MZI / FPI optical fiber temperature strain sensor based on cascade connection of 8-shaped structure and air cavity structure, preparation method and measurement method

Abstract

The invention relates to the technical field of optical fiber sensors, in particular to an MZI / FPI optical fiber temperature strain sensor based on cascade connection of an 8-shaped structure and an air cavity structure and a preparation method and a measurement method.The MZI / FPI optical fiber temperature strain sensor comprises the air cavity structure and a 8-shaped structure single-mode optical fiber, the air cavity structure comprises a first single-mode optical fiber, a SiO2 air microtube and a second single-mode optical fiber which are connected in sequence, and the first single-mode optical fiber, the SiO2 air microtube and the second single-mode optical fiber are sequentially connected. The input end of the first single-mode optical fiber is connected with the broadband light source, the middle part of the 8-shaped structure single-mode optical fiber is looped twice by penetrating in and out of the capillary tube to form a bent structure, and the two ends of the 8-shaped structure single-mode optical fiber are arranged in parallel in the vertical direction and are respectively connected with the output end of the second single-mode optical fiber and the spectrum analyzer. A single-mode fiber is greatly bent twice to form an 8-shaped structure for signal excitation and coupling, and the 8-shaped structure is cascaded with an air cavity structure to form an MZI / FPI mixed structure, so that high-precision measurement of temperature and strain can be realized at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensors, and in particular to an MZI / FPI optical fiber temperature strain sensor based on a cascade of a figure-8 structure and an air cavity structure, a preparation method, and a measurement method. Background Art

[0002] Fiber optic sensors have many advantages such as simple and compact structure, strong anti-electromagnetic interference ability, and high sensitivity. They are widely used in many sensing fields, such as temperature, humidity, strain, lateral pressure, pressure sensing, etc. Among many fiber optic sensors, fiber optic Mach Zehnder interferometer sensors have their unique advantages, such as high temperature sensitivity, dual-parameter simultaneous measurement, and good stability. Therefore, fiber optic Mach Zehnder interferometer sensors have developed very rapidly. Among them, the measurement of temperature is an important application field. According to existing literature reports, the temperature sensitivity of the balloon structure can reach 150 μm / ℃. At the same time, the high-precision measurement of strain can also be achieved by using FP fiber interferometers. A more convenient approach is to use femtosecond laser to melt an air cavity, or to use a hollow microtube to melt onto an optical fiber to form an air cavity. The deformation of the air cavity is used to change the optical path difference of the interference. This change can be observed on the spectrum analyzer and characterized as the movement of the spectrum line, thereby achieving high-precision measurement of strain. There are also literature reports on the field of simultaneous dual-parameter measurement. For example, there is a Fabry-Perot high-precision optical fiber sensor made of Bragg grating that can measure temperature and strain simultaneously, and its temperature measurement accuracy reaches 10.88pm / ℃. However, so far, there is no literature reporting a method for high-precision simultaneous measurement of temperature and strain dual parameters in the field of optical fiber sensing. Summary of the invention

[0003] In view of the deficiencies of the prior art, the present invention provides an MZI / FPI optical fiber temperature strain sensor based on a cascade of an 8-shaped structure and an air cavity structure, as well as a preparation method and a measurement method. An 8-shaped structure is formed by bending a single-mode optical fiber twice in a large range for signal excitation and coupling, and cascaded with the air cavity structure to form an MZI / FPI hybrid structure. MZ interference is used to achieve high-sensitivity measurement of temperature, and FP interference is used to achieve high-sensitivity sensing of strain, so that high-precision measurement of temperature and strain can be achieved simultaneously.

[0004] The technical solution provided by the present invention is as follows:

[0005] The invention provides an MZI / FPI optical fiber temperature strain sensor based on the cascade of an 8-shaped structure and an air cavity structure. The sensor comprises an air cavity structure and an 8-shaped structure single-mode optical fiber, wherein the air cavity structure comprises a first single-mode optical fiber, a SiO2 air microtube and a second single-mode optical fiber which are connected in sequence, the input end of the first single-film optical fiber is connected to a broadband light source, the middle part of the 8-shaped structure single-mode optical fiber is looped twice by passing in and out of a capillary to form a curved structure, and the two ends of the 8-shaped structure single-mode optical fiber are arranged in parallel in a vertical direction and are respectively connected to the output end of the second single-mode optical fiber and a spectrum analyzer.

[0006] Furthermore, when the middle portion of the single-mode optical fiber with the figure-8 structure is looped twice by passing in and out of the capillary, the first loop is in a clockwise direction and the second loop is in a counterclockwise direction.

[0007] Furthermore, the transverse diameter of the curved structure is 20±3 mm, and the longitudinal diameter is 13±3 mm.

[0008] Furthermore, the length of the SiO2 air microtube is 60 μm.

[0009] Furthermore, the inner diameter of the SiO2 air micro-tube is not greater than the diameters of the first single-mode optical fiber and the second single-mode optical fiber.

[0010] Furthermore, the capillary has a length of 10±2 mm and an inner diameter of 300-400 μm.

[0011] Furthermore, the first single-mode optical fiber, the second single-mode optical fiber and the figure-8 structure single-mode optical fiber are all single-mode optical fibers of model SMF-28, and the core diameter and cladding diameter are 8.2 μm and 125 μm, respectively.

[0012] Furthermore, the single-mode optical fiber with the figure-8 structure does not strip off the coating layer.

[0013] The present invention also provides a method for preparing the MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure, comprising the following steps: S1, fusing one end of the SiO2 air micro-tube to one end of the first single-mode optical fiber, cutting the SiO2 air micro-tube to a desired length, and then fusing the second single-mode optical fiber to the other end of the SiO2 air micro-tube to form an air cavity structure; S2, passing a section of single-mode optical fiber through a capillary, making a loop clockwise and then passing through the capillary in the reverse direction to form a first curved structure, adjusting the transverse diameter and the longitudinal diameter of the first curved structure, and fixing the curved structure with ultraviolet glue, and then passing through the capillary after making a loop counterclockwise to form a second curved structure, adjusting the transverse diameter and the longitudinal diameter of the second curved structure, and fixing the curved structure with ultraviolet glue to obtain an 8-shaped structure single-mode optical fiber; S3, connecting the above-mentioned air cavity structure and the 8-shaped structure single-mode optical fiber and then connecting them to a broadband light source and a spectrum analyzer respectively.

[0014] The present invention also provides a method for measuring temperature strain using the MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure, comprising the following steps:

[0015] Using a broadband light source as an emission source of an optical signal, injecting the optical signal into a first single-mode optical fiber of the sensor;

[0016] The optical signal is reflected twice in the air cavity structure, forming FP interference and generating a reflection spectrum; the reflection spectrum is formed by superposition of the reflected light signals on the interface between the air cavity structure and the single-mode optical fiber; the reflection spectrum is used to measure stress;

[0017] The optical signal continues to be transmitted to the upper bend structure at the right end of the 8-shaped single-mode optical fiber. Part of the optical signal is excited from the core to the cladding, and then coupled back to the core at the lower bend part at the right end. Subsequently, it undergoes a similar mode conversion again at the upper bend structure at the left end, and is coupled back to the core at the lower bend structure at the left end, forming MZ interference and finally obtaining a transmission spectrum. The transmission spectrum is used to measure temperature.

[0018] Beneficial Effects

[0019] The present invention proposes a method based on the cascade of an 8-shaped structure and an air cavity structure to realize MZ / FP interference, and to manufacture a corresponding optical fiber sensor. The structure has the characteristics of high-sensitivity sensing for temperature and strain. On the basis of the balloon-shaped structure, the 8-shaped structure can better excite the light signal and realize better MZ interference. At the same time, compared with other types of optical fiber sensing structure designs, the single-mode optical fiber of the 8-shaped structure part does not need to strip the optical fiber coating, which greatly reduces the possibility of optical fiber breakage. The cascaded air cavity structure can realize FP interference, and has a very low impact on MZ interference. The sensor structure proposed in the present invention can simultaneously give play to the advantages of MZ / FP interference and can realize simultaneous measurement of temperature and strain. The entire structure is simple and compact, with high firmness, and can be made into a miniature high-precision sensor. At the same time, the production cost is low, the raw materials are abundant, and it is conducive to the production of products. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the structure and principle diagram of the MZI / FPI optical fiber temperature stress sensor of the present invention with a cascaded 8-shaped structure and an air cavity structure;

[0021] Figure 2 This is the production flow chart of single-mode optical fiber with figure-8 structure;

[0022] Figure 3It is a schematic diagram of the fusion and processing of single-mode optical fiber and SiO2 air micro-tube;

[0023] Figure 4 It is a schematic diagram of the fabrication of the air cavity structure;

[0024] Figure 5 It is a structural schematic diagram of the MZI / FPI optical fiber temperature stress sensor of the present invention in which an 8-shaped structure and an air cavity structure are cascaded;

[0025] Figure 6 It is a temperature measurement experimental device;

[0026] Figure 7 It is a strain measurement experimental device.

[0027] Explanation of the accompanying drawings: 1. first single-mode optical fiber; 2. SiO2 air microtube; 3. second single-mode optical fiber; 4. single-mode optical fiber with figure-8 structure; 5. capillary. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0029] Example 1

[0030] like Figure 1 As shown, an embodiment of the present invention provides an MZI / FPI optical fiber temperature strain sensor based on a cascade of an 8-shaped structure and an air cavity structure, including an air cavity structure and an 8-shaped structure single-mode optical fiber 4, wherein the air cavity structure includes a first single-mode optical fiber 1, a SiO2 air microtube 2, and a second single-mode optical fiber 3 connected in sequence, an input end of the first single-film optical fiber 1 is connected to a broadband light source, and the middle part of the 8-shaped structure single-mode optical fiber 8 is looped twice by passing in and out of the capillary 4 to form a curved structure, and its two ends are arranged in parallel in a vertical direction and are respectively connected to the output end of the second single-mode optical fiber 3 and a spectrum analyzer. The temperature strain sensor has both an air cavity optical fiber Fabry-Perot interferometer and an 8-shaped structure MZ interferometer, wherein the first single-mode optical fiber 1, the SiO2 air microtube 2, and the second single-mode optical fiber 2 connected in sequence constitute a Fabry-Perot interferometer, and the Fabry-Perot interferometer uses the air cavity to produce a high-sensitivity sensing of pressure to measure pressure. The single-mode optical fiber with a figure-8 structure constitutes an MZ interferometer, and the MZ interferometer uses the characteristic that the figure-8 structure is sensitive to temperature changes to measure temperature changes.

[0031] In this embodiment, a single-mode optical fiber and a SiO2 microtube 2 are fused into an air cavity to form FP interference, and a pressure sensor can be made by utilizing the high sensitivity of the air cavity to pressure. On this basis, the output end of the second single-mode optical fiber is connected to a single-mode optical fiber with an 8-shaped structure to form a Mach-Zehnder interference structure, which can be made into a temperature sensor.

[0032] In this embodiment, the middle portion of the single-mode optical fiber 4 with the figure-8 structure is looped twice by passing through the capillary 5, the first loop is in a clockwise direction and the second loop is in a counterclockwise direction.

[0033] In this embodiment, the lateral diameter of the curved structure is 20±3 mm, and the longitudinal diameter is 13±3 mm.

[0034] In this embodiment, the length of the SiO2 air micro-tube 2 is 60 μm.

[0035] In this embodiment, the inner diameter of the SiO 2 air micro-tube 2 is not greater than the diameter of the first single-mode optical fiber 1 and the second single-mode optical fiber 3 .

[0036] In this embodiment, the capillary 5 has a length of 10±2 mm and an inner diameter of 300-400 μm.

[0037] In this embodiment, the first single-mode optical fiber 1, the second single-mode optical fiber 3 and the figure-8 structure single-mode optical fiber 5 are all single-mode optical fibers of model SMF-28, and the core diameter and cladding diameter are 8.2 μm and 125 μm respectively.

[0038] In this embodiment, the coating layer of the single-mode optical fiber 5 with a figure-8 structure is not stripped.

[0039] Example 2

[0040] The embodiment of the present invention provides a method for preparing the MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure as described in Embodiment 1, comprising the following steps: S1, fusing one end of the SiO2 air micro-tube to one end of the first single-mode optical fiber, cutting the SiO2 air micro-tube to a desired length, and then fusing the second single-mode optical fiber to the other end of the SiO2 air micro-tube to form an air cavity structure; S2, passing a section of single-mode optical fiber through a capillary, making a loop clockwise and then passing through the capillary in the reverse direction to form a first curved structure, adjusting the transverse diameter and the longitudinal diameter of the first curved structure, and fixing the curved structure with ultraviolet glue, and then passing through the capillary after making a loop counterclockwise to form a second curved structure, adjusting the transverse diameter and the longitudinal diameter of the second curved structure, and fixing the curved structure with ultraviolet glue to obtain an 8-shaped structure single-mode optical fiber; S3, connecting the above-mentioned air cavity structure and the 8-shaped structure single-mode optical fiber and then connecting them to a broadband light source and a spectrum analyzer respectively.

[0041] Specifically, Figure 2-4 As shown, the preparation materials require single-mode optical fiber (SMF-28, Corning) and hollow microtube (HCF), and the equipment required includes optical fiber fusion splicer (80S, Fujikura), spectrum analyzer (AQ6370D, Yokogawa, Optical Spectrum Analyzer, OSA), broadband light source (Benchtop Broadband Source, BBS), optical fiber cleaver (CKFC-1, CommKing), micro-displacement platform, optical fiber clamp, and microscope.

[0042] like Figure 2 As shown in the figure 8 single-mode optical fiber production flow chart. Figure 2 As shown in (a), take a section of single-mode optical fiber, such as Figure 2 As shown in (b), the single-mode optical fiber is passed through the capillary, looped clockwise, and then passed through the capillary in the reverse direction to form a first curved structure. The transverse diameter and longitudinal diameter of the first curved structure are adjusted, and the curved structure is fixed with ultraviolet glue, as shown in FIG. Figure 2 As shown in (c), the second curved structure is formed by looping counterclockwise and then passing through the capillary. The transverse diameter and longitudinal diameter of the second curved structure are adjusted, and the curved part structure is fixed with ultraviolet glue to obtain an 8-shaped single-mode optical fiber;

[0043] like Figure 3 As described above, the schematic diagram of the fusion and processing of single-mode optical fiber and SiO2 air micro-tube. First, as Figure 3 As shown in (a), a single-mode optical fiber and a SiO2 air microtube are fixed on the optical fiber fusion splicer using an optical fiber clamp and fused together using the optical fiber fusion splicer. Then, on the micro-displacement platform, after finding the fusion point using a microscope, 60μm is cut in the direction of the SiO2 microtube. The schematic diagram after cutting is as follows Figure 3 (b) shown.

[0044] Then, use a fiber fusion splicer to fix this section of structure and another section of single-mode optical fiber on the fiber fusion splicer's fiber clamp, and then use the fiber fusion splicer to fusion-splice them together to form a Figure 4 The air cavity structure shown.

[0045] After the above steps, the single-mode optical fiber with the prepared figure-8 structure is connected to the air cavity structure to form an MZI / FPI optical fiber sensor with a figure-8 structure and an air cavity structure cascaded. Figure 5 shown.

[0046] Example 3

[0047] The embodiment of the present invention further provides a method for measuring temperature strain using the MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure described in Embodiment 1, comprising the following steps:

[0048] Using a broadband light source as an emission source of an optical signal, injecting the optical signal into a first single-mode optical fiber of the sensor;

[0049] The optical signal is reflected twice in the air cavity structure, forming FP interference and generating a reflection spectrum; the reflection spectrum is formed by superposition of the reflected light signals on the interface between the air cavity structure and the single-mode optical fiber; the reflection spectrum is used to measure stress;

[0050] The optical signal continues to be transmitted to the upper bend structure at the right end of the 8-shaped single-mode optical fiber. Part of the optical signal is excited from the core to the cladding, and then coupled back to the core at the lower bend part at the right end. Subsequently, it undergoes a similar mode conversion again at the upper bend structure at the left end, and is coupled back to the core at the lower bend structure at the left end, forming MZ interference and finally obtaining a transmission spectrum. The transmission spectrum is used to measure temperature.

[0051] Specifically, the optical signal passes through the air cavity structure from the left end, and generates a reflection at the interface between the single-mode optical fiber and the air cavity. A part of the optical signal continues to be transmitted in the core, and a second reflection is generated at the interface between the air cavity and the single mode. The two reflections reach the left end optical fiber outlet, forming FP interference, and a reflection spectrum is obtained. The optical signal is then transmitted and reaches the upper bending structure at the right end. A part of the optical signal is excited from the core to the cladding and continues to be transmitted. At the lower bending part, the cladding signal is coupled back to the core. The optical signal continues to be transmitted in the single-mode optical fiber and reaches the upper bending structure at the left end. A part of the optical signal is excited from the core to the cladding again. The optical signal continues to be transmitted, and at the lower bending structure at the left end, the cladding signal is coupled back to the core, forming MZ interference. Finally, the optical signal is transmitted to the right single-mode optical fiber and out. A transmission spectrum can be obtained. Temperature can be measured by the transmission spectrum, and strain can be measured by the reflection spectrum. Figure 1 The black arrow represents the core light signal, the yellow arrow represents the cladding light signal, the light gray represents the core, the dark gray represents the cladding, the green arrow represents the reflected light signal, and the white represents the air cavity. The formula for the transmission spectrum is as follows:

[0052]

[0053] Wherein, I1 represents the core optical signal, I2 represents the cladding optical signal, and cosφ represents the phase difference.

[0054]

[0055] in, is the phase difference between the core mode and the cladding mode, is the effective refractive index RI difference between the core and the mth cladding mode, G is the interaction length between the two bending structures where they are excited and coupled, is the input wavelength. The free spectral range (FSR) can be expressed as:

[0056]

[0057] It can be seen that FSR increases as the interference length G decreases. Equal to (2N+1)π, N=1, 2, 3..., the transmittance reaches a valley value at this wavelength, as follows:

[0058]

[0059] in, is the central wavelength of the mth order interference trough. When temperature changes are applied to the Mach-Zehnder sensing part, Both the interference length G will change, resulting in a shift in the spectral trough.

[0060] Δ λ N λ N = [ 1 Δ n eff m ∂ （ Δ n eff m ） ∂ T + 1 L ∂ L ∂ T ] Δ T + [ 1 + 1 Δ n eff m ∂ （ Δ n eff m ） ∂ ε ] ε

[0061] Represents the deformation caused by an applied temperature change.

[0062] The formula for the reflectance spectrum is as follows:

[0063]

[0064] Among them, I is the intensity of the interference light, I1 is the intensity of the first reflected light, I2 is the intensity of the second reflected light, φ air is the phase shift of the air cavity, and the specific calculation formula is as follows:

[0065]

[0066] Where n1 is the pressure of the air and L is the length of the air cavity. When strain is applied, L will change, resulting in a series of changes.

[0067] like Figure 6 The figure shows a schematic diagram of a device for measuring temperature. Light is emitted from a light source and enters an adjustable temperature box, in which the prepared microstructure is placed. The temperature in the box ranges from 30°C to 50°C, and the transmission spectrum of the spectrometer is measured every 1°C. Through program calculation, the sensitivity characteristics of the sensor to temperature can be obtained.

[0068] like Figure 7The figure shows a schematic diagram of the device for measuring strain. The sensor is fixed on the micro-displacement platform with glue, and the distance between the two ends of the micro-displacement platform is recorded. Light is emitted from the light source (BBS), passes through the optical fiber sensor, and is connected to the optical spectrum analyzer (OSA). Set the initial displacement to 0mm, control the micro-displacement platform, and move from 0 to 20mm. Record the movement of the spectrum line on the spectrometer every 1mm. , the sensitivity characteristics of the sensor to strain can be obtained.

[0069] The present invention proposes a method based on the cascade of an 8-shaped structure and an air cavity structure to produce an MZI / FPI hybrid structure, which can simultaneously achieve high-precision measurement of temperature and strain. The structure is inspired by the balloon-type MZI optical fiber sensor. As a common MZI sensor structure, the balloon-type structure uses a large-scale bending of the optical fiber to achieve optical signal excitation and coupling. The 8-shaped structure proposed by the present invention only requires a single-mode optical fiber and a small section of a hollow microtube for fixation. The 8-shaped structure has two large-scale fiber bends, which can achieve excitation and coupling of optical signals, and realize MZ interference for measuring temperature. With the cascaded air cavity structure, FP interference can be realized for measuring strain. At the same time, the sensor has a simple production process, high sensitivity to temperature and strain, and low cost.

Claims

1. A MZI / FPI optical fiber temperature strain sensor based on a cascade of an 8-shaped structure and an air cavity structure, characterized in that: The invention comprises an air cavity structure and an 8-shaped structure single-mode optical fiber, wherein the air cavity structure comprises a first single-mode optical fiber, a SiO2 air microtube and a second single-mode optical fiber connected in sequence, the input end of the first single-film optical fiber is connected to a broadband light source, the middle part of the 8-shaped structure single-mode optical fiber is looped twice by passing in and out of a capillary to form a curved structure, and the two ends thereof are arranged in parallel in a vertical direction and are respectively connected to the output end of the second single-mode optical fiber and a spectrum analyzer.

2. The MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to claim 1, characterized in that: The middle portion of the single-mode optical fiber with a figure-8 structure is looped twice by passing through the capillary tube, the first loop is in a clockwise direction and the second loop is in a counterclockwise direction.

3. The MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to claim 1, characterized in that: The curved structure has a transverse diameter of 20±3 mm and a longitudinal diameter of 13±3 mm.

4. The MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to claim 1, characterized in that: The length of the SiO2 air microtube is 60 μm.

5. The MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to claim 1, characterized in that: The inner diameter of the SiO2 air micro-tube is not greater than the diameters of the first single-mode optical fiber and the second single-mode optical fiber.

6. The MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to claim 1, characterized in that: The capillary has a length of 10±2 mm and an inner diameter of 300-400 μm.

7. The MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to claim 1, characterized in that: The first single-mode optical fiber, the second single-mode optical fiber and the figure-8 structure single-mode optical fiber are all single-mode optical fibers of model SMF-28, and the core diameter and cladding diameter are 8.2 μm and 125 μm respectively.

8. The MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to claim 1, characterized in that: The single-mode optical fiber with a figure-8 structure does not strip off the coating layer.

9. A method for preparing the MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, fusing one end of the SiO2 air micro-tube to one end of the first single-mode optical fiber, cutting the SiO2 air micro-tube to a desired length, and then fusing the second single-mode optical fiber to the other end of the SiO2 air micro-tube to form an air cavity structure; S2, passing a section of single-mode optical fiber through a capillary, making a loop clockwise and then passing through the capillary in the reverse direction to form a first curved structure, adjusting the transverse diameter and the longitudinal diameter of the first curved structure, and fixing the curved structure with ultraviolet glue, and then passing through the capillary after making a loop counterclockwise to form a second curved structure, adjusting the transverse diameter and the longitudinal diameter of the second curved structure, and fixing the curved structure with ultraviolet glue to obtain an 8-shaped structure single-mode optical fiber; S3, connecting the above-mentioned air cavity structure and the 8-shaped structure single-mode optical fiber and then connecting them to a broadband light source and a spectrum analyzer respectively.

10. A method for measuring temperature strain using the MZI / FPI optical fiber temperature strain sensor based on the cascade of the figure-8 structure and the air cavity structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: Using a broadband light source as an emission source of an optical signal, injecting the optical signal into a first single-mode optical fiber of the sensor; The optical signal is reflected twice in the air cavity structure, forming FP interference and generating a reflection spectrum; the reflection spectrum is formed by superposition of the reflected light signals on the interface between the air cavity structure and the single-mode optical fiber; the reflection spectrum is used to measure stress; The optical signal continues to be transmitted to the upper bend structure at the right end of the 8-shaped single-mode optical fiber. Part of the optical signal is excited from the core to the cladding, and then coupled back to the core at the lower bend part at the right end. Subsequently, it undergoes a similar mode conversion again at the upper bend structure at the left end, and is coupled back to the core at the lower bend structure at the left end, forming MZ interference and finally obtaining a transmission spectrum. The transmission spectrum is used to measure temperature.

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