Multi-channel Fabry-Perot gas detection optical fiber sensor based on functional material

Abstract

The invention discloses a multi-channel Fabry-Perot gas detection optical fiber sensor based on a functional material. The multi-channel Fabry-Perot gas detection optical fiber sensor comprises a super-continuum spectrum light source, a spectrum analyzer and a methane gas detection unit, the super-continuum spectrum light source, the spectrum analyzer and the methane gas detection unit are respectively connected with three input ports of the optical fiber circulator; the methane gas detection unit comprises an introduction single-mode optical fiber, a hollow optical fiber filled with a functional material and a polarization-maintaining single-core single-hole optical fiber which are sequentially welded in an arc discharge manner. The content of the methane gas is indirectly monitored by measuring the change of the refractive index of the filling functional material, and the in-situ measurement of the methane gas can be realized. Through the optical fiber sensing technology, high-precision measurement of methane gas in dangerous environments such as underground gas detection and petroleum pipelines is achieved, the method has the advantages of being easy and convenient to operate, rapid in measurement, low in cost and the like, and a new method is provided for methane gas detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing, and particularly relates to a multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials. Background Art

[0002] Due to its unique advantages, such as high sensitivity, anti-electromagnetic interference, corrosion resistance, high pressure resistance, etc., optical fiber sensors have been widely used in many fields. They have broad application prospects in fields such as petrochemical industry, environmental monitoring, healthcare, and mining safety. Optical fiber sensors use light as the information carrier and do not generate electric sparks, making them suitable for gas detection in flammable and explosive environments.

[0003] Currently, for the detection of flammable and explosive gases, online monitoring systems, infrared imaging technology, portable detectors, etc. are mainly used, but they have disadvantages such as poor gas selectivity, the need for regular maintenance of equipment and high costs, and complex operation of high-end equipment. Summary of the Invention

[0004] The present invention is proposed to solve the problems existing in the prior art for the detection methods of flammable and explosive gases, such as online monitoring systems, infrared imaging technology, portable detectors, etc., which have poor gas selectivity, the need for regular maintenance of equipment and high costs, and complex operation of high-end equipment. Its purpose is to provide a multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials.

[0005] The present invention is achieved through the following technical solutions:

[0006] A multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials, comprising a supercontinuum light source, a spectral analyzer, and a methane gas detection unit; the supercontinuum light source, the spectral analyzer, and the methane gas detection unit are respectively connected to three input ports of an optical fiber circulator.

[0007] In the above technical solution, the methane gas detection unit includes an input single-mode optical fiber, a hollow optical fiber filled with functional materials, and a polarization-maintaining single-core single-hole optical fiber that are arc-discharge welded in sequence.

[0008] In the above technical solution, the input single-mode optical fiber, the hollow optical fiber, and the polarization-maintaining single-core single-hole optical fiber are welded using an optical fiber fusion splicer to form an FP optical fiber sensor.

[0009] In the above technical solution, the model of the introduced single-mode optical fiber is Corning SMF-28, its outer diameter is 125 μm, its refractive index at 1550 nm is 1.444, the core diameter is 8.2 μm, and the refractive index at 1550 nm is 1.449; the outer diameter of the hollow optical fiber is 125 μm and the inner diameter is 50 μm; the outer diameter of the single-core single-hole polarization-maintaining optical fiber is 125 μm, its refractive index at 1550 nm is 1.444, the core diameter is 8.2 μm, the refractive index at 1550 nm is 1.449, and its air hole diameter is 20 μm.

[0010] In the above technical solution, the functional material filled in the hollow optical fiber is a hydrogel added with metal-organic framework materials.

[0011] In the above technical solution, the functional material is obtained by directly adding metal-organic framework materials to the hydrogel solution through a sol-gel process.

[0012] In the above technical solution, the functional material is filled into the hollow optical fiber through a liquid gun.

[0013] In the above technical solution, the preparation method of the methane gas detection unit includes the following steps:

[0014] (Ⅰ) After removing the coating layer of the introduced single-mode optical fiber, place the introduced single-mode optical fiber on a high-precision three-dimensional optical fiber displacement platform, and arc discharge and fuse the hollow optical fiber with the introduced single-mode optical fiber;

[0015] (Ⅱ) Use a high-precision three-dimensional optical fiber displacement platform to adjust, and use an optical fiber cutter to ensure that the length of the hollow optical fiber is L1;

[0016] (Ⅲ) Under a microscope, fill the functional material into the hollow optical fiber using a liquid gun;

[0017] (Ⅳ) Using a high-precision three-dimensional optical fiber displacement platform, weld another polarization-maintaining single-core single-hole optical fiber (33) with a length of L2 after the introduced single-mode optical fiber - hollow optical fiber structure filled with the functional material, and the methane gas detection unit is obtained.

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

[0019] The present invention provides a multi-channel Fabry-Perot gas detection fiber optic sensor based on functional materials. By combining functional materials for identifying methane gas and modifying such functional materials into the fiber optic sensor, a simple and efficient methane gas detection sensor is obtained. The soft nature of the hydrogel used as the filling material in the hollow fiber of the present invention can well solve the fitting problem between the rigid fiber optic sensor and the specific recognition element, enabling it to be filled inside the optical fiber for direct detection. This method shortens the mass transfer distance and improves the mass transfer efficiency, thus realizing in-situ real-time monitoring. To further improve the specific detection effect, functional materials are added to the hydrogel system, and the functionalized hydrogel is filled in the fiber optic sensor to construct an FP fiber optic sensing unit.

[0020] The present invention indirectly monitors the content of methane gas by measuring the change in the refractive index of the filled functional material, and can realize the in-situ measurement of methane gas. Through fiber optic sensing technology, high-precision measurement of methane gas in dangerous environments such as underground gas detection and oil pipelines is realized, with the advantages of simple operation, rapid measurement, low cost, etc., providing a new method for methane gas detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of the present invention;

[0022] Figure 2 is a schematic structural diagram of the methane gas detection unit in the present invention;

[0023] Figure 3 is a refractive index response reflection spectrogram of the Fabry-Perot fiber optic sensor.

[0024] Wherein:

[0025] 1. Supercontinuum light source; 2. Spectral analyzer; 3. Methane gas detection unit; 31. Introduced single-mode optical fiber; 32. Hollow optical fiber; 33. Polarization-maintaining single-core single-hole optical fiber; 4. Fiber optic circulator.

[0026] For those of ordinary skill in the art, without creative efforts, other related drawings can be obtained based on the above drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] In order to enable those skilled in the art of the present technology to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with the specification drawings and through specific embodiments.

[0028] As Figure 1 shown, a multi-channel Fabry-Perot gas detection fiber optic sensor based on functional materials includes a supercontinuum light source 1, a spectral analyzer 2, and a methane gas detection unit 3;

[0029] The supercontinuum light source 1, the spectral analyzer 2, and the methane gas detection unit 3 are respectively connected to three ports of the fiber optic circulator 4;

[0030] The three ports of the fiber optic circulator 4 are respectively connected to the supercontinuum light source 1, the spectral analyzer 2, and the methane gas detection unit 3 using single-mode optical fibers. The fiber optic circulator is mainly used for the directional transmission of optical signals and the processing of reflected signals. The optical signal emitted by the supercontinuum light source 1 is input from port one of the fiber optic circulator 4, and the optical signal is transmitted through port two of the fiber optic circulator to the methane gas detection unit 3. The reflected optical signal returned from the methane gas detection unit 3 is output through port three of the fiber optic circulator, and the reflected optical signal is transmitted to the spectral analyzer 2 for analyzing the change of the interference spectrum.

[0031] The methane gas detection unit 3 includes an input single-mode optical fiber 31, a hollow optical fiber 32 filled with a functional material, and a polarization-maintaining single-core single-hole optical fiber 33 that are arc-discharge welded in sequence; the input single-mode optical fiber 31, the hollow optical fiber 32, and the polarization-maintaining single-core single-hole optical fiber 33 are welded using a fiber optic fusion splicer Furukawa, S178A, Japan to form an FP fiber optic sensor;

[0032] The model of the input single-mode optical fiber 31 is Corning SMF-28, its cladding outer diameter is 125μm, the refractive index of the outer cladding at 1550nm is 1.444, the core diameter is 8.2μm, and the refractive index of the core at 1550nm is 1.449;

[0033] The outer diameter of the hollow optical fiber 32 is 125μm and the inner diameter is 50μm;

[0034] The outer diameter of the single-core single-hole polarization-maintaining optical fiber 33 is 125μm, the refractive index of its outer cladding at 1550nm is 1.444, the core diameter is 8.2μm, the refractive index of the core at 1550nm is 1.449, and its air hole diameter is 20μm.

[0035] The functional material filled in the hollow optical fiber 32 is a hydrogel added with metal-organic framework materials (MOFs). The metal-organic framework materials (MOFs) are materials with a high specific surface area and adjustable pore size. For example, including but not limited to CuBDC (copper benzene dicarboxylate), ZIF-8, UiO-66 can be used for the storage and separation of methane; the functional material is obtained by directly adding metal-organic framework materials (MOFs) to the hydrogel solution through a sol-gel process.

[0036] The functional material is filled into the hollow optical fiber through a liquid gun.

[0037] The preparation method of the methane gas detection unit 3 includes the following steps:

[0038] (Ⅰ) After removing the coating layer of the single-mode fiber 31 introduced, place the single-mode fiber 31 introduced on a high-precision three-dimensional fiber displacement platform, and arc-discharge weld the hollow fiber 32 with the single-mode fiber 31 introduced.

[0039] (Ⅱ) Adjust using a high-precision three-dimensional fiber displacement platform, and use a fiber cutter to ensure that the length of the hollow fiber is L1.

[0040] (Ⅲ) Under a microscope, fill the hollow fiber 32 with the functional material using a liquid gun.

[0041] (Ⅳ) Using a high-precision three-dimensional fiber displacement platform, weld a polarization-maintaining single-core single-hole fiber 33 with a length of L2 to the structure of the single-mode fiber 31 - hollow fiber 32 filled with the functional material, and then the methane gas detection unit 3 is obtained.

[0042] Principle of the present invention:

[0043] The air hole of the polarization-maintaining single-core single-hole fiber 33 serves as a channel for gas to enter the functional material filled in the hollow fiber 32. Methane gas is indirectly identified and its content is measured by monitoring the change in the refractive index of the functional material filled in the hollow fiber 32; the hollow fiber 32 is filled with the functional material, and the MOF material is doped in the hydrogel to specifically identify methane gas.

[0044] When methane gas enters the hollow fiber 32 filled with the functional material through the polarization-maintaining single-core single-hole fiber 33, the refractive index in the hollow fiber 32 filled with the functional material will change. Based on this change, methane gas can be warned through a spectral analyzer.

[0045] The sensor of the present invention has three mirrors, which are respectively the end face of the single-mode fiber 31 introduced, the left end face and the right end face of the polarization-maintaining single-core single-hole fiber 33. The end face of the single-mode fiber 31 introduced and the left end face of the polarization-maintaining single-core single-hole fiber 33 form a double-beam interference, denoted as FP1, with a length of L1. Similarly, the left end face and the right end face of the polarization-maintaining single-core single-hole fiber 33 form a silica FP cavity, denoted as FP2, with a length of L2. The longest FP3 is composed of the end face of the single-mode fiber 31 introduced and the right end face of the polarization-maintaining single-core single-hole fiber 33, and its length is L1 + L2. FPI1 serves as the sensing cavity, and FP2 serves as the reference cavity. When the free spectral ranges of FPI1 and FPI2 are close, an optical vernier effect is generated, which can effectively improve the sensitivity of refractive index measurement, and thus improve the gas detection sensitivity.

[0046] The reflection intensity Ir of the Fabry - Perot cavity of the double-beam interference can be expressed as:

[0047]

[0048] Where: $E_0$ is the optical intensity of the supercontinuum light source 1; $R_1$ and $R_2$ are the reflection coefficients of the input single-mode fiber 31 and the polarization-maintaining single-core single-hole fiber 33 respectively, $n$ is the refractive index of the hollow fiber 32 after filling with the functional material, $L_1$ is the length of the hollow fiber 32, $L_2$ is the length of the polarization-maintaining single-core single-hole fiber 33, and $\lambda$ is the wavelength of the input light.

[0049] When methane gas with different contents passes through the filled hollow fiber 32, the refractive index $n$ will change. Figure 2 This is the refractive index response reflection spectrogram of the Fabry-Perot fiber sensor. It can be seen that as the refractive index increases, the envelope drifts towards the short-wave direction, and thus the content of methane gas in the sample to be measured can be determined.

[0050] The FP fiber sensor has advantages such as a direct plug-in type and a compact structure; the preparation cost is low, and the temperature stability of the transmission spectrum is good; the Fabry-Perot methane gas detection fiber sensor based on functional materials established in the present invention is different from the prior art. By fusing the hollow fiber and the single-mode fiber and filling with the functional material, the simple and efficient methane detection is indirectly realized through the drift of the resonant wavelength of the spectral analyzer. At the same time, by modifying the functionalized hydrogel inside the hollow fiber, the polarization-maintaining single-core single-hole fiber has both air holes to form a gas channel and fiber end-face reflection, forming an FP fiber sensor. This sensor can be applied to dangerous monitoring environments such as underground gas detection and oil pipeline detection.

[0051] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship 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 orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0052] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0053] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials, characterized in that: It comprises a supercontinuum light source (1), a spectrum analyzer (2) and a methane gas detection unit (3); the supercontinuum light source (1), the spectrum analyzer (2) and the methane gas detection unit (3) are respectively connected to three input ports of an optical fiber circulator (4).

2. The multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials according to claim 1, characterized in that: The methane gas detection unit (3) comprises an introduced single-mode optical fiber (31), a hollow optical fiber (32) filled with a functional material, and a polarization-maintaining single-core single-hole optical fiber (33) which are sequentially arc-discharge-fused.

3. The multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials according to claim 2, characterized in that: The introduced single-mode optical fiber (31), the hollow optical fiber (32) and the polarization-maintaining single-core single-hole optical fiber (33) are fused together using an optical fiber fusion splicer to form an FP optical fiber sensor.

4. The multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials according to claim 2, characterized in that: The introduced single-mode optical fiber (31) is of Corning SMF-28, with an outer diameter of 125 μm, a refractive index of its outer diameter cladding at 1550 nm of 1.444, a core diameter of 8.2 μm, and a refractive index of the core at 1550 nm of 1.449; the outer diameter of the hollow optical fiber (32) is 125 μm and the inner diameter is 50 μm; the outer diameter of the single-core single-hole polarization-maintaining optical fiber (33) is 125 μm, a refractive index of its outer diameter cladding at 1550 nm of 1.444, a core diameter of 8.2 μm, and a refractive index of the core at 1550 nm of 1.449, and the air hole diameter is 20 μm.

5. The multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials according to claim 2, characterized in that: The functional material filled in the hollow optical fiber (32) is a hydrogel added with a metal organic framework material.

6. The multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials according to claim 5, characterized in that: The functional material is obtained by directly adding metal organic framework materials into the hydrogel solution through a sol-gel process.

7. The multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials according to claim 6, characterized in that: The functional material is filled into the hollow optical fiber through a liquid gun.

8. The multi-channel Fabry-Perot gas detection optical fiber sensor based on functional materials according to claim 2, characterized in that: The method for preparing the methane gas detection unit (3) comprises the following steps: (I) after removing the coating layer of the introduced single-mode optical fiber (31), the introduced single-mode optical fiber (31) is placed on a high-precision optical fiber three-dimensional displacement platform, and the hollow optical fiber (32) and the introduced single-mode optical fiber (31) are arc-discharge-fused; (II) Use a high-precision optical fiber three-dimensional displacement platform to adjust and use an optical fiber cutting knife to cut the hollow optical fiber; (III) Under a microscope, the functional material is filled into the hollow optical fiber (32) using a liquid gun; (IV) Using a high-precision optical fiber three-dimensional displacement platform, a single-mode optical fiber (31)-hollow optical fiber (32) filled with functional materials is introduced and then fused with a polarization-maintaining single-core single-hole optical fiber (33) to obtain a methane gas detection unit (3).

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