Raman high spatial resolution fiber temperature sensing device and method based on multi-wavelength laser

Abstract

This invention belongs to the field of distributed optical fiber sensing technology, specifically relating to a high spatial resolution optical fiber temperature sensing device and method based on bidirectional Raman scattering using multi-wavelength lasers. The device includes a pulsed laser source, a wavelength division multiplexer (WDM), a sensing optical fiber, a filter, a first avalanche photodetector, a second avalanche photodetector, a data acquisition card, and a computer. The output end of the pulsed laser source is connected to the input end of the WDM, the transmission end of the WDM is connected to one end of the sensing optical fiber, the reflection end of the WDM is connected to the first avalanche photodetector, and the other end of the sensing optical fiber is connected to the second avalanche photodetector via a filter. The output ends of the first and second avalanche photodetectors are connected to the computer via the data acquisition card. This invention can improve the spatial resolution and temperature measurement accuracy of the system.

Description

Technical Field

[0001] This invention belongs to the field of distributed optical fiber sensing technology, specifically relating to a high spatial resolution optical fiber temperature sensing device and method based on bidirectional Raman scattering of multi-wavelength lasers. Background Technology

[0002] Raman distributed fiber optic sensing technology can monitor the continuous distribution of temperature physical quantities along the fiber in real time. Due to its advantages such as long distance, resistance to electromagnetic interference, passivity, and high sensitivity, it has been widely used in many fields such as structural health monitoring of large facilities and leakage detection of industrial facilities.

[0003] Raman distributed fiber optic sensing technology utilizes the relationship between the intensity of Raman scattering signals in an optical fiber and temperature to detect temperature changes at different locations along the fiber. Spatial resolution characterizes the minimum fiber length that the sensing fiber can resolve, and is a crucial technical indicator for Raman distributed fiber optic sensing technology. When the length of the fiber to be measured is less than the system's spatial resolution, the measured temperature will be lower than the actual ambient temperature. Therefore, the spatial resolution of a Raman distributed fiber optic sensing system also reflects the minimum fiber length required for the system to accurately measure the temperature of the surrounding environment. Existing Raman distributed fiber optic sensing systems primarily use spontaneous backscattering Raman for distributed fiber optic temperature sensing. The detection signals used are pulse signals with pulse widths ranging from tens to tens of nanoseconds, and their positioning principle is based on the pulse-time-of-flight method. The spatial resolution mainly depends on the pulse width of the light source. Limited by the pulse width, the spatial resolution of existing Raman distributed fiber optic systems is limited to the meter level, making it difficult to meet the higher performance requirements of fields such as dam, bridge, pipeline, power grid, and tunnel leakage monitoring.

[0004] Therefore, it is necessary to improve the existing Raman distributed fiber optic temperature demodulation method to overcome the technical bottleneck that the spatial resolution of Raman distributed fiber optic sensing systems is limited to the meter level, thereby meeting the major social demand and application prospects of high spatial resolution temperature monitoring. Summary of the Invention

[0005] To address the technical problem of insufficient spatial resolution in existing Raman distributed fiber optic sensing systems, this invention proposes a high spatial resolution fiber optic temperature sensing device and method based on multi-wavelength laser bidirectional Raman scattering, thereby improving the spatial resolution of Raman distributed fiber optic sensing systems.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a bidirectional Raman scattering high spatial resolution fiber optic temperature sensing device based on multi-wavelength laser, comprising: a pulsed laser source, a wavelength division multiplexer, a sensing fiber, a filter, a first avalanche photodetector, a second avalanche photodetector, a data acquisition card, and a computer. The output end of the pulsed laser source is connected to the input end of the wavelength division multiplexer, the transmission end of the wavelength division multiplexer is connected to one end of the sensing fiber, the reflection end of the wavelength division multiplexer is connected to the first avalanche photodetector, the other end of the sensing fiber is connected to the second avalanche photodetector through a filter, and the output ends of the first avalanche photodetector and the second avalanche photodetector are connected to a computer through a data acquisition card. The pulsed laser source is used to output multiple pulsed lasers of different wavelengths in a time-division multiplexing manner. After passing through a wavelength division multiplexer, the pulsed lasers excite Raman backscattered anti-Stokes light signals and Raman forward scattered anti-Stokes light signals in the sensing fiber. The Raman backscattered anti-Stokes light signals and Raman forward scattered anti-Stokes light signals are received by the first avalanche photodetector and the second avalanche photodetector, respectively, and then collected by the data acquisition card and sent to the computer. The computer is used to demodulate the location of the temperature change zone based on the intensity of the Raman backscattered anti-Stokes light signal, and to demodulate the temperature of each small temperature change zone based on the intensity of the Raman forward scattered anti-Stokes light signal at different wavelengths.

[0007] The aforementioned bidirectional Raman scattering high spatial resolution fiber optic temperature sensing device based on multi-wavelength lasers further includes a first optical coupler, a first continuous laser source, a second optical coupler, and a second continuous laser source. The transmission end of the wavelength division multiplexer is connected to the first beam splitting end of the first optical coupler, the output end of the first continuous laser source is connected to the second beam splitting end of the first optical coupler, and the common end of the first optical coupler is connected to one end of the sensing fiber. The other end of the sensing fiber is connected to the common end of the second optical coupler, the first beam splitting end of the second optical coupler is connected to the input end of the filter, and the output end of the second continuous laser source is connected to the second beam splitting end of the second optical coupler. The first and second continuous laser sources are used to generate Raman gain for the Raman backscattered anti-Stokes light signal and the Raman forward scattered anti-Stokes light signal in the sensing fiber, respectively, by inputting laser light.

[0008] The pulsed laser source includes a first pulsed laser, a second pulsed laser, and an optical switch. The output terminals of the first and second pulsed lasers are connected to the first and second input terminals of the optical switch, and the output terminal of the optical switch is connected to the input terminal of a wavelength division multiplexer. The computer is used to demodulate the Raman backscattered anti-Stokes scattering signal intensity excited by the laser output from the first pulse laser to obtain the location of the temperature change zone, and to demodulate the Raman forward scattered anti-Stokes scattering signal intensity excited by multiple lasers of different wavelengths output from the second pulse laser to obtain the temperature of each small temperature change zone.

[0009] The filter is a wavelength division multiplexer.

[0010] Furthermore, this invention also provides a high spatial resolution fiber optic temperature sensing method based on bidirectional Raman scattering using multi-wavelength lasers, implemented using the aforementioned sensing device, comprising the following steps: Step 1, Calibration Stage: Place the entire sensing fiber at a constant ambient temperature. In this process, the pulsed laser source is adjusted to output pulsed lasers of different wavelengths in a time-division manner. The Raman backscattered anti-Stokes light signal intensity excited by the pulsed lasers of each wavelength is detected by the first avalanche photodetector and the second avalanche photodetector, respectively. Raman forward anti-Stokes scattering signal intensity ; Step 2, Measurement Stage: Place the sensing fiber in the environment to be measured, repeat Step 1, and use the first and second avalanche photodetectors to detect the Raman backscattered anti-Stokes light signal intensity excited by pulsed lasers at various wavelengths. Raman forward anti-Stokes scattering signal intensity ; Step 3, Calculation Stage: Based on the Raman backscattered anti-Stokes light signal measured in the calibration and measurement stages, calculate the location of the temperature change zone in the sensing fiber. Then, based on the Raman forward scattered anti-Stokes light signal intensity measured in the calibration and measurement stages, calculate the temperature of each small temperature change zone in the sensing fiber, thereby obtaining the temperature along the sensing fiber.

[0011] In step 3, the demodulation of the temperature of each small temperature variation zone includes the following steps: Step 3.1: Calculate the temperature increment vector. The calculation formula is as follows: ; in, Represents the temperature function increment vector. , , , …, They represent the 1st, 2nd, ..., The temperature function increment corresponding to each small temperature variation zone Indicates the number of small temperature variation zones. This indicates the number of wavelengths in a pulsed laser. express The attenuation integral weight matrix, This represents the relative intensity vector of the Raman forward anti-Stokes scattered light signal. Represents a constant; Step 3.2: Calculate the demodulation temperature of each small temperature variation zone. The calculation formula is as follows: ; ; in, Indicates the first The absolute temperature values ​​of each small temperature variation zone; Indicates Raman frequency shift, Denotes Planck's constant. Represents the Boltzmann constant. Indicates the first Temperature function increment in a small temperature variation zone This represents the temperature function value corresponding to the calibration temperature. Indicates the position on the sensing fiber. The calibration temperature, Indicates the position on the sensing fiber. The demodulation temperature.

[0012] Step 3.1 further includes calculating the relative intensity vector of the Raman forward anti-Stokes scattered light signal. The steps and calculation formula are as follows: ; in, , , …, These represent the 1st, 2nd, ..., The relative intensity corresponding to each wavelength , , …, These represent the 1st, 2nd, ..., 1st avalanche photodetectors detected by the second avalanche photodetector during the measurement phase. The intensity of the Raman forward anti-Stokes scattered light signal corresponding to each wavelength of pulsed laser. , , …, These represent the 1st, 2nd, ..., th avalanche photodetectors detected during the calibration phase in the second avalanche photodetector. The intensity of the Raman forward anti-Stokes scattered light signal corresponding to each wavelength of pulsed laser.

[0013] In step 3.1, the attenuation integral weight matrix The calculation formula is: ; in, Represents the decay integral weight matrix No. Line 1 Column elements, Indicates the number of locations of the sensing fibers. Indicates the location number of the sensing fiber. and They represent the first The attenuation coefficients of the incident light and Raman forward anti-Stokes scattered light signals corresponding to each wavelength in the sensing fiber.

[0014] In step 3, the temperature of each small temperature variation zone is obtained by demodulation calculation using a computer.

[0015] Compared with existing distributed fiber optic sensing technologies, this invention provides a high spatial resolution fiber optic temperature sensing device and method based on bidirectional Raman scattering using multi-wavelength lasers. By measuring the intensity of the Raman backscattered anti-Stokes light signal in the sensing fiber during the calibration and measurement phases, and jointly demodulating it, the device locates a small temperature variation region along the fiber (its spatial length is less than the spatial scale corresponding to the full width at half maximum (FWHM) of the pulsed laser). Based on the known location of this small temperature variation region, by measuring the intensity of the Raman forward-scattered anti-Stokes light signal in the sensing fiber excited by a multi-wavelength pulsed laser source during the calibration and measurement phases, the difference is used to construct a linear equation system, thereby accurately demodulating the precise temperature of the small temperature variation region. This leads to the accurate distributed temperature along the entire fiber. Therefore, this invention has the following beneficial effects: (1) The spatial resolution of the system is determined by the sampling rate. Therefore, this invention solves the technical bottleneck of the existing Raman distributed fiber optic sensing system, which is based on the pulse time-of-flight method for positioning and whose spatial resolution mainly depends on the pulse width of the light source. It is expected to optimize the spatial resolution of the Raman distributed fiber optic sensing system to the pm level and break through the technical bottleneck of the existing system, which is limited to the meter level due to the pulse width.

[0016] (2) The present invention can accurately demodulate the temperature in a small temperature variation zone, thereby improving the measurement accuracy of temperature sensing. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a bidirectional Raman scattering high spatial resolution fiber optic temperature sensing device based on multi-wavelength laser provided in Embodiment 1 of the present invention. Figure 2This is a schematic diagram of the structure of a bidirectional Raman scattering high spatial resolution fiber optic temperature sensing device based on multi-wavelength laser provided in Embodiment 2 of the present invention; In the diagram: 1: Pulsed laser source, 2: Wavelength division multiplexer, 3: First optical coupler, 4: First continuous laser source, 5: Sensing fiber, 6: Second optical coupler, 7: Second continuous laser source, 8: Filter, 9: First avalanche photodetector, 10: Second avalanche photodetector, 11: Data acquisition card, 12: Computer, 13: First pulsed laser, 14: Second pulsed laser, 15: Optical switch. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 like Figure 1 As shown, Embodiment 1 of the present invention provides a bidirectional Raman scattering high spatial resolution fiber optic temperature sensing device based on multi-wavelength lasers, comprising: a pulsed laser source 1, a wavelength division multiplexer 2, a sensing fiber 5, a filter 8, a first avalanche photodetector 9, a second avalanche photodetector 10, a data acquisition card 11, and a computer 12.

[0020] The output end of the pulsed laser source 1 is connected to the input end of the wavelength division multiplexer 2. The transmission end of the wavelength division multiplexer 2 is connected to one end of the sensing fiber 5. The reflection end of the wavelength division multiplexer 2 is connected to the first avalanche photodetector 9. The other end of the sensing fiber 5 is connected to the second avalanche photodetector 10 through the filter 8. The output ends of the first avalanche photodetector 9 and the second avalanche photodetector 10 are connected to the computer 12 through the data acquisition card 11.

[0021] In this embodiment, the pulsed laser source 1 is used to output multiple pulsed lasers of different wavelengths in a time-division multiplexing manner. After passing through the wavelength division multiplexer 2, the pulsed lasers are excited to spontaneous Raman scattering in the sensing fiber 5, generating Raman backscattered anti-Stokes light signals and Raman forward scattered anti-Stokes light signals. The Raman backscattered anti-Stokes light signals and Raman forward scattered anti-Stokes light signals are received by the first avalanche photodetector 9 and the second avalanche photodetector 10, respectively, and then collected by the data acquisition card 11 and sent to the computer 12. The computer 12 is used to demodulate the location of the small temperature variation region based on the intensity of the Raman backscattered anti-Stokes light signal, and to demodulate the temperature of each small temperature variation region based on the intensity of the Raman forward scattered anti-Stokes light signal at different wavelengths, thereby obtaining the accurate distributed temperature along the entire sensing fiber 5. Here, a small temperature variation region refers to a temperature variation region whose length is less than the spatial scale corresponding to the full width at half maximum (FWHM) of the pulsed laser.

[0022] Specifically, in this embodiment, the sensing fiber 5 has a nonlinear parameter greater than 10 W. -1 km -1 The nonlinear optical fiber has a core diameter of 62.5 μm. The port wavelengths of the wavelength division multiplexer 2 are as follows: the input wavelength is the pulsed laser wavelength, the transmission port wavelength is the pulsed laser wavelength and the corresponding Raman anti-Stokes scattered light signal wavelength, and the reflection port wavelength is the corresponding Raman anti-Stokes scattered light signal wavelength.

[0023] Specifically, in this embodiment, the filter 8 can also be a wavelength division multiplexer. Its input port wavelength is the pulse laser wavelength / the wavelength of the Raman anti-Stokes scattered light signal, and its output port wavelength is the wavelength of the Raman anti-Stokes scattered light signal.

[0024] Specifically, in this embodiment, the center wavelength of the pulsed laser output from pulsed laser source 1 is tunable, with an output pulse wavelength of approximately 1550 nm. For example, the wavelengths are 1545 nm, 1546 nm, 1547 nm, ..., 1554 nm. The spontaneous Raman scattering excited in the sensing fiber generates a Raman anti-Stokes scattering light signal with a wavelength that is blue-shifted by 100 nm relative to the pulsed laser.

[0025] Specifically, both the first optical coupler 3 and the second optical coupler 6 are 2×1 optical couplers.

[0026] Furthermore, such as Figure 1As shown in this embodiment, the bidirectional Raman scattering high spatial resolution fiber optic temperature sensing device based on multi-wavelength lasers further includes a first optical coupler 3, a first continuous laser source 4, a second optical coupler 6, and a second continuous laser source 7. The transmission end of the wavelength division multiplexer 2 is connected to the first splitting end of the first optical coupler 3, the output end of the first continuous laser source 4 is connected to the second splitting end of the first optical coupler 3, and the common end of the first optical coupler 3 is connected to one end of the sensing fiber 5. The other end of the sensing fiber 5 is connected to the common end of the second optical coupler 6, the first splitting end of the second optical coupler 6 is connected to the input end of the filter 8, and the output end of the second continuous laser source 7 is connected to the second splitting end of the second optical coupler 6. The first continuous laser source 4 and the second continuous laser source 7 are respectively used to input lasers to generate Raman gain for the Raman backscattered anti-Stokes light signal and the Raman forward scattered anti-Stokes light signal in the sensing fiber 5.

[0027] In this embodiment, the center wavelength of the continuous laser output by the first continuous laser source 4 and the second continuous laser source 7 is tunable. The center wavelength is set to have a blue shift of 200 nm relative to the pulsed laser output by the pulsed laser source 1. By inputting continuous laser into the sensing fiber 5 through the first continuous laser source 4 and the second continuous laser source 7, Raman gain can be generated on the spontaneous Raman anti-Stokes scattered light signal excited in the sensing fiber 5.

[0028] Specifically, in this embodiment, the Raman backscattering anti-Stokes scattering signal used to locate the small temperature variation region only requires collecting one set of data excited by a single-wavelength pulsed laser. The Raman forward anti-Stokes scattering signal used to accurately demodulate the temperature of the small temperature variation region requires collecting multiple sets of data excited by multiple wavelength pulsed lasers, and the number of wavelengths... The number is greater than that of small temperature change zones. .

[0029] Example 2 like Figure 2 As shown, Embodiment 2 of the present invention provides a bidirectional Raman scattering high spatial resolution fiber optic temperature sensing device based on multi-wavelength lasers. Unlike Embodiment 1, in this embodiment, the pulsed laser source 1 includes a first pulsed laser 13, a second pulsed laser 14, and an optical switch 15. The output terminals of the first pulsed laser 13 and the second pulsed laser 14 are respectively connected to the first and second input terminals of the optical switch 15, and the output terminal of the optical switch 15 is connected to the input terminal of the wavelength division multiplexer 2.

[0030] The computer 12 is used to demodulate the Raman backscattered anti-Stokes light signal intensity excited by the laser output from the first pulsed laser 13 to obtain the location of the small temperature variation region, and to demodulate the Raman forward scattered anti-Stokes light signal intensity excited by multiple lasers of different wavelengths output by the second pulsed laser 14 to obtain the temperature of each small temperature variation region. An optical switch is used to switch the pulsed laser input to the sensing fiber 5. The second pulsed laser 14 is a pulsed laser whose wavelength can be continuously tuned; therefore, it can measure Raman forward scattered anti-Stokes light at multiple wavelengths. The first pulsed laser 13 can be a continuously tuned pulsed laser or a single-wavelength pulsed laser; only the Raman backscattered anti-Stokes light signal intensity at a single wavelength is needed to demodulate and obtain the location of the small temperature variation region along the fiber.

[0031] In this embodiment, spontaneous Raman scattering is excited by two pulsed lasers. The location of the small temperature variation region is obtained by demodulating the Raman backscattered anti-Stokes scattering signal intensity generated by the laser output from the first pulsed laser 13. The temperature of each small temperature variation region is obtained by demodulating the Raman forward scattering anti-Stokes scattering signal intensity generated by multiple lasers with different wavelengths output by the second pulsed laser 14 at different time intervals. Therefore, the power of the pulsed laser used to excite the Raman backscattered anti-Stokes scattering signal in the sensing fiber and the power of the pulsed laser used to excite the Raman forward scattering anti-Stokes scattering signal in the sensing fiber are independent of each other; that is, there is no relationship between their powers. Therefore, the measurement device in this embodiment has better robustness.

[0032] Example 3 Embodiment 3 of the present invention provides a high spatial resolution fiber optic temperature sensing method based on bidirectional Raman scattering using multi-wavelength lasers. Figure 1 or Figure 2 The sensor device shown includes the following steps: Step 1, Calibration Stage: Place the entire sensing fiber 5 in a constant ambient temperature. In this process, the pulsed laser source is adjusted to output pulsed lasers of different wavelengths in a time-division manner. The Raman backscattered anti-Stokes light signal intensity excited by the pulsed lasers of each wavelength is detected by the first avalanche photodetector 9 and the second avalanche photodetector 10, respectively. Raman forward anti-Stokes scattering signal intensity ; Step 2, Measurement Stage: Place the sensing fiber 5 in the environment to be measured, repeat Step 1, and use the first avalanche photodetector 9 and the second avalanche photodetector 10 to detect the Raman backscattered anti-Stokes light signal intensity excited by pulsed laser at various wavelengths. Raman forward anti-Stokes scattering signal intensity ; Step 3: Calculate the location of the small temperature change region in the sensing fiber 5 based on the Raman backscattered anti-Stokes light signal measured during the calibration and measurement stages. Then, calculate the temperature of the small temperature change region in the sensing fiber 5 based on the Raman forward scattered anti-Stokes light signal intensity measured during the calibration and measurement stages, thereby obtaining the temperature along the sensing fiber 5.

[0033] For the measuring device in Embodiment 2, the optical switch 15 is used to switch the light source during both the calibration and measurement stages. First, the first pulsed laser 13 outputs pulsed laser light of one or more wavelengths. Then, the location of the small temperature change region is determined based on the Raman backscattered anti-Stokes light signal excited by the pulsed laser. After switching to the second pulsed laser 14 via the optical switch 15, the second pulsed laser 14 outputs multiple pulsed laser lights of different wavelengths in a time-division manner. Then, the temperature corresponding to each small temperature change region is obtained by demodulating the intensity of the Raman forward scattered anti-Stokes light signal of each different wavelength.

[0034] The working principle and demodulation principle of this invention are described below.

[0035] The pulsed laser emitted from pulsed laser source 1 enters sensing fiber 5 after passing through the first wavelength division multiplexer 2, exciting spontaneous Raman scattering at various points along the entire sensing fiber 5. During this process, the pulsed laser simultaneously excites Raman backscattered anti-Stokes light signals and Raman forward scattered anti-Stokes light signals, both exhibiting a 100 nm blue shift in wavelength. The Raman backscattered anti-Stokes light signal returns to the first wavelength division multiplexer 2 and is output from the reflection port, where it is detected by the first avalanche photodetector 9. The Raman forward scattered anti-Stokes light signal is transmitted to filter 8 and output from its terminal, where it is detected by the second avalanche photodetector 10.

[0036] During the calibration phase, optical fiber propagation is used. The location is used as a reference point to obtain the Raman backscattered anti-Stokes light signal generated in the sensing fiber. The intensity of the Raman backscattered anti-Stokes light signal detected by the first avalanche photodetector 9 is... It can be represented as: ; (1) During the measurement phase, propagation is carried out via optical fiber. The location is used as a reference point to obtain the Raman backscattered anti-Stokes light signal generated in the sensing fiber, and the intensity of the Raman backscattered anti-Stokes light signal detected in the first avalanche photodetector 9 is used. It can be represented as: ; (2) The temperature function appearing in equations (1)-(2) and The expression is as follows: ; (3) ; (4) Combining formulas (1)-(4), the ratio of the Raman backscattered anti-Stokes light signal intensity during the measurement stage and the calibration stage is: ; (5) Solving for: ; (6) in, This indicates the power of the pulsed laser. This represents a coefficient related to the Raman backscattering cross section. This represents the backscattering factor of the sensing fiber. This indicates the frequency of the Raman backscattered anti-Stokes light signal. and These represent the attenuation coefficients of the incident light and the Raman backscattered anti-Stokes light signals in the sensing fiber, respectively. This indicates the location where Raman scattering occurs on the sensing fiber. Indicates Raman frequency shift, Denotes Planck's constant. This represents the Boltzmann constant.

[0037] The temperature distribution along the sensing fiber can be obtained from the temperature demodulation result of formula (5). When the length of the temperature-varying region is greater than or equal to the spatial scale corresponding to the full width at half maximum (FWHM) of the pulsed laser, the temperature of the temperature-varying region can be accurately located and demodulated simply by measuring the Raman backscattered anti-Stokes light signal intensity during the calibration and measurement stages. The size of the temperature-varying region can also be determined by measuring the Raman backscattered anti-Stokes light signal intensity during the calibration and measurement stages. However, when the length of the temperature-varying region is less than the spatial scale corresponding to the full width at half maximum (FWHM) of the pulsed laser, it is defined as a small temperature-varying region. The Raman backscattered anti-Stokes light signal intensity can only determine the location of the small temperature-varying region, and the demodulated temperature result is less than the actual ambient temperature. Therefore, the device and method proposed in this invention focus on the accurate demodulation of the temperature of the small temperature-varying region in the sensing fiber 5.

[0038] Specifically, if, during the demodulation of the Raman backscattered anti-Stokes scattering signal intensity in the calibration and measurement stages, only a temperature-varying region with a length greater than or equal to the spatial scale corresponding to the full width at half maximum (FWHM) of the pulsed laser is found, the temperature of this temperature-varying region can be directly and accurately located and demodulated using only the spontaneous Raman backscattered light, without the need to additionally collect the spontaneous forward Raman scattering signal. If a small temperature-varying region is found through the location of the Raman backscattered anti-Stokes scattering signal, whether it is the only small temperature-varying region or a small temperature-varying region coexisting with other non-small temperature-varying regions, then the temperature of the small temperature-varying region needs to be demodulated using the forward and backward anti-Stokes scattering light proposed in this invention.

[0039] Assuming that based on the temperature demodulation results of the Raman backscattered anti-Stokes light signal intensity, there exists on the sensing fiber... There is a small temperature variation zone where only the location can be known; that is, apart from these areas, the sensing fiber is at room temperature everywhere.

[0040] Assuming the pulsed laser source outputs 1 second in 1 minute... Lasers of different wavelengths, the wavelengths are represented as... , ,…, The incident light is directed onto sensing fiber 5 to excite the Raman forward anti-Stokes scattering signal. For the first... The total light intensity received by the second avalanche photodetector 10 at each wavelength. It is the superposition of the scattered light intensity at all locations on the sensing fiber.

[0041] During the calibration phase, the intensity of the Raman forward anti-Stokes scattered light signal detected in the second avalanche photodetector can be expressed as: ; (7) in, This indicates the number of avalanche photodetectors 10 detected during the calibration phase. wavelength The intensity of the Raman forward anti-Stokes scattered light signal corresponding to the pulsed laser, where, Indicates the position on the sensing fiber. , This indicates the number of sampling points on the sensing fiber 5, which is related to the fiber length and the sampling rate of the data acquisition card. This indicates the power of the pulsed laser. This represents a coefficient related to the Raman forward scattering cross section. This represents the forward scattering factor of the sensing fiber. This indicates the frequency of the Raman forward anti-Stokes scattered light signal. and They represent the first The attenuation coefficients of the incident light and Raman forward anti-Stokes scattered light signals corresponding to each wavelength in the sensing fiber. Let ,but: ; (8) During the measurement phase, the intensity of the Raman forward anti-Stokes scattered light signal detected in the second avalanche photodetector can be expressed as: ; (9) in, This indicates the number of avalanche photodetectors 10 detected during the measurement phase. wavelength The intensity of the Raman forward anti-Stokes scattered light signal corresponding to the pulsed laser, due to The temperature change in the small temperature range causes a functional increment in the intensity of the Raman forward anti-Stokes scattered light signal as follows: ; (10) By combining equations (8) and (10), we can obtain: ; (11) because Temperature changes in a small temperature variation region cause an increase in the intensity of the Raman forward anti-Stokes scattering signal. The relative intensity can be expressed as: ;(12) in, Indicates the first The relative intensity corresponding to each wavelength.

[0042] Build decay integral weight matrix ,Right now: ; (13) Among them, the attenuation integral weight matrix No. Line 1 Column elements Through the first The wavelength at the ... Characterized by the attenuation integral of each temperature change region, it can be expressed as: ;(14) in, and They represent the first The attenuation coefficients of the incident light and Raman forward anti-Stokes scattered light signals corresponding to each wavelength in the sensing fiber 5.

[0043] Increment vector of temperature function values ​​in the temperature change zone It can be represented as: ; (15) in, , , …, These represent the 1st, 2nd, ..., The temperature function increment corresponding to each small temperature variation zone , , …, These represent the 1st, 2nd, ..., The temperature corresponding to each small temperature variation zone , , …, Representing temperature , , …, The corresponding temperature function value.

[0044] The relative intensity vector of the Raman forward anti-Stokes scattered light signal It can be represented as: ; (16) in, , , …, These represent the 1st, 2nd, ..., The relative intensity corresponding to each wavelength , , …, These represent the 1st, 2nd, ..., 1st avalanche photodetectors 10 detected during the measurement phase. The intensity of the Raman forward anti-Stokes scattered light signal corresponding to each wavelength of pulsed laser. , , …, These represent the 1st, 2nd, ..., th avalanche photodetectors 10 detected during the calibration phase. The intensity of the Raman forward anti-Stokes scattered light signal corresponding to each wavelength of pulsed laser.

[0045] Combining formula (12), a system of linear equations can be established: ; (17) Solving for: ; (18) Therefore, the increment vector of the temperature function value in each small temperature variation zone can be calculated using formula (18). ; According to formula (15), we have: ; (19) Combining the expressions for the temperature function (3)-(4), we get: ; (20) ; (twenty one) in, Indicates the first Absolute temperature values ​​of small temperature variation zones; Indicates Raman frequency shift, Denotes Planck's constant. Represents the Boltzmann constant. Indicates the first Temperature function increment in a small temperature variation zone This represents the temperature function value corresponding to the calibration temperature. Indicates position The calibration temperature, Indicates position Demodulation temperature, Indicates the first A small temperature variation region, 1≤j≤q.

[0046] Therefore, when the length of the temperature-varying region is less than the spatial scale corresponding to the full width at half maximum (FWHM) of the pulsed laser, after obtaining the position of the small temperature-varying region by demodulating the intensity of the Raman backscattered anti-Stokes light signal, the temperature of the small temperature-varying region can be accurately demodulated by the Raman forward scattered anti-Stokes light signal in the sensing fiber 5, and thus the accurate distributed temperature along the entire sensing fiber 5 can be obtained.

[0047] Based on the above demodulation principle, step 3, obtaining the temperature of each small temperature variation zone through demodulation, includes the following steps: Step 3.1: Calculate the temperature increment vector using the formula (18) above.

[0048] Step 3.1 further includes calculating the relative intensity vector of the Raman forward anti-Stokes scattered light signal. The calculation formula is the above formula (16).

[0049] In step 3.1, the attenuation integral weight matrix The calculation formula is the above formula (14).

[0050] Step 3.2: The demodulation temperature calculation formula for each small temperature variation zone is the above formula (20) and (21).

[0051] Furthermore, in step 3, the above demodulation calculation process is performed by computer 12 to obtain the temperature of each small temperature variation zone.

[0052] In summary, this invention provides a high spatial resolution fiber optic temperature sensing device and method based on multi-wavelength laser bidirectional Raman scattering. By measuring the intensity of the Raman backscattered anti-Stokes light signal in the sensing fiber during the calibration and measurement phases, and jointly demodulating it, a small temperature variation region (spatial length smaller than the spatial scale corresponding to the full width at half maximum of the pulsed laser) along the fiber is located. Based on the known location of the small temperature variation region, by measuring the intensity of the Raman forward scattered anti-Stokes light signal in the sensing fiber excited by the multi-wavelength pulsed laser source during the calibration and measurement phases, a linear equation system is constructed using their difference, thereby accurately demodulating the accurate temperature of the small temperature variation region, and thus obtaining the accurate distributed temperature along the entire fiber. Therefore, the spatial resolution of the system in this invention is determined by the sampling rate, solving the technical bottleneck of existing Raman distributed fiber optic sensing systems where the spatial resolution mainly depends on the pulse width of the light source due to the pulse time-of-flight method as the positioning principle. Furthermore, this invention has the potential to optimize the spatial resolution of the Raman distributed fiber optic sensing system to the PM level, overcoming the technical bottleneck of existing systems where the spatial resolution is limited to the meter level due to pulse width constraints.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high spatial resolution fiber optic temperature sensing device based on multi-wavelength laser bidirectional Raman scattering, characterized in that, include: Pulsed laser source (1), wavelength division multiplexer (2), sensing fiber (5), filter (8), first avalanche photodetector (9), second avalanche photodetector (10), data acquisition card (11), computer (12). The output end of the pulsed laser source (1) is connected to the input end of the wavelength division multiplexer (2), the transmission end of the wavelength division multiplexer (2) is connected to one end of the sensing fiber (5), the reflection end of the wavelength division multiplexer (2) is connected to the first avalanche photodetector (9), the other end of the sensing fiber (5) is connected to the second avalanche photodetector (10) through the filter (8), and the output ends of the first avalanche photodetector (9) and the second avalanche photodetector (10) are connected to the computer (12) through the data acquisition card (11). The pulsed laser source (1) is used to output multiple pulsed lasers of different wavelengths in a time division manner. After passing through the wavelength division multiplexer (2), the pulsed lasers excite Raman backscattered anti-Stokes light signals and Raman forward scattered anti-Stokes light signals in the sensing fiber (5). The Raman backscattered anti-Stokes light signals and Raman forward scattered anti-Stokes light signals are received by the first avalanche photodetector (9) and the second avalanche photodetector (10) respectively, and then collected by the data acquisition card (11) and sent to the computer (12). The computer (12) is used to demodulate the location of the temperature change zone based on the intensity of the Raman backscattered anti-Stokes light signal, and to demodulate the temperature of each small temperature change zone based on the intensity of the Raman forward scattered anti-Stokes light signal of different wavelengths.

2. The high spatial resolution fiber optic temperature sensing device based on multi-wavelength laser bidirectional Raman scattering according to claim 1, characterized in that, It also includes a first optical coupler (3), a first continuous laser source (4), a second optical coupler (6), and a second continuous laser source (7). The transmission end of the wavelength division multiplexer (2) is connected to the first beam splitting end of the first optical coupler (3), the output end of the first continuous laser source (4) is connected to the second beam splitting end of the first optical coupler (3), and the common end of the first optical coupler (3) is connected to one end of the sensing fiber (5). The other end of the sensing fiber (5) is connected to the common end of the second optical coupler (6), the first beam splitting end of the second optical coupler (6) is connected to the input end of the filter (8), and the output end of the second continuous laser source (7) is connected to the second beam splitting end of the second optical coupler (6). The first continuous laser source (4) and the second continuous laser source (7) are used to generate Raman gain for the Raman backscattered anti-Stokes light signal and the Raman forward scattered anti-Stokes light signal in the sensing fiber (5) by inputting laser light.

3. The high spatial resolution fiber optic temperature sensing device based on multi-wavelength laser bidirectional Raman scattering according to claim 1, characterized in that, The pulsed laser source (1) includes a first pulsed laser (13), a second pulsed laser (14), and an optical switch (15). The output terminals of the first pulsed laser (13) and the second pulsed laser (14) are connected to the first and second input terminals of the optical switch (15), and the output terminal of the optical switch (15) is connected to the input terminal of the wavelength division multiplexer (2). The computer (12) is used to demodulate the Raman backscattered anti-Stokes scattering light signal intensity excited by the laser output of the first pulse laser (13) to obtain the location of the temperature change zone, and to demodulate the temperature of each small temperature change zone according to the Raman forward scattered anti-Stokes scattering light signal intensity excited by multiple lasers of different wavelengths output by the second pulse laser (14) in a time-division manner.

4. The high spatial resolution fiber optic temperature sensing device based on multi-wavelength laser bidirectional Raman scattering according to claim 1, characterized in that, The filter (8) is a wavelength division multiplexer.

5. A high spatial resolution fiber optic temperature sensing method based on bidirectional Raman scattering using multi-wavelength lasers, implemented using a sensing device according to any one of claims 1-4, characterized in that... Includes the following steps: Step 1, Calibration Stage: Place the entire sensing fiber (5) at a constant ambient temperature. In this process, the pulsed laser source (1) is adjusted to output pulsed lasers of different wavelengths in a time-division manner. The Raman backscattered anti-Stokes light signal intensity excited by the pulsed lasers of each wavelength is detected by the first avalanche photodetector (9) and the second avalanche photodetector (10). Raman forward anti-Stokes scattering signal intensity ; Step 2, Measurement Stage: Place the sensing fiber (5) in the environment to be measured, repeat Step 1, and use the first avalanche photodetector (9) and the second avalanche photodetector (10) to detect the Raman backscattered anti-Stokes light signal intensity excited by pulsed laser at various wavelengths. Raman forward anti-Stokes scattering signal intensity ; Step 3, Calculation stage: Based on the Raman backscattered anti-Stokes light signal measured in the calibration stage and the measurement stage, calculate the location of the temperature change zone in the sensing fiber (5). Then, based on the Raman forward scattered anti-Stokes light signal intensity measured in the calibration stage and the measurement stage, calculate the temperature of each small temperature change zone in the sensing fiber (5), and thus obtain the temperature along the sensing fiber (5).

6. The high spatial resolution fiber optic temperature sensing method based on bidirectional Raman scattering using multi-wavelength lasers according to claim 5, characterized in that, In step 3, the demodulation of the temperature of each small temperature variation zone includes the following steps: Step 3.1: Calculate the temperature increment vector. The calculation formula is as follows: ； in, Represents the temperature function increment vector. , , , …, These represent the 1st, 2nd, ..., The temperature function increment corresponding to each small temperature variation zone Indicates the number of small temperature variation zones. This indicates the number of wavelengths in a pulsed laser. express The attenuation integral weight matrix, This represents the relative intensity vector of the Raman forward anti-Stokes scattered light signal. Represents a constant; Step 3.2: Calculate the demodulation temperature of each small temperature variation zone. The calculation formula is as follows: ； ； in, Indicates the first The absolute temperature values ​​of each small temperature variation zone; Indicates Raman frequency shift, Denotes Planck's constant. Represents Boltzmann's constant. Indicates the first Temperature function increment in a small temperature variation zone This represents the temperature function value corresponding to the calibration temperature. Indicates the position on the sensing fiber. The calibration temperature, Indicates the position on the sensing fiber. The demodulation temperature.

7. The high spatial resolution fiber optic temperature sensing method based on multi-wavelength laser bidirectional Raman scattering according to claim 6, characterized in that, Step 3.1 further includes calculating the relative intensity vector of the Raman forward anti-Stokes scattered light signal. The steps and calculation formula are as follows: ； in, , , …, These represent the 1st, 2nd, ..., The relative intensity corresponding to each wavelength , , …, These represent the 1st, 2nd, ..., 1st avalanche photodetectors (10) detected during the measurement phase. The intensity of the Raman forward anti-Stokes scattered light signal corresponding to each wavelength of pulsed laser. , , …, These represent the 1st, 2nd, ..., th avalanche photodetectors (10) detected during the calibration phase. The intensity of the Raman forward anti-Stokes scattered light signal corresponding to each wavelength of pulsed laser.

8. The high spatial resolution fiber optic temperature sensing method based on multi-wavelength laser bidirectional Raman scattering according to claim 5, characterized in that, In step 3.1, the attenuation integral weight matrix The calculation formula is: ； in, Represents the decay integral weight matrix No. Line number Column elements, Indicates the number of locations of the sensing fibers. Indicates the location number of the sensing fiber. and They represent the first The attenuation coefficients of the incident light and Raman forward anti-Stokes scattered light signals corresponding to each wavelength in the sensing fiber.

9. A high spatial resolution fiber optic temperature sensing method based on bidirectional Raman scattering using multi-wavelength lasers, as described in any one of claims 5 to 8, characterized in that... In step 3, the temperature of each small temperature variation zone is obtained by demodulation calculation using a computer (12).

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