Long-distance double-sideband single-ended BOTDA (Brillouin Optical Time Domain Analysis) sensing system and method based on terminal passive device

Abstract

The invention relates to a distributed optical fiber sensing system, and discloses a long-distance double-sideband single-ended BOTDA sensing system and method based on a tail end passive device, an optical signal output by a laser is divided into two paths after passing through a first beam splitter, and one path is modulated into double-sideband continuous light which is output to a coupler as detection light; the other path is modulated into pulsed light which is output to the coupler as pump light; after being coupled by the coupler, the light enters a sensing optical fiber through a first circulator, and the tail end of the sensing optical fiber is connected with a passive device; a pump reflector in the passive device reflects pump light in the sensing optical fiber and enables double-sideband detection light to return to the sensing optical fiber after transmission, and an isolator isolates the reflected pump light so that the pump light cannot return to the sensing optical fiber; and after transmission, the double-sideband detection light returning to the sensing optical fiber acts with the back pumping light, then enters a photoelectric detector and is demodulated to obtain a sensing signal along the optical fiber. According to the invention, the signal-to-noise ratio and the sensing distance of a single-ended BOTDA sensing system are greatly improved.

Description

Technical Field

[0001] The present invention relates to a distributed optical fiber sensing system, in particular to a long-distance double-sideband single-ended BOTDA sensing system and method based on an end passive device, which can realize double-sideband long-distance sensing of a single-ended BOTDA sensing system. Background Art

[0002] Distributed optical fiber sensing technology has the advantages of small size, light weight, anti-electromagnetic interference, corrosion resistance, and can realize real-time monitoring of various physical quantities at any position along the optical fiber. It has important application value in the fields of national defense, military, aerospace, etc. Among them, the Brillouin optical time domain analysis (BOTDA) sensing system has the advantages of being sensitive to both temperature and strain and high measurement accuracy, and is widely used in the safety monitoring of major infrastructure such as transportation, power, petrochemical, and civil engineering. Traditional BOTDA technology requires the pump light and the probe light to be incident from both ends of the optical fiber respectively, and the actual sensing distance is only half of the optical fiber length, and the other half of the optical fiber is not utilized.

[0003] In 1996, Marc Niklès et al. proposed a single-ended BOTDA system, which uses the Fresnel reflected light of the previous pulsed light as the probe light, and realizes the sensing measurement of the entire optical fiber by continuously changing the time interval between the two pulsed lights. However, the intensity of the Fresnel reflected light is only 4% of the incident light, resulting in a small signal (Optics Letters, 1996, 21(10): 758-760.). In 1809, Qingsong Cui et al. used the Fresnel reflected light of the pump pulse substrate at the far end as the probe light. The probe light being continuous light is more convenient for distributed measurement, but the problem of small signal still cannot be solved (Applied Optics, 1809, 48(30): 5823-5828.). In 1811, Qingsong Cui et al. proposed to use the Rayleigh scattered light of the pump pulsed light substrate as the probe light to realize a single-ended BOTDA system. However, the Rayleigh scattering signal is also relatively weak, and it will also be affected by the relevant Rayleigh noise during the measurement process, resulting in a low signal-to-noise ratio of the system and limited measurement distance (IEEE Sensors Journal, 1810, 11(2): 399-403.). In 1819, Jin Xu et al. used a cascaded fiber Bragg grating set at the end of the optical fiber. Utilizing the characteristic that the reflection spectrum of the fiber Bragg grating can be used as a filter, the pulsed light is filtered out and the probe light is retained (Measurement Science and Technology, 1819, 30(3): 035105.). However, using the reflection spectrum of the fiber Bragg grating can only return the single-sideband probe light to the optical fiber to generate stimulated Brillouin scattering with the forward-propagating pump pulsed light. The pulsed light only undergoes a single gain or loss, and the energy of the pulsed light is unstable during the sensing process, making it difficult to achieve long-distance sensing. The scheme of using a mirror to reflect the probe light at the end of the optical fiber will also return the pump pulsed light to the optical fiber at the same time. The backward-propagating pump pulsed light will generate stimulated Brillouin scattering with the forward-propagating continuous light. The continuous light carrying the stimulated Brillouin information returns to the optical fiber through the mirror at the end of the optical fiber and generates stimulated Brillouin scattering with the forward-propagating pump pulsed light, and is finally received by the photodetector. Since the probe light carries the information of two stimulated Brillouin scatterings, a large measurement error will be generated.

[0004] In summary, it is necessary to improve the single-ended BOTDA system in the prior art to ensure that the double-sideband probe light can better compensate the energy of the pulsed light, thereby realizing the long-distance measurement of the single-ended BOTDA system. Summary of the Invention

[0005] In order to further improve the measurement distance of the single-ended BOTDA system and increase the signal-to-noise ratio, the present invention proposes a long-distance double-sideband single-ended BOTDA sensing system and method based on an end passive device.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A long-distance double-sideband single-ended BOTDA sensing system based on end passive devices, including a laser, the optical signal output by the laser is divided into two paths after passing through a first beam splitter. One path is modulated by a modulator into double-sideband continuous light with a frequency of ν0±f RF and is output as probe light to a coupler; the other path is modulated by a semiconductor optical amplifier into pulsed light and is output as pump light to the coupler; where ν0 represents the frequency of the laser, and f RF represents the driving frequency of the modulator;

[0007] The probe light and the pump light are coupled by the coupler and enter the sensing optical fiber through a first circulator. The end of the sensing optical fiber is connected to a passive device; the passive device includes a pump reflector and an isolator; the pump reflector is used to reflect the pump light in the sensing optical fiber and also to transmit the double-sideband probe light and return it to the sensing optical fiber. The isolator is used to isolate the reflected pump light so that it cannot return to the sensing optical fiber; after the double-sideband probe light transmitted and returned to the sensing optical fiber interacts with the backward pump light, it is output through the first circulator and enters an optical filter to filter out one sideband, and then enters a photodetector to be converted into an electrical signal and enters a data acquisition and analysis system for demodulation to obtain the sensing signal along the optical fiber.

[0008] The pump reflector is a fiber Bragg grating.

[0009] The isolator is an optical isolator. The passive device further includes a second beam splitter. The end of the sensing optical fiber is connected to the input end of the second beam splitter. One output end of the second beam splitter is connected to the input end of the optical isolator, and the other output end of the second beam splitter is connected to the transmission end of the pump reflector. The reflection end of the pump reflector is connected to the output end of the optical isolator.

[0010] The isolator is an optical circulator. The passive device further includes a second beam splitter. The end of the sensing optical fiber is connected to the input end of the second beam splitter. One output end of the second beam splitter is connected to the input end of the optical circulator, and the other output end of the second beam splitter is connected to the transmission end of the pump reflector. The reflection end of the pump reflector is connected to the middle end of the optical circulator.

[0011] The above-mentioned long-distance double-sideband single-ended BOTDA sensing system based on end passive devices further includes a second circulator. The double-sideband probe light output through the first circulator is transmitted to the optical filter through the second circulator. After one sideband is filtered out by reflection of the optical filter, it returns to the second circulator and is output and then enters the photodetector.

[0012] The optical filter is a fiber Bragg grating, and the modulator is an electro-optic modulator.

[0013] The optical filter is a narrowband filter.

[0014] The described long-distance dual-band single-ended BOTDA sensing system based on end passive devices further includes a continuous erbium-doped fiber amplifier and a pulsed erbium-doped fiber amplifier. The continuous erbium-doped fiber amplifier is arranged between the modulator and the coupler and is used to amplify the dual-band continuous light output by the modulator. The pulsed erbium-doped fiber amplifier is arranged between the semiconductor optical amplifier and the coupler and is used to amplify the pulsed light output by the semiconductor optical amplifier.

[0015] The described long-distance dual-band single-ended BOTDA sensing system based on end passive devices further includes a microwave signal source and a pulse generator. The microwave signal source is used to drive the modulator, and the pulse generator is used to drive the semiconductor optical amplifier.

[0016] In addition, the present invention also provides a sensing method for a long-distance dual-band single-ended BOTDA sensing system based on end passive devices, including the following steps:

[0017] S1. Start the device;

[0018] S2. Sweep the driving frequency of the electro-optic modulator near the Brillouin frequency shift to cause stimulated Brillouin gain and loss effects between the dual-band probe light and the pump pulse light in the sensing fiber;

[0019] S3. Collect and analyze the Brillouin time series signal through a photodetector and a data acquisition and analysis system, and demodulate the position and intensity information of the temperature / strain along the sensing fiber.

[0020] The present invention has the following beneficial effects compared with the prior art:

[0021] 1. The present invention uses a passive device connected to the end of the sensing fiber to suppress the reflection of the pump light, retains the transmission of the probe light and returns it to the sensing fiber again, realizing the single-ended input and bidirectional transmission of the pump light and the probe light in the sensing fiber, effectively preventing measurement errors caused by the stimulated Brillouin scattering effect between the pulsed light returning to the fiber and the continuous light transmitting forward. In addition, in the present invention, the continuous probe light signal is strong and the noise is small, greatly improving the signal-to-noise ratio, and long-distance high-precision sensing can be achieved. Compared with the dual-ended BOTDA sensing system where the sensing distance is only half of the sensing fiber, the actual sensing distance of the present invention is equal to the length of the sensing fiber, and it has more potential for long-distance measurement. In addition, it also overcomes the problems of small signal, large noise, and low signal-to-noise ratio in the single-ended BOTDA system that uses the backward Rayleigh scattering light or Fresnel reflection light of continuous light as the probe light in the prior art.

[0022] 2. In addition, the passive device connected to the end of the optical fiber in the present invention includes a fiber Bragg grating. By using the transmission spectrum of the fiber Bragg grating, two sidebands of the probe light can be completely retained. Injecting the double-sideband probe light into the optical fiber, the energy of the pulsed light remains stable during the sensing process, which is more suitable for long-distance sensing. This overcomes the problem in the prior art that in a single-ended BOTDA system based on a fiber Bragg grating, only the high-frequency probe light or the low-frequency probe light is reflected back into the optical fiber by using the reflection spectrum of the fiber Bragg grating, and during the sensing process, the pulsed light is only affected by the gain or loss of the single-sideband probe light, resulting in unstable pulsed light power and short sensing distance.

[0023] In summary, the present invention proposes a long-distance double-sideband single-ended BOTDA sensing system and method based on an end passive device, which greatly improves the signal-to-noise ratio of the system in the case of single-ended incidence. The device is simple and easy to implement, effectively improves the sensing distance of the single-ended BOTDA system, and can achieve higher-performance distributed temperature / strain sensing. Brief Description of the Drawings

[0024] Figure 1 Schematic diagram of the structure of a long-distance double-sideband single-ended BOTDA sensing system based on a combination of end passive devices provided in the first embodiment of the present invention;

[0025] Figure 2 Schematic diagram of the structure of a long-distance double-sideband single-ended BOTDA sensing system based on a combination of end passive devices provided in the second embodiment of the present invention;

[0026] Figure 3 Reflection light and transmission spectrum diagram of the pump reflector in the first embodiment of the present invention;

[0027] Figure 4 Comparison diagram of the measured values when the pulsed light and the continuous light are simultaneously returned to the optical fiber by using a mirror and the measured values of the traditional BOTDA system;

[0028] Figure 5 Comparison diagram of the measured values using the present invention and the measured values of the traditional BOTDA system;

[0029] In the figure: 1 - laser; 2 - first beam splitter; 3 - modulator; 4 - microwave signal source; 5 - continuous erbium-doped fiber amplifier; 6 - pulse generator; 7 - semiconductor optical amplifier; 8 - pulsed erbium-doped fiber amplifier; 9 - coupler; 10 - first circulator; 11 - sensing optical fiber; 12 - passive device; 13 - second circulator; 14 - optical filter; 15 - photodetector; 16 - data acquisition and analysis system; 17 - second beam splitter; 18 - isolator; 19 - pump reflector. Detailed Embodiment

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0031] Embodiment 1

[0032] As Figure 1 shown, Embodiment 1 of the present invention provides a long-distance double-sideband single-ended BOTDA sensing system based on an end passive device, including a laser 1, a first beam splitter 2, a modulator 3, a semiconductor optical amplifier 7, a coupler 9, a first circulator 10, a sensing optical fiber 11, a passive device 12, an optical filter 14, a photodetector 15, and a data acquisition and analysis system 16. The optical signal output by the laser 1 is divided into two paths after passing through the first beam splitter 2. One path is modulated by the modulator 3 into double-sideband continuous light with frequencies of ν0±f RF and output as probe light to the coupler 9; the other path is modulated by the semiconductor optical amplifier 7 into pulsed light and output as pump light to the coupler 9; where ν0 represents the frequency of the laser 1, and f RF represents the driving frequency of the modulator 3.

[0033] In this embodiment, the probe light and the pump light are coupled by the coupler 9 and then enter the sensing optical fiber 11 through the first circulator 10. The end of the sensing optical fiber 11 is connected to the passive device 12; the passive device 12 includes a pump reflector 19 and an isolator 18; the pump reflector 19 is used to reflect the pump light in the sensing optical fiber 11 and also to transmit the double-sideband probe light and return it to the sensing optical fiber 11, and the isolator 18 is used to isolate the reflected pump light so that it cannot return to the sensing optical fiber 11; after the double-sideband probe light transmitted and returned to the sensing optical fiber 11 interacts with the backward pump light propagating from the coupler 9 to the passive device 12, it is output through the first circulator 10 and then enters the optical filter 14 to filter out one sideband, and then enters the photodetector 15 to be converted into an electrical signal and then enters the data acquisition and analysis system 16 for demodulation to obtain the sensing signal along the optical fiber. By processing the data, the position and intensity information of the temperature / strain along the optical fiber are demodulated.

[0034] Specifically, in a long-distance double-sideband single-ended BOTDA sensing system based on an end passive device in this embodiment, when measuring, the driving frequency of the modulator 3 scans near the Brillouin frequency shift.

[0035] Specifically, in this embodiment, the pump reflector 19 is a fiber Bragg grating with a reflection wavelength equal to the wavelength of the pump light, and the isolator 18 is an optical isolator. As Figure 1As shown, the passive device 12 further includes a second beam splitter 17. The end of the sensing optical fiber 11 is connected to the input end of the second beam splitter 17. One output end of the second beam splitter 17 is connected to the input end of the optical isolator, and the other output end of the second beam splitter 17 is connected to the transmission end of the pump reflector 19. The reflection end of the pump reflector 19 is connected to the output end of the optical isolator. Then, the detection light and the pump light at the end of the sensing optical fiber 11 are split into two beams by the second beam splitter 17. One beam output from the first output end is incident on the pump reflector 19 after passing through the optical unidirectional device 18. Then, the pump reflector 19 reflects the pump light therein, making it return along the original path to the unidirectional device 18 and being isolated by it and unable to return to the first output end of the second beam splitter 17. The detection light and the pump light output from the second output end are incident on the optical isolator serving as the unidirectional device 18 after passing through the pump reflector 19 and also cannot return to the second beam splitter 17. The signal transmitted through the pump reflector 19 only includes the double-sideband detection light, which returns to the sensing optical fiber 11 after passing through the second output end of the second beam splitter 17 and undergoes stimulated Brillouin gain and loss effects with the counter-propagating pump light in the sensing optical fiber 11.

[0036] As Figure 3 shown, in this embodiment, the reflection light and transmission spectrum diagram of the fiber Bragg grating serving as the pump reflector 19 are as follows. By making the reflection wavelength of the fiber Bragg grating exactly correspond to the wavelength of the pump light, the pump light can be well suppressed in the transmission spectrum of the pump reflector 19, and then the double-sideband detection light is retained.

[0037] Specifically, as Figure 1 shown, in this embodiment, a second circulator 13 is further included. The double-sideband detection light output from the first circulator 10 is transmitted to the optical filter 14 after passing through the second circulator 13, and after being reflected by the optical filter 14 to filter out one sideband, it returns to the second circulator 13 and is output and then enters the photodetector 15.

[0038] Furthermore, in this embodiment, the optical filter 14 is a fiber Bragg grating with a reflection wavelength equal to one sideband of the double-sideband detection light, and the modulator 3 is an electro-optic modulator. The reflection spectrum of the fiber Bragg grating exactly corresponds to the low-frequency or high-frequency detection light component, so it can filter other frequencies and then only retain the low-frequency or high-frequency component to enter the subsequent photodetector 15. In this embodiment, the optical filter 14 can also adopt a narrowband filter.

[0039] Furthermore, in this embodiment, a microwave signal source 4 and a pulse generator 6 are further included; the microwave signal source 4 is used to drive the modulator 3, and the pulse generator 6 is used to drive the semiconductor optical amplifier 7. The pulse generator 6 is specifically an arbitrary sequence generator.

[0040] Further, in this embodiment, a continuous erbium-doped fiber amplifier 5 and a pulsed erbium-doped fiber amplifier 8 are further included. The continuous erbium-doped fiber amplifier 5 is disposed between the modulator 3 and the coupler 9 and is used to amplify the double-sideband continuous light output by the modulator 3. The pulsed erbium-doped fiber amplifier 8 is disposed between the semiconductor optical amplifier 7 and the coupler 9 and is used to amplify the pulsed light output by the semiconductor optical amplifier 7.

[0041] Embodiment 2

[0042] As Figure 2 shown, Embodiment 2 of the present invention provides a long-distance double-sideband single-ended BOTDA sensing system based on end passive devices. The same as Embodiment 1, it includes a laser 1, a first beam splitter 2, a modulator 3, a semiconductor optical amplifier 7, a coupler 9, a first circulator 10, a sensing optical fiber 11, a passive device 12, an optical filter 14, a photodetector 15, and a data acquisition and analysis system 16. The passive device 12 includes a second beam splitter 17, a pump reflector 19, and an isolator 18.

[0043] Different from Embodiment 1, in this embodiment, the isolator 18 is an optical circulator. The end of the sensing optical fiber 11 is connected to the input end of the second beam splitter 17. One output end of the second beam splitter 17 is connected to the input end of the optical circulator. The other output end of the second beam splitter 17 is connected to the transmission end of the pump reflector 19. The reflection end of the pump reflector 19 is connected to the middle end of the optical circulator. In this embodiment, the optical circulator can also play a role of unidirectional isolation, so that the pump optical signal reflected by the reflection end of the pump reflector 19 cannot return to the sensing optical fiber 11 through the second circulator, and the backward pump optical signal in the sensing optical fiber 11 is suppressed.

[0044] Specifically, in this embodiment, the pump reflector 19 is a fiber Bragg grating with a reflection wavelength equal to the pump optical wavelength, the optical filter 14 is a fiber Bragg grating with a reflection wavelength equal to one sideband of the double-sideband detection light, and the modulator 3 is an electro-optic modulator.

[0045] Further, in this embodiment, a microwave signal source 4 and a pulse generator 6 are further included. The microwave signal source 4 is used to drive the modulator 3, and the pulse generator 6 is used to drive the semiconductor optical amplifier 7. The pulse generator 6 is specifically an arbitrary sequence generator.

[0046] Further, in this embodiment, a continuous erbium-doped fiber amplifier 5 and a pulsed erbium-doped fiber amplifier 8 are further included. The continuous erbium-doped fiber amplifier 5 is disposed between the modulator 3 and the coupler 9 and is used to amplify the double-sideband continuous light output by the modulator 3. The pulsed erbium-doped fiber amplifier 8 is disposed between the semiconductor optical amplifier 7 and the coupler 9 and is used to amplify the pulsed light output by the semiconductor optical amplifier 7.

[0047] Embodiment 3

[0048] Embodiment 3 of the present invention provides a sensing method for a long - distance double - sideband single - ended BOTDA sensing system based on a terminal passive device described in Embodiment 1 or Embodiment 2, including the following steps:

[0049] S1. Start the device;

[0050] S2. Sweep the driving frequency of the electro - optic modulator 3 near the Brillouin frequency shift, so that the double - sideband probe light and the pump pulse light undergo stimulated Brillouin gain and loss effects in the sensing optical fiber 11;

[0051] S3. Collect the Brillouin time - series signal through the photodetector 15 and the data acquisition and analysis system 16, and perform analysis and processing to demodulate the temperature / strain position and intensity information along the sensing optical fiber.

[0052] As Figure 4 shown, it is a comparison schematic diagram of the sensing signal obtained by the single - ended BOTDA system based on a mirror and the sensing signal obtained by the traditional double - ended BOTDA system, Figure 4 indicating that when the single - ended BOTDA system based on a mirror is used for long - distance sensing, since the backward - transmitted pump pulse light will undergo stimulated Brillouin scattering with the forward - transmitted continuous light, the continuous light carrying the stimulated Brillouin information returns to the optical fiber through the fiber - end mirror and undergoes stimulated Brillouin scattering with the forward - transmitted pump pulse light. The superposition of the two stimulated Brillouin scattering effects leads to inaccurate measurement results.

[0053] As Figure 5 shown, it is a comparison schematic diagram of the sensing signal obtained by the single - ended BOTDA system of the present invention and the sensing signal obtained by the traditional double - ended BOTDA system, Figure 5 indicating that the single - ended BOTDA system of the present invention can achieve a sensing distance of 12000 m without introducing measurement errors, and its measurement accuracy can be comparable to that of the traditional double - ended BOTDA system.

[0054] In summary, the present invention proposes a long - distance double - sideband single - ended BOTDA sensing system and method based on a terminal passive device. A passive device is connected to the end of the sensing optical fiber to suppress the reflection of the pump light, and the transmitted probe light is retained and returned to the sensing optical fiber again, realizing the single - end input and bidirectional transmission of the pump light and the probe light in the sensing optical fiber, effectively preventing measurement errors caused by the stimulated Brillouin scattering between the pulsed light returning to the optical fiber and the forward - transmitted continuous light; in the case of single - end incidence, the signal - to - noise ratio of the system is greatly improved, the device is simple and easy to implement, the sensing distance of the single - ended BOTDA system is effectively increased, and higher - performance distributed temperature / strain sensing can be achieved.

[0055] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and 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 long-distance double-sideband single-ended BOTDA sensing system based on end passive devices, characterized in that, It includes a laser (1). The optical signal output by the laser (1) is split into two paths after passing through a first beam splitter (2). One path is modulated by a modulator (3) into double-sideband continuous light with a frequency of ν0±f RF and is output as probe light to a coupler (9); the other path is modulated by a semiconductor optical amplifier (7) into pulsed light and is output as pump light to the coupler (9); where ν0 represents the frequency of the laser (1), and f RF represents the driving frequency of the modulator (3). The probe light and the pump light are coupled by a coupler (9) and then enter the sensing optical fiber (11) through a first circulator (10). The end of the sensing optical fiber (11) is connected to a passive device (12); the passive device (12) includes a pump reflector (19) and an isolator (18); the pump reflector (19) is used to reflect the pump light in the sensing optical fiber (11), and is also used to transmit the double-sideband probe light and then return it to the sensing optical fiber (11). The isolator (18) is used to isolate the reflected pump light so that it cannot return to the sensing optical fiber (11); after the double-sideband probe light transmitted and returned to the sensing optical fiber (11) interacts with the backward pump light, it is output through the first circulator (10) and then enters an optical filter (14) to filter out one sideband, and then enters a photodetector (15) to be converted into an electrical signal and then enters a data acquisition and analysis system for demodulation to obtain the sensing signal along the optical fiber.

2. The long-distance double-sideband single-ended BOTDA sensing system based on an end passive device according to claim 1, characterized in that, The pump reflector (19) is a fiber Bragg grating.

3. A long-distance double-sideband single-ended BOTDA sensing system based on a terminal passive device according to claim 1, characterized in that, The isolator (18) is an optical isolator. The passive device (12) further includes a second beam splitter (17). The end of the sensing optical fiber (11) is connected to the input end of the second beam splitter (17). One output end of the second beam splitter (17) is connected to the input end of the optical isolator, and the other output end of the second beam splitter (17) is connected to the transmission end of the pump reflector (19). The reflection end of the pump reflector (19) is connected to the output end of the optical isolator.

4. A long-distance double-sideband single-ended BOTDA sensing system based on a terminal passive device according to claim 1, characterized in that, The isolator (18) is an optical circulator. The passive device (12) further includes a second beam splitter (17). The end of the sensing optical fiber (11) is connected to the input end of the second beam splitter (17). One output end of the second beam splitter (17) is connected to the input end of the optical circulator, and the other output end of the second beam splitter (17) is connected to the transmission end of the pump reflector (19). The reflection end of the pump reflector (19) is connected to the middle end of the optical circulator.

5. A long-distance double-sideband single-ended BOTDA sensing system based on an end passive device according to claim 1, characterized in that, It further includes a second circulator (13). The double-sideband probe light output through the first circulator (10) is transmitted to the optical filter (14) through the second circulator (13). After one sideband is filtered out by reflection of the optical filter (14), it returns to the second circulator (13) and is output and then enters the photodetector (15).

6. A long-distance double-sideband single-ended BOTDA sensing system based on an end passive device according to claim 5, characterized in that, The optical filter (14) is a fiber Bragg grating, and the modulator (3) is an electro-optic modulator.

7. A long-distance dual-band single-ended BOTDA sensing system based on an end passive device according to claim 1, characterized in that, The optical filter (14) is a narrowband filter.

8. A long-distance double-sideband single-ended BOTDA sensing system based on an end passive device according to claim 1, characterized in that, It further includes a continuous erbium-doped fiber amplifier (5) and a pulsed erbium-doped fiber amplifier (8). The continuous erbium-doped fiber amplifier (5) is arranged between the modulator (3) and the coupler (9) and is used to amplify the double-sideband continuous light output by the modulator (3); the pulsed erbium-doped fiber amplifier (8) is arranged between the semiconductor optical amplifier (7) and the coupler (9) and is used to amplify the pulsed light output by the semiconductor optical amplifier (7).

9. A long-distance double-sideband single-ended BOTDA sensing system based on an end passive device according to claim 1, characterized in that, It further includes a microwave signal source (4) and a pulse generator (6); the microwave signal source (4) is used to drive the modulator (3), and the pulse generator (6) is used to drive the semiconductor optical amplifier (7).

10. A sensing method for a long-distance double-sideband single-ended BOTDA sensing system based on an end passive device according to any one of claims 1 to 9, characterized in that, It includes the following steps: S1. Start the device; S2. Sweep the driving frequency of the electro-optic modulator (3) near the Brillouin frequency shift, so that the double-sideband probe light and the pump pulse light generate stimulated Brillouin gain and loss effects in the sensing optical fiber (11); S3. Collect the Brillouin time-series signal through the photodetector (15) and the data acquisition and analysis system (16), analyze and process it, and demodulate the position and intensity information of the temperature / strain along the sensing optical fiber.

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