Multi-core optical fiber end face hydrogen and air pressure decoupling sensor and preparation method thereof

Abstract

The invention belongs to the technical field of optical fiber sensing, and particularly relates to a multi-core optical fiber end face hydrogen and air pressure decoupling sensor and a preparation method thereof. The sensor of the present invention comprises: a multi-core fiber; the micro cantilever beam and the closed cavity structure located on the end face of the multi-core optical fiber are directly printed on the end face of the optical fiber through a femtosecond laser two-photon polymerization technology; the palladium film positioned on the upper surface of the micro-structure is formed by plating through an electron beam evaporation technology, so that the micro-cantilever has hydrogen sensitivity; and the cavity is sealed by ultraviolet glue. According to the invention, hydrogen and air pressure can be measured at the same time in a micro-channel, an air chamber, an air storage and storage tank and other scenes, the sensor has the characteristics of small size, easy integration, high sensitivity, reliability and safety, and a reliable hydrogen monitoring function can be realized in a pressure fluctuation environment.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber sensing technology, specifically relating to a multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor and its preparation method. Background Technology

[0002] Benefiting from their unique advantages such as resistance to electromagnetic interference, chemical corrosion, small size, and economical cost, fiber optic sensors have received widespread research and attention in the field of sensing technology, and have gradually become a research focus in this area. Among various fiber optic sensors, single-core fiber optic sensors have the most mature technology and have been successfully developed and applied in many fields such as high-temperature environment monitoring, gas detection, and biosensing. The excellent biocompatibility, arc-free characteristics, and high sensitivity of this type of sensor fully demonstrate the enormous development potential of fiber optic technology in the biomedical field and in sensing applications under extreme conditions.

[0003] However, it is undeniable that traditional single-core fiber optic sensors have significant limitations: on the one hand, their detection function is mainly focused on a single physical or chemical parameter, making it difficult to adapt to the actual needs of simultaneously detecting multiple parameters in complex environments; on the other hand, changes in other irrelevant parameters in the environment can easily introduce interference errors into the measurement process, which greatly limits the accuracy and precision of the sensor. To improve this situation, some studies have attempted to achieve multi-parameter sensing and parameter compensation by fabricating multiple sensing elements such as fiber gratings and interferometers inside the core of a single-core fiber. However, this method is prone to signal crosstalk between sensing elements and introduces additional transmission losses, ultimately leading to a decrease in the overall performance of the sensor. In addition, some studies have used fiber bundles to achieve discrete detection of multiple parameters. While this approach can expand the measurement dimension to some extent, it increases the size of the sensor and makes the structure of the entire sensing system more complex, thus limiting its widespread use in miniaturized and integrated applications.

[0004] The emergence of multi-core optical fibers provides an effective solution to the aforementioned problems. By integrating several independent fiber cores into a single fiber, they form a multi-channel optical transmission path. This not only offers a compact structure but also further expands the integration space and dimensions of optical sensing elements. Researchers have already successfully achieved precise sensing of parameters such as bending, torsion angles, and acceleration in multiple directions by incorporating fiber grating structures into the individual cores of multi-core optical fibers. In addition to accurate measurement of parameter values, they also possess the ability to identify the direction of the parameters. Furthermore, by integrating different types and materials of optical sensing elements on different fiber cores, the measurement range of the sensors can be further expanded from single-parameter measurement to simultaneous detection of multiple parameters. The simultaneous measurement of temperature and humidity is the most typical application example. This improvement significantly enhances the adaptability of fiber optic sensors to complex environments.

[0005] Hydrogen, as a clean gas, possesses both antioxidant and anti-inflammatory medicinal properties and efficient energy applications, making it highly valuable. However, its inherent flammability and explosiveness pose significant safety risks during transportation, storage, and practical application, placing stringent demands on its detection technology. Optical fiber, as a waveguide for optical signal transmission, offers the significant advantage of arc-free operation, enabling detection without contact with the gas being measured, making it an ideal device for detecting flammable and explosive gases like hydrogen. In recent years, various fiber-optic-based hydrogen sensors have been extensively researched and developed; however, existing research largely focuses on detecting only the single parameter of hydrogen concentration, which is insufficient to meet the practical detection needs of complex application scenarios. Especially when detecting hydrogen concentration in high-pressure environments, pressure changes can trigger significant spectral interference, leading to severe cross-sensitivity issues. This drastically reduces the accuracy of hydrogen concentration measurements, failing to provide reliable safety guarantees for hydrogen energy-related applications. Based on this, multi-core optical fiber technology is used to realize the synchronous decoupled detection of hydrogen concentration and pressure in hydrogen energy safety and related application fields, which effectively solves the problem of cross-sensitivity, improves the accuracy and reliability of detection, and has extremely important theoretical research significance and practical application value. Summary of the Invention

[0006] The purpose of this invention is to provide a small-sized, easily integrated, highly sensitive, reliable and secure multi-core fiber end-face hydrogen and gas pressure decoupling sensor and its fabrication method.

[0007] The multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor proposed in this invention includes:

[0008] Multi-core optical fiber 1, that is, a single optical fiber containing multiple parallel cores; and:

[0009] A cavity 21, located at the end face directly above a fiber core and sealed by UV adhesive, has a sensing film 25 on top. The sensing film 25 is used to block light emitted from the fiber core. The end face of the fiber core and the lower surface of the film 25 on the top of the cavity 21 serve as two mirrors to form an air Fabry-Perot interferometer.

[0010] An inclined shielding cover 26 is located above the cavity 21 and connected to the surrounding support pillars 24; the shielding cover 26 is used to shield palladium metal during the preparation process to prevent it from depositing on the top film of the cavity 2, causing sensor cross-sensitivity, reducing the influence of multi-beam interference to facilitate spectral demodulation.

[0011] The microcantilever beam 31 is hydrogen-sensitive. One end of it is connected to the lower side of the inclined shielding cover 26, and the other end is suspended and located on the upper end face of another fiber core, blocking the light emitted from the fiber core. The end face of the fiber core and the lower surface of the microcantilever beam serve as two mirrors to form a Fabry-Perot interferometer in air medium.

[0012] Palladium film 32 covering the upper surfaces of inclined shielding cover 26 and microcantilever beam 31;

[0013] The cavity 2 has a connecting pipe 23 on its side, which is used to facilitate the cleaning of unpolymerized photoresist inside the cavity by the developing solution and the subsequent sealing with ultraviolet ester.

[0014] Furthermore:

[0015] The cavity 21, the shielding cover 26 and the microcantilever beam 31 are directly printed on the end face of the optical fiber by femtosecond laser two-photon polymerization.

[0016] The palladium film 32 is located on the upper surface of the microcantilever beam and the shielding cover, and is deposited by electron beam evaporation technology;

[0017] The cavity 21 can be in the shape of a hollow cylinder, prism, or other structures.

[0018] The palladium film is deposited on the upper surface of the microcantilever beam and the shielding cover, and its shape is consistent with that of the microcantilever beam and the shielding cover.

[0019] Furthermore:

[0020] The number of cores in the multi-core optical fiber 1 is N, where N≥2;

[0021] The cavity 21 has a height of 5~200μm, a wall thickness of 2~10μm, and a top circular film 25 with a thickness of 0.1~5μm;

[0022] The length of the side pipe 23 of the cavity 21 is 5~30μm and the diameter is 2~20μm;

[0023] The thickness of the shielding cover 26 is 1~10μm, and the tilt angle is 8°~60°;

[0024] The microcantilever beam 31 has a length of 5~50μm, a width of 2~50μm, and a thickness of less than 20μm;

[0025] The thickness of the palladium film 32 is less than 1 μm;

[0026] This invention also provides a method for fabricating the above-mentioned multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor, the specific steps of which are as follows:

[0027] (1) Based on the core diameter, core distribution and core spacing of the multi-core optical fiber, considering the adhesion between the polymer structure and the end face of the optical fiber, design a matching cavity, and considering the mechanical properties of the polymer material, design a matching micro cantilever beam.

[0028] (2) Cut the multi-core fiber flat with a cleaver, immerse the fiber end face in photoresist, and assemble it onto the femtosecond laser processing platform. Observe the CCD imaging and move the platform to find the fiber end face. Select a suitable processing start position, focus the femtosecond laser through the oil immersion objective lens, and process the micro cantilever beam and cavity designed in step (1) with the help of a high-precision displacement platform.

[0029] (3) Use a developer to remove the unpolymerized photoresist from the sample processed in step (2) to obtain the polymerized microcantilever beam and cavity structure, and use an ultraviolet lamp for polymerization reinforcement;

[0030] (4) Place the reinforced sample from step (3) together with a single-mode optical fiber with a small amount of UV adhesive on its end face on a precision displacement platform. Observe the CCD imaging and slowly move the platform to immerse the channel on the side wall of the cavity into the UV adhesive. Once the adhesive flows in and seals the channel, immediately separate the two optical fibers to prevent the adhesive from continuing to flow into the cavity. Then, cure the adhesive in the channel by irradiation with a UV lamp.

[0031] (5) Electron beam evaporation is used to coat the sample after filling the adhesive in step (4) with a palladium film on the upper surface of the microcantilever beam to make the sample hydrogen sensitive.

[0032] In this invention, once the air pressure fluctuates in the environment where the sensor is located, the top thin film 25 will deform due to the air pressure difference between the inside and outside of the cavity, which will cause the length of the Fabry-Perot interferometer cavity to change. By monitoring the change of its interference signal, the air pressure change in the environment can be measured.

[0033] In this invention, once the sensor is in a hydrogen environment, the palladium film absorbs hydrogen and expands, creating a stress difference between the palladium film and the microcantilever beam, causing the microcantilever beam to bend. By monitoring the changes in the interference signal, the hydrogen concentration in the environment can be measured.

[0034] The closed cavity Fabry-Perot interferometer formed by the polymer film and the fiber core end face has different effects on gas pressure and hydrogen concentration. and The Fabry-Perot interferometer formed by the microcantilever beam exhibits high sensitivity to both gas pressure and hydrogen concentration. and The sensitivity, and satisfying the formula:

[0035] ,

[0036] in, and capital letters These are the total wavelength shifts caused by changes in atmospheric pressure and hydrogen concentration in the environment for a closed-cavity Fabry-Perot interferometer and a microcantilever Fabry-Perot interferometer, respectively. The atmospheric pressure changes in the environment can be calculated using the formula. and changes in hydrogen concentration .

[0037] This invention proposes a multi-core fiber optic end-face hydrogen and gas pressure decoupled sensor. A cavity and micro-cantilever beam structure are directly printed on the fiber end-face using femtosecond laser two-photon polymerization technology, and a palladium film is deposited on the upper surface of the micro-cantilever beam using electron beam evaporation, giving it hydrogen sensitivity. This multi-core fiber optic end-face sensor can simultaneously measure hydrogen and gas pressure in scenarios such as microchannels, gas chambers, and gas ducts. It features small size, easy integration, high sensitivity, and high reliability and safety, and can effectively and in real-time monitor hydrogen concentration and pressure changes during hydrogen transportation. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention.

[0039] Figure 2 This is a schematic diagram of the multi-core fiber end face, microcantilever beam structure, and enclosed cavity in Embodiment 1 of the present invention.

[0040] Figure 3 This is a scanning electron microscope image of the sensor in Embodiment 1 of the present invention.

[0041] Figure 4 The reflection spectra of the microcantilever beam and the closed cavity in Embodiment 1 of the present invention are shown.

[0042] Figure 5 The images show the reflection spectra of the microcantilever beam and the enclosed cavity under different gas pressures and hydrogen concentrations in Embodiment 1 of the present invention.

[0043] Figure 6 This is a schematic diagram of the structure of Embodiment 2 of the present invention.

[0044] Figure 7This is a flowchart of the fabrication method of the multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor in this invention.

[0045] The numbers in the diagram are as follows: 1 is a multi-core optical fiber, 2 is a closed cavity structure, 21 is a cavity, 22 is the port of pipe 23, 23 is a pipe, 24 is a support column, 25 is a sensing film, 26 is a shielding cover, 3 is a micro cantilever beam structure, 31 is a micro cantilever beam, 32 is a palladium film, 4 is a two-photon polymerization photoresist, 5 is a femtosecond laser, 6 is a single-mode optical fiber, and 7 is a UV adhesive. Detailed Implementation

[0046] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0047] Example 1: A multi-core fiber optic end-face hydrogen and gas pressure decoupling sensor, the structure of which is described in [reference needed]. Figure 1 As shown, it includes a multi-core optical fiber, a micro-cantilever beam structure, and a closed cavity. The multi-core optical fiber 1 includes a cladding and multiple parallel cores; the closed cavity structure 2 includes an outer wall 21, cured UV adhesive 22, a conduit 23, a support block 24, a sensing film 25, and a shielding cover 26; the micro-cantilever beam structure 3 includes a micro-cantilever beam 31 and a palladium film 32.

[0048] Figure 2 This is a schematic diagram of the multi-core optical fiber end face, micro-cantilever beam structure, and closed cavity of Embodiment 1 of the present invention.

[0049] Figure 3 This is a scanning electron microscope image of the sensor in Embodiment 1 of the present invention.

[0050] The multi-core optical fiber 1 has 4 cores, which are arranged in a square pattern.

[0051] The enclosed cavity structure 2 is located above a fiber core. The cavity 21 is a hollow cylinder. The side channels 23 are filled with UV adhesive and then cured. The top film 25 of the cavity is used to block light emitted from the fiber core. The end face of the fiber core and the lower surface of the top film 25 of the cavity act as two mirrors to form an air Fabry-Perot interferometer. Above the cavity is an inclined circular shielding cover 26, surrounded by supporting pillars 24, which are used to shield palladium metal to prevent it from depositing on the top film of the cavity and causing cross-sensitivity of the sensor, and to reduce the influence of multi-beam interference to facilitate spectral demodulation. Once the air pressure in the sample's environment fluctuates, the top film 25 will deform due to the pressure difference between the inside and outside of the cavity, which will cause a change in the cavity length of the Fabry-Perot interferometer. By monitoring the change in its interference signal, the change in air pressure in the environment can be measured.

[0052] The microcantilever beam structure is connected to the closed cavity 21 at position 3, suspended above another fiber core, and blocks light emitted from the fiber core. The end face of the fiber core and the lower surface of the microcantilever beam act as two mirrors, forming a Fabry-Perot interferometer in air medium. A palladium film is deposited on the upper surface of the microcantilever beam as a functional layer, with a shape consistent with the microcantilever beam. Once the sample is placed in a hydrogen environment, the palladium film absorbs hydrogen and expands, creating a stress difference between the palladium film and the microcantilever beam, causing the microcantilever beam to bend. By monitoring the changes in the interference signal, the hydrogen concentration in the environment can be measured.

[0053] The circular film at the top of the enclosed cavity has a radius of 30 μm and a height of 30 μm. The side pipe has a length of 25 μm and a diameter of 10 μm. The palladium metal shielding cover above has a thickness of 2 μm.

[0054] The microcantilever has a length of 40 μm, a width of 20 μm, a thickness of 2 μm, and a height of 40 μm. A 10 × 10 μm hollow region is created in the middle of the microcantilever beam to improve its sensitivity to deformation.

[0055] Figure 4 The reflection spectra of the microcantilever beam and the closed cavity in Embodiment 1 of the present invention are shown.

[0056] The reflectance spectrum of the sensor was characterized by connecting a broadband light source, a spectrometer, a 3dB coupler, and a sample integrating a four-core fiber fan-in / fan-out device. The microcantilever beam reflectance spectrum showed a fringe contrast of 1.14dB at a resonant wavelength of 1442.65nm and a free spectral range of 27.05nm. The closed cavity reflectance spectrum showed a fringe contrast of 19.45dB at a resonant wavelength of 1417.74nm and a free spectral range of 46.84nm. The strong absorption effect of the palladium metal thin film and the asymmetric reflection characteristics of the microcantilever beam Fabry-Perot interferometer cavity severely suppressed multi-beam interference, resulting in a significant reduction in the fringe contrast of the microcantilever beam reflectance spectrum.

[0057] Figure 5 The images show the reflection spectra of the microcantilever beam and the enclosed cavity under different gas pressures and hydrogen concentrations in Embodiment 1 of the present invention.

[0058] Hydrogen and nitrogen gases were mixed via a three-way connector, with a third microchannel serving as the output channel for the mixture. The sensor was installed within this third microchannel. The concentrations of hydrogen and nitrogen in the mixture were regulated by two gas flow meters. The reflectance spectrum was continuously monitored using a broadband light source and a spectrometer. During the measurement, the sensor was positioned at an ambient temperature of 23.5°C. The hydrogen concentration was gradually increased from 0% to 4% in 0.5% (volume ratio) increments, with a 15-minute time interval between each test point to ensure sufficient sensor response. When hydrogen first entered the pipe, the reflectance spectrum shifted towards shorter wavelengths; a blue shift of 28.03 nm occurred near 1645 nm as the hydrogen concentration increased from 0% to 4%. Polynomial fitting of the experimental data yielded a sensitivity of -15.02 nm / % for the microcantilever Fabry-Perot interferometer to hydrogen concentration. Because the sensing film at the top of the enclosed cavity is blocked by the upper cover, no palladium metal is deposited on its surface. Therefore, the film is not sensitive to changes in hydrogen concentration, and its hydrogen concentration sensitivity is 0 nm / .

[0059] To investigate the sensor's response to pressure changes, it was placed in a chamber connected to a high-pressure nitrogen cylinder and a pressure gauge. The chamber pressure was increased from 0 MPa to 0.5 MPa in 100 kPa increments at room temperature. With increasing pressure, a blue shift occurred in the reflection spectrum of the closed cavity. The tracking resonant wavelength showed a linear relationship with the pressure, and linear fitting calculations yielded a sensitivity of -76.98 nm / MPa to pressure. At a constant temperature, when the gas pressure changed, the refractive index of the gas in the Fabry-Perot interference cavity formed by the lower surface of the microcantilever beam and the fiber end face also changed. Within the pressure range of 0 MPa to 0.5 MPa, the wavelength of the microcantilever beam's interference spectrum red-shifted with increasing pressure. Fitting analysis of the wavelength data revealed a sensitivity of 4 nm / MPa to pressure.

[0060] Therefore, the dual-parameter sensitivity coefficient matrix can be expressed as:

[0061] ,

[0062] in, and These are the total wavelength shifts caused by changes in atmospheric pressure and hydrogen concentration in the environment for a closed-cavity Fabry-Perot interferometer and a microcantilever Fabry-Perot interferometer, respectively. The atmospheric pressure changes in the environment can be calculated using the formula. and changes in hydrogen concentration .

[0063] With its inherent safety, high sensitivity, and high reliability, this sensor has great application potential in the real-time monitoring of hydrogen energy systems and in confined or hazardous environments.

[0064] Example 2: A multi-core fiber optic end-face hydrogen and gas pressure decoupling sensor, its structure is as follows. Figure 6 As shown.

[0065] The multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor includes a multi-core optical fiber, a closed cavity, and a micro-cantilever beam structure. The multi-core optical fiber 1 includes a cladding and multiple parallel cores; the closed cavity structure 2 includes a cavity 21, cured UV adhesive 22, a conduit 23, a support block 24, a sensing film 25, and a shielding cover 26; the micro-cantilever beam structure 3 includes a micro-cantilever beam 31 and a palladium film 32.

[0066] The multi-core optical fiber has 4 cores, which are arranged in a square pattern.

[0067] The circular film at the top of the enclosed cavity has a radius of 30 μm and a height of 40 μm. The side pipe has a length of 30 μm and a diameter of 10 μm. The palladium metal shielding cover above has a thickness of 2 μm.

[0068] The microcantilever beam is rectangular in shape, with a length of 40μm, a width of 15μm, a thickness of 1.5μm, and a height of 50μm.

[0069] The above embodiments also provide a method for fabricating a multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor, such as... Figure 7 As shown, the specific steps include:

[0070] (1) Based on the core diameter, core distribution and core spacing of the multi-core optical fiber, considering the adhesion between the polymer structure and the end face of the optical fiber, design a matching cavity outer wall thickness, and considering the mechanical properties of the polymer material, design a matching micro cantilever beam.

[0071] In this step, by measuring the core diameter, core distribution, and core spacing of the multi-core optical fiber, the fiber cores for forming the air Fabry-Perot interferometer and the polymer Fabry-Perot interferometer are selected respectively. Considering the adhesion between the polymer and the end face of the optical fiber, a suitable cavity bottom area and pre-processing position are designed. Considering the mechanical properties of the polymer material, a suitable shape and size of the micro cantilever beam 31 are designed, and the design model is modeled using software.

[0072] (2) Cut the multi-core fiber flat with a cleaver, immerse the fiber end face in photoresist, and assemble it onto the femtosecond laser processing platform. Observe the CCD imaging and move the platform to find the fiber end face. Select a suitable processing start position, focus the femtosecond laser through the oil immersion objective lens, and process the cavity and micro cantilever beam designed in step (1) with the help of a high-precision displacement platform.

[0073] In this step, the multi-core optical fiber is cut flat using a cleaver, the fiber end face is immersed in two-photon polymerized photoresist 4, and it is assembled onto the femtosecond laser processing platform using an optical fiber clamp. The precision displacement platform is adjusted and CCD imaging is used to achieve clear focusing on the fiber end face. The platform is adjusted to the initial processing point according to the design scheme, and the femtosecond laser 5 is focused using a high numerical aperture oil immersion objective lens. With the help of a high-precision displacement platform, the cavity and microcantilever beam structure are printed according to the optimized processing parameters such as scanning speed, scanning path, laser energy, and slicing method.

[0074] (3) Use a developer to remove the unpolymerized photoresist from the sample processed in step (2) to obtain the polymerized cavity and microcantilever beam structure, and use an ultraviolet lamp for polymerization reinforcement.

[0075] In this step, the sample after polymerization in step (2) is immersed in the developer to remove the unpolymerized photoresist. The optimized developer composition and development time are controlled to obtain a thoroughly developed cavity and microcantilever beam structure. The microcantilever beam structure is then reinforced by irradiation with ultraviolet light for a period of time.

[0076] (4) Place the reinforced sample from step (3) and a single-mode optical fiber with a small amount of UV adhesive on its end face on a precision displacement platform. Observe the CCD imaging and slowly move the platform to immerse the channel on the sidewall of the cavity into the UV adhesive. Once the adhesive flows in and seals the channel, immediately separate the two optical fibers to prevent the adhesive from continuing to flow into the cavity. Then, cure the adhesive in the channel by UV irradiation to complete the sealing of the cavity.

[0077] (5) The sample developed in step (4) is coated with a palladium film on the upper surface of the microcantilever beam using electron beam evaporation technology to make the sample hydrogen sensitive.

[0078] In this step, the sample that has been sealed in step (4) is placed in an electron beam evaporation coating instrument with the fiber end face facing the target material. The coating chamber is evacuated to achieve the optimized gas chamber pressure. The fiber sample is coated with a palladium film of a certain thickness by controlling the voltage, current and time.

[0079] Finally, the specific embodiments described above can be partially adjusted by those skilled in the art in different ways without departing from the principles and spirit of this invention, and are not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor, characterized in that, include: Multi-core optical fiber (1) means that a single optical fiber contains multiple parallel cores; as well as: The cavity (21) is located at the end face directly above a certain fiber core. It is a closed cavity formed by curing UV adhesive. The top of the cavity is a sensing film (25), which is used to block the light emitted from the fiber core. The end face of the fiber core and the lower surface of the top film (25) serve as two mirrors to form an air Fabry-Perot interferometer. An inclined shielding cover (26) is located above the cavity (21) and is connected to the cavity (21) through the surrounding support pillars (24); the inclined shielding cover (26) is used to shield palladium metal during the preparation process to prevent it from depositing on the top film of the cavity (21), causing the sensor to be cross-sensitive, reducing the influence of multi-beam interference to facilitate spectral demodulation; The microcantilever beam (31) is hydrogen-sensitive. One end of it is connected to the lower side of the inclined shielding cover (26), and the other end is suspended and located on the upper end face of another fiber core, blocking the light emitted from the fiber core. The end face of the fiber core and the lower surface of the microcantilever beam serve as two mirrors to form a Fabry-Perot interferometer in air medium. A palladium film (32) is applied to the upper surface of the inclined shielding cover (26) and the microcantilever beam (31); The cavity (21) has a connecting pipe (23) on its side, which is used to facilitate the cleaning of the unpolymerized photoresist inside the cavity by the developer and the subsequent sealing with UV adhesive.

2. The multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor according to claim 1, characterized in that: The cavity (21), the tilted shielding cover (26), and the microcantilever beam (31) are directly printed on the end face of the optical fiber by femtosecond laser two-photon polymerization; The palladium film (32) is located on the upper surface of the microcantilever beam and the shielding cover and is deposited by electron beam evaporation technology.

3. The multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor according to claim 1, characterized in that: The cavity (21) is in the shape of a hollow cylinder or a prism; The palladium film (32) is coated on the upper surface of the microcantilever beam and the shielding cover, and its shape is consistent with that of the microcantilever beam and the shielding cover.

4. The multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor according to claim 1, characterized in that: The number of cores in the multi-core optical fiber (1) is N, where N≥2; The cavity (21) has a height of 5~200μm, a wall thickness of 2~10μm, and a top film (25) thickness of 0.1~5μm; The length of the side pipe (23) of the cavity (21) is 5~30μm and the diameter is 2~20μm; The thickness of the shield (26) is 1~10μm and the tilt angle is 8°~60°.

5. The multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor according to claim 1, characterized in that: The length of the microcantilever beam (31) is 5~50μm, the width is 2~50μm, and the thickness is less than 20μm; The thickness of the palladium film (32) is less than 1 μm.

6. The method for fabricating the multi-core optical fiber end-face hydrogen and gas pressure decoupling sensor as described in any one of claims 1-5, characterized in that: The specific steps are as follows: (1) Based on the core diameter, core distribution and core spacing of the multi-core optical fiber, considering the adhesion between the polymer structure and the end face of the optical fiber, design a matching cavity, and considering the mechanical properties of the polymer material, design a matching micro cantilever beam. (2) Cut the multi-core fiber flat with a cleaver, immerse the fiber end face in photoresist, and assemble it onto the femtosecond laser processing platform. Observe the CCD imaging and move the platform to find the fiber end face. Select a suitable processing start position, focus the femtosecond laser through the oil immersion objective lens, and process the micro cantilever beam and cavity designed in step (1) with the help of a high-precision displacement platform. (3) Use a developer to remove the unpolymerized photoresist from the sample processed in step (2) to obtain the polymerized microcantilever beam and cavity structure, and use an ultraviolet lamp for polymerization reinforcement; (4) Place the reinforced sample from step (3) together with a single-mode optical fiber with a small amount of UV adhesive on its end face on a precision displacement platform, observe the CCD imaging and slowly move the platform to immerse the tube on the side wall of the cavity into the UV adhesive. Once the adhesive flows in and seals the tube, immediately separate the two optical fibers to prevent the adhesive from continuing to flow into the cavity. Then, irradiate the tube with a UV lamp to cure the adhesive. (5) Electron beam evaporation is used to coat the sample after filling the adhesive in step (4) with a palladium film on the upper surface of the microcantilever beam to make the sample hydrogen sensitive.

Images