A phase-sensitive distributed fiber temperature measurement device and method based on a tuned laser

Abstract

The present application belongs to the field of optical fiber sensing technology, and particularly relates to a phase-sensitive distributed optical fiber temperature measuring device and method based on a tunable laser, which comprises a tunable laser, a pulse modulation module, a sensing module and a temperature measuring module, and is characterized in that: the tunable laser is used to calibrate different absolute temperatures corresponding to different center wavelengths by using the variable wavelength characteristics of the tunable laser, and the actual temperature to be measured is demodulated through a correlation demodulation module and a temperature calibration module; the injection locking technology is adopted to eliminate the wavelength drift problem of the tunable laser, suppress the harmonics generated in the frequency sweeping light modulation process of the tunable laser, and improve the measurement accuracy of the system. The present application solves the problem that the phase-sensitive optical fiber measurement method cannot measure the absolute temperature, and can be widely used in the field of high-precision distributed optical fiber temperature measurement.

Description

Technical fields:

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a phase-sensitive distributed fiber optic temperature measurement device and method based on tuned laser. Background technology:

[0002] Phase-sensitive optical time-domain reflectometer This is a distributed fiber optic sensing technology capable of quantitatively measuring external disturbances at any fiber optic location, boasting advantages such as simple structure and high sensitivity. A modulated probe pulse is injected into the sensing fiber, generating a backscattered Rayleigh light signal during transmission. This signal is highly sensitive to changes in external temperature or strain. The backscattered Rayleigh light is converted into a beat frequency electrical signal after entering a photodetector. When the strain or temperature at the fiber location changes, the fiber's length and refractive index change, leading to a phase change in the corresponding position of the echo signal. This phase change is used to demodulate the external temperature or strain change; however... The technology lacks the ability to calibrate temperatures and cannot measure absolute temperatures.

[0003] In 2016, a Spanish research group proposed a direct detection method based on chirped pulse modulation. The system (WO2017093588A1) modulates a linear sweep frequency detection pulse with time-frequency correspondence characteristics, converting phase changes into time shifts in the scattering curve. Therefore, there is a linear relationship between the magnitude of external disturbances and the time delay of the scattering curve. The magnitude of external disturbances is demodulated using a cross-correlation algorithm.

[0004] In 2020, Bao Xiaoyi's research group at the University of Ottawa, Canada, proposed a high-performance distributed sensing system based on fiber grating arrays and multi-frequency database demodulation (Bao Xiaoyi, et al., Strain measurement range enhanced chirped pulse). The proposed Multi-Frequency Database Demodulation (MFDD) method establishes a database composed of echo curves obtained from chirped probe pulses with different initial optical wavelengths when dynamic strain occurs. When dynamic strain occurs, chirped pulses with fixed initial optical wavelengths are used to generate echo curves. During demodulation, cross-correlation calculations are performed between the measured curve and each reference curve. Finally, the cross-correlation result of the reference curve with the highest correlation coefficient is selected to determine the relative strain change. Then, based on the initial frequency difference, the overall strain change is calculated. This method increases the maximum strain measurement range by 3 times.

[0005] In 2020, Yang Jun's research group at Guangdong University of Technology proposed an optical time-domain reflectometer (CN112713929A) based on chirped pulses. Based on the system, the Sipmlex coding method is used to improve the signal-to-noise ratio of the system. In order to avoid coherence between adjacent pulses and ensure the linearity of the system, this method has special requirements for the laser source linewidth. In the demodulation process, inverse combination decoding is required, which is implemented by the inverse matrix of the cyclic Sipmlex matrix, and the amount of data to be processed is relatively large.

[0006] The challenge of Φ-OTDR technology lies in the measurement of absolute temperature. Φ-OTDR demodulation yields the change in external temperature, not the actual external temperature. This invention improves upon existing technology by providing a phase-sensitive optical time-domain reflectometer (OTDR) temperature measurement device and method based on a tuned laser. Building upon the high temperature accuracy of the phase-sensitive OTDR, the invention leverages the characteristic of the tuned laser to flexibly change the output wavelength, establishing a temperature-reference Rayleigh scattering curve dataset. The absolute temperature corresponding to the reference Rayleigh scattering curves under different initial wavelengths is pre-calibrated; then, the actual temperature to be measured is obtained through related demodulation. Summary of the Invention:

[0007] The purpose of this invention is to provide a phase-sensitive distributed fiber optic temperature measurement device and method based on tuned laser that can measure absolute temperature and has high temperature measurement accuracy.

[0008] The objective of this invention is achieved through the following measures:

[0009] A phase-sensitive distributed fiber optic temperature measurement method based on tuned laser, comprising the following steps:

[0010] S1: Calibration temperature – referencing Rayleigh scattering dataset;

[0011] S2: Measurement of absolute temperature;

[0012] Preferably, S1 includes the following steps:

[0013] S1.1: First connect a digital temperature controller 307 to the sensing fiber 302, set the initial wavelength of the tuned laser 1 to λ0, and the frequency sweep range to dλ. Use the digital temperature controller 307 to control the temperature of the sensing fiber 302 at T0. Record the Rayleigh scattering curve at this time as the reference Rayleigh scattering curve 40, and record T0 as the standard absolute temperature.

[0014] S1.2: Keep the temperature of the digital temperature controller 307 at T0, change the initial wavelength of the tuned laser 1 to λ0+Δλ, keep the frequency sweep range unchanged, and record the reference Rayleigh scattering curve collected at this time as 41;

[0015] S1.3: The wavelength of the tuned laser 1 is readjusted back to λ0, the frequency sweep range remains unchanged, and the temperature is increased by ΔT through the digital temperature controller 307. The temperature of the sensing fiber 302 is controlled to be T0+ΔT. After obtaining the Rayleigh scattering curve, cross-correlation is performed with the reference Rayleigh scattering curve 41, and the temperature difference Δt1 between the two is obtained by demodulation. Then, the absolute temperature T1 corresponding to the reference Rayleigh scattering curve 41 is calibrated as T1=T0+ΔT+Δt1.

[0016] S1.4: Using the same calibration method, with the frequency sweep range remaining unchanged, calibrate the center wavelength of the tuned laser 1 by changing Δλ to λ0-Δλ, λ0+2*Δλ, λ0-2*Δλ, and λ0+3*Δλ respectively. Record the obtained reference Rayleigh scattering curves 42, 43, 44, and 45. Then, perform cross-correlation calculations with Rayleigh scattering curves adjacent to the wavelengths to obtain the absolute temperatures corresponding to the reference Rayleigh scattering curves 42, 43, 44, and 45, respectively: T2=T0-ΔT+Δt2, T3=T0+2*ΔT+Δt3, T4=T0-2*ΔT+Δt4, and T5=T0+3*ΔT+Δt5. Combine the reference Rayleigh scattering curves 40, 41, 42, 43, 44, and 45 to form a Rayleigh scattering pattern, and then combine it with its corresponding absolute temperature to obtain the temperatures T0, T1, T2, T3, T4, and T5, thus obtaining the temperature-reference Rayleigh scattering curve dataset.

[0017] Preferably, S2 includes the following steps;

[0018] S2.1: Remove the digital temperature controller 307, connect the sensing fiber optic cable 302 to the environment to be measured, and keep the wavelength of the tuned laser 1 constant at λ0 and the frequency sweep range constant during the actual temperature measurement process. Set the detected Rayleigh scattering curve as the curve to be measured.

[0019] S2.2: Replace the reference curves sequentially, determine the correlation between the curve to be tested and each reference Rayleigh scattering curve in the temperature-reference Rayleigh scattering curve dataset, perform cross-correlation between the curve to be tested and the most relevant reference Rayleigh scattering curve in the temperature-reference Rayleigh scattering curve dataset, and demodulate to obtain the temperature difference Δt.

[0020] S2.3: Then, calibrate the absolute temperature T according to the reference Rayleigh scattering curve. n (0≤n≤5); the actual temperature T = T is calculated. n +Δt(0≤n≤5).

[0021] The temperature difference ΔT adjusted by the digital temperature controller 307 each time the temperature changes must satisfy the condition: ΔT=Δλ*10 -8 :

[0022] The calibration temperature of the digital temperature controller 307—the initial temperature when referencing the Rayleigh scattering curve—must meet the condition: 20℃≤T0≤30℃.

[0023] The temperature change accuracy of the digital temperature controller 307, dT, must meet the condition: dT≤0.01℃.

[0024] A phase-sensitive distributed fiber optic temperature measurement device based on tuned laser includes a tuned laser 1, a signal modulation module 2, a sensing module 3, and a temperature measurement system 4.

[0025] The chirped continuous light 11 emitted by the tuned laser 1 enters the sensing module 3 through the signal modulation module 2, and the resulting backscattering Rayleigh curve enters the temperature measurement system 4; the temperature measurement system 4 performs correlation demodulation on the Rayleigh scattering curve to be measured and the temperature obtained under different initial wavelengths—the reference Rayleigh scattering curve dataset—to obtain the absolute temperature to be measured.

[0026] The output terminal 101a of the tuned laser is connected to the first terminal 201a of the first circulator, the second terminal 201b of the first circulator is connected to the slave laser 202, the third terminal 202c of the first circulator is connected to the input terminal 203a of the pulse modulator, the driving terminal 203c of the pulse modulator is connected to the output terminal 204a of the signal generator, and the output terminal 203b of the pulse modulator is connected to the first terminal 301a of the second circulator.

[0027] The output terminal 202b of the signal generator outputs a pulse electrical signal 23 with a pulse width of τ, which drives the pulse modulator 203 to modulate the chirped continuous light 11 into a detection chirped pulse 24 with a sweep frequency range of dλ.

[0028] The pulse modulator is an acousto-optic modulator or a semiconductor optical amplifier, used to generate high extinction ratio optical pulses, with an extinction ratio ER ≥ 30 dB.

[0029] The output terminal 203b of the pulse modulator is connected to the first terminal 301a of the second circulator, the second terminal 301b of the second circulator is connected to the sensing fiber 302, the third terminal 301c of the second circulator is connected to the input terminal 303a of the optical amplifier, the output terminal 303b of the optical amplifier is connected to the input terminal 304a of the filter, the output terminal 304b of the filter is connected to the input terminal 305a of the detector, the output terminal 305b of the detector is connected to the input terminal 306a of the data acquisition card, and the output terminal 306b of the data acquisition card is connected to the temperature calibration module 401.

[0030] The sensing fiber 302 is a single-mode fiber, a polarization-maintaining fiber, or a multimode fiber;

[0031] The optical amplifier 303 is used to amplify the backscattered Rayleigh light signal injected into the detector 305 and increase its peak power.

[0032] The filter 304 is used to filter out the spontaneous emission noise of the optical amplifier 303;

[0033] The detector 305 is a single-ended photodetector that converts the received Rayleigh scattering light signal into a beat frequency electrical signal.

[0034] The tunable wavelength range λ of the tunable laser 1 must satisfy the following conditions: 1540.0 mm ≤ λ ≤ 1560.0 nm; the maximum sweepable frequency range λ max The following conditions must be met, λ max ≥10nm;

[0035] The wavelength variation accuracy of the tuned laser 1 is less than or equal to 0.01 nm; the sweep frequency range dλ needs to meet the following conditions: 0.01 nm ≤ dλ ≤ 10 nm;

[0036] The wavelength variation Δλ of the tuned laser 1 must meet the condition: 0.15nm ≤ Δλ ≤ 0.2nm;

[0037] The slave laser 202 is also a tunable laser, and the wavelength tunable range λ1 must meet the following conditions: 1540.0nm≤λ1≤1560.0nm; wavelength change accuracy Δλ1≤0.01nm.

[0038] Compared with the prior art, the advantages of the present invention are as follows:

[0039] 1. This invention is a distributed fiber optic temperature measurement device and method based on a tuned laser. By utilizing the controllable output wavelength and sweep frequency range of the tuned laser, a dataset of temperature-Rayleigh scattering reference curves corresponding to detection pulses in different sweep frequency ranges is obtained. The temperature difference between the Rayleigh scattering curve to be measured and the reference Rayleigh scattering curve is demodulated using a cross-correlation algorithm. Then, the actual temperature to be measured is calculated based on the absolute temperature corresponding to each reference Rayleigh scattering curve, thus solving the problem that the Φ-OTDR system cannot measure absolute temperature.

[0040] 2. By adjusting the center wavelength of the slave laser to fall at the center of the modulation sideband in different sweep frequency ranges, the high-order harmonics generated during the sweep frequency modulation of the tuned laser can be suppressed, the measurement accuracy of the system can be improved, and the problem of wavelength drift of the tuned laser can also be solved.

[0041] 3. This invention uses a tuned laser to modulate the swept-frequency optical signal. Compared with the external modulation scheme, it can reduce the number of system components, such as a signal generator, an optical amplifier, and a filter, thus simplifying the system structure and reducing system cost. Attached image description:

[0042] Figure 1 The flowchart shows a phase-sensitive distributed fiber optic temperature measurement method based on tuned lasers.

[0043] Figure 2 Figure 1 shows a phase-sensitive distributed fiber optic temperature measurement device based on tuned laser.

[0044] Figure 3 A diagram of a phase-sensitive distributed optical fiber temperature calibration device based on tuned laser.

[0045] Figure 4 Reference Rayleigh scattering curve obtained after changing the initial wavelength of the tuned laser Specific implementation methods:

[0046] To more clearly illustrate the phase-sensitive distributed fiber optic temperature measurement device and method based on tuned laser proposed in this invention, the following description of the invention in conjunction with embodiments and accompanying drawings is provided in more detail, but should not be construed as limiting the scope of protection of this invention.

[0047] Figure 1 This is a phase-sensitive distributed fiber optic temperature measurement method based on tuned laser. The method steps include S1: calibrating the temperature by referring to a Rayleigh scattering curve dataset; S2: measuring the absolute temperature.

[0048] Figure 2 This is a schematic diagram of a phase-sensitive distributed fiber optic temperature measurement device based on a tuned laser, comprising four parts: a tuned laser 1, a signal modulation module 2, a sensing module 3, and an absolute temperature measurement module 4.

[0049] Figure 3 This is a schematic diagram of a phase-sensitive distributed optical fiber temperature calibration device based on tuned laser. Figure 2 In contrast, a digital temperature controller 307 is externally connected to the sensing fiber optic cable 302.

[0050] The tuned laser 1 outputs a chirped continuous light 11 with an initial wavelength λ0 of 1550.1 nm, an adjustable wavelength range of 1540.0 nm to 1560.0 nm, a wavelength adjustment accuracy of 0.01 nm, a frequency sweep range dλ of 4 nm, a wavelength change Δλ of 0.2 nm per cycle, and a wavelength change range of 1549.7 nm to 1550.7 nm.

[0051] The wavelength tunable range of the slave laser is also 1540.0 nm to 1560.0 nm, with a wavelength adjustment accuracy of 0.01 nm.

[0052] Pulse modulator 203 is a semiconductor optical amplifier with an extinction ratio ER of 32dB;

[0053] Optical amplifier 303 is an erbium-doped fiber amplifier;

[0054] Filter 304 is a 100GHz dense wavelength division multiplexing (WDM) filter.

[0055] The sensing fiber 302 is a single-mode fiber.

[0056] The digital temperature controller 307 has an initial temperature of 25℃, a temperature range of -15℃ to 85℃, and a temperature accuracy of 0.01℃.

[0057] Detector 305 is an InGaAs single-ended detector with a bandwidth of 4 GHz;

[0058] The sampling rate of the data acquisition card 306 is 10 Gsa / s;

[0059] The signal generator 204 outputs a synchronous pulse signal with a pulse width of 100ns to drive the pulse modulator 203 to output synchronously;

[0060] S1: Calibration temperature – the reference Rayleigh scattering curve includes the following steps;

[0061] S1.1: First, a digital temperature controller 307 is connected externally to the sensing fiber 302 to control the output of the tuned laser 1 to a first sweeping continuous light with a wavelength of 1550.1nm, a sweeping range of 4nm, and a pulse width of 200ns. Then, it is injected into the slave laser 202 through the first circulator 201. The driving voltage of the slave laser is adjusted to control the output wavelength of the slave laser to fall at the center of the sweeping bandwidth of the first continuous sweeping light, thus suppressing the extra harmonics generated by the tuned laser during the sweeping light modulation process. It is then injected into the pulse modulator 203 through the third terminal 201c of the first circulator to extract a first probe chirped pulse with a pulse width of 100ns, a sweeping range of 1550.1~1554.1nm, and a repetition rate of 20kHz.

[0062] The first detection chirp pulse is injected into the sensing fiber 302 through the second circulator 301. The digital temperature controller 307 controls the temperature of the sensing fiber to 25°C, and the backscattered Rayleigh light signal is obtained. The backscattered Rayleigh light signal is amplified by the optical amplifier 303, and then filtered by the filter 304 to remove the spontaneously amplified radiation before entering the detector 305. It is converted into a beat frequency electrical signal and recorded as the reference Rayleigh scattering curve 40. It is then acquired and saved by the acquisition card 306.

[0063] S1.2: The output wavelength of the tuned laser 1 is adjusted to 1550.3nm, and a second sweeping continuous light with a sweeping range of 4nm and a width of 200ns is also output. Then, it is injected into the slave laser 202 through the first circulator 201. The drive voltage of the slave laser is adjusted to control the output wavelength of the slave laser to 1552.3nm, so that it falls in the center of the sweeping bandwidth of the second continuous sweeping light, and suppresses the extra harmonics generated by the tuned laser during the sweeping light modulation process. It is then injected into the pulse modulator 203 through the third end 201c of the first circulator, and a second probe chirped pulse with a pulse width of 100ns, a sweeping range of 1550.3~1554.3nm, and a repetition rate of 20kHz is extracted.

[0064] The second detection chirped pulse is injected into the sensing fiber 302 through the second circulator 301. The digital temperature controller 307 controls the temperature of the sensing fiber to remain at 25°C, thus obtaining the backscattered Rayleigh light signal. The backscattered Rayleigh light signal is amplified by the optical amplifier 303, and then filtered by the filter 304 to remove spontaneous emission noise before entering the detector 305. It is converted into a beat frequency electrical signal and recorded as the reference Rayleigh scattering curve 41, which is then acquired and saved by the acquisition card 306.

[0065] S1.3: According to the formula When the wavelength change Δλ is 0.2 nm, the corresponding frequency shift Δυ is 25 G. The temperature change ΔT should be 18 °C. Using Rayleigh scattering curve 40 as the reference curve and Rayleigh scattering curve 41 as the curve to be measured, the result obtained after correlation and demodulation should be 18 °C. The absolute temperature value corresponding to Rayleigh scattering curve 41 should be 43 °C. To eliminate the influence of experimental errors, the digital temperature controller is used to change the temperature of the sensing fiber to 43 °C. The wavelength of the tuned laser is readjusted back to 1550.1 nm, keeping the sweep range unchanged. The Rayleigh scattering curve at this point is obtained. This Rayleigh scattering curve is cross-correlated with the reference Rayleigh scattering curve 41, and the frequency shift is obtained through demodulation. Then, according to the formula... The temperature difference Δt1 is obtained, and the absolute temperature corresponding to the reference Rayleigh scattering curve 41 is determined to be T1 = 43℃ + Δt1;

[0066] S1.4: Repeat the above steps, successively changing the wavelength of the tuned laser to 1549.9nm, 1550.5nm, 1549.7nm, and 1550.7nm, while keeping the frequency sweep range at 4nm, to obtain the second, third, fourth, and fifth probe chirp pulses. Acquire the corresponding reference Rayleigh scattering curves 42, 43, 44, and 45 through the acquisition card 306.

[0067] Cross-correlation calculation is performed between the reference Rayleigh scattering curve 42 and the Rayleigh scattering curve obtained with an initial wavelength of 1550.1 nm, a frequency sweep range of 4 nm, and a digital temperature controller temperature of 7 °C to obtain the absolute temperature T2 corresponding to the reference Rayleigh scattering curve 42 = 7 °C + Δt2.

[0068] Cross-correlation calculation is performed between the reference Rayleigh scattering curve 43 and the Rayleigh scattering curve obtained with an initial wavelength of 1550.1 nm, a frequency sweep range of 4 nm, and a digital temperature controller temperature of 61 °C to obtain the absolute temperature T3 corresponding to the reference Rayleigh scattering curve 43 = 61 °C + Δt3.

[0069] Cross-correlation is performed between the reference Rayleigh scattering curve 44 and the Rayleigh scattering curve obtained with an initial wavelength of 1550.1 nm, a frequency sweep range of 4 nm, and a digital temperature controller temperature of -11℃, to obtain the absolute temperature T4 corresponding to the reference Rayleigh scattering curve 44 = -11℃ + Δt4.

[0070] Cross-correlation calculation is performed between the reference Rayleigh scattering curve 45 and the Rayleigh scattering curve obtained with an initial wavelength of 1550.1 nm, a frequency sweep range of 4 nm, and a digital temperature controller temperature of 79 °C to obtain the absolute temperature T5 corresponding to the reference Rayleigh scattering curve 45 = 79 °C + Δt5.

[0071] The obtained Rayleigh scattering curves 40, 41, 42, 43, 44, and 45 are combined to form a Rayleigh scattering curve pattern. Combined with their corresponding absolute temperatures T0 = 25℃, T1 = 43℃ + Δt1, T2 = 7℃ + Δt2, T3 = 61℃ + Δt3, T4 = -11℃ + Δt4, and T5 = 79℃ + Δt5, the temperature is obtained—referencing the Rayleigh scattering curve dataset; temperature error Δt. n The condition is met: -1℃≤Δt n ≤1℃.

[0072] S2.1: Remove the digital temperature controller 307, connect the sensing fiber optic cable 302 to the environment under test, readjust the output wavelength of the tuned laser to 1550.1nm, output a sweep frequency range of 4nm, and a pulse width of 200ns for the first continuous sweep frequency light, modulate to obtain the first probe chirped pulse, inject it into the sensing fiber optic cable 302 through the second circulator 301 to obtain the Rayleigh scattering light signal, enter the detector 305 to be converted into a beat frequency electrical signal, record the Rayleigh scattering curve at this time as the Rayleigh scattering curve under test, and acquire it by the acquisition card 306 and enter the relevant demodulation module;

[0073] S2.2: Perform correlation calculations between the Rayleigh scattering curve to be measured and the reference Rayleigh scattering curve in the temperature-reference Rayleigh scattering curve dataset, compare the correlations, and find the reference Rayleigh scattering curve that is most correlated with the Rayleigh scattering curve to be measured, according to the formula... Demodulation yields the temperature difference Δt.

[0074] S2.3: Based on the temperature-referenced Rayleigh scattering curve dataset, the absolute temperature T corresponding to the reference Rayleigh scattering curve. n The actual temperature to be measured, T = T, is calculated. n +Δt.

[0075] Based on the characteristics of correlation demodulation in a phase-sensitive optical time-domain reflectometer (OTDR), when the frequency shift of the Rayleigh scattering curve caused by external disturbances or temperature changes is less than or equal to 5% of the system's sweep frequency range, the measured Rayleigh scattering curve and the reference Rayleigh scattering curve still exhibit correlation. However, when the frequency shift exceeds 5%, the measured Rayleigh scattering curve and the reference Rayleigh scattering curve will lose correlation to some extent, leading to errors in the demodulation results. Therefore, the maximum strain or temperature that a phase-sensitive OTD can demodulate should not exceed 5% of the system's sweep frequency range. The sweep frequency range of this device is set to 4 nm, or 500 GHz. Therefore, the maximum frequency shift for single-pass cross-correlation demodulation should be 25 GHz. According to the formula... Δt = ±18℃, therefore, the temperature range that this device can measure should be: -29±1℃≤T≤97±1℃.

[0076] All components in the above embodiments can be commercially available products. This invention aims to protect their connection relationships and implementation principles; therefore, it does not limit the model or other specifications of each product. The positional relationships described in the accompanying drawings are for illustrative purposes only and should not be construed as limitations of this patent.

[0077] As can be seen from the specific examples, this invention proposes a distributed fiber optic temperature measurement device and method based on a tuned laser. While maintaining high temperature measurement accuracy, it calibrates the absolute temperature corresponding to the detection chirped pulses with different initial wavelengths based on the controllable output wavelength and sweep frequency range of the tuned laser. This provides a reference absolute temperature for the actual temperature measurement process, thereby solving the problem that phase-sensitive optical time-domain reflectometers cannot measure absolute temperature and expanding the application scenarios of the system.

[0078] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other changes or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A phase-sensitive distributed fiber optic temperature measurement method based on tuned laser, characterized in that, The method includes the following steps: S1 Temperature calibration – referencing Rayleigh scattering curve dataset, S2 Absolute temperature measurement; its feature is that by utilizing the controllable wavelength and frequency sweep range of the output light of the tuned laser, the absolute temperature is measured using a phase-sensitive optical time-domain reflectometer structure. S1 calibration temperature – referencing Rayleigh scattering dataset, including the following steps: S1.1: First, connect a digital temperature controller (307) to the sensing fiber (302), set the initial wavelength of the tuned laser (1) to λ0, and the frequency sweep range to dλ. Use the digital temperature controller (307) to control the temperature of the sensing fiber (302) at T0, record the Rayleigh scattering curve at this time as the reference Rayleigh scattering curve L0 (40), and record T0 as the standard temperature. S1.2: Keep the temperature of the digital temperature controller (307) at T0, change the initial wavelength of the tuned laser (1) to λ0+Δλ, keep the frequency sweep range unchanged, and record the Rayleigh scattering curve collected at this time as the reference Rayleigh scattering curve L1 (41). S1.3: The wavelength of the tuned laser (1) is readjusted back to λ0, the sweep frequency range is kept unchanged, the temperature is increased by ΔT by the digital temperature controller (307), and the temperature of the sensing fiber (302) is controlled to be T0+ΔT. After obtaining the Rayleigh scattering curve, cross-correlation is performed with the reference Rayleigh scattering curve L1 (41), and the temperature difference Δt1 between the two is obtained by demodulation. Then, the absolute temperature T1 corresponding to the reference Rayleigh scattering curve L1 (41) is calibrated to be T1=T0+ΔT+Δt1. S1.4: Following the same calibration method, keeping the system sweep frequency range unchanged, the center wavelength of the tuned laser (1) is changed to λ0-Δλ, λ0+2*Δλ, λ0-2*Δλ and λ0+3*Δλ with a step size of Δλ. The obtained reference Rayleigh scattering curves L2(42), L3(43), L4(44) and L5(45) are recorded. Then, cross-correlation is performed with the Rayleigh scattering curves obtained when the initial wavelength is λ0 and the digital temperature controller temperature is changed to T0-ΔT, T0+2*ΔT, T0-2*ΔT and T0+3*ΔT respectively to obtain the reference Rayleigh scattering curves. The absolute temperatures corresponding to L2(42), L3(43), L4(44), and L5(45) are T2=T0-ΔT+Δt2, T3=T0+2*ΔT+Δt3, T4=T0-2*ΔT+Δt4, and T5=T0+3*ΔT+Δt5. The Rayleigh scattering patterns are formed by combining the reference Rayleigh scattering curves L0(40), L1(41), L2(42), L3(43), L4(44), and L5(45), and then combined with their corresponding absolute temperatures T0, T1, T2, T3, T4, and T5 to obtain the temperature-reference Rayleigh scattering curve dataset.

2. The phase-sensitive distributed fiber optic temperature measurement method based on tuned laser according to claim 1, characterized in that, S2 determination of absolute temperature includes the following steps: S2.1: Remove the digital temperature controller (307), connect the sensing fiber (302) to the environment to be measured, keep the wavelength of the tuned laser (1) constant at λ0 during the actual temperature measurement process, and keep the frequency sweep range constant, and set the detected Rayleigh scattering curve as the curve to be measured. S2.2: Replace the reference curves sequentially, determine the correlation between the curve to be tested and each reference Rayleigh scattering curve in the temperature-reference Rayleigh scattering curve dataset, perform cross-correlation between the curve to be tested and the most relevant reference Rayleigh scattering curve in the temperature-reference Rayleigh scattering curve dataset, and demodulate to obtain the temperature difference Δt. S2.3: Absolute temperature T calibrated according to the reference Rayleigh scattering curve. n The actual temperature T = T is calculated. n +Δt, where 0≤n≤5.

3. The phase-sensitive distributed fiber optic temperature measurement method based on tuned laser according to claim 1, characterized in that, The digital temperature controller (307) wherein: 1) The temperature difference ΔT adjusted by the digital temperature controller (307) each time the temperature changes must meet the condition: ΔT=Δλ*10 -8 ; 2) The calibration temperature of the digital temperature controller (307) mentioned above—the initial temperature when referring to the Rayleigh scattering curve, T0 must meet the condition: 20℃≤T0≤30℃; 3) The temperature change accuracy of the digital temperature controller (307) mentioned above, dT, must meet the condition: dT≤0.01℃.

4. A phase-sensitive distributed fiber optic temperature measurement device based on a tuned laser, used to implement the method of any one of claims 1 to 3, the device comprising a tuned laser (1), a signal modulation module (2), a sensing module (3), and a temperature measurement system (4), characterized in that: The chirped continuous light (11) emitted by the tuned laser (1) enters the sensing module (3) through the signal modulation module (2), and the resulting backscattering Rayleigh curve enters the temperature measurement system (4). The absolute temperature to be measured is obtained by performing correlation demodulation on the Rayleigh scattering curve to be measured and the temperature obtained under different initial wavelengths in the temperature measurement system (4) – the reference Rayleigh scattering curve dataset.

5. The phase-sensitive distributed fiber optic temperature measurement device based on tuned laser according to claim 4, characterized in that, The signal modulation module (2) mentioned above, wherein: 1) The output terminal (101a) of the tuned laser is connected to the first terminal (201a) of the first circulator, the second terminal (201b) of the first circulator is connected to the slave laser (202), the third terminal (202c) of the first circulator is connected to the input terminal (203a) of the pulse modulator, the driving terminal (203c) of the pulse modulator is connected to the output terminal (204a) of the signal generator, and the output terminal (203b) of the pulse modulator is connected to the first terminal (301a) of the second circulator; 2) The output terminal (204a) of the signal generator outputs a pulse electrical signal (23) with a pulse width of τ, which drives the pulse modulator (203) to modulate the chirped continuous light (11) into a detection chirped pulse (24) with a sweep frequency range of dλ; 3) The pulse modulator is an acousto-optic modulator or a semiconductor optical amplifier, used to generate high extinction ratio optical pulses with an extinction ratio ER ≥ 30dB.

6. The phase-sensitive distributed fiber optic temperature measurement device based on tuned laser according to claim 4, characterized in that, The sensing module (3) mentioned above, wherein: 1) The output terminal (203b) of the pulse modulator is connected to the first terminal (301a) of the second circulator, and the second terminal (301b) of the second circulator is connected to the sensing fiber (302); the third terminal (301c) of the second circulator is connected to the input terminal (303a) of the optical amplifier, the output terminal (303b) of the optical amplifier is connected to the input terminal (304a) of the filter, the output terminal (304b) of the filter is connected to the input terminal (305a) of the detector, the output terminal (305b) of the detector is connected to the input terminal (306a) of the data acquisition card, and the output terminal (306b) of the data acquisition card is connected to the temperature calibration module (401); 2) The sensing fiber (302) is a single-mode fiber, a polarization-maintaining fiber, or a multimode fiber; 3) The optical amplifier (303) is used to amplify the backscattered Rayleigh light signal injected into the detector 305 and increase its peak power; 4) The filter (304) is used to filter out the spontaneously radiated noise of the amplifier (303); 5) The detector (305) is a single-ended photodetector that converts the received backscattered Rayleigh light signal into a beat frequency electrical signal.

7. A phase-sensitive distributed fiber optic temperature measurement device based on tuned laser according to claim 4, characterized in that, The tuned laser (1) mentioned above, wherein: 1) The wavelength tunable range λ of the tunable laser (1) needs to meet the following conditions: 1540.0nm≤λ≤1560.0nm; 2) The wavelength variation accuracy of the tuned laser (1) is less than or equal to 0.01 nm; the sweep frequency range dλ needs to meet the following conditions: 0.1 nm ≤ dλ ≤ 10 nm; 3) The wavelength change Δλ of the tuned laser (1) for each change needs to meet the following condition: 0.1nm≤Δλ≤0.2nm.

8. A phase-sensitive distributed fiber optic temperature measurement device based on tuned laser according to claim 5, characterized in that, The slave laser (202) wherein: The slave laser (202) is also a tunable laser, and the wavelength tunable range λ1 must meet the following conditions: 1540.0nm≤λ1≤1560.0nm; wavelength change accuracy Δλ1≤0.01nm.

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