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

Abstract

The invention provides a long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser, and relates to the technical field of fiber laser and fiber sensing. The device 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, an ytterbium-doped random fiber laser, a first single-mode fiber, an erbium-doped fiber, a sensing FBG, a broadband FBG, a photoelectric detector and an oscilloscope. According to the invention, 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 the detection precision can be eliminated; secondly, a novel high-order hybrid amplification technology combining high-order random fiber laser amplification with remote pump erbium-doped fiber amplification is adopted, and the problem that the distance of an FBG sensing system is not long enough can be solved; meanwhile, the sensing capacity of the system is further improved by combining a time division multiplexing and wavelength division multiplexing mixed FBG multiplexing mode with dual-wavelength differential operation.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber laser and optical fiber sensing, and in particular to a long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random optical fiber laser. Background Art

[0002] Since FBG was first reported by KOHill in 1978, FBG has become a key passive device widely used in optical fiber communication systems. At the same time, as a structural sensitive element, FBG can also be used as a new type of sensor. Its structure can change with the changes of physical quantities such as external temperature and strain. 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 delay characteristics of existing chaotic semiconductor laser sources will lead to the reduction of the performance of the correlated optical time domain reflectometer system, and the distance and multiplexing capacity of the FBG sensing system based on the correlated optical time domain reflectometer are still limited. Therefore, exploring new detection light sources, signal amplification methods and sensing capacity improvement methods that meet the needs of long-distance and high spatial resolution FBG sensing 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 sensor 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 achieve the capacity improvement of FBG sensor systems. This hybrid multiplexing technology can multiply the multiplexing capacity of FBG sensor systems. The FBG sensor system based on correlated optical time domain reflectometer can solve the problem of mutual restriction between the sensing distance and spatial resolution of the FBG sensor system based on pulsed optical time domain reflectometer. In optical amplification technology, distributed amplification technology and remote pump amplification technology can effectively improve the sensing range of the FBG sensor system based on correlated optical time domain reflectometer.

[0004] FBG sensing technology can be widely used in structural health monitoring of various infrastructures. In particular, long-distance FBG sensing systems can be used for large-scale relay-free monitoring of submarine optical cables, which is a hot research topic now. Submarine optical cables are mostly distributed in the deep sea, where the environment is complex and harsh, and the monitoring and maintenance costs are high. In addition, for long-distance FBG sensing system monitoring, the maintenance of relay stations is also a burden. Therefore, the submarine optical cable transmission network urgently needs a long-distance relay-free FBG sensing system solution. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a long-distance FBG sensing system based on a tunable Er-Yb co-doped random fiber laser, and realizes long-distance, high spatial resolution FBG sensing, improves the multiplexing capacity of the system sensing FBG, and provides a solution for large-scale relay-free sensing monitoring such as submarine optical cable transmission networks.

[0006] A long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser comprises a tunable erbium-ytterbium co-doped random fiber laser, a 10:90 coupler, a circulator, a wavelength division multiplexer, a fiber ring 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;

[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 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;

[0008] 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 Er-Yb co-doped random fiber laser is connected to a 10:90 coupler, the 90% port of the 10:90 coupler is connected to a port of the first circulator, and the 10% port of the 10:90 coupler is connected to the first photodetector; the three ports of the first circulator are connected to a port of the second circulator, and the two ports of the second circulator are connected to a broadband FBG; the light of the 10% port of the 10:90 coupler is detected by the first photodetector as a reference light signal, and the light of the 90% port is sent to the first circulator as a signal light;

[0009] 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, the erbium-doped optical fiber is located in the first single-mode optical fiber, and the length of the erbium-doped optical fiber is 15m;

[0010] The FBG sensing system adopts a hybrid multiplexing technology of time division multiplexing technology and wavelength division multiplexing technology, and sets a plurality of groups of sensing FBGs with different reflection wavelengths at different positions of the first single-mode optical fiber, and each group of sensing FBGs is spaced 5m-20m apart, and the reflection center wavelengths of the sensing FBGs in each group are different, and the sensing FBG reflection wavelength range is 1520nm-1580nm, and the sensing FBG reflectivity is the same; the return light signal reflected by the sensing FBG passes through the second circulator, is filtered by the broadband FBG, and then enters the second photodetector, and is finally collected by the oscilloscope; the return light signal carries external information, and the reference light is cross-correlated with the return light signal, and the wavelength scanning method combined with the dual-wavelength differential demodulation method is used to restore the external information;

[0011] The ytterbium-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 optical fiber is in the range of 2-10 m, and the output power of the tunable erbium-ytterbium co-doped random optical fiber laser is greater than or equal to 100 mW.

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

[0014] The beneficial effects of adopting the above technical solution are:

[0015] 1. The present invention adopts the sixth-order random fiber laser amplification technology, and further combines the random laser amplification technology with remote pumped erbium-doped fiber amplification to form a hybrid amplification technology, which can effectively extend the system's non-relay sensing distance.

[0016] 2. In the traditional FBG sensing system based on correlated optical time domain reflectometry, the semiconductor chaotic light source used has a time delay characteristic. The present invention uses erbium-ytterbium co-doped random fiber laser as the detection light signal, which can avoid the influence of the time delay characteristic on the system sensing performance, and the hybrid amplification method used will not introduce the time delay characteristic.

[0017] 3. The long-distance FBG sensing system of the present invention adopts a hybrid multiplexing method combining time division multiplexing and wavelength division multiplexing to improve the multiplexing capacity of the system. The sensing FBGs are divided into several groups, each group of FBGs is distributed at different positions of the optical fiber, and the central wavelengths of the FBGs in each group are different. Time division multiplexing scheme and wavelength division multiplexing scheme are used for demodulation respectively. Through the multiplexing method of wavelength division multiplexing and time division multiplexing hybrid, each band of the detection light source can be efficiently utilized, greatly improving the number of sensing FBG multiplexing of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural block diagram of the tunable Er-Yb co-doped random fiber laser of the present invention;

[0019] Figure 2 It is a time domain trace diagram and an autocorrelation curve diagram of the output of the tunable Er-Yb co-doped random fiber laser of the present invention;

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

[0021] Figure 3 This is a block diagram of a large-capacity FBG sensing system based on a tunable Er-Yb co-doped random fiber laser according to Embodiment 1 of the present invention;

[0022] Figure 4 This is a block diagram of a long-distance correlated optical time domain reflectometer FBG sensing system based on a novel high-order hybrid amplification method according to the second embodiment of the present invention;

[0023] Figure 5 A long-distance, large-capacity FBG sensing system based on high-order hybrid amplification and wavelength division multiplexing technology according to the third embodiment of the present invention;

[0024] Figure 6 This is a diagram showing the simulation results of the power distribution of large-capacity FBG sensing signals in a 175km link of the present invention;

[0025] Markings in the figure: 1. Tunable Erbium-Ytterbium co-doped random fiber laser; 1-1. 976nm semiconductor laser; 1-2. Tunable filter; 1-3. 1:1 coupler; 1-4. Combiner; 1-5. Erbium-Ytterbium co-doped fiber; 1-6. Second single-mode fiber; 1-7. Isolator; 2. 10:90 coupler; 3. First circulator; 4. First wavelength division multiplexer; 5. Fiber ring mirror; 6. Second wavelength division multiplexer; 7. Ytterbium-doped random fiber laser; 8. 1:99 coupler; 9. First single-mode fiber; 10. Sensing FBG; 11. Erbium-doped fiber; 12. Second circulator; 13. Broadband FBG; 14. First photodetector; 15. Second photodetector; 16. Oscilloscope. DETAILED DESCRIPTION

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

[0027] A long-distance FBG sensing system based on a tunable erbium-ytterbium co-doped random fiber laser comprises a tunable erbium-ytterbium co-doped random fiber laser, a 10:90 coupler, a circulator, a wavelength division multiplexer, a fiber ring 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 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 laser output by the 976nm semiconductor laser into the erbium-ytterbium co-doped optical fiber, two output ports of the 1:1 coupler are connected to the tunable filter to provide wavelength selection point feedback, the erbium-ytterbium co-doped optical fiber provides active gain, the second single-mode optical fiber provides random Rayleigh scattering, and the second single-mode optical fiber is remotely connected to the isolator to ensure unidirectional operation of the optical path.

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

[0030] The working principle of the tunable erbium-ytterbium co-doped random fiber laser: a 976nm semiconductor laser 1-1 is injected into the erbium-ytterbium co-doped fiber 1-5 through the beam combiner 1-4, and 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 signal end of the front-end pump beam combiner is connected to the 1:1 coupler 1-3, and the two output ends of the coupler are connected to the wavelength tunable filter 1-2 to form a filter point feedback, which is used to determine the random fiber laser lasing wavelength. By adopting erbium-ytterbium co-doped gain, low threshold and high efficiency random fiber laser output can be achieved. Further, by adjusting the central wavelength of the tunable filter 1-2, a high-power C-band range wavelength tunable random fiber laser detection light source can be achieved.

[0031] like Figure 2 (a) and (b) show Figure 1 The time domain trace diagram and autocorrelation curve diagram of the random laser output by the tunable Er-Yb 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 delta function-like autocorrelation curve, has good autocorrelation characteristics and no time delay characteristics, which is conducive to further improving the system's sensing distance and positioning accuracy.

[0032] The circulator includes a first circulator 3 and a second circulator 12, and the photodetector includes a first photodetector 14 and a second photodetector 15; the output end of the tunable Er-Yb co-doped random fiber laser is connected to a 10:90 coupler 2, the 90% port of the 10:90 coupler 2 is connected to a port of the first circulator 3, and the 10% port of the 10:90 coupler is connected to the first photodetector 14; the three ports of the first circulator 3 are connected to a port of the second circulator 12, and the two ports of the second circulator 12 are connected to 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 to the first circulator 3 as a signal light;

[0033] The wavelength division multiplexer includes a first wavelength division multiplexer 4 and a second wavelength division multiplexer 6; the three ports of the first circulator 3 are connected to the reflection port of the first wavelength division multiplexer 4, the output end of the ytterbium-doped random fiber laser is connected to 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 fiber 9 to realize distributed random laser amplification, the erbium-doped fiber 11 is located in the first single-mode fiber 9 to realize remote pumping erbium-doped fiber amplification and extend the system sensing distance, wherein the length of the erbium-doped fiber 11 is 15m; the ytterbium-doped random fiber laser provides pumping, the fiber ring mirror 5 provides broadband reflection, the first single-mode fiber provides Rayleigh scattering and Raman gain, and Stokes light of the first to fifth orders is generated in the first single-mode fiber, wherein the fifth-order Stokes light is used as direct pumping to amplify the signal light;

[0034] The FBG sensing system adopts a hybrid multiplexing technology of time division multiplexing technology and wavelength division multiplexing technology. Several groups of sensing FBGs 10 with different reflection wavelengths are arranged at different positions of the first single-mode optical fiber. Each group of sensing FBGs is spaced 5m-20m apart. The reflection center wavelengths of the sensing FBGs 10 in each group are different. The sensing FBG reflection wavelength range is 1520nm-1580nm, and the sensing FBG reflectivity is the same. The return light signal reflected by the sensing FBG passes through the second circulator, is filtered by the broadband FBG, and the residual pump light and cascade Stokes light are filtered out, and then enters the second photodetector 15, and is finally collected by the oscilloscope 16. The return light signal carries external information, and the reference light is cross-correlated with the return light signal, and the wavelength scanning method combined with the dual-wavelength differential demodulation method is used to restore the external information.

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

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

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

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

[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] Example 1

[0041] like Figure 3 As shown, this example is a FBG sensing system based on a tunable Er-Yb co-doped random fiber laser. The tunable Er-Yb 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 to the first port of the circulator 3, the 10% port is connected to the first photodetector 14, the second port of the first circulator 3 is connected to the first single-mode fiber 9, and the third port of the first circulator 3 is connected to 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 set at different positions of the first single-mode fiber 9. The sensing FBG reflection wavelength range is 1520-1580nm.

[0042] Working principle of the present invention: The tunable Er-Yb co-doped random fiber laser 1 can achieve C-band laser output, and the output light is divided into two parts by a 10:90 coupler, wherein the light at the 10% port is detected by the first photodetector 14 as a reference light signal, and the light at the 90% port is sent into the first single-mode optical fiber 9 as a detection light via the first port and the second port of the first circulator 3. The sensing FBG10 is the sensing element of the system. Due to its structural sensitivity, the central wavelength of its reflection spectrum changes with the change of the physical quantity of the external environment. The sensing FBG10 reflects the signal light and makes the backward signal light carry external information. The return light signal is detected by the second photodetector 15 via 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 return light signal are cross-correlated, and the external temperature change is restored by the dual-wavelength differential demodulation method. The reflection spectrum of the sensing FBG10 has a Gaussian line shape:

[0043]

[0044] where λ B represents the central wavelength of the reflection spectrum of the sensing FBG10, and B is the spectral bandwidth. In order to obtain the wavelength drift of the fiber Bragg grating, a dual-wavelength differential algorithm is performed using detection signals of two different wavelengths (λ1 and λ2). The wavelength interval between λ1 and λ2 is defined as Δλ. Since the spectrum of the fiber Bragg grating will drift with changes in temperature or strain, the effective reflectivity of the sensing fiber Bragg grating to the two detection signals will also change accordingly. The intensity of the reflection signal of different wavelengths is expressed as:

[0045]

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

[0047]

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

[0049] Example 2

[0050] like Figure 4 As shown, this example is a long-distance FBG sensing system based on 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 invention 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 an 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 to provide broadband point feedback for the high-order random laser, forming a forward semi-open cavity structure, combined with the stimulated Raman scattering gain and distributed backward Rayleigh scattering feedback in the optical fiber, to achieve one to five orders of cascaded random fiber laser lasing. The generated fifth-order random fiber laser is further used as a direct pump for the C-band detection light and amplified in the optical fiber link. Random laser amplification technology can avoid the time delay characteristics introduced in traditional distributed Raman amplification systems during the amplification process.

[0051] The remote-pumped erbium-doped fiber amplification technology in the long-distance FBG sensing system described in the present invention is a point-type amplification method in which a pump light source and an erbium-doped fiber 11 providing active gain are separated. 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 fiber 9, an erbium-doped fiber 11 and an ytterbium-doped random fiber laser 7. Under the action of the pump light, the signal light first undergoes stimulated Raman scattering amplification, and then is amplified by the residual 1480nm pump in the erbium-doped fiber and transmitted to the tail end of the fiber.

[0052] The amplified backscattered light is transmitted to the front end of the optical fiber link, output by the circulator, filtered by broadband FBG, residual pump light and cascade Stokes light are filtered out, and then injected into the second photodetector 15. By performing cross-correlation calculation on the reference light and the backscattered light, the reflection event of the optical fiber link can be located. Further, by adopting a dual-wavelength differential demodulation method, the peak values ​​of the demodulated cross-correlation functions of the two different wavelength detection light signals are differentially calculated. The peak difference is linearly related to the FBG wavelength drift, and FBG sensing can be realized. Therefore, the present invention adopts a new high-order hybrid amplification method, combined with a wavelength scanning correlated optical time domain reflectometer, to achieve long-distance FBG sensing.

[0053] Example 3

[0054] like Figure 5 As shown, this example is a long-distance, 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, and a high-power tunable erbium-ytterbium co-doped random fiber laser 1 is used to output different wavelength detection light and inject it into the first single-mode optical fiber 9, and different wavelength sensing FBGs 10 are set at the same position in the optical fiber link, and the same wavelength sensing FBGs 10 can be set at different positions to realize the FBG multiplexing method of wavelength division multiplexing and time division multiplexing. The sensor FBG 10 in the optical fiber link can be located by the return time of the backscattered light. By calculating the cross-correlation function of the return light signal detected by the receiving end and the reference light, the cross-correlation strength of the FBG signals at different positions and wavelengths can be obtained. Further, the wavelength scanning method is combined with the dual-wavelength differential demodulation method to achieve 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 1090nm pump with a power of 5.65W is used. When a 15m long erbium-doped fiber is located at 80km of the optical fiber link, and FBGs with a reflectivity of 5% are set at 25km, 37.5km, 50km, 62.5km, 75km, 124km, 136.5km, 149km, 161.5km, and 174km in the 175km optical fiber link, the power distribution of the backscattered signal light is as follows: Figure 5As shown in the figure, it 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 backward Rayleigh scattering signal, and the signal-to-noise ratio is high. Therefore, a long-distance, large-capacity correlated 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 embodiment, by introducing random laser amplification technology and remote pumped erbium-doped fiber amplification technology to amplify the optical signal of the sensing system, the system's relay-free sensing distance can be effectively extended. The FBG multiplexing method that combines wavelength division multiplexing and time division multiplexing is used to improve the FBG multiplexing capacity of the FBG sensing system. By utilizing a hybrid multiplexing method that combines Raman gain with erbium-doped active fiber gain, a high-power tunable erbium-ytterbium co-doped random fiber laser is used to output detection light of different wavelengths and inject it into the sensing optical fiber, which efficiently utilizes the spatial distance of the sensing optical fiber, extends the sensing distance of the system, and increases the number of sensing FBG multiplexing of the system. The simulation results of the power distribution of large-capacity FBG sensing signals in a 175km link in this embodiment are shown in the figure below. Figure 6 shown.

[0057] The above description is only a preferred embodiment of the present disclosure and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the above-mentioned inventive concept. For example, the above-mentioned features are replaced with the technical features with similar functions disclosed in the embodiments of the present disclosure (but not limited to) 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 Er-Yb co-doped random fiber laser, 10:90 coupler, circulator, wavelength division multiplexer, fiber ring mirror, Yb-doped random fiber laser, first single-mode fiber, Er-doped fiber, sensing FBG, broadband FBG, photodetector and oscilloscope; 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 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 Er-Yb co-doped random fiber laser is connected to a 10:90 coupler, the 90% port of the 10:90 coupler is connected to a port of the first circulator, and the 10% port of the 10:90 coupler is connected to the first photodetector; the three ports of the first circulator are connected to a port of the second circulator, and the two ports of the second circulator are connected to a broadband FBG; the light of the 10% port of the 10:90 coupler is detected by the first photodetector as a reference light signal, and the light of the 90% port is sent to the first circulator as a 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, the erbium-doped optical fiber is located in the first single-mode optical fiber, and the length of the erbium-doped optical fiber is 15m.

2. A 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 arranged at different positions of the first single-mode optical fiber. The interval between each group of sensing FBGs is 5m-20m. The reflection center wavelengths of the sensing FBGs in each group are 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 a broadband FBG, then enters a second photodetector, and is finally collected by an oscilloscope. The return light signal carries external information, and a cross-correlation operation is performed between the reference light and the return light signal, and a wavelength scanning method combined with a dual-wavelength differential demodulation method is used to restore the external information.

3. The long-distance FBG sensing system based on 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 ring mirror is connected to the first wavelength division multiplexer through a port.

4. The long-distance FBG sensing system based on 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 optical fiber laser is greater than or equal to 100mW.

5. The long-distance FBG sensing system based on 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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