JP4870771B2 - Optical fiber temperature distribution measuring device, optical fiber temperature distribution measuring method, and optical fiber temperature distribution measuring system - Google Patents

Description

The present invention relates to an optical fiber temperature distribution measuring device, an optical fiber temperature distribution measuring method, and an optical fiber temperature distribution measuring system for optically remotely measuring the temperature distribution of an optical fiber.
This application is based on international application number PCT / JP2006 / 318858, the entire contents of which are referenced and introduced in this application.

  As a method for measuring the temperature distribution of an optical fiber for optically measuring the temperature distribution of the optical fiber, a combination of the principle of distance measurement by OTDR (Optical Time Domain Reflectometry) and the principle of temperature measurement by detection of Raman scattered light is combined. Are known (see, for example, Patent Document 1 and Non-Patent Document 1).

  14A and 14B are explanatory diagrams showing the principle of temperature distribution measurement of an optical fiber described in Patent Document 1, FIG. 14A is a principle diagram of measurement of temperature distribution, and FIG. 14B is a diagram of backscattered light. It is a wavelength distribution diagram. In measuring the temperature distribution, the incident pulsed light 4 passes through the optical fiber 2 to be measured, and the backscattered light 6 generated at the scattering point 5 is optically converted and output as an output light 7 to a wavelength separator (not shown). This is performed using a configuration including a beam splitter 3, a signal detection unit (not shown) that detects a signal output from the wavelength separator, a signal processing unit (not shown), and the like.

Next, a method for measuring the temperature distribution of the optical fiber will be described. First, when incident pulsed light 4 having a wavelength λ ₀ generated by a light source (not shown) is incident on the optical fiber 2 to be measured, backscattered light 6 appears at a scattering point 5 that is a propagation process, and is incident on the incident end side. Come back. Here, the distance from the incident end to the scattering point 5 is L, the time from the incident time of the incident pulsed light 4 to the detection time of the backscattered light 6 is t, the refractive index of the optical fiber 2 to be measured is n, and in vacuum Is C ₀ and the speed of light in the optical fiber 2 to be measured is C,
C = C ₀ / n ---- (1)
L = C · t / 2 −−−−− (2)
It becomes. Therefore, the position of the scattering point 5 is quantitatively determined by the equation (2).

On the other hand, the backscattered light 6 includes Rayleigh light 20, Stokes light 21, and anti-Stokes light 22, as shown in FIG. 14B. Wavelength lambda ₀ next to the Rayleigh light 20 when the wavelength is lambda ₀ of the incident pulse light 4, and the wavelength shift amount and [Delta] [lambda], the wavelength lambda _AS wavelength lambda _S and the anti-Stokes light 22 of the Stokes light 21,
λ _S = λ ₀ + Δλ −−−− (3)
λ _AS = λ ₀ −Δλ −−−− (4)
It becomes.

When representing the received light intensity of the Stokes light 21 of the wavelength lambda _S in backscattering light generated in the scattering points with I _S, the reverse light-receiving intensity of the Stokes light 22 having a wavelength lambda _AS in I _AS, receiving intensity of the Stokes light 21 the ratio of the received light intensity I _aS the I _S and the anti-Stokes light 22 is dependent on the absolute temperature T of the scattering point 5 in 2 optical fiber to be measured,
I _AS / I _S = A · exp (−h · C · Δλ / k _B · T) ---- (5)
The relationship shown in Here, h is the Planck constant (J · S), Δλ is the Raman shift amount (m ⁻¹ ), k _B is the Boltzmann constant (J / K), T is the absolute temperature (K), and A is the performance of the measurement system. It is a fixed constant. Accordingly, the temperature of the scattering point is quantitatively determined. Further, only the anti-Stokes light 22 is a function of the absolute temperature T of the scattering point 5 in the optical fiber 2 to be measured,
I _AS = B · (1 / (exp (h · C · Δλ / k _B T) −1)) −−−− (6)
The relationship shown in Here, B is a constant determined by the performance of the measurement system. From the above, the temperature of the scattering point 5 can be obtained quantitatively.
Note that Stokes light and anti-Stokes light generated at a certain scattering point in the optical fiber away from the measuring device are attenuated by absorption and scattering by the optical fiber during propagation of the optical fiber. In the prior art, the amount of attenuation of Stokes light and anti-Stokes light during propagation through the optical fiber is corrected by regarding it as constant per unit distance.

According to the conventional method for measuring the temperature distribution of an optical fiber, the position and temperature of the scattering point can be obtained as described above.
Japanese Patent No. 3030663 JPDakin, et al: Distributed Optical Fiber Raman Temperature Sensor using a Semiconductor Light Source and Detector `` ELECTRONICS LETTERS '' June 20, 1985, Vol.21 No.13 p.569-570

  However, the conventional optical fiber temperature distribution measuring method has the following problems. FIG. 14A shows the measurement principle of an optical fiber according to the prior art. When the measured optical fiber 2 is in a hydrogen atmosphere (when hydrogen is contained in the measurement atmosphere 30) during actual temperature distribution measurement, Hydrogen molecules diffuse into the measurement optical fiber 2. Then, the backscattered light 6 generated at the scattering point 5 and returning to the apparatus side is absorbed by the diffused hydrogen molecules, and the received light intensity detected by the signal detection unit decreases. Even if the scattering point 5 itself is not in a hydrogen atmosphere, if the optical fiber to be measured is in a hydrogen atmosphere in a certain portion between the scattering point 5 and the apparatus, the received light intensity is reduced. The amount of decrease in received light intensity due to absorption of hydrogen molecules, that is, the amount of increase in optical transmission loss is wavelength-dependent, so the received light intensity of Stokes light and anti-Stokes light corresponding to the measurement temperature of the scattering point is different due to hydrogen molecules. There is a problem in that accurate temperature information cannot be obtained because the value includes optical transmission loss. References (N. Uchida and N. Uesugi, “Infrared Optical Loss Increase in Silica Fibers due to Hydrogen”, J. Lightwave Technol., Vol LT-4, No.8, pp.1132-1138, Aug. 1986 .)), The optical transmission loss in the hydrogen atmosphere includes absorption loss (hydrogen molecule absorption) caused by molecular vibration caused by hydrogen molecules diffused in the optical fiber, and hydrogen molecules and optical fiber. Light transmission loss resulting from a chemical reaction with OH group, such as OH group absorption loss due to OH group formation. In the present invention, an increase in optical transmission loss due to hydrogen molecules means an increase in optical transmission loss due to absorption of hydrogen molecules unless otherwise specified.

  As an example of the influence on the optical transmission based on the presence of hydrogen molecules, FIGS. 15A and 15B show the distance in the presence of hydrogen molecules and the received light intensity detected by the measuring device, and FIG. 15A is a characteristic diagram of Stokes light. FIG. 15B is a characteristic diagram of anti-Stokes light. FIG. 16 shows the relationship between the distance when hydrogen molecules are present and the temperature measurement value calculated by the prior art.

  15A and 15B, the Stokes light and the anti-Stokes light under conditions where the hydrogen partial pressure is different from 0 MPa, 0.04 MPa, 0.07 MPa, and 0.09 MPa in the relationship between the distance of the optical fiber to be measured and the received light intensity. The characteristics of each are shown. As shown in FIG. 15A, the Stokes light tends to decrease in received light intensity due to attenuation as the length (distance) of the optical fiber to be measured increases, and to significantly decrease the received light intensity as the hydrogen partial pressure increases. I know that there is. In addition, as shown in FIG. 15B, it can be seen that the same tendency exists for the anti-Stokes light.

  In this way, the optical transmission loss increases due to the diffusion of hydrogen molecules in the optical fiber to be measured, and an error occurs between the measured temperature value and the true value as shown in FIG. This error becomes more prominent as the distance of the optical fiber to be measured and the hydrogen partial pressure are larger.

  Accordingly, an object of the present invention is to provide an optical fiber temperature distribution measuring apparatus, an optical fiber temperature distribution measuring method, and an optical fiber temperature distribution measuring system capable of measuring an accurate temperature even when the optical fiber is in a hydrogen atmosphere. Is to provide.

According to the first aspect of the present invention, the light source that makes the pulsed light incident on the optical fiber to be measured, and the predetermined light included in the backscattered light generated in the optical fiber to be measured based on the incidence of the pulsed light A signal detection unit for detecting the received light intensity of the light, and calculating a value corresponding to a change amount of the received light intensity due to absorption of hydrogen molecules of the optical fiber to be measured based on the received light intensity of the predetermined light, and based on the value have a signal processing unit that corrects the received light intensity of the predetermined light corresponding to the temperature of the measured optical fiber, the signal processing unit on the basis of the value corresponding to the amount of change of the received light intensity of the Stokes light, the The received light intensity of the anti-Stokes light corresponding to the temperature of the optical fiber to be measured is corrected, or the signal processing unit responds to the amount of change in received light intensity obtained based on the wavelength of the temperature measuring pulse light output from the light source. Based on the measured value. To provide an optical fiber temperature distribution measuring apparatus for correcting a received light intensity of the predetermined light corresponding to the temperature of the constant light fiber.

  The signal detection unit may detect the received light intensity of Stokes light and anti-Stokes light included in the backscattered light as the predetermined light.

  The signal detection unit may detect received light intensity of Stokes light, anti-Stokes light, and Rayleigh light included in the backscattered light as the predetermined light.

  The signal processing unit receives light intensity of the predetermined light according to the temperature of the optical fiber to be measured based on a value corresponding to a change amount of light reception intensity obtained based on a wavelength of 1240 nm light output from another light source. May be corrected.

  Furthermore, according to the second feature of the present invention, an optical fiber temperature distribution measuring system using the optical fiber to be measured comprising a pure silica core optical fiber and the optical fiber temperature distribution measuring device according to the first feature of the present invention. I will provide a.

According to the third aspect of the present invention, the pulsed light is incident on the optical fiber to be measured from the light source, and the predetermined amount included in the backscattered light generated in the optical fiber to be measured based on the incidence of the pulsed light. And detecting a light receiving intensity of the light, calculating a value according to a change amount of the light receiving intensity due to absorption of hydrogen molecules of the optical fiber to be measured based on the light receiving intensity of the predetermined light, and measuring the light to be measured based on the value Correct the received light intensity of the predetermined light according to the temperature of the optical fiber ,
The correction of the light reception intensity of the predetermined light is performed by correcting the light reception intensity of the anti-Stokes light according to the temperature of the optical fiber to be measured based on the Stokes light included in the backscattered light as the predetermined light, or The received light intensity of Stokes light and anti-Stokes light corresponding to the temperature of the optical fiber to be measured is corrected based on Rayleigh light included in the backscattered light as predetermined light, or the backscattered light as the predetermined light An optical fiber temperature distribution measuring method for correcting received light intensity of Stokes light and anti-Stokes light according to the temperature of the optical fiber to be measured based on Rayleigh light of 1240 nm light included in the optical fiber is provided.

  Furthermore, according to the fourth aspect of the present invention, a light source that makes pulsed light incident on the optical fiber to be measured, and light included in backscattered light generated in the optical fiber to be measured based on the incidence of the pulsed light A signal detector for detecting the received light intensity of a plurality of predetermined lights including anti-Stokes light and reference light, and signal processing for calculating the temperature distribution of the optical fiber to be measured using the received light intensity of the anti-Stokes light The signal processing unit calculates the amount of change in the received light intensity of the reference light due to absorption of hydrogen molecules in the optical fiber to be measured for each point, and the hydrogen intensity relative to the received light intensity of the anti-Stokes light is calculated. A correction unit that performs correction for adding the amount of change in the light intensity of the anti-Stokes light due to hydrogen molecule absorption calculated based on the amount of change in the light intensity of the reference light due to molecular absorption; Anti-strike Using the received light intensity of the box beam to provide an optical fiber temperature distribution measuring device having a temperature distribution calculator for the calculation of the temperature distribution.

The amount of change in the light reception intensity of the anti-Stokes light due to the hydrogen molecule absorption may be calculated by multiplying the amount of change in the light reception intensity of the reference light due to the hydrogen molecule absorption by a predetermined coefficient.

The predetermined coefficient may further include a coefficient calculation unit that sets a value obtained by dividing the amount of change in the light intensity of the anti-Stokes light due to the absorption of hydrogen molecules by the amount of change in the light intensity of the reference light due to the absorption of hydrogen molecules. Good.

  A coefficient for calculating the predetermined coefficient as a value for correcting the light reception intensity of the anti-Stokes light so as to become the measurement temperature based on a measurement temperature measured by a temperature sensor arranged in the vicinity of the optical fiber to be measured. You may have a calculating part.

You may further have the coefficient data acquisition part which inputs the said predetermined coefficient from the outside.

A reference for determining a change amount of the light intensity of the reference light due to a temperature difference, and adding a change amount of the light intensity of the reference light due to the temperature difference to the light intensity of the reference light at each point of the measured optical fiber. You may further have a light correction part.

Based on the temperature distribution measurement result in the previous measurement, the amount of change in the received light intensity of the reference light due to the temperature difference may be determined.

The amount of change in the received light intensity of the reference light due to the temperature difference may be determined based on the latest temperature distribution measurement result.

Furthermore, according to a fifth aspect of the present invention, an optical fiber temperature distribution using the optical fiber to be measured, which is an optical fiber having a pure silica core, and the optical fiber temperature distribution measuring apparatus according to the fourth aspect of the present invention. Provide a measurement system.

  According to the sixth aspect of the present invention, the light included in the backscattered light that is incident on the optical fiber to be measured from the light source and is generated in the optical fiber to be measured based on the incidence of the pulsed light. An optical fiber temperature distribution measuring method for detecting a light receiving intensity of a plurality of predetermined lights including an anti-Stokes light and a reference light and calculating a temperature distribution of the optical fiber to be measured using the light receiving intensity of the anti-Stokes light. The amount of change in received light intensity of the reference light due to absorption of hydrogen molecules in the optical fiber to be measured is calculated at each point, and the received light intensity of the reference light due to absorption of hydrogen molecules is compared with the received light intensity of the anti-Stokes light. The amount of change in the received light intensity of the anti-Stokes light due to absorption of hydrogen molecules calculated based on the amount of change is corrected for each point, and the received light intensity of the anti-Stokes light corrected is used to To provide an optical fiber temperature distribution measuring method of the calculation of degrees distribution.

The amount of change in the light reception intensity of the anti-Stokes light due to the hydrogen molecule absorption may be calculated by multiplying the amount of change in the light reception intensity of the reference light due to the hydrogen molecule absorption by a predetermined coefficient.

  The predetermined coefficient may be a value obtained by dividing the amount of change in the light reception intensity of the anti-Stokes light due to the hydrogen molecule absorption by the amount of change in the light reception intensity of the reference light due to the hydrogen molecule absorption.

The predetermined coefficient is calculated as a value for correcting the light reception intensity of the anti-Stokes light so as to be the measurement temperature based on a measurement temperature measured by a temperature sensor disposed in the vicinity of the optical fiber to be measured. Also good.

The predetermined coefficient may be input from the outside.

The first temperature distribution measurement is performed at a stage where hydrogen molecules are not diffused into the optical fiber to be measured and the influence of hydrogen molecule absorption is small, and the first temperature distribution measurement result is obtained at the second temperature measurement. The amount of change in the received light intensity of the reference light due to the temperature difference is determined, and the amount of change in the received light intensity of the reference light due to the temperature difference is added to the received light intensity of the reference light at each point of the measured optical fiber. May be.

  As shown in FIGS. 17A and 17B, the optical fiber has different optical transmission loss depending on the wavelength. Further, as shown in the figure, the optical transmission loss changes when the optical fiber is exposed to atmospheres having different hydrogen partial pressures (0 MPa, 0.05 MPa, 0.09 MPa, 0.15 MPa, and 0.20 MPa). As shown in FIGS. 17A and 17B, when the hydrogen partial pressure increases, the optical transmission loss tends to increase.

  FIGS. 18A and 18B show an increase in the optical transmission loss of the optical fiber based on the optical transmission loss in the absence of hydrogen (ie, 0 MPa) in order to clarify the tendency shown in FIGS. 17A and 17B. For each hydrogen partial pressure (0.05 MPa, 0.09 MPa, 0.15 MPa, and 0.20 MPa). Further, FIG. 19A and FIG. 19B illustrate the ratio of the increase in optical transmission loss at other wavelengths of 850 nm, 1240 nm, 1300 nm, 1450 nm, 1650 nm, and 1690 nm with reference to 1550 nm at which the optical transmission loss in the quartz optical fiber is small. To do. From these charts, it can be seen that the increase in the optical transmission loss of the optical fiber is proportional to the hydrogen partial pressure.

Therefore, the increase amount [Delta] L _j of the optical transmission loss of the optical fiber by the hydrogen molecules at a given wavelength j, the increment [Delta] L _i of the optical transmission loss of the optical fiber by the hydrogen molecules at other wavelengths _i ΔL j _/ ΔL i = K (k is a constant) ---- (7)
Have the relationship. When the ratio k corresponding to the increase in the optical transmission loss at the wavelength i and the wavelength j is determined, the increase ΔL _i in the optical transmission loss due to hydrogen molecules at other wavelengths i can be obtained. The increase amounts ΔL _{j and} ΔL _i of optical transmission loss are due to absorption by hydrogen molecules, and k does not depend on the type of optical fiber. Further, k depends on the wavelength, but does not depend on the temperature or the amount of hydrogen.
Further, if the amount of increase in optical transmission loss due to hydrogen molecules of other wavelengths i is determined, the amount of increase in optical transmission loss due to hydrogen molecules of a certain wavelength j can also be obtained. Therefore, the constant k is calculated based on the ratio of the amount of change in received light intensity due to hydrogen molecules at other wavelengths i to the amount of change in light intensity received by hydrogen molecules at a certain wavelength j using light of other wavelengths i as reference light. Then, by measuring the amount of change in received light intensity due to hydrogen molecules of other wavelengths i, the amount of change in light intensity received by hydrogen molecules of a certain wavelength j can be calculated. In addition, if the constant k is determined from the past measurement results, it is possible to measure the amount of change in the received light intensity by hydrogen molecules of other wavelengths i without performing the measurement for calculating k each time. It is also possible to calculate the amount of change in received light intensity due to hydrogen molecules.

  According to the present invention, the temperature can be accurately measured even when the optical fiber is in a hydrogen atmosphere.

FIG. 1 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to a first embodiment of the present invention. FIG. 2 is a flowchart for _{obtaining the} Stokes light reception intensity I _S0 (x) and the anti-Stokes light reception intensity I _AS0 (x) according to the first embodiment. FIG. 3 is a flowchart for determining the k value according to the first embodiment. FIG. 4 is a flowchart showing a temperature measurement procedure in the optical fiber temperature distribution measurement system according to the first embodiment. FIG. 5A is a characteristic diagram illustrating a temperature measurement result in a case where the correction of the light reception intensity of the anti-Stokes light is not performed in the temperature measurement based on the light reception intensity of the anti-Stokes light. FIG. 5B is a characteristic diagram showing a temperature measurement result when the light intensity of the anti-Stokes light is corrected in the temperature measurement based on the light intensity of the anti-Stokes light. FIG. 6 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to the second embodiment of the present invention. FIG. 7 is a flowchart for _{obtaining the} Stokes light reception intensity I _S0 (x), the anti-Stokes light reception intensity I _AS0 (x), and the Rayleigh light reception intensity I _R0 (x) according to the second embodiment. is there. FIG. 8 is a flowchart for determining the l value and the m value according to the second embodiment. FIG. 9 is a flowchart showing a temperature measurement procedure in the optical fiber temperature distribution measurement system according to the second embodiment. FIG. 10 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to the third embodiment of the present invention. 11, third Stokes light of the received light intensity _{I S0} according to the embodiment of (x), the anti-Stokes light of the received light intensity _{I AS0} (x), and the light-receiving intensity of the Rayleigh light 1240nm light _{I R'0} (x ) Is a flowchart for obtaining. FIG. 12 is a flowchart for determining the n value and the o value according to the third embodiment. FIG. 13 is a flowchart showing a temperature measurement procedure in the optical fiber temperature distribution measurement system according to the third embodiment. FIG. 14A is a diagram showing the principle of temperature distribution measurement of a conventional optical fiber. FIG. 14B is a wavelength distribution diagram of backscattered light of a conventional optical fiber. FIG. 15A is a characteristic diagram showing the relationship between the distance of Stokes light and the light reception intensity when hydrogen molecules are present. FIG. 15B is a characteristic diagram showing the relationship between the distance of the anti-Stokes light and the received light intensity when hydrogen molecules are present. FIG. 16 is a diagram showing the relationship between the measured temperature value and the distance due to the diffusion of hydrogen molecules in the optical fiber to be measured. FIG. 17A is a characteristic diagram showing the amount of optical transmission loss with respect to the wavelength of the optical fiber to be measured. FIG. 17B is a table showing optical transmission loss amounts for each wavelength of the optical fiber to be measured. FIG. 18A is a characteristic diagram showing an increase in optical transmission loss with respect to the wavelength of the optical fiber to be measured. FIG. 18B is a table showing an increase in optical transmission loss for each wavelength of the optical fiber under measurement. FIG. 19A is a characteristic diagram showing the rate of increase in optical transmission loss at other wavelengths with 1550 nm as a reference. FIG. 19B is a table showing the ratio of the increase in optical transmission loss at other wavelengths with 1550 nm as a reference. FIG. 20 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to the fourth embodiment of the present invention. FIG. 21 is a schematic configuration diagram showing an optical fiber temperature distribution measurement system according to the fifth embodiment of the present invention. FIG. 22 is a schematic configuration diagram showing an optical fiber temperature distribution measurement system according to the sixth embodiment of the present invention. FIG. 23 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to the seventh embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 1A 1240nm light source 1B Temperature measuring light source 2 Optical fiber 3 to be measured 3 Beam splitter 4 Incident pulse light 5 Scattering point 6 Back scattered light 7 Output light 8 Wavelength separation part 9 Signal detection part 9A Stokes light detection part 9B Anti-Stokes light detection Unit 9C Rayleigh light detection unit 9D 1240nm light detection unit 9E reference light detection unit 10 signal processing unit 10A correction unit 10B temperature distribution calculation unit 10C coefficient calculation unit 10D coefficient data capturing unit 10E reference light correction unit 11 display unit 12 temperature sensor 13 temperature Conversion unit 20 Rayleigh light 21 Stokes light 22 Anti-Stokes light 30 Measurement atmosphere

(First embodiment)
FIG. 1 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to a first embodiment of the present invention. The optical fiber temperature distribution measurement system according to the present embodiment causes the light source 1, the optical fiber 2 to be measured, and the incident pulsed light 4 to enter the optical fiber 2 to be measured and is generated at the scattering point 5 of the optical fiber 2 to be measured. A beam splitter 3 that converts the path of the backscattered light 6 and outputs the output light 7 to the wavelength separation unit 8; a wavelength separation unit 8 that separates the light output from the beam splitter 3 into Stokes light and anti-Stokes light; A signal detector 9 having a Stokes light detector 9A for detecting the Stokes light separated by the wavelength separator 8 and an anti-Stokes light detector 9B for detecting the anti-Stokes light, the incident timing of the incident pulsed light 4, and the measurement target Based on the time difference from the detection timing of the backscattered light 6 generated at the scattering point 5 in the optical fiber 2, the scattering point (measurement point) of the measured optical fiber 2 from the incident end. 5, a signal processing unit 10 that calculates the temperature of the optical fiber 2 to be measured by correcting the light reception intensity of the anti-Stokes light from the signal detected by the signal detection unit 9, and a calculation in the signal processing unit 10 And a display unit 11 for displaying results and the like. In the figure, a state in which the optical fiber 2 to be measured is in a hydrogen atmosphere is shown. The optical fiber temperature distribution measuring device in the present invention is the light source 1, the beam splitter 3, the wavelength separation unit 8, the signal detection unit 9, the signal processing unit 10, and the display excluding the measured optical fiber 2 in FIG. The part comprised from the part 11 is pointed out. Further, the optical fiber temperature distribution measuring system refers to the whole including the optical fiber temperature distribution measuring device and the measured optical fiber 2.

  2 to 4 are flowcharts showing a temperature measurement procedure in the optical fiber temperature distribution measurement system shown in FIG. 1. Hereinafter, referring to FIGS. 2 to 4, the received light intensity of anti-Stokes light by Stokes light is shown. The temperature measurement of the optical fiber to be measured for correcting the above will be described.

  First, the optical fiber 2 to be measured used for measurement is connected to the light source 1 in a hydrogen-free atmosphere (a state in which no hydrogen is present in the measurement atmosphere 30) (S1). Incident pulsed light 4 is incident (S2). In the optical fiber 2 to be measured, backscattered light 6 (λ, λ + Δλ, λ−Δλ) generated at the scattering point 5 in the course of propagation appears and returns to the incident end side. The beam splitter 3 optically converts the backscattered light 6 and outputs it to the wavelength separator 8 (S3).

The wavelength separation unit 8 separates the Stokes light (λ + Δλ) and the anti-Stokes light (λ−Δλ) included in the backscattered light 6 and outputs them to the signal detection unit 9 (S4). The signal detection unit 9 receives the Stokes light at the Stokes light detection unit 9A, and detects the received light intensity I _S0 (x). Here, x represents the distance from the incident end to the scattering point 5. Further, the anti-Stokes light detector 9B receives the anti-Stokes light and detects its received light intensity I _AS0 (x) (S5).

  Next, the optical fiber 2 to be measured is connected to the light source 1 in a hydrogen atmosphere (a state in which hydrogen is present in the measurement atmosphere 30) (S6), and the incident pulsed light 4 having the wavelength λ from the light source 1 to the optical fiber 2 to be measured. Is incident (S7). Back scattered light 6 (λ, λ + Δλ, λ−Δλ) generated at a scattering point 5 of the measured optical fiber 2 based on the incident pulsed light 4 appears and returns to the incident end side. The beam splitter 3 optically converts the backscattered light 6 and outputs it to the wavelength separator 8 (S8).

The wavelength separation unit 8 separates the Stokes light (λ + Δλ) and the anti-Stokes light (λ−Δλ) included in the backscattered light 6 and outputs them to the signal detection unit 9 (S9). The signal detection unit 9 receives the Stokes light in the Stokes light detection unit 9A, and detects the received light intensity I _S1 (x). Further, the anti-Stokes light detector 9B receives the anti-Stokes light and detects its received light intensity I _AS1 (x) (S10).

Next, the change amount ΔI _S (x) of the received light intensity of the Stokes light by the hydrogen molecules, that is, the received light intensity I _S1 (x) of the Stokes light by the measured optical fiber 2 in the hydrogen atmosphere and the measured value in the atmosphere without hydrogen. A difference from the received light intensity I _S0 (x) of the Stokes light by the optical fiber 2 is obtained (ΔI _S (x) = I _S1 (x) −I _S0 (x)). Similarly, the amount of change ΔI _AS (x) of the light reception intensity of anti-Stokes light by hydrogen molecules, that is, the light reception intensity I _AS1 (x) of anti-Stokes light by the optical fiber 2 to be measured in a hydrogen atmosphere and in an atmosphere without hydrogen A difference from the light reception intensity I _AS0 (x) of the anti-Stokes light by the measured optical fiber 2 is obtained (ΔI _AS (x) = I _AS1 (x) −I _AS0 (x)). Furthermore, the ratio of the change amount ΔI _S (x) of the light intensity of Stokes light due to hydrogen molecules to the change amount ΔI _AS (x) of the light intensity of the anti-Stokes light,
ΔI _AS (x) / ΔI _S (x) = k −−−− (8)
Is obtained (S11).
Note that the value of k can be obtained from the amount of change in the received light intensity of Stokes light and anti-Stokes light as described above, but the optical fiber made of hydrogen molecules shown in FIGS. 18A and 18B and FIGS. 19A and 19B. It can also be obtained from the wavelength dependence data of the increase in optical transmission loss.

Next, the optical fiber 2 to be measured is connected to the light source 1 in a hydrogen atmosphere where the measurement is actually performed (the hydrogen is present in the measurement atmosphere 30 where the measurement is actually performed) (S12). The incident pulsed light 4 of wavelength λ is incident on 2 (S13). The beam splitter 3 optically converts the backscattered light 6 generated based on the incident pulsed light 4 and outputs it to the wavelength separator 8 (S14), separates the Stokes light and the anti-Stokes light, and outputs them to the signal detector 9. (S15). The signal detector 9 receives the Stokes light at the Stokes light detector 9A and detects the received light intensity I _S (x), and the anti-Stokes light detector 9B receives the anti-Stokes light and receives the received light intensity I _AS (x). Is detected (S16).

Next, the signal processing unit 10 computes a signal based on the received light intensity of the Stokes light and the anti-Stokes light, thereby obtaining the temperature of the optical fiber 2 to be measured.
If the received light intensity of anti-Stokes light excluding the influence of hydrogen is I _AS ′ (x),
I _AS '(x) = I _AS (x) −ΔI _AS (x) −−−− (9)
From the equation (8), ΔI _AS (x) = k · ΔI _S (x), so this is substituted into the equation (9),
I _AS ′ (x) = I _AS (x) −k · ΔI _S (x) −−−− (10)
In addition, the amount of change in received light intensity due to hydrogen molecules of Stokes light is
ΔI _S (x) = I _S1 (x) −I _S0 (x) −−−− (11)
Substituting this into equation (10)
I _AS ′ (x) = I _AS (x) −k · (I _S1 (x) −I _S0 (x)) −−−− (12)
Thus, the received light intensity of the anti-Stokes light excluding the influence of hydrogen is obtained using the change in the received light intensity of the Stokes light (S17).

  Since the received light intensity of the corrected anti-Stokes light thus obtained is a function of the absolute temperature T of the scattering point 5 in the optical fiber 2 to be measured as described above, it is scattered based on the equation (6). The temperature at point 5 can be accurately obtained (S18).

  5A and 5B are characteristic diagrams showing temperature measurement based on the light reception intensity of the anti-Stokes light, FIG. 5A shows a temperature measurement result without correcting the light reception intensity of the anti-Stokes light, and FIG. 5B shows the anti-Stokes light. The temperature measurement result which performed correction | amendment of the received light intensity of is shown. Here, temperature measurement results at hydrogen partial pressures of 0 MPa, 0.04 MPa, 0.07 MPa, and 0.09 MPa are shown.

(Effects of the first embodiment)
According to the first embodiment, the optical fiber under measurement is based on the received intensity of the Stokes light and the anti-Stokes light obtained by measuring the temperature of the optical fiber 2 under measurement in a hydrogen-free atmosphere and in a hydrogen atmosphere. The value (ratio) k corresponding to the amount of change in the received light intensity based on the hydrogen molecule absorption of 2 is obtained, and the reaction obtained by making the incident pulsed light 4 incident on the optical fiber 2 to be measured in a hydrogen atmosphere in which measurement is actually performed. The light reception intensity of Stokes light can be corrected using the light reception intensity of Stokes light.

  Therefore, as shown in the measurement result of FIG. 5B, the accurate temperature measurement result excluding the influence of hydrogen in the measurement environment is obtained from the temperature measurement result including the optical transmission loss due to hydrogen molecules shown in the measurement result of FIG. 5A. Can do.

(Second Embodiment)
FIG. 6 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to the second embodiment of the present invention. In the second embodiment, a wavelength separation unit 8 that separates light output from the beam splitter 3 into Stokes light, anti-Stokes light, and Rayleigh light, and Stokes light that is separated by the wavelength separation unit 8 are detected. It differs from the first embodiment in that it has a signal detector 9 having a light detector 9A, an anti-Stokes light detector 9B for detecting anti-Stokes light, and a Rayleigh light detector 9C for detecting Rayleigh light. is doing. FIG. 6 also shows a state where the optical fiber 2 to be measured is in a hydrogen atmosphere. In the following description, parts having the same configuration and the same function as those of the first embodiment are denoted by common reference numerals.

  FIGS. 7 to 9 are flowcharts showing a temperature measurement procedure in the optical fiber temperature distribution measurement system shown in FIG. 6. Hereinafter, referring to FIGS. 7 to 9, the Stokes light is based on the received light intensity of Rayleigh light. Next, temperature measurement of the optical fiber to be measured for correcting the received light intensity of the anti-Stokes light will be described.

  First, the optical fiber 2 to be measured used for measurement is connected to the light source 1 in an atmosphere without hydrogen (S20), and the incident pulsed light 4 having the wavelength λ is incident on the optical fiber 2 to be measured from the light source 1 (S21). . In the optical fiber 2 to be measured, backscattered light 6 (λ, λ + Δλ, λ−Δλ) generated in the propagation process at a certain scattering point 5 appears and returns to the incident end side. The beam splitter 3 optically converts the backscattered light 6 and outputs it to the wavelength separation unit 8 (S22).

The wavelength separation unit 8 separates the Stokes light (λ + Δλ), the anti-Stokes light (λ−Δλ), and the Rayleigh light (λ) included in the backscattered light 6 and outputs them to the signal detection unit 9 (S23). The signal detector 9 receives the Stokes light at the Stokes light detector 9A and detects the received light intensity I _S0 (x), and the anti-Stokes light detector 9B receives the anti-Stokes light and detects the received light intensity I _AS0 (x). Then, the Rayleigh light detection unit 9C receives the Rayleigh light and detects the received light intensity I _R0 (x) (S24).

  Next, the optical fiber 2 to be measured is connected to the light source 1 in a hydrogen atmosphere (S25), and incident pulsed light 4 having a wavelength λ is incident from the light source 1 to the optical fiber 2 to be measured (S26). Back scattered light 6 (λ, λ + Δλ, λ−Δλ) generated at a scattering point 5 of the measured optical fiber 2 based on the incident pulsed light 4 appears and returns to the incident end side. The beam splitter 3 optically converts the backscattered light 6 and outputs it to the wavelength separator 8 (S27).

The wavelength separation unit 8 separates the Stokes light (λ + Δλ), the anti-Stokes light (λ−Δλ), and the Rayleigh light (λ) included in the backscattered light 6 and outputs them to the signal detection unit 9 (S28). In the signal detector 9, the Stokes light detector 9A receives the Stokes light and detects the received light intensity I _S1 (x), and the anti-Stokes light detector 9B receives the anti-Stokes light and detects the received light intensity I _AS1 (x). The Rayleigh light detector 9C receives the Rayleigh light and detects the received light intensity I _R1 (x) (S29).

Next, the change amount ΔI _S (x) of the received light intensity of the Stokes light by the hydrogen molecules, that is, the received light intensity I _S1 (x) of the Stokes light by the measured optical fiber 2 in the hydrogen atmosphere and the measured value in the atmosphere without hydrogen. A difference from the received light intensity I _S0 (x) of the Stokes light by the optical fiber 2 is obtained (ΔI _S (x) = I _S1 (x) −I _S0 (x)). Similarly, the amount of change ΔI _R (x) in the light receiving intensity of Rayleigh light by hydrogen molecules, that is, the light receiving intensity I _R1 (x) of Rayleigh light by the optical fiber 2 to be measured in a hydrogen atmosphere and the measurement in an atmosphere without hydrogen. A difference from the light receiving intensity I _R0 (x) of the Rayleigh light by the optical fiber 2 is obtained (ΔI _R (x) = I _R1 (x) −I _R0 (x)). Further, for the optical fiber 2 to be measured, the ratio of the change amount ΔI _S (x) of the Stokes light reception intensity to the change amount ΔI _R (x) of the Rayleigh light reception intensity due to hydrogen molecules,
ΔI _S (x) / ΔI _R (x) = l −−−− (13)
Is obtained (S30).

Next, the amount of change ΔI _AS (x) of the light intensity of the anti-Stokes light due to hydrogen molecules, that is, the light intensity I _AS1 (x) of the anti-Stokes light by the optical fiber 2 to be measured in the hydrogen atmosphere A difference from the light reception intensity I _AS0 (x) of the anti-Stokes light by the measured optical fiber 2 is obtained (ΔI _AS (x) = I _AS1 (x) −I _AS0 (x)). Further, for the optical fiber 2 to be measured, the ratio of the change amount ΔI _AS (x) of the light intensity of the anti-Stokes light to the change amount ΔI _R (x) of the Rayleigh light intensity due to hydrogen molecules,
ΔI _AS (x) / ΔI _R (x) = m −−−− (14)
Is obtained (S31).

Next, the optical fiber 2 to be measured is connected to the light source 1 in a hydrogen atmosphere in which measurement is actually performed (S32), and incident pulsed light 4 having a wavelength λ is incident on the optical fiber 2 to be measured from the light source 1 (S33). . The beam splitter 3 converts the path of the backscattered light 6 generated based on the incident pulsed light 4 and outputs it to the wavelength separating unit 8 (S34), and separates the Stokes light, the anti-Stokes light, and the Rayleigh light to generate the signal detecting unit 9 (S35). The signal detector 9 receives the Stokes light at the Stokes light detector 9A and detects the received light intensity I _S (x), and the anti-Stokes light detector 9B receives the anti-Stokes light and detects the received light intensity I _AS (x). Then, the Rayleigh light detection unit 9C receives the Rayleigh light and detects the received light intensity I _R (x) (S36).

Next, the signal processing unit 10 computes a signal based on the received light intensity of Stokes light, anti-Stokes light, and Rayleigh light, thereby obtaining the temperature of the optical fiber 2 to be measured.
When the received light intensity of Stokes light excluding the influence of hydrogen is I _S ′ (x),
_{I S '(x) = I} S (x) -ΔI S (x) ---- (15)
From the equation (13), ΔI _S (x) = l · ΔI _R (x), so this is substituted into the equation (15),
_{I S '(x) = I} S (x) -l · ΔI R (x) ---- (16)
In addition, the amount of change in the received light intensity due to hydrogen molecules in Rayleigh light is
ΔI _R (x) = I _R1 (x) −I _R0 (x) −−−− (17)
Substituting this into equation (16)
_{I S '(x) = I} S (x) -l · (I R1 (x) -I R0 (x)) ---- (18)
Thus, the received light intensity of Stokes light excluding the influence of hydrogen is obtained using the change in the received light intensity of Rayleigh light (S37).

Next, assuming that the light receiving intensity of the anti-Stokes light excluding the influence of hydrogen is I _AS ′ (x),
I _AS '(x) = I _AS (x) −ΔI _AS (x) −−−− (19)
From the equation (14), ΔI _AS (x) = m · ΔI _R (x), so this is substituted into the equation (19),
I _AS ′ (x) = I _AS (x) −m · ΔI _R (x) −−−− (20)
In addition, the amount of change in the received light intensity due to hydrogen molecules in Rayleigh light is
ΔI _R (x) = I _R1 (x) −I _R0 (x) −−−− (21)
Substituting this into equation (20)
I _AS ′ (x) = I _AS (x) −m · (I _R1 (x) −I _R0 (x)) −−−− (22)
Thus, the received light intensity of anti-Stokes light excluding the influence of hydrogen is obtained using the change in the received light intensity of Rayleigh light (S38).

  The corrected Stokes light and anti-Stokes light obtained in this way are a function of the absolute temperature T of the scattering point 5 in the optical fiber 2 to be measured as described above, and are thus scattered based on the equation (5). The temperature at point 5 can be accurately obtained (S39).

(Effect of the second embodiment)
According to the second embodiment, the measurement target is based on the received light intensity of Stokes light, anti-Stokes light, and Rayleigh light obtained by measuring the temperature of the optical fiber 2 to be measured in an atmosphere without hydrogen and in a hydrogen atmosphere. Since values (ratio) l and m corresponding to the amount of change in received light intensity due to absorption of hydrogen molecules in the optical fiber 2 are obtained, the incident pulse light 4 is incident on the optical fiber 2 to be measured in a hydrogen atmosphere in which measurement is actually performed. It is possible to correct the received light intensity of anti-Stokes light and the received light intensity of Stokes light using the received light intensity of Rayleigh light. Since Rayleigh light is extremely less temperature dependent than Stokes light and anti-Stokes light, the values (ratio) l and m can be applied regardless of the ambient temperature of the optical fiber. Further, as a simple form based on this embodiment, an embodiment in which temperature measurement is performed based on Rayleigh light and anti-Stokes light without using Stokes light is also conceivable.

(Third embodiment)
FIG. 10 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to the third embodiment of the present invention. In the third embodiment, light having a wavelength λr different from the wavelength λ of the temperature measurement light is used as the reference light for measuring the amount of change in the received light intensity. Specifically, as shown in FIG. 18A, since 1240 nm is a wavelength at which an increase in optical transmission loss due to hydrogen molecules appears remarkably, light having a wavelength of 1240 nm is used as reference light. In the third embodiment, the 1240 nm light source 1A that makes 1240 nm light incident on the optical fiber 2 to be measured via the beam splitter 3, the light source 1B for temperature measurement, and the light output from the beam splitter 3 are converted into Stokes light and antireflective light. A wavelength separation unit 8 that separates into Stokes light and 1240 nm light, a Stokes light detection unit 9A that detects Stokes light separated by the wavelength separation unit 8, an anti-Stokes light detection unit 9B that detects anti-Stokes light, and 1240 nm The second embodiment is different from the first embodiment in that it includes a signal detection unit 9 including a 1240 nm light detection unit 9D that detects light. FIG. 10 also shows a state in which the optical fiber 2 to be measured is in a hydrogen atmosphere.

  FIG. 11 to FIG. 13 are flowcharts showing a temperature measurement procedure in the optical fiber temperature distribution measurement system shown in FIG. 10. Hereinafter, referring to FIG. 11 to FIG. 13, Stokes light based on Rayleigh light of 1240 nm light. The temperature measurement of the optical fiber to be measured for correcting the received light intensity of the anti-Stokes light will be described.

  First, the optical fiber 2 to be measured used for measurement is connected to the 1240 nm light source 1A in an atmosphere free of hydrogen (S40), and the incident pulsed light 4 having the wavelength λr (= 1240 nm) from the 1240 nm light source 1A to the optical fiber 2 to be measured. Is incident (S41). In the measured optical fiber 2, backscattered light 6 (λr, λr + Δλr, λr−Δλr) generated in the propagation process at a certain scattering point 5 appears and returns to the incident end side. The beam splitter 3 optically converts the backscattered light 6 and outputs it to the wavelength separator 8 (S42).

The wavelength separation unit 8 separates the Rayleigh light of 1240 nm light included in the backscattered light 6 and outputs it to the signal detection unit 9 (S43). In the signal detector 9, the 1240 nm light detector 9D receives Rayleigh light of 1240 nm light, and detects the received light intensity I _R′0 (x) (S44).

  Next, the optical fiber 2 to be measured is connected to the temperature measuring light source 1B in an atmosphere without hydrogen (S45), and the incident pulsed light 4 having the wavelength λ is incident on the optical fiber 2 to be measured from the temperature measuring light source 1B. (S46). The beam splitter 3 changes the optical path of the backscattered light 6 (λ, λ + Δλ, λ−Δλ) generated at the scattering point 5 of the measured optical fiber 2 based on the incident pulsed light 4 and outputs it to the wavelength separation unit 8. (S47).

The wavelength separator 8 separates the Stokes light (λ + Δλ) and the anti-Stokes light (λ−Δλ) included in the backscattered light 6 and outputs them to the signal detector 9 (S48). The signal detector 9 receives the Stokes light at the Stokes light detector 9A and detects the received light intensity I _S0 (x), and the anti-Stokes light detector 9B receives the anti-Stokes light and detects the received light intensity I _AS0 (x). (S49).

Next, the optical fiber 2 to be measured is connected to the 1240 nm light source 1A in a hydrogen atmosphere (S50), and the wavelength λr (= 1240 nm) incident pulsed light 4 is incident, Rayleigh light is separated from backscattered light 6 generated based on the incident light, and 1240 nm light detecting unit 9D of signal detecting unit 9 receives 1240 nm light of Rayleigh light. The intensity I _R′1 (x) is detected (S51).

Next, the optical fiber 2 to be measured is connected to the temperature measurement light source 1B in a hydrogen atmosphere (S52), and the wavelength λ is applied to the optical fiber 2 to be measured in the same manner as the operation performed in an atmosphere without hydrogen. , The Stokes light and the anti-Stokes light are separated from the backscattered light 6 generated based on the incident pulsed light 4 and output to the signal detector 9. The signal detection unit 9 receives the Stokes light in the Stokes light detection unit 9A, and detects the received light intensity I _S1 (x). Further, the anti-Stokes light detector 9B receives the anti-Stokes light and detects the received light intensity I _AS1 (x) (S53).

Next, with respect to the optical fiber 2 to be measured, the change amount ΔI _S of the Stokes light reception intensity of the incident pulsed light 4 having the wavelength λ with respect to the change amount ΔI _{R ′} (x) of the Rayleigh light of 1240 nm light due to hydrogen molecules. x) ratio,
ΔI _S (x) / ΔI _{R ′} (x) = n −−−− (23)
Is obtained (S54).

Next, for the optical fiber 2 to be measured, the change amount ΔI _AS of the light intensity of the anti-Stokes light of the incident pulsed light 4 of the wavelength λ with respect to the change amount ΔI _{R ′} (x) of the Rayleigh light of 1240 nm light due to hydrogen molecules. The ratio of (x),
ΔI _AS (x) / ΔI _{R ′} (x) = o −−−− (24)
Is obtained (S55).

Next, the optical fiber 2 to be measured is connected to the 1240 nm light source 1A in a hydrogen atmosphere where the measurement is actually performed (S56), and the incident pulsed light 4 having the wavelength λr (= 1240 nm) is input from the 1240 nm light source 1A to the optical fiber 2 to be measured. , And the Rayleigh light of 1240 nm light is separated from the backscattered light 6 generated at the scattering point 5 and output to the signal detection unit 9. The signal detection unit 9 receives the Rayleigh light of 1240 nm light in the 1240 nm light detection unit 9D, and detects the received light intensity I _{R ′} (x) (S57).

Next, the optical fiber 2 to be measured is connected to the temperature measuring light source 1B in a hydrogen atmosphere where the measurement is actually performed (S58), and the incident pulsed light 4 having the wavelength λ is applied from the temperature measuring light source 1B to the optical fiber 2 to be measured. , And the Stokes light and the anti-Stokes light are separated from the backscattered light 6 generated at the scattering point 5 and output to the signal detector 9. The signal detector 9 receives the Stokes light at the Stokes light detector 9A and detects the received light intensity I _S (x), and the anti-Stokes light detector 9B receives the anti-Stokes light and detects the received light intensity I _AS (x). (S59).

Next, the signal processing unit 10 calculates the temperature of the optical fiber 2 to be measured by processing signals based on the received intensity of the Stokes light and anti-Stokes light of the incident pulsed light 4 having the wavelength λ and the Rayleigh light of 1240 nm light. Ask.
When the received light intensity of the Stokes light of the incident pulsed light 4 having the wavelength λ excluding the influence of hydrogen is I _S ′ (x),
_{I S '(x) = I} S (x) -ΔI S (x) ---- (25)
From the equation (23), ΔI _S (x) = n · ΔI _{R ′} (x), so this is substituted into the equation (25),
_{I S '(x) = I} S (x) -n · ΔI R (x) ---- (26)
In addition, the optical transmission loss amount of Rayleigh light of 1240 nm light is
ΔI _{R ′} (x) = I _R′1 (x) −I _R′0 (x) −−−− (27)
Substituting this into equation (26)
_{I S '(x) = I} S (x) -n · (I R'1 (x) -I R'0 (x)) ---- (28)
Thus, a value obtained by correcting the light reception intensity of the Stokes light of the incident pulsed light 4 having the wavelength λ with the light reception intensity of the Rayleigh light of 1240 nm light is obtained (S60).

Next, assuming that the light receiving intensity of the anti-Stokes light of the incident pulsed light 4 having the wavelength λ excluding the influence of hydrogen is I _AS ′ (x)
I _AS '(x) = I _AS (x) −ΔI _AS (x) −−−− (29)
From the equation (24), ΔI _AS (x) = o · ΔI _{R ′} (x), so this is substituted into the equation (29),
I _AS ′ (x) = I _AS (x) −o · ΔI _{R ′} (x) −−−− (30)
In addition, the optical transmission loss amount of Rayleigh light of 1240 nm light is
ΔI _{R ′} (x) = I _R′1 (x) −I _R′0 (x) −−−− (31)
Substituting this into equation (30)
_{I AS '(x) = I} AS (x) -o · (I R'1 (x) -I R'0 (x)) ---- (32)
Thus, a value obtained by correcting the light reception intensity of the anti-Stokes light of the incident pulsed light 4 having the wavelength λ with the light reception intensity of the Rayleigh light of 1240 nm light is obtained (S61).

  The corrected Stokes light and anti-Stokes light obtained in this way are a function of the absolute temperature T of the scattering point 5 in the optical fiber 2 to be measured as described above, and are thus scattered based on the equation (5). The temperature at point 5 can be accurately obtained (S62).

(Effect of the third embodiment)
According to the third embodiment, the Stokes light and the anti-Stokes light of the incident pulsed light 4 having the wavelength λ obtained by measuring the temperature of the optical fiber 2 to be measured in an atmosphere without hydrogen and in a hydrogen atmosphere. Based on the intensity and the light receiving intensity of Rayleigh light of 1240 nm light, values (ratio) n, o corresponding to the amount of change in the light receiving intensity based on the hydrogen molecule absorption of the optical fiber 2 to be measured are obtained. Accordingly, the light intensity of the anti-Stokes light and the light intensity of the Stokes light obtained based on the incident pulsed light 4 having the wavelength λ incident on the optical fiber 2 to be measured in the hydrogen atmosphere in which the measurement is actually performed are 1240 nm light. It becomes possible to correct based on the light receiving intensity of the Rayleigh light. As shown in FIG. 18A, 1240 nm light has a wavelength at which an increase in optical transmission loss due to hydrogen molecules appears remarkably, and therefore can be corrected with high sensitivity.

  Further, as a simple form based on the present embodiment, temperature measurement is not performed based on the Rayleigh light of 1240 nm light and the anti-Stokes light of incident pulse light 4 of wavelength λ, without using the Stokes light of incident pulse light 4 of wavelength λ. Embodiments to perform are also conceivable. Further, in the present embodiment, the 1240 nm light source 1A and the temperature measuring light source 1B are configured as separate light sources, but a single light source unit including the 1240 nm light source and the temperature measuring light source is used as the optical fiber 2 to be measured. It is also possible to connect and switch between the two light sources. Alternatively, the wavelength of the temperature measurement light source 1B may be changed so that 1240 nm light and an optical signal of another wavelength for temperature measurement are successively incident on the optical fiber 2 to be measured in a time division manner.

(Fourth embodiment)
FIG. 20 is a schematic configuration diagram showing an optical fiber temperature distribution measuring system according to the fourth embodiment. In the fourth embodiment, a wavelength separator 8 that separates light output from the beam splitter 3 into reference light and anti-Stokes light, and a reference light detector 9E that detects the reference light separated by the wavelength separator 8. The signal processing unit 9 further includes a signal processing unit 10 that calculates the temperature distribution of the optical fiber 2 to be measured using the received light intensity of the anti-Stokes light, and the signal processing unit 10 includes hydrogen of the optical fiber 2 to be measured. The amount of change in the received light intensity of the reference light due to molecular absorption is calculated for each measurement point, and the effect of the hydrogen molecule absorption loss calculated based on the change in the received light intensity of the reference light against the light intensity of the anti-Stokes light. A correction unit 10A that performs correction to add the amount of change in the light reception intensity of the anti-Stokes light to each measurement point, and a temperature distribution calculation unit 10B that calculates a temperature distribution based on the light reception intensity of the corrected anti-Stokes light. In is different from the first embodiment. FIG. 20 also shows a state where the optical fiber 2 to be measured is in a hydrogen atmosphere.

Here, “correction to add the amount of change in the light intensity of anti-Stokes light depending on the influence of hydrogen molecule absorption loss”
I _AS ′ (x) = I _AS (x) −ΔI _AS (x) −−−− (33)
Because
I _AS ′ (x) = I _AS (x) −p · ΔI _Rf (x) −−−− (34)
(P is a _{constant, ΔI Rf (x) = I} Rf1 (x) -I Rf0 (x))
Means correction based on. Here, ΔI _Rf (x) is the amount of change in the received light intensity of the reference light, and the received light intensity I _Rf0 (x) of the reference light of the measured optical fiber 2 in the atmosphere without hydrogen and the measured light in the hydrogen atmosphere. It is obtained from the difference in the received light intensity I _Rf1 (x) of the reference light of the fiber 2. As described above, the change amount ΔI _AS (x) of the received light intensity of the anti-Stokes light due to the influence of the hydrogen molecule absorption loss is obtained by multiplying the change amount ΔI _Rf (x) of the received light intensity of the reference light due to the hydrogen molecule absorption loss by the coefficient p. Can be calculated. In addition, the same code | symbol is attached | subjected about the part which has the same structure and 1st function as 1st Embodiment. The reference light means light other than the anti-Stokes light of the incident pulsed light 4 incident from the temperature measurement light source 1, and means Stokes light, Rayleigh light, or light of other wavelengths (for example, light of 1240 nm). To do.

Further, the signal processing unit 10 divides the change amount ΔI _AS (x) of the received light intensity of the anti-Stokes light due to the absorption of hydrogen molecules by the change amount ΔI _Rf (x) of the received light intensity of the reference light due to the absorption of hydrogen molecules. You may further have the coefficient calculating part 10C to calculate. Further, the fourth embodiment may be applied to other embodiments.

(Fifth embodiment)
FIG. 21 is a schematic configuration diagram showing an optical fiber temperature distribution measurement system according to the fifth embodiment of the present invention. In the fifth embodiment, one or a plurality of temperature sensors 12 that are installed in the vicinity of the optical fiber 2 to be measured in a hydrogen atmosphere and measure the temperature of the optical fiber 2 to be measured; This is different from the fourth embodiment in that it further includes a temperature conversion unit 13 that converts a signal into a temperature. FIG. 21 also shows a state where the optical fiber 2 to be measured is in a hydrogen atmosphere. In addition, the same code | symbol is attached | subjected about the part which has the same structure and the same function as 4th Embodiment.

In the fifth embodiment, the correction unit 10A multiplies the change amount ΔI _Rf (x) of the received light intensity of the reference light by the hydrogen molecule by a predetermined coefficient p to change the received light intensity of the anti-Stokes light ΔI by the hydrogen molecule ΔI. _AS (x) is calculated, and the received intensity of the anti-Stokes light is corrected based on the calculation result. The temperature distribution calculation unit 10B calculates the temperature of the optical fiber 2 to be measured at the measurement point based on the corrected received light intensity of the anti-Stokes light. The temperature sensor 12 measures the temperature at the measurement point of the optical fiber 2 to be measured, and transmits a signal indicating the temperature to the temperature converter 13 to the temperature converter 13 by wire or wirelessly. The temperature conversion unit 13 converts the signal received from the temperature sensor 12 into a temperature. The coefficient calculation unit 10C corrects the coefficient p for correction so that the calculation result of the temperature of the optical fiber 2 to be measured measured by the temperature sensor 12 and the temperature of the optical fiber 2 to be measured calculated by the temperature distribution calculation unit 10B match. Is calculated.

  In the fifth embodiment, the coefficient p is calculated based on the measured temperature of the optical fiber 2 detected by the temperature sensor 12 installed in the vicinity of the optical fiber 2 to be measured. It is possible to measure the temperature of the optical fiber 2 to be measured without measuring the change in the received light intensity of the anti-Stokes light and the reference light in a hydrogen atmosphere and in a hydrogen atmosphere without calculating the coefficient p based on these measurement results. . Therefore, even when the value of the coefficient p changes due to a change in the output wavelength of the light source 1, the received light intensity of the anti-Stokes light can be accurately corrected without being affected by the change. Further, by providing a plurality of temperature sensors 12, even when the temperature difference between the measurement points of the optical fiber 2 to be measured is large, highly accurate correction can be performed. In addition, the fifth embodiment may be applied to other embodiments.

(Sixth embodiment)
FIG. 22 is a schematic configuration diagram showing an optical fiber temperature distribution measurement system according to the sixth embodiment. In the sixth embodiment, the light processing intensity of the anti-Stokes light by the hydrogen molecule calculated by the signal processing unit 10 based on the change amount of the light receiving intensity of the reference light by the hydrogen molecule with respect to the light reception intensity of the anti-Stokes light. The difference from the fourth embodiment is that it further includes a coefficient data capturing unit 10D that inputs a coefficient p used for correction from the outside when adding the amount of change for each measurement point. FIG. 22 also shows a state where the optical fiber 2 to be measured is in a hydrogen atmosphere. In addition, the same code | symbol is attached | subjected about the part which has the same structure and the same function as 4th Embodiment. In addition, the sixth embodiment may be applied to other embodiments.

(Seventh embodiment)
FIG. 23 is a schematic configuration diagram showing an optical fiber temperature distribution measurement system according to the seventh embodiment. Stokes light has a temperature dependence that is lower than the temperature dependence of anti-Stokes light. For this reason, in the equation (11), when measuring the received light intensity I _S0 (x) of the Stokes light in the hydrogen-free atmosphere and the received light intensity I _S1 (x) of the Stokes light in the hydrogen atmosphere, the optical fiber to be measured When there is a difference between the two ambient temperatures, an error occurs in the amount of change in the Stokes light reception intensity calculated by the equation (11) due to the difference in the Stokes light reception intensity caused by the difference in the ambient temperature. However, the error problem can be solved by subtracting the difference in received light intensity caused by the difference in ambient temperature from the amount of change in received light intensity of the Stokes light calculated by the equation (11).

  In the seventh embodiment, the signal processing unit 10 determines the amount of change in the received light intensity of the reference light due to the difference in ambient temperature of the measured optical fiber 2, and the measured optical fiber with respect to the received light intensity of the reference light Each of the measurement points 2 is different from the fourth embodiment in that it further includes a reference light correction unit 10E that adds a change amount of the received light intensity of the reference light due to a difference in ambient temperature. FIG. 23 also shows a state in which the optical fiber 2 to be measured is in a hydrogen atmosphere. In addition, the same code | symbol is attached | subjected about the part which has the same structure and the same function as 4th Embodiment.

  In the seventh embodiment, the amount of change in the received light intensity of the reference light due to the difference in ambient temperature of the measured optical fiber 2 can be obtained as follows. First, the first temperature distribution measurement is performed at a stage where hydrogen molecules are not diffused in the optical fiber 2 to be measured and the influence of hydrogen molecule absorption is small. Next, when measuring the temperature distribution for the second time, the amount of change in the received light intensity of the reference light due to the difference in ambient temperature is determined based on the result obtained by the first temperature distribution measurement. Furthermore, in the next and subsequent measurements, the amount of change in the received light intensity of the reference light due to the temperature difference can be determined based on the result obtained in the previous temperature distribution measurement, and the same process can be repeated.

  Further, when it is determined that the ambient temperature of the measured optical fiber 2 for measuring the received light intensity of the reference light is different from the ambient temperature set by the signal processing unit 10 as a result of the latest temperature distribution measurement, the latest measurement is performed. Based on the temperature, the ambient temperature for measuring the received light intensity of the reference light is set. Furthermore, the amount of change in the received light intensity of the reference light due to the difference in ambient temperature is corrected based on the relationship data of the change in the received light intensity of the reference light due to the difference between the ambient temperature and the ambient temperature. Based on the corrected received light intensity of the reference light, the temperature distribution of the measured optical fiber 2 is measured again.

  Since the temperature can be measured by the conventional technique in an atmosphere where there is little influence of hydrogen molecule absorption, this measurement temperature is used as the initial temperature when correcting the amount of change in the received light intensity of the reference light due to the difference in ambient temperature. be able to. The reference light correction unit 10E can also be applied to the fifth and sixth embodiments.

  The light source wavelengths of the temperature measurement light sources used in the first to seventh embodiments include the 850 nm band, the 1060 nm band, the 1300 nm band, the 1550 nm band, and the like, but the present invention is not limited to these wavelengths. Absent.

Various optical fibers can be used as the optical fiber 2 to be measured used in the first to seventh embodiments, but it is particularly preferable to use a pure quartz core fiber.
In a hydrogen atmosphere, in addition to the increase in optical transmission loss due to diffusion of hydrogen molecules, the above-mentioned reference (N. Uchida and N. Uesugi, “Infrared Optical Loss Increase in Silica Fibers due to Hydrogen”, J. Lightwave Technol. , Vol LT-4, No.8, pp.1132-1138, Aug. 1986), as a result of chemical reaction between hydrogen molecules and glass defects in the optical fiber, There is a problem that the absorption loss such as the OH group absorption loss due to the increase. The correction of received light intensity according to the present invention is not effective for errors due to these absorption losses. On the other hand, it is known that the increase in absorption loss hardly occurs in the pure silica core fiber. This is described, for example, in the reference (H. Kanamori et al “Transmission Characteristics and Reliability of Pure-Silica-Core Single-Mode Fibers”, J. Lightwave Technol., Vol LT-4, No. 8, pp. 1144- 1150, Aug. 1986)). Therefore, by using a pure silica core fiber that does not chemically react with hydrogen, absorption loss resulting from a chemical reaction between hydrogen molecules and an optical fiber can be prevented, so that the temperature distribution of the present invention that corrects the influence of hydrogen molecule absorption is corrected. It is effective to apply a pure silica core fiber as a measurement system fiber.
Therefore, when a pure silica core fiber is used in the temperature distribution measuring system of the present invention, there is an effect that an error can be further reduced as compared with the case where another optical fiber is used.

  According to the optical fiber temperature distribution measuring device, the optical fiber temperature distribution measuring method, and the optical fiber temperature distribution measuring system of the present invention, it is possible to correct optical transmission loss due to hydrogen molecules of Stokes light and anti-Stokes light in a hydrogen atmosphere. Even in a hydrogen atmosphere, accurate temperature measurement is possible.

Claims (24)

A light source for inputting pulsed light into the optical fiber to be measured;
A signal detection unit that detects a light receiving intensity of predetermined light included in backscattered light generated in the measured optical fiber based on incidence of the pulsed light;
A value corresponding to the amount of change in received light intensity due to absorption of hydrogen molecules in the measured optical fiber is calculated based on the received light intensity of the predetermined light, and the predetermined value corresponding to the temperature of the measured optical fiber is calculated based on the value. the received light intensity of the light to have a signal processing unit for correcting the,
The said signal processing part is an optical fiber temperature distribution measuring apparatus which correct | amends the light reception intensity | strength of the anti-Stokes light according to the temperature of the said to-be-measured optical fiber based on the value according to the variation | change_quantity of the light reception intensity | strength of Stokes light . A light source for inputting pulsed light into the optical fiber to be measured;
A signal detection unit that detects a light receiving intensity of predetermined light included in backscattered light generated in the measured optical fiber based on incidence of the pulsed light;
A value corresponding to the amount of change in received light intensity due to absorption of hydrogen molecules in the measured optical fiber is calculated based on the received light intensity of the predetermined light, and the predetermined value corresponding to the temperature of the measured optical fiber is calculated based on the value. the received light intensity of the light to have a signal processing unit for correcting the,
The signal processing unit is configured to output the predetermined light according to the temperature of the optical fiber to be measured based on a value corresponding to a change amount of received light intensity obtained based on a wavelength of temperature measurement pulsed light output from the light source. Optical fiber temperature distribution measuring device that corrects the received light intensity . The optical fiber temperature distribution measuring device according to claim 1 or 2 , wherein the signal detection unit detects the received light intensity of Stokes light and anti-Stokes light included in the backscattered light as the predetermined light. 3. The optical fiber temperature distribution measuring device according to claim 1, wherein the signal detection unit detects received light intensity of Stokes light, anti-Stokes light, and Rayleigh light included in the backscattered light as the predetermined light. The signal processing unit receives light intensity of the predetermined light according to the temperature of the optical fiber to be measured based on a value corresponding to a change amount of light reception intensity obtained based on a wavelength of 1240 nm light output from another light source. The optical fiber temperature distribution measuring device according to claim 1 or 2 , wherein the optical fiber temperature distribution is corrected. An optical fiber temperature distribution measuring system using the measured optical fiber made of a pure silica core optical fiber and the optical fiber temperature distribution measuring apparatus according to any one of claims 1 to 5 . Pulse light is incident on the optical fiber to be measured from the light source,
Detecting the received light intensity of the predetermined light included in the backscattered light generated in the measured optical fiber based on the incidence of the pulsed light;
Based on the received light intensity of the predetermined light, a value corresponding to the amount of change in received light intensity due to absorption of hydrogen molecules in the optical fiber to be measured is calculated,
Based on the value, the received light intensity of the predetermined light corresponding to the temperature of the optical fiber to be measured is corrected ,
The correction of the light reception intensity of the predetermined light is performed by correcting the light reception intensity of the anti-Stokes light according to the temperature of the optical fiber to be measured based on the Stokes light included in the backscattered light as the predetermined light. Distribution measurement method. Pulse light is incident on the optical fiber to be measured from the light source,
Detecting the received light intensity of the predetermined light included in the backscattered light generated in the measured optical fiber based on the incidence of the pulsed light;
Based on the received light intensity of the predetermined light, a value corresponding to the amount of change in received light intensity due to absorption of hydrogen molecules in the optical fiber to be measured is calculated,
Based on the value, the received light intensity of the predetermined light corresponding to the temperature of the optical fiber to be measured is corrected ,
The correction of the light receiving intensity of the predetermined light is performed based on the Rayleigh light included in the backscattered light as the predetermined light.
An optical fiber temperature distribution measuring method for correcting received light intensity of Stokes light and anti-Stokes light according to the temperature of Iva . Pulse light is incident on the optical fiber to be measured from the light source,
Detecting the received light intensity of the predetermined light included in the backscattered light generated in the measured optical fiber based on the incidence of the pulsed light;
Based on the received light intensity of the predetermined light, a value corresponding to the amount of change in received light intensity due to absorption of hydrogen molecules in the optical fiber to be measured is calculated,
Based on the value, the received light intensity of the predetermined light corresponding to the temperature of the optical fiber to be measured is corrected ,
The correction of the light reception intensity of the predetermined light is based on the Rayleigh light of 1240 nm light included in the backscattered light as the predetermined light, and the light reception intensity of Stokes light and anti-Stokes light according to the temperature of the optical fiber to be measured. Fiber temperature distribution measurement method for correcting A light source for inputting pulsed light into the optical fiber to be measured;
A signal detection unit that detects light reception intensities of a plurality of predetermined lights that are included in backscattered light generated in the optical fiber to be measured based on incidence of the pulsed light and that include anti-Stokes light and reference light; ,
A signal processing unit that calculates the temperature distribution of the optical fiber to be measured using the light reception intensity of the anti-Stokes light,
The signal processing unit calculates the amount of change in received light intensity of the reference light due to absorption of hydrogen molecules in the optical fiber to be measured for each point, and the reference light due to absorption of hydrogen molecules with respect to the received light intensity of the anti-Stokes light. A correction unit that performs correction to add the amount of change in the light reception intensity of the anti-Stokes light due to absorption of hydrogen molecules calculated based on the amount of change in the light reception intensity of each light, and light reception of the corrected anti-Stokes light An optical fiber temperature distribution measuring device comprising: a temperature distribution calculating unit that calculates the temperature distribution using intensity. The optical fiber temperature distribution measurement according to claim 10 , wherein the amount of change in the light reception intensity of the anti-Stokes light due to the absorption of hydrogen molecules is calculated by multiplying the amount of change in the light reception intensity of the reference light due to the absorption of hydrogen molecules by a predetermined coefficient. apparatus. The predetermined coefficients, according to claim 11, further comprising a coefficient calculating section for a value obtained by dividing the change amount of the received light intensity of the reference light amount of change in the received light intensity of the anti-Stokes light by the hydrogen molecules absorbed by the hydrogen molecular absorption Optical fiber temperature distribution measuring device. A coefficient for calculating the predetermined coefficient as a value for correcting the light reception intensity of the anti-Stokes light so as to become the measurement temperature based on a measurement temperature measured by a temperature sensor arranged in the vicinity of the optical fiber to be measured. The optical fiber temperature distribution measuring device according to claim 11 , further comprising an arithmetic unit. The optical fiber temperature distribution measuring device according to claim 11, further comprising a coefficient data capturing unit that inputs the predetermined coefficient from the outside. A reference for determining a change amount of the light intensity of the reference light due to a temperature difference, and adding a change amount of the light intensity of the reference light due to the temperature difference to the light intensity of the reference light at each point of the measured optical fiber. 12. The optical fiber temperature distribution measuring device according to claim 11 , further comprising an optical correction unit. The optical fiber temperature distribution measuring device according to claim 15 , wherein a change amount of the received light intensity of the reference light due to the temperature difference is determined based on a temperature distribution measurement result in the previous measurement. 16. The optical fiber temperature distribution measuring device according to claim 15 , wherein the amount of change in received light intensity of the reference light due to the temperature difference is determined based on the latest temperature distribution measurement result. An optical fiber temperature distribution measurement system using the optical fiber to be measured, which is an optical fiber having a pure quartz core, and the optical fiber temperature distribution measurement device according to claim 10 . Pulse light is incident on the optical fiber to be measured from the light source,
It is light included in backscattered light generated in the measured optical fiber based on the incidence of the pulsed light, and detects the received light intensity of a plurality of predetermined lights including anti-Stokes light and reference light,
An optical fiber temperature distribution measurement method for calculating a temperature distribution of the optical fiber to be measured using a light receiving intensity of the anti-Stokes light,
The amount of change in the received light intensity of the reference light due to the absorption of hydrogen molecules in the optical fiber to be measured is calculated at each point, and the change in the received light intensity of the reference light due to the absorption of hydrogen molecules with respect to the received light intensity of the anti-Stokes light. The amount of change in received light intensity of the anti-Stokes light due to absorption of hydrogen molecules calculated based on the amount is corrected for each point,
An optical fiber temperature distribution measuring method for calculating the temperature distribution by using the received light intensity of the corrected anti-Stokes light. 20. The optical fiber temperature distribution measurement according to claim 19 , wherein the amount of change in the light reception intensity of the anti-Stokes light due to the absorption of hydrogen molecules is calculated by multiplying the amount of change in the light reception intensity of the reference light due to the absorption of hydrogen molecules by a predetermined coefficient. Method. 21. The optical fiber temperature according to claim 20 , wherein the predetermined coefficient is a value obtained by dividing a change amount of the light reception intensity of the anti-Stokes light due to the hydrogen molecule absorption by a change amount of the light reception intensity of the reference light due to the hydrogen molecule absorption. Distribution measurement method. The predetermined coefficient is calculated as a value for correcting the light reception intensity of the anti-Stokes light so as to be the measured temperature based on a measured temperature measured by a temperature sensor disposed in the vicinity of the measured optical fiber. Item 20. An optical fiber temperature distribution measuring method according to Item 20 . 21. The optical fiber temperature distribution measuring method according to claim 20, wherein the predetermined coefficient is inputted from the outside. The first temperature distribution measurement is performed at a stage where hydrogen molecules are not diffused into the optical fiber to be measured and the influence of hydrogen molecule absorption is small, and the first temperature distribution measurement result is obtained at the second temperature measurement. The amount of change in the received light intensity of the reference light due to the temperature difference is determined, and the amount of change in the received light intensity of the reference light due to the temperature difference is added to the received light intensity of the reference light at each point of the measured optical fiber. The optical fiber temperature distribution measuring method according to claim 19 .

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