Quick response optical fiber temperature sensor and preparation method thereof

Abstract

The invention discloses a quick response optical fiber Fabry-Perot temperature sensor, which comprises a laser, the laser is used for emitting incident light, the laser is connected with an optical fiber circulator, the optical fiber circulator is simultaneously connected with a temperature sensing head and a photoelectric detector, and the photoelectric detector is connected with a controller; the temperature sensing head is composed of an optical fiber, a miniature silicon wafer and a reflecting film, the end face of the optical fiber is connected with one face of the miniature silicon wafer, an interface between the end face of the optical fiber and the miniature silicon wafer is a first cavity face, and the reflecting film is formed on the other face of the miniature silicon wafer. An interface between the reflecting film and the miniature silicon wafer is a second cavity surface, and the incident light is continuously reflected on the first cavity surface and the second cavity surface to form Fabry-Perot interference to obtain reflected light. The invention provides the optical fiber Fabry-Perot temperature sensor which is compact in structure, high in response speed and simple in system and the preparation method thereof.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic sensing, and particularly relates to a fast-response fiber optic temperature sensor based on a micro silicon-based Fabry-Perot interferometer structure and a preparation method thereof. The sensor has a fast response ability in the sub-millisecond range and is applicable to the field of transient temperature measurement. Background Art

[0002] Temperature sensors with fast response capabilities have important applications in fields such as electrical equipment monitoring, turbine monitoring, seawater temperature measurement, and atmospheric boundary measurement. There are also some application scenarios, such as nuclear reactors, controlled nuclear fusion, supersonic wind tunnels, and large transformer monitoring, where the measurement environment is extremely complex during transient temperature changes, and there are influences such as strong electricity, strong magnetism, strong electromagnetic interference, and nuclear radiation. These scenarios not only require the temperature sensor to accurately respond to temperature field changes but also pose extremely high requirements for the environmental adaptability and reliability of the sensor.

[0003] Fiber optic temperature sensors have the advantages of small size, light weight, anti-electromagnetic interference, resistance to harsh environments, strong remote sensing capabilities, and the ability to perform distributed or quasi-distributed measurements, and have been widely used in temperature measurements in complex electromagnetic environments. These application scenarios are usually accompanied by transient temperature changes, and require the response time of the fiber optic temperature sensor to reach the millisecond level or even the sub-millisecond level to capture instantaneous temperature information. Currently, there have been many experimental studies on the fast-response measurement of temperature using fiber optic temperature sensors.

[0004] There has been a lot of work on studying the fast response capabilities of general FBG fiber optic temperature sensors, and the response time of the sensors has been improved to dozens of milliseconds to ten milliseconds (Zhang Dengpan, Wang Jin, Wang Yongjie. Fast response characteristics of fiber Bragg grating ocean temperature sensors [J]. Opto-Electronic Engineering, 2015, 42(3):7. ZHANG D, WANG J, WANG Y, DAI X. A fastresponse temperature sensor based on fiber Bragg grating [J]. MeasurementScience and Technology, 2014, 25(7). Zhao Lin, Wang Jiqiang, Li Zhen, etc. A high-temperature fast-response fiber optic temperature sensor. CN115560876A. 2022. Wang Yongjie, Li Fang, Liu Yuliang, etc. Fiber optic temperature sensor for fast ocean temperature measurement. CN102494802A. 2011.). The characteristics of the fiber optic temperature sensors developed in the above work are that the fiber itself is used as the sensing unit, and its response speed is limited by the relatively low thermal diffusivity of the silica material used in the fiber.

[0005] There have been some attempts to use materials with a larger thermal diffusivity as the sensing unit of fiber optic temperature sensors. For example, silicon with a thermal diffusivity one order of magnitude higher than that of silica is used to fabricate the sensing head, but the potential of silicon in high-speed temperature sensing has not been fully explored (Meng Hua, Li Haiyang, Cao Zhanqi. A fiber optic Fabry-Perot temperature sensor for rapid ocean temperature measurement [J]. Chinese Journal of Lasers, 2018, 45(12):5.). In 2015, the research group of Han Ming from Michigan State University fabricated a high-resolution and fast-response fiber optic temperature sensor based on a silicon Fabry-Perot cavity by attaching a silicon pillar to the tip of a single-mode fiber to form a Fabry-Perot cavity (LIU G, HAN M, HOU W. High-resolution and fast-response fiber-optic temperature sensor using silicon Fabry-Pérot cavity [J]. Optics Express, 2015, 23(6)). These studies provide new ideas for further improving the response speed of fiber optic temperature sensors.

[0006] Although the silicon-based fiber optic Fabry-Perot temperature sensor can effectively improve the response speed, at present, expensive high-speed spectrometers or spectral demodulators are required in the fast-response fiber optic Fabry-Perot temperature sensor system to obtain spectral signals, and a large amount of spectral data processing is also needed to obtain the temperature value. Not only is the system complex and the cost too high, which becomes a bottleneck restricting the further improvement of the sensor's response speed, but also the application prospect of this type of sensor is limited. Therefore, it is necessary to redesign the structure of the fiber optic Fabry-Perot temperature sensor system, get rid of the dependence of the sensor on the spectral demodulation and analysis part, reduce the system cost and complexity, and clear the obstacles for improving the response speed. Summary of the Invention

[0007] Aiming at the defects of the prior art, the present invention provides a fast-response fiber optic temperature sensor and its preparation method.

[0008] A fast-response fiber optic Fabry-Perot temperature sensor includes a laser for emitting incident light. The laser is connected to a fiber optic circulator, which is simultaneously connected to a temperature sensing head and a photodetector. The photodetector is connected to a controller. The temperature sensing head is composed of a fiber, a micro silicon chip, and a reflective film. One end face of the fiber is connected to one side of the micro silicon chip, and the interface between the end face of the fiber and the micro silicon chip is the first cavity surface. The reflective film is formed on the other side of the micro silicon chip, and the interface between the reflective film and the micro silicon chip is the second cavity surface. The incident light is continuously reflected on the first cavity surface and the second cavity surface to form Fabry-Perot interference, and the reflected light is obtained.

[0009] Optionally, the micro silicon chip is formed from the device layer silicon of an SOI wafer; the photodetector is used to convert the reflected light into a voltage signal; the controller demodulates the temperature according to the reflected light by intensity demodulation method; the intensity of the reflected light monotonically increases with temperature within the temperature range; the intensity of the reflected light is related to the reflectivity R on the two mirrors of the Fabry - Perot cavity and is also related to the optical path that the light experiences in the cavity. The intensity I of the reflected light r can be expressed as

[0010]

[0011] where I i is the intensity of the incident laser light, δ is the phase difference between two adjacent reflected light beams, and its relationship with the cavity length h is δ = 4πnh / λ; where λ is the wavelength of the incident light and n is the refractive index of the Fabry - Perot cavity.

[0012] A preparation method of an optical fiber Fabry - Perot temperature sensor, characterized by comprising the following steps: Step a, evaporating a metal reflective film on the surface of the SOI wafer device layer; Step b, partially etching the SOI wafer substrate layer and the silicon dioxide insulating layer to expose the device layer; Step c, using a laser to cut the device layer to obtain a micro silicon chip with a reflective film; Step d, coupling the micro silicon chip with the end face of the optical fiber to obtain the sensing head.

[0013] Optionally, the reflective film is a metal film with a thickness of 100 nm; in Step b, first, ultraviolet light is used to pattern - etch the substrate, and then reactive ions are implanted in the pattern to remove a part of the substrate in the pattern, thereby forming a blind hole in the substrate that penetrates the substrate and reaches the silicon dioxide insulating layer. Then, a hydrofluoric acid solution is injected into the blind hole, and the silicon dioxide insulating layer in the blind hole is corroded with the hydrofluoric acid solution to expose the device layer; in Step d, the optical fiber with a clean end face obtained by cutting the optical fiber is fixed on the adjustment bracket on one side of the coupling table, and optical curing glue is applied to the end face of the optical fiber. Then, the micro silicon chip cut by the laser is transferred to the adjustment bracket on the other side of the coupling table. The micro silicon chip and the end face of the optical fiber are coupled together by adjusting the adjustment bracket, and the optical curing glue on the sensing head is modified by irradiating with an ultraviolet lamp to obtain the temperature sensing head.

[0014] The beneficial effects of the present invention are as follows: The present invention aims to solve the problems of limited response speed, complex system, and small free spectral range of existing optical fiber Fabry - Perot temperature sensors, and provides an optical fiber Fabry - Perot temperature sensor with a compact structure, fast response speed, and simple system and its preparation method. Description of the Drawings

[0015] Figure 1 Structure of the optical fiber Fabry - Perot temperature sensor

[0016] Figure 2 Chrome film is deposited on the silicon of the device layer of the SOI wafer;

[0017] Figure 3 The SOI wafer after etching away the silicon of the substrate layer and the silicon dioxide of the insulating layer is etched;

[0018] Figure 4 The silicon of the device layer is laser cut to obtain micro silicon wafers;

[0019] Figure 5 The end face of the optical fiber is coupled with the micro silicon wafer to obtain a sensing head;

[0020] Figure 6 The sensing head of the fabricated fiber optic Fabry - Perot temperature sensor;

[0021] Figure 7 The time response curve of the fiber optic Fabry - Perot temperature sensor. Specific Embodiments

[0022] To make the above - mentioned objects, features and advantages of the present invention more obvious and understandable, the following will describe the specific embodiments of the present invention in detail with reference to the accompanying drawings, so that the above - mentioned and other objects, features and advantages of the present invention will be more clear. The same reference numerals indicate the same parts in all the drawings. The drawings are not deliberately drawn to scale, and the focus is on showing the gist of the present invention.

[0023] Generally speaking, the present invention proposes a fast - response fiber optic Fabry - Perot temperature sensor and its preparation method. The method is to fabricate a micro - silicon wafer with a thickness of about ten microns using MEMS technology and couple it to the end face of the optical fiber to form a very short Fabry - Perot cavity structure. The diameter of the silicon wafer is equivalent to the diameter of the optical fiber, and its micro - size enables the temperature response to be completed quickly. Moreover, the reduction of the cavity length increases the free spectral range in the reflection spectrum, and the monotonic interval of the temperature response corresponding to intensity demodulation increases, greatly reducing the complexity of the system, and obtaining a fiber optic Fabry - Perot temperature sensor with a compact structure, fast response speed and simple system.

[0024] The structure of the fast - response fiber optic Fabry - Perot temperature sensor of the present invention is as Figure 1 shown. It includes a laser 1, the laser 1 is used to emit laser, the laser 1 is connected to an optical fiber circulator 2, the optical fiber circulator 2 is simultaneously connected to a temperature sensing head 3 and a photodetector 4, and the photodetector 4 is connected to a controller 5.

[0025] The temperature sensing head 3 is composed of an optical fiber 3-1, a micro silicon chip 3-2, and a reflective film 3-3. The reflective film 3-3 can be a chromium film. The interface between the end face of the optical fiber 3-1 and the micro silicon chip 3-2 is a cavity surface, and the interface between the micro silicon chip 3-2 and the reflective film 3-3 is the second cavity surface. The incident light is continuously reflected on the two cavity surfaces to form a Fabry-Perot interference.

[0026] In the present invention, the laser emitted from the laser 1 passes through the optical fiber circulator 2 and is incident on the temperature sensing head 3 that responds to the external temperature. The laser is reflected by the front and back surfaces of the Fabry-Perot cavity in the sensing head 3 and interferes with each other, and then enters the photodetector 4 through the optical fiber circulator, is converted into a voltage signal, collected by the controller 5, and converted into a temperature signal to output the temperature value.

[0027] The demodulation scheme of the controller 5 for the temperature solution is intensity demodulation. By selecting an appropriate wavelength of the laser, the reflected light intensity can be made to increase monotonically with temperature within a specific temperature range. The intensity of the reflected light is related to the reflectivity R on the two cavity mirrors of the Fabry-Perot cavity and is also related to the optical path that the light experiences in the cavity. The intensity I of the reflected light r can be simply expressed as

[0028]

[0029] where I i is the intensity of the incident laser light, δ is the phase difference between two adjacent reflected light beams, and its relationship with the cavity length h is δ = 4πnh / λ. Here, λ is the wavelength of the incident light, and n is the refractive index of the Fabry-Perot cavity. The phase difference of the light beam changes with the changes in the cavity length and the refractive index, and the intensity of the reflected light also changes periodically with the cavity length. The relationship curve between the reflectivity and the wavelength can be calculated by formula (1) and is approximately sinusoidal and periodically changing.

[0030] Crystalline silicon has a relatively large thermo-optic coefficient and is temperature-dependent. At room temperature (T0 = 300K), its refractive index is n0 = 3.48, and the relationship between the refractive index n and the temperature T can be described by the following formula

[0031] n(T) = n0 + C1(T - T0) + C2(T - T0) 2 / 2 (2)

[0032] where C1 = 1.862×10 -4 、C2 = 2.591×10 -7 and C3 = -1.490×10 -10 are respectively the first-order thermo-optic coefficient, the second-order thermo-optic coefficient, and the third-order thermo-optic coefficient of silicon in the 1.5μm optical fiber communication band. The thermal expansion coefficient of silicon at room temperature is α0 = 2.616×10 -6 K -1Substituting the above parameters into the reflectivity formula (1), the variation of the reflectivity of the temperature sensor head with temperature can be obtained. Since the thermal expansion coefficient of silicon has a relatively small influence on the temperature variation of reflectivity, which is nearly two orders of magnitude smaller than the thermo-optic coefficient, the thermo-optic effect plays a major role during the process of the sensor head 3 responding to temperature.

[0033] Next, combined with Figures 2 to 6 the preparation method of the sensor head 3 of the fiber optic Fabry-Perot temperature sensor of the present invention will be introduced. The sensor head 3 of the fast-response fiber optic Fabry-Perot temperature sensor is fabricated by using MEMS technology and fiber waveguide coupling technology. The specific preparation method is as follows:

[0034] a. Evaporate a metal reflective film on the surface of the SOI wafer device layer.

[0035] The SOI (Silicon-On-Insulator) wafer is a special semiconductor material, which consists of three layers: a substrate 6 (silicon substrate), a silicon dioxide insulating layer 7 (the middle insulating layer), and a device layer 8 (the top silicon layer). Use electron beam evaporation to evaporate a 100-nm metal reflective film 9, such as a chromium film, on the silicon surface of the device layer 8 of the SOI as the reflective layer, obtaining a wafer structure as Figure 2 shown.

[0036] b. Etch the SOI wafer substrate layer and the silicon dioxide insulating layer.

[0037] A certain pattern of the substrate 6 can be etched away using photolithography and reactive ion etching to expose the silicon dioxide insulating layer 7. Then, use hydrofluoric acid solution to etch and remove the silicon dioxide insulating layer 7 to expose the device layer 8, presenting a thin film state as Figure 3 shown.

[0038] Specifically, a laser can be used to pattern-etch the substrate 6 to etch out the required pattern on the substrate 6, for example, it can be a circular pattern. Then, reactive ions are injected into the circular pattern to remove a part of the substrate in the pattern, thereby forming a sinkhole 10 in the substrate 6. The sinkhole 10 penetrates the substrate 6 and reaches the silicon dioxide insulating layer 7. After that, hydrofluoric acid solution is injected into the sinkhole 10, and the silicon dioxide insulating layer 7 in the sinkhole 10 is etched away using the hydrofluoric acid solution, thereby exposing the device layer 8.

[0039] c. Use a laser to cut the device layer to obtain a micro silicon wafer with a reflective film.

[0040] Use a fine laser to cut and etch the remaining silicon film of the device layer 8, and through the set laser cutting circular route, obtain a micro silicon wafer 11 with a chromium reflective layer as Figure 4 shown.

[0041] d. Couple the micro silicon chip with the end face of the optical fiber to obtain the sensing head 3.

[0042] Fix the optical fiber 3-1 with a clean end face obtained by cutting the optical fiber on the adjustment rack on one side of the coupling table, and apply photo-curing glue on the end face of the optical fiber. Then transfer the micro silicon chip 11 cut by laser to the other adjustment rack on the coupling table, couple the micro silicon chip 11 and the end face of the optical fiber together by adjusting the adjustment rack, and irradiate with ultraviolet light to modify the photo-curing glue on the sensing head, so as to obtain Figure 5 the temperature sensing head 3 as shown.

[0043] Experimental Example

[0044] (1) Evaporate a chromium reflective film with a thickness of 100 nm on the surface of the SOI wafer device layer.

[0045] (2) Etch the substrate silicon and silicon dioxide insulating layer of the SOI wafer.

[0046] a. Use photolithography and development to make a photoresist pattern of the silicon structure to be removed on the surface of the substrate silicon of the SOI wafer; b. Reactively ion etch to etch away the substrate layer silicon until the silicon dioxide insulating layer is exposed and stop; c. Use a 2% hydrofluoric acid solution to corrode and remove the silicon dioxide layer to obtain the silicon thin film of the device layer.

[0047] (3) Laser cut the silicon of the device layer to obtain a micro silicon chip

[0048] a. Use fine laser to cut the silicon film of the device layer into circular micro silicon chips with a diameter of 125 μm.

[0049] (4) Coupling of the micro silicon chip and the end face of the optical fiber

[0050] a. Cut the optical fiber with an optical fiber cutter to obtain a clean end face of the optical fiber; b. Fix the cut optical fiber on the adjustment rack on one side of the coupling table; c. Apply ultraviolet photo-curing glue on the end face of the optical fiber under the assistance of a microscope; d. Paste the silicon wafer cut by laser on the adjustment rack on the other side of the coupling table; e. Align and press the silicon wafer and the end face of the optical fiber tightly by adjusting the adjustment rack; f. Irradiate with ultraviolet light for 10 min to modify and cure the ultraviolet photo-curing glue.

[0051] (5) Connection of the fiber optic Fabry-Perot temperature sensor

[0052] a. Fusion splice the laser with a fiber pigtail to the first channel fiber of the fiber optic circulator; b. Connect the sensing head pigtail and the second channel of the fiber optic circulator through a fiber optic connector; c. Connect the third channel connector of the fiber optic circulator to the photodetector; d. Connect the electrical signal output by the photodetector to the ADC pin of the single-chip microcomputer in the controller; e. The single-chip microcomputer outputs the temperature value according to the fitted intensity-temperature corresponding data.

[0053] The physical diagram of the temperature sensor head 3 fabricated in this experimental example is as follows Figure 6 As shown, after connecting it to the laser 1, optical fiber circulator 2, photodetector 4, and controller 5, an optical fiber Fabry-Perot temperature sensor system is formed. The time response characteristics of the optical fiber Fabry-Perot temperature sensor are tested by the water immersion method. The sensor head is quickly inserted into water at 55 °C, and the temperature signal output by the controller 5 is recorded. The response time of the sensor head is obtained by analyzing the temperature change curve. The response time curve of the optical fiber temperature sensor obtained by the test is as follows Figure 7 As shown. According to the definition that the response time of the sensor is the time required for the temperature to change to 63.2% of the steady-state temperature, the response time of the optical fiber temperature sensor is 0.54 ms obtained from the curve.

[0054] As can be seen from the above description, the fast-response optical fiber Fabry-Perot temperature sensor and its preparation method of the present invention use an SOI wafer and are completed by film coating, photolithography, etching, and laser cutting in the MEMS process to obtain a micro silicon wafer made of the silicon of the SOI wafer device layer. A micro silicon wafer in the order of ten micrometers is fabricated by the MEMS process and coupled to the end face of the optical fiber to form a very short Fabry-Perot cavity structure, which is combined with the laser 1, photodetector 4, and controller 5 to form an intensity-demodulated optical fiber Fabry-Perot temperature sensor. The size of the sensor head is miniaturized, and it can quickly respond to the ambient temperature.

[0055] On one surface of the micro silicon wafer, there is a metal reflection film 9, which is used to reflect the light incident on the micro silicon wafer and at the same time block the influence of the change in the external refractive index on the sensor signal. The sensor head part of the fabricated optical fiber Fabry-Perot temperature sensor is completed by optical coupling between the end face of the optical fiber and the micro silicon wafer, and a tight connection is formed by curing with an optical curing adhesive between the end face of the optical fiber and the micro silicon wafer. The optical fiber Fabry-Perot temperature sensor system uses the combination of the laser 1, photodetector 4, and controller 5 to complete intensity demodulation to obtain the temperature value. The system is simple and has a low cost. By using a micro silicon wafer coupled with the end face of the optical fiber, a compact miniaturized sensor head 3 is fabricated, and the response speed of the sensor is increased to the sub-millisecond level.

[0056] In the present invention, other micro-optical fiber structures can be used to replace the end face of the optical fiber, such as tapered optical fiber, Wiener optical fiber, photonic crystal fiber, etc., to form a Fabry-Perot cavity with the micro silicon wafer. The metal film can be replaced with other metal materials instead of the chromium film, such as metals like gold, silver, copper, platinum, etc., or a dielectric film can also be used for replacement. The optical fiber circulator can be replaced with an optical fiber beam splitter or an optical fiber coupler instead of the optical fiber circulator.

[0057] The fiber optic Fabry-Perot temperature sensor proposed by the present invention has the ability of rapid response. By using a micro silicon chip as the sensing unit and taking advantage of the relatively large thermal diffusion coefficient and thermo-optic coefficient of silicon, the response time of the sensor reaches 0.54 ms, meeting the requirements of transient temperature measurement. The system structure is simple. By adopting the intensity demodulation method, the system structure is simplified, the cost is reduced, and the improvement of the system performance is no longer restricted by the performance of other components of the system. The sensing head has a compact and miniaturized structure. The structure of the sensor probe is compact, and the diameter of the sensing unit is only the same as that of the optical fiber (125 μm), and the length is only on the order of 10 μm, truly achieving miniaturization and being suitable for temperature measurement in narrow spaces under complex environments.

[0058] Many specific details are set forth in the above description to facilitate a thorough understanding of the present invention. However, the above description is only a preferred embodiment of the present invention, and the present invention can be implemented in many other ways different from those described herein. Therefore, the present invention is not limited by the specific embodiments disclosed above. At the same time, any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention, or modify it into equivalent embodiments with equivalent changes. All simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the protection of the technical solution of the present invention.

Claims

1. A fast response optical fiber Fabry-Perot temperature sensor, characterized in that: The invention comprises a laser, wherein the laser is used to emit incident light, the laser is connected to an optical fiber circulator, the optical fiber circulator is connected to a temperature sensing head and a photodetector at the same time, and the photodetector is connected to a controller; the temperature sensing head is composed of an optical fiber, a micro silicon chip and a reflective film, the end face of the optical fiber is connected to one side of the micro silicon chip, the interface between the end face of the optical fiber and the micro silicon chip is a first cavity surface, the reflective film is formed on the other side of the micro silicon chip, the interface between the reflective film and the micro silicon chip is a second cavity surface, the incident light is continuously reflected on the first cavity surface and the second cavity surface to form Fabry-Perot interference, and the reflected light is obtained.

2. The temperature sensor according to claim 1, characterized in that: The micro silicon chip is formed from the device layer silicon of the SOI wafer.

3. The temperature sensor according to claim 1, characterized in that: The photodetector is used to convert the reflected light into a voltage signal.

4. The temperature sensor according to claim 3, characterized in that: The controller demodulates the temperature by an intensity demodulation method based on the reflected light.

5. The temperature sensor according to claim 4, characterized in that: The reflected light intensity increases monotonically with temperature within the temperature range.

6. The temperature sensor according to claim 5, characterized in that: The intensity of the reflected light is related to the reflectivity R of the two mirrors of the Fabry-Perot cavity and the optical path of the light in the cavity. r It can be expressed as Among them I i is the incident laser intensity, δ is the phase difference between two adjacent reflected light beams, and its relationship with the cavity length h is δ=4πnh / λ; where λ is the wavelength of the incident light and n is the refractive index of the Fabry-Perot cavity.

7. A method for preparing the optical fiber Fabry-Perot temperature sensor according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step a, evaporating a metal reflective film on the surface of the device layer of the SOI wafer; Step b, partially etching the SOI wafer substrate layer and the silicon dioxide insulating layer to expose the device layer; Step c, cutting the device layer by laser to obtain a micro silicon wafer with a reflective film; Step d: coupling the micro silicon chip with the end face of an optical fiber to obtain the sensor head.

8. The preparation method according to claim 7, characterized in that: The reflective film is a metal coating film.

9. The preparation method according to claim 7, characterized in that: In the step b, the substrate is first patterned and etched using ultraviolet lithography, and then reactive ions are injected into the pattern to remove a portion of the substrate in the pattern, thereby forming a countersunk hole on the substrate, and the countersunk hole penetrates the substrate and reaches the silicon dioxide insulating layer. Thereafter, a hydrofluoric acid solution is injected into the countersunk hole, and the hydrofluoric acid solution is used to corrode the silicon dioxide insulating layer in the countersunk hole, thereby exposing the device layer.

10. The preparation method according to claim 7, characterized in that: In the step d, the optical fiber with a clean optical fiber end face obtained by cutting the optical fiber is fixed on an adjustment frame on one side of the coupling table, and photocuring glue is applied to the optical fiber end face. Then, the micro silicon chip cut by laser is transferred to another adjustment frame of the coupling table, and the micro silicon chip and the optical fiber end face are coupled together by adjusting the adjustment frame. The photocuring glue on the sensor head is modified by irradiation with ultraviolet light, thereby obtaining the temperature sensor head.

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