Temperature-pressure-heat flow three-parameter composite micro-nano sensor and preparation method thereof

Abstract

This invention discloses a composite micro / nano sensor with three parameters: temperature, pressure, and heat flux, and its fabrication method. The composite micro / nano sensor includes a sensitive core and an encapsulation shell surrounding the sensitive core. The main optical fiber of the sensitive core is connected in series with a Fabry-Perot resonant cavity. A pressure-sensitive diaphragm layer is formed at the end of the Fabry-Perot resonant cavity away from the main optical fiber. Pressure is detected through the cooperation of the pressure-sensitive diaphragm layer and the Fabry-Perot resonant cavity, and temperature is detected through a coaxial thermocouple. The heat flux can be calculated by inverse calculation from the temperature, realizing the simultaneous monitoring of multiple parameters. It has the characteristics of high temperature resistance, electromagnetic interference resistance, and small repeatability error.

Description

Technical Field

[0001] This invention belongs to the field of extreme environment sensing and testing technology, specifically relating to a composite micro / nano sensor with three parameters: temperature, pressure, and heat flux, and its fabrication method. Background Technology

[0002] The importance of extreme environment sensing testing is self-evident, as it is crucial for safety, efficiency, and quality control in many critical fields. In particular, the measurement of temperature, heat flux, and pressure in extreme environments is of great concern in aerospace, marine engineering, energy exploration, and petrochemicals. In the aerospace field, with the rapid development of hypersonic vehicles and the continuous increase in flight Mach numbers, the problem of aerodynamic heating on the vehicle surface is becoming increasingly serious. This can lead to severe ablation of the vehicle's structural shape, a decrease in structural strength and stiffness, and a serious threat to the flight safety of hypersonic vehicles. Simultaneously, during the operation of hypersonic vehicle engines, a series of abnormal factors, such as surge, inlet distortion, poor nozzle atomization, and mutual interference between components, can lead to combustion instability. Combustion instability can cause vibration and fatigue in the thin-walled structure of the engine combustion chamber, shortening its service life, and even causing the engine to shut down in mid-air, resulting in serious accidents. Therefore, real-time monitoring of the temperature, heat flux, and pressure parameters of key components of hypersonic vehicles can provide crucial data for scientific research on hypersonic vehicles, and help to better understand and improve the design of vehicle structures and thermal protection systems.

[0003] Conventional measurement methods are often affected by extreme environments, which may cause measurement deviations or render sensors malfunctioning. To address this challenge, the use of fiber optic sensors or coaxial thermocouples has become a popular solution, as both offer advantages such as high temperature resistance, immunity to electromagnetic interference, and low repeatability error. While fiber optic sensors and coaxial thermocouples perform excellently in high-temperature environments, most currently only achieve single-parameter measurements. Simultaneous monitoring of multiple parameters, such as temperature, pressure, and heat flux, remains a challenge. Therefore, the development and application of multi-parameter sensors hold enormous potential, providing more comprehensive and accurate monitoring solutions for engineering fields operating in extreme environments. Summary of the Invention

[0004] The purpose of this invention is to provide a temperature-pressure-heat flux three-parameter composite micro / nano sensor and its fabrication method. This temperature-pressure-heat flux three-parameter composite micro / nano sensor can simultaneously measure three parameters: temperature, pressure, and heat flux.

[0005] The technical solution of the present invention is as follows:

[0006] A composite micro / nano sensor with three parameters of temperature, pressure, and heat flux includes a sensing core and an encapsulation shell surrounding the sensing core.

[0007] The sensitive core includes a main optical fiber, a coaxial thermocouple, and an end face thin film layer. The sensitive core has a detection end and a connection end. A Fabry-Perot resonant cavity is fabricated at the end of the main optical fiber near the detection end. A pressure-sensitive diaphragm layer is formed at the end of the Fabry-Perot resonant cavity away from the main optical fiber. The pressure-sensitive diaphragm layer undergoes elastic deformation in response to pressure, causing the cavity length of the Fabry-Perot resonant cavity to change.

[0008] A coaxial thermocouple includes a negative electrode thin film layer, an insulating layer, and a positive electrode thin film layer arranged sequentially outward along the sidewall of the main optical fiber, as well as an end face thin film layer disposed on the end face of the detection end. The end face thin film layer conducts through the negative electrode thin film layer and the positive electrode thin film layer. The negative electrode thin film layer and the positive electrode thin film layer are respectively made of two metals or alloys with different thermoelectric properties. When the coaxial thermocouple is heated, a potential difference is generated between the positive electrode thin film layer and the negative electrode thin film layer.

[0009] In some possible implementations, the Fabry-Perot resonant cavity is a sealed cavity formed by fusing a section of hollow fiber at one end of the main optical fiber using arc discharge technology, and then fusing the hollow fiber with a matching optical fiber.

[0010] In some possible implementations, the encapsulation housing includes a front sleeve, a rear protective tube, and a thermocouple plug connected in sequence;

[0011] The sensitive core is wrapped and fixed by the front sleeve and the end face of the detection end is exposed. The positive electrode thin film layer and the negative electrode thin film layer are respectively connected to a metal wire. The two metal wires are insulated from each other. The metal wires pass through the front sleeve and the rear protective tube and are connected to the thermocouple plug.

[0012] In some possible implementations, the inner diameter of the front sleeve is the same as the outer diameter of the sensitive core.

[0013] In some possible implementations, the front end sleeve, main optical fiber, hollow optical fiber, and mating optical fiber are made of the same material, and the metal wire is made of the same material as the positive or negative electrode thin film layer to which it is connected.

[0014] In some possible implementations, the length of the front-end sleeve is comparable to the length of the main optical fiber.

[0015] In some possible implementations, the back-end protection tube is filled with high-temperature insulating powder.

[0016] A method for fabricating the above-mentioned composite micro / nano sensor includes the following steps:

[0017] (1) A section of hollow fiber is fused at one end of the main optical fiber using arc discharge technology. The hollow fiber is then fused with the matching fiber to form a sealed Fabry-Perot resonant cavity.

[0018] (2) Mechanical polishing is used to form a pressure-sensitive diaphragm layer on the end face of the Fabry-Perot resonant cavity away from the main optical fiber.

[0019] (3) A coaxial thermocouple is deposited on the main optical fiber to obtain a sensitive core. The coaxial thermocouple includes a negative electrode thin film layer, an insulating layer and a positive electrode thin film layer formed sequentially on the side wall of the main optical fiber, as well as an end face thin film layer disposed on the end face of the main optical fiber near the detection end.

[0020] (4) Connect a metal wire to the negative electrode thin film layer and the positive electrode thin film layer respectively;

[0021] (5) The sensitive core is placed inside the packaging shell.

[0022] In some possible implementations, the encapsulation housing includes a front sleeve, a rear protective tube, and a thermocouple plug in sequence. The front sleeve, the main optical fiber, the hollow optical fiber, and the mating optical fiber are made of the same material. The sensitive core is wrapped and fixed by the front sleeve and exposed at the end face of the detection end. The metal wire passes through the front sleeve and the rear protective tube and is connected to the thermocouple plug.

[0023] The preparation method also includes step (6) laser heating treatment of the front end sleeve, so that the inner wall of the front end sleeve collapses due to heat and wraps around the sensitive core.

[0024] In some possible implementations, the negative electrode thin film layer, insulating layer, positive electrode thin film layer, and end face thin film layer are formed by magnetron sputtering.

[0025] The present invention has at least the following beneficial effects:

[0026] (1) The composite micro-nano sensor of the present invention detects pressure through the combination of pressure-sensitive diaphragm layer and Fabry resonant cavity, and detects temperature through coaxial thermocouple. The heat flow can be calculated by inverting the temperature, thus realizing the monitoring of multiple parameters at the same time. It has the characteristics of high temperature resistance, electromagnetic interference resistance, and small repeatability error.

[0027] (2) In some possible implementations, the sensitive core and the front end sleeve are welded by laser heat treatment, so that the sensitive core and the package shell are integrated, which improves the poor shock resistance of the coaxial thermocouple and is conducive to realizing the composite micro-nano sensor to measure high temperature and high heat flux in harsh environments. Attached Figure Description

[0028] Figure 1 This is a schematic diagram showing the arrangement of the main optical fiber, the Fabry-Perot resonant cavity, and the pressure-sensitive diaphragm layer in the embodiment.

[0029] Figure 2 This is a diagram of the sensitive core structure in the embodiment;

[0030] Figure 3 This is a top view of the sensitive core in the embodiment;

[0031] Figure 4 This is a structural diagram of the composite micro / nano sensor used in this embodiment.

[0032] Figure 5 This is a schematic diagram of the connection structure between the sensitive core and the metal wire in the embodiment;

[0033] Figure 6 This is a schematic diagram of the connection structure between the thermocouple plug and the metal wire in the embodiment.

[0034] Explanation of reference numerals in the attached figures: 1-Sensitive core; 11-Main optical fiber; 111-Faber resonant cavity; 112-Pressure-sensitive diaphragm layer; 121-Negative electrode thin film layer; 122-Insulating layer; 123-Positive electrode thin film layer; 124-End face thin film layer; 2-Encapsulation shell; 21-Front end sleeve; 22-Rear end protection tube; 23-Thermocouple plug; 24-Compression fitting; 25-Screw; 26-Metal wire. Detailed Implementation

[0035] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0036] It should be noted that the terms "front" and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0037] This application does not specifically limit the high temperature referred to in terms such as "high temperature environment," "high temperature resistance," and "high temperature insulation." Those skilled in the art can select existing materials to fabricate various components of the composite micro / nano sensor as needed to adapt to different test temperatures. For example, the high-temperature insulating powder in the insulating layer 122 and the rear protective tube 22 can be made of alumina, zirconium oxide, or hafnium oxide; the negative electrode thin film layer 121 can be selected from, but is not limited to, tungsten-rhenium alloy and platinum-rhodium alloy; the positive electrode thin film layer 123 can be selected from, but is not limited to, tungsten and platinum; the metal wire 26 is made of the same material as the negative electrode thin film layer 121 or the positive electrode thin film layer 123 to which it is connected; the main optical fiber 11, hollow optical fiber, mating optical fiber, and front end sleeve 21 can be made of silicon oxide or sapphire; the rear protective tube 22 can be made of stainless steel. The end face thin film layer is made of metal or alloy material and is used to conduct the positive electrode thin film layer 123 and the negative electrode thin film layer 121; its specific material is the same as that of the positive electrode thin film layer 123 or the negative electrode thin film layer 121.

[0038] Among them, the metal wire 26 connected to the positive electrode thin film layer 123 is made of the same material as the positive electrode thin film layer 123, and the metal wire 26 connected to the negative electrode thin film layer 121 is made of the same material as the negative electrode thin film layer 121; the main optical fiber 11, hollow optical fiber, mating optical fiber and front end sleeve 21 are made of the same material to maintain the homogeneity of the above components.

[0039] refer to Figure 1-3 This embodiment provides a composite micro / nano sensor with three parameters: temperature, pressure, and heat flux. It includes a sensing core 1 and an encapsulation shell 2 surrounding the sensing core 1. The sensing core 1 includes a main optical fiber 11 and a coaxial thermocouple. The sensing core 1 has opposing detection and connection ends, wherein, as shown... Figure 1 As shown, a Fabry-Perot resonant cavity 111 is fabricated at the end of the main optical fiber 11 near the detection end. A flat pressure-sensitive diaphragm layer 112 is formed at the end of the Fabry-Perot resonant cavity 111 away from the main optical fiber 11 through mechanical grinding. The high-temperature resistant main optical fiber 11 and the Fabry-Perot resonant cavity 111 are connected in series, with the Fabry-Perot resonant cavity 111 serving as the pressure-sensitive component at the end of the main optical fiber 11. The pressure-sensitive diaphragm layer 112 undergoes elastic deformation in response to pressure, causing a change in the cavity length of the Fabry-Perot resonant cavity 111. By measuring the change in the cavity length of the Fabry-Perot resonant cavity 111, the spatial pressure value can be calculated, thereby achieving the measurement of external pressure.

[0040] The coaxial thermocouple is formed on the surface of the main optical fiber 11 by magnetron sputtering, specifically, as shown in... Figure 2 and Figure 3 As shown, the coaxial thermocouple includes a negative electrode thin film layer 121, an insulating layer 122, and a positive electrode thin film layer 123 arranged sequentially outward from the sidewall of the ring-body optical fiber 11, as well as an end face thin film layer 124 disposed on the end face of the detection end. The end face thin film layer 124 conducts the negative electrode thin film layer 121 and the positive electrode thin film layer 123. The negative electrode thin film layer 121 and the positive electrode thin film layer 123 are respectively made of two metals or alloys with different thermoelectric properties. When the coaxial thermocouple is heated, a potential difference is generated between the positive electrode thin film layer 123 and the negative electrode thin film layer 121 to measure the temperature of the object to be measured. The heat flux can be calculated by inverting the temperature.

[0041] First refer to Figure 4 The encapsulation housing 2 includes a front sleeve 21, a rear protective tube 22, and a thermocouple plug 23 connected in sequence. The sensitive core 1 is wrapped and fixed by the front sleeve 21, and the end face of the sensing end of the sensitive core 1 is flush with the front sleeve 21. The front sleeve 21 is laser-heated, causing its inner wall to collapse and wrap around the sensitive core 1, thus protecting the sensitive core 1 while also providing a barrier and fixation effect, improving the poor shock resistance of coaxial thermocouples. Figure 5As shown, a metal wire 26 is connected to both the positive electrode thin film layer 123 and the negative electrode thin film layer 121. The two metal wires 26 are insulated from each other. The metal wires 26 pass through the front sleeve 21 and the rear protective tube 22 and are connected to the thermocouple plug 23. Figure 4 and 6 As shown, the rear metal protective tube is connected to the thermocouple plug 23 via a compression fitting 24. The ends of the two metal wires 26 away from the positive electrode thin film layer 123 or the negative electrode thin film layer 121 are connected to the inside of the thermocouple plug 23 by screws 25 through threaded clamping, thereby leading out the signal.

[0042] In this embodiment, the rear protective tube 22 is filled with high-temperature insulating powder to achieve insulation between the two metal wires 26. In other possible implementations, an insulating sleeve can also be used to cover the sidewalls of the metal wires 26 to prevent the two metal wires 26 from conducting and causing a short circuit.

[0043] In this embodiment, the main optical fiber 11 has a length of 15 cm and a diameter of 0.2 mm. Before laser heat treatment, the inner diameter of the front end sleeve 21 can be slightly larger than the outer diameter of the main optical fiber 11. After laser heat treatment, its inner diameter is the same as the outer diameter of the main optical fiber 11. The negative electrode thin film layer 121 has a length of 80 mm and a thickness of 5 μm; the insulating layer 122 has a length of 60 mm and a thickness of 2 μm; and the positive electrode thin film layer 123 has a length of 40 mm and a thickness of 5 μm.

[0044] The following is a detailed description of a method for fabricating a composite micro / nano sensor provided in this embodiment. The method includes the following steps:

[0045] (1) A section of hollow fiber is fused at one end of the main optical fiber 11 using arc discharge technology. The hollow fiber is then fused with the matching fiber to form a sealed Fabry-Perot resonant cavity 111.

[0046] (2) Mechanical polishing is used to form a pressure-sensitive diaphragm layer 112 on the end face of the Fabry-Perot resonant cavity 111 away from the main optical fiber 11.

[0047] (3) A coaxial thermocouple is deposited on the main optical fiber 11 to obtain a sensitive core 1. The coaxial thermocouple includes a negative electrode thin film layer 121, an insulating layer 122 and a positive electrode thin film layer 123 formed sequentially on the side wall of the main optical fiber 11, and an end face thin film layer 124 disposed on the end face of the main optical fiber 11 near the detection end.

[0048] (4) Connect a metal wire 26 to the negative electrode thin film layer 121 and the positive electrode thin film layer 123 respectively;

[0049] (5) The sensitive core 1 is placed inside the encapsulation housing 2.

[0050] In the above steps, the Fabry-Perot resonant cavity 111 uses arc discharge technology to fuse a section of hollow fiber to the tail end of the main optical fiber 11. The hollow fiber is then fused with the matching fiber to form a sealed cavity. The end face of the fused main optical fiber 11 is mechanically polished to obtain a flat pressure-sensitive diaphragm layer 112. The specific preparation method is as follows:

[0051] 1.1 Use wire strippers to remove the coating layer from the surface of the main optical fiber 11 to be processed, and clean it with an alcohol swab. Then, cut the cleaned main optical fiber 11 with a dedicated fiber optic cleaver to obtain a flat fiber end face, and fix it inside the fiber optic fusion splicer. Cut the hollow-core optical fiber with a dedicated fiber optic cleaver to obtain a flat fiber end face, and fix it at the other end of the fiber optic fusion splicer.

[0052] 1.2 Using the manual fusion splicing mode of the fiber optic fusion splicer, the end-face positions of the main optical fiber 11 and the hollow optical fiber to be fused are adjusted. Appropriate discharge parameters, discharge time, and advance distance are set, and electrode discharge is performed to achieve end-face fusion of the corresponding optical fibers.

[0053] 1.3 A CCD vision fiber optic cleaving platform is used to accurately position the spliced ​​hollow fiber and cut the hollow fiber according to the required length of the Fabry-Perot resonant cavity 111.

[0054] 1.4 Use an ultrasonic cleaner to clean the cleaved end face of the hollow fiber and then place it back into the fiber fusion splicer. It is particularly important to ensure that the end face of the cleaved hollow fiber is thoroughly cleaned to avoid affecting its subsequent optical properties.

[0055] 1.5 Place the mating fiber in the fiber optic fusion splicer, adjust the corresponding fusion parameters, and fusion splice the mating fiber and the cleaned hollow fiber at the ends away from the main fiber 11 together. The hollow fiber forms a Fabry-Perot resonant cavity 111 by fusion splicing with the main fiber 11 and the mating fiber.

[0056] The specific operation of step (2) to form the pressure-sensitive diaphragm layer 112 is as follows:

[0057] 2.1 A CCD vision fiber optic cutting platform is used to accurately position the spliced ​​mating optical fiber and cut the mating optical fiber according to the required length (thickness) of the pressure-sensitive diaphragm layer 112.

[0058] 2.2 Due to the limitations of the precision of the CCD vision fiber cutting platform, the thickness of the mating fiber after cutting in step 2.1 will still be greater than the actual required thickness of the pressure-sensitive membrane layer 112. Therefore, it is necessary to use abrasive paper with different roughness to grind the mating fiber. During the grinding process, the grinding situation is observed in real time using a microscope, and the signal is monitored using a spectral analyzer to obtain a thinner pressure-sensitive membrane layer 112.

[0059] The detailed fabrication process of the coaxial thermocouple thin film layer deposited on the main optical fiber 11 in step (3) is as follows: the main optical fiber 11 is ultrasonically cleaned and dried in anhydrous ethanol, and then the negative electrode thin film layer 121, the insulating layer 122, the positive electrode thin film layer 123, and the end face thin film layer 124 are sequentially magnetron sputtered. The magnetron sputtering steps are as follows:

[0060] 3.1 Open the vent valve of the vacuum chamber. When the vacuum chamber pressure is the same as the atmospheric pressure, open the vacuum chamber door and fix the main optical fiber 11 on the clamp in the vacuum chamber. The clamp is connected to a retractable and rotatable motor. Then close the vacuum chamber door and close the vent valve.

[0061] 3.2 Turn on the mechanical pump to perform the first stage of vacuuming and simultaneously turn on the vacuum gauge.

[0062] 3.3 First, turn on the molecular pump cooling water, then start the molecular pump for secondary vacuuming. The vacuum level should be below 1×10⁻⁶. -2 When Pa is reached, turn on the temperature control system and set the temperature.

[0063] 3.4 Vacuum degree below 3×10 -3 Once the vacuum chamber temperature has stabilized, open the argon gas inlet valve and adjust the argon gas pressure.

[0064] 3.5 Turn on the RF power and warm up for 30 minutes.

[0065] 3.6 Perform magnetron sputtering according to the following process parameters:

[0066] The sputtering power of the positive electrode thin film layer 123 and the negative electrode thin film layer 121 is 100W, the sputtering gas is argon, and the back vacuum degree before sputtering is less than 8×10⁻⁶. -4 Pa, sputtering pressure 0.95 Pa, sputtering time 40 min, sputtering interval 20 min;

[0067] The sputtering power of the insulating layer 122 was 150W, the sputtering gas was argon:oxygen = 6:1 (volume ratio), and the back vacuum before sputtering was less than 8×10⁻⁶. -4 The sputtering pressure was 1.0 Pa, the sputtering time was 40 min, and the sputtering interval was 20 min.

[0068] The sputtering power of the end face thin film layer is 100W, the sputtering gas is argon, and the back vacuum degree before sputtering is less than 8×10.-4 The sputtering pressure was 0.95 Pa, the sputtering time was 8 min, and the sputtering interval was 20 min.

[0069] The final sputtered negative electrode thin film layer 121, insulating layer 122, and positive electrode thin film layer 123 have thicknesses of 5 μm, 2 μm, and 5 μm, respectively, with an end-face thin film layer thickness of 1 μm. By manipulating the extension and retraction of the fixture, the lengths of the negative electrode thin film layer 121, insulating layer 122, and positive electrode thin film layer 123 are 80 mm, 60 mm, and 40 mm, respectively.

[0070] 3.7 After sputtering, the sample was cooled and the pumping system was turned off. The sample was then annealed at high temperature in an argon atmosphere using a vacuum annealing furnace at a heating rate of 5℃ / min and held at 400℃ for 12 hours to obtain the sensitive core 1.

[0071] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A composite micro / nano sensor with three parameters: temperature, pressure, and heat flux, characterized in that, Includes a sensitive core and an encapsulation shell that surrounds the sensitive core; The sensitive core includes a main optical fiber, a coaxial thermocouple, and an end face thin film layer. The sensitive core has a connection end and a detection end. A Fabry-Perot resonant cavity is formed at the end of the main optical fiber near the detection end. A pressure-sensitive diaphragm layer is formed at the end of the Fabry-Perot resonant cavity away from the main optical fiber. The pressure-sensitive diaphragm layer undergoes elastic deformation in response to pressure, causing a change in the cavity length of the Fabry-Perot resonant cavity. The coaxial thermocouple includes a negative electrode thin film layer, an insulating layer, and a positive electrode thin film layer arranged sequentially outward along the sidewall of the main optical fiber, as well as an end face thin film layer disposed on the end face of the detection end. The end face thin film layer conducts the negative electrode thin film layer and the positive electrode thin film layer. The negative electrode thin film layer and the positive electrode thin film layer are respectively made of two metals or alloys with different thermoelectric properties. When the coaxial thermocouple is heated, a potential difference is generated between the positive electrode thin film layer and the negative electrode thin film layer. The encapsulation housing includes a front end sleeve, a rear end protective tube, and a thermocouple plug connected in sequence. The sensitive core is wrapped and fixed by the front end sleeve and the end face of the detection end is exposed. The positive electrode thin film layer and the negative electrode thin film layer are respectively connected to a metal wire. The two metal wires are insulated from each other. The metal wires pass through the front end sleeve and the rear end protective tube and are connected to the thermocouple plug.

2. The composite micro / nano sensor as described in claim 1, characterized in that, The Fabry-Perot resonant cavity is a sealed cavity formed by fusing a section of hollow fiber at one end of the main optical fiber using arc discharge technology, and then fusing the hollow fiber with a matching optical fiber.

3. The composite micro / nano sensor as described in claim 2, characterized in that, The inner diameter of the front end sleeve is the same as the outer diameter of the sensitive core.

4. The composite micro / nano sensor as described in claim 2 or 3, characterized in that, The front end sleeve, the main optical fiber, the hollow optical fiber, and the mating optical fiber are made of the same material, and the metal wire is made of the same material as the positive electrode thin film layer or the negative electrode thin film layer to which it is connected.

5. The composite micro / nano sensor as described in claim 4, characterized in that, The length of the front end sleeve is approximately the same as the length of the main optical fiber.

6. The composite micro / nano sensor as described in claim 2, characterized in that, The rear protective tube is filled with high-temperature insulating powder.

7. A method for fabricating a composite micro / nano sensor according to any one of claims 1-6, characterized in that, Includes the following steps: (1) A section of hollow fiber is fused at one end of the main optical fiber using arc discharge technology, and the hollow fiber is then fused with the matching fiber to form a sealed Fabry-Perot resonant cavity. (2) Mechanically polish the mating optical fiber to form a pressure-sensitive diaphragm layer on the end face of the Fabry-Perot resonant cavity away from the main optical fiber; (3) A coaxial thermocouple is deposited on the main optical fiber to obtain a sensitive core. The coaxial thermocouple includes a negative electrode thin film layer, an insulating layer and a positive electrode thin film layer formed sequentially on the sidewall of the main optical fiber, and an end face thin film layer disposed on the end face of the main optical fiber near the detection end. (4) Connect a metal wire to the negative electrode thin film layer and the positive electrode thin film layer respectively; (5) The sensitive core is placed inside the packaging housing.

8. The preparation method according to claim 7, characterized in that, The encapsulation housing includes a front sleeve, a rear protective tube, and a thermocouple plug in sequence. The front sleeve, the main optical fiber, the hollow optical fiber, and the mating optical fiber are made of the same material. The sensitive core is wrapped and fixed by the front sleeve and the end face of the detection end is exposed. The metal wire passes through the front sleeve and the rear protective tube and is in communication with the thermocouple plug. The preparation method further includes step (6) laser heating treatment of the front end sleeve, so that the inner wall of the front end sleeve collapses due to heat and wraps around the sensitive core.

9. The preparation method according to claim 7 or 8, characterized in that, The negative electrode thin film layer, the insulating layer, the positive electrode thin film layer, and the end face thin film layer are formed by magnetron sputtering.

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