Multi-microcavity gas detection optical fiber sensor with hollow microcavity film structure

Abstract

The invention belongs to the technical field of optical fiber sensing application, and particularly relates to a multi-microcavity gas detection optical fiber sensor with a hollow-out microcavity film structure and a manufacturing method and a detection method of the multi-microcavity gas detection optical fiber sensor. The sensor is composed of a multi-fiber-core single-mode optical fiber and a plurality of hollow micro-cavity films. The matrix material of the hollow-out microcavity film is commercial photoresist, the hollow-out microcavity film is composed of a hollow-out microcavity base, a hollow-out film and a doped gas-sensitive particle film, the hollow-out microcavity base is located on the end face of the multi-fiber-core single-mode optical fiber core, the hollow-out film is located on the upper surface of the hollow-out microcavity base, and the doped gas-sensitive particle film is located on the lower surface of the hollow-out microcavity base. The doped gas-sensitive particle film is positioned on the upper surface of the hollowed-out film, and the hollowed-out microcavity bases of the plurality of hollowed-out microcavity films are different in height. The gas detection device overcomes the influence caused by competitive adsorption of various gases to sensitive materials and mutual interference of signals caused by different gases, has accuracy and reliability in detection, expands the gas detection range, simplifies the structure of a detection system, and is good in detection performance, small in size, low in cost and high in practicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing applications, and in particular relates to a multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure, and a manufacturing method and a detection method thereof. Background Art

[0002] Fiber optic gas sensors are widely used for gas detection in complex environments due to their many advantages, such as small size, light weight, good flexibility, strong resistance to electromagnetic interference, and high chemical stability. However, existing fiber optic gas sensors have many defects when detecting multiple gases. For example, when detecting multiple gases, spectral absorption fiber optic gas sensors are affected by the cross-absorption of multiple gases, and the overlap of absorption spectra of different gases leads to low detection accuracy. Another example is multi-gas sensors based on fiber gratings. In complex gas environments, the competitive adsorption of multiple gases on sensitive materials and the interference of Bragg wavelength drift caused by different gases seriously affect the accuracy and reliability of detection. Another example is the photonic crystal-based fiber optic gas sensor disclosed in "Study on Functional Modification of Fiber and Gas Sensing Characteristics Based on Photonic Crystal Fluorescence Enhancement Effect". When detecting multiple gases, it has the problems of limited gas detection range and poor performance in detecting multiple gases simultaneously.

[0003] Furthermore, existing multi-gas simultaneous detection systems and optical fiber end-face micromachining technologies also suffer from low precision in simultaneous detection and processing of multiple gas components. For example, patent publication CN103792201A discloses a multi-component gas optical pressure sensor and its detection method. While this sensor achieves multi-component gas detection through a specific structure, its detection system is complex and places high demands on the light source, optical path adjustment, and signal processing. This not only increases equipment costs but also limits its widespread application in practical scenarios. Summary of the Invention

[0004] In order to solve the problems of low detection accuracy, poor anti-interference ability, poor accuracy and reliability, complex system and high detection cost of the above-mentioned existing multi-gas optical fiber detection sensors, the present invention provides a multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure, and its manufacturing method and detection method.

[0005] The technical solution adopted by the present invention is: a multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure, the multi-microcavity gas detection optical fiber sensor is composed of a multi-core single-mode optical fiber and a plurality of hollow microcavity films capable of detecting different gases; the matrix material of the hollow microcavity film is commercial photoresist, the hollow microcavity film is composed of a hollow microcavity base, a hollow film and a doped gas-sensitive particle film, the hollow microcavity base is located on the end face of the core of the multi-core single-mode optical fiber, the hollow film is located on the upper surface of the hollow microcavity base, the doped gas-sensitive particle film is located on the upper surface of the hollow film, and the hollow microcavity bases of the plurality of hollow microcavity films have different heights.

[0006] Furthermore, the multi-core single-mode optical fiber is a four-core single-mode optical fiber, and the center line connecting the four cores is a regular quadrilateral; the number of the multiple hollow microcavity films is four, namely the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film and the fourth hollow microcavity film, and the four hollow microcavity films correspond to the four cores.

[0007] Furthermore, the doped gas-sensitive particle film of the first hollow microcavity film is a film doped with Pt / TiO2 nanoparticles, the doped gas-sensitive particle film of the second hollow microcavity film is a film doped with WO3 quantum dots, the doped gas-sensitive particle film of the third hollow microcavity film is a film doped with Pd / Al2O3 nanosheets, and the doped gas-sensitive particle film of the fourth hollow microcavity film is a film doped with Au-ZnO nanorods.

[0008] Furthermore, the cladding diameter of the four-core single-mode optical fiber is 120-130 μm, the core diameter is 8-10 μm, and the spacing between two adjacent cores is 33-37 μm; the diameters of the hollow microcavity bases of the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film, and the fourth hollow microcavity film are all 9-11 μm, and their heights are 26-30 μm, 38-42 μm, 46-50 μm, and 61-66 μm, respectively; the thicknesses of the hollow films and doped gas-sensitive particle films of the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film, and the fourth hollow microcavity film are less than 3 μm and 5 μm, respectively.

[0009] Furthermore, the cladding diameter of the four-core single-mode optical fiber is 125μm, the core diameter is 9μm, and the spacing between two adjacent cores is 35μm; the diameters of the hollow microcavity bases of the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film and the fourth hollow microcavity film are all 10μm, and their heights are 28μm, 40μm, 48μm and 63.5μm respectively; the thicknesses of the hollow films and doped gas-sensitive particle films of the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film and the fourth hollow microcavity film are 2.5μm and 4.5μm respectively.

[0010] Furthermore, a method for manufacturing a multi-microcavity gas detection optical fiber sensor having a hollow microcavity film structure comprises the following steps: Step 1, take a section of four-core single-mode optical fiber, clean the end face of the four-core single-mode optical fiber, and cut it flat with a cutting knife, place the flattened standard four-core single-mode optical fiber on the optical fiber clamp and fix it; drop commercial photoresist on the tip of the four-core single-mode optical fiber to immerse the end face; then transfer the clamped four-core single-mode optical fiber to the femtosecond laser induced TPP equipment for processing; in order to ensure that the hollow microcavity film has a good printing morphology, use a 25-100x oil immersion lens (numerical aperture NA=1.4) during focusing; import the pre-designed hollow microcavity film model into the system of the processing equipment, control the movement of the femtosecond laser induced TPP system by scanning path, use commercial photoresist to print 4 hollow microcavity bases with a diameter of 10μm and heights of 28μm, 40μm, 48μm and 63.5μm above the core of the four-core single-mode optical fiber, and print a hollow film with a thickness of 2.5μm on the upper surface of the four hollow microcavity bases; Step 2: Soak the optical fiber printed by femtosecond laser two-photon polymerization in a soaking solution for 2 minutes. The soaking solution is a mixture of acetone and isopropyl alcohol in a volume ratio of 1:5. After soaking, clean the uncured photoresist. Step 3: Fix the optical fiber processed in Step 2 on the optical fiber clamp, then transfer the clamped optical fiber to the femtosecond laser-induced TPP equipment for processing. Add commercial photoresist doped with Pt / TiO2 nanoparticles on the hollow film of the hollow microcavity base with a height of 28μm, ensuring that the photoresist solution covers the entire hollow film. Use commercial photoresist doped with Pt / TiO2 nanoparticles to print a specific film with a thickness of 4.5μm on the upper surface of the hollow film. This specific film is used for H2 detection. Step 4: Add a commercial photoresist doped with WO3 quantum dots onto the hollow film of the hollow microcavity base with a height of 40 μm, ensuring that the photoresist solution covers the entire hollow film. Then, print a 4.5 μm thick specific film on the upper surface of the hollow film using the commercial photoresist doped with WO3 quantum dots. This specific film is used for NO2 detection. Step 5: Add a commercial photoresist doped with Pd / Al2O3 nanosheets onto the hollow film of the hollow microcavity base with a height of 48 μm, ensuring that the photoresist solution covers the entire hollow film. Then, print a 4.5 μm thick specific film on the upper surface of the hollow film using the commercial photoresist doped with Pd / Al2O3 nanosheets. This specific film is used to detect CH4. Step 6: Add a commercial photoresist doped with Au-ZnO nanorods onto the 63.5 μm-high hollow film of the hollow microcavity base, ensuring that the photoresist solution covers the entire hollow film. Then, print a 4.5 μm-thick specific film on the upper surface of the hollow film using the commercial photoresist doped with Au-ZnO nanorods. This specific film is used for CO detection. Step seven, curing: After cleaning the residual photoresist on the gas detection optical fiber sensor obtained in step six, irradiate it with ultraviolet light for 4-6 minutes for curing, and after curing, a four-microcavity gas detection optical fiber sensor is obtained.

[0011] Furthermore, in the process of femtosecond laser two-photon polymerization printing using a femtosecond laser-induced TPP device, the power of the femtosecond laser is 10-50 mW, the repetition rate is 80 MHz, the operating wavelength is 800 nm, the scanning speed is 800 µm / s, the line spacing is 100 nm-1 µm, and the slice spacing is 100 nm-1 µm.

[0012] Furthermore, a detection method for detecting multiple gases using a multi-microcavity gas detection optical fiber sensor having a hollow microcavity film structure comprises the following steps: In the first step, a broadband light source (BBS, 600-1700 nm), an optical spectrum analyzer (OSA, 0.02 nm resolution, YOKOGAWA, AQ6317C), a 3dB coupler, an optical switch, an MCF fan input / output device (FAN-4C), and a four-microcavity gas detection fiber optic sensor in a mixing chamber were sequentially connected via single-mode optical fiber fusion splicing to form a detection system. The mixing chamber is a five-way connection made of plastic tubing, with four microchannels for the gas to be measured and one microchannel for N2 gas concentration adjustment. A four-core fiber fan-in / fan-out device enables a one-to-one connection between each core in the multi-core fiber and a different single-mode single-core pigtail, facilitating the splitting and combining of optical signals.

[0013] In the second step, the gas flow rates of H2, NO2, CH4, CO to be detected and N2 for gas concentration adjustment are controlled by the intelligent gas flowmeter on the input gas pipe. While maintaining the total flow rate at 500 mL / min, the flow rates of H2, NO2, CH4, CO and N2 are adjusted by computer to achieve gas concentration regulation. The four-microcavity gas detection fiber optic sensor transmits the detection data to the fiber optic spectrum analyzer for data analysis.

[0014] The beneficial effects of the present invention are as follows: the multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure adopts different sensitive materials with specificity, which overcomes the influence of competitive adsorption of multiple gases on sensitive materials and mutual interference of signals caused by different gases, making its detection accurate and reliable. By doping different concentrations of specific sensitive particles in the photoresist, the gas detection range is expanded. Femtosecond laser two-photon polymerization technology is used to integrate multiple different heights on the end face of the multi-core optical fiber, and different sensitive materials with specificity are doped in the hollow microcavity film. Compared with the existing bulky and complex simultaneous detection system of multiple gases, the structure of the detection system is simplified, the detection performance is good, the volume is small, the cost is low, and the practicality is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the interference principle of the optical fiber end face micro-thin film sensor in Example 1.

[0016] Figure 2 It is a structural diagram of the multi-microcavity gas detection optical fiber sensor in the second embodiment.

[0017] Figure 3 It is a structural schematic diagram of the hollow microcavity film in Example 2.

[0018] Figure 4 Schematic diagram of a detection system for simultaneously detecting multiple gases using a multi-microcavity gas detection optical fiber sensor in Example 2.

[0019] Figure 5 This is a reflection spectrum diagram of the four-microcavity gas detection optical fiber sensor in Example 2.

[0020] Figure 6 1 is a reflection spectrum diagram of H2 at different concentrations in Example 2.

[0021] Figure 7 It is a linear fitting diagram between the spectral variation and the concentration H2 in Example 2.

[0022] Figure 8 1 is a reflection spectrum diagram of different concentrations of NO2 in Example 2.

[0023] Figure 9 It is a linear fitting diagram between the spectral variation and the NO2 concentration in Example 2.

[0024] Figure 10 1 is a reflection spectrum diagram of CH4 at different concentrations in Example 2.

[0025] Figure 11 It is a linear fitting diagram between the spectral variation and the CH4 concentration in Example 2.

[0026] Figure 121 is a reflection spectrum diagram of CO at different concentrations in Example 2.

[0027] Figure 13 It is a linear fitting diagram between the spectral change and the CO concentration in Example 2.

[0028] Figure numerals: 1. first hollow microcavity film; 2. second hollow microcavity film; 3. third hollow microcavity film; 4. fourth hollow microcavity film; 5. multi-core single-mode optical fiber; 6. hollow microcavity base; 7. hollow film; 8. doped gas-sensitive particle film. DETAILED DESCRIPTION Example

[0029] like Figure 1 The figure shows the interferometry principle of a fiber optic sensor for simultaneous detection of different gases at room temperature. The multi-core fiber sensor consists of a single-mode fiber (SMF) and a microcavity film. The fiber endface and the two surfaces of the microcavity film form an interference pattern (FPI). Light reflected from the fiber endface interferes with light reflected from the inner and outer surfaces of the microcavity film, forming three-beam interference spectra. An air microcavity (FPI1) is formed between the fiber endface and the inner surface of the microcavity film; a polymer microcavity (FPI2) is formed between the outer and inner surfaces of the microcavity film; and a hybrid microcavity (FPI3) is formed between the fiber endface and the outer surface of the microcavity film. Compared to FPI1 and FPI2, the light intensity of FPI3 is relatively weak, and the light intensity of FPI2 is fixed after cantilever fabrication. Therefore, when force is applied to the microcavity film, changes in the reflection spectrum are caused by changes in FPI1 in the air medium. The free spectral range of FPI1 is calculated as: (1) Where λ is the resonant wavelength, L is the cavity length of the FP cavity, and n is the refractive index of the medium inside the FP cavity.

[0030] When a micro-force is applied to the micro-cavity film, the film will deform, which will cause the length of the FPI cavity to change, resulting in a shift in the resonant wavelength in the SMF reflection spectrum. Therefore, the deformation of the micro-cavity film can be tracked by monitoring the change in the resonant wavelength in the reflection spectrum, thereby obtaining the force applied to the film. The wavelength change ( Dl ) and FP cavity variation ( DL ) is simplified into the following formula: (2); Example

[0031] Based on the interference principle of the optical fiber end surface micro-film sensor of the first embodiment, this embodiment designs a multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure, such as Figure 2 and Figure 3 As shown, the multi-microcavity gas detection fiber optic sensor consists of a multi-core single-mode optical fiber 5 and multiple hollow microcavity films capable of detecting different gases. The matrix material of the hollow microcavity films is commercial photoresist (IP Dip), and the hollow microcavity films are composed of a hollow microcavity base 6, a hollow film 7, and a doped gas-sensitive particle film 8. The hollow microcavity base 6 is located on the end face of the core of the multi-core single-mode optical fiber 5, the hollow film 7 is located on the upper surface of the hollow microcavity base 6, and the doped gas-sensitive particle film 8 is located on the upper surface of the hollow film 7. The multi-core single-mode optical fiber 5 is a four-core single-mode optical fiber, and the center line connecting the four cores forms a regular quadrilateral. There are four hollow microcavity films: a first hollow microcavity film 1, a second hollow microcavity film 2, a third hollow microcavity film 3, and a fourth hollow microcavity film 4, corresponding to the four cores. The doped gas-sensitive particle film 8 of the first hollow microcavity film 1 is a film doped with Pt / TiO2 nanoparticles, the doped gas-sensitive particle film 8 of the second hollow microcavity film 2 is a film doped with WO3 quantum dots, the doped gas-sensitive particle film 8 of the third hollow microcavity film 3 is a film doped with Pd / Al2O3 nanosheets, and the doped gas-sensitive particle film 8 of the fourth hollow microcavity film 4 is a film doped with Au-ZnO nanorods. The cladding diameter of the four-core single-mode optical fiber is 125μm, the core diameter is 9μm, and the spacing between two adjacent cores is 35μm; the diameter of the hollow microcavity base 6 of the first hollow microcavity film 1, the second hollow microcavity film 2, the third hollow microcavity film 3 and the fourth hollow microcavity film 4 is 10μm, and their heights are 28μm, 40μm, 48μm and 63.5μm respectively; the thickness of the hollow film 7 and the doped gas-sensitive particle film 8 of the first hollow microcavity film 1, the second hollow microcavity film 2, the third hollow microcavity film 3 and the fourth hollow microcavity film 4 are 2.5μm and 4.5μm respectively.

[0032] The multi-microcavity gas detection fiber optic sensor features a hollowed-out microcavity film structure, fixed at one end and freely suspended at the other. The hollowed-out microcavity film structure exhibits highly elastic suspension properties at its center. Even slight changes in the external environment will cause the film to deform, resulting in changes in the FPI cavity length and, in turn, a shift in the resonant wavelength in the SMF reflection spectrum. When the gas-sensing film absorbs the sensitive gas, its volume expands, creating a stress difference between the photoresist layer and the gas-sensing film layer, causing the microcavity film to bend toward the fiber end face. This process is reversible. When the concentration of the sensitive gas decreases, the sensitive gas molecules are reduced and detached from the surface of the gas-sensing film, causing the microcavity film to return to a flat surface. This establishes a relationship between the sensitive gas concentration and the FP cavity length of the microcavity film.

[0033] like Figure 4As shown, a detection method for detecting multiple gases using a multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure includes the following steps: In the first step, a broadband light source (BBS, 600-1700 nm), an optical spectrum analyzer (OSA, 0.02 nm resolution, YOKOGAWA, AQ6317C), a 3dB coupler, an optical switch, an MCF fan input / output device (FAN-4C), and a four-microcavity gas detection fiber optic sensor in a mixing chamber were sequentially connected via single-mode optical fiber fusion splicing to form a detection system. The mixing chamber is a five-way connection made of plastic tubing, with four microchannels for the gas to be measured and one microchannel for N2 gas concentration adjustment. A four-core fiber fan-in / fan-out device enables a one-to-one connection between each core in the multi-core fiber and a different single-mode single-core pigtail, facilitating the splitting and combining of optical signals.

[0034] In the second step, the gas flow rates of H2, NO2, CH4, CO to be detected and N2 for gas concentration adjustment are controlled by the intelligent gas flowmeter on the input gas pipe. While maintaining the total flow rate at 500 mL / min, the flow rates of H2, NO2, CH4, CO and N2 are adjusted by computer to achieve gas concentration regulation. The four-microcavity gas detection fiber optic sensor transmits the detection data to the fiber optic spectrum analyzer for data analysis.

[0035] like Figure 5 As shown in the figure, this figure is a reflection spectrum diagram of the four-microcavity gas detection optical fiber sensor, where serial number 1 is the reflection spectrum diagram of the first hollow microcavity film, serial number 2 is the reflection spectrum diagram of the second hollow microcavity film. Serial number 3 is the reflection spectrum diagram of the third hollow microcavity film, and serial number 4 is the reflection spectrum diagram of the fourth hollow microcavity film. The free spectral range of the first hollow microcavity film near the wavelength of 1573.25 nm is 44 nm. According to formula (1), the cavity length of the first hollow microcavity film (microcantilever) is approximately 28 µm. The free spectral range of the second hollow microcavity film near the wavelength of 1499.75 nm is 28 nm. According to formula (1), the cavity length of the second hollow microcavity film (microcantilever) is approximately 40 µm. The free spectral range of the third hollow microcavity film (microcantilever) near the wavelength of 1469.6 nm is 22.5 nm. According to formula (1), the cavity length of the third hollow microcavity film (microcantilever) is approximately 48 µm. The free spectral range of the fourth hollow microcavity film near the wavelength of 1412.8 nm is 18.5 nm. According to formula (1), the cavity length of the fourth hollow microcavity film (microcantilever) is approximately 63.5 µm. As shown above, the reflection spectra of the four FPIs have different FSRs, which is conducive to a wide measurement range.

[0036] like Figure 6 and Figure 7 As shown, Figure 6 is the reflection spectrum of H2 at different concentrations, Figure 7 is the linear fitting diagram between the spectral variation and the concentration H2. Figure 6 and Figure 7 It can be seen that the sensitivity curve of the first hollow microcavity film optical cavity to H2 concentration is in the concentration range of 0-2%, and the sensitivity of the optical fiber sensor is 10.9 nm / %.

[0037] like Figure 8 and Figure 9 As shown, Figure 8 is the reflectance spectrum of different concentrations of NO2, Figure 9 It is the linear fitting diagram between the spectral variation and the concentration of NO2. Figure 8 and Figure 9 It can be seen that the sensitivity curve of the second hollow microcavity film optical cavity to NO2 concentration is in the concentration range of 0-4.5%, and the sensitivity of the optical fiber sensor is 3.8 nm / %.

[0038] like Figure 10 and Figure 11 As shown, Figure 10 is the reflection spectrum of CH4 at different concentrations. Figure 11 is the linear fitting diagram between the spectral variation and CH4 concentration. Figure 10 and Figure 11 It can be seen that the sensitivity curve of the third hollow microcavity film optical cavity to CH4 concentration is in the concentration range of 0-4%, and the sensitivity of the optical fiber sensor is 1.86 nm / %.

[0039] like Figure 12 and Figure 13 As shown, Figure 12 is the reflectance spectrum of different concentrations of NO2, Figure 13 It is the linear fitting diagram between the spectral variation and the concentration of NO2. Figure 12 and Figure 13 It can be seen that the sensitivity curve of the fourth hollow microcavity film optical cavity to NO2 concentration is in the concentration range of 0-8%, and the sensitivity of the optical fiber sensor is 0.66 nm / %.

[0040] By doping commercial photoresists with varying concentrations of Pt / TiO2 nanoparticles, WO3 quantum dots, Pd / Al2O3 nanosheets, and Au-ZnO nanorods, photoresists with specificity for H2, NO2, CH4, and CO were obtained. This overcomes the problems of competitive adsorption of multiple gases on sensitive materials, signal interference caused by different gases, and the limited gas detection range. Existing photoresists generally lack the ability to specifically detect specific gases, or have poor specificity. The multi-microcavity gas detection fiber sensor, by doping commercial photoresists with different gas-sensitive materials, enables the photoresist to be specific for multiple gases, resolving the poor gas detection specificity of existing photoresists and improving detection accuracy and reliability.

[0041] Example 3 The structure of the optical fiber sensor in this embodiment is the same as that in Example 2, but the dimensions are different. In this embodiment, the cladding diameter of the four-core single-mode optical fiber is 120 μm, the core diameter is 8 μm, and the spacing between two adjacent cores is 33 μm; the diameters of the hollow microcavity bases of the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film, and the fourth hollow microcavity film are all 9 μm, and their heights are 28 μm, 38 μm, 46 μm, and 61 μm, respectively; the thicknesses of the hollow films and doped gas-sensitive particle films of the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film, and the fourth hollow microcavity film are less than 2 μm and 4 μm, respectively.

[0042] Example 4 The structure of the optical fiber sensor in this embodiment is the same as that in Example 2, but the dimensions are different. In this embodiment, the cladding diameter of the four-core single-mode optical fiber is 130 μm, the core diameter is 10 μm, and the spacing between two adjacent cores is 37 μm; the diameters of the hollow microcavity bases of the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film, and the fourth hollow microcavity film are all 11 μm, and their heights are 30 μm, 42 μm, 50 μm, and 66 μm, respectively; the thicknesses of the hollow films and doped gas-sensitive particle films of the first hollow microcavity film, the second hollow microcavity film, the third hollow microcavity film, and the fourth hollow microcavity film are less than 2.9 μm and 4.9 μm, respectively.

[0043] Example 5 The structure of the hollow microcavity base of the multi-microcavity gas detection optical fiber sensor is preferably a tube with rectangular grooves on the circumference, and the rectangular grooves are evenly distributed around the circumference; the structure of the hollow film is preferably a film with circular grooves corresponding to the rectangular grooves. The structure of the hollow microcavity base and the hollow film of the multi-microcavity gas detection optical fiber sensor is not limited to the shape of this embodiment; as long as the hollow microcantilever beam structure is satisfied, it falls within the scope of protection of this patent. In addition, in order to expand the gas detection range, the size of the hollow microcavity base is not limited to the specific dimensions in the above embodiment, and the specific materials doped in the commercial photoresist are also not limited to the four specific materials in the above embodiment, such as materials specific to volatile organic compounds (VOCs).

[0044] Example 6 A method for manufacturing a multi-microcavity gas detection optical fiber sensor having a hollow microcavity film structure comprises the following steps: Step 1. Take a section of four-core single-mode optical fiber, clean the end face of the four-core single-mode optical fiber, and cut it flat with a cutting knife. Place the flattened standard four-core single-mode optical fiber on the optical fiber clamp and fix it; drop commercial photoresist on the tip of the four-core single-mode optical fiber to immerse the end face; then transfer the clamped four-core single-mode optical fiber to the femtosecond laser induced TPP equipment for processing; in order to ensure that the hollow microcavity film is printed in good morphology, use a 25-100x oil immersion lens (numerical aperture NA=1.4) during focusing; import the pre-designed hollow microcavity film model into the system of the processing equipment, control the movement of the femtosecond laser induced TPP system through the scanning path, use commercial photoresist to print 4 hollow microcavity bases with a diameter of 10μm and heights of 28μm, 40μm, 48μm and 63.5μm respectively above the core of the four-core single-mode optical fiber, and at the same time print a hollow film with a thickness of 2.5μm on the upper surface of the four hollow microcavity bases.

[0045] Step 2: Soak the optical fiber printed by femtosecond laser two-photon polymerization in step 1 in a soaking solution for 2 minutes. The soaking solution is a mixture of acetone and isopropyl alcohol in a volume ratio of 1:5. After soaking, clean the uncured photoresist.

[0046] Step 3. Fix the optical fiber processed in step 2 on the optical fiber clamp, and then transfer the clamped optical fiber to the femtosecond laser-induced TPP equipment for processing. Add commercial photoresist doped with Pt / TiO2 nanoparticles on the hollow film of the hollow microcavity base with a height of 28μm, ensuring that the photoresist solution covers the entire hollow film. Use commercial photoresist doped with Pt / TiO2 nanoparticles to print a specific film with a thickness of 4.5μm on the upper surface of the hollow film. This specific film is used to detect H2.

[0047] Step 4: Add commercial photoresist doped with WO3 quantum dots onto the hollow film of the hollow microcavity base with a height of 40 μm, ensuring that the photoresist solution covers the entire hollow film. Use commercial photoresist doped with WO3 quantum dots to print a specific film with a thickness of 4.5 μm on the upper surface of the hollow film. This specific film is used to detect NO2.

[0048] Step 5. Add commercial photoresist doped with Pd / Al2O3 nanosheets onto the hollow film of the hollow microcavity base with a height of 48 μm, ensuring that the photoresist solution covers the entire hollow film. Use commercial photoresist doped with Pd / Al2O3 nanosheets to print a specific film with a thickness of 4.5 μm on the upper surface of the hollow film. This specific film is used to detect CH4.

[0049] Step 6: Add a commercial photoresist doped with Au-ZnO nanorods onto the hollow film of the hollow microcavity base with a height of 63.5 μm, ensuring that the photoresist solution covers the entire hollow film. Then, print a 4.5 μm thick specific film on the upper surface of the hollow film using the commercial photoresist doped with Au-ZnO nanorods. This specific film is used for CO detection.

[0050] Step seven, curing: After cleaning the residual photoresist on the gas detection optical fiber sensor obtained in step six, irradiate it with ultraviolet light for 4-6 minutes for curing, and after curing, a four-microcavity gas detection optical fiber sensor is obtained.

[0051] In order to achieve the best printing effect of the hollow microcavity film, during the femtosecond laser two-photon polymerization printing process using a femtosecond laser induced TPP device, the power of the femtosecond laser was 10-50 mW, the repetition rate was 80 MHz, the operating wavelength was 800 nm, the scanning speed was 800 µm / s, the line spacing was 100 nm-1 µm, and the slice spacing was 100 nm-1 µm.

[0052] Two-photon polymerization technology utilizes the two-photon absorption effect of femtosecond lasers to trigger polymerization of photosensitive materials only at the laser's focal point, achieving submicron resolution (with a minimum feature size of up to 120 nm). This property enables precise control of the geometry and internal structure of the microcavity when printing hollow microcavity film structures on the end face of an optical fiber, meeting the high surface quality and shape accuracy requirements of optical devices. Four microcavities with hollow microcavity film structures at different heights are integrated on the end face of a four-core optical fiber. Due to the highly elastic suspension properties at the center of the hollow microcavity film structure, this solves the problem of the large size and complexity of existing simultaneous multi-gas detection systems.

Claims

1. A multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure, characterized by: The multi-microcavity gas detection optical fiber sensor is composed of a multi-core single-mode optical fiber (5) and a plurality of hollow microcavity films capable of detecting different gases; the matrix material of the hollow microcavity film is commercial photoresist, and the hollow microcavity film is composed of a hollow microcavity base (6), a hollow film (7) and a doped gas-sensitive particle film (8); the hollow microcavity base (6) is located on the end face of the core of the multi-core single-mode optical fiber (5), the hollow film (7) is located on the upper surface of the hollow microcavity base (6), and the doped gas-sensitive particle film (8) is located on the upper surface of the hollow film (7); and the hollow microcavity bases (6) of the plurality of hollow microcavity films have different heights.

2. The multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure according to claim 1, characterized in that: The multi-core single-mode optical fiber (5) is a four-core single-mode optical fiber, and the center line connecting the four cores is a regular quadrilateral; the number of the plurality of hollow microcavity films is four, namely a first hollow microcavity film (1), a second hollow microcavity film (2), a third hollow microcavity film (3) and a fourth hollow microcavity film (4), and the four hollow microcavity films correspond to the four cores.

3. The multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure according to claim 2, characterized in that: The doped gas-sensitive particle film (8) of the first hollow microcavity film (1) is a film doped with Pt / TiO2 nanoparticles, the doped gas-sensitive particle film (8) of the second hollow microcavity film (2) is a film doped with WO3 quantum dots, the doped gas-sensitive particle film (8) of the third hollow microcavity film (3) is a film doped with Pd / Al2O3 nanosheets, and the doped gas-sensitive particle film (8) of the fourth hollow microcavity film (4) is a film doped with Au-ZnO nanorods.

4. The multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure according to claim 2 or 3, characterized in that: The cladding diameter of the four-core single-mode optical fiber is 120-130 μm, the core diameter is 8-10 μm, and the spacing between two adjacent cores is 33-37 μm; the diameters of the hollow microcavity bases (6) of the first hollow microcavity film (1), the second hollow microcavity film (2), the third hollow microcavity film (3), and the fourth hollow microcavity film (4) are all 9-11 μm, and their heights are 26-30 μm, 38-42 μm, 46-50 μm, and 61-66 μm, respectively; the thicknesses of the hollow films (7) and the doped gas-sensitive particle films (8) of the first hollow microcavity film (1), the second hollow microcavity film (2), the third hollow microcavity film (3), and the fourth hollow microcavity film (4) are less than 3 μm and 5 μm, respectively.

5. The multi-microcavity gas detection optical fiber sensor with a hollow microcavity film structure according to claim 4, characterized in that: The cladding diameter of the four-core single-mode optical fiber is 125 μm, the core diameter is 9 μm, and the spacing between two adjacent cores is 35 μm; the diameters of the hollow microcavity bases (6) of the first hollow microcavity film (1), the second hollow microcavity film (2), the third hollow microcavity film (3), and the fourth hollow microcavity film (4) are all 10 μm, and their heights are 28 μm, 40 μm, 48 μm, and 63.5 μm, respectively; the thicknesses of the hollow films (7) and the doped gas-sensitive particle films (8) of the first hollow microcavity film (1), the second hollow microcavity film (2), the third hollow microcavity film (3), and the fourth hollow microcavity film (4) are 2.5 μm and 4.5 μm, respectively.

6. A method for fabricating a multi-microcavity gas detection optical fiber sensor having a hollow microcavity film structure, characterized by: The preparation method comprises the following steps: Step 1: Take a section of four-core single-mode optical fiber, clean the end face of the four-core single-mode optical fiber, and cut it flat with a cutting knife, place the flattened standard four-core single-mode optical fiber on an optical fiber clamp and fix it; drip commercial photoresist onto the tip of the four-core single-mode optical fiber to immerse the end face; then transfer the clamped four-core single-mode optical fiber to a femtosecond laser-induced TPP device for processing; import the pre-designed hollow microcavity film model into the system of the processing equipment, control the movement of the femtosecond laser-induced TPP system through a scanning path, and use commercial photoresist to print four hollow microcavity bases with a diameter of 10 μm and heights of 28 μm, 40 μm, 48 μm and 63.5 μm above the core of the four-core single-mode optical fiber, and at the same time print a hollow film with a thickness of 2.5 μm on the upper surface of the four hollow microcavity bases; Step 2: Soak the optical fiber printed by femtosecond laser two-photon polymerization in a soaking solution for 2 minutes. The soaking solution is a mixture of acetone and isopropyl alcohol in a volume ratio of 1:

5. After soaking, clean the uncured photoresist. Step 3: Fix the optical fiber processed in Step 2 on the optical fiber clamp, then transfer the clamped optical fiber to the femtosecond laser-induced TPP equipment for processing, drip a commercial photoresist doped with Pt / TiO2 nanoparticles on the hollow film of the hollow microcavity base with a height of 28μm, ensure that the photoresist solution covers the entire hollow film, and print a specific film with a thickness of 4.5μm on the upper surface of the hollow film using the commercial photoresist doped with Pt / TiO2 nanoparticles. This specific film is used for H2 detection; Step 4: Add a commercial photoresist doped with WO3 quantum dots onto the hollow film of the hollow microcavity base with a height of 40 μm, ensuring that the photoresist solution covers the entire hollow film. Then, print a 4.5 μm thick specific film on the upper surface of the hollow film using the commercial photoresist doped with WO3 quantum dots. This specific film is used for NO2 detection. Step 5: Add a commercial photoresist doped with Pd / Al2O3 nanosheets onto the hollow film of the hollow microcavity base with a height of 48 μm, ensuring that the photoresist solution covers the entire hollow film. Then, print a 4.5 μm thick specific film on the upper surface of the hollow film using the commercial photoresist doped with Pd / Al2O3 nanosheets. This specific film is used to detect CH4. Step 6: Add a commercial photoresist doped with Au-ZnO nanorods onto the 63.5 μm-high hollow film of the hollow microcavity base, ensuring that the photoresist solution covers the entire hollow film. Then, print a 4.5 μm-thick specific film on the upper surface of the hollow film using the commercial photoresist doped with Au-ZnO nanorods. This specific film is used for CO detection. Step seven, curing: After cleaning the residual photoresist on the gas detection optical fiber sensor obtained in step six, irradiate it with ultraviolet light for 4-6 minutes for curing, and after curing, a four-microcavity gas detection optical fiber sensor is obtained.

7. The method for manufacturing a multi-microcavity gas detection optical fiber sensor having a hollow microcavity film structure according to claim 6, characterized in that: In the process of femtosecond laser two-photon polymerization printing using a femtosecond laser-induced TPP device, the power of the femtosecond laser is 10-50 mW, the repetition rate is 80 MHz, the operating wavelength is 800 nm, the scanning speed is 800 µm / s, the line spacing is 100 nm-1 µm, and the slice spacing is 100 nm-1 µm.

8. A method for detecting multiple gases using a multi-microcavity gas detection optical fiber sensor having a hollow microcavity film structure, characterized in that: The detection method includes the following steps: The first step was to connect a broadband light source, a fiber optic spectrum analyzer, a 3dB coupler, an optical switch, an MCF fan input / output device, and a four-microcavity gas detection fiber optic sensor in a mixed gas chamber via single-mode fiber fusion splicing to form a detection system. The mixed gas chamber is a five-way connection made of plastic tubing. Four of the microchannels are for the gas to be measured, and one microchannel is for the nitrogen gas concentration adjustment. In the second step, the gas flow rates of H2, NO2, CH4, CO to be detected and N2 for gas concentration adjustment are controlled by the intelligent gas flowmeter on the input gas pipe. While maintaining the total flow rate at 500 mL / min, the flow rates of H2, NO2, CH4, CO and N2 are adjusted by computer to achieve gas concentration regulation. The four-microcavity gas detection fiber optic sensor transmits the detection data to the fiber optic spectrum analyzer for data analysis.

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