Long-distance FBG sensing system based on tunable erbium-ytterbium co-doped random fiber laser

Abstract

The application provides a long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser, relates to the technical fields of fiber lasers and fiber sensing, and specifically comprises a tunable erbium-ytterbium co-doped random fiber laser, a 10:90 coupler, a circulator, a wavelength division multiplexer, a fiber loop mirror, a ytterbium-doped random fiber laser, a first single-mode fiber, an erbium-doped fiber, a sensing FBG, a broadband FBG, a photodetector and an oscilloscope; the erbium-ytterbium co-doped random fiber laser is used as a detection light source of the COTDR, so that the influence of time delay characteristics on detection accuracy can be eliminated; secondly, the application adopts a new high-order mixed amplification technology of high-order random fiber laser amplification combined with remote pumping erbium-doped fiber amplification, so that the problem of insufficient length of the FBG sensing system can be solved; meanwhile, the application utilizes a mixed FBG multiplexing mode of time division multiplexing and wavelength division multiplexing combined with double-wavelength differential operation, so that the sensing capacity of the system is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fiber laser and fiber sensing technology, and in particular to a long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser. BACKGROUND

[0002] Since FBG was first reported by K.O. Hill in 1978, FBG has become a key passive device widely used in optical fiber communication systems. At the same time, as a kind of structural sensitive element, the Bragg fiber grating FBG can also be used as a new type of sensor. The structure can change with the change of external temperature, strain and other physical quantities. It has the characteristics of anti-electromagnetic interference, small size, good corrosion resistance, easy multiplexing and high sensitivity, and is suitable for use in extremely harsh environments. The inherent time delay characteristics of the existing chaotic semiconductor laser source will lead to a decrease in the performance of the related optical time domain reflectometer system, and the distance and multiplexing capacity of the FBG sensing system based on the related optical time domain reflectometer are still limited. Therefore, exploring new types of probe light sources, signal amplification methods and sensing capacity improvement methods that meet the long-distance and high spatial resolution FBG sensing requirements has become a research hotspot.

[0003] In the FBG large-capacity multiplexing technology, time division multiplexing technology and wavelength division multiplexing technology are widely used in FBG sensing systems. Compared with these two multiplexing technologies, the hybrid multiplexing technology of time division multiplexing technology and wavelength division multiplexing technology has become a new solution to realize the capacity improvement of the FBG sensing system. This hybrid multiplexing technology can multiply the multiplexing capacity of the FBG sensing system. The FBG sensing system based on the related optical time domain reflectometer can solve the problem of mutual restriction of sensing distance and spatial resolution of the FBG sensing system based on the pulse optical time domain reflectometer. In the optical amplification technology, the distributed amplification technology and the remote pumping amplification technology can effectively improve the sensing range of the FBG sensing system based on the related optical time domain reflectometer.

[0004] FBG sensing technology can be widely used in the structural health monitoring of various infrastructures. In particular, long-distance FBG sensing systems can be used for large-scale relay-free monitoring of submarine cables, which is a popular research content. Submarine cables are mostly distributed in deep sea, and the environment is complex and harsh, with high monitoring and maintenance costs. Moreover, for long-distance FBG sensing system monitoring, the maintenance of relay stations is also a burden, so there is an urgent need for a long-distance relay-free FBG sensing system solution for submarine cable transmission networks. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser, and realizes long-distance and high spatial resolution FBG sensing, improves the multiplexing capacity of the system sensing FBG, and provides a solution for large-range unrepeatered sensing monitoring of submarine cable transmission networks.

[0006] A long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser, comprising a tunable erbium-ytterbium co-doped random fiber laser, a 10:90 coupler, a circulator, a wavelength division multiplexer, a fiber loop mirror, a ytterbium-doped random fiber laser, a first single-mode optical fiber, an erbium-doped optical fiber, a sensing FBG, a broadband FBG, a photodetector, and an oscilloscope;

[0007] The tunable erbium-ytterbium co-doped random fiber laser comprises a 976nm semiconductor laser, a tunable filter, a 1:1 coupler, a beam combiner, an erbium-ytterbium co-doped optical fiber, a second single-mode optical fiber, and an isolator, wherein the beam combiner couples the 976nm semiconductor laser into the erbium-ytterbium co-doped optical fiber, two output ports of the 1:1 coupler and the tunable filter are connected to provide wavelength selection point feedback, and the second single-mode optical fiber is connected with the isolator at a distal end;

[0008] The circulator comprises a first circulator and a second circulator, and the photodetector comprises a first photodetector and a second photodetector; an output end of the tunable erbium-ytterbium co-doped random fiber laser is connected with the 10:90 coupler, a 90% port of the 10:90 coupler is connected with a port of the first circulator, and a 10% port of the 10:90 coupler is connected with the first photodetector; three ports of the first circulator are connected with a port of the second circulator, and two ports of the second circulator are connected with the broadband FBG; light of the 10% port of the 10:90 coupler is detected by the first photodetector as a reference light signal, and light of the 90% port is sent into the first circulator as a signal light;

[0009] The wavelength division multiplexer comprises a first wavelength division multiplexer and a second wavelength division multiplexer; three ports of the first circulator are connected with a reflection port of the first wavelength division multiplexer, an output end of the ytterbium-doped random fiber laser is connected with a through port of the second wavelength division multiplexer, signal light and pump light output by the ytterbium-doped random fiber laser are coupled into the first single-mode optical fiber, and the erbium-doped optical fiber is located in the first single-mode optical fiber, wherein the length of the erbium-doped optical fiber is 15m;

[0010] The FBG sensing system adopts time division multiplexing technology and wavelength division multiplexing technology hybrid multiplexing technology, a plurality of groups of sensing FBGs with different reflection wavelengths are arranged at different positions of the first single-mode optical fiber, the sensing FBGs in each group are spaced 5m-20m apart, the reflection center wavelengths of the sensing FBGs in each group are different, the reflection wavelengths of the sensing FBGs are the same, the reflection wavelengths of the sensing FBGs are 1520nm-1580nm, and the reflection rates of the sensing FBGs are the same; the reflected light signals of the sensing FBGs pass through the second circulator, are filtered by the broadband FBG, then enter the second photoelectric detector, and are finally collected by the oscilloscope; the reflected light signals carry external information, the reference light and the reflected light signals are correlated, the wavelength scanning method is combined with the double-wavelength differential demodulation method to restore the external information.

[0011] The erbium-ytterbium co-doped random fiber laser provides high-order amplification pumping, and the fiber ring mirror is connected to the first wavelength division multiplexer through a port.

[0012] The length of the erbium-ytterbium co-doped fiber ranges from 2m to 10m, and the output power of the tunable erbium-ytterbium co-doped random fiber laser is greater than or equal to 100mW.

[0013] The total length of the first single-mode optical fiber is set to 1km-180km.

[0014] The technical scheme has the beneficial effects that:

[0015] 1. The six-order random fiber laser amplification technology is adopted, the random laser amplification technology is combined with the remote pumping erbium-doped fiber amplification to form a hybrid amplification technology, and the system can be effectively extended without relay sensing.

[0016] 2. In the traditional FBG sensing system based on the correlation optical time domain reflectometer, the semiconductor chaotic light source used has a time delay characteristic. The erbium-ytterbium co-doped random fiber laser is used as a detection light signal, the influence of the time delay characteristic on the sensing performance of the system can be avoided, and the hybrid amplification method used does not introduce the time delay characteristic.

[0017] 3. The long-distance FBG sensing system adopts a hybrid multiplexing mode of time division multiplexing and wavelength division multiplexing to improve the multiplexing capacity of the system, the sensing FBGs are divided into a plurality of groups, the FBGs in each group are distributed at different positions of the optical fiber, the center wavelengths of the FBGs in each group are different, and the time division multiplexing scheme and the wavelength division multiplexing scheme are used for demodulation. Through the hybrid multiplexing method of wavelength division multiplexing and time division multiplexing, each waveband of the detection light source can be efficiently utilized, and the number of sensing FBGs in the system can be greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The tunable erbium-ytterbium co-doped random fiber laser is a structural block diagram;

[0019] Figure 2 Time-domain trace diagram and autocorrelation curve diagram of tunable erbium-ytterbium co-doped random fiber laser output of the present application;

[0020] Wherein (a) is a time-domain trace diagram, and (b) is an autocorrelation curve diagram;

[0021] Figure 3 Block diagram of a large-capacity FBG sensing system based on the tunable erbium-ytterbium co-doped random fiber laser of the first embodiment of the present application;

[0022] Figure 4 Block diagram of a long-distance correlation optical time-domain reflectometer FBG sensing system based on a new high-order hybrid amplification method of the second embodiment of the present application;

[0023] Figure 5 Long-distance and large-capacity FBG sensing system based on high-order hybrid amplification and wavelength division multiplexing technology of the third embodiment of the present application;

[0024] Figure 6 Simulation result diagram of large-capacity FBG sensing signal power distribution in a 175km link of the present application;

[0025] In the figure, 1 is a tunable erbium-ytterbium co-doped random fiber laser, 1-1 is a 976nm semiconductor laser, 1-2 is a tunable filter, 1-3 is a 1:1 coupler, 1-4 is a beam combiner, 1-5 is an erbium-ytterbium co-doped fiber, 1-6 is a second single-mode fiber, 1-7 is an isolator, 2 is a 10:90 coupler, 3 is a first circulator, 4 is a first wavelength division multiplexer, 5 is a fiber loop mirror, 6 is a second wavelength division multiplexer, 7 is an ytterbium-doped random fiber laser, 8 is a 1:99 coupler, 9 is a first single-mode fiber, 10 is a sensing FBG, 11 is an erbium-doped fiber, 12 is a second circulator, 13 is a broadband FBG, 14 is a first photodetector, 15 is a second photodetector, and 16 is an oscilloscope. DETAILED DESCRIPTION

[0026] The specific embodiments of the present application are described in further detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application but are not used to limit the scope of the present application.

[0027] A long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser includes a tunable erbium-ytterbium co-doped random fiber laser, a 10:90 coupler, a circulator, a wavelength division multiplexer, a fiber loop mirror, an ytterbium-doped random fiber laser, a first single-mode fiber, an erbium-doped fiber, a sensing FBG, a broadband FBG, a photodetector, and an oscilloscope.

[0028] The tunable erbium-ytterbium co-doped random laser includes a 976 nm semiconductor laser, a tunable filter, a 1:1 coupler, a combiner, an erbium-ytterbium co-doped fiber, a second single-mode fiber and an isolator, wherein the combiner couples the laser output of the 976 nm semiconductor laser into the erbium-ytterbium co-doped fiber, the two output ports of the 1:1 coupler and the tunable filter are connected to provide wavelength selection point feedback, the erbium-ytterbium co-doped fiber provides active gain, the second single-mode fiber provides random Rayleigh scattering, and the second single-mode fiber is connected with the isolator at a far end to ensure one-way operation of the optical path.

[0029] As shown in Figure 1 The tunable erbium-ytterbium co-doped random fiber laser 1 structure block diagram used in the embodiment is shown. It includes a 976 nm semiconductor laser 1-1, a tunable filter 1-2, a 1:1 coupler 1-3, a combiner 1-4, an erbium-ytterbium co-doped fiber 1-5, a second single-mode fiber 1-6 and an isolator 1-7. The combiner 1-4 is logically connected with the input port of the 1:1 coupler 1-3 at a signal end, connected with the 976 nm semiconductor laser 1-1 at a pump end, and connected with the erbium-ytterbium co-doped fiber 1-5 at a common port.

[0030] The working principle of the tunable erbium-ytterbium co-doped random fiber laser is as follows. The 976 nm semiconductor laser 1-1 injects the erbium-ytterbium co-doped fiber 1-5 through the combiner 1-4, the erbium-ytterbium co-doped fiber 1-5 provides active gain, and the second single-mode fiber 1-6 provides backward Rayleigh scattering feedback. The front-end pump combiner signal end is connected with the 1:1 coupler 1-3, the two output ends of the coupler are connected with the wavelength tunable filter 1-2, and a filter point feedback is formed to determine the random fiber laser wavelength. By using erbium-ytterbium co-doped gain, low threshold and high efficiency random fiber laser output can be realized. Further, by adjusting the center wavelength of the tunable filter 1-2, a high-power C-band range wavelength tunable random fiber laser probe source can be realized.

[0031] As shown in Figure 2 (a) and (b) respectively show Figure 1 The time-domain trace diagram and the autocorrelation curve diagram of the output random laser of the tunable erbium-ytterbium co-doped random fiber laser are shown. The output random laser shows strong random fluctuations in the time domain, which is a favorable condition for correlation analysis. The output random laser has a δ function-like autocorrelation curve, has good autocorrelation characteristics and no time delay characteristics, and is conducive to further improving the system sensing distance and positioning accuracy.

[0032] The circulator comprises a first circulator 3 and a second circulator 12, and the photodetector comprises a first photodetector 14 and a second photodetector 15; the output end of the tunable erbium-ytterbium co-doped random fiber laser is connected with a 10:90 coupler 2, the 90% port of the 10:90 coupler 2 is connected with a port of the first circulator 3, and the 10% port of the 10:90 coupler is connected with the first photodetector 14; the three ports of the first circulator 3 are connected with a port of the second circulator 12, and the two ports of the second circulator 12 are connected with a broadband FBG 13; the light of the 10% port of the 10:90 coupler 2 is detected by the first photodetector 14 as a reference light signal, and the light of the 90% port is sent into the first circulator 3 as a signal light.

[0033] The wavelength division multiplexer comprises a first wavelength division multiplexer 4 and a second wavelength division multiplexer 6; the three ports of the first circulator 3 are connected with a reflection port of the first wavelength division multiplexer 4, the output end of the ytterbium-doped random fiber laser is connected with the second wavelength division multiplexer 6, the signal light and the pump light output by the ytterbium-doped random fiber laser 7 are coupled into the first single-mode optical fiber 9, distributed random laser amplification is realized, the erbium-doped fiber 11 is located in the first single-mode optical fiber 9, remote-pumped erbium-doped fiber amplification is realized, and the sensing distance of the system is extended, wherein the length of the erbium-doped fiber 11 is 15 m; the ytterbium-doped random fiber laser provides pumping, the fiber circulator 5 provides broadband reflection, the first single-mode optical fiber provides Rayleigh scattering and Raman gain, and first-order to fifth-order Stokes light is generated in the first single-mode optical fiber, wherein the fifth-order Stokes light is used as direct pumping to amplify the signal light.

[0034] The FBG sensing system adopts a time division multiplexing technology and a wavelength division multiplexing technology, a plurality of groups of sensing FBGs 10 with different reflection wavelengths are arranged at different positions of the first single-mode optical fiber, the sensing FBGs in each group are spaced apart by 5 m-20 m, the reflection center wavelengths of the sensing FBGs 10 in each group are different, the reflection wavelengths of the sensing FBGs are in the range of 1520 nm-1580 nm, and the reflection rates of the sensing FBGs are the same; the reflected light signals of the sensing FBGs pass through the second circulator, are filtered by the broadband FBG to remove residual pump light and cascade Stokes light, then enter the second photodetector 15, and are finally collected by an oscilloscope 16; the reflected light signals carry external information, the reference light and the reflected light signals are subjected to cross-correlation operation, the wavelength scanning method is combined with a double-wavelength differential demodulation method to restore the external information.

[0035] The ytterbium-doped random fiber laser 7 provides high-order amplification pumping, the fiber circulator 5 is connected with the through port of the first wavelength division multiplexer, and broadband point feedback is provided for the first-order to fifth-order Stokes light.

[0036] The erbium-ytterbium co-doped fiber has a length in the range of 2-10m, and the tunable erbium-ytterbium co-doped random fiber laser has an output power greater than or equal to 100mW.

[0037] The total length of the first single-mode fiber 9 is set to be 1km-180km.

[0038] The FBG sensing system can realize the measurement of parameters such as temperature, strain, displacement and angle by using different packaging methods, and can realize fiber fault detection and sensing distance greater than 50km.

[0039] The detection signal amplification method of the FBG sensing system includes but is not limited to high-order random fiber laser amplification, remote-pumped erbium-doped fiber amplification and distributed Raman amplification.

[0040] Embodiment 1

[0041] As shown in Figure 3 The present example is an FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser. The tunable erbium-ytterbium co-doped random fiber laser 1, the 10:90 coupler 2, the first circulator 3, the first single-mode fiber 9 and the sensing FBG 10 are connected in sequence. The logic of the 10:90 coupler 2 is that the 90% port 2-1 is connected with the first port of the circulator 3, and the 10% port is connected with the first photodetector 14. The second port of the first circulator 3 is connected with the first single-mode fiber 9, and the third port of the first circulator 3 is connected with the second photodetector 15. The sensing FBG 10 is distributed in the first single-mode fiber 9, and 200 sensing FBGs with different reflection wavelengths are arranged at different positions of the first single-mode fiber 9. The reflection wavelength range of the sensing FBG is 1520-1580nm.

[0042] The working principle of the present application is as follows: the tunable erbium-ytterbium co-doped random fiber laser 1 can realize C-band range laser output. The output light is divided into two parts by the 10:90 coupler, wherein the light of the 10% port is detected by the first photodetector 14 as a reference light signal, and the light of the 90% port is sent into the first single-mode fiber 9 through the first port and the second port of the first circulator 3 as a detection light. The sensing FBG 10 serves as a sensing element of the system. Due to its structural sensitivity, the reflection spectrum center wavelength changes with the change of the external environmental physical quantity. The sensing FBG 10 reflects the signal light and makes the back signal light carry the external information. The back light signal is detected by the second photodetector 15 through the second port and the third port of the first circulator 3, and finally collected by the oscilloscope 16. The reference light signal and the back light signal are cross-correlated, and the external temperature change is restored by using the double-wavelength differential demodulation method. The reflection spectrum of the sensing FBG 10 has a Gaussian line shape.

[0043]

[0044] where λ B represents the center wavelength of the reflected spectrum of the sensing FBG 10, and B is the spectral bandwidth. In order to obtain the wavelength shift of the fiber Bragg grating, a dual-wavelength differential algorithm is adopted by using two different wavelengths (λ1 and λ2) of the probe signal. The wavelength interval of λ1 and λ2 is defined as Δλ. Since the spectrum of the fiber Bragg grating will shift with the change of temperature or strain, the effective reflectivity of the sensing fiber Bragg grating to the two probe signals will also change accordingly. The intensity of the reflected signals of different wavelengths is represented as:

[0045]

[0046] Therefore, the peak power difference (PPD) of the cross-correlation function of the signals with two wavelengths is:

[0047]

[0048] where M is a constant, equal to Δλ(Δλ+2λ1), and N is equal to -2Δλ. In the case of fixed signal wavelength, the PPD is linearly related to the wavelength of the sensing FBG, and the wavelength of the sensing FBG is linearly related to the change of the ambient temperature or strain.

[0049] Example 2

[0050] As shown in Figure 4 , the present example is a long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser and hybrid amplification technology. The random laser amplification technology in the long-distance FBG sensing system described in the present application is characterized in that the pump light is transmitted in the first single-mode optical fiber 9 and generates random laser. The structure can be composed of a first wavelength division multiplexer 4, a second wavelength division multiplexer 6, a 1:99 coupler 8, a first single-mode optical fiber 9, and a ytterbium-doped random fiber laser 7. The pump light generated by the ytterbium-doped random fiber laser 7 enters the first single-mode optical fiber 9 through the second wavelength division multiplexer 6. The reflection port of the first wavelength division multiplexer is connected to the fiber ring mirror 5, which provides broadband point feedback for high-order random laser, forming a forward semi-open cavity structure. Combined with the stimulated Raman scattering gain and distributed backscattering feedback in the optical fiber, first-order to fifth-order cascaded random fiber laser lasing is realized. The generated fifth-order random fiber laser further serves as direct pumping of C-band probe light and amplifies it in the optical fiber link. The random laser amplification technology can avoid the time delay characteristics introduced in the traditional distributed Raman amplification system during the amplification process.

[0051] The long-distance FBG sensing system of the application is a point amplification method in which the pump light source and the doped erbium fiber 11 providing active gain are separated, and the structure can be composed of a first wavelength division multiplexer 4, a second wavelength division multiplexer 6, a 1:99 coupler 8, a first single-mode optical fiber 9, the doped erbium fiber 11, and a doped ytterbium random fiber laser 7. Under the action of the pump light, the signal light first experiences stimulated Raman scattering amplification, and then is transmitted to the tail end of the optical fiber after being amplified by residual 1480 nm pump in the doped erbium fiber.

[0052] The amplified backscattered light is transmitted to the front end of the optical fiber link, is output through the circulator, is filtered through the broadband FBG to filter out the residual pump light and the cascaded Stokes light, and then is injected into the second photodetector 15. The reflection event of the optical fiber link can be located by performing cross-correlation operation on the reference light and the backscattered light. Further, by using the double-wavelength differential demodulation method, the peak values of the demodulation cross-correlation functions of the two different wavelength detection light signals are differentially calculated, and the peak value difference is linearly related to the FBG wavelength drift, so that the FBG sensing can be realized. Therefore, the new high-order hybrid amplification method is adopted, and the wavelength scanning correlation optical time domain reflectometer is combined, so that the long-distance FBG sensing can be realized.

[0053] Example 3

[0054] As shown in Figure 5 , the present example is a long-distance and large-capacity FBG sensing system based on high-order hybrid amplification and wavelength division multiplexing technology. The system is characterized in that the hybrid amplification method described in Example 2 is used, a high-power tunable erbium-ytterbium co-doped random fiber laser 1 is used to output different wavelength detection light to inject into the first single-mode optical fiber 9, different wavelength sensing FBGs 10 are arranged at the same position in the optical fiber link, and the same wavelength sensing FBGs 10 can be arranged at different positions, so as to realize the FBG multiplexing method combined with wavelength division multiplexing and time division multiplexing. The sensing FBGs 10 in the optical fiber link can be located by the backscattered light return time. The cross-correlation intensity of the FBG signals at different positions and different wavelengths can be obtained by calculating the cross-correlation function of the back light signal and the reference light detected at the receiving end. Further, the wavelength scanning method is combined with the double-wavelength differential demodulation method to realize the improvement of the FBG sensing capacity.

[0055] A theoretical model of the FBG sensing system based on the new high-order hybrid amplification technology is established. Through simulation calculation, a 1090 nm pump with a power of 5.65 W is used, a 15 m long doped erbium fiber is located at the position of 80 km in the optical fiber link, and FBGs with a reflectivity of 5% are arranged at positions of 25 km, 37.5 km, 50 km, 62.5 km, 75 km, 124 km, 136.5 km, 149 km, 161.5 km, and 174 km in the 175 km optical fiber link. The power distribution of the backscattered signal light is as shown in Figure 5It can be seen that the new high-order hybrid amplification technology can effectively amplify the sensing signal light in the 175km link, and the FBG sensing signal is clearly visible compared to the back Rayleigh scattering signal, and the signal-to-noise ratio is high. Therefore, a long-distance, large-capacity related optical time domain reflectometer FBG sensing system based on high-order hybrid amplification and wavelength division multiplexing technology can be realized.

[0056] Therefore, in the above exemplary embodiments, by introducing the random laser amplification technology and the remote-pumped erbium-doped fiber amplification technology to amplify the sensing system optical signal, the unrepeatered sensing distance of the system can be effectively extended. The FBG multiplexing capacity of the FBG sensing system is improved by using the wavelength division multiplexing and time division multiplexing composite FBG multiplexing method. The hybrid multiplexing method combining Raman gain and erbium-doped active optical fiber gain is used to inject different wavelength probe lights output by a high-power tunable erbium-ytterbium co-doped random fiber laser into the sensing optical fiber, efficiently utilize the spatial distance of the sensing optical fiber, extend the sensing distance of the system, and improve the sensing FBG multiplexing number. The simulation result graph of the large-capacity FBG sensing signal power distribution in the 175km link in the embodiment is shown in FIG. 6. Figure 6

[0057] The above description is only the preferred embodiments of the present disclosure and the explanation of the applied technical principles. Those skilled in the art should understand that the scope of the application involved in the embodiments of the present disclosure is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or equivalent features without departing from the above inventive concept. For example, the above features and the technical features disclosed in the embodiments of the present disclosure (but not limited to) having similar functions are replaced with each other to form a technical solution.​

Claims

1. A long-distance FBG sensing system based on a tunable Er-Yb co-doped random fiber laser, characterized in that: Including tunable erbium-ytterbium co-doped random fiber laser, 10:90 coupler, circulator, wavelength division multiplexer, fiber loop mirror, ytterbium-doped random fiber laser, first single-mode fiber, erbium-doped fiber, sensing FBG, broadband FBG, photodetector and oscilloscope; The tunable erbium-ytterbium co-doped random fiber laser includes a 976nm semiconductor laser, a tunable filter, a 1:1 coupler, a beam combiner, an erbium-ytterbium co-doped fiber, a second single-mode fiber, and an isolator, wherein the beam combiner couples the 976nm semiconductor laser into the erbium-ytterbium co-doped fiber, two output ports of the 1:1 coupler are connected to the tunable filter to provide wavelength selection point feedback, and the second single-mode fiber is remotely connected to the isolator; The circulator includes a first circulator and a second circulator, and the photodetector includes a first photodetector and a second photodetector; the output end of the tunable erbium-ytterbium co-doped random fiber laser is connected to a 10:90 coupler, the 90% port of the 10:90 coupler is connected to a first port of the first circulator, and the 10% port of the 10:90 coupler is connected to the first photodetector; the third port of the first circulator is connected to a first port of the second circulator, and the second port of the second circulator is connected to a broadband FBG; light from the 10% port of the 10:90 coupler is detected by the first photodetector as a reference light signal, and light from the 90% port is sent into the first circulator as signal light; The wavelength division multiplexer includes a first wavelength division multiplexer and a second wavelength division multiplexer; the three ports of the first circulator are connected to the reflection port of the first wavelength division multiplexer, the output end of the ytterbium-doped random fiber laser is connected to the through port of the second wavelength division multiplexer, the signal light and the pump light output by the ytterbium-doped random fiber laser are coupled into the first single-mode optical fiber, and the erbium-doped optical fiber is located in the first single-mode optical fiber, wherein the length of the erbium-doped optical fiber is 15m.

2. The long-distance FBG sensing system based on a tunable Er-Yb co-doped random fiber laser according to claim 1, characterized in that: The FBG sensing system adopts a hybrid multiplexing technology of time division multiplexing technology and wavelength division multiplexing technology. Several groups of sensing FBGs with different reflection wavelengths are set at different positions of the first single-mode optical fiber. The interval between each group of sensing FBGs is 5m-20m. The reflection center wavelength of the sensing FBGs in each group is different. The reflection wavelength range of the sensing FBGs is 1520nm-1580nm, and the reflectivity of the sensing FBGs is the same. The return light signal reflected by the sensing FBG passes through a second circulator, is filtered by the broadband FBG, then enters a second photodetector, and is finally collected by an oscilloscope. The return light signal carries external information. By performing cross-correlation calculation with the reference light and the return light signal, the external information is restored using a wavelength scanning method combined with a dual-wavelength differential demodulation method.

3. The long-distance FBG sensing system based on a tunable Er-Yb co-doped random fiber laser according to claim 1, characterized in that: The ytterbium-doped random fiber laser provides high-order amplification pumping, and the fiber loop mirror is connected to the first wavelength division multiplexer through a port.

4. The long-distance FBG sensing system based on a tunable Er-Yb co-doped random fiber laser according to claim 1, characterized in that: The length of the erbium-ytterbium co-doped optical fiber ranges from 2m to 10m, and the output power of the tunable erbium-ytterbium co-doped random fiber laser is greater than or equal to 100mW.

5. The long-distance FBG sensing system based on a tunable Er-Yb co-doped random fiber laser according to claim 1, characterized in that: The total length of the first single-mode optical fiber is set to 1km-180km.

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