BOTDR demodulation method based on Brillouin frequency shift and power combination
By employing a BOTDR demodulation method that combines Brillouin frequency shift and power, the problem of insufficient spatial resolution in BOTDR system measurements in the subpulse event region is solved, achieving high-precision measurement of the length and temperature of the subpulse event region, reducing system complexity and saving costs.
Patent Information
- Application Number
- CN202510923853.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-04
- Publication Date
- 2025-11-18
AI Technical Summary
Existing BOTDR systems have insufficient spatial resolution when measuring subpulse event regions, resulting in large measurement errors and failing to meet the high-precision engineering measurement needs of nuclear power plants, submarine cables, and other applications.
A BOTDR demodulation method based on the joint Brillouin frequency shift and power is adopted. By acquiring the Brillouin frequency shift and power along the sensing fiber, the length and temperature information of the subpulse event region are demodulated using the first and second relational equations.
Simultaneous measurement of the length and temperature of the subpulse event region was achieved, improving measurement accuracy, reducing system complexity, and saving costs.
Smart Images
Figure CN120979548A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of distributed optical fiber sensing technology, in particular to a BOTDR demodulation method based on BFS and power combination, which is used to improve the spatial resolution of the BOTDR system and realize the measurement of sub-pulse event area length and temperature / strain. BACKGROUND
[0002] The Brillouin optical time domain reflectometry system (BOTDR) is widely used in the monitoring of various large-scale infrastructures due to its advantages such as single-end incidence and full-distributed sensing. Its monitoring mechanism is based on the self-generated Brillouin scattering effect in the optical fiber, and the physical quantities along the optical fiber are measured according to the sensitive characteristics of the Brillouin scattering signal to temperature / strain. However, the self-generated Brillouin scattering signal has the problem of low intensity and is easily disturbed by noise. Increasing the peak power of the probe pulse or increasing the pulse width can effectively reduce the influence of noise on the measurement results. However, the peak power of the probe pulse is limited by factors such as stimulated Brillouin scattering effect and nonlinear effect. On the other hand, increasing the pulse width can improve the signal-to-noise ratio of the system, but will result in a decrease in spatial resolution. As an important performance indicator in the BOTDR system, the spatial resolution directly determines the monitoring and positioning ability of the event area in engineering applications. With the continuous expansion of the application scenarios of the BOTDR system, higher requirements are put forward for the measurement ability of the event area, especially in high-precision engineering measurement such as nuclear power plants and submarine cables, where the spatial resolution often reaches sub-meter or even centimeter level to accurately identify fault points, otherwise it will lead to false detection or even missed detection, which will seriously affect the safety of the project. When measuring sub-pulse event areas using traditional BOTDR technology, serious measurement errors will occur. Therefore, further improving the measurement ability of the event area and realizing sub-pulse spatial resolution are important problems that need to be solved in the BOTDR system. SUMMARY
[0003] In order to solve the problem of insufficient spatial resolution of the BOTDR system in the prior art and the inability to accurately measure the sub-pulse event area, the present application proposes a BOTDR demodulation method based on BFS and power combination, which can realize the simultaneous measurement of sub-pulse event area length and temperature.
[0004] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows: a BOTDR demodulation method based on BFS and power combination, comprising the following steps: Step 1: acquiring the Brillouin frequency shift of the sensing optical fiber along the line through the BOTDR device and the corresponding power; Step 2: obtaining a first relationship equation and a second relationship equation; the first relationship equation and the second relationship equation are: ; ; wherein, k slope denotes the slope of the Brillouin frequency shift with respect to the length of the event region, a slope denotes the slope of the power variation corresponding to the Brillouin frequency shift spectrum of the event region with respect to the length of the event region, and T denotes the temperature, and respectively denote corresponding relationship equations; Step 3: demodulating to obtain the length and temperature information of the sub-pulse event region according to the collected signal, the first relationship equation and the second relationship equation.
[0005] The calculation formula for demodulating to obtain the length and temperature information of the sub-pulse event region is: ; wherein, L and and respectively denote the length and temperature information of the event region, denotes the power variation corresponding to the Brillouin frequency shift in the Brillouin gain spectrum of the event region with respect to the normal temperature region under the same spatial resolution.
[0006] The BOTDR demodulation method based on the joint of the Brillouin frequency shift and the power further includes the step of performing a pre-calibration experiment on the BOTDR device to obtain the first relationship equation and the second relationship equation.
[0007] The pre-calibration experiment on the BOTDR device to obtain the first relationship equation and the second relationship equation includes the following steps: Step 0.1: setting a section of the sensing optical fiber of the BOTDR device in a constant temperature room, controlling the temperature of the constant temperature room to be a constant temperature by using a temperature control device, and measuring and obtaining the Brillouin frequency shift and power information of the optical fiber along the line under the length by the BOTDR device; Step 0.2: keeping the temperature of the constant temperature room unchanged, changing the length of the sensing optical fiber set in the constant temperature room multiple times, and ensuring that the length of the sensing optical fiber in the constant temperature room is always less than the length of the spatial resolution, and repeatedly measuring and obtaining the Brillouin frequency shift and power information of the optical fiber along the line; Step 0.3: changing the temperature of the constant temperature room to another constant temperature, and repeating step 0.2; Step 0.4: linearly fitting the Brillouin frequency shift of the event region and the length of the event region at each temperature respectively, and obtaining the corresponding k slope , at different temperatures; a slope , at different temperatures; k slope anda slope fitting with temperature, respectively, to obtain a first relationship equation and a second relationship equation.
[0008] The first relationship equation and the second relationship equation are linear equations, i.e.: ; ; wherein, a’ is a slope a linear coefficient of temperature, a 0 ’ is a slope an initial value of k’ is k slope a linear coefficient of temperature, k 0 ’ represents k slope an initial value of T represents temperature.
[0009] In the step 3, the demodulation formula is: ; wherein, k 0represents an initial value of Brillouin shift, L and and respectively represent length and temperature information of an event region, represents power change of Brillouin shift in Brillouin gain spectrum of the event region relative to power of a normal temperature region under same spatial resolution.
[0010] The BOTDR device comprises a continuous laser, a first coupler, a pulse modulator, a pulse light amplifier, a first optical filter, an optical circulator, a sensing optical fiber, a polarization scrambler, a second optical filter, an erbium-doped fiber amplifier, a second coupler, a photodetector and a signal acquisition and processing unit. The continuous laser of the continuous laser output is divided into two beams after the first coupler, one of which is modulated into pulsed light by a pulse modulator, then amplified and filtered by a pulsed light amplifier and a first optical filter, and then enters a sensing optical fiber through an optical circulator, where a back-Briouin scattering signal is generated, and the back-Briouin scattering signal is emitted to a second coupler after being amplified and filtered by an erbium-doped fiber amplifier and a second optical filter in turn; the other beam is directly emitted to the second coupler as reference light after a depolarizer, and the back-Briouin scattering signal and the reference light enter the second optical fiber coupler to couple, and a beat frequency signal is generated and sent to a signal acquisition and processing unit after photoelectric conversion by a photodetector, and three-dimensional Briouin frequency shift information and power information of the sensing optical fiber along the line are obtained by the signal acquisition and processing unit.
[0011] The signal acquisition and processing unit comprises a low-noise amplifier, a mixer, a band-pass filter, a detector and a data acquisition and processing module. The signal output by the photodetector is amplified by the low-noise amplifier, mixed by the mixer, the frequency of the Briouin scattering signal is reduced, the signal after frequency reduction is filtered and detected by the band-pass filter and the detector in turn, the output signal of the detector is collected and processed by the data acquisition and processing module, the Briouin gain spectrum of the sensing optical fiber along the line is obtained, the Briouin frequency shift is fitted, and the power at the maximum Briouin frequency shift is taken as the power value at the position.
[0012] The signal acquisition and processing unit further comprises a signal generator, the output end of the signal generator is connected with the input end of the mixer, and the signal generator is used for reducing the frequency of the Briouin signal by inputting a high-frequency signal to the mixer.
[0013] Compared with the prior art, the present application has the following beneficial effects: (1) The present application introduces the Briouin scattering light power value as a detection index, and proposes a BOTDR demodulation method based on the combination of BFS and power, which breaks through the limitation of pulse width and can realize the measurement of sub-pulse event area length.
[0014] (2) The present application proposes a BOTDR demodulation method based on the combination of BFS and power, which realizes the joint demodulation of sub-pulse event area length and temperature / strain by measuring BFS and power, and greatly improves the measurement accuracy of temperature / strain compared with the traditional demodulation scheme.
[0015] (3) Compared with the existing scheme for improving the spatial resolution of BOTDR, the present application does not increase the system complexity, greatly saves the cost of system construction, and has more feasible application value. BRIEF DESCRIPTION OF DRAWINGS
[0016] Figure 1A flowchart of a BFS and power joint-based BOTDR demodulation method provided for an embodiment of the present application is shown in the figure. Figure 2 A structural diagram of a BOTDR system used for an embodiment of the present application is shown in the figure. Figure 3 A sub-pulse event region length and temperature demodulation principle diagram for an embodiment of the present application is shown in the figure. Figure 4 A BFS and event region length and temperature relationship result diagram obtained for an embodiment of the present application is shown in the figure, where (a) is a linear fitting result of the Brillouin frequency shift and the event region length corresponding to different temperatures, and (b) is a linear fitting result of the slope and the temperature corresponding to different temperatures. k slope A relationship curve linearly fitted with the temperature; Figure 5 A power and event region length and temperature relationship result diagram obtained for an embodiment of the present application is shown in the figure, where (a) is a linear fitting result of the power change and the event region length corresponding to different temperatures, and (b) is a linear fitting result of the slope and the temperature corresponding to different temperatures. a slope A relationship curve linearly fitted with the temperature; In the figure, 1 is a continuous laser, 2 is a first coupler, 3 is a pulse modulator, 4 is a pulse amplifier, 5 is a first optical filter, 6 is an optical circulator, 7 is a sensing optical fiber, 8 is a polarization scrambler, 9 is a second optical filter, 10 is an erbium-doped fiber amplifier, 11 is a second coupler, 12 is a photodetector, 13 is a low-noise amplifier, 14 is a frequency mixer, 15 is a signal generator, 16 is a band-pass filter, 17 is a detector, and 18 is a data acquisition and processing system. DETAILED DESCRIPTION
[0017] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.
[0018] As shown in the figure, the embodiments of the present application provide a BOTDR demodulation method based on the joint of the Brillouin frequency shift and the power, which includes the following steps: Figure 1 Step 1: Obtain the Brillouin frequency shift and the corresponding power of the sensing optical fiber along the line through the BOTDR device.
[0019] As shown in the figure, the embodiments of the present application provide a BOTDR demodulation method based on the joint of the Brillouin frequency shift and the power, which includes the following steps: Figure 2 As shown, in the embodiment, the BOTDR device comprises a continuous laser 1, a first coupler 2, a pulse modulator 3, a pulse light amplifier 4, a first optical filter 5, an optical circulator 6, a sensing optical fiber 7, a polarization scrambler 8, a second optical filter 9, an erbium-doped fiber amplifier 10, a second coupler 11, a photodetector 12, and a signal acquisition and processing unit. The continuous laser output by the continuous laser 1 is split into two beams after the first coupler 2, one of which is modulated into pulse light by the pulse modulator 3, and then amplified and filtered by the pulse light amplifier 4 and the first optical filter 5, and enters the sensing optical fiber 7 through the optical circulator 6, where the self-British scattering effect occurs, and the back-British scattering signal generated is emitted to the second coupler 11 after being amplified and filtered by the erbium-doped fiber amplifier 10 and the second optical filter 9 in turn; the other beam is directly emitted to the second coupler 11 as reference light after the polarization scrambler 8, and the back-British scattering signal and the reference light enter the second optical fiber coupler 11 to be coupled, the beat frequency signal generated enters the photodetector 12 for photoelectric conversion and is sent to the signal acquisition and processing unit, and the three-dimensional British frequency shift information and power information of the sensing optical fiber along the line are obtained by the signal acquisition and processing unit.
[0020] Specifically, in the embodiment, the signal acquisition and processing unit comprises a low-noise amplifier 13, a mixer 14, a band-pass filter 16, a detector 17, and a data acquisition and processing module 18; the signal output by the photodetector 12 is amplified by the low-noise amplifier 13, mixed by the mixer 14, the frequency of the British scattering signal is reduced, the signal after frequency reduction is filtered and detected by the band-pass filter 16 and the detector 17 in turn, the output signal of the detector 17 is collected and processed by the data acquisition and processing module 18, and the British gain spectrum of the sensing optical fiber along the line is obtained, the British frequency shift is fitted, and the power at the maximum British frequency shift is taken as the power value at the position.
[0021] Further, in the embodiment, the signal acquisition and processing unit further comprises a signal generator 15, the output end of the signal generator 15 is connected with the input end of the mixer 14, and the signal generator 15 is used for reducing the frequency of the British signal by inputting a high-frequency signal to the mixer 14.
[0022] Step 2: obtaining a first relationship equation and a second relationship equation; the first relationship equation and the second relationship equation are a relationship equation of the slope of the British frequency shift relative to the length of the event region and the temperature and a relationship equation of the slope of the power change corresponding to the British frequency shift spectrum of the event region relative to the length of the event region and the temperature; specifically, the first relationship equation and the second relationship equation are: ; (1) ; (2) wherein,k slope denotes the slope of the Brillouin frequency shift versus the event region length, a slope denotes the slope of the Brillouin frequency shift spectrum corresponding power difference versus the event region length, T denotes temperature, and respectively denote corresponding relationship equations; wherein the power difference is the power change of the Brillouin frequency shift corresponding power in the Brillouin gain spectrum relative to the power of the normal temperature region under the same spatial resolution, that is, the difference between the two powers.
[0023] Step 3: demodulating to obtain the sub-pulse event region length and temperature information according to the first relationship equation and the second relationship equation.
[0024] Specifically, in the embodiment, the calculation formula for demodulating to obtain the sub-pulse event region length and temperature information is: ; (3) Wherein, L and and respectively denote the length and temperature information of the sub-pulse event region. denotes the power change of the Brillouin frequency shift corresponding power in the Brillouin gain spectrum of the event region relative to the power of the normal temperature region under the same spatial resolution.
[0025] Further, the BOTDR demodulation method based on the joint of the Brillouin frequency shift and the power of the embodiment further includes the step of performing a pre-calibration experiment on the BOTDR device to obtain the first relationship equation and the second relationship equation.
[0026] Specifically, in the embodiment, the pre-calibration experiment on the BOTDR device to obtain the first relationship equation and the second relationship equation includes the following steps: Step 0.1: set a section of the sensing optical fiber of the BOTDR device in a constant temperature room, control the temperature to be a constant temperature by using a temperature control device, and measure and obtain the Brillouin frequency shift and power information of the optical fiber along the line under the length by the BOTDR device; Step 0.2: keep the temperature of the constant temperature room unchanged, change the length of the sensing optical fiber set in the constant temperature room multiple times, and ensure that the length of the sensing optical fiber in the constant temperature room is always less than the length of the spatial resolution, and repeatedly measure and obtain the Brillouin frequency shift and power information of the optical fiber along the line; Step 0.3: change the temperature of the constant temperature room to another constant temperature, and repeat step 0.2; Step 0.4: linearly fit the Brillouin frequency shift of the event region and the event region length at each temperature respectively, and obtain the corresponding k slope , fit the power difference and the event region length at each temperature respectively, and obtain the correspondinga slope , and k slope , and a slope are fitted with temperature respectively, to obtain a first relationship equation and a second relationship equation.
[0027] Specifically, in the embodiment, the first relationship equation and the second relationship equation are linear equations, i.e.: ; (4) ; (5) wherein, a’ is a linear coefficient of temperature, a slope an initial value of the Brillouin frequency shift; a 0 ’ is a linear coefficient of temperature, a slope an initial value of the Brillouin frequency shift; k’ is a linear coefficient of temperature, k slope an initial value of the Brillouin frequency shift; k 0 ’ represents k slope an initial value of the Brillouin frequency shift; T represents temperature; Therefore, substituting the equations (4) and (5) into the equation (3) can know that, in the step 3, the demodulation formula is: ; (6) wherein, k 0 represents an initial value of the Brillouin frequency shift, L and and respectively represent a length of the event region and temperature information, represent a power change of the Brillouin frequency shift in the Brillouin gain spectrum of the event region relative to a power of the normal temperature region under the same spatial resolution, represents the Brillouin frequency shift.
[0028] The demodulation principle of the demodulation method of the present application will be introduced below with reference to Figure 3 .
[0029] The Brillouin gain spectrum detected by one probe pulse can be regarded as a superposition value of n sampling points in the pulse width, and the mathematical expression is: (7) wherein, g Bi ( v, v Bi ) and v Bi is the first iBrillouin gain spectrum and BFS of a segment, Δ v Bi and g0 represents the full width at half maximum (FWHM) and peak gain of the Brillouin gain spectrum, v represents the range of the sweep. When measuring the sub-pulse event region, the normal temperature region and the temperature change region are contained in the Brillouin signal at the same time, and formula (7) is further expressed as: (8) The first half of formula (8) is the BGS of the normal temperature region, and the second half is the BGS of the temperature change region. Therefore G ( v, z n The center frequency of formula (7) is determined by two parts, and the influence factors of the center frequency are explored after normalization: (9) Where x is the normalized sweep range, that is x = v - v B ( T 0) / (Δ v B / 2 ). Let r be the ratio of the length of the temperature change region to the spatial resolution, a be the normalized frequency shift, that is a ( T )= C T ( T - T 0) / (Δ v B / 2 ). Then G 0( x )and G T ( x )are expressed as: (10) (11) Since the BGS is Lorentz-shaped, the BFS can be calculated by derivation. By ignoring the high-order terms generated by derivation, the calculation result of the center frequency is obtained: (12) This formula can be further written as: (13) Where, C T is the temperature linear coefficient of the BFS, generally 1.1 MHz / ℃, v ( T0) represents the BFS in the normal temperature range. From equation (8), it can be seen that the Brillouin frequency shift... v B and r The relationship is linear, meaning that when the external temperature is constant, the BFS is linearly related to the event region length. The linear coefficient is also temperature-dependent; the higher the temperature, the higher the linear coefficient. Therefore, equation (8) can be further written as: (14) in k slope This is the coefficient corresponding to the BFS and the event region length. k 0 represents the BFS value at room temperature. L The length of the event region, where the linear coefficients are... k slope This can be further expressed as: (15) in k’ for k slope The linear coefficient with temperature, k 0 ’ represent k slope The initial value. Substituting equation (15) into (14) yields: (16) The above formula shows v B Based on the length of the event area L and temperature T A joint decision.
[0030] When the temperature in the optical fiber changes, the Brillouin scattering signal changes accordingly, dividing the scattered light power in the subpulse event region into two parts: a normal temperature region and a temperature-varying region. (17) in P The scattered light power in the subpulse event region, P 1 and P 2 represents the power values in the normal temperature region and the temperature-varying region, respectively. The difference between the scattered light power in the subpulse event region and the power in the entire normal temperature region is obtained: (18) Where Δ P The power difference of the scattered light is shown in equation (13). It can be seen that the power difference depends on the length of the temperature-varying region and the amount of power change. For the temperature-varying region, the experimental results from TR Parker et al. show that when the change in Brillouin scattered light power caused by fiber stress is ignored, the change in scattered light power has the following relationship with temperature change: (19) where ΔP is the change of power of the Brillouin scattering light, P B is the power of the Brillouin scattering light in the constant temperature region, P B T 0) is the power of the Brillouin scattering light in the constant temperature region, C P,T is the coefficient of the power change with temperature, which is generally (0.36±0.06)% / ℃. Substituting equation (19) into equation (18) gives: (20) Simplifying the above equation gives: (21) where a slope is the corresponding coefficient of the power difference of the sub-pulse event region and the length of the event region. When the temperature is constant, a slope is a constant, i.e., there is a linear relationship between the power difference of the scattered light and the length of the event region. The linear coefficient a slope is related to the temperature change and the power in the constant temperature region, so a relationship can be further established as: (22) where a’ is the linear coefficient of a slope and temperature, a 0 ’ is the initial value of a slope . When the temperature in the constant temperature region is constant, all the coefficients are constants, i.e., a slope and the temperature in the temperature change region have a linear relationship. Substituting equation (22) into equation (21) gives: (23) The above equation shows that the power difference and the length of the event region L and the temperature T jointly determine the power difference.
[0031] It can be seen that there is a strict linear relationship between the Brillouin frequency shift and the length of the event region, k slope and the power of the scattered light, a slope and the temperature. Having determined k', k 0 ’、a’ and a 0 ’ The BFS and power of the system can be measured to demodulate the length and temperature of the sub-pulse event region.
[0032] In this embodiment, the BFS and power distribution of the optical fiber along the line under different sub-pulse event region lengths and temperatures are obtained through pre-calibration experiments to measure the BOTDR device, to calibrate the coefficients of the first and second relationship equations of the BOTDR device, and then the BFS and power distribution of the sensing optical fiber along the line are measured, which are substituted into equation (6) to demodulate the length and temperature of the event region.
[0033] Specifically, when calibrating the first and second relationship equations, first, the BFS and power of the Brillouin frequency shift under different event region lengths at the same set temperature are calculated, and then the BFS is fitted with the event region length to obtain the slope k slope Meanwhile, the power change is fitted with the event region length to obtain the slope a slope , and then the temperature is changed, and the process is repeated to obtain the slope k slope and a slope at different temperatures, and then k slope , a slope and the temperature are fitted to obtain the first and second relationship equations, and the fitting results are shown in Figure 4 , 5 .
[0034] In specific implementation, the Brillouin frequency shift and power in the sensing optical fiber are measured by the BOTDR device, and then the length and temperature values of the event region can be demodulated according to equations (17) and (23).
[0035] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.
Claims
1. A BOTDR demodulation method based on Brillouin frequency shift and power combination, characterized in that, Includes the following steps: Step 1: Acquire the Brillouin frequency shift along the sensing fiber using a BOTDR device. and the corresponding power; Step 2: Obtain the first relation equation and the second relation equation; the first relation equation and the second relation equation are as follows: ； ； in, k slope This represents the slope of the Brillouin frequency shift relative to the event region length. a slope The slope of the power change relative to the length of the Brillouin shift spectrum in the event region is represented by T, where T represents temperature. and These represent the corresponding relational equations; Step 3: Based on the acquired signal, the first relational equation, and the second relational equation, demodulate to obtain the subpulse-level event region length and temperature information.
2. The BOTDR demodulation method based on Brillouin frequency shift and power combination according to claim 1, characterized in that, The formulas for calculating the length and temperature of the subpulse event region obtained from demodulation are as follows: ； Among them, L and and represent the length and temperature information of the event region, respectively. This represents the change in power corresponding to the Brillouin frequency shift in the Brillouin gain spectrum of the event region relative to the power in the normal temperature region at the same spatial resolution.
3. The BOTDR demodulation method based on Brillouin frequency shift and power combination according to claim 1, characterized in that, It also includes the steps of performing a pre-calibration experiment on the BOTDR device to obtain the first relational equation and the second relational equation.
4. The BOTDR demodulation method based on Brillouin frequency shift and power combination according to claim 3, characterized in that, The pre-calibration experiment of the BOTDR device to obtain the first and second relational equations includes the following steps: Step 0.1: Place a section of the sensing fiber of the BOTDR device in a constant temperature chamber and use a temperature control device to keep its temperature constant. Use the BOTDR device to measure and obtain the Brillouin frequency shift and power information along the fiber. Step 0.2: Keep the temperature of the constant temperature chamber constant, change the length of the sensing fiber set in the constant temperature chamber multiple times, and ensure that the length of the sensing fiber in the constant temperature chamber is always less than the length of the spatial resolution. Repeat the measurement to obtain the Brillouin frequency shift and power information along the fiber. Step 0.3: Change the temperature of the constant temperature chamber to maintain another constant temperature, and repeat step 0.2; Step 0.4: Perform linear fitting between the Brillouin frequency shift and the event region length at each temperature to obtain the corresponding values at different temperatures. k slope By fitting the power change of the event region to the event region length at each temperature, the corresponding values at different temperatures can be obtained. a slope Then k slope and a slope By fitting the equations to temperature, we obtain the first and second relational equations.
5. The BOTDR demodulation method based on Brillouin frequency shift and power combination according to claim 3, characterized in that, The first and second relational equations are linear equations, that is: ； ； in, a’ for a slope The linear coefficient with temperature, a 0 ’ for a slope The initial value; k’ for k slope The linear coefficient with temperature, k 0 ’ represent k slope The initial value; T Indicates temperature.
6. The BOTDR demodulation method based on Brillouin frequency shift and power combination according to claim 5, characterized in that, In step 3, the demodulation formula is: ； in, k 0 represents the initial value of the Brillouin shift, L and and represent the length and temperature information of the event region, respectively. This represents the change in power corresponding to the Brillouin frequency shift in the Brillouin gain spectrum of the event region relative to the power in the normal temperature region at the same spatial resolution.
7. The BOTDR demodulation method based on Brillouin frequency shift and power combination according to claim 1, characterized in that, The BOTDR device includes: a continuous laser (1), a first coupler (2), a pulse modulator (3), a pulsed optical amplifier (4), a first optical filter (5), an optical circulator (6), a sensing fiber (7), a polarization scrambler (8), a second optical filter (9), an erbium-doped fiber amplifier (10), a second coupler (11), a photodetector (12), and a signal acquisition and processing unit. The continuous laser output from the continuous laser (1) is split into two beams after passing through the first coupler (2). One beam is modulated into pulse light by the pulse modulator (3), and then amplified and filtered by the pulse light amplifier (4) and the first optical filter (5). After passing through the optical circulator (6), it enters the sensing fiber (7). Spontaneous Brillouin scattering occurs in the sensing fiber (7). The backscattered Brillouin signal is emitted through the optical circulator (6) and then amplified and filtered by the erbium-doped fiber amplifier (10) and the second optical filter (9) before being emitted to the second coupler (11). The other beam is used as a reference light and is emitted directly to the second coupler (11) after passing through the polarizer (8). The backscattered Brillouin signal and the reference light enter the second fiber coupler (11) for coupling. The resulting beat frequency signal enters the photodetector (12) for photoelectric conversion and is then sent to the signal acquisition and processing unit. The signal acquisition and processing unit acquires and processes the three-dimensional Brillouin frequency shift information and power information along the sensing fiber.
8. The BOTDR demodulation method based on Brillouin frequency shift and power combination according to claim 7, characterized in that, The signal acquisition and processing unit includes: a low-noise amplifier (13), a mixer (14), a bandpass filter (16), a detector (17), and a data acquisition and processing module (18). The signal output by the photodetector (12) is amplified by the low-noise amplifier (13) and then mixed by the mixer (14) to reduce the frequency of the Brillouin scattering signal. The reduced signal is then filtered and detected by the bandpass filter (16) and the detector (17) in sequence. The data acquisition and processing module (18) acquires and processes the output signal of the detector (17) to obtain the Brillouin gain spectrum along the sensing fiber, fits the Brillouin frequency shift, and takes the power at the maximum Brillouin frequency shift as the power value at that position.
9. The BOTDR demodulation method based on Brillouin frequency shift and power combination according to claim 7, characterized in that, The signal acquisition and processing unit also includes a signal generator (15), the output of which is connected to the input of a mixer (14) to reduce the frequency of the Brillouin signal input to the mixer (14).