjusted by using a difference between a set instruction value of the tunable filter and an actually extracted wavelength value using a specific peak wavelength of the broadband light source as a reference wavelength value. A fiber bragg grating physical quantity measuring method characterized by suppressing temperature dependence of a variable filter characteristic. A broadband light source that generates light having a spread in a wavelength band, a wavelength tunable filter that selectively extracts band light of a predetermined wavelength band from the light, an optical pulsing device that generates an optical pulse from the band light, In a fiber Bragg grating physical quantity measuring device provided with a sensing FBG element connected to the optical pulsing device via an optical fiber provided in a physical quantity measuring object, and a reference wavelength FBG element connected to the optical fiber, Adjusting the operating ambient temperature of the broadband light source, the wavelength tunable filter, and the reference wavelength FBG element to be within a predetermined range, and using the peak wavelength of the reference wavelength FBG element as a reference wavelength value, the wavelength tunable filter The temperature dependence of the wavelength tunable filter is suppressed by utilizing the difference between the set instruction value of the wavelength and the actually extracted wavelength value. Fiber Bragg grating physical quantity measuring method according to symptoms.

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