Fiber optic sensor based on multi-parameter response mechanism of cascaded FFPI cavity

Abstract

The optical fiber sensor based on the multi-parameter response mechanism of the cascaded FFPI cavity includes a ceramic tube No. 1 and a ceramic tube No. 2 arranged in the ceramic tube No. 1, wherein a sapphire wafer No. 1 is embedded in the bottom of the ceramic tube No. 1, and a sapphire wafer No. 2 is provided at one end of the ceramic tube No. 2 extending into the ceramic tube No. 1, and an FFPI-1 cavity is formed in the ceramic tube No. 1 and between the sapphire wafer No. 1 and the sapphire wafer No. 2; a pure quartz optical fiber is provided in the ceramic tube No. 2, wherein an optical fiber core is wrapped inside the pure quartz optical fiber, and an FFPI-2 cavity is formed in the ceramic tube No. 2 and between one end of the pure quartz optical fiber close to the sapphire wafer No. 2 and the sapphire wafer No. 2; an FFPI-3 cavity is further provided in the pure quartz optical fiber located in the ceramic tube No. 2; the present invention quantitatively analyzes the crosstalk perception between different parameters under the action of high temperature and multi-physical field coupling, establishes a multi-parameter superposition response model and a crosstalk elimination model, combines the high-temperature resistant materials of sapphire and ceramic tubes, and is resistant to high temperature, large strain, and high pressure, and has high measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to an optical fiber sensor based on a multi-parameter response mechanism of a cascaded FFPI cavity. Technical Background

[0002] Fiber optic sensing technology, with its high-temperature resistance, corrosion resistance, and resistance to electromagnetic interference, holds significant application prospects in high-end equipment such as aircraft engines, hypersonic engines, and large gas turbines. Taking aircraft engines as an example, the load-bearing conditions of their high-temperature flow passages are extremely complex. In addition to having to withstand temperatures of 1200°C and above, they also have to withstand the combined effects of high pressure, thermal stress, and deformation, which can easily lead to a variety of failures. These failures can often be monitored by measuring key parameters such as high temperature, strain, and gas pressure. Therefore, real-time online monitoring of key parameters such as temperature, strain, and pressure within the engine's high-temperature flow passages can provide an important basis for ensuring safe engine operation and determining the engine's operating status. It also provides important data support for engine design and power performance evaluation.

[0003] Among existing measurement methods, non-contact methods such as infrared radiation and temperature-indicating paint for high temperature measurement, digital image correlation and phosphorescence for strain measurement, and pressure-inducing tube methods for pressure measurement are difficult to achieve real-time measurement within the complex and confined spaces of high-temperature flow passages in aircraft engines. Electrical contact measurement methods, such as resistive sensors, are susceptible to interference from corrosive gases and electromagnetic effects and cannot withstand temperatures exceeding 1200°C. Furthermore, the need for simultaneous measurement of multiple parameters significantly increases the complexity of electrical sensor leads, posing a risk to aircraft engine operation. In recent years, the development of fiber-optic integrated sensors has provided new approaches for the simultaneous measurement of multiple key parameters within high-temperature flow passages. Through the compact integration of composite sensing microstructures, in-situ sensing of multiple parameters can be achieved simultaneously. Compared with structures such as fiber Bragg Gratings (FBG) and Mach–Zehnder interferometer (MZI), fiber Fabry-Perot interferometer (FFPI) has the characteristics of reflective sensing, miniaturized cascade structure, and large spectral effective bandwidth. It can meet the development needs of miniaturization, lightweight and high precision of sensors and has important research value.

[0004] Quartz optical fiber offers excellent optical properties, high-temperature resistance, and mature fabrication processes, making it suitable for the development of high-performance integrated sensors. Currently, research on quartz fiber FFPI (Four-dimensional Pipeline Imaging) has largely focused on single- or dual-parameter sensing, making it difficult to simultaneously measure high temperature, strain, and pressure. At temperatures of 900°C, crystals begin to precipitate within the quartz fiber material, disrupting its microstructural consistency and increasing its brittleness and susceptibility to damage. Studies have shown that the tensile limit of quartz fiber after high-temperature annealing is only 3400με, which is insufficient to measure the high strains of 15,000με and pressures of 5MPa required for aircraft engines.

[0005] Patent application for "A multi-core optical fiber distributed sensing system and measurement method"

[0006] (CN116539189A) uses Raman distributed fiber optic sensing technology to achieve distributed temperature and bend measurement. A wavelength division multiplexer is used to split Raman scattered light into Stokes and anti-Stokes light. Temperature data is demodulated using the anti-Stokes light, and bend data is demodulated from the Stokes light. This solution directly demodulates temperature from the anti-Stokes light and equates bend loss with bend detection results, which reduces the temperature detection accuracy and bend measurement accuracy of the sensing system. Summary of the Invention

[0007] To overcome the deficiencies of the above-mentioned prior art, the present invention aims to provide a high-temperature, high-pressure strain fiber integrated sensor based on the multi-parameter response mechanism of a cascaded FFPI (Fiber Fabry-Perot Interferometer) cavity. By utilizing the corresponding reflection interference spectra generated when the FFPI cavity length changes under different assembly conditions, the cascaded FFPI cavity achieves parametric response and crosstalk elimination under the action of multiple physical fields, thereby realizing simultaneous and precise perception of temperature, strain, and pressure.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A fiber optic sensor based on a multi-parameter response mechanism of a cascaded FFPI cavity comprises a first ceramic tube 1 and a second ceramic tube 2 sleeved within the first ceramic tube 1. A first sapphire wafer 6 is embedded in the bottom of the first ceramic tube 1, and a second sapphire wafer 8 is provided at one end of the second ceramic tube 2 extending into the first ceramic tube 1. An FFPI-1 cavity 7 is formed within the first ceramic tube 1 and between the first sapphire wafer 6 and the second sapphire wafer 8. A pure quartz optical fiber 3 is provided within the second ceramic tube 2, and an optical fiber core 4 is wrapped within the pure quartz optical fiber 3. An FFPI-2 cavity 9 is formed within the second ceramic tube 2 and between the end of the pure quartz optical fiber 3 close to the second sapphire wafer 8 and the second sapphire wafer 8. An FFPI-3 cavity 10 is also provided within the pure quartz optical fiber 3 located within the second ceramic tube.

[0010] The wall of the No. 1 ceramic tube 1 is provided with an air hole 5 connected to the FFPI-1 cavity 7.

[0011] The pure quartz optical fiber 3 is fixedly connected to the inner wall of the second ceramic tube 2.

[0012] The second ceramic tube 2 is slidably connected relative to the first ceramic tube 1 .

[0013] The maximum deformation of the second sapphire wafer 8 is less than 0.3 times of its thickness.

[0014] The cavity lengths of the FFPI-1 cavity 7 and the FFPI-2 cavity 9 will change with temperature, while the cavity length of the FFPI-3 cavity 10 will only change with temperature. The relationship between temperature and cavity length is as follows:

[0015]

[0016]

[0017] Where: T is the measured temperature; T0 is the initial temperature; α q is the thermal expansion coefficient of pure quartz optical fiber 3; α s is the thermal expansion coefficient of the material being tested, ΔL FFPI-3-T ΔL is the length change of FFPI-3 cavity 10 caused by temperature change; FFPI-2-T ΔL is the length change of FFPI-2 cavity 9 caused by temperature change; FFPI-1-T is the change in length of FFPI-1 cavity 7 caused by temperature change; They represent the lengths of the FFPI-1 cavity 7, the FFPI-2 cavity 9, and the FFPI-3 cavity 10 at the initial temperature T0, respectively.

[0018] The air pressure in the FFPI-1 cavity 7 is made consistent with the external air pressure to be measured through the air hole 5; the pressure difference formed by the external air pressure to be measured and the air pressure in the FFPI-2 cavity 9 causes the second sapphire wafer 8 to deform, and the cavity length of the FFPI-2 cavity 9 changes accordingly.

[0019] There is a linear relationship between the pressure difference between the external pressure to be measured and the pressure in the FFPI-2 cavity 9 and the maximum deformation at the center of the second sapphire wafer 8, which is expressed as:

[0020]

[0021] Where, P 气 Indicates the external air pressure, P FFPI-2represents the internal pressure of the FFPI-2 cavity 9, b represents the thickness of the second sapphire wafer 8, r represents the effective radius of the second sapphire wafer 8, δ represents the Poisson's ratio of the second sapphire wafer 8, E is the elastic modulus of the second sapphire wafer 8, and Δd is the deformation at the center of the second sapphire wafer 8, that is, the change in the length of the FFPI-2 cavity 9.

[0022] The change in the length of the FFPI-1 cavity 7 is only related to the strain. At this time, the strain value of the FFPI-1 cavity 7 is expressed as:

[0023]

[0024] Where ΔL FFPI-1 is the total deformation of cavity 7 of FFPI-1, ΔL FFPI-1 After subtracting the cavity length change ΔL of FFPI-1 cavity 7 due to temperature change FFPI-1-T After calculating the cavity length change Δd due to the pressure change, the strain value at cavity 7 of FFPI-1 is obtained by comparing it with the length of cavity 7 of FFPI-1 at the initial temperature T0.

[0025] The FFPI-2 cavity 9 and the FFPI-3 cavity 10 inside the pure quartz optical fiber 3 are formed by femtosecond laser processing.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention uses pure quartz optical fiber for sensing. By cascading multiple FFPI cavities and analyzing and designing them based on the response characteristics of each FFPI cavity to different physical parameters, it achieves precise perception of temperature, strain, and pressure at the same time.

[0028] 2. The present invention uses a nested ceramic sleeve, and the sliding range is not limited by the tension and compression limits of the optical fiber material, which can achieve the measurement of a very large strain range.

[0029] 3. The present invention utilizes the high hardness and high melting point characteristics of sapphire material to enable the sensor to meet the measurement requirements of ultra-high pressure.

[0030] 4. The present invention uses ceramic materials to integrate with the sensing part, which can protect the sensing part under ultra-high temperature conditions, thereby realizing temperature measurement in an ultra-high temperature environment.

[0031] 5. Through the response mechanism of the multi-parameter optical fiber sensor of the present invention under the action of multiple physical fields with different air pressure, temperature and stress conditions, multi-parameter sensing and crosstalk elimination are realized, solving the problem of multi-parameter perception crosstalk, so that the sensor of the present invention can accurately measure the temperature, pressure and strain of the structure under any multi-physical field conditions.

[0032] In summary, the present invention integrates a pure quartz fiber optic sensor with a ceramic tube structure and combines it with femtosecond laser etching technology to solve the problem of crosstalk perception between temperature, strain, and pressure under the coupling of multiple physical fields, and realizes the simultaneous and precise measurement of temperature, strain, and pressure under ultra-high temperature, large strain, and high pressure conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the sensor structure designed for the present invention.

[0034] Figure 2 Schematic diagram of the sensor optical signal transmission of the present invention.

[0035] Figure 3 A multi-parameter perception and crosstalk cancellation model designed for the present invention.

[0036] Figure 4 Schematic diagram of the simulation model of the structure designed by the present invention.

[0037] Figure 5 The length variation curves of each FFPI cavity under different loading conditions in the simulation analysis of the present invention are as follows: Figure 5 (a) is the length change of each FFPI during the application of tension and airflow, Figure 5 (b) The length change of each FFPI at different temperatures.

[0038] In the figure: 1. Ceramic tube No. 1; 2. Ceramic tube No. 2; 3. Pure quartz optical fiber; 4. Optical fiber core; 5. Air hole; 6. Sapphire wafer No. 1; 7. FFPI-1 cavity; 8. Sapphire wafer No. 2; 9. FFPI-2 cavity; 10. FFPI-3 cavity; 11. Incident light; 12. Reflected light; 13. Air flow inflow surface; 14. Air flow outflow surface; 15. Air domain outside the structure; 16. Air hole; 17. Optical fiber of the non-sensing part of the sensor; 18. Heating area; 19. The surface of the structure that applies tension; 20. Structure; 21. FFPI part of the sensor. DETAILED DESCRIPTION

[0039] The present invention will be described in further detail below with reference to the accompanying drawings.

[0040] like Figure 1As shown, a fiber optic sensor based on a multi-parameter response mechanism of a cascaded FFPI cavity includes a No. 1 ceramic tube 1 and a No. 2 ceramic tube 2 sleeved in the No. 1 ceramic tube 1, wherein a No. 1 sapphire wafer 6 is embedded in the bottom of the No. 1 ceramic tube 1, and a No. 2 sapphire wafer 8 is provided at one end of the No. 2 ceramic tube 2 extending into the No. 1 ceramic tube 1, and an FFPI-1 cavity 7 is formed in the No. 1 ceramic tube 1 and between the No. 1 sapphire wafer 6 and the No. 2 sapphire wafer 8; a pure quartz optical fiber 3 is provided in the No. 2 ceramic tube 2, and an optical fiber core 4 is wrapped inside the pure quartz optical fiber 3, and an FFPI-2 cavity 9 is formed in the No. 2 ceramic tube 2 and between the end of the pure quartz optical fiber 3 close to the No. 2 sapphire wafer 8 and the No. 2 sapphire wafer 8; an FFPI-3 cavity 10 is also provided inside the pure quartz optical fiber 3 located in the No. 2 ceramic tube.

[0041] The wall of the No. 1 ceramic tube 1 is provided with an air hole 5 connected to the FFPI-1 cavity 7.

[0042] The pure quartz optical fiber 3 is fixedly connected to the inner wall of the second ceramic tube 2.

[0043] The second ceramic tube 2 is slidably connected relative to the first ceramic tube 1 .

[0044] The FFPI-2 cavity 9 and the FFPI-3 cavity 10 inside the pure quartz optical fiber 3 are formed by femtosecond laser processing.

[0045] like Figure 2 As shown, the incident light signal is emitted from the pure quartz optical fiber 3 along the inner optical fiber core 4 in the direction away from the No. 1 ceramic tube 1, and sequentially transmits through the FFPI-3 cavity 10, the FFPI-2 cavity 9, and the FFPI-1 cavity 7, and generates corresponding reflection interference spectra according to the length changes of the FFPI-3 cavity 10, the FFPI-2 cavity 9, and the FFPI-1 cavity 7 under different conditions.

[0046] Multi-parameter sensing and crosstalk cancellation models such as Figure 3 The structure proposed by the present invention is subjected to finite element analysis simulation, and the simulation model is shown as follows: Figure 4As shown, the integrated fiber optic sensor was modeled in the "ANSYS Workbench" software, and the "FluidFlow (Fluent)", "Steady-State Thermal (ANSYS)" and "Static Structural (ANSYS)" modules were used to carry out fluid-heat-solid coupling simulations to observe the response mechanism of the integrated fiber optic sensor under different air pressure, temperature and stress conditions. The material used for the structure to be tested 20 in the model is a high-temperature resistant nickel alloy. The size of the structure to be tested 20 is 100 times the size of the sensor FFPI part 21. An air domain 15 is set outside the structure to be tested, and an airflow is set. The airflow flows in from the airflow inlet surface 13, passes through the structure to be tested, and flows out from the airflow outlet surface 14. First, air pressure is applied to the structure 20 by the airflow, and the applied air pressure starts from zero and increases by 10 each time. 4 Pa up to 10 5 Pa. The structure to be tested is provided with an air hole 16, which connects the external air space 15 and the FFPI-1 cavity 7 inside the integrated optical fiber sensor. 5 On the basis of Pa being constant, a tensile force is applied to the right end face 19 of the structure. The tensile force increases by 10N each time from zero to 100N. The length changes of FFPI-1 cavity 7, FFPI-2 cavity 9 and FFPI-3 cavity 10 during the process of changing air pressure and tensile force are shown as follows: Figure 5 (a). Then, the pressure is kept at 10 5 Pa and a tensile force of 100N, a temperature load is applied to the heating area 18. The applied temperature is increased from 22°C (the initial temperature of the structure) to 42°C in a gradient of 2°C. The cavity length changes of FFPI-1 cavity 7, FFPI-2 cavity 9 and FFPI-3 cavity 10 under different temperature load conditions are shown in the figure below. Figure 5 (b) shown.

[0047] The length changes of FFPI-1 cavity 7, FFPI-2 cavity 9 and FFPI-3 cavity 10 under the influence of different physical parameters in the simulation are as follows Figure 5 As shown in the figure, the FFPI-3 cavity 10 measurement results are used to compensate for the temperature of FFPI-1 cavity 7 and FFPI-2 cavity 9, eliminating temperature crosstalk. The compensated FFPI-2 cavity 9 measurement results are then used to compensate for the air pressure of FFPI-1 cavity 7, eliminating air pressure crosstalk, ultimately achieving simultaneous and accurate sensing of temperature, strain, and pressure.

[0048] When the temperature changes, the lengths of the FFPI-1 cavity 7, FFPI-2 cavity 9, and FFPI-3 cavity 10 in the cascaded FFPI sensor structure will change accordingly:

[0049]

[0050] Where: T is the measured temperature; T0 is the initial temperature; αq is the thermal expansion coefficient of pure quartz optical fiber 3; α s is the thermal expansion coefficient of the material being tested, ΔL FFPI-3-T ΔL is the length change of FFPI-3 cavity 10 caused by temperature change; FFPI-2-T ΔL is the length change of FFPI-2 cavity 9 caused by temperature change; FFPI-1-T is the change in length of FFPI-1 cavity 7 caused by temperature change; They represent the lengths of the FFPI-1 cavity 7, the FFPI-2 cavity 9, and the FFPI-3 cavity 10 at the initial temperature T0, respectively.

[0051] Due to the sensor's structural design, FFPI-1 cavity 7 changes with both the measured pressure and strain. FFPI-2 cavity 9 also changes with the measured pressure. FFPI-3 cavity 10, on the other hand, is only temperature-dependent. Therefore, FFPI-3 cavity 10 is used for temperature measurement. The temperature characteristics of FFPI-2 cavity 9 in equation (2) are used for temperature compensation when measuring pressure in FFPI-2 cavity 9, while the temperature characteristics of FFPI-1 cavity 7 in equation (3) are used for temperature compensation when measuring strain in FFPI-1 cavity 7.

[0052] When the maximum deformation of the second sapphire wafer 8 is less than 0.3 times its thickness, the change in external pressure on the second sapphire wafer 8 and the maximum deformation at its center are linearly related, which can be expressed as:

[0053]

[0054] Where, P 气 Indicates the external air pressure, P FFPI-2 represents the internal pressure of FFPI-2 cavity 9, b represents the thickness of sapphire wafer 8, r represents the effective radius of sapphire wafer 8, δ represents the Poisson's ratio of sapphire wafer 8, E represents the elastic modulus of sapphire wafer 8, and Δd represents the deformation at the center of sapphire wafer 8, i.e., the change in the length of FFPI-2 cavity 9. According to the sensor's structural design, in addition to temperature influences, FFPI-1 cavity 7 also changes with changes in the strain to be measured. In this case, FFPI-2 cavity 9 is only affected by air pressure. FFPI-1 cavity 7 is connected to the outside air through an air hole, and the air pressure inside the cavity remains consistent with that outside. Δd calculated in formula (4) is used for air pressure compensation during strain measurement of FFPI-1 cavity 7.

[0055] The change in the length of cavity 7 of FFPI-1 is only related to the strain. The strain value measured in cavity 7 of FFPI-1 can be expressed as:

[0056]

[0057] Where ΔL FFPI-1 is the total deformation of cavity 7 of FFPI-1, ΔL FFPI-1 After subtracting the length of the FFPI-1 cavity 7 due to temperature and pressure changes, the strain value of the structure is obtained by comparing it with the length of the FFPI-1 cavity 7 at the initial temperature T0.

[0058] Compared with existing technologies, the present invention cleverly combines a ceramic tube structure with pure quartz optical fiber to construct multiple FFPI cavities that can eliminate crosstalk with each other through the measured data. The optical fiber etched with femtosecond laser technology can simultaneously and accurately measure data under conditions of higher temperatures, greater strains, and higher pressures, while simultaneously utilizing the ceramic tube structure to protect the multiple FFPI cavities for measuring parameters.

Claims

1. An optical fiber sensor based on a multi-parameter response mechanism of a cascaded FFPI cavity, comprising a first ceramic tube (1) and a second ceramic tube (2) sheathed in the first ceramic tube (1), characterized in that: A No. 1 sapphire wafer (6) is embedded in the bottom of the No. 1 ceramic tube (1); a No. 2 sapphire wafer (8) is provided at one end of the No. 2 ceramic tube (2) extending into the No. 1 ceramic tube (1); an FFPI-1 cavity (7) is formed in the No. 1 ceramic tube (1) and between the No. 1 sapphire wafer (6) and the No. 2 sapphire wafer (8); a pure quartz optical fiber (3) is provided in the No. 2 ceramic tube (2); an optical fiber core (4) is wrapped inside the pure quartz optical fiber; and a pure quartz optical fiber (3) is provided in the No. 2 ceramic tube (2) and one end of the pure quartz optical fiber (3) close to the No. 2 sapphire wafer (8) is connected to the No. 2 sapphire wafer (8). A FFPI-2 cavity (9) is formed between the two FFPI-1 cavities (7); a FFPI-3 cavity (10) is further provided inside the pure quartz optical fiber (3) in the second ceramic tube; the FFPI-1 cavity (7) is used for strain measurement, the FFPI-2 cavity (9) is used for air pressure measurement, and the FFPI-3 cavity (10) is used for temperature measurement; the measurement result of the FFPI-3 cavity (10) is used to compensate the temperature of the FFPI-1 cavity (7) and the FFPI-2 cavity (9) to eliminate temperature crosstalk, and the air pressure of the FFPI-1 cavity (7) is compensated based on the measurement result of the compensated FFPI-2 cavity (9) to eliminate air pressure crosstalk; The wall of the No. 1 ceramic tube (1) is provided with an air hole (5) connected to the FFPI-1 cavity (7); The pure quartz optical fiber (3) is fixedly connected to the inner wall of the second ceramic tube (2); The second ceramic tube (2) is slidably connected relative to the first ceramic tube (1); The FFPI-1 cavity (7) is configured to have its internal air pressure consistent with the external air pressure to be measured through the air hole (5); The pressure difference formed by the external pressure to be measured and the pressure in the FFPI-2 cavity (9) causes the second sapphire wafer (8) to deform, and the cavity length of the FFPI-2 cavity (9) changes accordingly.

2. The optical fiber sensor based on the multi-parameter response mechanism of the cascaded FFPI cavity according to claim 1, characterized in that: The maximum deformation of the second sapphire wafer (8) is less than 0.3 times its thickness.

3. The optical fiber sensor based on the multi-parameter response mechanism of the cascaded FFPI cavity according to claim 1, characterized in that: The cavity lengths of the FFPI-1 cavity (7) and the FFPI-2 cavity (9) will change with temperature, while the cavity length of the FFPI-3 cavity (10) will only change with temperature. The relationship between temperature and cavity length is as follows: Where: T is the measured temperature; T0 is the initial temperature; α q is the thermal expansion coefficient of pure quartz optical fiber (3); α s is the thermal expansion coefficient of the material being tested, ΔL FFPI-3-T is the length change of the FFPI-3 cavity (10) caused by temperature change; ΔL FFPI-2-T ΔL is the length change of the FFPI-2 cavity (9) caused by temperature change; FFPI-1-T is the change in length of the FFPI-1 cavity (7) caused by temperature change; They respectively represent the lengths of the FFPI-1 cavity (7), the FFPI-2 cavity (9) and the FFPI-3 cavity (10) at the initial temperature T0.

4. The optical fiber sensor with a multi-parameter response mechanism based on a cascaded FFPI cavity according to claim 1, characterized in that: There is a linear relationship between the pressure difference between the external pressure to be measured and the pressure in the FFPI-2 cavity (9) and the maximum deformation at the center of the second sapphire wafer (8), which is expressed as: Where, P 气 Indicates the external air pressure, P FFPI-2 represents the internal pressure of the FFPI-2 cavity (9), b represents the thickness of the second sapphire wafer (8), r represents the effective radius of the second sapphire wafer (8), δ represents the Poisson's ratio of the second sapphire wafer (8), E is the elastic modulus of the second sapphire wafer (8), and Δd is the deformation at the center of the second sapphire wafer (8), that is, the change in the cavity length of the FFPI-2 cavity (9).

5. The optical fiber sensor based on the multi-parameter response mechanism of the cascaded FFPI cavity according to claim 4, characterized in that: Among the FFPI-1 cavity (7), FFPI-2 cavity (9) and FFPI-3 cavity (10), only the change in the cavity length of the FFPI-1 cavity (7) is related to the strain. At this time, the strain value of the FFPI-1 cavity (7) is expressed as: Where ΔL FFPI-1 is the total deformation of the FFPI-1 cavity (7), ΔL FFPI-1 After subtracting the cavity length change ΔL of the FFPI-1 cavity (7) due to temperature change, FFPI-1-T and Δd, Δd is the deformation at the center of the second sapphire wafer (8), and By comparison, we can get the strain value at FFPI-1 cavity (7). is the cavity length of the FFPI-1 cavity (7) at the initial temperature T0.

6. The optical fiber sensor with a multi-parameter response mechanism based on a cascaded FFPI cavity according to claim 1, characterized in that: The FFPI-2 cavity (9) and the FFPI-3 cavity (10) inside the pure quartz optical fiber (3) are formed by femtosecond laser processing.

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