Gas detection probe

Abstract

The utility model relates to the technical field of gas concentration detection, in particular to a gas detection probe which comprises a first fiber bragg grating, a fiber group and a second fiber bragg grating, one end of the fiber group is connected with the first fiber bragg grating, and the other end is connected with the second fiber bragg grating; the optical fiber group comprises multiple sections of photonic crystal optical fibers and multiple sections of hollow-core optical fibers, the photonic crystal optical fibers and the hollow-core optical fibers are connected in a staggered mode, one section of hollow-core optical fiber is connected between every two adjacent sections of photonic crystal optical fibers, and one ends of the two sections of photonic crystal optical fibers on the outermost side are connected with the first optical fiber bragg grating and the second optical fiber bragg grating respectively; the side surface of the incident end of each section of hollow fiber is provided with a micropore, and the micropore is deep to the pore channel of the fiber. The Raman scattering effect and the Rayleigh scattering effect are generated under the action of laser and gas molecules, so that the Raman signal intensity is obviously enhanced, and the concentration detection sensitivity is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of gas concentration detection, and more specifically, to a gas detection probe. Background Art

[0002] In industrial production processes, many gases, such as chlorine, hydrogen, and oxygen, are often used as raw materials or reaction media. Leakage of certain gases can not only cause serious harm to operators but also pollute the surrounding environment. Therefore, monitoring systems are crucial in these industries to ensure worker safety and environmental protection. Existing remote gas concentration monitoring systems are often complex, difficult to install, and inconvenient to maintain.

[0003] In 2011, Lu Ying et al. proposed an active intracavity absorption-based acetylene concentration detection system and method. This system utilizes acetylene's absorption of laser light at wavelengths near its absorption spectrum within a photonic crystal fiber resonant cavity. The system then analyzes the absorbance to determine the acetylene concentration. This method uses gas absorption spectroscopy to detect gas concentration, but the absorption spectrum signal is unstable and, in some cases, can be interfered with by other gases or molecules, reducing detection selectivity and affecting the clarity and accuracy of the spectrum. Utility Model Content

[0004] The purpose of the utility model is to overcome the shortcomings of the prior art that the gas absorption spectrum signal is unstable and affects the detection accuracy, and to provide a gas detection probe to effectively improve the accuracy of gas detection.

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

[0006] A gas detection probe is provided, comprising a first fiber Bragg grating, an optical fiber group, and a second fiber Bragg grating; one end of the optical fiber group is connected to the first fiber Bragg grating, and the other end is connected to the second fiber Bragg grating; the optical fiber group comprises multiple sections of photonic crystal fiber and multiple sections of hollow-core fiber, the photonic crystal fiber and the hollow-core fiber are interlaced, a 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 connected to the first fiber Bragg grating and the second fiber Bragg grating, respectively; a microhole is provided on the side of the incident end of each section of the hollow-core fiber, and the microhole is deep enough to reach the fiber channel.

[0007] The utility model provides a gas detection probe. The function of the photonic crystal fiber is mainly to selectively filter unnecessary light waves according to the size of its inner hole, and retain the characteristic Raman light to be detected. The 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 micropore serves as a channel for the gas molecules to be detected 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. The collection efficiency is several orders of magnitude higher than that of existing probes. A fiber Bragg grating (FBG) is set at each end of the optical fiber group. These two FBGs form a special resonant cavity. Microholes are set in the hollow-core optical fiber, and gas enters the optical fiber through the microholes. When high-power laser is coupled from the first FBG into the interior of the probe, the laser interacts with gas molecules to produce Raman scattering and Rayleigh scattering effects. The Raman scattering effect produces forward Stokes and backward Stokes light. The backward Stokes light is reflected by the first FBG as forward Stokes light, which fully interacts with gas molecules to produce Raman scattered light, significantly enhancing the Raman signal intensity and thus improving the concentration detection sensitivity. In addition, the number and length of the photonic crystal fiber and hollow-core optical fiber segments, as well as the dimensions of the microholes and hollow silicon tubes, can be modified and adjusted according to needs. Different size parameters can detect different gases, and have a wide range of applications.

[0008] Furthermore, each hollow-core optical fiber segment is provided with only one micropore. The diameter, number, and arrangement of the probe's micropores all contribute to the gas diffusion rate. According to existing research theory, larger micropore diameters, greater micropore numbers, and evenly distributed micropores shorten the gas diffusion equilibrium time. However, increasing the micropore diameter and number can increase optical fiber transmission loss, making the fiber more susceptible to breakage and reducing mechanical stability.

[0009] Furthermore, the photonic crystal fiber includes a coating layer, a cladding layer and a core in sequence from the outside to the inside; the core includes a plurality of non-contact hollow silica tubes, and the plurality of hollow silica tubes are evenly spaced along the circumference of the core.

[0010] Furthermore, the hollow-core optical fiber includes a coating layer, a cladding layer, and a hollow-core optical fiber channel from the outside to the inside.

[0011] The primary function of photonic crystal fiber is to selectively filter unwanted light waves through the size of its inner pore, retaining the characteristic Raman light that passes through. The characteristic Raman light has a small scattering cross-sectional area, and the inner pore of the photonic crystal fiber is perfectly suited to confine it within a narrow pipe. This allows for highly efficient collection of Raman scattered light, ensuring accurate gas detection. Conventional hollow-core fiber is used as a connecting material, fusing two sections of photonic crystal fiber together using a fusion splicer. The micropore serves as a channel for the gas molecules to be measured to enter the inner pore of the photonic crystal fiber. Using the inner pore of the photonic crystal fiber as a transmission channel allows for highly efficient collection of Raman light, with collection efficiency exceeding that of existing probes by several orders of magnitude.

[0012] Furthermore, the thickness of the coating layer is 55μm to 65μm; the thickness of the cladding is 180μm to 220μm; the diameter of the fiber core is 35μm to 45μm; the diameter of the hollow silica tube is 13μm to 14μm, and the wall thickness is 200nm to 220nm; the diameter of the optical fiber channel is 35μm to 45μm.

[0013] Furthermore, there are 6 hollow silicon tubes.

[0014] Furthermore, the diameter of the micropore is 2 μm to 4 μm. The micropore diameter is 2 μm to 4 μm, which can ensure high drilling accuracy, short balancing time and low loss.

[0015] Furthermore, the length of each section of the photonic crystal fiber is 20 mm to 40 mm; the length of each section of the hollow-core fiber is 8 mm to 15 mm.

[0016] Furthermore, the lengths of the first fiber Bragg grating and the second fiber Bragg grating are both 8 mm to 15 mm.

[0017] Furthermore, the photonic crystal fiber has a total of 7 sections, and the hollow-core fiber has a total of 6 sections. Each hollow-core fiber section has a microhole, and the six hollow-core fiber sections have a total of 6 microholes. This number can avoid the loss of optical fiber transmission caused by microholes while ensuring the stability of the entire probe structure and preventing breakage.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] The utility model provides a gas detection probe that utilizes an optical fiber group and fiber Bragg gratings at both ends to form a specific resonant cavity, and utilizes the interaction between laser and gas molecules to generate Raman scattering effect and Rayleigh scattering effect, so that the Raman signal intensity is significantly enhanced, thereby improving the concentration detection sensitivity; in addition, the number and length of the photonic crystal fiber and hollow-core optical fiber, as well as the size of the micropore and hollow silicon tube, can be modified and adjusted according to demand. Different size parameters can detect different gases, and the application range is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural diagram of the gas detection probe;

[0021] Figure 2 This is a schematic diagram of the structure of the photonic crystal core of the gas detection probe;

[0022] Figure 3 Schematic diagram of the structure of the hollow-core optical fiber of the gas detection probe.

[0023] Figure 4 Schematic diagram of a remote monitoring system when gas detection probes are used for chlorine gas detection.

[0024] In the accompanying drawings: 1. First fiber Bragg grating; 2. Second fiber Bragg grating; 3. Photonic crystal fiber; 4. Hollow-core fiber; 5. Microhole; 6. Fiber channel; 7. Coating layer; 8. Cladding; 9. Hollow silica tube; 100. Probe; 200. Gas chamber; 300. Optical amplifier; 400. Spectrometer; 500. Pump source; 600. Single-mode fiber. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with specific embodiments. The accompanying drawings are for illustrative purposes only and are schematic, not actual, representations. They should not be construed as limiting this patent. To better illustrate the embodiments of the present invention, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted from the drawings.

[0026] 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 so on indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0027] Example 1

[0028] This embodiment is a first embodiment of a gas detection probe 100, comprising a first fiber Bragg grating 1, an optical fiber group, and a second fiber Bragg grating 2; one end of the optical fiber group is connected to the first fiber Bragg grating 1, and the other end is connected to the second fiber Bragg grating 2; the optical fiber group comprises multiple sections of photonic crystal fibers 3 and multiple sections of hollow-core fibers 4, the photonic crystal fibers 3 and the hollow-core fibers 4 are interlaced, a section of the hollow-core fibers 4 is connected between two adjacent sections of the photonic crystal fibers 3, and one end of the two outermost sections of the photonic crystal fibers 3 is connected to the first fiber Bragg grating 1 and the second fiber Bragg grating 2, respectively; a microhole 5 is provided on the side surface of the incident end of each section of the hollow-core fiber 4, and the microhole 5 is deep into the fiber channel 6.

[0029] The present invention provides a gas detection probe 100. The photonic crystal fiber 3 mainly functions to selectively filter unnecessary light waves by the size of its inner hole, retaining the characteristic Raman light to be detected. Ordinary hollow-core optical fiber is used as a connecting material, and two sections of photonic crystal fiber 3 are fused together by a fusion splicer. The micropore 5 serves as a channel for the gas molecules to be detected to enter the inner hole of the photonic crystal fiber 3. By using the inner hole of the photonic crystal fiber 3 as a transmission channel, Raman light can be collected with extremely high efficiency, and the collection efficiency is several orders of magnitude higher than that of the existing probe 100. A fiber Bragg grating is set at each end of the optical fiber group. These two fiber Bragg gratings form a special resonant cavity. A microhole 5 is set on the hollow-core optical fiber 4, and the gas enters the interior of the optical fiber through the microhole 5. When a high-power laser is coupled from the first fiber Bragg grating 1 to the interior of the probe 100, the laser interacts with the gas molecules to produce Raman scattering effect and Rayleigh scattering effect. The Raman scattering effect will produce forward Stokes and backward Stokes light. The backward Stokes light is reflected by the first fiber Bragg grating 1 as forward Stokes light, which fully interacts with the gas molecules to produce Raman scattered light, so that the Raman signal intensity is significantly enhanced, thereby improving the concentration detection sensitivity. In addition, the number and length of the photonic crystal fiber 3 and the hollow-core optical fiber 4, as well as the dimensions of the microhole 5 and the hollow silicon tube 9 can be modified and adjusted according to needs. Different size parameters can be used to detect different gases, and the application range is wide.

[0030] In this embodiment, each section of hollow-core optical fiber 4 is provided with only one microhole 5. The diameter, number, and arrangement of the microholes 5 in the probe 100 all serve to control the gas diffusion rate. According to existing research theory, larger microhole 5 diameters, greater number of microholes 5, and evenly distributed microholes shorten the gas diffusion equilibrium time. However, increasing the diameter and number of microholes 5 can increase optical fiber transmission loss, susceptibility to fiber breakage, and reduced mechanical stability.

[0031] The photonic crystal fiber 3 comprises, from the outside in, a coating 7, a cladding 8, and a core. The core comprises multiple non-contact hollow silica tubes 9, which are evenly spaced along the circumference of the core. The hollow-core fiber 4 comprises, from the outside in, a coating 7, a cladding 8, and a hollow fiber channel 6.

[0032] The primary function of the photonic crystal fiber 3 is to selectively filter unwanted light waves through the size of its inner pore, retaining the characteristic Raman light to be detected. The characteristic Raman light has a small scattering cross-sectional area, and the inner pore of the photonic crystal fiber 3 perfectly confines it within a narrow pipe, allowing for highly efficient collection of Raman scattered light and ensuring accurate gas detection. Conventional hollow-core fiber serves as the connecting material, fusing two sections of photonic crystal fiber 3 together using a fusion splicer. The micropore 5 serves as a channel for the gas molecules to be detected to enter the inner pore of the photonic crystal fiber 3. Using the inner pore of the photonic crystal fiber 3 as a transmission channel allows for extremely efficient collection of Raman light, exceeding the efficiency of existing probes by several orders of magnitude.

[0033] Principle: A set of specific fiber Bragg gratings (FBGs) is placed at both ends of a short-distance transmission optical fiber. The incident light oscillates continuously back and forth between the two gratings, increasing the intensity of the excitation light and the number of molecules participating in Raman scattering. As the laser travels back and forth within the resonant cavity, it enhances the laser intensity and effective optical path length, allowing it to fully interact with sample molecules, significantly increasing the number of molecules participating in Raman scattering. This effect is similar to the superposition of multiple Rayleigh scattering effects in long-distance transmission optical fibers in random fiber lasers, ultimately outputting a beam of light with a specific wavelength. When high-power laser light is coupled from the first FBG 1 into the probe 100, it interacts with gas molecules to produce Raman and Rayleigh scattering effects. The Raman scattering effect generates forward Stokes and backward Stokes light. The backward Stokes light is reflected by the first FBG 1 as forward Stokes light, which fully interacts with gas molecules to generate Raman scattered light, significantly enhancing the Raman signal intensity and thus improving concentration detection sensitivity.

[0034] Example 2

[0035] Based on Example 1, this embodiment provides specific parameter data for a gas detection probe 100 suitable for chlorine gas detection. In this embodiment, the coating layer 7 has a thickness of 55 to 65 μm; the cladding layer 8 has a thickness of 180 to 220 μm; the fiber core has a diameter of 35 to 45 μm; the hollow silica tube 9 has a diameter of 13 to 14 μm, with a wall thickness of 200 to 220 nm; and the fiber channel 6 has a diameter of 35 to 45 μm. Six hollow silica tubes 9 are provided. The microholes 5 have a diameter of 2 to 4 μm. This 2 to 4 μm diameter ensures high drilling accuracy, short balancing time, and low loss. Each section of the photonic crystal fiber 3 has a length of 20 to 40 mm; each section of the hollow core fiber 4 has a length of 8 to 15 mm. The lengths of the first and second fiber Bragg gratings 1 and 2 are both 8 to 15 mm. The photonic crystal fiber 3 comprises seven sections, while the hollow-core fiber 4 comprises six sections. Each section of the hollow-core fiber 4 is provided with a microhole 5, resulting in a total of six microholes 5 in the six sections of the hollow-core fiber 4. This number of microholes 5 minimizes fiber transmission losses caused by the microholes 5 while ensuring the structural stability of the entire probe 100 and preventing breakage.

[0036] In this embodiment, if Figure 1 As shown, the entire probe 100 is 0.29m long and is composed of seven segments of photonic crystal fiber 3, six segments of hollow-core fiber 4 modified with microholes 5, and a fiber Bragg grating (FBG) at each end. Each segment of photonic crystal fiber 3 is 30mm long and approximately 560μm in diameter; each segment of hollow-core fiber 4 modified with microholes 5 is 10mm long and approximately 560μm in diameter. The microholes 5 have a diameter of 3μm and are arranged in an evenly drilled pattern. The microholes 5 are spaced 40mm apart, and there are six microholes 5. The fiber Bragg grating is 10mm long.

[0037] like Figure 2 As shown, the inner wall of the cladding 8 of the photonic crystal fiber 3 is composed of 6 non-contact hollow silica tubes 9 (diameter 14.37μm, wall thickness 210nm, spacing 5μm) evenly arranged around the core. The core diameter is 39μm, the coating layer 7 thickness is about 60μm, the cladding 8 thickness is about 200μm, and the optical fiber transmission wavelength is 575nm.

[0038] like Figure 3 As shown, the coating layer 7 of the hollow core optical fiber 4 has a thickness of about 60 μm, the cladding 8 has a thickness of about 200 μm, the hollow core tube has a diameter of about 39 μm, and the microhole 5 has a diameter of 3 μm.

[0039] like Figure 4 FIG. 1 is a schematic diagram of a remote monitoring system in which the probe 100 of the present invention is applied to chlorine gas detection.

[0040] According to the characteristic Raman light wavelength frequency shift range of Cl2, it is within 550-600nm. The specific value will vary slightly depending on the experimental conditions and instrument accuracy. The utility model takes the middle value of 575nm. This determines the specific wavelength parameter (575nm) of the Bragg grating selected at both ends of the probe 100. The optical fiber modified with the surface microhole 5 is used as the probe 100. A set of fiber Bragg gratings are placed at both ends of the probe 100, wherein the first fiber Bragg grating 1 (FBGa) has a reflectivity of 0.01 for 1064nm wavelength light and a reflectivity of 0.99 for 575nm wavelength light, which is equivalent to total internal reflection; the second fiber Bragg grating 2 (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 100, 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" composed of FBG1 (the reflectivity for 1064nm wavelength light is 0.99, and the reflectivity for 964nm wavelength light is 0.01) and FBGb, fully interacting with gas molecules to generate Raman scattered light. The 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 point, Cl₂ gas of varying concentrations is introduced into gas chamber 200. Gas molecules freely diffuse through micropores 5 into hollow silicon tube 9. High-power pump light of a specific wavelength (1064 nm) is then coupled into one end of probe 100. (Advantage: laser light of this wavelength is in the infrared region, and chlorine molecules have little absorption spectrum at this wavelength, thus avoiding spectral overlap with chlorine itself.) When different Cl₂ concentrations are introduced, the laser light and gas molecules fully interact within probe 100, producing characteristic Raman light of varying power levels. The peak intensity of this characteristic Raman light is analyzed, and the experiment is repeated at various Cl₂ concentrations to obtain an average value. The data is then processed to derive a relationship between Cl₂ concentration and the peak intensity of the characteristic Raman light. Finally, probe 100 is placed in the test environment, and the Cl₂ concentration can be inferred from this relationship.

[0041] This embodiment is only for reference. By modifying the various parameter data of the probe 100, it can be made capable of detecting other gases. The principles of different gas detection are similar and will not be listed here one by one.

[0042] Example 3

[0043] The other structures of this embodiment are the same as those of Example 1. The difference is that in this embodiment, two adjacent sections of the photonic crystal core are connected using a specific glue, and the micropores 5 are modified at the connection point to allow gas to smoothly enter the inner hole of the photonic crystal core through the micropores 5. Of course, in addition to the two groups of methods provided in Example 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 5 need to be modified at the connection point to ensure that gas molecules can smoothly enter the inner hole of the photonic crystal fiber 3.

[0044] 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.

[0045] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. A person skilled in the art will be able to make other variations or modifications based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A gas detection probe, characterized in that: The invention comprises a first fiber Bragg grating (1), an optical fiber group, and a second fiber Bragg grating (2); one end of the optical fiber group is connected to the first fiber Bragg grating (1), and the other end is connected to the second fiber Bragg grating (2); the optical fiber group comprises multiple sections of photonic crystal optical fibers (3) and multiple sections of hollow-core optical fibers (4); the photonic crystal optical fibers (3) and the hollow-core optical fibers (4) are staggered and connected, a section of the hollow-core optical fiber (4) is connected between two adjacent sections of the photonic crystal optical fibers (3), and one end of the two outermost sections of the photonic crystal optical fibers (3) is connected to the first fiber Bragg grating (1) and the second fiber Bragg grating (2); a microhole (5) is provided on the side surface of the incident end of each section of the hollow-core optical fiber (4), and the microhole (5) is deep into the optical fiber channel (6).

2. The gas detection probe according to claim 1, characterized in that: Each section of the hollow-core optical fiber (4) is provided with only one microhole (5).

3. The gas detection probe according to claim 2, characterized in that: The photonic crystal optical fiber (3) comprises a coating layer (7), a cladding layer (8) and a core in sequence from the outside to the inside; the core comprises a plurality of non-contact hollow silica tubes (9), and the plurality of hollow silica tubes (9) are evenly spaced and distributed along the circumference of the core.

4. The gas detection probe according to claim 3, characterized in that: The hollow-core optical fiber (4) comprises, from the outside to the inside, a coating layer (7), a cladding layer (8), and a hollow optical fiber channel (6).

5. The gas detection probe according to claim 4, characterized in that: The thickness of the coating layer (7) is 55 μm to 65 μm; the thickness of the cladding layer (8) is 180 μm to 220 μm; the diameter of the fiber core is 35 μm to 45 μm; the diameter of the hollow silicon tube (9) is 13 μm to 14 μm, and the wall thickness is 200 nm to 220 nm; the diameter of the optical fiber channel (6) is 35 μm to 45 μm.

6. The gas detection probe according to claim 5, characterized in that: There are six hollow silicon tubes (9).

7. The gas detection probe according to claim 5, characterized in that: The diameter of the micropores (5) is 2 μm to 4 μm.

8. The gas detection probe according to claim 5, characterized in that: The length of each section of the photonic crystal optical fiber (3) is 20 mm to 40 mm; the length of each section of the hollow core optical fiber (4) is 8 mm to 15 mm.

9. The gas detection probe according to any one of claims 1 to 8, characterized in that: The lengths of the first fiber Bragg grating (1) and the second fiber Bragg grating (2) are both 8 mm to 15 mm.

10. The gas detection probe according to claim 9, characterized in that: The photonic crystal optical fiber (3) is provided with 7 sections in total; the hollow core optical fiber (4) is provided with 6 sections in total.

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