BOCDR distributed optical fiber sensing device and method based on chaotic optical path matching detection

Abstract

The invention belongs to the field of distributed optical fiber sensing monitoring, and discloses a BOCDR distributed optical fiber sensing device based on chaotic optical path matching detection. The device comprises a chaotic light source, an optical isolator, a first optical fiber coupler, an erbium-doped optical fiber amplifier, a grating optical filter, a first optical fiber circulator, a sensing optical fiber, an optical delay line, a second optical fiber coupler, a first photoelectric detector, a second photoelectric detector and a spectrum analyzer, according to the invention, the optical path matching base point is determined through the cross-correlation of the chaos reference light and the chaos pump light, and the distributed measurement of the Brillouin correlation domain reflection is realized by using the chaos optical path matching and coherent beat frequency method, so that the spatial resolution of the system can be improved.

Description

Technical Field

[0001] This invention belongs to the field of distributed optical fiber sensing and monitoring, specifically a BOCDR (Brillouin Optical Coherence Domain Reflectometry) distributed optical fiber sensing device and method based on chaotic optical path matching detection, which can perform high spatial resolution measurements. Background Technology

[0002] Distributed fiber optic temperature sensing systems offer advantages such as resistance to electromagnetic interference and chemical corrosion, long-distance and wide-range temperature and strain monitoring, and ease of on-site implementation. They can detect temperature and shape changes along the fiber with high sensitivity, finding wide and important applications from national defense and security to daily life. A key theoretical basis for distributed fiber optic sensing technology based on Brillouin scattering is the Brillouin frequency shift. Microscopic particles in the fiber medium spontaneously or under stimulation generate a sound field, which can be viewed as a grating moving along the fiber axis, causing periodic modulation of the fiber's refractive index. The sound field in the fiber interacts with the incident pump light, causing a shift in the frequency of the scattered light, i.e., the Brillouin frequency shift. When the temperature and stress along the fiber change, the physical parameters of the fiber medium change, causing a change in the Brillouin frequency shift. In other words, the Brillouin frequency shift is modulated by temperature and stress. The Brillouin frequency shift, obtained by calculating the difference between the Brillouin peak value and the center frequency of the incident light, contains information about the temperature and strain of the fiber, thus enabling fiber optic sensing.

[0003] Based on the principles of temperature and strain localization, several Brillouin sensing technologies have been developed: Brillouin Optical Coherent Domain Analysis (BOCDA), Brillouin Optical Coherent Domain Reflectometry (BOCDR), Brillouin Optical Time Domain Analysis (BOTDA), and Brillouin Optical Time Domain Reflectometry (BOTDR). Each of these four Brillouin optical sensing technologies has its own advantages and disadvantages. BOTDA and BOTDR technologies utilize time-of-flight methods to locate temperature and strain, resulting in simple system structures and the ability to achieve long-distance measurements at the tens of kilometers level. However, limited by phonon lifetime, the spatial resolution of the system measurements is relatively low, only at the meter level. BOCDA and BOCDR technologies utilize correlation methods to locate temperature and strain, offering higher spatial resolution, but their system structures are relatively complex. Compared to the BOCDA system, the BOCDR system is a single-ended system, making it easier to apply in practice. It uses a coupler to split the light source into two paths, and by detecting the autocorrelation signal between the scattered signal light and the reference light through self-heterodyne detection, it measures the frequency shift and intensity of the Brillouin scattering signal, thereby obtaining the distribution of fiber temperature and strain. BOCDR technology has the advantage of high spatial resolution, achieving even higher spatial resolutions. For example, in 2010, Mizuno et al. proposed a dual-modulation pulse BOCDR scheme achieving a spatial resolution of 20 cm; in 2016, Lee et al. proposed a slope-assisted BOCDR technique, achieving a spatial resolution of 13.9 cm. However, the spatial resolution of these BOCDR techniques is limited by the modulation parameters, only on the order of centimeters, and they have higher system complexity, making them difficult to implement in practical applications. Taking tunnel disaster monitoring as an example, in the tunnel lining crack deterioration assessment standard, crack width d > 5 mm is considered severe cracking, crack width 3 mm < d < 5 mm is considered relatively severe cracking, crack width d < 3 mm is considered moderate cracking, and general cracks without a development trend are considered minor cracking. To achieve accurate monitoring and location of lining cracks in extra-long tunnels with goaf areas ranging from 2.0km to 5.0km, the spatial resolution of distributed sensing needs to be <3 mm. Existing BOCDR technologies are difficult to achieve this level, making it particularly important to find a BOCDR technology with millimeter-level spatial resolution while ensuring the ease of system implementation. Summary of the Invention

[0004] To address the technical problem that the spatial resolution of existing Brillouin optical sensing systems cannot reach the millimeter level, this invention proposes a BOCDR distributed optical fiber sensing device and method based on chaotic optical path matching detection, which can achieve millimeter-level high spatial resolution measurement while ensuring long sensing distance.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a BOCDR distributed optical fiber sensing device based on chaotic optical path matching detection, comprising: a chaotic light source, an optical isolator, a first optical fiber coupler, an erbium-doped fiber amplifier, a grating optical filter, a first optical fiber circulator, a sensing fiber, an optical delay line, a second optical fiber coupler, a first photodetector, a second photodetector, and a spectrum analyzer. The output of the chaotic light source is connected to the input of the first fiber coupler via an optical isolator. The first fiber coupler splits the chaotic laser output from the chaotic light source into two beams: a chaotic pump beam and a chaotic reference beam, which are then output from the first and second outputs, respectively. The first output of the first fiber coupler is connected to one end of the sensing fiber via an erbium-doped fiber amplifier, a grating filter, and a first fiber circulator. The second output is connected to one end of an optical delay line, and the other end of the optical delay line is connected to the first input of the second fiber coupler. The second input of the second fiber coupler is connected to the reflecting end of the first fiber circulator. The output of the second fiber coupler is connected to the first photodetector, and the reflecting end of the first fiber circulator is also connected to the second photodetector. The output of the first photodetector is connected to the spectrum analyzer, which is used to collect the beat spectrum; the optical delay line is used to achieve optical path matching between the chaotic pump light and the chaotic reference light.

[0006] The aforementioned BOCDR distributed optical fiber sensing device based on chaotic optical path matching detection further includes a computing unit, which is used to obtain temperature strain information by demodulating the beat spectrum collected by the spectrum analyzer.

[0007] Both the first and second fiber optic couplers are 1×2 fiber optic couplers with a splitting ratio of 50:50.

[0008] The chaotic light source includes a laser, a second fiber circulator, a third fiber coupler, an attenuator, and a polarization scrambler; the output end of the laser is connected to the input end of the second fiber circulator, and the output end of the second fiber circulator is connected to the input end of the third fiber coupler; the first output end of the third fiber coupler is connected to the optical isolator, and the second output end is connected to the reflector of the second fiber circulator after passing through the attenuator and the polarization scrambler.

[0009] The third fiber coupler is a 1×2 fiber coupler with a splitting ratio of 50:50.

[0010] The BOCDR distributed optical fiber sensing device based on chaotic optical path matching detection further includes an optical switch. The input end of the optical switch is connected to the reflective end of the first optical fiber circulator, the first output end is connected to the second input end of the second optical fiber coupler, and the second output end is connected to the second photodetector.

[0011] The BOCDR distributed fiber optic sensing device based on chaotic optical path matching detection further includes an oscilloscope, and the output terminals of the first photodetector and the second photodetector are connected to the oscilloscope.

[0012] Furthermore, this invention also provides a BOCDR distributed optical fiber sensing method based on chaotic optical path matching detection, implemented using the aforementioned distributed optical fiber sensing device, comprising the following steps: Step 1: Connect the reflector of the first fiber optic circulator to the second photodetector; Step 2: In the sensing fiber An event zone is set at the location, and the Brillouin scattering signals generated by the chaotic reference light and the chaotic pump light in the sensing fiber are received by the first photodetector and the second photodetector respectively, and cross-correlation operation is performed on the two optical signals. Step 3: Determine the time delay of the two optical signals based on the peak positions of the cross-correlation calculation. And based on the delay Determine the optical path matching reference point for the two optical signals; Step 4: Control the reflection end of the first fiber optic circulator to connect to the second input end of the second fiber optic coupler; adjust the optical delay line to change the optical path of the chaotic reference light so that its optical path matching point is located at different positions along the sensing fiber; receive the beat frequency signals of the Brillouin scattering signal and the chaotic reference signal through the first photodetector; and collect the beat frequency signals at different optical path matching points using a spectrum analyzer. Step 5: Extract the Brillouin gain spectrum based on the beat frequency signal corresponding to each optical path matching point, demodulate it to obtain the temperature strain information along the sensing fiber, and realize distributed sensing.

[0013] In step 2, the detection signals from the first and second photodetectors are output to an oscilloscope, and cross-correlation calculations are performed using the oscilloscope to obtain the time delay of the two optical signals. The value of .

[0014] In step 4, the formula for adjusting the optical delay line is: ); in, This indicates the optical path adjustment of the optical delay line during the measurement phase. and These represent the fiber lengths corresponding to the measurement point and the optical path matching reference point, respectively.

[0015] Compared with the prior art, the present invention has the following advantages: 1. This invention uses chaotic laser as the light source of the BOCDR distributed fiber optic sensing device. Chaotic laser has the characteristics of broadband, noise-like characteristics, random amplitude fluctuations, and autocorrelation curves that are delta-like functions. Since the spectral bandwidth of chaotic laser can reach the 20GHz level, and the spatial resolution of the sensing device is determined by the bandwidth of the chaotic light source, this invention can achieve a spatial resolution at the millimeter level. Moreover, it can realize distributed temperature and strain measurements that are independent of the sensing distance and spatial resolution, thereby achieving high spatial resolution sensing over long distances.

[0016] 2. This invention employs chaotic optical path matching detection to achieve Brillouin correlation domain demodulation. Only an additional photodetector needs to be connected before measurement to determine the optical path matching baseline. Subsequent measurements can then be performed directly. During measurement, the measurement point can be directly located using the optical delay line length. Therefore, this invention ensures system simplicity and avoids the problems of technical complexity, stringent experimental requirements, and high system complexity associated with existing technologies that utilize dual-modulation pulses to improve the spatial resolution and sensing distance of BOCDR. Furthermore, it avoids the difficulty in simultaneously achieving both spatial resolution and sensing distance in Brillouin optical sensing technology. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a distributed optical fiber sensing device based on chaotic optical path matching and Brillouin optical correlation domain reflection provided in Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the connection of the device in the optical path matching stage in Embodiment 2 of the present invention; Figure 3 This is a schematic diagram of the connection of the device in the measurement stage of Embodiment 2 of the present invention; 1-Laser, 2-Second fiber circulator, 3-Third fiber coupler, 4-Attenuator, 5-Polarization scrambler, 6-Optical isolator, 7-First fiber coupler, 8-Erbium-doped fiber amplifier, 9-Grate optical filter, 10-First fiber circulator, 11-Sensing fiber, 12-Optical delay line, 13-Second fiber coupler, 14-First photodetector, 15-Second photodetector, 16-Oscilloscope, 17-Spectrum analyzer. Detailed Implementation

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

[0019] Example 1 like Figure 1 As shown, Embodiment 1 of the present invention provides a distributed optical fiber sensing device based on chaotic optical path matching and Brillouin optical correlation domain reflection, including: a chaotic light source, an optical isolator 6, a first optical fiber coupler 7, an erbium-doped fiber amplifier 8, a grating optical filter 9, a first optical fiber circulator 10, a sensing fiber 11, an optical delay line 12, a second optical fiber coupler 13, a first photodetector 14, a second photodetector 15, and a spectrum analyzer 17.

[0020] The output end of the chaotic light source is connected to the input end of the first fiber coupler 7 via an optical isolator 6. The first fiber coupler 7 is used to split the chaotic laser output from the chaotic light source into two beams: a chaotic pump beam and a chaotic reference beam, which are then output from the first output end and the second output end, respectively. The first output end of the first fiber coupler 7 is connected to one end of the sensing fiber 11 via an erbium-doped fiber amplifier 8, a grating filter 9, and a first fiber circulator 10. The second output end is connected to one end of the optical delay line 12, and the other end of the optical delay line 12 is connected to the first input end of the second fiber coupler 13. The second input end of the second fiber coupler 13 is connected to the reflecting end of the first fiber circulator 10. The output end of the second fiber coupler 13 is connected to the first photodetector 14, and the reflecting end of the first fiber circulator 10 is also connected to the second photodetector 15. The output terminal of the first photodetector 14 is connected to the spectrum analyzer 17, which is used to collect the beat spectrum; the optical delay line 12 is used to achieve optical path matching between the chaotic pump light and the chaotic reference light.

[0021] Furthermore, the distributed optical fiber sensing device based on chaotic optical path matching and Brillouin optical correlation domain reflection described in this embodiment also includes a computing unit, which is used to obtain temperature strain information by demodulating the beat spectrum collected by the spectrum analyzer 17.

[0022] Furthermore, in this embodiment, both the first fiber coupler 7 and the second fiber coupler 13 are 1×2 fiber couplers with a splitting ratio of 50:50.

[0023] Further, in this embodiment, the chaotic light source includes a laser 1, a second fiber circulator 2, a third fiber coupler 3, an attenuator 4, and a polarizer 5. The output end of the laser 1 is connected to the input end of the second fiber circulator 2, and the output end of the second fiber circulator 2 is connected to the input end of the third fiber coupler 3. The first output end of the third fiber coupler 3 is connected to the optical isolator 6, and the second output end is connected to the reflecting end of the second fiber circulator 2 after passing through the attenuator 4 and the polarizer 5. Using a feedback-type chaotic laser as the light source for a distributed fiber optic sensing system with Brillouin coherence domain reflection results in a simple structure and stable performance. The feedback intensity of the laser 1 is adjusted by the attenuator 4; the polarization state of the feedback optical loop is controlled by the polarizer 5; and the optical isolator 6 is used to prevent unnecessary light reflection into the laser 1. By observing the spectrum of the emitted light from the chaotic loop using a spectrometer and adjusting the feedback intensity and polarization state of the chaotic loop to an appropriate range, the successful generation of a chaotic laser can be observed.

[0024] In this embodiment, the driving current of the erbium-doped fiber amplifier 8 is increased while the input power is measured, so that the chaotic pump light is amplified to 400mW by the erbium-doped fiber amplifier 8 and injected into the sensing fiber. The power of the chaotic reference light is measured to be 120mW, and the power of the chaotic laser in the scattering loop is 118mW. The two powers are similar, and two peaks are observed in the spectrum obtained by beat frequency. The left peak represents Rayleigh scattering light, and the right peak represents chaotic Stokes light. The frequency of the right peak carries the temperature information of the measured point. The sensing fiber is placed inside a water bath, and the temperature setting of the water bath is adjusted to increase from 20℃ to 50℃ in 5℃ steps for temperature measurement experiments. It is observed that as the temperature increases, the right chaotic Stokes peak gradually shifts towards higher frequencies.

[0025] Specifically, in this embodiment, the third fiber coupler 3 is a 1×2 fiber coupler with a splitting ratio of 50:50.

[0026] Furthermore, the distributed fiber optic sensing device based on chaotic optical path matching and Brillouin optical correlation domain reflection in this embodiment also includes an optical switch 18. The input end of the optical switch 18 is connected to the reflective end of the first fiber optic circulator 10, the first output end is connected to the second input end of the second fiber optic coupler 13, and the second output end is connected to the second photodetector 15. Alternatively, in this embodiment, the optical switch 18 may not be used; instead, the optical path can be manually switched and adjusted so that the fiber optic patch cord at the reflective end of the first fiber optic circulator 10 is connected to the second photodetector 15 during the optical path matching stage and to the second fiber optic coupler 13 during the measurement stage.

[0027] Furthermore, the distributed optical fiber sensing device based on chaotic optical path matching and Brillouin optical correlation domain reflection in this embodiment also includes an oscilloscope 16, and the output terminals of the first photodetector 14 and the second photodetector 15 are connected to the oscilloscope 16.

[0028] The working principle of this embodiment is as follows: Chaotic light is used as the pump light signal. After the chaotic pump light enters the sensing fiber 11, it undergoes Brillouin scattering, generating chaotic Stokes light and chaotic anti-Stokes light. The transmission direction of the chaotic anti-Stokes light is opposite to that of the incident light, and the difference between its frequency and that of the chaotic pump light is [value missing]. This is a Brillouin shift, which carries temperature and strain information about the fiber optic probe location. Reference light. Coherent beat frequency is achieved between the backward chaotic Stokes light and the coherent beat frequency signal at the second fiber coupler 13; the resulting beat frequency signal then passes through the first photodetector 14 to obtain a frequency of The electrical signal is then displayed by the spectrum analyzer 17, and after data processing, the temperature and strain information along the optical fiber is obtained.

[0029] Example 2 Embodiment 2 of the present invention provides a distributed optical fiber sensing method based on chaotic optical path matching and Brillouin optical correlation domain reflection, comprising the following steps: Step 1: Connect the reflective end of the first fiber optic circulator 10 to the second photodetector 15.

[0030] Step 2: Optical path matching stage.

[0031] like Figure 2 As shown, in this embodiment, in the sensing fiber 11 An event zone is set at the location, and the Brillouin scattering signals generated by the chaotic reference light and chaotic pump light in the sensing fiber 11 are received by the first photodetector 14 and the second photodetector 15, respectively. Cross-correlation is performed on the two optical signals; the time delay of the two optical signals is determined based on the peak position of the cross-correlation operation; and the time delay is then used to determine the time delay. Determine the optical path matching reference point for the two optical signals.

[0032] Specifically, in step 2, the detection signals of the first photodetector 14 and the second photodetector 15 are output to the oscilloscope 16, and cross-correlation calculation is performed using the oscilloscope 16 to obtain the time delay values ​​of the two optical signals.

[0033] Specifically, in this embodiment, the formula for calculating the optical path matching reference point is: L0 = L3 + c (1) Where L0 represents the fiber length corresponding to the optical path matching reference point. denoted by time delay, c represents the speed of light in a vacuum, and n represents the refractive index of the optical fiber.

[0034] Step 3: Measurement phase.

[0035] like Figure 3 As shown, the reflective end of the first fiber optic circulator 10 is connected to the second input end of the second fiber optic coupler 13; the optical delay line 12 is adjusted to change the optical path difference between the two optical signals so that their optical path matching points are located at different positions along the sensing fiber 11; the beat frequency signals of the Brillouin scattering signal and the chaotic reference signal are received by the first photodetector 14; and the beat frequency signals at different optical path matching points are collected by the spectrum analyzer 17.

[0036] Specifically, in this embodiment, when the Brillouin scattering signals generated by the chaotic reference light and the chaotic pump light in the sensing fiber 11 satisfy the optical path matching condition, we have: (2) (3) in, This represents the distance from the chaotic light output by the chaotic source after passing through the first fiber coupler 7 to the point before being injected into the sensing fiber 11. This represents the distance from the Brillouin scattered light generated in the sensing fiber 11, from its emission from the first fiber circulator 10 to its entry into the second fiber coupler 13 before the beat frequency. and These represent the optical path lengths of the reference path during the optical path matching stage and the measurement stage, respectively. and These represent the fiber lengths corresponding to the measurement point and the optical path matching reference point, respectively.

[0037] The amplitude and phase characteristics of chaotic lasers change irregularly over time. Therefore, chaotic reference light and Brillouin scattered light cannot be directly detected by beat frequency after coupling. Beat frequency can only occur when the optical path lengths of the two beams are equal. Therefore, it is necessary to synchronize the two beams in a certain way before detection. Specifically, there are: (4) in, Let be the coherence length of the chaotic laser. The refractive index of the optical fiber. Let c be the linewidth of the light source and c be the speed of light in a vacuum. The final achieved spatial resolution is _____. This means that the linewidth of the light source This directly determines the spatial resolution, enabling millimeter-scale sensing using higher-performance chaotic light sources. When the optical path difference between two beams is less than the coherence length, they have the same chaotic state, allowing for beat frequency analysis.

[0038] In other words, due to the chaotic nature of chaotic light, only the Brillouin scattering signal at the optical path matching point can experience Brillouin gain; that is, the optical path matching point is actually the measurement point. Therefore, the location of the measurement point is determined by the optical path length of the reference path. Control, Adjust The length of the optical path can change the position of the optical path matching point, thereby matching different measurement points on the sensing fiber and realizing measurement along the fiber.

[0039] In this embodiment, the presence of jumpers and internal optical fibers in the optical path leads to distance... It is difficult to determine; in actual measurements, the right side of the equation exists. and With two variables, the location of the measurement point cannot be determined.

[0040] Specifically, according to formulas (2) and (3): (5) in, This represents the optical path adjustment amount of the optical delay line 12 during the measurement phase. Therefore, during the optical path matching phase, by setting a temperature change event region with a known location, the optical path matching base point is determined using autocorrelation, and each measurement point along the sensing fiber can be determined using formula (5). The corresponding optical path adjustment amount of optical delay line 12 .

[0041] Step 5: Demodulation stage: Extract the Brillouin gain spectrum based on the beat frequency signal corresponding to each optical path matching point, demodulate to obtain the temperature information along the sensing fiber 11, and realize distributed sensing.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A BOCDR distributed fiber optic sensing device based on chaotic optical path matching detection, characterized in that, include: Chaotic light source, optical isolator (6), first fiber coupler (7), erbium-doped fiber amplifier (8), grating optical filter (9), first fiber circulator (10), sensing fiber (11), optical delay line (12), second fiber coupler (13), first photodetector (14), second photodetector (15), spectrum analyzer (17). The output end of the chaotic light source is connected to the input end of the first fiber coupler (7) via an optical isolator (6). The first fiber coupler (7) is used to split the chaotic laser output from the chaotic light source into two beams: a chaotic pump beam and a chaotic reference beam, which are then output from the first output end and the second output end, respectively. The first output end of the first fiber coupler (7) is connected to one end of the sensing fiber (11) via an erbium-doped fiber amplifier (8), a grating filter (9), and a first fiber circulator (10). The second output end is connected to one end of an optical delay line (12). The other end of the optical delay line (12) is connected to the first input end of the second fiber coupler (13). The second input end of the second fiber coupler (13) is connected to the reflection end of the first fiber circulator (10). The output end of the second fiber coupler (13) is connected to the first photodetector (14). The reflection end of the first fiber circulator (10) is also connected to the second photodetector (15). The output of the first photodetector (14) is connected to the spectrum analyzer (17), which is used to collect the beat spectrum; the optical delay line (12) is used to achieve optical path matching between the chaotic pump light and the chaotic reference light.

2. The BOCDR distributed fiber optic sensing device based on chaotic optical path matching detection according to claim 1, characterized in that, It also includes a calculation unit, which is used to obtain temperature strain information by demodulating the beat spectrum collected by the spectrum analyzer (17).

3. The BOCDR distributed fiber optic sensing device based on chaotic optical path matching detection according to claim 1, characterized in that, The first fiber coupler (7) and the second fiber coupler (13) are both 1×2 fiber couplers with a splitting ratio of 50:

50.

4. The BOCDR distributed fiber optic sensing device based on chaotic optical path matching detection according to claim 1, characterized in that, The chaotic light source includes a laser (1), a second fiber circulator (2), a third fiber coupler (3), an attenuator (4), and a polarization scrambler (5); the output end of the laser (1) is connected to the input end of the second fiber circulator (2), and the output end of the second fiber circulator (2) is connected to the input end of the third fiber coupler (3); the first output end of the third fiber coupler (3) is connected to the optical isolator (6), and the second output end is connected to the reflection end of the second fiber circulator (2) after passing through the attenuator (4) and the polarization scrambler (5).

5. The BOCDR distributed fiber optic sensing device based on chaotic optical path matching detection according to claim 4, characterized in that, The third fiber coupler (3) is a 1×2 fiber coupler with a splitting ratio of 50:

50.

6. The BOCDR distributed fiber optic sensing device based on chaotic optical path matching detection according to claim 1, characterized in that, It also includes an optical switch (18), the input end of which is connected to the reflective end of the first optical fiber circulator (10), the first output end of which is connected to the second input end of the second optical fiber coupler (13), and the second output end of which is connected to the second photodetector (15).

7. The BOCDR distributed fiber optic sensing device based on chaotic optical path matching detection according to claim 1, characterized in that, It also includes an oscilloscope (16), the output terminals of the first photodetector (14) and the second photodetector (15) are connected to the oscilloscope (16).

8. A BOCDR distributed optical fiber sensing method based on chaotic optical path matching detection, implemented using the distributed optical fiber sensing device according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Connect the reflective end of the first fiber optic circulator (10) to the second photodetector (15); Step 2: In the sensing fiber (11) An event zone is set at the location, and the Brillouin scattering signals generated in the sensing fiber (11) by the first photodetector (14) and the second photodetector (15) are respectively received, and the cross-correlation operation is performed on the two optical signals. Step 3: Determine the time delay of the two optical signals based on the peak positions of the cross-correlation calculation. And based on the delay Determine the optical path matching reference point for the two optical signals; Step 4: Control the reflection end of the first fiber optic circulator (10) to connect to the second input end of the second fiber optic coupler (13); adjust the optical delay line (12) to change the optical path of the chaotic reference light so that its optical path matching point is located at different positions along the sensing fiber (11); receive the beat frequency signals of the Brillouin scattering signal and the chaotic reference signal through the first photodetector (14); and use the spectrum analyzer (17) to collect the beat frequency signals at different optical path matching points. Step 5: Extract the Brillouin gain spectrum based on the beat frequency signal corresponding to each optical path matching point, demodulate to obtain the temperature strain information along the sensing fiber (11), and realize distributed sensing.

9. The BOCDR distributed fiber optic sensing method based on chaotic optical path matching detection according to claim 8, characterized in that, In step 2, the detection signals from the first photodetector (14) and the second photodetector (15) are output to an oscilloscope (16). The oscilloscope (16) is used to perform cross-correlation calculations to obtain the time delay of the two optical signals. The value of .

10. The BOCDR distributed fiber optic sensing method based on chaotic optical path matching detection according to claim 8, characterized in that, In step 4, the adjustment formula for the optical delay line (12) is: )； in, This indicates the optical path adjustment amount of the optical delay line (12) during the measurement phase. and These represent the fiber lengths corresponding to the measurement point and the optical path matching reference point, respectively.

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