A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification

Abstract

The present invention discloses a passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification, and relates to the field of optical technology. The technical points of the present invention include: the system includes an optical emission subsystem, an optical pulse modulation subsystem, a down-conversion subsystem, an echo amplification and filtering subsystem, a Brillouin heterodyne detection subsystem, a signal acquisition and processing subsystem, and a remote pump amplification subsystem; wherein the remote pump amplification subsystem is used for distributed amplification of detection optical signals, including a remote pump unit, a time-delay optical fiber, a wavelength division multiplexer, and a remote gain unit. The present invention adopts bypass remote pump technology to suppress the nonlinear effect of optical fiber caused by excessive pump light power in the bypass remote pump scheme, realize ultra-long distance sensing, and can achieve higher spatial resolution, measurement accuracy, and measurement efficiency at the same sensing distance.

Description

Technical Field

[0001] The invention relates to the field of optical technology, and in particular to a passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification. Background Art

[0002] With the development of UHV technology in my country, the distance of the relay-free transmission section of the power system has been gradually increased, realizing ultra-long-distance and ultra-large-capacity power transmission, and the transmission length has now exceeded 400km. UHV lines are the main way to transmit hydropower and wind power in Northwest China. However, this cross-regional and long-distance transmission poses a huge challenge to the safe operation of optical cables. Overhead lines are vulnerable to threats when the meteorological and geographical environment is complex, so the safety monitoring of the lines is of great significance.

[0003] Distributed optical fiber sensing technology has the advantages of long distance, distributed, no need for remote power supply, no electromagnetic interference, high sensitivity, etc., and is particularly suitable for monitoring power communication optical cables. Brillouin optical time-domain reflectometer (BOTDR) uses the linear relationship between the frequency shift change of spontaneous Brillouin scattered light in the optical fiber and the temperature and strain changes to achieve distributed temperature and strain sensing, and can directly and effectively detect the mechanical tension changes of the optical cable caused by external natural stress. However, the sensing distance of commercial equipment of this technology is currently around 100km, and the transmission distance is limited, which limits its large-scale development and application in power systems. Therefore, the development of long-distance Brillouin optical time-domain reflectometer is of great significance. At the same time, due to the particularity of power optical cables, their transmission section is long and there is no relay station in the middle of the line, which makes active relay amplification technology unable to be applied to this application scenario. Therefore, how to achieve ultra-long distance transmission of passive relay amplification is an important problem that needs to be solved urgently. Summary of the invention

[0004] In view of the above problems, the present invention proposes a passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification to realize an ultra-long distance BOTDR sensing system while eliminating relay power supply, which is convenient for flexible application in the field of ultra-long distance monitoring.

[0005] A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification comprises: an optical emission subsystem, an optical pulse modulation subsystem, a down-conversion subsystem, an echo amplification and filtering subsystem, a Brillouin heterodyne detection subsystem, a signal acquisition and processing subsystem, and a remote pump amplification subsystem; the optical emission subsystem is respectively connected to the optical pulse modulation subsystem and the down-conversion subsystem, the optical pulse modulation subsystem is connected to a sensing optical fiber, and its echo signal is connected to the echo amplification and filtering subsystem, the echo amplification and filtering subsystem and the down-conversion subsystem are respectively connected to the Brillouin heterodyne detection subsystem, and the Brillouin heterodyne detection subsystem is connected to the signal acquisition and processing subsystem;

[0006] Among them, the optical emission subsystem is used to generate two continuous optical signals; the optical pulse modulation subsystem is used to modulate one continuous optical signal into a detection optical pulse; the down-conversion subsystem is used to modulate the other continuous optical signal into a reference light; the echo amplification and filtering subsystem is used to amplify the Brillouin scattered light and filter out a sideband effective Brillouin scattered signal; the Brillouin heterodyne detection subsystem is used to perform Brillouin signal heterodyne detection, and perform filtering and detection to convert the scattered light signal into an electrical signal; the signal acquisition and processing subsystem is used to sense the signal The remote pump amplification subsystem is used for detecting the distributed amplification of the optical signal. The remote pump amplification subsystem includes a remote pump unit, a time-delay optical fiber, a wavelength division multiplexer, and a remote gain unit. The optical pulse modulation subsystem is connected to one end of the first optical fiber to be tested, and the other end of the first optical fiber to be tested is connected to the first port of the wavelength division multiplexer. The output end of the remote pump unit is connected to the second port of the wavelength division multiplexer via the time-delay optical fiber, and the third port of the wavelength division multiplexer is connected to the second optical fiber to be tested. The two ends of the remote gain unit are respectively fused with the second optical fiber to be tested and the third optical fiber to be tested.

[0007] Further, the optical emission subsystem includes a laser and an optical fiber coupler; the optical pulse modulation subsystem includes a first pulse source, a first electro-optical modulator, a second pulse source, a second electro-optical modulator, a first erbium-doped fiber amplifier, and a first circulator; the down-conversion subsystem includes a third electro-optical modulator, a microwave modulator, a polarization controller, and an optical attenuator; 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 third electro-optical modulator at the same time, the first electro-optical modulator is driven by the first pulse source, the output end of the first electro-optical modulator is connected to the input end of the second electro-optical modulator, the second electro-optical modulator is driven by the second pulse source, the output end of the second electro-optical modulator is connected to the input end of the first erbium-doped fiber amplifier, and the output end of the first erbium-doped fiber amplifier is connected to the first optical signal port of the first circulator; the third electro-optical modulator is driven by the microwave modulator, the output port of the third electro-optical modulator is connected to the input end of the polarization controller, and the output end of the polarization controller is connected to the input port of the optical attenuator.

[0008] Further, the echo amplification and filtering subsystem includes a second erbium-doped fiber amplifier, a second circulator, and a fiber grating filter; the Brillouin heterodyne detection subsystem includes a four-port coupler, a balanced detector, and a filter detector; the signal acquisition and processing subsystem includes a data acquisition card and a computer; 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 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, the output end of the filter detector is connected to the electrical signal input end of the data acquisition card, and the data acquisition card is connected to the computer.

[0010] Furthermore, the remote pumping unit is a distributed Raman amplifier, and the remote gain unit is an erbium-doped optical fiber.

[0011] Furthermore, the output power range of the laser is 30mw-45mw, and the wavelength range is 1548nm-1551nm; the coupling ratio of the optical fiber coupler is 98:2, 95:5, 90:10 or 80:20.

[0012] Furthermore, the output optical power of the remote pump unit ranges from 600mw to 1w, and the central wavelength ranges from 1455nm to 1480nm.

[0013] Furthermore, the central wavelength range of the fiber grating filter is 1548nm-1551nm, and the bandwidth is 0.1nm; the detection bandwidth range of the balanced detector is 200MHz-300MHz.

[0014] Furthermore, the data acquisition card collects the Brillouin scattering time domain signal at each scanning frequency to obtain the Brillouin spectrum at each position point; after obtaining the Brillouin spectrum at each position point, the computer performs fitting processing on the Brillouin spectrum 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 the point. B (T,ε).

[0015] Furthermore, the Brillouin frequency shift v B (T,ε) relative to the initial Brillouin frequency shift v B (T 0 ,ε 0 ) is the temperature change ΔT or strain change Δε of the optical fiber to be tested, that is:

[0016] v B (T,ε)=C v,T ΔT+C v,ε Δε+v B (T 0 ,ε 0 )

[0017] Among them, C v,T and C v,ε represent the Brillouin frequency shift temperature coefficient and the Brillouin frequency shift strain coefficient respectively.

[0018] The beneficial technical effects of the present invention are:

[0019] The present invention proposes a passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification, which adopts bypass remote pump technology to achieve ultra-long distance sensing. It only needs to install a remote pump unit at the signal transmitting end, and install erbium-doped optical fiber as a remote gain medium on the optical path to be measured. The remote gain medium does not need to be powered, and a passive relay scheme is adopted, which is convenient for implementation in the field of ultra-long distance monitoring.

[0020] The ultra-long-distance BOTDR sensing system based on bypass remote pump amplification described in the present invention, compared with the remote pump amplification scheme in which the signal light and the pump light are transmitted in the same fiber core, uses a bypass scheme in which two optical fibers are respectively injected into the signal light and the pump light and the light is combined through a dense wavelength division multiplexer. This can further improve the power of the Raman pump light and achieve longer-distance transmission. This is because the amplification effect near the pump end in the remote pump scheme is significant, resulting in the rapid accumulation of the amplified detection light nonlinear effect near the pump end, generating nonlinear effects such as stimulated Brillouin and stimulated Raman, which deteriorates the quality of the detection light signal, limits the power of the Raman pump source, and affects the improvement of the sensing distance. The bypass remote pump method can effectively avoid the degradation of the front-end signal caused by the increase in the pump light power and improve the measurement distance.

[0021] The ultra-long-distance BOTDR sensing system based on bypass remote pump amplification described in the present invention can achieve higher spatial resolution, higher measurement accuracy and faster measurement time at the same sensing distance due to the significant improvement of the signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood by reading the detailed description below with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, in which:

[0023] Figure 1 The present invention is a schematic structural diagram of a passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification.

[0024] Figure 2 Another structural schematic diagram of a passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification described in the present invention.

[0025] Figure 3 An example diagram of the Brillouin center frequency shift obtained by fitting each point in the remote pumping system.

[0026] Figure 4 This is an example diagram of the Brillouin center frequency shift obtained by fitting at each point in an embodiment of the present invention.

[0027] Figure 5 This is an example diagram of the standard deviation accuracy of three repeated measurements in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] 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 only 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. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0029] Reference Figure 1 A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification includes: an optical transmission subsystem, an optical pulse modulation subsystem, a down-conversion subsystem, an echo amplification and filtering subsystem, a Brillouin heterodyne detection subsystem, a signal acquisition and processing subsystem, and a remote pump amplification subsystem; the optical transmission subsystem is respectively connected to the optical pulse modulation subsystem and the down-conversion subsystem; the optical pulse modulation subsystem is connected to the sensing optical fiber, and its echo signal is connected to the echo amplification and filtering subsystem, and the echo amplification and filtering subsystem and the down-conversion subsystem are respectively connected to the Brillouin heterodyne detection subsystem; the Brillouin heterodyne detection subsystem is connected to the signal acquisition and processing subsystem.

[0030] Reference Figure 2 A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification specifically includes: a laser 1, a fiber coupler 2, a first pulse source 3, a first electro-optic modulator 4, a second pulse source 5, a second electro-optic modulator 6, a first erbium-doped fiber amplifier 7, a first circulator 8, a first optical fiber to be tested 9, a remote pumping unit 10, a delay optical fiber 11, a wavelength division multiplexer 12, a second optical fiber to be tested 13, a remote gain unit 14, a third optical fiber to be tested 15, a third electro-optic modulator 16, a microwave modulator 17, a polarization controller 18, an optical attenuator 19, a second erbium-doped fiber amplifier 20, a second circulator 21, a fiber grating filter 22, a four-port coupler 23, a balanced detector 24, a filter detector 25, a data acquisition card 26, and a computer 27; wherein,

[0031] The laser 1 and the fiber coupler 2 form an optical transmission subsystem for generating two continuous optical signals, which are used to modulate the detection pulse light and the local reference light respectively.

[0032] The first pulse source 3, the first electro-optical modulator 4, the second pulse source 5, the second electro-optical modulator 6, the first erbium-doped fiber amplifier 7, and the first circulator 8 constitute an optical pulse modulation subsystem for generating detection light pulses. The cascaded electro-optical modulators are used to generate high extinction ratio detection light pulses, so that the extinction ratio of the detection light is increased from 30dB to 60dB, thereby improving the overall measurement capability of the system, and the first erbium-doped fiber amplifier 7 is used to amplify the detection light pulses.

[0033] The remote pump amplification subsystem includes a remote pump unit 10, a delay fiber 11, a wavelength division multiplexer 12, and a remote gain unit 14. The remote pump amplification subsystem is used for distributed amplification of the detection optical signal, wherein the remote pump unit 10 is a distributed Raman amplifier, generally 1480nm, and the remote gain unit 14 is an erbium-doped fiber (EDF). The long-distance BOTDR system uses an erbium-doped fiber amplifier to amplify the detection pulse and echo, and the measurement length can reach about 80km. After the sensing distance exceeds 80km, the signal-to-noise ratio is poor. In order to improve the signal-to-noise ratio, the detection pulse width needs to be increased, but the excessive input fiber optical power will cause various nonlinear effects in the optical fiber. Different from the traditional erbium-doped fiber amplification technology, Raman amplification uses ordinary optical fiber as a gain medium, and has an amplification effect on the light within the gain bandwidth transmitted along the optical fiber, avoiding the concentrated amplification of the detection pulse light. Usually, Raman amplification can make the measurement distance reach 100km. However, with the development of the power communication network, the longest station distance has exceeded 400km, and even using BOTDR for double-end measurement cannot meet the measurement length requirements. The study uses remote pumping technology to further amplify the signal. Traditional remote pumping technology uses the signal transmitting end to couple the Raman amplifier and fuse a remote gain unit, namely erbium-doped fiber (EDF), at a certain position in the middle of the line. Due to the diverse levels of erbium ions in erbium-doped fiber, when the signal is stored in a high-energy level system, if a photon works, the photon will stimulate the EDF to release energy. After the energy is released, all information will return to a lower energy level state, and the energy generated will be transmitted with the help of new photons. EDF can amplify the signal and realize passive relay amplification. The wavelength range of EDF is 980mm-1480mm. Under this scheme, the measurement length can be increased to 150km. At this time, the Raman optical power is generally around 600mW. If you want to further increase the measurement distance, you need a larger Raman optical power. However, too high Raman optical power will cause nonlinear effects of the optical fiber, degrade the quality of the detection optical signal, and reduce the measurement length. Therefore, in order to further increase the measurement length, a bypass remote pumping solution is adopted. By using two fiber cores to inject detection light and remote pumping light respectively, and then combining the two beams of light through a dense wavelength division multiplexer (DWDM) at 20 km, the Raman optical power can be further increased. The typical value is 800mw, which effectively avoids the nonlinear effect of the front end and increases the measurement length. The distance reaches 209km.

[0034] The sensing optical fiber includes a first optical fiber to be tested 9, a second optical fiber to be tested 13 and a third optical fiber to be tested 15, wherein the first optical fiber to be tested 9 and the delay optical fiber 11 are two cores of an optical cable. At a junction box about 20 km away from the originating end, the detection light and the remote pump light are combined into a beam through a dense wavelength division multiplexer and injected into the second sensing optical fiber to be tested 13, the remote gain unit 14 and the third sensing optical fiber to be tested 15.

[0035] The down-conversion subsystem includes a third electro-optical modulator 16 , a microwave modulator 17 , a polarization controller 18 , and an optical attenuator 19 , which are used to modulate the continuous light emitted by the laser into reference light, and perform polarization state control through the polarization controller 18 , and further perform attenuation through the attenuator 19 .

[0036] The echo amplification and filtering subsystem includes a second erbium-doped fiber amplifier 20, a second circulator 21, and a fiber grating filter 22, which are used to amplify the Brillouin scattered light and filter out a sideband effective Brillouin scattered signal.

[0037] The Brillouin heterodyne detection subsystem includes a four-port coupler 23, a balanced detector 24, and a filter detector 25, which are used to perform heterodyne detection of Brillouin signals, and perform filtering and detection to convert the scattered light signals into electrical signals.

[0038] The signal acquisition and processing subsystem includes a data acquisition card 26 and a computer 27, which are used for acquiring and processing sensor signals.

[0039] Specifically, the optical signal output end of the laser 1 is connected to the optical signal input end of the optical fiber coupler 2, and 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-optic modulator 4 and the input end of the third electro-optic modulator 16 at the same time. The first electro-optic modulator 4 is driven by the first pulse source 3, and the output end of the first electro-optic modulator 4 is connected to the input end of the second electro-optic modulator 6. The second electro-optic modulator 6 is driven by the second pulse source 5, and the output end of the second electro-optic modulator 6 is connected to the input end of the first erbium-doped fiber amplifier 7. The output end of the first erbium-doped fiber amplifier 7 is connected to the first optical signal port 8-1 of the first circulator 8, the second port 8-2 of the first circulator is connected to the first optical fiber 9 to be tested, the other end of the first optical fiber 9 to be tested is connected to the first port of the wavelength division multiplexer 12, the output end of the remote pump unit 10 is connected to the second port of the wavelength division multiplexer 12 via the delay fiber 11, the third port of the wavelength division multiplexer 12 is connected to the second optical fiber 13 to be tested, and the two ends of the remote gain unit (erbium-doped fiber) 14 are connected to the second optical fiber to be tested in the joint box. 13 and the third optical fiber to be tested 15 are fused, the third port 8-3 of the first circulator 8 is connected to the input port of the second erbium-doped fiber amplifier 20, the output port of the second erbium-doped fiber amplifier 20 is connected to the first port 21-1 of the second circulator 21, the second port 21-2 of the second circulator 21 is connected to the fiber grating filter 22, and the third port 21-3 of the second circulator 21 is connected to the first port of the four-port coupler 23; the third electro-optic modulator 16 is driven by the microwave modulator 17, the output port of the third electro-optic modulator 16 is connected to the input end of the polarization controller 18, the output end of the polarization controller 18 is connected to the input port of the optical attenuator 19, the output port of the optical attenuator 19 is connected to the second port of the four-port coupler 23, the third and fourth ports of the four-port coupler 23 are connected to the two input ports of the balanced detector 24, the output port of the balanced detector 24 is connected to the filter detector 25, the output end of the filter detector 25 is connected to the electrical signal input end of the data acquisition card 26, and the data acquisition card 26 is connected to the computer 27 through PCIE.

[0040] Among them, the output power range of the laser 1 is 30mw~45mw, and the wavelength range is 1548nm~1551nm. The coupling ratio of the fiber coupler 2 is 98:2, 95:5, 90:10 or 80:20. The output optical power range of the remote pump unit 10 is 600mw~1w, and the central wavelength range is 1455nm~1480nm. The central wavelength range of the fiber grating filter 22 is 1548nm~1551nm, and the bandwidth is 0.1nm. The detection bandwidth range of the balanced detector 24 is 200MHz~300MHz. The length of the delay fiber 11 is 20km, and the first optical fiber to be tested 9 is at the same distance as the delay optical fiber 11, realizing remote amplification without the need for line power supply.

[0041] The bypass remote pumping scheme refers to the detection pulse light directly coupled with the Raman amplifier and then entering the optical fiber to be tested. Since the Raman pump light amplifies the incoming detection pulse light, it is easy to cause nonlinear effects, so the peak power of the detection pulse light cannot be too high. The passive relay ultra-long distance BOTDR sensing system based on bypass remote pumping amplification described in the present invention adopts bypass remote pumping technology to suppress the optical fiber nonlinear effect caused by excessive detection light power in the bypass remote pumping scheme.

[0042] The passive relay ultra-long-distance BOTDR sensing system based on bypass remote pump amplification described in the present invention adopts bypass remote pump technology to achieve ultra-long-distance sensing. It only needs to install a remote pump unit at the signal transmitting end, and install erbium-doped optical fiber as a remote gain medium on the optical path to be measured. The remote gain medium does not need to be powered, and a passive relay solution is adopted, which is easy to implement in the field of ultra-long-distance monitoring.

[0043] Compared with the remote pump amplification scheme in which the signal light and the pump light are transmitted in the same fiber core, the ultra-long-distance BOTDR sensing system based on bypass remote pump amplification described in the present invention uses a bypass scheme in which two optical fibers are respectively injected into the signal light and the pump light and the light is combined through a dense wavelength division multiplexer. This can further improve the power of the Raman pump light and achieve longer-distance transmission. This is because the amplification effect near the pump end in the remote pump scheme is significant, resulting in rapid accumulation of the nonlinear effect of the amplified detection light near the pump end, generating nonlinear effects such as stimulated Brillouin and stimulated Raman, which deteriorates the quality of the detection light signal, limits the power of the Raman pump source, and affects the improvement of the sensing distance. The bypass remote pump method can effectively avoid the degradation of the front-end signal caused by the increase in the pump light power and improve the measurement distance.

[0044] The ultra-long-distance BOTDR sensing system based on bypass remote pump amplification described in the present invention can achieve higher spatial resolution, higher measurement accuracy and faster measurement time at the same sensing distance due to the significant improvement of the signal-to-noise ratio.

[0045] A working method of a passive relay ultra-long-distance BOTDR sensing system based on bypass remote pump amplification is realized by relying on the ultra-long-distance BOTDR sensing system based on bypass remote pump amplification. The continuous optical signal output by the laser 1 is divided into two paths by an optical fiber coupler; the continuous optical signal of the upper branch is cascade-modulated into an optical pulse signal by a first electro-optical modulator 4 and a second electro-optical modulator 6, and is optically power amplified by a first erbium-doped fiber amplifier 7, and then injected into a first optical fiber to be tested 9 through a second optical signal port 8-2 of a first circulator 8, the output end of the optical fiber to be tested is connected to a wavelength division multiplexer 12, and the output end of a remote pump unit 10 is connected to a delay optical fiber 11 The output signal of the delay optical fiber 11 and the output signal of the first optical fiber to be tested 9 are combined by the wavelength division multiplexer 12 and injected into the second optical fiber to be tested 13 at the same time. The two ends of the remote gain unit (erbium-doped optical fiber) 14 are respectively fused with the second optical fiber to be tested 13 and the third optical fiber to be tested 15 in the joint box. The back Brillouin scattered light signal in the optical fiber is output through the third optical signal port 8-3 of the first circulator 8 and then amplified by the second erbium-doped fiber amplifier 20. Then, it is injected into the fiber grating filter 22 through the second optical signal port 21-2 of the second circulator 21 to filter out broadband noise, and enters the four-port coupler 23 through the third port 21-3 of the second circulator 21;

[0046] The continuous optical signal of the downlink is modulated into a reference optical signal by the third electro-optical modulator 16, and after the polarization state is adjusted by the polarization controller 18, it is attenuated by the optical attenuator 19 and then enters the four-port coupler 23 to be mixed with the echo signal. The two output signals enter the balanced detector 24 through the third and fourth ports of the four-port coupler 23 for photoelectric conversion. The obtained electrical signal is then filtered by the detector 25 to extract the signal envelope, and is collected by the data acquisition card 26. The signal collected by the acquisition card is connected to the computer 27 through PCIE to realize signal processing.

[0047] By changing the frequency of the microwave source 17 to perform frequency sweeping, the Brillouin scattering time domain signal of the used frequency is obtained, the frequency sweeping range is set to ensure the integrity of the Brillouin scattering spectrum, and the Brillouin scattering time domain signal at each sweeping frequency is collected by the data acquisition card 26, thereby obtaining the Brillouin spectrum of each position point;

[0048] Furthermore, the Brillouin spectra collected at each position of the optical fiber are 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 v at that point. B (T,ε), the Brillouin frequency shift relative to the initial Brillouin frequency shift v B (T 0 ,ε 0 ) represents the change in temperature ΔT or strain Δε, as shown in formula (1):

[0049] v B(T,ε)=C v,T ΔT+C v,ε Δε+v B (T 0 ,ε 0 ) (1)

[0050] Among them C v,T and C v,ε are the Brillouin frequency shift temperature coefficient and the Brillouin frequency shift strain coefficient, respectively.

[0051] The present invention can improve the sensing distance based on remote pump amplification. Erbium-doped fiber is added to the optical fiber to be tested. 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 information will return to a lower energy level state, and the energy generated will be transmitted with the help of new photons, thereby extending the measurement distance.

[0052] When the remote pumping system adopts the bypass pumping method, the signal light and the pumping light are transmitted in the same fiber core. Due to the characteristic of remote pumping, the amplification effect is most significant near the pump end, which causes the nonlinear effect of the amplified detection light to accumulate rapidly near the pump end, resulting in nonlinear effects such as stimulated Brillouin and stimulated Raman, which deteriorates the signal quality of the detection light and affects the improvement of the sensing distance. The bypass remote pumping method can effectively avoid the influence of the front-end signal degradation caused by the increase of the pump light power, further improve the power of the Raman pump light, and achieve longer-distance transmission. At the same time, the erbium-doped fiber is combined as the remote gain unit to realize ultra-long-distance Brillouin fiber sensing.

[0053] Figure 3 The Brillouin center frequency shift is obtained by fitting each point of the remote pumping system. The sensing distance of the BOTDR system is 150 km. Figure 4 The Brillouin center frequency shift obtained by fitting each point of the system proposed in the present invention is shown in FIG. 1 . By comparison, the present invention successfully increases the sensing distance of the BOTDR system to 209 km. The 5 m erbium-doped optical fiber 13 is located at a position of 118 km. The signal provided by the remote pump unit 9 is used as pump excitation to realize remote pump amplification, eliminating the necessity of relay power supply.

[0054] Figure 5 This is the standard deviation accuracy of three repeated measurements of the system proposed in the present invention, and the test accuracy is 5MHz within a range of 200km.

[0055] Although the spirit and principle 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 disclosed specific embodiments, and the division of various aspects does not mean that the features in these aspects cannot be combined to benefit, and such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the attached claims.

Claims

1. A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification, characterized in that: include: Optical emission subsystem, optical pulse modulation subsystem, down-conversion subsystem, echo amplification and filtering subsystem, Brillouin heterodyne detection subsystem, signal acquisition and processing subsystem, remote pump amplification subsystem; The optical emission subsystem is respectively connected to the optical pulse modulation subsystem and the down-conversion subsystem, the optical pulse modulation subsystem is connected to the sensing optical fiber, and its echo signal is connected to the echo amplification and filtering subsystem, the echo amplification and filtering subsystem and the down-conversion subsystem are respectively connected to the Brillouin heterodyne detection subsystem, and the Brillouin heterodyne detection subsystem is connected to the signal acquisition and processing subsystem; Among them, the optical emission subsystem is used to generate two continuous optical signals; the optical pulse modulation subsystem is used to modulate one continuous optical signal into a detection optical pulse; the down-conversion subsystem is used to modulate another continuous optical signal into a reference light; the echo amplification and filtering subsystem is used to amplify the Brillouin scattered light and filter out a sideband effective Brillouin scattered signal; the Brillouin heterodyne detection subsystem is used to perform Brillouin signal heterodyne detection, and perform filtering and detection to convert the scattered light signal into an electrical signal; the signal acquisition and processing subsystem is used for the acquisition and processing of sensor signals; the remote pump amplification subsystem is used for the distributed amplification of the detection optical signal, The remote pump amplification subsystem comprises a remote pump unit (10), a time-delay optical fiber (11), a wavelength division multiplexer (12), and a remote gain unit (14); the optical pulse modulation subsystem is connected to one end of a first optical fiber to be tested (9); the other end of the first optical fiber to be tested (9) is connected to a first port of the wavelength division multiplexer (12); the output end of the remote pump unit (10) is connected to a second port of the wavelength division multiplexer (12) via the time-delay optical fiber (11); the third port of the wavelength division multiplexer (12) is connected to a second optical fiber to be tested (13); and two ends of the remote gain unit (14) are fused with the second optical fiber to be tested (13) and the third optical fiber to be tested (15) respectively; The optical emission subsystem comprises a laser (1) and an optical fiber coupler (2); the optical pulse modulation subsystem comprises a first pulse source (3), a first electro-optical modulator (4), a second pulse source (5), a second electro-optical modulator (6), a first erbium-doped fiber amplifier (7), and a first circulator (8); the down-conversion subsystem comprises a third electro-optical modulator (16), a microwave modulator (17), a polarization controller (18), and an optical attenuator (19); the optical signal output end of the laser (1) is connected to the optical signal input end of the optical fiber coupler (2), and the two optical signal output ends of the optical fiber coupler (2) are respectively and simultaneously connected to the optical signal input end of the first electro-optical modulator (4) and the output end of the third electro-optical modulator (16). The first electro-optic modulator (4) is driven by the first pulse source (3), the output end of the first electro-optic modulator (4) is connected to the input end of the second electro-optic modulator (6), the second electro-optic modulator (6) is driven by the second pulse source (5), the output end of the second electro-optic modulator (6) is connected to the input end of the first erbium-doped fiber amplifier (7), and the output end of the first erbium-doped fiber amplifier (7) is connected to the first optical signal port (8-1) of the first circulator (8); the third electro-optic modulator (16) is driven by the microwave modulator (17), the output port of the third electro-optic modulator (16) is connected to the input end of the polarization controller (18), and the output end of the polarization controller (18) is connected to the input port of the optical attenuator (19).

2. A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification according to claim 1, characterized in that: The echo amplification and filtering subsystem comprises a second erbium-doped fiber amplifier (20), a second circulator (21), and a fiber grating filter (22); the Brillouin heterodyne detection subsystem comprises a four-port coupler (23), a balanced detector (24), and a filter detector (25); the signal acquisition and processing subsystem comprises a data acquisition card (26) and a computer (27); the third port (8-3) of the first circulator (8) is connected to the input port of the second erbium-doped fiber amplifier (20), the output port of the second erbium-doped fiber amplifier (20) is connected to the first port (21-1) of the second circulator (21), the second port (21-2) of the second circulator (21) is connected to the fiber grating filter (22), and the third port (21-3) of the second circulator (21) is connected to the first port of the four-port coupler (23); The output port of the optical attenuator (19) is connected to the second port of the four-port coupler (23), the third and fourth ports of the four-port coupler (23) are connected to the two input ports of the balanced detector (24), the output port of the balanced detector (24) is connected to the filter detector (25), the output end of the filter detector (25) is connected to the electrical signal input end of the data acquisition card (26), and the data acquisition card (26) is connected to the computer (27).

3. A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification according to claim 1, characterized in that: The remote pumping unit (10) is a distributed Raman amplifier, and the remote gain unit (14) is an erbium-doped optical fiber.

4. A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification according to claim 1, characterized in that: The output power range of the laser (1) is 30mw-45mw, and the wavelength range is 1548nm-1551nm; the coupling ratio of the optical fiber coupler (2) is 98:2, 95:5, 90:10 or 80:

20.

5. A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification according to claim 3, characterized in that: The output optical power range of the remote pump unit (10) is 600mw-1w, and the central wavelength range is 1455nm-1480nm.

6. A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification according to claim 2, characterized in that: The central wavelength range of the fiber grating filter (22) is 1548nm-1551nm, and the bandwidth is 0.1nm; the detection bandwidth range of the balanced detector (24) is 200MHz-300MHz.

7. A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification according to claim 2, characterized in that: The data acquisition card (26) acquires the Brillouin scattering time domain signal at each scanning frequency to obtain the Brillouin spectrum at each position point; after obtaining the Brillouin spectrum at each position point, the computer (27) performs fitting processing on the Brillouin spectrum 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 the point. B (T,ε).

8. A passive relay ultra-long distance BOTDR sensing system based on bypass remote pump amplification according to claim 7, characterized in that: The Brillouin frequency shift v B (T,ε) relative to the initial Brillouin frequency shift v B The change of (T0, ε0) represents the temperature change ΔT or strain change Δε of the optical fiber to be tested, that is: v B (T,ε)=C v,T ΔT+C v,ε No+v B (T0,ε0) Among them, C v,T and C v,ε represent the Brillouin frequency shift temperature coefficient and the Brillouin frequency shift strain coefficient respectively.

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