A long-distance BOTDR sensing system based on Raman and remote-pumping amplification and a signal acquisition method

Abstract

The application discloses a kind of based on Raman and remote pump amplification ultra-long distance BOTDR sensing system and signal acquisition method, it is related to optical fiber signal measurement technical field.The technical points of the present application include: the ultra-long distance BOTDR sensing system includes laser, optical fiber coupler, pulse source, first electro-optic modulator, polarization controller, first doped fiber amplifier, circulator, Raman amplifier, wavelength division multiplexer, fiber to be measured, erbium-doped fiber, second electro-optic modulator, microwave modulator, optical attenuator, second doped fiber amplifier, second circulator, fiber grating filter, four-port coupler, balanced detector, filter / detector and data acquisition card.The present application adopts Raman amplification and remote pump technology to realize ultra-long distance sensing, adopts passive relay scheme, and is convenient to realize in ultra-long distance monitoring field;Under the same sensing distance, higher spatial resolution can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber signal measurement, and in particular to an ultra-long distance BOTDR sensing system based on Raman and remote pump amplification and a signal acquisition method. Background Art

[0002] Brillouin optical time-domain reflectometer (BOTDR) uses the linear relationship between the frequency shift of spontaneous Brillouin scattered light in optical fibers and changes in temperature and strain to achieve distributed temperature and strain sensing. It has the advantages of long measurement distance, high detection sensitivity, intrinsic safety, anti-electromagnetic radiation, no need for power supply at the sensor end, single-ended injection, and simple structure. It has been widely used in power line, oil and gas pipeline, and large-scale infrastructure monitoring.

[0003] Currently, the maximum measurement distance of commercial BOTDRs is 100 kilometers. However, in long-distance monitoring, particularly of overhead transmission lines, approximately 45% of the network relay cable lengths in power backbone communication networks exceed 200 km. Even with current measurement capabilities, even simultaneous dual-end measurement will prevent strain measurement along a portion of the cable length, limiting the technology's widespread application in the power sector. The weak spontaneous Brillouin scattering signal limits the sensing distance. Conventional methods of increasing the optical power injected into the fiber can improve the measurement distance to a certain extent. However, when the optical power injected into the fiber exceeds a certain range, fiber nonlinear effects such as self-phase modulation and pump depletion are easily induced, causing the reverse Brillouin scattering signal to rapidly decay, preventing further increases in the measurement distance. Current technologies for improving the sensing distance of BOTDR systems include erbium-doped fiber amplification, Raman amplification, and pulse coding-based performance optimization. For example, in 2016, Professor Song Mouping's research group at Zhejiang University combined forward fiber amplification with BOTDR, achieving 100km sensing at a spatial resolution of 40m and a measurement accuracy of 3°C; in 2019, Ma Xiangjie and others from Jinan University used forward Raman amplification to achieve a sensing distance of about 100km, and achieved a temperature measurement accuracy of 1.2°C at 50km; in 2019, Nageswara Lalam and others combined distributed Raman amplification and erbium-doped fiber amplifier relay amplification to achieve a sensing distance of 150km.

[0004] While the aforementioned existing technologies have effectively improved the sensing range of BOTDR systems, research on long-distance BOTDR systems exceeding 100 kilometers has been limited. Sensing solutions exceeding 100 km typically employ active relay amplification, which requires power supply and is therefore ineffective in practical power systems. Therefore, further extending the BOTDR system's optical fiber sensing range, improving the uniformity of the gain distribution across the entire fiber, and realizing a low-cost, high-performance, ultra-long-distance Brillouin optical time-domain reflectometry system remain key challenges. Summary of the Invention

[0005] To this end, the present invention proposes an ultra-long distance BOTDR sensing system and a signal acquisition method based on Raman and remote pump amplification, in an effort to solve or at least alleviate at least one of the above problems.

[0006] According to one aspect of the present invention, an ultra-long distance BOTDR sensing system based on Raman and remote pump amplification is provided, the system comprising: a laser, a fiber coupler, a pulse source, a first electro-optical modulator, a polarization controller, a first erbium-doped fiber amplifier, a circulator, a Raman amplifier, a wavelength division multiplexer, a fiber to be tested, an erbium-doped fiber, a second electro-optical modulator, a microwave modulator, an optical attenuator, a second erbium-doped fiber amplifier, a second circulator, a fiber grating filter, a four-port coupler, a balanced detector, a filter / detector, and a data acquisition card; wherein,

[0007] The optical signal output end of the laser is connected to the optical signal input end of the optical fiber coupler, and the two optical signal output ends of the optical fiber coupler are respectively connected to the optical signal input end of the first electro-optical modulator and the input end of the second electro-optical modulator. The first electro-optical modulator is driven by a pulse source. The output end of the first electro-optical modulator is connected to the input end of the polarization controller. The output of the polarization controller is connected to the first erbium-doped fiber amplifier. The output end of the first erbium-doped fiber amplifier is connected to the first optical signal port of the first circulator. The second port of the first circulator is connected to the first port of the wavelength division multiplexer. The output end of the Raman amplifier is connected to the second port of the wavelength division multiplexer. The third port of the wavelength division multiplexer is connected to an optical fiber to be tested. An erbium-doped fiber is connected between the two optical fibers to be tested.

[0008] The third port of the first circulator is connected to the input port of the second erbium-doped fiber amplifier, the output port of the second erbium-doped fiber amplifier is connected to the first port of the second circulator, the second port of the second circulator is connected to the fiber grating filter, and the third port of the second circulator is connected to the first port of the four-port coupler;

[0009] The second electro-optical modulator is driven by the microwave modulator, the output port of the second electro-optical modulator is connected to the input port of the optical attenuator, the output port of the optical attenuator is connected to the second port of the four-port coupler, the third and fourth ports of the four-port coupler are connected to the two input ports of the balanced detector, the output port of the balanced detector is connected to the filter detector, and the output end of the filter / detector is connected to the electrical signal input end of the data acquisition card.

[0010] Furthermore, the output power range of the laser is 200mW to 300mW, and the wavelength range is 1549 to 1551nm.

[0011] Furthermore, the coupling ratio of the optical fiber coupler is 95:5 or 90:10 or 80:20 or 70:30.

[0012] Furthermore, the output optical power of the Raman amplifier ranges from 300mW to 800mW, and the center wavelength ranges from 1450nm to 1480nm.

[0013] Furthermore, the central wavelength of the fiber Bragg grating filter is 1550 nm and the bandwidth is 0.1 nm.

[0014] Furthermore, the detection bandwidth of the balanced detector ranges from 200 MHz to 300 MHz.

[0015] According to another aspect of the present invention, a signal acquisition method is provided. The method is implemented based on the ultra-long-distance BOTDR sensing system. The ultra-long-distance BOTDR sensing system includes:

[0016] Laser, fiber coupler, pulse source, first electro-optic modulator, polarization controller, first erbium-doped fiber amplifier, circulator, Raman amplifier, wavelength division multiplexer, optical fiber to be tested, erbium-doped fiber, second electro-optic modulator, microwave modulator, optical attenuator, second erbium-doped fiber amplifier, second circulator, fiber Bragg grating filter, four-port coupler, balanced detector, filter / detector and data acquisition card;

[0017] The continuous optical signal output by the laser is divided into two paths by the optical fiber coupler: the continuous optical signal of the upper branch is modulated into an optical pulse signal by the first electro-optical modulator, the polarization state is adjusted by the polarization controller, and then the optical power is amplified by the first erbium-doped fiber amplifier. The optical signal is then injected into the wavelength division multiplexer through the second optical signal port of the first circulator. The optical signal output by the wavelength division multiplexer and the optical signal output by the Raman amplifier are simultaneously injected into a test optical fiber. An erbium-doped fiber is connected between the two test optical fibers; the back Brillouin scattered optical signal in the optical fiber is output through the third optical signal port of the first circulator, and then the optical power is amplified by the second erbium-doped fiber amplifier. The optical signal is then injected into the fiber Bragg grating filter through the second optical signal port of the second circulator to filter out broadband noise, and then enters the four-port coupler through the third port of the second circulator.

[0018] The continuous optical signal from the drop channel is modulated into a reference optical signal by the second electro-optical modulator. After being attenuated by the optical attenuator, it enters the four-port coupler and is mixed with the echo signal. The two output signals enter the balanced detector through the third and fourth ports of the four-port coupler for photoelectric conversion. The resulting electrical signal is then filtered / detected to extract the signal envelope and recorded in real time by the data acquisition card.

[0019] By changing the frequency of the microwave modulator to perform a frequency sweep, the Brillouin scattering time domain signal of the corresponding frequency is obtained. The frequency sweep range is set to ensure the integrity of the Brillouin scattering spectrum. The Brillouin scattering time domain signal at each sweep frequency is collected by a data acquisition card to obtain the Brillouin spectrum at each position point.

[0020] Furthermore, the Brillouin spectrum is fitted to obtain a fitted Brillouin scattering spectrum, and the frequency point corresponding to the maximum value in the fitted spectrum is the Brillouin frequency shift v of that point. B (T,ε).

[0021] Furthermore, the Brillouin frequency shift v B (T,ε) relative to the initial Brillouin frequency shift v B The change in (T0, ε0) represents the temperature change ΔT or strain change Δε of the optical fiber to be tested, that is:

[0022] v B (T,ε)=C v,T ΔT+C v,ε Δε+v B (T0,ε0)

[0023] Among them, C v,T and C v,ε represent the Brillouin frequency shift temperature coefficient and the Brillouin frequency shift strain coefficient, respectively.

[0024] The beneficial technical effects of the present invention are:

[0025] The present invention proposes an ultra-long-distance BOTDR sensing system and signal acquisition method based on Raman and remote pump amplification. The system adopts forward Raman amplification and remote pumping technology to achieve ultra-long-distance sensing, and adopts a passive relay scheme to facilitate implementation in the field of ultra-long-distance monitoring. At the same sensing distance, it can achieve higher spatial resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily apparent by reading the following detailed description with reference to the accompanying drawings, in which several embodiments of the present invention are shown by way of example and not limitation, in which:

[0027] Figure 1 This is a schematic structural diagram of an ultra-long-distance BOTDR sensing system based on Raman and remote pump amplification according to an embodiment of the present invention;

[0028] Figure 2 1 is an example diagram of Brillouin frequency shift measurement results in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are provided solely to enable those skilled in the art to better understand and implement the present invention, and are not intended to limit the scope of the present invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. Specific implementation method one:

[0031] Refer to the attached Figure 1 An ultra-long distance BOTDR sensing system based on Raman and remote pump amplification includes: a laser 1, a fiber coupler 2, a pulse source 3, a first electro-optic modulator 4, a polarization controller 5, a first erbium-doped fiber amplifier 6, a circulator 7, a Raman amplifier 8, a wavelength division multiplexer 9, a test fiber 10, an erbium-doped fiber 11, a second electro-optic modulator 12, a microwave modulator 13, an optical attenuator 14, a second erbium-doped fiber amplifier 15, a second circulator 16, a fiber Bragg grating filter 17, a four-port coupler 18, a balanced detector 19, a filter detector 20, and a data acquisition card 21;

[0032] The optical signal output end of the laser 1 is connected to the optical signal input end of the optical fiber coupler 2. The two optical signal output ends of the optical fiber coupler 2 are respectively connected to the optical signal input end of the first electro-optical modulator 4 and the input end of the second electro-optical modulator 12. The first electro-optical modulator 4 is driven by a pulse source 3. The output end of the first electro-optical modulator 4 is connected to the input end of the polarization controller 5. The output of the polarization controller 5 is connected to the first erbium-doped fiber amplifier 6. The output end of the first erbium-doped fiber amplifier 6 is connected to the first optical signal port 7-1 of the first circulator 7. The second port 7-2 of the first circulator is connected to the first port of the wavelength division multiplexer 9. The output end of the Raman amplifier 8 is connected to the second port of the wavelength division multiplexer 9. The third port of the wavelength division multiplexer 9 is connected to an optical fiber to be tested 10. An erbium-doped fiber 11 is connected between the two optical fibers to be tested 10.

[0033] The third port 7-3 of the first circulator 7 is connected to the input port of the second erbium-doped fiber amplifier 15, the output port of the second erbium-doped fiber amplifier 15 is connected to the first port 16-1 of the second circulator 16, the second port 16-2 of the second circulator 16 is connected to the fiber grating filter 17, and the third port 16-3 of the second circulator 16 is connected to the first port of the four-port coupler 18;

[0034] The second electro-optical modulator 12 is driven by the microwave modulator 13. The output port of the second electro-optical modulator 12 is connected to the input port of the optical attenuator 14. The output port of the optical attenuator 14 is connected to the second port of the four-port coupler 18. The third and fourth ports of the four-port coupler 18 are connected to the two input ports of the balanced detector 19. The output port of the balanced detector 19 is connected to the filter detector 20. The output end of the filter detector 20 is connected to the electrical signal input end of the data acquisition card 21.

[0035] In this embodiment, preferably, the output power range of the laser 1 is 200 mW to 300 mW, and the wavelength range is 1549 to 1551 nm.

[0036] In this embodiment, preferably, the coupling ratio of the optical fiber coupler 2 is 95:5 or 90:10 or 80:20 or 70:30.

[0037] In this embodiment, preferably, the output optical power range of the Raman amplifier 8 is 300 mW-800 mW, and the center wavelength range is 1450 nm-1480 nm.

[0038] In this embodiment, preferably, the central wavelength of the fiber Bragg grating filter 17 is 1550 nm and the bandwidth is 0.1 nm.

[0039] In this embodiment, preferably, the detection bandwidth of the balanced detector 19 ranges from 200 MHz to 300 MHz.

[0040] The ultra-long-distance BOTDR sensing system based on Raman and remote pump amplification described in this embodiment adopts forward Raman amplification and remote pumping technology to achieve ultra-long-distance sensing, while eliminating relay power supply, facilitating flexible application in the field of ultra-long-distance monitoring; at the same sensing distance, higher spatial resolution can be achieved. Specific implementation method 2:

[0042] A signal acquisition method, i.e., a working method of an ultra-long-distance BOTDR sensing system based on Raman and remote pump amplification, is implemented based on the above-mentioned ultra-long-distance BOTDR sensing system based on Raman and remote pump amplification. The signal acquisition process includes:

[0043] The continuous optical signal output by the laser 1 is split into two paths by the optical fiber coupler 2: the continuous optical signal of the upper branch is modulated into an optical pulse signal by the first electro-optical modulator 4, polarization state adjusted by the polarization controller 5, and then optical power amplified by the first erbium-doped fiber amplifier 6. The optical signal is then injected into the wavelength division multiplexer 9 through the second optical signal port 7-2 of the first circulator 7. The optical signal output by the wavelength division multiplexer 9 and the optical signal output by the Raman amplifier 8 are simultaneously injected into a test optical fiber 10. An erbium-doped optical fiber 11 is connected between the two test optical fibers 10. The back Brillouin scattered optical signal in the optical fiber is output through the third optical signal port 7-3 of the first circulator 7, optical power amplified by the second erbium-doped fiber amplifier 15, and then injected into the fiber Bragg grating filter 17 through the second optical signal port 16-2 of the second circulator 16 to filter out broadband noise. The optical signal enters the four-port coupler 18 through the third port of the second circulator 16.

[0044] The dropped continuous optical signal is modulated into a reference optical signal by the second electro-optical modulator 12. After being attenuated by the optical attenuator 14, it enters the four-port coupler 18 and is mixed with the echo signal. The two output signals pass through the third and fourth ports of the four-port coupler 18 and enter the balanced detector 19 for photoelectric conversion. The resulting electrical signal then passes through the filter detector 20 to extract the signal envelope and is recorded in real time by the data acquisition card 21.

[0045] By changing the frequency of the microwave modulator 13 and performing a frequency sweep, a Brillouin scattering time domain signal of the corresponding frequency is obtained. The frequency sweep range is set to ensure the integrity of the Brillouin scattering spectrum. The Brillouin scattering time domain signal at each sweep frequency is collected by the data acquisition card 21 to obtain the Brillouin spectrum at each position point.

[0046] Furthermore, the Brillouin spectra collected at each point of the optical fiber are fitted to obtain the fitted Brillouin scattering spectrum. The frequency point corresponding to the maximum value in the fitted spectrum is the Brillouin frequency shift v at that point. B (T,ε), the Brillouin frequency shift relative to the initial Brillouin frequency shift v BThe change in (T0,ε0) represents the change in temperature ΔT or strain Δε, as shown in formula (1);

[0047] v B (T,ε)=C v,T ΔT+C v,ε Δε+v B (T0,ε0) (1)

[0048] Among them, C v,T and C v,ε are the Brillouin frequency shift temperature coefficient and the Brillouin frequency shift strain coefficient, respectively.

[0049] In the BOTDR system, the signal light and backscattered light attenuate significantly during long-distance transmission, reducing the signal-to-noise ratio. To improve the signal-to-noise ratio of the sensing system, the power and pulse width of the pump light can be increased. Low-power pump light is transmitted linearly when injected into the optical fiber. However, when the power exceeds a certain threshold, various fiber nonlinear effects are triggered. Simply increasing the input optical power cannot increase the sensing distance. Distributed Raman amplification effectively solves this problem.

[0050] The BOTDR system based on Raman amplification uses ordinary single-mode optical fiber as the gain medium to perform distributed amplification of light within the gain bandwidth transmitted along the optical fiber, avoiding the centralized amplification of the pulsed detection light. While increasing the transmitted light intensity, it also avoids the fiber nonlinear effect caused by excessive optical power.

[0051] Raman pump light and signal light are injected into the optical fiber at the same time. In the case of continuous light, the power coupling equation of Raman pump light and signal light can be expressed as:

[0052]

[0053]

[0054] Among them, P R 、P B are the powers of Raman pump light and signal light, α R , α B and v R 、v B are the loss coefficient and frequency of two different wavelengths of light transmitted in the optical fiber, g R is the Raman gain coefficient, which mainly depends on the Raman wavelength, A c is the finite core area of ​​the optical fiber. In formula (2) The term represents the gain process of Raman pump light acting on signal light. In formula (3), represents the coupling process between Raman pump light and signal light in optical fiber transmission, is the attenuation of pump light, and α B P B(z) and α R P R (z) represents the transmission loss of the signal light and the Raman pump light in the optical fiber. Ideally, the Raman pump light power is much greater than the signal light. Ignoring the effects of device insertion loss and high-order Stokes light, the Raman gain of the small signal is shown in formula (4):

[0055]

[0056] Where K represents the polarization coefficient used to correct the gain coefficient.

[0057] For a given system, the sensing fiber parameters and pump wavelength are fixed, and the Raman gain effect is solely dependent on the Raman pump optical power. Excessive optical power can cause fiber nonlinearity and degrade sensing performance, while too low an optical power cannot achieve the desired gain effect. Choosing an appropriate Raman optical power is crucial. Using Raman distributed amplification, BOTDR sensing can achieve hundreds of kilometers of range.

[0058] Furthermore, based on Raman and remote pump amplification, the sensing distance can be further improved. By adding erbium-doped fiber to the optical fiber to be measured, the erbium-doped fiber can amplify the signal. Since the erbium ion levels in the erbium-doped fiber are diverse, when the signal is stored in a high-energy-level system, if a photon works, the photon will stimulate the erbium-doped fiber to release energy. After the energy is released, all the information will return to a lower energy level, and the energy generated will be transmitted with the help of new photons, thereby extending the measurement distance.

[0059] Figure 2 The Brillouin center frequency shift obtained by fitting at each point in the system successfully increased the sensing distance of the BOTDR system to 150km. The 5m erbium-doped optical fiber was used at the 77.6km position. The signal provided by the Raman amplifier was used as pump excitation to achieve remote pump amplification, eliminating the need for relay power supply.

[0060] Furthermore, for systems with and without erbium-doped fiber, at the same sensing distance, the system with erbium-doped fiber has a higher signal-to-noise ratio and can achieve higher spatial resolution.

[0061] Although the spirit and principles of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the specific embodiments disclosed, and the division into various aspects does not mean that the features of these aspects cannot be combined to benefit. Such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An ultra-long distance BOTDR sensing system based on Raman and remote pump amplification, characterized in that: include: Laser (1), fiber coupler (2), pulse source (3), first electro-optic modulator (4), polarization controller (5), first erbium-doped fiber amplifier (6), circulator (7), Raman amplifier (8), wavelength division multiplexer (9), optical fiber to be tested (10), erbium-doped fiber (11), second electro-optic modulator (12), microwave modulator (13), optical attenuator (14), second erbium-doped fiber amplifier (15), second circulator (16), fiber Bragg grating filter (17), four-port coupler (18), balanced detector (19), filter / detector (20) and data acquisition card (21); wherein, The optical signal output end of the laser (1) is connected to the optical signal input end of the optical fiber coupler (2), the two optical signal output ends of the optical fiber coupler (2) are respectively connected to the optical signal input end of the first electro-optical modulator (4) and the input end of the second electro-optical modulator (12), the first electro-optical modulator (4) is driven by a pulse source (3), the output end of the first electro-optical modulator (4) is connected to the input end of the polarization controller (5), the output of the polarization controller (5) is connected to the first erbium-doped fiber amplifier (6), the output end of the first erbium-doped fiber amplifier (6) is connected to the first optical signal port (7-1) of the first circulator (7), the second port (7-2) of the first circulator is connected to the first port of the wavelength division multiplexer (9), the output end of the Raman amplifier (8) is connected to the second port of the wavelength division multiplexer (9), the third port of the wavelength division multiplexer (9) is connected to a test optical fiber (10), and an erbium-doped optical fiber (11) is connected between the two test optical fibers (10); The third port (7-3) of the first circulator (7) is connected to the input port of the second erbium-doped fiber amplifier (15), the output port of the second erbium-doped fiber amplifier (15) is connected to the first port (16-1) of the second circulator (16), the second port (16-2) of the second circulator (16) is connected to the fiber grating filter (17), and the third port (16-3) of the second circulator (16) is connected to the first port of the four-port coupler (18); The second electro-optical modulator (12) is driven by the microwave modulator (13). The output port of the second electro-optical modulator (12) is connected to the input port of the optical attenuator (14). The output port of the optical attenuator (14) is connected to the second port of the four-port coupler (18). The third and fourth ports of the four-port coupler (18) are connected to the two input ports of the balanced detector (19). The output port of the balanced detector (19) is connected to the filter detector (20). The output end of the filter / detector (20) is connected to the electrical signal input end of the data acquisition card (21).

2. The ultra-long distance BOTDR sensing system based on Raman and remote pump amplification according to claim 1, characterized in that: The output power range of the laser (1) is 200mW~300mW, and the wavelength range is 1549~1551nm.

3. The ultra-long distance BOTDR sensing system based on Raman and remote pump amplification according to claim 1, characterized in that: The coupling ratio of the optical fiber coupler (2) is 95:5 or 90:10 or 80:20 or 70:

30.

4. The ultra-long distance BOTDR sensing system based on Raman and remote pump amplification according to claim 1, characterized in that: The output optical power of the Raman amplifier (8) ranges from 300mW to 800mW, and the central wavelength ranges from 1450nm to 1480nm.

5. The ultra-long distance BOTDR sensing system based on Raman and remote pump amplification according to claim 1, characterized in that: The fiber grating filter (17) has a central wavelength of 1550 nm and a bandwidth of 0.1 nm.

6. The ultra-long distance BOTDR sensing system based on Raman and remote pump amplification according to claim 1, characterized in that: The detection bandwidth of the balanced detector (19) ranges from 200 MHz to 300 MHz.

7. A signal acquisition method, characterized in that: The method is implemented based on the ultra-long-distance BOTDR sensing system according to any one of claims 1 to 6, wherein the ultra-long-distance BOTDR sensing system comprises: Laser (1), fiber coupler (2), pulse source (3), first electro-optic modulator (4), polarization controller (5), first erbium-doped fiber amplifier (6), circulator (7), Raman amplifier (8), wavelength division multiplexer (9), optical fiber to be tested (10), erbium-doped fiber (11), second electro-optic modulator (12), microwave modulator (13), optical attenuator (14), second erbium-doped fiber amplifier (15), second circulator (16), fiber Bragg grating filter (17), four-port coupler (18), balanced detector (19), filter / detector (20) and data acquisition card (21); The continuous optical signal output by the laser (1) is divided into two paths by the optical fiber coupler (2): the continuous optical signal of the upper branch is modulated into an optical pulse signal by the first electro-optical modulator (4), the polarization state is adjusted by the polarization controller (5), and then the optical power is amplified by the first erbium-doped fiber amplifier (6), and then injected into the wavelength division multiplexer (9) through the second optical signal port (7-2) of the first circulator (7). The optical signal output by the wavelength division multiplexer (9) and the optical signal output by the Raman amplifier (8) are simultaneously injected into a waiting In the test optical fiber (10), an erbium-doped optical fiber (11) is connected between two optical fibers to be tested (10); the back Brillouin scattered light signal in the optical fiber is output through the third optical signal port (7-3) of the first circulator (7), amplified by the second erbium-doped optical fiber amplifier (15), injected into the fiber Bragg grating filter (17) through the second optical signal port (16-2) of the second circulator (16) to filter out broadband noise, and enters the four-port coupler (18) through the third port of the second circulator (16); The continuous optical signal of the downlink is modulated into a reference optical signal by the second electro-optical modulator (12), attenuated by the optical attenuator (14), and then enters the four-port coupler (18) to be mixed with the echo signal. The two output signals enter the balanced detector (19) through the third and fourth ports of the four-port coupler (18) for photoelectric conversion. The obtained electrical signal is then extracted from the signal envelope by the filter / detector (20) and recorded in real time by the data acquisition card (21); By changing the frequency of the microwave modulator (13) to perform frequency sweeping, a Brillouin scattering time domain signal of the corresponding frequency is obtained. The frequency sweeping range is set to ensure the integrity of the Brillouin scattering spectrum. The Brillouin scattering time domain signal at each sweeping frequency is collected by a data acquisition card (21), thereby obtaining the Brillouin spectrum of each position point.

8. A signal acquisition method according to claim 7, characterized in that: After obtaining the Brillouin spectrum of each position point, the Brillouin spectrum is fitted to obtain a fitted Brillouin scattering spectrum. The frequency point corresponding to the maximum value in the fitted spectrum is the Brillouin frequency shift of the point. .

9. A signal acquisition method according to claim 8, characterized in that: The Brillouin frequency shift Relative to the initial Brillouin frequency shift The change in temperature of the optical fiber to be tested is characterized by the change in temperature of the optical fiber to be tested. or strain change ,Right now: ， in, and represent the Brillouin frequency shift temperature coefficient and the Brillouin frequency shift strain coefficient, respectively.

Images