Gas concentration remote monitoring system

Abstract

The invention relates to a gas concentration remote monitoring system. Comprising a detection probe, a first fiber bragg grating, a second fiber bragg grating, an optical amplifier, a spectrometer and a pumping source, one end of the detection probe is connected with the optical amplifier, and the other end is connected with the second fiber bragg grating; the other end of the optical amplifier is connected with the spectrograph; the other end of the second fiber bragg grating is connected with the first fiber bragg grating; the pumping source is respectively connected with the first fiber bragg grating and the optical amplifier; wherein the detection probe comprises a third fiber bragg grating, a fourth fiber bragg grating and an optical fiber group with micropore modification; two ends of the fiber group are respectively connected with the third fiber bragg grating and the fourth fiber bragg grating. The gas concentration is remotely detected by utilizing the Raman scattering effect and combining with the remote optical amplifier, and the system has the advantages of simple structure, high stability, higher signal remote transmission efficiency and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of gas monitoring, and more specifically, to a gas concentration remote monitoring system. Background Art

[0002] In industrial production processes, many gases such as (chlorine, hydrogen, oxygen, etc.) are often used as raw materials or reaction media. The leakage of certain gases can not only cause serious harm to operators, but also pollute the surrounding environment. Therefore, monitoring systems are particularly critical in these industries to ensure the safety of workers and environmental protection. Most of the existing gas concentration remote detection systems have complex structures, are difficult to install, and are inconvenient for subsequent maintenance.

[0003] In 2011, Lu Ying et al. proposed an active intracavity absorption type acetylene concentration detection system and detection method, which uses acetylene to absorb laser light with a wavelength near its absorption spectrum in the resonant cavity of a photonic crystal fiber, and inverts the acetylene concentration by analyzing the absorbance of acetylene. This method uses gas absorption spectroscopy to detect gas concentration, but the absorption spectrum signal is unstable and may be interfered by other gases or molecules in some cases, which reduces the selectivity of detection and affects the clarity and accuracy of the spectrum. Moreover, after long-distance transmission, the signal is weak and difficult to detect. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art that the gas absorption spectrum is used to detect gas concentration, but the absorption spectrum signal is unstable, which affects the detection accuracy, and to provide a gas concentration remote monitoring system to improve the detection accuracy and stability.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A gas concentration remote monitoring system is provided, comprising a detection probe, a first fiber Bragg grating, a second fiber Bragg grating, an optical amplifier, a spectrometer and a pump source; one end of the detection probe is connected to the optical amplifier, and the other end is connected to the second fiber Bragg grating; the other end of the optical amplifier is connected to the spectrometer; the other end of the second fiber Bragg grating is connected to the first fiber Bragg grating; the pump source is connected to the first fiber Bragg grating and the optical amplifier, respectively; wherein the detection probe comprises a third fiber Bragg grating, a fourth fiber Bragg grating and an optical fiber group with microhole modification; the two ends of the optical fiber group are connected to the third fiber Bragg grating and the fourth fiber Bragg grating, respectively.

[0007] The invention provides a gas concentration remote monitoring system. For a detection probe, a fiber Bragg grating is respectively arranged at both ends of an optical fiber group, the two fiber Bragg gratings form a special resonant cavity, a microhole is arranged on a hollow-core optical fiber, and gas enters the optical fiber from the microhole; when a high-power laser is coupled from a third fiber Bragg grating and incident into the probe, the laser reacts with gas molecules to generate Raman scattering effect and Rayleigh scattering effect, the Raman scattering effect will generate forward Stokes light and backward Stokes light, the backward Stokes light is reflected by the third fiber Bragg grating as forward Stokes light, and the backward Stokes light is reflected by the third fiber Bragg grating as forward Stokes light, while the Rayleigh scattered light and the laser that does not react with gas molecules are repeatedly transmitted in another special "resonant cavity" formed by the first fiber Bragg grating and the second fiber Bragg grating, fully react with gas molecules to generate Raman scattered light, multiple Raman scattered lights are coherently superimposed and output from the first fiber Bragg grating, so that the Raman signal intensity is significantly enhanced, thereby improving the concentration detection sensitivity. The present invention adds a set of fiber Bragg gratings, namely the first fiber Bragg grating and the second fiber Bragg grating, to the transmission optical fiber, so that the pump light source is repeatedly transmitted in this special "resonant cavity", increasing the transmission optical path, thereby enhancing the laser lasing effect. In summary, the use of Raman scattering effect and combined with a remote optical amplifier to remotely detect gas concentration has the advantages of simple system structure, high stability, and higher efficiency of long-distance signal transmission compared to the traditional use of gas absorption spectrum to detect gas concentration.

[0008] Furthermore, the optical fiber group includes multiple sections of photonic crystal optical fibers, which are sequentially connected by glue, and microholes are provided at the connection between each two sections of photonic crystal optical fibers, and the microholes are connected to the internal channels of the photonic crystal optical fibers. Two adjacent sections of photonic crystal fiber cores are connected by specific glue, and microholes are modified at the connection, so that gas can smoothly enter the inner hole of the photonic crystal fiber core from the microholes.

[0009] Furthermore, the optical fiber group includes multiple sections of photonic crystal fiber and multiple sections of hollow core fiber, the photonic crystal fiber and the hollow core fiber are staggered and connected, one section of the hollow core fiber is connected between two adjacent sections of the photonic crystal fiber, and one end of the two outermost sections of the photonic crystal fiber is respectively connected to the third fiber Bragg grating and the fourth fiber Bragg grating; each section of the hollow core fiber is provided with a microhole on the side of the incident end, and the microhole is as deep as the fiber channel. The main function of the photonic crystal fiber is to selectively filter unnecessary light waves by the size of its inner hole, and retain the characteristic Raman light to be measured; ordinary hollow core fiber is used as a connecting material, and two sections of photonic crystal fiber are fused together by a fusion splicer; the microhole is used as a channel for the gas molecules to be measured to enter the inner hole of the photonic crystal fiber. The inner hole of the photonic crystal fiber is used as a transmission channel, which can collect Raman light with extremely high efficiency, and the collection efficiency is several orders of magnitude higher than that of existing probes.

[0010] Furthermore, the first fiber Bragg grating and the second fiber Bragg grating are connected via a single-mode optical fiber; the pump source and the optical amplifier, and the optical amplifier and the spectrometer are connected via a single-mode optical fiber.

[0011] Furthermore, the length of the single-mode optical fiber between the first fiber Bragg grating and the second fiber Bragg grating is at least 30 km. When high-power pump light is transmitted in the transmission optical fiber, the pump light will undergo Raman scattering effect, generating low-frequency Stokes light, and the generated Stokes light will undergo irregular Rayleigh scattering in the transmission optical fiber. When the transmission optical fiber is long enough, the multiple Rayleigh scattering effect of the Stokes light in the long-distance transmission optical fiber is equivalent to a special "resonant cavity", and the high-frequency pump light serves as an excitation source to form a special laser; therefore, the monitoring system provided by the present invention can be used for long-distance gas concentration monitoring, especially for remote monitoring greater than 30 km.

[0012] Furthermore, the length of the single-mode optical fiber between the pump source and the optical amplifier, and between the optical amplifier and the spectrometer is at most 30 km.

[0013] Furthermore, the photonic crystal fiber includes a coating layer, a cladding layer, and a core from the outside to the inside; the core includes a plurality of non-contact hollow silicon tubes, and the plurality of hollow silicon tubes are evenly spaced and distributed along the circumference of the core; the hollow core fiber includes a coating layer, a cladding layer, and a hollow fiber channel from the outside to the inside. The main function of the photonic crystal fiber is to selectively filter unnecessary light waves by the size of its inner hole, and retain the characteristic Raman light to be measured. The scattering cross-sectional area of ​​the characteristic Raman light is small, and the inner hole of the photonic crystal fiber can just well confine it in a narrow pipe, and can collect Raman scattered light with extremely high efficiency, ensuring the accuracy of gas detection; ordinary hollow core fiber is used as a connecting material, and two sections of photonic crystal fiber are fused together by a fusion splicer; micropores are used as channels for the gas molecules to be measured to enter the inner hole of the photonic crystal fiber, and the micropores are on ordinary hollow core fibers.

[0014] Furthermore, the thickness of the coating layer is 55μm to 65μm; the thickness of the cladding layer is 180μm to 220μm; the diameter of the core is 35μm to 45μm; the diameter of the hollow silicon tube is 13μm to 14μm, and the wall thickness is 200nm to 220nm; the diameter of the optical fiber channel is 35μm to 45μm; the diameter of the micropore is 2μm to 4μm; the length of each section of the photonic crystal fiber is 20mm to 40mm; the length of each section of the hollow core fiber is 8mm to 15mm. The size of the probe is not unique, and the parameters are adjusted according to the type of gas molecules to be measured. The most core size is the inner hole diameter of the photonic crystal fiber, which directly determines the accuracy of detecting the gas to be measured and the precision of the concentration of the gas to be measured. In actual gas monitoring applications, the length requirements of the probe are also different. At this time, it is necessary to optimize the parameters of the specific probe length and structural dimensions. The following will briefly introduce the basis for parameter optimization. The probe's micropore diameter, number of micropores, and arrangement all serve the gas diffusion rate. According to existing research theories, the larger the micropore diameter, the greater the number of micropores, and when the micropores are evenly distributed, the shorter the gas diffusion equilibrium time. However, an increase in the diameter and number of micropores will cause an increase in optical fiber transmission loss, and will also make the optical fiber prone to breakage and reduce mechanical stability. Therefore, after comprehensive consideration, the number of micropores is determined to be 6; when the number of micropores is within 10, the optical fiber loss introduced by micropore modification can be ignored.

[0015] Furthermore, the lengths of the third fiber Bragg grating and the fourth fiber Bragg grating are both 8 mm to 15 mm.

[0016] Furthermore, the photonic crystal optical fiber is provided with 7 sections in total; the hollow core optical fiber is provided with 6 sections in total; and each section of the hollow core optical fiber is provided with only one microhole.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] A gas concentration remote monitoring system of the present invention utilizes the Raman scattering effect and combines with a remote optical amplifier to remotely detect gas concentration. Compared with the traditional method of detecting gas concentration using gas absorption spectroscopy, it has the advantages of simple system structure, high stability, and higher efficiency of long-distance signal transmission. In addition, the probe size can be optimized and modified according to needs to monitor different gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the structure of the gas concentration remote monitoring system.

[0020] Figure 2 Schematic diagram of the structural principle between multiple resonant cavities in the gas concentration remote monitoring system.

[0021] Figure 3 Schematic diagram of the probe structure in the gas concentration remote monitoring system.

[0022] Figure 4 Schematic diagram of the photonic crystal fiber structure in the gas concentration remote monitoring system.

[0023] Figure 5 Schematic diagram of the hollow-core optical fiber structure in the gas concentration remote monitoring system.

[0024] Figure 6 is the Raman gain curve of the optical fiber.

[0025] In the attached drawings: 1. probe; 11. third fiber Bragg grating; 12. fourth fiber Bragg grating; 13. photonic crystal fiber; 14. hollow core fiber; 15. microhole; 16. coating layer; 17. cladding; 18. fiber channel; 19. hollow silicon tube; 2. first fiber Bragg grating; 3. second fiber Bragg grating; 4. optical amplifier; 5. spectrometer; 6. pump source. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with specific implementation methods. The accompanying drawings are only used for exemplary descriptions and are only schematic diagrams, not actual drawings, and cannot be understood as limiting this patent; in order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the accompanying drawings may be omitted.

[0027] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limitations on this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0028] Embodiment 1:

[0029] like Figures 1 to 5 As shown, this embodiment is a first embodiment of a gas concentration remote monitoring system, comprising a detection probe 1, a first fiber Bragg grating 2, a second fiber Bragg grating 3, an optical amplifier 4, a spectrometer 5 and a pump source 6; one end of the detection probe 1 is connected to the optical amplifier 4, and the other end is connected to the second fiber Bragg grating 3; the other end of the optical amplifier 4 is connected to the spectrometer 5; the other end of the second fiber Bragg grating 3 is connected to the first fiber Bragg grating 2; the pump source 6 is respectively connected to the first fiber Bragg grating 2 and the optical amplifier 4; wherein the detection probe 1 comprises a third fiber Bragg grating 11, a fourth fiber Bragg grating 12 and an optical fiber group modified with microholes 15; the two ends of the optical fiber group are respectively connected to the third fiber Bragg grating 11 and the fourth fiber Bragg grating 12.

[0030] The present invention provides a gas concentration remote monitoring system. For a detection probe 1, a fiber Bragg grating is respectively arranged at both ends of an optical fiber group, and the two fiber Bragg gratings form a special resonant cavity. A microhole 15 is arranged on a hollow-core optical fiber 14, and gas enters the optical fiber from the microhole 15. When a high-power laser is coupled from a third fiber Bragg grating 11 and incident into the probe 1, the laser reacts with gas molecules to generate Raman scattering effect and Rayleigh scattering effect, and the Raman scattering effect generates forward Stokes light and backward Stokes light. The backward Stokes light is reflected by the third fiber Bragg grating 11 as forward Stokes light, and the backward Stokes light is reflected by the third fiber Bragg grating 11 as forward Stokes light. At the same time, the Rayleigh scattered light and the laser that does not react with the gas molecules are repeatedly transmitted in another special "resonant cavity" formed by the first fiber Bragg grating 2 and the second fiber Bragg grating 3, and fully react with the gas molecules to generate Raman scattered light. Multiple Raman scattered lights are coherently superimposed and output from the first fiber Bragg grating 2, so that the Raman signal intensity is significantly enhanced, thereby improving the concentration detection sensitivity. The present invention adds a set of fiber Bragg gratings, namely the first fiber Bragg grating 2 and the second fiber Bragg grating 3, to the transmission optical fiber, so that the pump light source is repeatedly transmitted in this special "resonant cavity", increasing the transmission optical path, thereby enhancing the laser lasing effect. In summary, the use of Raman scattering effect and combined with a remote optical amplifier to remotely detect gas concentration has the advantages of simple system structure, high stability, and higher efficiency of long-distance signal transmission compared to the traditional use of gas absorption spectrum to detect gas concentration.

[0031] Specific as Figure 3 As shown, the optical fiber group includes multiple sections of photonic crystal fiber 13 and multiple sections of hollow core fiber 14, the photonic crystal fiber 13 and the hollow core fiber 14 are staggered and connected, a section of hollow core fiber 14 is connected between two adjacent sections of photonic crystal fiber 13, and one end of the two outermost sections of photonic crystal fiber 13 is connected to the third fiber Bragg grating 11 and the fourth fiber Bragg grating 12 respectively; each section of hollow core fiber 14 is provided with a micro hole 15 on the side of the incident end, and the micro hole 15 is as deep as the fiber channel 18. The main function of the photonic crystal fiber 13 is to selectively filter unnecessary light waves by the size of its inner hole, and retain the characteristic Raman light to be measured; the ordinary hollow core fiber is used as a connecting material, and the two sections of photonic crystal fiber 13 are fused together by a fusion splicer; the micro hole 15 is used as a channel for the gas molecules to be measured to enter the inner hole of the photonic crystal fiber 13, and the inner hole of the photonic crystal fiber 13 is used as a transmission channel, which can collect Raman light with extremely high efficiency, and the collection efficiency is several orders of magnitude higher than that of the existing probe 1.

[0032] like Figure 1As shown, the first fiber Bragg grating 2 and the second fiber Bragg grating 3 are connected by a single-mode fiber; the pump source 6 and the optical amplifier 4, and the optical amplifier 4 and the spectrometer 5 are connected by a single-mode fiber; the length of the single-mode fiber between the pump source 6 and the optical amplifier 4, and the optical amplifier 4 and the spectrometer 5 is at most 30 km. The length of the single-mode fiber between the first fiber Bragg grating 2 and the second fiber Bragg grating 3 is at least 30 km. When high-power pump light is transmitted in the transmission fiber, the pump light will undergo Raman scattering effect to generate low-frequency Stokes light. The generated Stokes light will undergo irregular Rayleigh scattering in the transmission fiber. When the transmission fiber is long enough, the multiple Rayleigh scattering effect of the Stokes light in the long-distance transmission fiber is equivalent to a special "resonant cavity". The high-frequency pump light serves as an excitation source to constitute a special laser; therefore, the monitoring system provided by the present invention can be used for long-distance gas concentration monitoring, especially for remote monitoring greater than 30 km.

[0033] like Figure 4 and Figure 5 As shown, the photonic crystal fiber 13 includes a coating layer 16, a cladding layer 17 and a core from the outside to the inside; the core includes a plurality of non-contact hollow silicon tubes 19, and the plurality of hollow silicon tubes 19 are evenly spaced and distributed along the circumference of the core; the hollow core fiber 14 includes a coating layer 16, a cladding layer 17, and a hollow fiber channel 18 from the outside to the inside. The main function of the photonic crystal fiber 13 is to selectively filter unnecessary light waves by the size of its inner hole, and retain the characteristic Raman light to be measured. The scattering cross-sectional area of ​​the characteristic Raman light is small, and the inner hole of the photonic crystal fiber 13 can just well confine it in a narrow pipe, and can collect Raman scattered light with extremely high efficiency, ensuring the accuracy of gas detection; the ordinary hollow core fiber is used as a connecting material, and two sections of the photonic crystal fiber 13 are fused together by a fusion splicer; the microhole 15 is used as a channel for the gas molecules to be measured to enter the inner hole of the photonic crystal fiber 13, and the microhole 15 is on the ordinary hollow core fiber.

[0034] The working principle of a gas concentration remote monitoring system in this embodiment is as follows:

[0035] The gas concentration remote monitoring system provided in this embodiment combines the structural features of optical fiber sensing technology, Raman scattering technology, photonic crystal fiber 13 modified by microhole 15, multiple groups of specific fiber Bragg gratings and remote gain units. Different concentrations of the gas to be measured are introduced near the photonic crystal fiber 13 (probe 1) modified by microhole 15, and then a group of fiber Bragg gratings resonate and self-excite to generate a high-power laser of a specific wavelength by remote pump light. The laser and the gas molecules to be measured are confined within the range of the probe 1 by another group of specific fiber Bragg gratings to form a resonant cavity. The two fully interact to scatter a strong Raman signal light, which is further amplified and compensated by EDFA and transmitted to the receiving end over a long distance for Raman spectrum analysis. After that, different concentrations of gas are introduced separately and multiple experiments are performed to obtain the linear relationship between gas concentration and Raman signal light intensity. In actual monitoring, by detecting the Raman signal light intensity of the gas to be measured at the receiving end, and combining the relationship between the two, the concentration of the gas to be measured near the probe 1 can be inferred.

[0036] like Figure 1 As shown in the figure, it is a schematic diagram of the system structure of this embodiment, where the gas to be measured is Cl 2 To explain, according to Cl 2 The characteristic Raman light wavelength frequency shift range is within 550-600nm. The specific value will vary slightly according to the experimental conditions and instrument accuracy. In this embodiment, the middle value of 575nm is taken. The specific wavelength parameter (575nm) of the Bragg grating selected at both ends of the probe 1 is thus determined. The optical fiber modified with the surface microholes 15 is used as the probe 1. A group of Bragg gratings are placed at both ends of the probe 1, wherein the third fiber Bragg grating 11 (FBGa) has a reflectivity of 0.01 for 1064nm wavelength light and a reflectivity of 0.99 for 575nm light, which is equivalent to total reflection; the other fourth fiber Bragg grating 12 (FBGb) has a reflectivity of 0.99 for 1064nm wavelength light and a reflectivity of 0.01 for 575nm wavelength light. This pair of fiber Bragg gratings forms a special "resonant cavity". When a high-power laser with a wavelength of 1064nm is coupled from FBGa and incident into the interior of the probe 1, the laser interacts with gas molecules to produce Raman scattering and Rayleigh scattering effects. The Raman scattering effect will produce forward Stokes and backward Stokes light. The backward Stokes light is reflected by FBGa as forward Stokes light. At the same time, the Rayleigh scattered light and the laser that has not interacted with the gas molecules are repeatedly transmitted in another special "resonant cavity" formed by the first fiber Bragg grating 2FBG1 (the reflectivity of 1064nm wavelength light is 0.99, and the reflectivity of 964nm wavelength light is 0.01) and the second fiber Bragg grating 3FBGb, which fully interacts with gas molecules to produce Raman scattered light. Multiple Raman scattered lights are coherently superimposed and output from FBG1, which significantly enhances the Raman signal intensity, thereby improving the concentration detection sensitivity. At this time, different concentrations of Cl are introduced into the gas chamber. 2Gas molecules diffuse freely from micropores 15 to the inside of hollow silicon tube 19. At this time, high-power pump light of a specific wavelength (1064nm) is coupled from one end of probe 1 (advantage: the laser of this wavelength is in the infrared region, and chlorine molecules rarely have an absorption spectrum at this wavelength, which can avoid overlapping with the spectrum of chlorine itself). When different concentrations of Cl 2 When the laser and gas molecules fully interact in the probe 1, they will output chlorine characteristic Raman light of different powers. By analyzing the peak intensity of the characteristic Raman light, the concentration of Cl 2 Repeat the experiment to find the average value, and finally process the data to obtain Cl 2 The relationship between concentration and characteristic Raman light peak intensity. Finally, probe 1 is placed in the test environment to infer Cl from this relationship. 2 Concentration. Figure 2 , which is a schematic diagram of the structural relationship of several key resonant cavities in the remote monitoring system provided in this embodiment.

[0037] Next, we will introduce how to obtain the 1064nm wavelength laser:

[0038] According to the principle of random fiber lasers: when the transmission fiber transmits high-power pump light, if the pump input fiber light power is large enough, the pump light energy output by the transmission fiber will drop sharply and generate high-power Stokes light. The pump light energy is transferred to the Stokes light generated by Raman scattering. This phenomenon is defined as the stimulated Raman effect. The working mechanism of random fiber lasers is a typical stimulated Raman effect. When the transmission fiber is long enough, the multiple Rayleigh scattering effect of Stokes light in the transmission fiber is equivalent to a special "resonant cavity". The high-frequency pump light serves as an excitation source to form a special laser. When the transmitted pump light power is greater than the lasing threshold power, the transmitted pump light will undergo stimulated Raman lasing and generate laser light. Figure 6 As shown in the figure, the Raman gain curve of G.652 optical fiber shows that the Stokes light gain is the largest when the pump light has a wavelength difference of 100nm. When high-power pump light is input into the working medium of the random fiber laser, the random fiber laser will quickly produce a "longitudinal mode competition effect" similar to that of a traditional laser, and then stably output a laser with a wavelength difference of 100nm from the pump light. Therefore, a high-power pump light with a wavelength of 964nm is selected as the laser excitation source, and a single-mode optical fiber is used for the transmission optical fiber. A set of fiber Bragg gratings FBG1 and FBG2 (with a reflectivity of 0.99 for 964nm wavelength light and a reflectivity of 0.01 for 1064nm wavelength light) is added to the transmission optical fiber, so that the pump light source is repeatedly transmitted in this special "resonant cavity", increasing the transmission optical path, thereby enhancing the laser lasing effect.

[0039] In this embodiment, the optical amplifier 4 (EDFA) is an optical device for amplifying optical signals. Its full name is "Erbium-Doped Fiber Amplifier". Its working principle is mainly to use erbium-doped optical fiber as a gain medium, and to excite the erbium ions in the optical fiber through a pump light source to make it transition to a high energy level. When an external input signal passes through, the signal will be amplified due to the transition amplification effect of the erbium ions. In this way, the amplification of the optical signal is achieved, which plays a role in enhancing the intensity of the optical signal and improving the transmission distance and quality of the optical fiber communication system. Therefore, EDFA plays a vital role in the optical fiber communication system. The wavelength of the remote pump gain light source is generally 1480nm.

[0040] Most existing gas detection systems have complex structures, and have both circuits and optical paths, which are difficult to install and maintain later. The present embodiment has the advantages of simple system structure, easy installation and low cost.

[0041] Most existing gas detection devices use gas absorption spectroscopy to detect gas concentration, but the absorption spectrum signal is unstable and may be interfered by other gases or molecules in some cases, which reduces the selectivity of detection and affects the clarity and accuracy of the spectrum. This embodiment uses Raman spectroscopy to detect gas concentration, which has high selectivity and stability.

[0042] In the prior art, most long-distance transmission of optical signals adopts the light-electric-light conversion method, which means that a relay station must be established in the middle to amplify and compensate the optical signal for long-distance transmission. However, the maintenance cost of the relay station is high, which is not conducive to long-distance transmission systems. This embodiment adopts a remote pump transmission system to achieve long-distance transmission of optical signals. The remote gain unit only has a simple light-light amplification process and no complex photoelectric conversion process. Therefore, the remote gain unit has a simple structure, low requirements on external application conditions, and low subsequent maintenance costs.

[0043] Embodiment 2:

[0044] The other structures of this embodiment are the same as those of embodiment 1, except that, in this embodiment, two adjacent sections of the photonic crystal core are connected by using a specific glue, and the micropores 15 are modified at the connection, so that the gas can smoothly enter the inner hole of the photonic crystal core from the micropores 15. Of course, in addition to the two groups of methods provided in embodiment 1 and this embodiment, other connection methods can also be used. The most important thing is that no matter which connection method is used, the micropores 15 need to be modified at the connection to ensure that the gas molecules can smoothly enter the inner hole of the photonic crystal fiber 13.

[0045] Embodiment 3:

[0046] Based on Example 1, this embodiment provides specific parameter data of the gas detection probe 1, so that it can be applied to the detection of chlorine. In this embodiment, the thickness of the coating layer 16 is 55μm to 65μm; the thickness of the cladding 17 is 180μm to 220μm; the diameter of the core is 35μm to 45μm; the diameter of the hollow silicon tube 19 is 13μm to 14μm, and the wall thickness is 200nm to 220nm; the diameter of the optical fiber channel 18 is 35μm to 45μm. There are 6 hollow silicon tubes 19. The diameter of the microhole 15 is 2μm to 4μm. The diameter of the microhole 15 is 2μm to 4μm, which can ensure the drilling accuracy, and has a shorter balancing time and lower loss. The length of each section of the photonic crystal fiber 13 is 20mm to 40mm; the length of each section of the hollow core optical fiber 14 is 8mm to 15mm. The lengths of the third fiber Bragg grating 11 and the fourth fiber Bragg grating 12 are both 8mm to 15mm. There are 7 sections of photonic crystal fiber 13 and 6 sections of hollow core fiber 14. Each section of hollow core fiber 14 is provided with a microhole 15, and 6 sections of hollow core fiber 14 have 6 microholes 15 in total. This number can avoid the loss of optical fiber transmission caused by the microholes 15 and ensure the stability of the entire probe 1 structure to avoid breakage.

[0047] In this embodiment, if Figure 3 As shown, the entire probe 1 is 0.29m long and is formed by fusion splicing 7 sections of photonic crystal fiber 13, 6 sections of hollow core fiber 14 modified by microholes 15, and a fiber Bragg grating (FBG) at each end. Each section of photonic crystal fiber 13 is 30mm long and has a diameter of about 560μm; each section of hollow core fiber 14 modified by microholes 15 is 10mm long and has a diameter of about 560μm, the diameter of the microholes 15 is 3μm, the layout is average drilling, the spacing between microholes 15 is 40mm, and the number of microholes 15 is 6; the length of the third fiber Bragg grating 11 and the fourth fiber Bragg grating 12 is 10mm.

[0048] like Figure 4 As shown, the inner wall of the cladding 17 of the photonic crystal fiber 13 is composed of 6 non-contact hollow silicon tubes 19 (diameter 14.37μm, wall thickness 210nm, spacing 5μm) evenly arranged around the core, the core diameter is 39μm, the coating layer 16 thickness is about 60μm, the cladding 17 thickness is about 200μm, and the optical fiber transmission wavelength is 575nm.

[0049] like Figure 5 As shown, the coating layer 16 of the hollow core optical fiber 14 has a thickness of about 60 μm, the cladding 17 has a thickness of about 200 μm, the hollow core tube has a diameter of about 39 μm, and the microhole 15 has a diameter of 3 μm.

[0050] This embodiment is only used as a reference, and other gases can be detected by modifying various parameter data of the probe 1. The detection principles of different gases are similar and will not be listed here one by one.

[0051] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0052] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A gas concentration remote monitoring system, characterized in that: The invention comprises a detection probe (1), a first fiber Bragg grating (2), a second fiber Bragg grating (3), an optical amplifier (4), a spectrometer (5) and a pump source (6); one end of the detection probe (1) is connected to the optical amplifier (4), and the other end is connected to the second fiber Bragg grating (3); the other end of the optical amplifier (4) is connected to the spectrometer (5); the other end of the second fiber Bragg grating (3) is connected to the first fiber Bragg grating (3); the pump source (6) is connected to the first fiber Bragg grating (2) and the optical amplifier (4) respectively; wherein the detection probe (1) comprises a third fiber Bragg grating (11), a fourth fiber Bragg grating (12) and an optical fiber group modified with microholes (15); the two ends of the optical fiber group are connected to the third fiber Bragg grating (11) and the fourth fiber Bragg grating (12) respectively.

2. The gas concentration remote monitoring system according to claim 1, characterized in that: The optical fiber group comprises a plurality of sections of photonic crystal optical fibers (13), the plurality of sections of the photonic crystal optical fibers (13) are connected in sequence by glue, and a microhole (15) is provided at the connection between every two sections of the photonic crystal optical fibers (13), the microhole (15) being connected to an internal channel of the photonic crystal optical fibers (13).

3. The gas concentration remote monitoring system according to claim 1, characterized in that: The optical fiber group comprises a plurality of sections of photonic crystal optical fibers (13) and a plurality of sections of hollow core optical fibers (14); the photonic crystal optical fibers (13) and the hollow core optical fibers (14) are connected in an interlaced manner; a section of the hollow core optical fiber (14) is connected between two adjacent sections of the photonic crystal optical fibers (13); one end of the two outermost sections of the photonic crystal optical fibers (13) is respectively connected to the third fiber Bragg grating (11) and the fourth fiber Bragg grating (12); a microhole (15) is provided on the side surface of the incident end of each section of the hollow core optical fiber (14), and the microhole (15) is as deep as the optical fiber channel (18).

4. The gas concentration remote monitoring system according to claim 3, characterized in that: The first fiber Bragg grating (2) and the second fiber Bragg grating (3) are connected via a single-mode optical fiber; the pump source (6) and the optical amplifier (4), and the optical amplifier (4) and the spectrometer (5) are connected via a single-mode optical fiber.

5. The gas concentration remote monitoring system according to claim 4, characterized in that: The length of the single-mode optical fiber between the first fiber Bragg grating (2) and the second fiber Bragg grating (3) is at least 30 km.

6. The gas concentration remote monitoring system according to claim 5, characterized in that: The length of the single-mode optical fiber between the pump source (6) and the optical amplifier (4), and between the optical amplifier (4) and the spectrometer (5) is at most 30 km.

7. The gas concentration remote monitoring system according to any one of claims 3 to 6, characterized in that: The photonic crystal optical fiber (13) comprises, from the outside to the inside, a coating layer (16), a cladding layer (17), and a core; the core comprises a plurality of non-contact hollow silica tubes (19), and the plurality of hollow silica tubes (19) are evenly spaced and distributed along the circumference of the core; the hollow core optical fiber (14) comprises, from the outside to the inside, a coating layer (16), a cladding layer (17), and a hollow optical fiber channel (18).

8. The gas concentration remote monitoring system according to claim 7, characterized in that: The coating layer (16) has a thickness of 55 μm to 65 μm; the cladding layer (17) has a thickness of 180 μm to 220 μm; the core has a diameter of 35 μm to 45 μm; the hollow silicon tube (19) has a diameter of 13 μm to 14 μm, and a wall thickness of 200 nm to 220 nm; the optical fiber channel (18) has a diameter of 35 μm to 45 μm; the microhole (15) has a diameter of 2 μm to 4 μm; the length of each section of the photonic crystal optical fiber (13) is 20 mm to 40 mm; the length of each section of the hollow core optical fiber (14) is 8 mm to 15 mm.

9. The gas concentration remote monitoring system according to claim 8, characterized in that: The lengths of the third fiber Bragg grating (11) and the fourth fiber Bragg grating (12) are both 8 mm to 15 mm.

10. The gas concentration remote monitoring system according to claim 8, characterized in that: The photonic crystal optical fiber (13) is provided with 7 sections in total; the hollow core optical fiber (14) is provided with 6 sections in total; and each section of the hollow core optical fiber (14) is provided with only one microhole (15).

Images