Microcavity optical fiber Fabry-Perot temperature sensor based on metal wire and preparation method thereof

Abstract

The invention relates to the field of temperature sensing, and particularly provides a microcavity optical fiber Fabry-Perot temperature sensor based on a metal wire and a preparation method thereof.The temperature sensor comprises an optical fiber, a hollow pipe and the metal wire, one end of the optical fiber is connected with one end of the hollow pipe, the inner diameter of the hollow pipe is smaller than the diameter of the optical fiber, and the end, away from the optical fiber, of the hollow pipe is closed; one end of the metal wire is fixedly arranged at the closed end of the hollow tube, the free end of the metal wire is opposite to the optical fiber, and a microcavity is formed between the end face of the free end of the metal wire and the end face of the side, close to the metal wire, of the optical fiber; incident laser enters from one end, far away from the hollow tube, of the optical fiber and exits from the incident end of the optical fiber after being reflected by the micro-cavity, the length of the micro-cavity is changed by the temperature, so that the spectrum of the emergent laser is changed, and the temperature change is detected by the spectrum. The invention further discloses a preparation method of the sensor. The micro-cavity optical fiber Fabry-Perot temperature sensor based on the metal wire can realize sensitive detection of high temperature.

Description

Technical Field

[0001] The present application relates to the field of temperature sensing, and in particular to a metal wire-based microcavity optical fiber Fabry-Perot temperature sensor and a preparation method thereof. Background Art

[0002] Fiber optic temperature sensors convert temperature changes into changes in optical signals and detect temperature changes through changes in optical signals. They have the advantages of small size and strong anti-electromagnetic interference ability, and are widely used in aerospace, shipbuilding, dams, environmental monitoring, chemical biology and other fields.

[0003] Traditional fiber optic temperature sensors mainly use fiber Bragg gratings, but when the temperature exceeds 600°C, long-term use or even exceeds 400°C will gradually degrade, causing the interference spectrum to disappear. Therefore, the sensor cannot detect higher temperatures and mainly uses auxiliary measures for indirect measurement, with low detection sensitivity and accuracy. Long-period fiber gratings written by carbon dioxide lasers can withstand high temperatures, but they are inconvenient to use due to their cross sensitivity to bending strain.

[0004] Since the cavity is made of fused silica optical fiber or capillary glass tube, and the photothermal coefficient and thermal expansion coefficient of the quartz material are low, the sensitivity of ordinary interferometric Fabry-Perot temperature detection is low. A document entitled “Ultrasensitive Temperature Sensor Based on a Fiber Fabry–Pérot Interferometer Created in a Mercury-Filled Silica Tube” (IEEE Photonics Journal, vol. 7, no. 6, pp. 1-9, Dec. 2015, Art no. 6803509.) discloses a Fabry–Pérot cavity, which improves the sensitivity of temperature detection by filling a capillary hollow glass tube or a hollow optical fiber constituting the cavity of the optical fiber Fabry–Pérot cavity with liquid and utilizing the high photothermal coefficient and high thermal expansion coefficient of the liquid; a document entitled “Highly-sensitive optical fiber temperature sensors based on PDMS / silica hybrid fiber structures” (Sens. Actuators A Phys. 2018, 284, 22-27) discloses a method for improving the sensitivity of temperature detection by filling a capillary hollow glass tube or a hollow optical fiber constituting the cavity of the optical fiber Fabry–Pérot cavity with plastic such as PDMS and utilizing the linear high negative photothermal coefficient of PDMS. However, both liquid and plastic PDMS are not resistant to high temperatures and will deteriorate, decompose or burn under high temperatures, making them unable to work in a high temperature environment. Therefore, existing optical fiber temperature sensors cannot achieve high-sensitivity detection at high temperatures. Summary of the invention

[0005] The purpose of the present invention is to provide a metal wire-based microcavity fiber Fabry-Perot temperature sensor and a preparation method thereof in view of the above-mentioned deficiencies in the prior art, so as to solve the problem that the existing fiber optic temperature sensors cannot achieve high-sensitivity detection at higher temperatures.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: The present application provides a metal wire-based microcavity fiber Fabry-Perot temperature sensor, which comprises an optical fiber, a hollow tube, and a metal wire. One end of the optical fiber is connected to one end of the hollow tube, the inner diameter of the hollow tube is smaller than the diameter of the optical fiber, the end of the hollow tube away from the optical fiber is closed, a metal wire is arranged inside the hollow tube, one end of the metal wire is fixedly arranged at the closed end of the hollow tube, the free end of the metal wire is opposite to the optical fiber, and a microcavity is formed between the end face of the free end of the metal wire and the end face of the optical fiber close to the metal wire. An incident laser is incident from the end of the optical fiber away from the hollow tube, and after being reflected by the microcavity, the laser is emitted from the incident end of the optical fiber. The temperature changes the length of the microcavity, thereby changing the spectrum of the emitted laser, and the temperature change is detected by the spectrum.

[0007] Further, the thermal expansion coefficient of the metal wire is greater than the thermal expansion coefficient of the hollow tube.

[0008] Furthermore, the length of the microcavity is 60-200 microns.

[0009] Furthermore, the thickness of the hollow tube of the microcavity sidewall is not uniform.

[0010] Furthermore, a concave structure is arranged on the end surface of the metal wire on the side close to the optical fiber.

[0011] Furthermore, the material of the metal wire is one of copper, aluminum, silver, gold, platinum, tungsten, brass, copper, steel, nickel-chromium alloy, and iron-aluminum-nickel alloy.

[0012] Furthermore, the optical fiber is co-linear with the central axis of the hollow tube.

[0013] Furthermore, the optical fiber is a single-mode optical fiber, and the hollow tube is a hollow capillary glass tube or a hollow photonic crystal optical fiber.

[0014] The present application also provides a method for preparing the above-mentioned metal wire-based microcavity optical fiber Fabry-Perot temperature sensor, the method comprising the following steps: First, the optical fiber and one end of the hollow tube are cut flat and fused together, a preset length of the hollow tube is retained, and the excess length of the hollow tube is cut off from the other end of the hollow tube; Then, insert the metal wire into the hollow tube, the length of the metal wire inserted is less than the length of the hollow tube, and cut off the excess metal wire so that the metal wire is flush with the end of the hollow tube away from the optical fiber; Finally, the metal wire is further inserted so that it completely enters the hollow tube, and the end of the hollow tube away from the optical fiber is heated and melted to close it and fix the metal wire.

[0015] Furthermore, the fusion splicing is achieved by using a fiber fusion splicer or a carbon dioxide laser for heating; the heating and melting is achieved by using an arc discharge or a carbon dioxide laser.

[0016] Compared with the prior art, the present invention has the following beneficial effects: the change in temperature causes the length of the metal wire to change, thereby changing the length of the microcavity. The metal wire has a thermal expansion coefficient much higher than that of the capillary glass tube. When the ambient temperature changes, the thermal expansion effect causes the length of the capillary glass tube and the metal wire to change, but the length change of the metal wire is much greater than that of the capillary glass tube, so that the length of the Fabry-Perot cavity (microcavity) changes. The change in cavity length is obtained by detecting the change in the interference spectrum, and then the detected temperature is determined. Increasing the length of the metal wire can increase the change in cavity length of the Fabry-Perot cavity caused by a unit temperature change, that is, increase the temperature sensitivity of the Fabry-Perot sensor. Since many commonly used metal wires have a melting point higher than 1000°C and are stable from room temperature to high temperature, the sensor can be used for temperature measurement from room temperature to high temperature. The high thermal expansion coefficient and interference effect of the metal wire are highly sensitive to the change in cavity length of the Fabry-Perot cavity, and the sensor has high sensitivity; and the metal wire has a high reflection efficiency, and the contrast of the interference fringes formed in the microcavity is high; the sensor sensitivity can also be adjusted by adjusting the length of the metal wire; since most metal wires have good high temperature resistance, the sensor of the present application can achieve sensitive detection of high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of a metal wire-based microcavity optical fiber Fabry-Perot temperature sensor provided by the present invention; Figure 2 A schematic diagram of a metal wire-based microcavity optical fiber Fabry-Perot temperature sensor provided by the present invention when in use; Figure 3 A schematic diagram of heating and melting during the preparation of a metal wire-based microcavity optical fiber Fabry-Perot temperature sensor provided by the present invention.

[0018] Icons: 1-optical fiber; 2-hollow tube; 3-metal wire; 4-laser light source; 5-spectrometer; 6-optical fiber circulator. DETAILED DESCRIPTION

[0019] In order to make the implementation process of the present invention clearer, it will be described in detail below with reference to the accompanying drawings.

[0020] The present invention provides a microcavity optical fiber Fabry-Perot temperature sensor based on metal wire, such as Figure 1 As shown, the temperature sensor includes an optical fiber 1, a hollow tube 2, and a metal wire 3. Specifically, one end of the optical fiber 1 is connected to one end of the hollow tube 2, and the other end of the optical fiber 1 is used to receive the incident laser and transmit the reflected laser. The hollow tube 2 is a hollow capillary glass tube or a hollow photonic crystal fiber. The central axis of the optical fiber 1 is colinear with that of the hollow tube 2, so that the center of the light field propagates along the central axis and the propagation loss is small. The optical fiber 1 can be a single-mode optical fiber or a multi-mode optical fiber. Preferably, the optical fiber 1 is a single-mode optical fiber, which is less expensive and the interference signal is easier to demodulate.

[0021] The inner diameter of the hollow tube 2 is smaller than the diameter of the optical fiber 1, and the laser can be transmitted to the hollow tube 2; the end of the hollow tube 2 away from the optical fiber 1 is closed, and the shape of the closed end is hemispherical, so that the metal wire 3 can be fixed so that the effect of the length change of the metal wire 3 under temperature change is only reflected at the unfixed end facing the optical fiber 1, changing the cavity length of the Fabry-Perot cavity; at the same time, the metal wire 3 is isolated from corrosion by external gases such as oxygen and water vapor, so that the performance of the metal wire 3 is stable in various application environments. The metal wire 3 is arranged inside the hollow tube 2; the thermal expansion coefficient of the metal wire 3 is greater than the thermal expansion coefficient of the hollow tube 2, so that when the temperature in the environment to be detected changes, the deformation degree of the metal wire 3 is greater, so that under the same temperature change, the length of the metal wire 3 changes more, so that the change of the reflected light spectrum is greater, and the temperature detection sensitivity is higher. The diameter of the metal wire 3 is smaller than the inner diameter of the hollow tube 2, and the diameter of the metal wire 3 is 0.7-0.9 times the inner diameter of the hollow tube 2, so that it is easy to put the metal wire 3 into the hollow tube 2 during production; it also ensures that the end face of the metal wire 3 is large enough and the reflected light intensity is sufficient, so as to obtain a high-quality Fabry-Perot cavity interference signal; at the same time, it also reserves space for the diameter change of the metal wire 3 when the temperature changes, so as to prevent the metal wire 3 from breaking the hollow tube 2 under high temperature environment and the metal wire 3 is too large in diameter and stuck by the hollow tube 2, so that its length change is suppressed by the hollow tube 2, reducing the temperature response sensitivity of the sensor. The length of the metal wire 3 is 60-200 microns shorter than the length of the hollow tube 2; in this way, the cavity length of the Fabry-Perot cavity is 60-200 microns, which can ensure that the light intensity reflected by the end face of the metal wire 3 coupled back to the optical fiber 1 is large enough, so as to obtain a strong Fabry-Perot cavity interference signal, which is easy to demodulate the signal; at the same time, the number of interference signal fringes (number of cycles) is relatively large, and a higher demodulation accuracy of the Fabry-Perot cavity length change or fringe drift can be obtained. The material of the metal wire 3 is one of copper, aluminum, silver, gold, platinum, tungsten, brass, copper, steel, nickel-chromium alloy, and iron-aluminum-nickel alloy; preferably, the material of the metal wire 3 is nickel-chromium alloy, which has low cost and a sufficiently high thermal expansion coefficient, which is 5-8 times that of the quartz capillary glass tube. The same length of the metal wire 3 can obtain a higher temperature sensitivity, and the melting point is as high as 1400°C, which is higher than the softening temperature of the capillary quartz glass tube. The thermal expansion coefficient of brass wire is basically the same as that of nickel-chromium alloy, but the melting point is only about 900°C, and the maximum operating temperature of the manufactured sensor is only 900°C. The thermal expansion coefficient of aluminum wire is slightly higher than that of nickel-chromium alloy, but the melting point is only more than 600 degrees, while the thermal expansion coefficient of steel is slightly lower, only about two-thirds of that of nickel-chromium alloy.

[0022] One end of the metal wire 3 is fixedly arranged at the closed end of the hollow tube 2, and the free end of the metal wire 3 is opposite to the end face of the optical fiber 1 connected to the end of the hollow tube 2. A microcavity, i.e., a Fabry-Perot interference cavity, is formed between the end face of the free end of the metal wire 3 and the end face of the optical fiber 1 close to the metal wire 3. The laser enters the microcavity and is reflected by the two end faces of the microcavity. The optical path of the laser in the microcavity is smaller than the coherence length of the light source. Interference occurs between the reflected light from the two end faces to form a reflected interference spectrum. The reflected laser is emitted from the incident end of the optical fiber 1 to obtain a reflected light spectrum. The length of the microcavity is different, and the optical path difference experienced by the light reflected from the end face of the optical fiber 1 and the end face of the metal wire 3 is different, so that the period of the reflected interference spectrum is different. The change in the length of the interference cavity will change the period of the reflected interference spectrum. The incident laser enters the microcavity from the end of the optical fiber 1 away from the hollow tube 2, and is reflected by the two end faces of the microcavity. When the optical path of the laser in the microcavity is less than the coherence length of the light source, interference occurs between the reflected light of the two end faces; the cavity length of the Fabry-Perot cavity needs to be less than 1 / 2 of the coherence length of the light source, otherwise no interference signal is generated. At the same time, since light diffuses in the Fabry-Perot cavity, when the cavity length is long, the light reflected back to the optical fiber 1 by the end face of the metal wire 3 is weak, resulting in a weak interference signal, making the demodulated cavity length less accurate, that is, the temperature measurement accuracy is low, so the cavity length of the Fabry-Perot cavity is designed to be 60-200 microns. Graphene and thermal insulation materials (rubber, etc.) are wrapped on the outside of the hollow tube 2. Graphene is wrapped on the outside of the metal wire 2, and the thermal insulation material is wrapped on the outside of the microcavity. Graphene has good thermal conductivity, which can make more heat in the environment be transferred to the metal wire 3, so that the length of the metal wire 3 changes more, and the detection sensitivity is improved. The thermal insulation material reduces the impact of heat on the microcavity, making the detection results more accurate; at the same time, the thermal insulation material also protects the microcavity segment to prevent it from breaking.

[0023] The present application scheme utilizes interference detection to detect the change of cavity length of the interference cavity by phase modulation of the light field. Since the reflectivity of the reflective end face of the optical fiber 1 is low, the reflected interference light is approximately regarded as a reflection passing through the end face of the metal wire 3 only once, and the formed reflection interference spectrum is approximately a double-beam interference spectrum. The two reflection surfaces of the optical fiber Fabry-Perot interference cavity are respectively formed by the end face of the metal wire 3 facing the single-mode optical fiber and the fusion point of the capillary glass tube of the single-mode optical fiber, and the cavity is formed by the gap between the two reflection end faces. Since the metal wire 3 has a high reflection efficiency, the contrast of the interference fringes of the manufactured Fabry-Perot cavity is high, which is conducive to signal demodulation to obtain accurate temperature values. The laser is emitted from the incident end of the optical fiber 1 to obtain a reflected light spectrum; the temperature in the environment to be detected causes the length of the metal wire 3 to change, thereby changing the position of the end face of the metal wire 3, causing the length of the microcavity to change, and finally changing the spectrum of the emitted laser, and the temperature change is detected by the spectrum; specifically, the change in the length of the metal wire 3 leads to a change in the length of the interference cavity, thereby changing the optical path difference between the end face of the optical fiber 1 and the end face of the metal wire 3, and then changing the interference fringe period in the reflection spectrum. Therefore, the length of the metal wire 3 corresponds to the period of the interference fringes. The higher the temperature, the longer the length of the metal wire 3, the shorter the length of the microcavity, the smaller the optical path difference between the end face of the optical fiber 1 and the reflected light of the end face of the metal wire 3, and the larger the period of the interference fringes in the reflection spectrum; the lower the temperature, the shorter the length of the metal wire 3, the longer the length of the microcavity, the larger the optical path difference between the end face of the optical fiber 1 and the reflected light of the end face of the metal wire 3, and the smaller the period of the interference fringes in the reflection spectrum.

[0024] Furthermore, the end face of the metal wire 3 reflecting light can be processed into a micro-concave surface by micro-machining technology, with a curvature radius of 100 μm-200 μm, a concave depth of 10 μm-30 μm, and a concave diameter of 50 μm-80 μm; in this way, the light field reflected by the metal wire 3 can be focused, and the diffusion of the light field in the Fabry-Perot cavity can be reduced, thereby increasing the light intensity of the reflected light reflected by the metal wire 3 coupled into the optical fiber 1. In this way, on the one hand, the intensity and contrast of the reflected interference spectrum signal are improved, thereby improving the accuracy of demodulating the cavity length change, that is, the temperature change through the reflected spectrum; on the other hand, since a good reflected spectrum signal quality can be maintained when the cavity length is long, the length of the Fabry-Perot cavity, that is, the range of the metal wire 3 allowed to change, can be increased, and at the same time, the length of the metal wire 3 can be increased, and the change of the length of the metal wire 3 per unit temperature change, that is, the sensitivity of the temperature measurement, can be increased without changing the measurement range.

[0025] Furthermore, the thickness of the hollow tube 2 on the side wall of the microcavity is different. The wall of the hollow tube 2 near the end of the optical fiber 1 is thicker, while the wall of the end near the metal wire 3 gradually becomes thinner. When the temperature changes, the expansion of the thick-walled area will be relatively small, while the expansion of the thin-walled area will be more significant. In this way, when the temperature changes at low temperatures, the change in the length of the microcavity is small, but when the temperature enters a higher range, the change in the cavity length accelerates, forming a nonlinear effect. Nonlinear length changes will cause the interference fringe period to change significantly in a high temperature environment, thereby improving the temperature detection sensitivity at high temperatures.

[0026] The optical path difference is not only related to the length of the propagation path, but also to the refractive index of the medium. When the photothermal effect material is filled in the microcavity, its refractive index will change when the temperature changes; the photothermal effect material can be a liquid crystal or a polymer material. The refractive index of the liquid crystal changes greatly with the temperature. When the temperature rises, the change in the refractive index of the photothermal effect material will cause the propagation speed of light in the microcavity to change, which in turn affects the position of the interference fringes; that is, the change in the optical path difference is also increased by the change in the refractive index, and the interference fringes period changes more, thereby increasing the sensitivity to temperature changes. Liquid crystal materials can be injected into the microcavity using liquid filling technology.

[0027] When using, Figure 2 As shown, it also includes a laser light source 4, a spectrometer 5, and a fiber circulator 6 (or a 1×2 coupler). The output end of the laser light source 4, the input end of the spectrometer 5, and the end of the optical fiber 1 in the above-mentioned sensor away from the hollow tube 2 are all connected to the fiber circulator 6, and are respectively connected to the three ports of the fiber circulator 6; specifically, the laser output by the laser light source 4 enters the optical fiber 1 in the sensor of the present application after passing through the fiber circulator 6, and temperature sensing is performed at the other end of the optical fiber 1. The reflected laser carrying temperature information enters the fiber circulator 6 and enters the spectrometer 5 through the fiber circulator 6; the spectrometer 5 can be connected to a computer for communication, and the computer is used to collect and process data. The laser light source 4 can be a broadband light source for providing a light source; specifically, the laser light source 4 outputs a laser with a certain bandwidth and wavelength range, generally a wavelength range of 1500nm to 1650nm. This light source is a commonly used light source in the communication band, with mature technology, high stability, and low cost.

[0028] The present application also provides a method for preparing the above-mentioned metal wire-based microcavity optical fiber Fabry-Perot temperature sensor, the method comprising the following steps: First, cut one end of the optical fiber 1 and the hollow tube 2 flat for easy fusion. Use an optical fiber fusion splicer or a carbon dioxide laser to fusion the two together, with the optical fiber 1 and the central axis of the hollow tube 2 being colinear. Keep the preset length of the hollow tube 2, and cut off the excess length of the hollow tube 2 from the other end of the hollow tube 2, that is, the end away from the optical fiber 1. Specifically, the preset length is 0.5-5 mm; for example, when using an optical fiber fusion splicer for fusion, align the single-mode optical fiber and the hollow tube 2 (quartz capillary, the outer diameter is the same as the diameter of the optical fiber 1, and the inner diameter is 0.5-0.8 times the outer diameter) in the fusion splicer, and at the same time, the fusion point is offset to the end of the hollow tube 2 by 50-100 microns to move the fusion discharge center, and the single-mode optical fiber discharge intensity of 0.5-0.8 is used for manual or automatic fusion. In this way, the fusion end face of the single-mode optical fiber is minimally damaged, while ensuring sufficient fusion strength.

[0029] Then, insert the metal wire 3 into the hollow tube 2, and the length of the metal wire 3 is less than the length of the hollow tube 2; that is, the end face of the metal wire 3 extending into one end of the hollow tube 2 does not contact the optical fiber 1, and there is a distance between them, forming a microcavity. Cut off the excess metal wire 3 so that the metal wire 3 is flush with the end of the hollow tube 2 away from the optical fiber 1. In order to ensure that the hollow tube 2 is not damaged during cutting, the metal wire 3 can be cut slightly longer than the hollow tube 2. Preferably, graphene can be wrapped at the end of the metal wire 3 away from the hollow tube 2, so that heat can be quickly transferred to the metal wire 3, causing a large change in the length of the metal wire 3, thereby improving the detection sensitivity; in addition, it is easier to melt during the heating and melting process, so that the fixing effect between the metal wire 3 and the hollow tube 3 is stronger.

[0030] Finally, the tip of the tapered optical fiber is used to further push the metal wire 3, and the pushing length is 20-50 microns, so that the metal wire 3 completely enters the hollow tube 2. In this way, when the other end of the hollow tube 2 is closed, the metal wire 3 is further pushed in order to facilitate heating and collapsing the hollow tube 2 to fix the metal wire 3, and at the same time, it is also sealed to isolate the outside oxygen, water vapor, etc. from corroding and damaging the metal wire 3 at high temperature. Heat and melt collapse the end of the hollow tube 2 away from the optical fiber 1 to close it and fix the metal wire 3. Use arc discharge or carbon dioxide laser for heating and melting collapse; specifically, as Figure 3 As shown, for example, when the optical fiber fusion splicer is used for thermal melting collapse, a higher discharge energy and a longer discharge time similar to the multimode optical fiber fusion splicing mode can be used, so that the shape of the closed end of the hollow tube 2 is as follows Figure 1The hemispherical shape shown has a diameter the same as that of the hollow tube 2. In this way, on the one hand, the hemispherical shape has a larger contact area with the outside world, which increases the heat conduction efficiency, allowing the metal wire 3 to respond to temperature changes more quickly, thereby improving the real-time response speed and sensitivity of the sensor; on the other hand, the hemispherical structure can effectively reduce the problem of mechanical stress concentration caused by temperature changes during thermal expansion, avoid structural deformation or damage due to excessive stress under high temperature conditions, and more uniform stress distribution, reduce the deformation inconsistency caused by interface unevenness, ensure that the expansion or contraction of the metal wire 3 is more linear and predictable, and thus improve the controllability of the change in the length of the microcavity. This more consistent expansion effect helps to improve the sensitivity of temperature detection; on the other hand, the hemispherical structure can reduce stray light or non-ideal reflection caused by plane reflection, reduce the stray light reflected back after transmission, improve the purity of the interference signal, and have higher detection sensitivity. The sensor prepared by the method of the present application is set in the environment to be detected. The change in temperature will cause the change in the length of the metal wire 3, and change the distance between the two end faces forming the microcavity, so that the length of the microcavity changes. The length of the microcavity is closely related to the temperature. Therefore, the reflection spectrum obtained by reflection of the optical fiber 1 is related to the temperature change in the environment to be detected, thereby realizing temperature detection.

[0031] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A microcavity fiber Fabry-Perot temperature sensor based on metal wire, characterized in that: The temperature sensor includes an optical fiber, a hollow tube, and a metal wire. One end of the optical fiber is connected to one end of the hollow tube. The inner diameter of the hollow tube is smaller than the diameter of the optical fiber. The end of the hollow tube away from the optical fiber is closed. The metal wire is arranged inside the hollow tube. One end of the metal wire is fixedly arranged at the closed end of the hollow tube. The free end of the metal wire is opposite to the optical fiber. A microcavity is formed between the end face of the free end of the metal wire and the end face of the optical fiber close to the metal wire. The incident laser is incident from the end of the optical fiber away from the hollow tube. After being reflected by the microcavity, the laser is emitted from the incident end of the optical fiber. The temperature changes the length of the microcavity, thereby changing the spectrum of the emitted laser. The temperature change is detected by the spectrum.

2. The metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 1, characterized in that: The thermal expansion coefficient of the metal wire is greater than the thermal expansion coefficient of the hollow tube.

3. The metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 2, characterized in that: The length of the microcavity is 60-200 microns.

4. The metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 3, characterized in that: The thickness of the hollow tube of the microcavity sidewall is uneven.

5. The metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 4, characterized in that: A concave structure is arranged on the end surface of the metal wire on the side close to the optical fiber.

6. The metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 5, characterized in that: The material of the metal wire is one of copper, aluminum, silver, gold, platinum, tungsten, brass, copper, steel, nickel-chromium alloy, and iron-aluminum-nickel alloy.

7. The metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 6, characterized in that: The optical fiber is colinear with the central axis of the hollow tube.

8. The metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 7, characterized in that: The optical fiber is a single-mode optical fiber; the hollow tube is a hollow capillary glass tube or a hollow photonic crystal optical fiber.

9. A method for preparing a metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 1, characterized in that: The method comprises the following steps: First, the optical fiber and one end of the hollow tube are cut flat and fused together, a preset length of the hollow tube is retained, and the excess length of the hollow tube is cut off from the other end of the hollow tube; Then, insert a metal wire into the hollow tube, wherein the length of the metal wire inserted is less than the length of the hollow tube, and cut off the excess metal wire so that the metal wire is flush with the end of the hollow tube away from the optical fiber; Finally, the metal wire is further inserted so that the metal wire completely enters the hollow tube, and the end of the hollow tube away from the optical fiber is heated and melted to close it, and the metal wire is fixed.

10. The method for preparing a metal wire-based microcavity fiber Fabry-Perot temperature sensor according to claim 9, characterized in that: The fusion is achieved by using an optical fiber fusion splicer or a carbon dioxide laser for heating; the heating and melting is achieved by using arc discharge or a carbon dioxide laser.

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