Multi-parameter distributed optical fiber detection system

Abstract

The utility model discloses a multi-parameter distributed optical fiber detection system, relates to the technical field of optical fiber sensing, and solves the problems that an existing multi-parameter acquisition system is complex in structure and high in construction cost, and an existing distributed optical fiber sensing system can only measure a single parameter. By adopting the standard single-mode optical fiber, Rayleigh scattering light capable of reflecting vibration information is generated based on the Rayleigh scattering effect, and Brillouin frequency shift capable of reflecting temperature and strain information is generated based on the Brillouin scattering effect, so that not only can the vibration information be acquired, but also the temperature and strain information can be acquired, and on the basis, the temperature and strain information can be acquired. According to the principle that the pulse width can directly influence the spatial resolution, the spatial resolution can be improved by changing the pulse width of Brillouin scattering, and more accurate temperature and strain information can be obtained.

Description

Technical Field

[0001] This utility model relates to the field of optical fiber sensing technology, specifically to a multi-parameter distributed optical fiber detection system. Background Technology

[0002] Multi-parameter fiber optic sensing technology has broad application prospects in health monitoring and diagnosis of large building structures, aerospace, petrochemical, and power systems. By achieving multi-parameter measurement of vibration, temperature, and strain, it can provide comprehensive and accurate monitoring data, providing strong support for the safe operation and maintenance of the system.

[0003] Traditionally, vibration, temperature, and strain measurements have relied on separate sensing systems. Each system requires not only dedicated sensors but also independent data acquisition and processing modules. This increases system construction costs and hinders effective data sharing and integration between systems, limiting the depth and breadth of data analysis and impacting the quality and efficiency of decision-making. Simultaneous monitoring of multiple parameters such as vibration, temperature, and strain on a single platform would significantly reduce system deployment costs, facilitate real-time data exchange and post-processing, thereby improving the overall effectiveness of data utilization and enhancing the accuracy and timeliness of positioning.

[0004] Therefore, based on existing research and inspired by the principles of single-parameter fiber optic sensing technology, researching multi-parameter fiber optic sensing is an urgent problem for engineers in this field to solve. Utility Model Content

[0005] This invention addresses the problems of existing multi-parameter acquisition systems being complex in structure and costly to build, and existing distributed fiber optic sensing systems only being able to measure a single parameter. It provides a multi-parameter distributed fiber optic sensing system that can use most optical components and demodulate Brillouin scattering and Rayleigh scattering signals to achieve synchronous acquisition of temperature, stress, and vibration information of standard single-mode optical fibers.

[0006] A multi-parameter distributed optical fiber detection system includes a first optical fiber coupler, an acousto-optic modulator, a distributed Bragg reflector, an optical circulator, a standard single-mode optical fiber, a second optical fiber coupler, a fiber Bragg grating filter, a wavelength division multiplexer, a third optical fiber coupler, a long-pulse laser, a first optical mixer, an optical switch, a first APD detector, a second optical mixer, a second APD detector, a first PD detector, a fourth optical fiber coupler, a high-speed data acquisition card, a high-resolution data acquisition card, and a dual-channel waveform generator.

[0007] The optical signal provided by the narrow linewidth laser source is split into two paths by the first fiber coupler.

[0008] One optical signal generates local oscillator light using a distributed Bragg reflector. The local oscillator light is split by a fourth fiber coupler and then enters a first optical mixer and a second optical mixer respectively. The other optical signal enters an acousto-optic modulator. The dual-channel waveform generator controls the acousto-optic modulator to modulate the optical signal into periodic pulse light, which then enters an optical circulator. The optical circulator transmits the periodic pulse light to the standard single-mode fiber, and the scattered light output from the circulator is then transmitted to the second fiber coupler.

[0009] The light is split into two paths by the second fiber coupler; one path of scattered light enters the wavelength division multiplexer to separate Rayleigh scattered light, which enters the first PD detector for photoelectric conversion and is then acquired by the high-resolution data acquisition card to obtain an electrical signal; the other path of scattered light enters the fiber Bragg grating filter to obtain Brillouin scattered light, which enters the third fiber coupler and is split into two paths.

[0010] When the amplitude of the periodic pulse light modulated by the acousto-optic modulator controlled by the dual-channel waveform generator is large, the dual-channel waveform generator controls the optical switch to turn off, and the Brillouin scattered light is output to the second optical mixer to beat with the local oscillator light in the second optical mixer to obtain a first beat frequency signal, which is input to the second APD detector for photoelectric conversion and then input to the high-speed data acquisition card.

[0011] When the amplitude of the periodic pulse light modulated by the acousto-optic modulator by the dual-channel waveform generator is small, the dual-channel waveform generator controls the optical switch to close, and the Brillouin scattered light enters the long pulse laser. It beats with the local oscillator light in the first optical mixer, and the obtained second beat frequency signal is transmitted to the first APD detector for photoelectric conversion and then transmitted to the high-speed data acquisition card.

[0012] The electrical signals acquired by the high-speed data acquisition card and the high-resolution data acquisition card are transmitted to the computer for signal analysis and detection.

[0013] The beneficial effects of this utility model are:

[0014] The detection system described in this novel uses standard single-mode optical fiber to generate Rayleigh scattered light that reflects vibration information based on the Rayleigh scattering effect, and generates Brillouin frequency shift that reflects temperature and strain information based on the Brillouin scattering effect. It can collect not only vibration information, but also temperature and strain information. Based on the principle that pulse width directly affects spatial resolution, by changing the pulse width of Brillouin scattering, the spatial resolution can be improved, and more accurate temperature and strain information can be obtained.

[0015] This novel system utilizes a dual-channel waveform generator to control an acousto-optic modulator to modulate light waves and generate pulsed light. Simultaneously, it controls the opening and closing of an optical switch based on the amplitude of the pulsed light. This addresses the influence of external factors, enabling the system to not only capture rapidly changing vibration information but also significantly increase the acquisition frequency of temperature and strain information. This ensures the collection of more data points and improves the accuracy and completeness of the data. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of a multi-parameter distributed optical fiber detection system according to the present invention.

[0017] In the diagram: 1. Narrow linewidth laser; 2. First fiber coupler; 3. Acousto-optic modulator; 4. Distributed Bragg reflector; 5. Erbium-doped fiber amplifier; 6. Bandpass filter; 7. Optical circulator; 8. Standard single-mode fiber; 9. Second fiber coupler; 10. Fiber Bragg grating filter; 11. Wavelength division multiplexer; 12. Third fiber coupler; 13. Optical isolator; 14. Long-pulse laser; 15. First optical mixer; 16. Optical switch; 17. First APD detector; 18. Second optical mixer; 19. Second APD detector; 20. Fifth fiber coupler; 21. First PD detector; 22. Polarization beam splitter; 23. Second PD detector; 24. Fourth fiber coupler; 25. High-speed data acquisition card; 26. High-resolution data acquisition card; 27. Dual-channel waveform generator; 28. Computer. Detailed Implementation

[0018] Combination Figure 1 This embodiment describes a multi-parameter distributed optical fiber detection system, which includes: a narrow-linewidth laser 1, a first optical fiber coupler 2, an acousto-optic modulator 3, a distributed Bragg reflector 4, an erbium-doped fiber amplifier 5, a bandpass filter 6, an optical circulator 7, a standard single-mode fiber 8, a second optical fiber coupler 9, a fiber Bragg grating filter 10, a wavelength division multiplexer 11, a third optical fiber coupler 12, an optical isolator 13, a long-pulse laser 14, a first optical mixer 15, an optical switch 16, a first APD detector 17, a second optical mixer 18, a second APD detector 19, a fifth optical fiber coupler 20, a first PD detector 21, a polarization beam splitter 22, a second PD detector 23, a fourth optical fiber coupler 24, a high-speed data acquisition card 25, a high-resolution data acquisition card 26, a dual-channel waveform generator 27, and a computer 28.

[0019] In this embodiment, a narrow-linewidth laser 1 is used as the light source. The light emitted by the laser passes through the first fiber coupler 2. One path of the light enters the distributed Bragg reflector 4 to generate local oscillator light, which then enters the fourth fiber coupler 24 for beam splitting and coherent beat frequency detection. The other path of the light passes through the acousto-optic modulator 3 controlled by the dual-channel waveform generator 27 and is modulated into pulsed light. The pulsed light is amplified by the erbium-doped fiber amplifier 5 to ensure the peak value of the pulse. The amplified pulsed light passes through the bandpass filter 6 and enters the first port of the optical circulator 7. It is then output from the second port of the optical circulator 7 to the standard single-mode fiber 8. Rayleigh scattering light based on the Rayleigh scattering effect and Brillouin scattering light based on the Brillouin scattering effect are generated in the standard single-mode fiber 8. The polarization state of the Rayleigh scattering light is related to the vibration signal experienced by the fiber, while the Brillouin scattering light is related to the temperature and strain signals experienced by the fiber. The scattered light enters from the second port of the optical circulator 7, is emitted from the third port and enters the second fiber coupler 9. One of the scattered lights enters the wavelength division multiplexer 11 and is separated to obtain Rayleigh scattered light. Then the Rayleigh scattered light enters the fifth fiber coupler 20.

[0020] The splitting ratio of the fifth fiber coupler 20 is a%:1-a%. One Rayleigh scattered light is directly output to the first PD detector 21 for photoelectric conversion, and the other Rayleigh scattered light is output to the polarization beam splitter 22, and then enters the second PD detector 23. The power of the Rayleigh scattered light entering the second PD detector 23 depends on the polarization state of the Rayleigh scattered light. Vibration information is obtained based on the optical power of the Rayleigh scattered light and is acquired on the high-resolution data acquisition card 26. The other scattered light enters the fiber Bragg grating filter 10 to obtain Brillouin scattered light, which enters the first port of the third fiber coupler 12.

[0021] When the amplitude of the light pulse is large, when the optical switch 16 controlled by the waveform generator 27 is turned off, the Brillouin scattered light is output from the third port of the third fiber coupler 12 and beats with the local oscillator light from the fourth fiber coupler 24 in the second optical mixer 18. The resulting beat frequency signal is input to the second APD detector 19 for photoelectric conversion, and then input to the high-speed data acquisition card 25. Temperature and strain information are obtained based on the Brillouin frequency shift.

[0022] When the optical pulse amplitude is small, the optical switch 16, controlled by the waveform generator 27, closes. The Brillouin scattered light is output from the second port of the third fiber coupler 12, passes through the optical isolator 13, and then enters the long-pulse laser 14. In the first optical mixer 15, it beats with the local oscillator light from the fourth fiber coupler 24. The resulting beat signal is transmitted to the first APD detector 17 for photoelectric conversion, and then transmitted to the high-speed data acquisition card 25. Since the signals transmitted from the second and third ports of the third fiber coupler 12 are both Brillouin scattered signals, the Brillouin scattered signal of one branch is not processed, while the Brillouin scattered signal of the other branch has its pulse width increased by the long-pulse laser 14. The difference in pulse width directly affects the spatial resolution. Therefore, when the optical switch 16 is closed, the temperature and strain information acquired on the high-speed data acquisition card 25 is more accurate than when the optical switch 16 is open.

[0023] In this embodiment, the dual-channel waveform generator 27 not only controls the acousto-optic modulator 3 to modulate the light in the 1.5-micron band into periodic pulse light, but also controls the opening and closing of the optical switch 16 according to the amplitude of the periodic pulse light.

[0024] The optical switch 16 is closed when the pulse amplitude is small in the periodic pulsed light. The Brillouin scattered light, which is acted upon by the long pulse laser, can increase the pulse width of the Brillouin scattered light. When the Brillouin scattered light with increased pulse width enters the first optical mixer 15, the local oscillator light emitted by the distributed Bragg reflector 4 beats with the Brillouin scattered light at this point. Finally, the corresponding Brillouin frequency shift is obtained on the high-speed data acquisition card 25. This allows for more accurate acquisition of external temperature and strain information.

[0025] The optical switch 16 is disconnected when the pulse amplitude is large in the periodic pulsed light to prevent some scattered light from entering the branch and being modulated by the long pulse laser 14, then beating with the local oscillator light and eventually back to the third fiber coupler 12, affecting the state of the Brillouin scattered light. Therefore, an optical isolator 13 is added between the third fiber coupler 12 and the long pulse laser 14 to block the backtracking of the scattered light. The Brillouin scattered light output from the third port of the third fiber coupler 12 beats with the local oscillator light emitted from the distributed Bragg reflector 4 in the second optical mixer 18. The resulting beat signal is transmitted to the second APD detector 19 for photoelectric conversion, and the resulting electrical signal is input to the high-speed data acquisition card 25 to collect temperature and strain information.

[0026] Because the pulse widths of the Brillouin scattered light on these two branches are different, and the difference in pulse width can directly affect the spatial resolution, the information on strain and temperature measured when the optical switch is closed (16) is more accurate than when the optical switch is open. In this way, the accuracy of the temperature and strain information determined by the Brillouin frequency shift is greatly improved, realizing multi-parameter sensing of temperature, strain and vibration.

[0027] In this embodiment, the optical switch 16 can be opened and closed according to the amplitude of the pulses in the periodic pulsed light. When the pulse amplitude is large, it is open. When external vibrations act on the optical fiber, they cause a phase change in the Rayleigh scattered light in the fiber, resulting in a change in the intensity of the interference light of the Rayleigh scattered light. High-amplitude pulses can enhance the effect of this phase change, making the vibration information more obvious. When the pulse amplitude is small, it is closed. When external temperature and strain act on the optical fiber, they cause a frequency shift change in the Brillouin scattered light in the fiber. Low-amplitude pulses can reduce the introduction of nonlinear noise, making the frequency shift change of the Brillouin scattered light more obvious. Since the vibration information changes rapidly, while the temperature and strain change slowly, in order to obtain more temperature and strain information, each periodic pulse of the periodic pulsed light can include multiple consecutive pulses with large amplitudes and pulses with small amplitudes, and the frequency and duty cycle of each pulse are the same. In this embodiment, the waveform can be generated by a dual-channel waveform generator 27. The dual-channel waveform generator 27 emits a 9kHz square wave, where the high pulse level amplitude is 1V, the low pulse level amplitude is 0.5V, the high pulse width is 30ns, the low pulse width is 10ns, and the ratio of high pulses to low pulses is 50:1. At this ratio, although the vibration information acquisition frequency decreases, it can still capture rapidly changing vibration signals. The acquisition frequency of temperature and strain information increases significantly, ensuring the collection of more data points and improving the accuracy and completeness of the data.

[0028] In this embodiment, the use of a long-pulse laser 14 can increase the pulse width of the Brillouin scattered light, resulting in different pulse widths of the Brillouin scattered light on the two branches. The difference in pulse width can affect the spatial resolution. Therefore, in the case of low pulse, when the optical switch 16 is closed, the Brillouin scattered light with the pulse width changed by the long-pulse laser 14 is compared with the unchanged Brillouin scattered light on the other branch, which can obtain more accurate data.

[0029] In this embodiment, a narrow-linewidth laser 1 is used to emit a 1.5-micron wavelength laser, with an output wavelength of 1550nm. In this wavelength band, the transmission loss of optical fiber is minimal, and it has high coherence, enabling long-distance optical signal transmission.

[0030] In this embodiment, the first fiber coupler 2 splits the laser beam into two paths with a splitting ratio of 90:10. 90% of the beam is input to the acousto-optic modulator 3, and 10% is input as the local oscillator to the distributed Bragg reflector 4. The second fiber coupler 9 splits the scattered light into two paths with a splitting ratio of 50:50. 50% of the scattered light enters the fiber Bragg grating filter 10, and 50% enters the wavelength division multiplexer 11. The third fiber coupler 12 and the fourth fiber coupler 24 both have a splitting ratio of 50:50.

[0031] In this embodiment, the distributed Bragg reflector 4 modulates the output of the light source by reflecting light of the same wavelength as the narrow linewidth laser 1, making it the desired local oscillator light. This can further improve the stability and monochromaticity of the laser, making it more suitable for use as a local oscillator light source in Brillouin scattering measurements.

[0032] In this embodiment, the erbium-doped fiber amplifier 5 amplifies the power of the optical pulse signal output by the pulsed light modulator. Since the output power of the acousto-optic modulator 3 is relatively low, the erbium-doped fiber amplifier 5 is needed to amplify the optical signal power to above 10mW, allowing the probe light energy to enter the standard single-mode fiber 8 through the first fiber circulator 7. The bandpass filter 6 is used to perform bandpass filtering on the periodic pulsed light passing through the erbium-doped fiber amplifier 5. Using the bandpass filter 6 to filter out the radiation noise introduced during the amplification process can improve the accuracy of information acquisition.

[0033] In this embodiment, the optical circulator 7 is used to output the optical pulse signal received at port 1 to the standard single-mode fiber 8 via port 2. The backscattering Rayleigh scattering and backscattering Brillouin scattering generated by the standard single-mode fiber 8 are input back to the optical circulator 7 via port 2 and output to the second fiber coupler 9 via port 3. The optical circulator 7 is a three-port fiber circulator, whose optical characteristics are that light input from port 1 can only be output from port 2, and light input from port 2 can only be output from port 3. Furthermore, the sensing fiber is a standard single-mode fiber for communication.

[0034] In this embodiment, the optical isolator 13 is used to prevent the Brillouin scattering signal from beating the local oscillator light back into the third fiber coupler 12, affecting the back-propagating optical signal and impacting the system's accuracy. The first optical mixer 15 is used to beat the Brillouin scattering light with its pulse width altered with the local oscillator light. The second optical mixer 18 is used to beat the Brillouin scattering light with its pulse width unchanged with the local oscillator light to obtain a beat frequency signal.

[0035] In this embodiment, the first APD detector 17 and the second APD detector 19 are used to detect beat frequency signals from the first optical mixer 15 and the second optical mixer 18 and convert them into electrical signals. They have high gain, are suitable for low light intensity signal detection, and also have high response speed and high sensitivity.

[0036] In this embodiment, the polarization beam splitter 22 separates the Rayleigh scattered light from the fifth fiber coupler 20 according to the parameters of the polarization beam splitter, wherein the power of the Rayleigh scattered light depends on the polarization state of the Rayleigh scattered light.

[0037] In this embodiment, the high-speed data acquisition card 25 is used to receive electrical signals from the first APD detector 17 and the second APD detector 19, perform high-speed sampling and storage, and use Fast Fourier Transform (FFT) to analyze the spectrum of the beat frequency signal and extract the Brillouin frequency shift. The high-resolution data acquisition card 26 is used to receive electrical signals from the first PD detector 21 and the second PD detector 23, and perform high-precision sampling and storage.

[0038] In this embodiment, the time taken as the time it takes for the light pulse emitted by the pulsed light source to return to the PD detector at the point X in the single-mode fiber is t. Then: t = X·n eff / c; where n eff ρ is the effective refractive index of a single-mode fiber, and c is the speed of light in a vacuum.

[0039] We can deduce that X = ct / n eff At time t, the Rayleigh scattered light powers received by the first PD detector 21 and the second PD detector 23 are respectively: P r1 =f r1 (t,v) and P r2 =f r2 (t,v); where v is the vibration intensity at point X in the single-mode fiber, and P r1 P is the power of the Rayleigh scattered light received by the first PD detector 21 at time t. r2 It is the power of the Rayleigh scattered light received by the second PD detector 23 at time t, a function f r1 (t,v) represents this dependency, namely the change in optical power detected by the first PD detector 21 under different times and vibration intensities, and the function f r2 (t,v) describes this dependency, namely the change in optical power detected by the second PD detector 23 under different times and vibration intensities; in order to eliminate the influence of pulsed source power jitter, P r1 / P r2 =f r1 (t,v) / f r2 (t,v).

[0040] By acquiring the power signals and corresponding times of the two PD detectors on computer 28, the distance X between the sensing points and vibration information can be obtained.

[0041] In this embodiment, Brillouin scattering is a scattering phenomenon caused by the elastic vibration of a medium when light waves propagate through it. The frequency of the Brillouin scattering signal differs from the frequency of the incident light by a Brillouin frequency shift Δf. B This frequency shift is related to the temperature and strain of the medium.

[0042] The high-speed data acquisition card 25 is used to acquire the electrical signal output by the photodetector. Then, the spectrum of the beat frequency signal is analyzed by Fast Fourier Transform (FFT) to extract the Brillouin frequency shift FFT(f). beat ).

[0043] The relationship between Brillouin frequency shift and temperature: Δf B (T)=Δf B (T0)+k T ·(T-T0); where: Δf B (T) is the Brillouin frequency shift at temperature T; Δf B (T0) is the Brillouin frequency shift at a reference temperature T0; k T It is the temperature coefficient, usually expressed in MHz / ℃.

[0044] Brillouin frequency shift Δf B The relationship between strain and fiber optic frequency can also be approximated by a linear relationship. Strain (mechanical stress) causes changes in the geometry and refractive index of the optical fiber, thus affecting the Brillouin frequency shift.

[0045] Δf B (∈)=Δf B (∈0)+k ∈ ·(∈-∈0); where: Δf B (∈) is the Brillouin frequency shift under strain ∈; Δf B (∈0) is the Brillouin frequency shift under reference strain ∈0; k ∈ It is the strain coefficient, usually expressed in MHz / με.

[0046] In practical applications, temperature and strain usually coexist, therefore the Brillouin frequency shift Δf B It can be expressed as a function of temperature and strain: Δf B (T,∈)=Δf B (T0,∈0)+k T ·(T-T0)+k ∈ ·(∈-∈0);

[0047] Where, Δf B(T0,∈0) is the Brillouin frequency shift at reference temperature T0 and reference strain ∈0.

[0048] This implementation method, based on B-OTDR and Φ-OTDR technologies, demodulates backscattered Rayleigh and Brillouin scattering signals on standard single-mode fiber, thereby achieving synchronous acquisition of temperature, stress, and vibration information of the standard single-mode fiber. Compared with traditional multi-group distributed fiber optic sensing systems, this system has a simpler structure, lower installation difficulty and cost, and can achieve simultaneous measurement of multiple information sources. It has high economic and social value.

[0049] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] The embodiments described above are merely illustrative of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model patent should be determined by the appended claims.

Claims

1. A multi-parameter distributed optical fiber detection system, characterized in that: The detection system includes a first fiber coupler (2), an acousto-optic modulator (3), a distributed Bragg reflector (4), an optical circulator (7), a standard single-mode fiber (8), a second fiber coupler (9), a fiber Bragg grating filter (10), a wavelength division multiplexer (11), a third fiber coupler (12), a long-pulse laser (14), a first optical mixer (15), an optical switch (16), a first APD detector (17), a second optical mixer (18), a second APD detector (19), a first PD detector (21), a fourth fiber coupler (24), a high-speed data acquisition card (25), a high-resolution data acquisition card (26), and a dual-channel waveform generator (27). The optical signal provided by the narrow linewidth laser (1) is split into two paths by the first fiber coupler (2); One optical signal generates local oscillator light using a distributed Bragg reflector (4). The local oscillator light is split by a fourth fiber coupler (24) and then enters the first optical mixer (15) and the second optical mixer (18) respectively. Another optical signal enters an acousto-optic modulator (3). The dual-channel waveform generator (27) controls the acousto-optic modulator (3) to modulate the optical signal into periodic pulse light and enters an optical circulator (7). The optical circulator (7) transmits the periodic pulse light to the standard single-mode fiber (8), and the scattered light output is then transmitted through the optical circulator (7) to the second fiber coupler (9). The light is split into two paths by the second fiber coupler (9); one path of scattered light enters the wavelength division multiplexer (11) to separate Rayleigh scattered light, which is then converted by the first PD detector (21) and then collected by the high-resolution data acquisition card (26) to obtain an electrical signal; the other path of scattered light enters the fiber Bragg grating filter (10) to obtain Brillouin scattered light, which enters the third fiber coupler (12) and is split into two paths. When the amplitude of the periodic pulse light modulated by the acousto-optic modulator (3) controlled by the dual-channel waveform generator (27) is large, the dual-channel waveform generator (27) controls the optical switch (16) to open, and the Brillouin scattered light is output to the second optical mixer (18) to beat the local oscillator light in the second optical mixer (18) to obtain the first beat frequency signal, which is input to the second APD detector (19) for photoelectric conversion and input to the high-speed data acquisition card (25); When the amplitude of the periodic pulse light modulated by the acousto-optic modulator (3) is small, the dual-channel waveform generator (27) controls the optical switch (16) to close, and the Brillouin scattered light enters the long pulse laser (14). It beats the local oscillator light in the first optical mixer (15) and transmits the obtained second beat frequency signal to the first APD detector (17) for photoelectric conversion and to the high-speed data acquisition card (25). The electrical signals acquired by the high-speed data acquisition card (25) and the high-resolution data acquisition card (26) are transmitted to the computer (28) for signal analysis and detection.

2. The multi-parameter distributed optical fiber detection system according to claim 1, characterized in that: It also includes an erbium-doped fiber amplifier (5) and a bandpass filter (6); the pulsed light is amplified by the erbium-doped fiber amplifier (5) and enters the optical circulator (7) through the bandpass filter (6).

3. The multi-parameter distributed optical fiber detection system according to claim 1, characterized in that: Brillouin and Rayleigh scattered light are generated in the standard single-mode fiber (8), and the Brillouin and Rayleigh scattered light are transmitted to the second fiber coupler (9) through the optical circulator (7).

4. The multi-parameter distributed optical fiber detection system according to claim 1, characterized in that: It also includes an optical isolator (13); the Brillouin scattered light is output through the third fiber coupler (12) and enters the long pulse laser (14) after passing through the optical isolator (13).

5. The multi-parameter distributed optical fiber detection system according to claim 1, characterized in that: The first fiber coupler (2) splits the optical signal into two paths with a splitting ratio of 90:

10. One path of light enters the distributed Bragg reflector (4) to generate local oscillating light; the other path of light is modulated into pulsed light by the acousto-optic modulator (3) controlled by the dual-channel waveform generator (27).

6. The multi-parameter distributed optical fiber detection system according to claim 1, characterized in that: It also includes a fifth fiber coupler (20), a polarization beam splitter (22), and a second PD detector (23); one scattered light enters the wavelength division multiplexer (11) and is separated into Rayleigh scattered light. The Rayleigh scattered light enters the fifth fiber coupler (20) and is split into two paths. One Rayleigh scattered light is converted into photoelectric light by the first PD detector (21) and then output to the high-resolution data acquisition card (26); the other Rayleigh scattered light enters the second PD detector (23) through the polarization beam splitter (22), and is converted into photoelectric light by the second PD detector (23) and then acquired by the high-resolution data acquisition card (26).

7. The multi-parameter distributed optical fiber detection system according to claim 1, characterized in that: The splitting ratio of the second fiber coupler (9) is 50:50, the splitting ratio of the fifth fiber coupler (20) is a%:1-a%, the splitting ratio of the third fiber coupler (12) is 50:50, and the coupling ratio of the fourth fiber coupler is 50:

50.

8. The multi-parameter distributed optical fiber detection system according to claim 1, characterized in that: The narrow linewidth laser (1) emits optical signals in the 1.5 micrometer band.

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