BOTDR demodulation method based on BFS slope assistance

Abstract

The invention relates to the field of distributed optical fiber sensing, and discloses a BOTDR demodulation method based on BFS slope assistance, and the method comprises the following steps: 1, obtaining BFS information along a sensing optical fiber through a BOTDR system; 2, extracting information of a BFS disturbance area, re-measuring the BFS disturbance area to obtain the length of the BFS disturbance area, and calculating the length of an event area according to the spatial distance corresponding to the pulse width; and step 3, acquiring a temperature-BFS slope auxiliary equation corresponding to the BOTDR system, calculating a BFS slope corresponding to the BFS disturbance region, and demodulating according to the temperature-BFS slope auxiliary equation to obtain the temperature of the BFS disturbance region. According to the invention, the measurement of the event area smaller than the pulse width length can be realized, the temperature / strain detection precision is greatly improved, and the demodulation algorithm is simple.

Description

Technical Field

[0001] The present invention relates to the field of distributed optical fiber sensing, and in particular to a BOTDR (Brillouin optical time domain reflectometry) demodulation method based on BFS (Brillouin frequency shift) slope assistance, which is used to improve the spatial resolution of the BOTDR system and realize temperature / strain measurement in an event zone smaller than a pulse width. Background Art

[0002] The Brillouin optical time-domain reflectometer (BOTDR) based on the spontaneous Brillouin scattering effect has the characteristics of single-ended incidence, simple system, low cost, and has broader application potential. For infrastructure such as bridges, tunnels, and high-density cable networks, early detection of temperature anomalies or deformations in small event areas is crucial to preventing accidents. Therefore, a high-spatial-resolution BOTDR sensing system can detect and solve problems in a timely manner before accidents cause significant damage, effectively avoiding major accidents. How to effectively improve the spatial resolution has become one of the important research contents of the BOTDR system.

[0003] Reducing the pulse width is the most direct way to improve the spatial resolution, but excessively reducing the pulse width will deteriorate the system signal-to-noise ratio and thus reduce the sensing distance. At the same time, due to the limitation of the phonon lifetime, when the pulse width is less than 10 ns, the BGS will also experience serious broadening, affecting the measurement accuracy. Therefore, spatial resolution and sensing distance have become an inherent contradiction in the BOTDR system. Different combined pulse schemes have been proposed to improve the spatial resolution of the BOTDR system, including the double pulse method, synthetic spectrum method, phase-shifted pulse method, differential spectrum crossover method and differential pulse method. The combined pulse is usually composed of two pulses with different pulse widths. The long pulse is used to excite the acoustic wave field, and the short pulse is used to improve the spatial resolution. The combined pulse improves the system performance by modulating parameters such as pulse width, phase, and interval, which obviously increases the complexity of the system and the measurement time. Another idea to improve the spatial resolution is to improve the signal processing method. Schemes such as iterative subdivision method, pulse subdivision superposition method, quadratic time-frequency transform, and image convolution have been verified in experiments. The use of combined pulse solutions or signal processing solutions will inevitably require the addition of high-performance devices or the introduction of new algorithms, which will increase costs. This has also become a reason restricting the industrialization of BOTDR.

[0004] Therefore, exploring effective solutions to improve spatial resolution without increasing system complexity and cost has become an important issue that the BOTDR system needs to solve. Summary of the invention

[0005] In order to solve the technical problem of insufficient spatial resolution of the BOTDR system in the prior art, the present invention proposes a BOTDR demodulation method based on BFS slope assistance to achieve improved spatial resolution.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a BOTDR demodulation method based on BFS slope assistance, comprising the following steps: Step 1: Obtain BFS information along the sensing optical fiber through the BOTDR device; Step 2: Extract the BFS disturbance zone information, obtain the length of the BFS disturbance zone, and calculate the length of the event zone according to the spatial distance corresponding to the pulse width; Step 3: Obtain the temperature-BFS slope auxiliary equation corresponding to the BOTDR system, calculate the BFS slope corresponding to the BFS disturbance zone, and demodulate the temperature of the BFS disturbance zone according to the temperature-BFS slope auxiliary equation.

[0007] In step 3, the slope corresponding to the BFS disturbance zone is calculated as the slope of the falling edge, and the calculation formula is: ; in, represents the slope of BFS in the disturbance region, and Respectively and The Brillouin frequency shift at and Respectively represent calculation The ending and starting positions.

[0008] The BOTDR demodulation method based on BFS slope assistance also includes the step of calibrating and obtaining the temperature-BFS slope auxiliary equation corresponding to the BOTDR system, and the specific method is: Step 0.1: Use a temperature control device to control the temperature of a section of the sensing optical fiber, and use the BOTDR system to measure and obtain the BFS information along the optical fiber; Step 0.2: Change the temperature of the section and repeat the measurement to obtain the BFS information along the optical fiber; Step 0.3: Obtain the corresponding BFS slope in the disturbance zone at each temperature, perform data fitting with the temperature, and obtain the temperature-BFS slope auxiliary equation.

[0009] In the step 0.3, the slope of the falling edge of the corresponding BFS at each temperature in the disturbance zone is obtained and then data fitting is performed with the temperature.

[0010] In step 0.3, when performing data fitting, the fitting equation is: ; in, represents the slope of BFS in the disturbance region, k and k0 represent fitting parameters, and T represents temperature.

[0011] The length of the event zone is calculated as: L = L1-L2; Among them, L1 represents the length of the BFS disturbance zone, and L2 represents the spatial distance corresponding to the pulse width.

[0012] The length of the BFS disturbance zone, L1, is the distance from the beginning of the disturbance zone to the point where it falls to 80% of the highest peak. The calculation formula for L2 is: L2=cT / n; Where c is the speed of light in vacuum, n is the refractive index in the sensing fiber, and T is the pulse width.

[0013] The BOTDR demodulation method based on BFS slope assistance adopts a BOTDR device comprising: Continuous laser, first coupler, pulse modulator, pulse optical amplifier, first optical filter, optical circulator, sensing optical fiber, polarization scrambler, second optical filter, erbium-doped fiber amplifier, second coupler, photodetector and signal acquisition and processing unit; The continuous laser output by the continuous laser is divided into two beams after passing through the first coupler, one of which is modulated into pulse light by a pulse modulator, then amplified and filtered by a pulse light amplifier and a first optical filter, and then enters the sensing optical fiber through an optical circulator, and a spontaneous Brillouin effect occurs in the sensing optical fiber. The generated backward Brillouin scattering signal is emitted through the optical circulator, and then amplified and filtered by an erbium-doped fiber amplifier and a second optical filter in sequence, and then emitted to the second coupler; the other beam is directly emitted to the second coupler as a reference light after passing through a polarization scrambler, and the backward Brillouin scattering signal and the reference light enter the second coupler for coupling, and the generated beat frequency signal enters the photoelectric detector for photoelectric conversion and is sent to the signal acquisition and processing unit, and the signal acquisition and processing unit acquires and processes the BFS information along the sensing optical fiber.

[0014] The signal acquisition and processing unit includes: 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 a low-noise amplifier and then mixed by a mixer to achieve frequency reduction of the Brillouin scattering signal. The frequency-reduced signal is filtered and detected by a bandpass filter and a detector in turn. The data acquisition and processing module collects and processes the output signal of the detector to obtain the BFS information along the sensing optical fiber.

[0015] The signal acquisition and processing unit further comprises a signal generator, and an output end of the signal generator is connected to an input end of the mixer.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention proposes a BOTDR demodulation method based on BFS slope assistance, which realizes the demodulation of the event zone length by measuring the length of the BFS disturbance zone, effectively avoiding the dependence of the event zone measurement capability on the pulse width, and can realize the measurement of the event zone length less than the pulse width.

[0017] (2) The present invention can realize temperature / strain demodulation of the event zone smaller than the pulse width by establishing a linear relationship between the falling edge slope of the BFS disturbance zone and the temperature or strain. Compared with the traditional demodulation scheme, the accuracy of temperature / strain is greatly improved.

[0018] (3) Compared with the existing BOTDR solutions for improving spatial resolution, the present invention does not introduce complex structures and demodulation algorithms, which greatly saves the cost of system construction and has more feasible application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic flow chart of a BOTDR demodulation method based on BFS slope assistance provided by an embodiment of the present invention; Figure 2 Schematic diagram of the structure of the BOTDR system used in the embodiment of the present invention; Figure 3 Schematic diagram of the BFS measurement principle of an embodiment of the present invention; Figure 4 This is a fitting diagram of the sum of the disturbance zone length and the event zone length plus the pulse width of BFS under different pulse widths obtained in an embodiment of the present invention; Figure 5 This is a diagram of BFS distribution results at different temperatures obtained in an embodiment of the present invention; Figure 6 This is a result diagram of the linear relationship between the BFS slope and temperature obtained in an embodiment of the present invention.

[0020] In the figure: 1 is a narrow linewidth laser, 2 is a first coupler, 3 is an optical attenuator, 4 is a pulse modulator, 5 is a pulse optical amplifier, 6 is a first optical filter, 7 is an optical circulator, 8 is a sensing optical fiber, 9 is a polarization scrambler, 10 is a second optical filter, 11 is an erbium-doped fiber amplifier, 12 is a second coupler, 13 is a photodetector, 14 is a low noise amplifier, 15 is a mixer, 16 is a signal generator, 17 is a bandpass filter, 18 is a detector, and 19 is a data acquisition and processing module. DETAILED DESCRIPTION

[0021] In order to make the purpose, 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 part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] like Figure 1 As shown, the embodiment of the present invention provides a BOTDR demodulation method based on BFS slope assistance, comprising the following steps: Step 1: Obtain the BFS information along the sensing optical fiber through the BOTDR device.

[0023] Specifically, Figure 2 As shown, the BOTDR device adopted in this embodiment includes a continuous laser 1, a first coupler 2, a pulse modulator 4, a pulse light amplifier 5, a first optical filter 6, an optical circulator 7, a sensing optical fiber 8, a polarization scrambler 9, a second optical filter 10, an erbium-doped fiber amplifier 11, a second coupler 12, a photodetector 13 and a signal acquisition processing unit; the continuous laser output by the continuous laser 1 is divided into two beams after passing through the first coupler 2, one of which is modulated into a pulse light by the pulse modulator 4, and then amplified and filtered by the pulse light amplifier 5 and the first optical filter 6, and then enters the sensing optical fiber through the optical circulator 7. In the optical fiber 8, a spontaneous Brillouin effect occurs in the sensing optical fiber 8, and the generated backward Brillouin scattering signal is emitted through the optical circulator 7, and then amplified and filtered by the erbium-doped fiber amplifier 11 and the second optical filter 10, and then emitted to the second coupler 12; another beam is used as a reference light and is directly emitted to the second coupler after passing through the polarization scrambler 9, and the backward Brillouin scattering signal and the reference light enter the second coupler 12 for coupling, and the generated beat frequency signal enters the photoelectric detector 13 for photoelectric conversion and is sent to the signal acquisition and processing unit, and the BFS information along the sensing optical fiber is obtained after being collected and processed by the signal acquisition and processing unit.

[0024] Furthermore, if Figure 2 As shown, in this embodiment, the signal acquisition and processing unit includes: a low noise amplifier 14, a mixer 15, a bandpass filter 17, a detector 18 and a data acquisition and processing module 19; the signal output by the photodetector 13 is amplified by the low noise amplifier 14, and then mixed by the mixer 15 to achieve frequency reduction of the Brillouin scattering signal. The frequency-reduced signal is filtered and detected by the bandpass filter 17 and the detector 18 in turn, and the data acquisition and processing module 19 collects and processes the output signal of the detector 18 to obtain BFS information along the sensing optical fiber.

[0025] Furthermore, if Figure 2As shown, in this embodiment, the signal acquisition processing unit further includes a signal generator 16, and the output end of the signal generator 16 is connected to the input end of the mixer 15. The function of the signal generator 16 is to generate a radio frequency signal, which is mixed in the mixer to achieve the down-conversion of the Brillouin signal. Figure 2 As shown, the BOTDR device in this embodiment further includes an optical attenuator 3 , which is arranged between the first coupler 2 and the pulse modulator 4 and is used to attenuate the continuous laser output by the first coupler 2 .

[0026] Specifically, in the BOTDR device used in this embodiment, the continuous laser 1 is a narrow linewidth laser with a wavelength of 1550nm and a linewidth of less than 1MHz, and the output end is connected to the input end of the first coupler 2 having two output ends through a single-mode optical fiber jumper; Specifically, in the BOTDR device adopted in this embodiment, the first coupler 2 and the second coupler 12 are optical fiber couplers. One output end of the first coupler 2 is connected to the input end of the first optical attenuator 3 through a single-mode optical fiber jumper; the output end of the first optical attenuator 3 is connected to the input end of the pulse modulator 4 through a single-mode optical fiber jumper; the output end of the pulse modulator 4 is connected to the input end of the pulse optical amplifier 5 through a single-mode optical fiber jumper; the output end of the pulse optical amplifier 5 is connected to the input end of the first optical filter 6 through a single-mode optical fiber jumper; the output end of the first optical filter 6 is connected to the input end of the optical circulator 7 through a single-mode optical fiber jumper; the reflection end of the optical circulator 7 is connected to the input sensing optical fiber 8 through a single-mode optical fiber jumper; the output end of the optical circulator 7 is connected to the input end of the erbium-doped optical fiber amplifier 11 through a single-mode optical fiber jumper; the output end of the erbium-doped optical fiber amplifier 11 is connected to the input end of the second optical filter 10 through a single-mode optical fiber jumper; the other output end of the first coupler 2 is connected to the input end of the erbium-doped optical fiber amplifier 11 through a single-mode optical fiber jumper The output end of the polarization scrambler 9 and the output end of the second optical filter 10 are respectively connected to the input end of the second coupler 12 through the single-mode optical fiber jumper; the output end of the second coupler 12 is connected to the input end of the photodetector 13 through the single-mode optical fiber jumper; the output end of the photodetector 13 is connected to the input end of the low-noise amplifier 14 through the radio frequency line; the output end of the low-noise amplifier 14 is connected to one input end of the mixer 15 through the radio frequency line, and the output end of the signal generator 16 is connected to the other input end of the mixer 15 through the radio frequency line; the output end of the mixer 15 is connected to the input end of the bandpass filter 17 through the radio frequency line; the output end of the bandpass filter 17 is connected to the input end of the detector 18 through the radio frequency line; the output end of the detector 18 is connected to the data acquisition processing module 19 through the radio frequency line.

[0027] Step 2: Extract the BFS disturbance zone information, obtain the length of the BFS disturbance zone, and calculate the length of the event zone based on the spatial distance corresponding to the pulse width. The length of the BFS disturbance zone is the length corresponding to the interval from the beginning of the BFS change to the end of the change.

[0028] Specifically, in this embodiment, the length calculation formula of the event area is: L = L1-L2; (1) Among them, L1 represents the length of the BFS disturbance zone, and L2 represents the spatial distance corresponding to the pulse width.

[0029] Specifically, in this embodiment, the length L1 of the BFS disturbance zone is defined as the distance from the disturbance zone starting to rise to 80% of the highest peak; the calculation formula of L2 is: L2=cT / n; (2) Where c is the speed of light in vacuum, n is the refractive index in the sensing fiber, and T is the pulse width.

[0030] Step 3: Obtain the temperature-BFS slope auxiliary equation corresponding to the BOTDR system, calculate the BFS slope corresponding to the BFS disturbance zone, and demodulate the temperature of the BFS disturbance zone according to the temperature-BFS slope auxiliary equation.

[0031] In step 3, the slope corresponding to the BFS disturbance zone is calculated as the slope of the falling edge, and the starting position and the ending position of the falling edge are selected for calculation, and the calculation formula is: ; (3) in, represents the slope of BFS in the disturbance region, and Respectively and The Brillouin frequency shift at and Respectively represent calculation The ending and starting positions.

[0032] Furthermore, the BFS slope-assisted BOTDR demodulation method of this embodiment further includes the step of calibrating and obtaining the temperature-BFS slope auxiliary equation corresponding to the BOTDR system, and the specific method is as follows: Step 0.1: Use a temperature control device to control the temperature of a section of the sensing optical fiber, and use the BOTDR system to measure and obtain the BFS information along the optical fiber; Step 0.2: Change the temperature of the section and repeat the measurement to obtain the BFS information along the optical fiber; Step 0.3: Obtain the corresponding BFS slope in the disturbance zone at each temperature, perform data fitting with the temperature, and obtain the temperature-BFS slope auxiliary equation.

[0033] Furthermore, in step 0.3, the slope of the falling edge of the corresponding BFS in the disturbance zone at each temperature is obtained, and the calculation formula is the above formula (3), which is then used to perform data fitting with the temperature.

[0034] Furthermore, in step 0.3, when performing data fitting, the fitting equation is: ; (4) in, represents the slope of the falling edge of BFS in the disturbance zone, k and k0 represent fitting parameters, and T represents temperature.

[0035] The demodulation principle of the present invention is introduced below.

[0036] like Figure 3 As shown in Figure 1, when the temperature and stress along the optical fiber are consistent, the Brillouin spectrum can be described by the following Lorentz formula: ; (5) is the Brillouin gain coefficient, represents the Brillouin peak gain, is the full width at half maximum of the Brillouin gain spectrum, is the Brillouin frequency shift, Indicates the range of the frequency sweep.

[0037] Because the Brillouin signal and the detection pulse propagate in opposite directions in the optical fiber, the Brillouin signal generated by the pulse front will be superimposed with the Brillouin signal generated by the adjacent part of the pulse front when it propagates backwards and is received by the detector. The superposition range is half of the spatial distance corresponding to the pulse width. If the length of the generated Brillouin signal is Δ z The optical fiber is divided into m segments of the same length. The received Brillouin signal is the superposition of the Brillouin signals generated on each segmented optical fiber, that is: ; (6) , , represent the Brillouin gain coefficient, Brillouin frequency shift, and half-maximum full width of the Brillouin gain spectrum on the i-th fiber segment, respectively. express The Brillouin peak gain at represents the Subbrilloun signal measured in the i-th segment.

[0038] Since the effects of temperature and strain on BFS are linear, strain is not considered and only temperature change is used to analyze the change of BFS.

[0039] As the pulse begins to enter the event region, Δ z The coverage range includes both the temperature change zone and the non-temperature change zone. At this time, formula (6) is further expressed as: (7) in, express BGS (Brillouin peak gain) at represents the Brillouin frequency shift in the non-temperature-varying region, represents the Brillouin frequency shift in the temperature variation region, Indicates the location of entry into the event zone.

[0040] Normalizing formula (7) yields: ; (8) in, x is the normalized sweep frequency range, express The normalized value of BGS at and Denote the normalized values ​​of BGS in the non-event area and event area, respectively. r represents the ratio of the temperature change zone length within the pulse coverage to the spatial resolution, and a represents the normalized frequency shift. At this time, by solving formula (8) for the center frequency, we can obtain the BGS peak value and r and a Approximately a linear relationship: ; (9) in, express The center frequency of BGS, It represents the normalized frequency shift related to temperature T.

[0041] Based on the above linear relationship, in this embodiment, the slope of the falling edge of BFS in the disturbance region is used to demodulate the temperature or strain.

[0042] Combining formula (3) and (9) and simplifying them, we can get the relationship between the slope of BFS in the disturbance zone and the temperature as follows: ; (10) It can be seen that there is a strict linear relationship between the slope and temperature, and the fitting parameters are determined. and Then the temperature can be demodulated by calculating the BFS slope.

[0043] In this embodiment, the demodulation of the event region length is performed by utilizing the length relationship between the disturbance region, the pulse width and the disturbance region. Figure 4 As shown, when the pulse width is different, the disturbance zone length of BFS is different. Experiments have found that for different pulse widths, the disturbance zone length of BFS is always equal to the sum of the length corresponding to the pulse width and the event zone length.

[0044] In specific implementation, it is necessary to first measure the length of the disturbance zone of the BFS, where the length of the BFS disturbance zone is 80% of the part from the beginning of the rise to the completion of the fall, because the pulse is not a standard rectangle with rising and falling edges. Then, the length of the event zone along the optical fiber can be measured by subtracting the pulse width from the length of the BFS disturbance zone.

[0045] like Figure 5 As shown, in this embodiment, the temperature-BFS slope auxiliary equation is calibrated by measuring the BFS distribution along the optical fiber at different temperatures, and then the measured slope is substituted into the calibrated temperature-BFS slope auxiliary equation to demodulate the temperature. Specifically, when calibrating the temperature-BFS slope auxiliary equation, the BFS slope at each temperature is calculated respectively, and it is fitted with the temperature, and then a linear relationship with the temperature is established. The fitting result is shown as follows: Figure 6 shown.

[0046] In a specific implementation, the slope of the falling edge of the BFS is measured, and then the temperature is demodulated assisted according to the linear relationship between the BFS slope and the temperature.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 BOTDR demodulation method based on BFS slope assistance, characterized in that: The following steps are involved: Step 1: Obtain BFS information along the sensing optical fiber through the BOTDR device; Step 2: Extract the BFS disturbance zone information, obtain the length of the BFS disturbance zone, and calculate the length of the event zone according to the spatial distance corresponding to the pulse width; Step 3: Obtain the temperature-BFS slope auxiliary equation corresponding to the BOTDR system, calculate the BFS slope corresponding to the BFS disturbance zone, and demodulate the temperature of the BFS disturbance zone according to the temperature-BFS slope auxiliary equation.

2. A BOTDR demodulation method based on BFS slope assistance according to claim 1, characterized in that: In step 3, the slope corresponding to the BFS disturbance zone is calculated as the slope of the falling edge, and the calculation formula is: ； in, represents the slope of BFS in the disturbance region, and Respectively and The Brillouin frequency shift at and Respectively represent calculation The ending and starting positions.

3. A BOTDR demodulation method based on BFS slope assistance according to claim 1, characterized in that: It also includes the step of calibrating the temperature-BFS slope auxiliary equation corresponding to the BOTDR system, and the specific method is: Step 0.1: Use a temperature control device to control the temperature of a section of the sensing optical fiber, and use the BOTDR system to measure and obtain the BFS information along the optical fiber; Step 0.2: Change the temperature of the section and repeat the measurement to obtain the BFS information along the optical fiber; Step 0.3: Obtain the corresponding BFS slope in the disturbance zone at each temperature, perform data fitting with the temperature, and obtain the temperature-BFS slope auxiliary equation.

4. The BOTDR demodulation method based on BFS slope assistance according to claim 3 is characterized in that: In the step 0.3, the slope of the falling edge of the corresponding BFS at each temperature in the disturbance zone is obtained and then data fitting is performed with the temperature.

5. The BOTDR demodulation method based on BFS slope assistance according to claim 3 is characterized in that: In step 0.3, when performing data fitting, the fitting equation is: ； in, represents the slope of BFS in the disturbance region, k and k0 represent fitting parameters, and T represents temperature.

6. The BOTDR demodulation method based on BFS slope assistance according to claim 1, characterized in that: The length of the event zone is calculated as: L = L1-L2; Among them, L1 represents the length of the BFS disturbance zone, and L2 represents the spatial distance corresponding to the pulse width.

7. A BOTDR demodulation method based on BFS slope assistance according to claim 6, characterized in that: The length of the BFS disturbance zone, L1, is the distance from the beginning of the disturbance zone to the point where it falls to 80% of the highest peak. The calculation formula for L2 is: L2=cT / n; Where c is the speed of light in vacuum, n is the refractive index in the sensing fiber, and T is the pulse width.

8. The BOTDR demodulation method based on BFS slope assistance according to claim 1, characterized in that: The BOTDR devices used include: A continuous laser (1), a first coupler (2), a pulse modulator (4), a pulse optical amplifier (5), a first optical filter (6), an optical circulator (7), a sensing optical fiber (8), a polarization scrambler (9), a second optical filter (10), an erbium-doped optical fiber amplifier (11), a second coupler (12), a photodetector (13), and a signal acquisition and processing unit; The continuous laser light output by the continuous laser (1) is divided into two beams after passing through the first coupler (2), one of which is modulated into pulse light by a pulse modulator (4), then amplified and filtered by a pulse light amplifier (5) and a first optical filter (6), and then enters the sensing optical fiber (8) through an optical circulator (7), where a spontaneous Brillouin effect occurs in the sensing optical fiber (8), and the generated backward Brillouin scattering signal is emitted through the optical circulator (7), amplified and filtered by an erbium-doped fiber amplifier (11) and a second optical filter (10) in sequence, and then emitted to the second coupler (12); the other beam is directly emitted to the second coupler as reference light after passing through a polarization scrambler (9), and the backward Brillouin scattering signal and the reference light enter the second coupler (12) for coupling, and the generated beat frequency signal enters the photoelectric detector (13) for photoelectric conversion, and then is sent to the signal acquisition and processing unit, where the signal acquisition and processing unit acquires BFS information along the sensing optical fiber.

9. A BOTDR demodulation method based on BFS slope assistance according to claim 8, characterized in that: The signal acquisition and processing unit comprises: a low noise amplifier (14), a mixer (15), a band pass filter (17), a detector (18) and a data acquisition and processing module (19); The signal output by the photodetector (13) is amplified by a low noise amplifier (14) and mixed by a mixer (51) to achieve frequency reduction of the Brillouin scattering signal. The frequency reduced signal is filtered and detected by a bandpass filter (17) and a detector (18) in sequence. The data acquisition and processing module (19) acquires and processes the output signal of the detector (18) to obtain BFS information along the sensing optical fiber.

10. The BOTDR demodulation method based on BFS slope assistance according to claim 9, characterized in that: The signal acquisition and processing unit further comprises a signal generator (16), the output end of the signal generator (16) being connected to the input end of the mixer (15).

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