JP6484125B2 - Temperature measuring apparatus and temperature measuring method - Google Patents

Description

  The present invention relates to a temperature measuring device and a temperature measuring method using an optical fiber.

  Optical fibers are widely used for communication applications, and are also used for measurement applications such as temperature measurement. As a temperature measurement method using an optical fiber, for example, a temperature measurement method using an FBG (Fiber Bragg Grating) sensor, a temperature measurement method using Raman scattered light, and the like are known.

  The temperature measurement method using Raman scattered light differs in temperature sensitivity of two components (anti-Stokes light and Stokes light) of Raman scattered light generated in the optical fiber when pulsed single wavelength light is incident on the optical fiber. Unlike conventional methods using thermocouples or temperature resistors, the temperature distribution of the path in which the optical fiber is laid can be measured. .

  However, in the temperature measurement method using Raman scattered light, for example, if the detected intensity of Raman scattered light changes due to factors other than temperature change such as optical fiber deterioration, the accuracy of temperature measurement decreases. End up.

  For such a problem, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-209225) discloses a backscattered light generated by the light pulse light incident on the optical fiber from the light source. A measuring device for measuring a temperature distribution in the longitudinal direction of an optical fiber by a light intensity distribution ratio of anti-Stokes light and Stokes light, a first light source that oscillates a first optical pulse, and the first optical pulse A second light source that oscillates a second light pulse having the same wavelength as the first anti-Stokes light of backscattering generated by the light source, and the same wavelength as the first Stokes light of backscattering generated from the first light pulse. A third light source that oscillates the third light pulse, and a first drive selection unit that selects and drives one of the first light source, the second light source, and the third light source to oscillate the light pulse. And the second light pulse and the second light pulse A temperature distribution having a temperature distribution calibration function, comprising: correction means for correcting transmission loss of the first anti-Stokes light and the first Stokes light in accordance with a change in transmission loss of the optical pulse of A measuring device is disclosed.

JP2011-209225A

  In the above prior art, the transmission loss is measured using an anti-Stokes light in Raman scattering and a laser light source capable of emitting light having a wavelength corresponding to the Stokes light. However, since the wavelengths of incident light and Raman scattered light are preliminarily selected in consideration of propagation loss in the optical fiber, they have the same wavelength as the anti-Stokes light and Stokes light, and have sufficient temperature stability and laser output. It is expected that a laser light source having an intensity is difficult to obtain.

  The present invention has been made in view of the above, and provides a temperature measuring apparatus and a temperature measuring method capable of improving measurement accuracy while relaxing wavelength conditions required for a laser light source used for temperature measurement. Objective.

  In order to achieve the above object, the present invention provides a first light source for injecting an optical pulse of a first wavelength into an optical fiber, and second and third wavelengths different from the first wavelength in the optical fiber. The first, second, and third light sources that are generated in the optical fiber by the incidence of light pulses from the first, second, and third light sources, and the second and third light sources that receive the light pulses, respectively. A coefficient of each term of the quadratic function is determined based on the light intensity of the scattered light having the wavelength, and is generated in the optical fiber when the light pulse having the first wavelength is incident based on the quadratic function. A loss calculation unit that calculates an attenuation change value from a predetermined reference at each wavelength corresponding to anti-Stokes light of Raman scattering and Stokes light, and an optical pulse generated by incidence of an optical pulse from the first light source. Of anti-Raman scattering A temperature calculation unit that calculates the temperature of the optical fiber based on the Stokes light and the light intensity of the Stokes light, and corrects the calculation result of the temperature of the optical fiber based on the calculation result of the change value of the attenuation. Shall be.

  Measurement accuracy can be improved while relaxing the wavelength conditions required for the laser light source used for temperature measurement.

It is a figure which shows roughly the whole structure of a temperature measuring apparatus. It is a figure which shows the relationship between the wavelength of the light which propagates an optical fiber, and the change of the propagation loss from the reference | standard in each wavelength. It is a flowchart which shows the process of a temperature measurement apparatus.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing an overall configuration of a temperature measuring apparatus according to the present embodiment.

  In FIG. 1, a temperature measuring apparatus 100 includes a semiconductor laser light source 1 (first light source) for making an optical pulse 6 having a wavelength λ 0 (first wavelength) incident on an optical fiber 6 for temperature measurement, and an optical fiber 6. A semiconductor laser light source 2 (second light source) for entering a light pulse of wavelength λ1 (second wavelength) and a semiconductor laser for entering a light pulse of wavelength λ2 (third wavelength) into the optical fiber 6 A light source 3 (third light source), an optical coupler 4 that couples light pulses incident from the semiconductor laser light sources 1 to 3 through the optical fibers 16a to 16c, and emits the light pulses to the optical fiber 6 side; A photodetector 8 for detecting light of wavelength λast from the side, a photodetector 9 for detecting light of wavelength λst, and photodetectors 10, 11, 12 for detecting light of wavelengths λ0, λ1, and λ2, respectively. , The optical fiber 17 The light splitter 13 that distributes to the photodetectors 8 to 12 through a to 17e and the light incident from the optical coupler 4 through the optical fiber 18 are incident on the optical fiber 6 and from the optical fiber 6 side. Based on the detection results from the optical circulator 5 and the optical detectors 10, 11, and 12 that make light incident on the optical splitter 13 through the optical fiber 19, the change in attenuation from the reference (described later) of the optical fiber 6 is calculated. A loss calculation unit 15 for performing attenuation calculation processing, and a temperature calculation processing for calculating the temperature of the optical fiber 6 based on the detection results from the photodetectors 8 and 9, and calculating the attenuation change value of the loss calculation unit 15. Operation of the temperature calculation unit 14 that performs temperature correction processing for correcting the calculation result of the temperature of the optical fiber 6 based on the result, and the operations of the semiconductor laser light sources 1, 2, 3 and the photodetectors 8, 9, 10, 11, 12 timing It is schematically composed of a control processing unit that controls the entire operation of the temperature measuring device comprising.

  The optical fiber 6 for temperature measurement is made of, for example, quartz glass (SiO 2), and is laid in the temperature measurement target range with one end connected to the temperature measurement device 100.

  The light pulse having the wavelength λ0 emitted from the semiconductor laser light source 1 is incident on the temperature measuring optical fiber 6 through the optical fiber 16a, the optical coupler 4, the optical fiber 18, and the optical circulator 5. The wavelength λ0 is set in advance in consideration of the propagation loss in the optical fiber 6. In addition, optical pulses having wavelengths λ 1 and λ 2 emitted from the semiconductor laser light sources 2 and 3 are transmitted through the optical fibers 16 b and 16 c, the optical coupler 4, the optical fiber 18, and the optical circulator 5. Is incident on.

  Light from the optical fiber 6 side is incident on the photodetectors 8 and 9 through the optical circulator 5, the optical fiber 19, the optical splitter 13, and the optical fibers 17a and 17b. The photodetector 8 detects Stokes light (wavelength λast, first anti-Stokes light) among light (backscattered light) returning to the light source side of the Raman scattered light generated in the optical fiber 6 by the optical pulse of wavelength λ0. . Further, the photodetector 9 detects Stokes light (wavelength λst, first anti-Stokes light) out of the light returning to the light source side of the Raman scattered light generated in the optical fiber 6 by the light pulse having the wavelength λ0.

  Light from the optical fiber 6 side is incident on the photodetectors 10, 11, and 12 through the optical circulator 5, the optical fiber 19, the optical splitter 13, and the optical fibers 17 c, 17 d, and 17 e. The photodetector 10 detects light having a wavelength λ0 (Rayleigh scattered light) out of the light returning to the light source side of the scattered light generated in the optical fiber 6 by the light pulse having the wavelength λ0. The photodetector 11 detects light of wavelength λ1 (Rayleigh scattered light) out of light returning to the light source side of scattered light generated in the optical fiber 6 by an optical pulse of wavelength λ1. The light detector 12 detects light having a wavelength λ2 (Rayleigh scattered light) out of the light returning to the light source side of the scattered light generated in the optical fiber 6 by the light pulse having the wavelength λ2.

  The temperature measuring device 100 of the present application is a Raman scattered light method, and the optical pulse having a wavelength λ 0 incident on one end of the optical fiber 6 is propagated through the core in the optical fiber 6. Two components (anti-Stokes light and Stokes light) of Raman scattered light generated by molecules are temperature-dependent, and temperature measurement is performed by utilizing the difference in temperature sensitivity between anti-Stokes light and Stokes light. Further, by specifying the place (position on the optical fiber 6) where the Raman scattered light is generated from the time from when the light pulse is incident on one end of the optical fiber 6 until the Raman scattered light returns, the light The temperature distribution along the fiber 6 is measured.

  Here, the attenuation calculation process in the loss calculation unit 15, the temperature calculation process in the temperature calculation unit 14, and the temperature correction process will be described.

  In the attenuation calculation process, when attenuation (propagation loss) changes due to deterioration of the material of the optical fiber 6 or the like, the wavelength of light propagating through the optical fiber 6 and the change [dB] in propagation loss from the reference at each wavelength Is based on the knowledge that the relationship is expressed by a quadratic function in a certain wavelength range (can be approximated), using the detection results from the photodetectors 10, 11, and 12 based on the attenuation reference of the optical fiber 6. Calculate the change value.

  Here, the standard of attenuation (propagation loss) is, for example, the correspondence between the attenuation (propagation loss) of the temperature measurement optical fiber 6 and the temperature of the measurement result, such as a value at the time of calibration of the temperature measuring device 100. At some point.

  FIG. 2 is a diagram showing the relationship between the wavelength of light propagating through an optical fiber and the change in propagation loss from the reference at each wavelength. The vertical axis represents the change in propagation loss [dB], and the horizontal axis represents the change in light loss. Each wavelength is shown.

  As shown in FIG. 2, the relationship between the wavelength of light propagating through the optical fiber 6 and the change [dB] in propagation loss from the reference at each wavelength can be approximated by a quadratic function. Therefore, if the values of three points (that is, three wavelengths) on the quadratic function are known, the coefficient of each term of the quadratic function can be calculated, and the quadratic function can be determined.

  In the attenuation calculation process, the loss calculation unit 15 first detects the detected value of the light intensity of the Rayleigh scattered light (wavelength λ 0) generated in the optical fiber 6 by the incidence of the wavelength λ 0 from the semiconductor laser light source 1, and the signal from the semiconductor laser light source 2. Light intensity detection value of Rayleigh scattered light (wavelength λ1) generated in the optical fiber 6 by the incidence of the wavelength λ1 and light of Rayleigh scattered light (wavelength λ2) generated in the optical fiber 6 by the incidence of the wavelength λ2 from the semiconductor laser light source 3 Intensity detection values are obtained from the photodetectors 10, 11, and 12, and the change values from the reference of attenuation of the optical fiber 6 at the wavelengths λ0, λ1, and λ2 are calculated.

  Subsequently, the propagation loss change [dB] is calculated from the attenuation change value, the coefficient of each term of the quadratic function representing the propagation loss change [dB] from the reference at each wavelength is calculated, and the quadratic function is calculated. decide. Subsequently, using the determined quadratic function, the propagation loss change [dB] of the wavelengths λast and λst is estimated, and the true value of the attenuation change value is calculated from the calculation (estimation) result. To the temperature calculation unit 14.

  The wavelengths λ1 and λ2 are set in a range in which the relationship between the wavelength of light propagated through the optical fiber 6 and the propagation loss can be approximated by a quadratic function. In other words, the wavelengths λ1 and λ2 do not include points at which the relationship of the propagation loss change [dB] from the reference at each wavelength changes suddenly (a point not represented by a quadratic function, a point at which the curvature changes abruptly, etc.). The range is set to include the wavelength λ0.

  For example, when the temperature measuring optical fiber 6 is formed of quartz glass (SiO 2), when the wavelength λ 0 is 780 nm, the wavelength λast is 760 nm and the wavelength λst is 810 nm. At this time, if the wavelengths λ1 and λ2 are set in the range of 760 to 810 nm, the relationship of the propagation loss change [dB] from the reference at each wavelength becomes a range represented by a quadratic function. For example, the wavelengths λ1 and λ2 may be set in a range of 650 to 920 nm. However, the wavelength near 945 nm is an absorption wavelength due to water contained in the optical fiber, and the wavelength near 630 nm is often an absorption wavelength due to the bond between silicon and oxygen. Since the relationship of the change [dB] is a point that is not represented by a quadratic function (a point that changes suddenly), the wavelengths λ1 and λ2 are set so that these wavelengths are not included in the range.

  In addition, the inventor has a large attenuation change with time especially in the vicinity of these absorption wavelengths, and in the vicinity of these wavelengths, the wavelength of light propagating through the optical fiber 6 and the change in propagation loss from the reference at each wavelength [dB]. Has a knowledge that the relation to can be approximated to a quadratic function well.

  In the temperature calculation process, the temperature of the optical fiber 6 is calculated based on the detection results from the photodetectors 8 and 9. That is, the anti-Stokes light and the Stokes light of the Raman scattered light generated by the light pulse having the wavelength λ0 incident on one end of the optical fiber 6 are temperature dependent, and the temperature sensitivity is different between the anti-Stokes light and the Stokes light. Is used to calculate the temperature of the optical fiber 6 based on the light intensity of anti-Stokes light and Stokes light obtained in advance and the relationship between the difference between them and the temperature of the optical fiber 6. Further, in the temperature calculation process, the location (position on the optical fiber 6) where the Raman scattered light is generated is determined from the time from when the light pulse is incident on one end of the optical fiber 6 until the Raman scattered light returns. Thus, the temperature distribution along the optical fiber 6 is measured.

  The temperature correction process is a process for correcting the calculation result of the temperature of the optical fiber 6 based on the calculation result of the attenuation change value of the loss calculation unit 15, and is incorporated into the temperature calculation process based on the following (Equation 1). Done.

  In the above equation 1, the true value obtained by the attenuation calculation process is used as the change value of the attenuation of the anti-Stokes light and the Stokes light.

  The temperature of the optical fiber 6 for temperature measurement is determined by the ratio of the light intensity of the anti-Stokes light and the Stokes light. As shown in the above (Equation 1), the anti-Stokes light intensity is changed by the attenuation of the anti-Stokes light wavelength The amount of decrease in the detected value of the anti-Stokes light due to the change in attenuation of the optical fiber 6 over time can be corrected, and the anti-Stokes light intensity equivalent to the state without the change in attenuation is calculated. be able to. The same applies to the Stokes light intensity. By dividing the Stokes light intensity by the change in attenuation of the Stokes light wavelength, the amount of decrease in the detected value of Stokes light due to the change in attenuation over time of the optical fiber 6 can be obtained. It can be corrected and can be calculated as the Stokes light intensity equivalent to the state where there is no change in attenuation.

  FIG. 3 is a flowchart showing processing of the temperature measuring device.

  In FIG. 3, the temperature measuring apparatus 100 first emits pulsed light of wavelength λ0 from the semiconductor laser light source 1 and enters the optical fiber 6 for temperature measurement, and has wavelengths λ0, λast, and λst from the optical fiber 6 side. The light is received by the photodetectors 8, 9, and 10 to measure the light intensity (step S10), and the measured values of the light with the wavelengths λast and λst at the photodetectors 8 and 9 are output to the temperature calculator 14 ( In step S20), the measured value of the light having the wavelength λ0 in the photodetector 10 is output to the loss calculator 15 (step S30).

  Next, pulsed light of wavelength λ1 is emitted from the semiconductor laser light source 2 and enters the optical fiber 6 for temperature measurement. The light of wavelength λ1 from the optical fiber 6 side is received by the photodetector 11 and the light intensity is increased. Measure (Step S40), output the measured value of the light of wavelength λ1 at the photodetector 11 to the loss calculator 15 (Step S50), emit the pulsed light of wavelength λ2 from the semiconductor laser light source 3, and measure the temperature The light having the wavelength λ2 from the optical fiber 6 side is received by the photodetector 12 and the light intensity is measured (step S60), and the measured value of the light having the wavelength λ2 by the photodetector 12 is measured. Is output to the loss calculator 15 (step S70).

  Subsequently, the loss calculation unit 15 estimates by calculating a change value (true value) of the attenuation of the light of the wavelengths λast and λst, and outputs the calculation result to the temperature calculation unit 14 (step S80).

  Subsequently, the temperature calculation unit 14 corrects the temperature of the optical fiber 6 for temperature measurement while calculating the temperature, and outputs the temperature calculation result to an external display device (not shown) or another device (step S90). finish.

  In the present embodiment, the case where the processing of the temperature measuring device is executed in the order of steps S10 to S90 has been described as an example. However, if the processing steps do not affect each other, they are executed at the same time, or the processing order is changed. Is possible. For example, the processing of step S40 and step S50, or the processing of step S60 and step S70 may be executed simultaneously. Further, if there is no influence on the light of other wavelengths in the optical coupler 4, the optical circulator 5, the optical splitter 13, etc., a series of processes in steps S10 to S30, a series of processes in steps S40 and S50, The order of execution of the series of processes in steps S60 and S70 can be changed, and the processes in steps S10 to S70 can be performed simultaneously.

  The effect of the present embodiment configured as described above will be described.

  The temperature measurement method using Raman scattered light differs in temperature sensitivity of two components (anti-Stokes light and Stokes light) of Raman scattered light generated in the optical fiber when pulsed single wavelength light is incident on the optical fiber. Is used to measure temperature. Therefore, for example, if the detection intensity of Raman scattered light changes due to factors other than temperature change such as degradation of the optical fiber, there is a problem that the accuracy of temperature measurement is lowered.

  In some conventional techniques, transmission loss is measured using a semiconductor laser light source capable of emitting light having a wavelength corresponding to anti-Stokes light and Stokes light in Raman scattering.

  However, the wavelength of anti-Stokes light or Stokes light is determined by the relationship between the emission wavelength of the semiconductor laser light source and the main material of the optical fiber for temperature measurement, taking into account the propagation loss in the optical fiber. Therefore, it is expected that it is difficult to obtain a laser light source having the same wavelength as the anti-Stokes light and the Stokes light, and having sufficient temperature stability and laser output intensity.

  On the other hand, in the present embodiment, an optical pulse having a wavelength λ0 is incident on the optical fiber 6, and optical pulses having wavelengths λ1 and λ2 different from the wavelength λ0 are incident on the optical fiber 6, and the wavelengths λ0, λ1, and λ2 are incident. The coefficient of each term of the quadratic function is determined based on the light intensity of the scattered light having the wavelengths λ0, λ1, and λ2 generated in the optical fiber 6 by the incidence of the optical pulse. A change in attenuation from a predetermined reference at each wavelength λast, λst of Raman scattering anti-Stokes light and Stokes light generated in the optical fiber 6 when an optical pulse is incident is calculated, and the optical pulse of wavelength λ0 is calculated. The temperature of the optical fiber 6 is calculated based on the anti-Stokes light of Raman scattering generated in the optical fiber 6 upon incidence and the light intensity of the Stokes light, and the light is calculated based on the calculation result of the attenuation change value. Since the calculation result of the temperature of the fiber 6 is corrected, the measurement accuracy can be improved while relaxing the wavelength condition required for the laser light source to be used.

  That is, it is not necessary to use a semiconductor laser light source that is difficult to obtain, and a light source that is easier to obtain or cheap can be used, so that the price of the temperature measuring device can be reduced.

  In addition, this invention is not limited to above-described embodiment, Various modifications are included. That is, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described.

  For example, in this embodiment, the wavelengths λ1 and λ2 are set as described above, but the relationship between the wavelength of light propagating through the optical fiber and the change in propagation loss [dB] from the reference at each wavelength is secondary. The wavelength λ1 and λ2 may be set to a range between the wavelength λast of the anti-Stokes light and the wavelength λst of the Stokes light. Even in this case, the same effect as the present embodiment can be obtained.

  In this embodiment, the case where a semiconductor laser light source is used as an example of the laser light source has been described. However, the present invention is not limited to this, and a laser light source using a laser medium other than a semiconductor may be used.

  The wavelengths λ1 and λ2 are the Raman scattering anti-Stokes light wavelength (λast) and the Stokes light wavelength (λst) generated in the optical fiber 6 by the optical pulse of wavelength λ0 incident on the optical fiber 6 from the semiconductor laser light source 1. ) And at least one of them may be set differently.

1 Semiconductor laser light source (first light source)
2 Semiconductor laser light source (second light source)
3 Semiconductor laser light source (third light source)
4 Optical coupler 5 Optical circulator 6 Temperature measurement optical fiber 7 Control processing unit 8-12 Photo detector 13 Splitter 14 Temperature calculation unit 15 Loss calculation unit 16a-16c, 17a-17e, 18, 19 Optical fiber 100 Temperature measurement apparatus

Claims (6)

A first light source for injecting a light pulse of a first wavelength into the optical fiber;
Second and third light sources for injecting optical pulses of second and third wavelengths different from the first wavelength into the optical fiber;
Based on the light intensity of the scattered light of the first, second, and third wavelengths generated in the optical fiber by the incidence of light pulses from the first, second, and third light sources, respectively, a quadratic function And a wavelength corresponding to anti-Stokes light and Stokes light of Raman scattering generated in the optical fiber when an optical pulse of the first wavelength is incident on the basis of the quadratic function. A loss calculator for calculating a change in attenuation from a predetermined reference in
The temperature of the optical fiber is calculated based on the anti-Stokes light of Raman scattering and the light intensity of the Stokes light generated in the optical fiber by the incidence of the light pulse from the first light source, and the change value of the attenuation is calculated. A temperature measurement device comprising: a temperature calculation unit that corrects a calculation result of the temperature of the optical fiber based on the result. A first light source for injecting a light pulse of a first wavelength into the optical fiber;
Second and third wavelength light pulses that are different from at least one of the wavelengths of anti-Stokes light and Stokes light of Raman scattering generated in the optical fiber upon incidence of the light pulse of the first wavelength are incident on the optical fiber. Second and third light sources to
The optical fiber based on the intensity of the scattered light having the first, second, and third wavelengths generated in the optical fiber by the incidence of light pulses from the first, second, and third light sources, respectively. A loss calculation unit that calculates a change in attenuation from a predetermined reference at each wavelength of the anti-Stokes light and the Stokes light;
The temperature of the optical fiber is calculated based on the anti-Stokes light of Raman scattering and the light intensity of the Stokes light generated in the optical fiber by the incidence of the light pulse from the first light source, and the change value of the attenuation is calculated. A temperature calculation unit for correcting the calculation result of the temperature of the optical fiber based on the result,
The loss calculation unit adjusts the light intensity of the scattered light having the first, second, and third wavelengths generated in the optical fiber by incidence of light pulses from the first, second, and third light sources, respectively. Based on the quadratic function, the coefficient of each term of the quadratic function is determined, and based on the quadratic function, the attenuation change value from the predetermined reference at each wavelength of the anti-Stokes light and the Stokes light of the optical fiber. A temperature measuring device characterized by calculating The temperature measuring device according to claim 2 , wherein
The second and third wavelengths are set in a range in which the relationship between the wavelength of light propagating through the optical fiber and the propagation loss can be approximated to the quadratic function, and includes the first wavelength. A temperature measuring device. The temperature measuring device according to claim 2 , wherein
The second and third wavelengths are set in a range that does not include a point where the relationship between the wavelength of light propagated through the optical fiber and the propagation loss changes suddenly, and includes the first wavelength. A temperature measuring device characterized by that. In the temperature measuring device according to claim 1 Symbol placement,
The temperature measuring device, wherein the second and third wavelengths are set in a range between the wavelength of the anti-Stokes light and the wavelength of the Stokes light. Injecting an optical pulse of a first wavelength into the optical fiber;
Injecting optical pulses of second and third wavelengths different from the first wavelength into the optical fiber;
Based on the light intensity of the scattered light of the first, second, and third wavelengths generated in the optical fiber by the incidence of the light pulses of the first, second, and third wavelengths, respectively, a quadratic function The coefficient of each term is determined, and based on the quadratic function, the Raman scattering anti-Stokes light generated in the optical fiber when the light pulse of the first wavelength is incident and the Stokes light at each wavelength in advance. Calculating a change in attenuation from a set standard;
The temperature of the optical fiber is calculated based on the light intensity of the anti-Stokes light and the Stokes light of Raman scattering generated in the optical fiber by the incidence of the optical pulse of the first wavelength, and the change value of the attenuation is calculated. And a step of correcting a calculation result of the temperature of the optical fiber based on the result.

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