A fiber optic hydrogen sensor based on cantilever beam film and its preparation method

Abstract

The present invention discloses a fiber optic hydrogen sensor based on a cantilever beam film. The sensor comprises an optical fiber with an inwardly extending cavity on one end face; and a planar cantilever beam film disposed on the end face of the optical fiber with the cavity and positioned in front of the cavity. The cantilever beam film in this fiber optic hydrogen sensor has a nanometer-level thickness, making it more sensitive to external hydrogen concentrations. Furthermore, the cavity of the Fabry-Perot interferometer is less susceptible to external influences such as light and temperature. The present invention also provides a method for preparing the aforementioned hydrogen sensor.

Description

Technical Field

[0001] The present invention relates to hydrogen sensor technology, and in particular to an optical fiber hydrogen sensor based on a cantilever beam film and a preparation method thereof. Background Art

[0002] Hydrogen is a clean energy source that produces only water when burned in air, potentially mitigating global warming associated with fossil fuel consumption. Furthermore, as an antioxidant, hydrogen has been widely used in medicine and biology for cancer prevention and inflammation treatment. However, when its volume concentration reaches its explosion limit of 4%, hydrogen becomes extremely explosive in air, posing safety concerns during its transportation, storage, and use. Therefore, the development of a fast and sensitive hydrogen sensor is of great significance in many energy, medical, and biological applications.

[0003] Resistor-based hydrogen sensors, including electrochemical and microelectromechanical (MEMS) sensors, have mature fabrication processes and are cost-effective. However, they still rely on electrical signals for demodulation, posing a potential risk of explosions triggered by sparks during signal readout. Fiber-optic hydrogen sensors, on the other hand, are being widely researched due to their ability to effectively avoid electromagnetic interference.

[0004] Currently, fiber optic hydrogen sensors are mainly divided into evanescent field type and fiber Bragg grating type. However, the application prospects of these two types of fiber optic hydrogen sensors are not great because the evanescent field type will expose the fiber core and thus weaken the strength of the sensor head, thereby affecting the mechanical properties and stability of the hydrogen sensor, while the fiber Bragg grating type is easily affected by external temperature interference.

[0005] The fiber optic sensor based on the combination of Fabry-Perot interferometer and sensitive material palladium measures hydrogen through changes in cavity length caused by stress. It is simple to manufacture and has low cost. At the same time, the structure of the cantilever beam with one end fixed and the other end free is extremely sensitive to changes in physical quantities such as stress, temperature, and mass applied to its surface. Therefore, it has extremely high response speed and sensitivity. Therefore, the fiber optic sensor based on the combination of Fabry-Perot interferometer, sensitive material palladium and cantilever beam has been widely studied in recent years.

[0006] Chinese patent number CN201911294643.0 discloses a fiber end-face microcantilever sensor and its preparation method. The fiber end-face microcantilever sensor comprises: an optical fiber, comprising a core and a cladding; a cantilever structure, polymerized onto one end face of the optical fiber using femtosecond laser two-photon polymerization technology; a polymer structure comprising a support and a microcantilever; a first end of the support bonded to the cladding of the optical fiber end face; one end of the microcantilever fixed to the second end of the support, and the other end suspended above the core to form a cantilever; the microcantilever is parallel to the end face of the optical fiber; and along a direction perpendicular to the optical fiber end face, the projection of the cantilever on the optical fiber end face covers the core. When the fiber end-face microcantilever sensor is a hydrogen sensor, the surface of the microcantilever has a hydrogen-sensitive palladium film.

[0007] The method for preparing the above-mentioned optical fiber end face micro-cantilever sensor includes the following steps: step S1, cutting one end of the optical fiber flat, placing the optical fiber flat and fixing it on a glass slide, providing support parts on the carrier slides on both sides of the optical fiber to prevent the cover glass from squeezing the optical fiber, dripping photoresist into the optical fiber end face so that the optical fiber end face is immersed in the photoresist, and covering it with a cover glass; step S2, using a 3D photolithography machine and femtosecond laser two-photon polymerization technology to form a polymer cantilever structure on the end face of the optical fiber, thereby obtaining an optical fiber sample with a cantilever structure; step S3, performing development: after curing is completed, removing the cover glass, immersing the sample and the glass slide in a developing solution, dissolving the unexposed photoresist in the solution, and retaining the cured polymer cantilever structure; step S4, using a magnetron sputtering coating device to coat the surface of the micro-cantilever with a hydrogen-sensitive thin film layer of palladium.

[0008] The cantilever beam structure described in the aforementioned patent is a three-dimensional structure consisting of a support and a microcantilever beam. The support provides support to form an air gap between the cantilever of the microcantilever and the core of the optical fiber. This air gap serves as the chamber of the Fabry-Perot interferometer. The overall thickness of the three-dimensional cantilever beam structure is relatively large, only capable of measuring at the micron level. This lack of compactness affects the sensitivity of hydrogen concentration detection. Furthermore, since the Fabry-Perot interferometer chamber is completely outside the core, the measurement accuracy is easily affected by external factors such as light and temperature. Summary of the Invention

[0009] In order to address the above-mentioned deficiencies in the prior art, the present invention provides a fiber optic hydrogen sensor based on a cantilever beam film, wherein the cantilever beam film has a small thickness and the cavity of the Fabry-Perot interferometer is less affected by external light, temperature, etc.

[0010] The present invention also provides a method for preparing the hydrogen sensor.

[0011] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0012] An optical fiber hydrogen sensor based on a cantilever beam film, comprising:

[0013] An optical fiber having an inwardly extending cavity on one end surface;

[0014] The cantilever beam film with a planar structure is arranged on the end surface of the optical fiber having the cavity and is located in front of the cavity.

[0015] Furthermore, the optical fiber includes a core and a cladding, and the cavity is located at least on an end face of the core.

[0016] Furthermore, the cantilever beam film includes a film periphery and a film cantilever located on the same plane, the film periphery is fixed on the cladding of the optical fiber end face, and has a hollow area corresponding to the cavity; the film cantilever is located in the hollow area of ​​the film periphery, one end is fixed to the film periphery, and the other end is suspended in front of the cavity and corresponds to the core of the optical fiber end face.

[0017] Furthermore, the projection of the thin film cantilever on the end face of the optical fiber is located in the chamber and covers the core of the end face of the optical fiber.

[0018] Furthermore, the cantilever beam film includes a suspended film layer disposed on the end face of the optical fiber, a supporting film layer disposed on the suspended film layer, and a hydrogen-sensitive film layer disposed on the supporting film layer.

[0019] Furthermore, the suspended film layer is a graphene film, the supporting film layer is a gold film, and the hydrogen-sensitive film layer is a palladium film.

[0020] A method for preparing a fiber optic hydrogen sensor based on a cantilever beam film, comprising the following steps:

[0021] S1: A cavity extending inward is made on one end face of the optical fiber;

[0022] S2: manufacturing a cantilever beam film with a planar structure on the end surface of the optical fiber having the cavity, wherein the cantilever beam film is located in front of the cavity.

[0023] Furthermore, in step S1, the steps of forming a cavity extending inward on one end face of the optical fiber are as follows:

[0024] S1.1: Cut one end of each of the two optical fibers flat;

[0025] S1.2: Heat the cut ends of the two optical fibers into an arc shape;

[0026] S1.3: Apply refractive index matching fluid to the arc-shaped end faces of the two optical fibers.

[0027] S1.4: Heating and fusing the end faces of the two optical fibers coated with the refractive index matching liquid, and simultaneously vaporizing the refractive index matching liquid to form a bubble cavity at the fusion site of the two optical fibers;

[0028] S1.5: Cut the two fused optical fibers in the middle of the bubble cavity to obtain two optical fibers with the cavity on one end face.

[0029] Furthermore, in step S1, the steps of forming a cavity extending inward on one end face of the optical fiber are as follows:

[0030] S1.1: Cut one end of an optical fiber flat;

[0031] S1.2: Using a femtosecond laser to etch a small hole in the flattened end face of the optical fiber;

[0032] S1.3: Heat-fusing the end face of the optical fiber having the small hole to the cut end face of another optical fiber, causing the gas in the small hole to expand due to the heat, thereby expanding the small hole to form a bubble cavity at the fusion point of the two optical fibers;

[0033] S1.4: Cut the two fused optical fibers in the middle of the bubble cavity to obtain two optical fibers with the cavity on one end face.

[0034] Furthermore, the cantilever beam film includes a suspended film layer, a supporting film layer, and a hydrogen-sensitive film layer. In step S2, the steps of forming a cantilever beam film with a planar structure on the end surface of the optical fiber having the cavity are as follows:

[0035] S2.1: forming a suspended thin film layer on the end surface of the optical fiber having the cavity;

[0036] S2.2: forming a supporting film layer on the suspended film layer;

[0037] S2.3: Etching the suspended film layer and the supporting film layer according to the planar structure of the cantilever beam film;

[0038] S2.4: forming a hydrogen-sensitive thin film layer on the supporting thin film layer.

[0039] Furthermore, the suspended film layer is a graphene film. In step S2.1, the steps of forming a layer of graphene film on the end face of the optical fiber having the cavity are as follows:

[0040] S2.1.1: Grow graphene on copper foil by chemical vapor deposition to obtain copper-based graphene;

[0041] S2.2.2: Cutting a small piece of the copper-based graphene and placing it in a FeCl3 solution, waiting for the FeCl3 solution to completely corrode the copper-based graphene, thereby obtaining a graphene film;

[0042] S2.2.3: Repeatedly filter the waste liquid in the FeCl3 solution using deionized water, so that the graphene film floats on the deionized water;

[0043] S2.2.4: After the end face of the optical fiber having the chamber is brought into contact with the graphene film on the deionized water, the graphene film on the deionized water is transferred to the end face of the optical fiber. After the water in the graphene film on the end face of the optical fiber evaporates, a suspended graphene film is formed.

[0044] The present invention has the following beneficial effects: in the optical fiber hydrogen sensor prepared by the optical fiber hydrogen sensor preparation method, the chamber of the Fabry-Perot interferometer is placed in the optical fiber, and then the cantilever beam film is produced on the end face of the optical fiber. Compared with the existing technology in which the chamber is placed outside and a three-dimensional cantilever beam structure is adopted, the chamber is placed in the optical fiber, which can reduce the influence of external light, temperature, etc. on the measurement accuracy. At the same time, the cantilever beam film is a planar structure with a small overall thickness that can reach the nanometer level. Not only is the structure more compact, but the nanometer-scale film is also more sensitive to the detection of external hydrogen concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A schematic cross-sectional view of the optical fiber hydrogen sensor based on the cantilever beam film provided by the present invention;

[0046] Figure 2 This is a schematic diagram of the end face of the optical fiber hydrogen sensor based on the cantilever beam film provided by the present invention;

[0047] Figure 3 This is a schematic diagram of the principle of the hydrogen concentration detection system based on the cantilever beam film provided by the present invention;

[0048] Figure 4 for Figure 3 The reflection spectrum of the hydrogen concentration detection system based on the cantilever beam film is shown;

[0049] Figure 5 A flowchart of the steps of the method for preparing a fiber optic hydrogen sensor based on a cantilever beam film provided by the present invention;

[0050] Figure 6 for Figure 5 The flowchart of step S1 in the method for preparing an optical fiber hydrogen sensor is shown;

[0051] Figure 7 for Figure 5A flowchart of another step S1 in the method for preparing an optical fiber hydrogen sensor is shown;

[0052] Figure 8 for Figure 5 FIG. 1 is a flow chart of another step S2 in the method for preparing an optical fiber hydrogen sensor. DETAILED DESCRIPTION

[0053] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0054] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are 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 therefore cannot be understood as limiting the present invention.

[0055] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first," "second," or "third" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0056] In the present invention, unless otherwise expressly specified or limited, terms such as "installed," "connected," "connect," "fixed," and "disposed" should be understood in a broad sense. For example, they may refer to fixed or detachable connections, or integration; mechanical or electrical connections; direct or indirect connections through an intermediate medium; or internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0057] Example 1

[0058] like Figure 1 and 2 As shown, a fiber optic hydrogen sensor 1 based on a cantilever beam film comprises:

[0059] The optical fiber 11 has a cavity 113 extending inward on one end surface;

[0060] The cantilever beam film 12 with a planar structure is disposed on the end surface of the optical fiber 11 having the cavity 113 and is located in front of the cavity 113 .

[0061] The optical fiber hydrogen sensor 1 places the chamber 113 of the Fabry-Perot interferometer within the optical fiber 11, and then forms the cantilever beam film 12 on the end face of the optical fiber 11. Compared with the existing technology in which the chamber 113 is external and a three-dimensional cantilever beam structure is adopted, the chamber 113 is built into the optical fiber 11, which can reduce the influence of external light, temperature, etc. on the measurement accuracy. At the same time, the cantilever beam film 12 is a planar structure with a small overall thickness that can reach the nanometer level. Not only is the structure more compact, but the nanometer-scale film is also more sensitive to external hydrogen concentration detection.

[0062] The cavity 113 is an open cavity that communicates with the outside world at the end face of the optical fiber 11. The optical fiber 11 includes a core 111 and a cladding 112. The cavity 113 is located at least on the end face of the core 111. Depending on the size of the cavity 113, the cavity 113 may also be located on the end face of the cladding 112. In this embodiment, the cavity 113 is located on the end faces of both the core 111 and the cladding 112. The core 111 corresponds to the center of the cavity 113, and the cladding 112 corresponds to the periphery of the cavity 113. The scope of the cavity 113 does not exceed the cladding 112.

[0063] The cantilever beam film 12 includes a film periphery 121 and a film cantilever 122 located on the same plane. The film periphery 121 is fixed on the cladding 112 of the end face of the optical fiber 11 and has a hollow area corresponding to the chamber 113; the film cantilever 122 is located in the hollow area of ​​the film periphery 121, one end is fixed to the film periphery 121, and the other end is suspended in front of the chamber 113, and corresponds to the core 111 of the end face of the optical fiber 11.

[0064] The film periphery 121 plays a supporting role in this case to support one end of the film cantilever 122, so that the other end of the film cantilever 122 can be suspended in front of the chamber 113 and correspond to the core 111 of the end face of the optical fiber 11; the projection of the film cantilever 122 on the end face of the optical fiber 11 is located in the chamber 113 and covers the core 111 of the end face of the optical fiber 11.

[0065] The chamber 113 is not closed by the thin film cantilever 122 , but is connected to the outside through a gap between the thin film cantilever 122 and the thin film periphery 121 .

[0066] The cantilever beam film 12 includes a suspended film layer disposed on the end surface of the optical fiber 11 , a supporting film layer disposed on the suspended film layer, and a hydrogen-sensitive film layer disposed on the supporting film layer.

[0067] In this embodiment, the suspended film layer is a graphene film, the supporting film layer is a gold film, and the hydrogen-sensitive film layer is a palladium film.

[0068] In this embodiment, the chamber 113 is a hemispherical cavity.

[0069] Example 2

[0070] Figure 3 As shown, a hydrogen concentration detection system based on a cantilever beam film includes:

[0071] The optical fiber hydrogen sensor 1 according to embodiment 1; and

[0072] Broadband light source 2, spectrometer 3, fiber optic circulator 4, hydrogen generator 6, hydrogen flow valve 7, nitrogen generator 8, nitrogen flow valve 9 and gas mixer 5,

[0073] The optical fiber circulator 4 has an incident end, a reflecting end and a transmitting end, the incident end is connected to the broadband light source 2, the reflecting end is connected to the spectrometer 3, and the transmitting end is connected to the end of the optical fiber hydrogen sensor 1 that does not have the cantilever beam film 12; the gas mixer 5 has a first air inlet end, a second air inlet end and an air outlet end, the hydrogen generator 6 is connected to the first air inlet end through the hydrogen flow valve 7, and the nitrogen generator 8 is connected to the second air inlet end through the nitrogen flow valve 9, and the end of the optical fiber hydrogen sensor 1 with the cantilever beam film 12 is placed in the air outlet.

[0074] The hydrogen concentration detection system also includes a host computer, which is communicated with the hydrogen flow valve 7 and the nitrogen flow valve 9 respectively to control the hydrogen flow valve 7 and the nitrogen flow valve 9 respectively, and realizes the hydrogen concentration ratio by controlling the flow of hydrogen and nitrogen.

[0075] The host computer can be, but is not limited to, a PC, an industrial computer, or an intelligent terminal.

[0076] In this embodiment, the gas mixer 5 is a T-shaped three-way plastic tube with an inner diameter of about 5 mm.

[0077] The test principle of the hydrogen concentration detection system is as follows:

[0078] When the cantilever beam film 12 composed of a suspended film layer, a supporting film layer and a hydrogen-sensitive film layer is suspended in front of the cavity 113 at the end face of the optical fiber 11, it forms a Fabry-Perot cavity with the optical fiber 11-air interface; the broadband light source 2 emits a detection light with a broadband spectrum into the incident end of the optical fiber circulator 4, and the detection light enters the optical fiber hydrogen sensor 1 from the transmission end through the optical fiber circulator 4, and returns to the optical fiber circulator 4 after being processed by the Fabry-Perot cavity, and finally enters the spectrometer 3 from the reflection end, and obtains the following Figure 4 The reflection spectrum of the Fabry-Perot interferometer shown in the figure; when the hydrogen-sensitive thin film layer on the cantilever beam film 12 absorbs hydrogen, its shape will change, thereby driving the thin film cantilever 122 on the cantilever beam film 12 to swing, thereby correspondingly changing the cavity length of the Fabry-Perot cavity. The change in cavity length is reflected as a shift in the resonant wavelength in the reflection spectrum received by the spectrometer 3. By fitting the relationship between the resonant wavelength shift and the hydrogen concentration, the hydrogen sensitivity of the optical fiber hydrogen sensor 1 can be obtained.

[0079] Example 3

[0080] A method for preparing an optical fiber hydrogen sensor 1 based on a cantilever beam film is provided, which is used to prepare the optical fiber hydrogen sensor 1 described in the first embodiment.

[0081] like Figure 5 As shown, the preparation method comprises the following steps:

[0082] S1: If Figure 1 and 2 As shown, a cavity 113 extending inward is formed on one end face of the optical fiber 11.

[0083] In step S1, the cavity 113 is an open cavity that is connected to the outside world on the end face of the optical fiber 11. The optical fiber 11 includes a core 111 and a cladding 112. The cavity 113 is located at least on the end face of the core 111. Depending on the size of the cavity 113, the cavity 113 may also be located on the end face of the cladding 112. In this embodiment, the cavity 113 is located on the end faces of both the core 111 and the cladding 112. The core 111 corresponds to the center of the cavity 113, and the cladding 112 corresponds to the periphery of the cavity 113. The scope of the cavity 113 does not exceed the cladding 112.

[0084] In this embodiment, the chamber 113 is a hemispherical cavity.

[0085] In one embodiment, Figure 6 As shown, the steps for forming an inwardly extending cavity 113 on one end face of the optical fiber 11 are as follows:

[0086] S1.1: Cut one end face of each of the two optical fibers 11 flat.

[0087] In step S1.1, an optical fiber 11 cutter may be used, but is not limited to, to cut one end face of one optical fiber 11 flat, and then cut one end face of another optical fiber 11 flat.

[0088] S1.2: Heat the cut end faces of the two optical fibers 11 into an arc shape.

[0089] In step S1.2, the cut end faces of the two optical fibers 11 can be placed at the two ends of the optical fiber 11 fusion splicer respectively, and the motor in the optical fiber 11 fusion splicer drives the cut end faces of the two optical fibers 11 to be moved to the outer edge of the heating center (the end faces of the two optical fibers 11 are not in contact), and then the discharge parameters are adjusted to heat the cut end faces of the two optical fibers 11 into an arc shape (the two optical fibers 11 are not fusion-spliced).

[0090] S1.3: Apply refractive index matching liquid to the arc-shaped end faces of the two optical fibers 11.

[0091] In step S1.3, the refractive index matching liquid can eliminate the reflection loss associated with the optical fiber 11-air interface.

[0092] S1.4: The end faces of the two optical fibers 11 coated with the refractive index matching liquid are heated and fused together, and the refractive index matching liquid is vaporized to form a bubble cavity at the fusion point of the two optical fibers 11.

[0093] In step S1.4, the end faces of the two optical fibers 11 coated with the refractive index matching liquid can be placed at the two ends of the optical fiber 11 fusion splicer respectively, and the end faces of the two optical fibers 11 coated with the refractive index matching liquid can be moved to the heating center (the end faces of the two optical fibers 11 are in contact) by the motor drive of the optical fiber 11 fusion splicer, and then the discharge parameters are adjusted to heat and fuse the end faces of the two optical fibers 11 coated with the refractive index matching liquid; during the fusion splicing process, the refractive index matching liquid will be vaporized by the heat, thereby forming a bubble cavity at the fusion point of the two optical fibers 11.

[0094] In this embodiment, the bubble cavity is a closed cavity and a spherical cavity.

[0095] S1.5: Cut the two fused optical fibers 11 in the middle of the bubble cavity to obtain two optical fibers 11 with the cavity 113 on one end face.

[0096] In step S1.5, the two fused optical fibers 11 can be placed on a two-dimensional displacement platform and fixed, and then under the monitoring of the CCD and the display, the two-dimensional displacement platform is controlled to move, and the bubble cavity at the fusion point of the two optical fibers 11 is positioned under the optical fiber 11 cutting knife, and then the optical fiber 11 cutting knife is controlled to cut the two fused optical fibers 11 from the middle of the bubble cavity, thereby obtaining two optical fibers 11 each having the cavity 113 on one end face.

[0097] In another specific embodiment, Figure 7 As shown, the steps for making an inwardly extending cavity 113 on one end face of the optical fiber 11 are as follows:

[0098] S1.1: Cut one end face of an optical fiber 11 flat.

[0099] In step S1.1, an optical fiber 11 cutter may be used, but is not limited to, to cut one end face of the optical fiber 11 flat.

[0100] S1.2: A small hole is etched on the flattened end face of the optical fiber 11 using a femtosecond laser.

[0101] In step S1.2, the optical fiber 11 is first placed on a three-axis displacement platform and fixed. Then, under the monitoring of the CCD and the display, the three-dimensional displacement platform is controlled to move, and the cut end face of the optical fiber 11 is moved to the focal position of the femtosecond laser. Then, the appropriate femtosecond laser output power is adjusted, and the emitted femtosecond laser spot is focused on the end face core 111 of the optical fiber 11 to etch the small hole on the end face core 111 of the optical fiber 11.

[0102] S1.3: The end face of the optical fiber 11 having the small hole is heated and fused with the end face of another optical fiber 11 that has been cut flat, and the gas in the small hole is expanded by heat, so that the small hole is enlarged at the fusion point of the two optical fibers 11 to form a bubble cavity.

[0103] One end face of the other optical fiber 11 can also be cut flat using an optical fiber 11 cutter, which can be performed in any step before step S1.3. Preferably, one end face of each of the two optical fibers 11 is cut flat in step S1.1.

[0104] In step S1.3, an optical fiber 11 with the small hole on one end face and another optical fiber 11 with one end face cut flat are placed in an optical fiber 11 fusion splicer, and the motor in the optical fiber 11 fusion splicer drives the end faces with the small hole and the cut flat end faces of the two optical fibers 11 to be moved to the heating center (the end faces of the two optical fibers 11 are in contact), and then the discharge parameters are adjusted to heat and fuse the end faces with the small hole and the cut flat end faces of the two optical fibers 11; during the fusion splicing process, the gas in the small hole will expand due to the heat, thereby causing the small hole to expand at the fusion point of the two optical fibers 11 to form a bubble cavity.

[0105] During the fusion splicing, the optical fiber 11 fusion splicer can be used to repeatedly discharge to control the expansion degree of the gas in the small hole, thereby adjusting the size of the bubble cavity.

[0106] In this embodiment, the bubble cavity is a closed cavity and a spherical cavity.

[0107] S1.4: Cut the two fused optical fibers 11 from the middle of the bubble cavity to obtain two optical fibers 11 with the cavity 113 on one end face.

[0108] In step S1.4, the two fused optical fibers 11 can be placed on a two-dimensional displacement platform and fixed, and then under the monitoring of the CCD and the display, the two-dimensional displacement platform is controlled to move, and the bubble cavity at the fusion point of the two optical fibers 11 is positioned under the optical fiber 11 cutting knife, and then the optical fiber 11 cutting knife is controlled to cut the two fused optical fibers 11 from the middle of the bubble cavity, thereby obtaining two optical fibers 11 each having the cavity 113 on one end face.

[0109] S2: A cantilever beam film 12 with a planar structure is manufactured on the end surface of the optical fiber 11 having the cavity 113 , and the cantilever beam film 12 is located in front of the cavity 113 .

[0110] In this embodiment, the cantilever beam film 12 includes a suspended film layer provided on the end surface of the optical fiber 11, a supporting film layer provided on the suspended film layer, and a hydrogen sensitive film layer provided on the supporting film layer; Figure 8 As shown, the steps of making a cantilever beam film 12 with a planar structure on the end surface of the optical fiber 11 having the cavity 113 are as follows:

[0111] S2.1: Fabricate a suspended thin film layer on the end surface of the optical fiber 11 having the cavity 113 .

[0112] In step S2.1, the area on the suspended film layer corresponding to the chamber 113 is suspended in front of the chamber 113, and the chamber 113 is sealed.

[0113] In this embodiment, the suspended film layer is a graphene film with a thickness of about 2 nm. The steps of forming a layer of graphene film on the end face of the optical fiber 11 having the cavity 113 are as follows:

[0114] S2.1.1: Grow graphene on copper foil by chemical vapor deposition to obtain copper-based graphene.

[0115] S2.2.2: Cut a small piece from the copper-based graphene and place it in a FeCl3 solution, waiting for the FeCl3 solution to completely corrode the copper-based graphene, thereby obtaining a graphene film.

[0116] In step 2.2.2, the concentration of the FeCl3 solution is about 0.075 g / ml.

[0117] S2.2.3: Repeatedly use deionized water to filter the waste liquid in the FeCl3 solution, so that the graphene film floats on the deionized water.

[0118] S2.2.4: The end face of the optical fiber 11 having the chamber 113 is brought into contact with the graphene film on the deionized water to transfer the graphene film on the deionized water to the end face of the optical fiber 11. After the water in the graphene film on the end face of the optical fiber 11 evaporates, a suspended graphene film is formed.

[0119] In step S2.2.4, the end face of the optical fiber 11 needs to be slowly moved to approach the graphene film on the deionized water until the end face of the optical fiber 11 contacts the graphene film, and then the end face of the optical fiber 11 is pulled away from the liquid surface; as the water evaporates, due to the existence of van der Waals force, the periphery of the graphene film will be adhered and fixed to the cladding 112 of the end face of the optical fiber 11, and the center of the graphene film will be suspended in front of the chamber 113.

[0120] S2.2: forming a supporting film layer on the suspended film layer.

[0121] In step S2.2, the supporting film layer can be produced by magnetron sputtering. First, the optical fiber 11 is fixed in the coating chamber of the magnetron sputtering coating apparatus so that the suspended film layer on the end face of the optical fiber 11 faces the film target material. Then, the magnetron sputtering coating apparatus is controlled to sputter the film target material onto the graphene film to form the supporting film layer.

[0122] During sputtering, the suspended film layer supports and suspends the supporting film layer, so that the supporting film layer and the suspended film layer are suspended together, thereby preventing the supporting film layer from sputtering onto the bottom of the chamber 113 .

[0123] In this embodiment, the supporting film layer is a gold film with a thickness of about 200 nm.

[0124] S2.3: Etching the suspension film layer and the support film layer according to the planar structure of the cantilever beam film 12 .

[0125] In step S2.3, the optical fiber 11 is placed on a three-axis displacement platform. Under the monitoring of the CCD and the display, the movement of the three-dimensional mobile platform is controlled to move the suspended film layer and the supporting film layer on the end face of the optical fiber 11 to the focus of the femtosecond laser. Then, the appropriate femtosecond laser output power is adjusted, and the light spot of the femtosecond laser is directly focused on the suspended film layer and the supporting film layer on the end face of the optical fiber 11. Then, the motion trajectory function of the femtosecond laser relative to the end face of the optical fiber 11 is set according to the suspended film layer and the supporting film layer. The motion trajectory of the femtosecond laser is precisely controlled by the three-axis displacement platform. The three-axis displacement platform drives the end face of the optical fiber 11 to move relative to the femtosecond laser according to the motion trajectory of the femtosecond laser, and finally etches the planar structure of the cantilever beam film 12 on the suspended film layer and the supporting film layer.

[0126] During etching, the supporting film layer supports and thickens the suspended film layer, so as to prevent the suspended film layer from collapsing due to being too thin during etching.

[0127] like Figure 1 and 2 As shown, the cantilever beam film 12 includes a film periphery 121 and a film cantilever 122 located on the same plane, the film periphery 121 is fixed on the cladding 112 of the end face of the optical fiber 11, and has a hollow area corresponding to the chamber 113; the film cantilever 122 is located in the hollow area of ​​the film periphery 121, one end is fixed to the film periphery 121, and the other end is suspended in front of the chamber 113, and corresponds to the core 111 of the end face of the optical fiber 11.

[0128] The film periphery 121 plays a supporting role in this case to support one end of the film cantilever 122, so that the other end of the film cantilever 122 can be suspended in front of the chamber 113 and correspond to the core 111 of the end face of the optical fiber 11; the projection of the film cantilever 122 on the end face of the optical fiber 11 is located in the chamber 113 and covers the core 111 of the end face of the optical fiber 11.

[0129] The chamber 113 is not closed by the thin film cantilever 122 , but is connected to the outside through a gap between the thin film cantilever 122 and the thin film periphery 121 .

[0130] S2.4: forming a hydrogen-sensitive thin film layer on the supporting thin film layer.

[0131] In step S2.4, the hydrogen-sensitive thin film layer can be produced by magnetron sputtering. First, the optical fiber 11 is fixed in the coating chamber of the magnetron sputtering coater so that the supporting thin film layer on the end face of the optical fiber 11 faces the hydrogen-sensitive target material. Then, the magnetron sputtering coater is controlled to sputter the hydrogen-sensitive target material onto the supporting thin film layer to form the hydrogen-sensitive thin film layer.

[0132] In this embodiment, the hydrogen sensitive thin film layer is a palladium thin film.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention rather than to limit them. Although the embodiments of the present invention are described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the embodiments of the present invention can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an optical fiber hydrogen sensor based on a cantilever beam film, characterized in that: The optical fiber hydrogen sensor comprises: An optical fiber having an inwardly extending cavity on one end surface; A cantilever beam film with a planar structure is provided on the end surface of the optical fiber having the cavity and is located in front of the cavity; The optical fiber includes a core and a cladding, the cavity is located at least on the end face of the core, the core corresponds to the center of the cavity, the cladding corresponds to the periphery of the cavity, and the range of the cavity does not exceed the cladding; the cantilever beam film includes a film periphery and a film cantilever located on the same plane, the film periphery is fixed to the cladding of the optical fiber end face, and has a hollow area corresponding to the cavity; the film cantilever is located in the hollow area of ​​the film periphery, one end is fixed to the film periphery, and the other end is suspended in front of the cavity and corresponds to the core of the optical fiber end face; the projection of the film cantilever on the optical fiber end face is located in the cavity and covers the core of the optical fiber end face; The preparation method comprises the following steps: S1: A cavity extending inward is made on one end face of the optical fiber; S2: forming a cantilever beam film with a planar structure on the end surface of the optical fiber having the cavity, wherein the cantilever beam film is located in front of the cavity; In step S1, the steps of forming an inwardly extending cavity on one end face of the optical fiber are as follows: S1.1: Cut one end of each of the two optical fibers flat; S1.2: Heat the cut ends of the two optical fibers into an arc shape; S1.3: Apply refractive index matching fluid to the arc-shaped end faces of the two optical fibers. S1.4: Heating and fusing the end faces of the two optical fibers coated with the refractive index matching liquid, and simultaneously vaporizing the refractive index matching liquid to form a bubble cavity at the fusion site of the two optical fibers; S1.5: Cut the two fused optical fibers in the middle of the bubble cavity to obtain two optical fibers with the cavity on one end face; The cantilever beam film includes a suspended film layer, a supporting film layer, and a hydrogen-sensitive film layer. In step S2, the steps of forming a cantilever beam film with a planar structure on the end surface of the optical fiber having the cavity are as follows: S2.1: forming a suspended thin film layer on the end surface of the optical fiber having the cavity; S2.2: forming a supporting film layer on the suspended film layer; S2.3: Etching the suspended film layer and the supporting film layer according to the planar structure of the cantilever beam film; S2.4: forming a hydrogen-sensitive thin film layer on the supporting thin film layer.

2. The method for preparing an optical fiber hydrogen sensor based on a cantilever beam film according to claim 1, characterized in that: In step S1, the step of forming a cavity extending inward on one end face of the optical fiber is replaced by: S1.1: Cut one end of an optical fiber flat; S1.2: Using a femtosecond laser to etch a small hole in the flattened end face of the optical fiber; S1.3: Heat-fusing the end face of the optical fiber having the small hole to the cut end face of another optical fiber, causing the gas in the small hole to expand due to the heat, thereby expanding the small hole to form a bubble cavity at the fusion point of the two optical fibers; S1.4: Cut the two fused optical fibers in the middle of the bubble cavity to obtain two optical fibers with the cavity on one end face.

3. The method for preparing a cantilever beam thin film optical fiber hydrogen sensor according to claim 1 or 2, characterized in that: The suspended film layer is a graphene film. In step S2.1, the steps of forming a layer of graphene film on the end face of the optical fiber having the cavity are as follows: S2.1.1: Grow graphene on copper foil by chemical vapor deposition to obtain copper-based graphene; S2.2.2: Cutting a small piece of the copper-based graphene and placing it in a FeCl3 solution, waiting for the FeCl3 solution to completely corrode the copper-based graphene, thereby obtaining a graphene film; S2.2.3: Repeatedly filter the waste liquid in the FeCl3 solution using deionized water, so that the graphene film floats on the deionized water; S2.2.4: After the end face of the optical fiber having the chamber is brought into contact with the graphene film on the deionized water, the graphene film on the deionized water is transferred to the end face of the optical fiber. After the water in the graphene film on the end face of the optical fiber evaporates, a suspended graphene film is formed.

4. The method for preparing a cantilever beam thin film optical fiber hydrogen sensor according to claim 3, characterized in that: The supporting film layer is a gold film, and the hydrogen sensitive film layer is a palladium film.

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