Temperature-refractive index double-parameter optical fiber sensor based on photosensitive polymer glue and preparation method of temperature-refractive index double-parameter optical fiber sensor

Abstract

The invention belongs to the technical field of sensors, and particularly relates to a temperature-refractive index double-parameter optical fiber sensor based on photosensitive polymer glue and a preparation method thereof.The temperature-refractive index double-parameter optical fiber sensor comprises a light source module, a sensing probe module and a data acquisition and analysis module, and the light source module comprises a super-continuum light source, a 2 * 2 optical fiber coupler and a fan-in and fan-out module; the super-continuous light source is connected to a first port of the 2 * 2 optical fiber coupler, and a third port and a fourth port of the 2 * 2 optical fiber coupler are connected to the fan-in and fan-out module. The reflecting mirror is formed in a photosensitive polymer glue end face growth mode, then the F-P resonant cavity is formed, a light beam is reflected back and forth between the reflecting mirror and the fiber core end face to form the F-P resonant cavity, PDMS material coating is combined to serve as a temperature sensing unit, the other one serves as a refractive index sensing unit, each fiber core can work independently, and the temperature sensing unit and the refractive index sensing unit can work independently. Therefore, the sensor with the structure can measure data of temperature and refractive index at the same time, and the optical fiber structure can be prevented from being influenced by the temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a temperature-refractive index dual-parameter optical fiber sensor based on photosensitive polymer glue and a preparation method thereof. Background Art

[0002] From basic theoretical research to practical application, fiber optic sensor technology has become an important tool in civil engineering, energy, aerospace, medical and other fields. In the future, with the addition of new materials and new technologies, as well as the advancement of intelligence and networking, fiber optic sensors will play a role in a wider range of scenarios, providing support for the security and development of modern society. However, today's sensors still have many drawbacks, such as insufficient integration, insufficient precision, and limited dynamic range of high-sensitivity sensors.

[0003] The micro-nano optical fiber temperature sensor based on vanadium dioxide and its preparation method proposed by the authorization announcement number CN10157101686A rely on complex processes such as hydrofluoric acid etching and magnetron sputtering, but require high-precision equipment and have environmental hazards, resulting in high preparation costs and long cycles. In addition, the existing cross-effects of temperature and refractive index are difficult to separate, and independent decoupled measurement cannot be achieved, resulting in reduced accuracy. In addition, some sensors are easily affected by environmental temperature and humidity after long-term use, such as pressure sensors, which suffer performance degradation due to material creep.

[0004] In view of the above problems, the present invention proposes a dual-core optical fiber sensor based on photosensitive polymer glue, which realizes high-precision synchronous measurement of temperature and refractive index by simplifying the process, innovating the structural design and signal processing technology. Summary of the invention

[0005] The purpose of the present invention is to provide a temperature-refractive index dual-parameter optical fiber sensor based on photosensitive polymer glue and a preparation method thereof, which can form a reflector and then constitute an FP resonant cavity. The light beam reflects back and forth between the reflector and the fiber core to form an FP resonant cavity, and each fiber core can work independently, so the sensor of this structure can measure temperature and refractive index data at the same time, and can avoid the optical fiber structure being affected by temperature.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A temperature-refractive index dual-parameter optical fiber sensor based on photosensitive polymer glue, comprising a light source module, a sensor probe module and a data acquisition and analysis module;

[0008] The light source module includes a supercontinuum light source, a 2×2 fiber coupler and a fan-in fan-out module;

[0009] The supercontinuum light source is connected to port one of the 2×2 fiber coupler, ports three and four of the 2×2 fiber coupler are connected to a fan-in fan-out module, and port two of the 2×2 fiber coupler is connected to a photodetector with a wavelength resolution of 0.01 nm;

[0010] The sensing probe module comprises a dual-core optical fiber, which comprises two cores, and the end faces of the two cores are respectively attached with photosensitive polymers of different lengths to form two independent FP resonant cavities; the outer surface of one of the photosensitive polymers is coated with PDMS as a temperature sensitive unit, and the other photosensitive polymer is used as a refractive index sensitive unit;

[0011] The data acquisition and analysis module includes an OSA, an FPGA and a computer device, which is used to convert the reflected light signal into an electrical signal, separate the interference signal corresponding to the temperature and the refractive index through a fast Fourier transform, and analyze the parameter change values ​​of the temperature and the refractive index based on the sensitivity matrix.

[0012] The photosensitive polymer comprises 91.5% of pentaerythritol triacrylate, 8% of methyldiethanolamine and 0.5% of eosin Y. After being cured, the refractive index of the photosensitive polymer is 1.52×2 optical fiber coupler.

[0013] The core diameter of the double-core optical fiber is 8.2 μm, the double-core spacing is 62.5 μm, and the cladding diameter is 5 μm.

[0014] The two FP resonant cavities have different cavity lengths, wherein the cavity length of the temperature sensitive unit is 30 μm, and the cavity length of the refractive index sensitive unit is about 35 μm.

[0015] The spectral range of the supercontinuum light source is 450nm to 2400nm, and is respectively injected into two cores of the dual-core optical fiber through a fan-in and fan-out module.

[0016] A method for preparing a temperature-refractive index dual-parameter optical fiber sensor based on photosensitive polymer glue, the method is used to prepare the above optical fiber sensor, the method comprising:

[0017] S1: Prepare the sensing probe module, immerse the dual-core optical fiber into the photosensitive polymer through the micro-manipulator arm, let the photosensitive polymer liquid naturally drop and contact the glass slide, and the photosensitive polymer solution forms a cylinder between the optical fiber and the glass slide through liquid tension;

[0018] S2: coating PDMS, dipping the photosensitive polymer cylinder into PDMS, and repeating the steps of S1 to generate another cylinder;

[0019] S3: Data acquisition and analysis: Use a supercontinuum light source to emit broad-spectrum light, separate the temperature and refractive index signals through FFT filtering, and combine the sensitivity matrix to eliminate crosstalk between parameters.

[0020] The coating steps of the PDMS are:

[0021] The dual-core optical fiber was immersed in PDMS to completely cover one of the photosensitive polymers, and then cured at 80°C for 90 minutes. The dipping and curing process was repeated to ensure that the PDMS thickness met the reflection requirements.

[0022] The sensitivity matrix is:

[0023]

[0024] The FFT filtering operation includes:

[0025] Extract the amplitude peak frequency corresponding to the temperature and refractive index in the original spectrum;

[0026] The two frequencies are bandpass filtered to separate the temperature signal and the refractive index signal.

[0027] The technical effects achieved by the present invention are:

[0028] The present invention uses a photosensitive polymer to form a reflector on the end face of the optical fiber to form an FP resonant cavity. The light beam reflects back and forth between the reflector and the fiber core to form the FP resonant cavity. The lengths of the cylinders on the surfaces of the two fiber cores are different, resulting in different test spectra, that is, each fiber core can work independently, so the sensor of this structure can measure temperature and refractive index data at the same time.

[0029] Since PDMS is attached to the surface of the optical fiber, the optical fiber structure can be protected from the influence of temperature. The coherence between the two laser beams of the wide-spectrum laser light source used in this test method is severely weakened after beam splitting by a 2×2 optical fiber coupler and a series of transmission processes. Therefore, the two laser signals will no longer interfere after passing through the 2×2 optical fiber coupler. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of a dual-parameter optical fiber sensor of the present invention;

[0031] Figure 2 It is a schematic diagram of the optical path propagation principle of the resonant cavity based on the photosensitive polymer glue in the present invention;

[0032] Figure 3 This is the result diagram of the fast Fourier transform of the original signal in the present invention.

[0033] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0034] 1. Light source module; 2. Sensor probe module; 3. Data acquisition and analysis module; 101. Supercontinuum light source; 102. 2×2 fiber coupler; 103. Fan-in fan-out module; 201. Dual-core optical fiber; 202. Photosensitive polymer; 203. PDMS; 301. OSA; 302. FPGA; 303. Computer equipment; 4. Physical contact boundary. DETAILED DESCRIPTION

[0035] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention.

[0036] Embodiment 1:

[0037] like Figure 1 - Figure 3 As shown, a temperature-refractive index dual-parameter optical fiber sensor based on photosensitive polymer glue includes a light source module 1, a sensor probe module 2 and a data acquisition and analysis module 3;

[0038] The light source module 1 includes a supercontinuum light source 101, a 2×2 fiber coupler 102 and a fan-in fan-out module 103;

[0039] The supercontinuum light source 101 is connected to port 1 of the 2×2 fiber coupler 102, ports 3 and 4 of the 2×2 fiber coupler 102 are connected to the fan-in fan-out module 103, and port 2 of the 2×2 fiber coupler 102 is connected to a photodetector with a wavelength resolution of 0.01 nm;

[0040] The sensing probe module 2 includes a dual-core optical fiber 201, which includes two cores. The end faces of the two cores are respectively attached with photosensitive polymers 202 of different lengths to form two independent FP resonant cavities to form a sensor probe. The outer surface of one photosensitive polymer 202 is coated with PDMS 203 as a temperature sensitive unit, and the other photosensitive polymer 202 is used as a refractive index sensitive unit. The core diameter of the dual-core optical fiber 201 is 8.2μm, the dual-core spacing is 62.5μm, and the cladding diameter is 125μm. The cavity lengths of the two FP resonant cavities are different, wherein the cavity length of the temperature sensitive unit is 30μm, and the cavity length of the refractive index sensitive unit is 35μm, which is ultra-high. The spectral range of the continuous light source 101 is 450nm to 2400nm, and it is respectively injected into the two cores of the dual-core optical fiber 201 through the fan-in and fan-out modules 103. The photosensitive polymer 202 includes 91.5% pentaerythritol triacrylate, 8% methyldiethanolamine, and 0.5% eosin Y. The refractive index of the photosensitive polymer 202 after curing is 1.512. A layer of PDMS203 is coated on the surface of the column, and the RI of PDMS203 can change in response to temperature changes. In addition, PDMS203 is also used as an isolation layer to minimize the impact of external RI changes on the temperature sensor. The PDMS203 is polydimethylsiloxane.

[0041] The data acquisition and analysis module 3 includes OSA301, FPGA302 and computer equipment 303, which are used to convert the reflected light signal into an electrical signal, and separate the interference signals corresponding to the temperature and refractive index through fast Fourier transform, analyze the parameter change values ​​of the temperature and refractive index based on the sensitivity matrix, and establish a matrix according to their respective sensitivities to solve the problem of mutual crosstalk between temperature and refractive index during the test. The computer equipment 303 is used to visualize the sensor data; display the sensor data such as temperature, strain, and vibration waveforms in real time, and store the original data and processing results locally or in the cloud. The OSA301 is a spectrum analyzer and the FPGA302 is a field programmable gate array.

[0042] Embodiment 2:

[0043] The preparation method is used to prepare the above-mentioned optical fiber sensor, and the preparation method comprises:

[0044] S1: Prepare the sensing probe module 2, immerse the dual-core optical fiber 201 into the photosensitive polymer 202 through a micro-manipulator, and let the photosensitive polymer 202 liquid naturally drop and contact the glass slide. The photosensitive polymer 202 solution forms a cylinder between the optical fiber and the glass slide through liquid tension, and is cured by a 532nm laser;

[0045] S2: coating PDMS 203, dipping the photosensitive polymer 202 cylinder into PDMS 203, and repeating the steps of S1 to generate another cylinder. The coating steps of PDMS 203 are as follows:

[0046] The dual-core optical fiber 201 is impregnated with PDMS 203 to completely cover one of the photosensitive polymers 202, and then cured at 80°C for 90 minutes. The impregnation and curing process is repeated to ensure that the thickness of PDMS 203 meets the reflection requirements;

[0047] S3: Data collection and analysis: Using the supercontinuum light source 101 to emit broad spectrum light, the temperature and refractive index signals are separated by FFT filtering; the FFT filtering operation includes:

[0048] Extract the amplitude peak frequency corresponding to the temperature and refractive index in the original spectrum;

[0049] The two frequencies are bandpass filtered to separate the temperature signal and the refractive index signal.

[0050] First, a micromanipulator is used to manipulate the dual-core optical fiber 201, and a certain amount of photopolymer solution is immersed in the dual-core optical fiber 201, so that the liquid forms a hemispherical shape on the end face of the optical fiber through natural drop.

[0051] Secondly, the dual-core optical fiber 201 is controlled to descend so that the photopolymer solution contacts a clean glass slide. The photopolymer solution forms a cylinder between the optical fiber and the glass slide through liquid tension, and a 5FPGA302nm laser with a power of 40μW is emitted into one of the photosensitive polymers 202 for 20 seconds. In this process, the length of the cylinder is controlled by adjusting the distance between the optical fiber and the slide, and the thickness of the photosensitive polymer 202 solution on the end face of the two cores of the dual-core optical fiber 201 is different, that is, the length of the formed cylinder is different. In this way, it can form two different FP resonant cavities and form different spectra. Including but not limited to the length difference of the two cylinders in the test, that is, as long as the lengths of the two cylinders are different, two different FP resonant cavities will be formed. When the light is reflected in the resonant cavity, two different spectra will be formed, and different results will be obtained. At the same time, it is not only applicable to dual-core optical fiber 201, but also to multi-core optical fiber. The above principle is also applicable.

[0052] Third, use anhydrous ethanol to remove excess photopolymer liquid on the end surface.

[0053] Fourth, impregnate the fiber with PDMS203 and ensure that the end of the column is completely coated with PDMS203. Then, let the fiber stand at 80°C for 90 minutes to cure PDMS203. In this step, by dipping and heating PDMS203 multiple times, the surface of the column can be covered with enough PDMS203. Finally, manipulate the TCF to be impregnated with the photopolymer solution again, and repeat the photopolymerization and cleaning process to ensure that the PDMS203 thickness at the end face of the dual-core optical fiber 201 reaches the expected good reflection effect.

[0054] The specific test method is as follows:

[0055] like Figure 1 As shown,

[0056] The supercontinuum light source 101 is connected to port 1 of the 2×2 fiber coupler 102, ports 3 and 4 are connected to the fan-in fan-out module 103, and then port 2 is connected to the OSA301 with a wavelength resolution of 0.01nm. The spectral laser emitted by the laser source enters from port 1 of the coupler, and then is split into two beams by the beam splitting function of the 2×2 fiber coupler 102, and then enters the fan-in fan-out module 103 through ports 3 and 4. Finally, it is reflected by the sensor to the original path within the 2×2 fiber coupler 102, enters the OSA301 from port 2, and finally captures the interference spectrum there.

[0057] In addition, in this experiment, we immersed the sensor in a semi-enclosed liquid environment, and as different liquids were introduced, the RI gradually increased from 1.333 to 1.413; at the same time, the temperature was gradually increased from about 10°C to about 90°C using a constant temperature and humidity test chamber. Then, at a temperature of 20°C, the sensor was used to test liquids with different refractive indices. Despite the fluctuations in the environmental RI, the temperature sensing spectrum remained relatively unchanged, indicating that the RI had little effect on the temperature sensor. In contrast, as the environmental RI increased, the RI sensing spectrum gradually shifted to shorter wavelengths.

[0058] The optical signal, such as the interference spectrum output by the FP resonant cavity, is transmitted to the photosensitive area of ​​the photodetector through optical fiber or free space.

[0059] Photodetector Photodiode converts incident light signal into current signal.

[0060] Temperature changes cause the FP cavity length to change due to thermal expansion effects, and changes in the refractive index cause the resonance peak to shift.

[0061] By monitoring the wavelength drift of multiple resonance peaks and combining the algorithm matrix equation to separate the influence of temperature and refractive index, the light intensity-wavelength data collected by the photoelectric detector needs to be matched with the temperature / refractive index calibration curve to achieve dual-parameter synchronous solution.

[0062] The simulation conditions are that the length of the temperature sensing column is 30μm, while the length of the RI sensing column end is 35μm; this results in significant differences in the period and width of the interference signal generated by the two columns. The original signal received by OSA301 is actually just the superposition of the intensity of the temperature sensing signal and the RI sensing signal. FPGA302 is used to convert the optical signal into an electrical signal, and the electrical signal is subjected to a fast Fourier transform FFT. By performing an FFT filtering operation on the original spectrum, the frequencies near the two amplitude peaks are selected for bandpass filtering, and specific signals are screened, and finally the spectrum corresponding to the temperature sensing signal and the RI sensing signal can be obtained.

[0063] Data obtained through simulation: Sensitivity K of temperature to RI sensor T-R The sensitivity of RI sensor to temperature is -0.03OSA301nm / RIU. R-T is -0.096nm / ℃, while the sensitivity of the temperature sensor itself is K T-T The sensitivity of the refractive index sensor itself is 1.187nm / ℃. R-R It is -272nm / RIU.

[0064] Substituting the sensitivity data obtained by simulation into the analysis matrix of dual parameter measurement mentioned in the above principle, the following matrix can be obtained:

[0065]

[0066] When the temperature and refractive index change differently, different results can be obtained. According to the above formula, the test results of the two parameters can be obtained through the changes of the two spectra, and the crosstalk problem between the two parameters can also be solved.

[0067] The basic structure of the FP resonant cavity in the above structure is composed of a reflector formed by a photosensitive polymer 202 and an optical fiber end face. The space inside the cavity is air. When light enters the FP resonant cavity, it is reflected multiple times between the mirrors to form multi-beam interference. When the phase difference of the interference light meets certain conditions, constructive or destructive interference occurs to form an interference spectrum. The intensity of the reflected light varies with the wavelength, showing interference fringes.

[0068] The interference condition of the FP resonant cavity is determined by the round-trip phase difference of the light in the cavity. When the light goes back and forth once in the cavity, the phase difference is:

[0069]

[0070] Among them, n is the refractive index of the medium in the cavity, L is the length of the resonant cavity, that is, the distance between the two mirrors, and λ is the wavelength of the incident light.

[0071] When the phase difference satisfies the constructive interference condition, that is:

[0072] Δφ=2πm(m=0,1,2,…) (2)

[0074] At this time, the interference of light increases and the intensity of reflected light reaches a maximum value. Substituting the phase difference formula into the equation, we get the resonance condition.

[0075]

[0076] After simplification, the resonant wavelength is obtained as:

[0077]

[0078] Here, m is the interference order.

[0079] After derivation, the reflected light intensity distribution of the FP resonant cavity can be expressed by the following formula:

[0080]

[0081] A parameter related to the reflectivity of the mirror is called the fineness or quality factor of the cavity.

[0082] By precisely designing the reflector parameters and cavity length, precise modulation of light and high-resolution measurement can be achieved.

[0083] Next, a matrix that can resolve the crosstalk between temperature and refractive index is introduced. By utilizing their respective sensitivities, a matrix that can accurately detect both temperature and refractive index RI values ​​can be constructed.

[0084]

[0085] Among them, Δλ T and Δλ R Represent the offset of temperature sensing spectrum and refractive index sensing spectrum respectively. The sensor sensitivities obtained in the above experiments are substituted into the formulas respectively, and the data are converted.

[0086] PDMS203 responds to temperature changes through thermal expansion effect and isolates external refractive index interference; the reflectivity of the physical contact boundary 4 between the dual-core optical fiber 201 and the photopolymer layer photosensitive polymer 202 is between 4% and 30%, which is used to optimize the interference contrast of the FP cavity, wherein the physical contact boundary 4 is the physical contact boundary between the optical fiber core 201 and the photopolymer layer 202;

[0087] The sensor for testing temperature and refractive index of the dual-core optical fiber 201 proposed by the present invention uses a photosensitive polymer 202 to form a reflector on the end face of the optical fiber to form an FP resonant cavity, and the light beam reflects back and forth between the reflector and the core to form an FP resonant cavity. In addition, the lengths of the cylinders on the surface of the two cores are different, resulting in different test spectra, that is, each core can work independently, so the sensor of this structure can simultaneously measure the temperature and refractive index data. Since PDMS203 is attached to the surface of the optical fiber, the optical fiber structure can also be prevented from being affected by temperature. The different lengths of the cylinders for testing the refractive index and temperature will cause the period and width of the interference signal generated by the two cylinders to be greatly different. The wide-spectrum laser light source used in the test method, after passing through the 2×2 optical fiber coupler 102 beam and a series of transmission processes, the coherence between the two laser beams is severely weakened, so the two laser signals will no longer interfere after passing through the coupler. Therefore, in this experimental method, a fast Fourier transform FFT is used to select the frequencies near the two amplitude peaks for bandpass filtering, and a specific signal is screened, and finally the spectrum corresponding to the temperature sensing signal and the RI sensing signal can be obtained.

[0088] The above is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to the conventional means in the art unless otherwise specified and limited.

Claims

1. A temperature-refractive index dual-parameter optical fiber sensor based on photosensitive polymer glue, characterized in that: It comprises a light source module (1), a sensor probe module (2) and a data acquisition and analysis module (3); The light source module (1) comprises a supercontinuum light source (101), a 2×2 optical fiber coupler (102) and a fan-in fan-out module (103); The supercontinuum light source (101) is connected to port one of the 2×2 optical fiber coupler (102), ports three and four of the 2×2 optical fiber coupler (102) are connected to a fan-in fan-out module (103), and port two of the 2×2 optical fiber coupler (102) is connected to a photodetector with a wavelength resolution of 0.01 nm; The sensing probe module (2) comprises a dual-core optical fiber (201), wherein the dual-core optical fiber (201) comprises two fiber cores, and the two fiber core end faces are respectively attached with photosensitive polymers (202) of different lengths to form two independent FP resonant cavities; the outer surface of one of the photosensitive polymers (202) is coated with PDMS (203) as a temperature sensitive unit, and the other photosensitive polymer (202) is used as a refractive index sensitive unit; The data acquisition and analysis module (3) comprises an OSA (301), an FPGA (302) and a computer device (303), and is used to convert the reflected light signal into an electrical signal, separate the interference signal corresponding to the temperature and the refractive index by fast Fourier transform, and analyze the parameter change values ​​of the temperature and the refractive index based on a sensitivity matrix.

2. The optical fiber sensor according to claim 1, characterized in that: The photosensitive polymer (202) includes 91.5% of pentaerythritol triacrylate, 8% of methyldiethanolamine, and 0.5% of eosin Y. After being cured, the photosensitive polymer (202) has a refractive index of 1.52×2 optical fiber coupler (102).

3. The optical fiber sensor according to claim 1, characterized in that: The core diameter of the double-core optical fiber (201) is 8.2 μm, the double-core spacing is 62.5 μm, and the cladding diameter is 2×2 optical fiber coupler (102) 5 μm.

4. The optical fiber sensor according to claim 1, characterized in that: The cavity lengths of the two FP resonant cavities are different, wherein the cavity length of the temperature sensitive unit is 30 μm, and the cavity length of the refractive index sensitive unit is 35 μm.

5. The optical fiber sensor according to claim 1, characterized in that: The spectral range of the supercontinuum light source (101) is 450 nm to 2400 nm, and is respectively injected into the two cores of the dual-core optical fiber (201) through a fan-in fan-out module (103).

6. A method for preparing a temperature-refractive index dual-parameter optical fiber sensor based on photosensitive polymer glue, characterized in that: The preparation method is used to prepare the optical fiber sensor according to any one of claims 1 to 5, and the preparation method comprises: S1: preparing a sensing probe module (2), immersing an optical fiber into a photosensitive polymer (202) by operating a mechanical arm, allowing the photosensitive polymer (202) liquid to naturally descend and contact a glass slide, and the photosensitive polymer (202) solution forms a cylinder between the optical fiber and the glass slide through liquid tension; S2: coating PDMS (203), dipping the photosensitive polymer (202) cylinder into PDMS (203), and repeating the steps of S1 to generate another cylinder; S3: Data acquisition and analysis: A supercontinuum light source (101) is used to emit broad spectrum light, and the temperature and refractive index signals are separated by FFT filtering, and the crosstalk between parameters is eliminated by combining the sensitivity matrix.

7. The preparation method according to claim 6, characterized in that: The coating steps of the PDMS (203) are: The dual-core optical fiber (201) is impregnated with PDMS (203) to completely cover one of the photosensitive polymers (202), and then cured at 80°C for 90 minutes. The impregnation and curing process is repeated to ensure that the thickness of the PDMS (203) meets the reflection requirements.

8. The preparation method according to claim 6, characterized in that: The sensitivity matrix is:

9. The preparation method according to claim 6, characterized in that: The FFT filtering operation includes: Extract the amplitude peak frequency corresponding to the temperature and refractive index in the original spectrum; The two frequencies are bandpass filtered to separate the temperature signal and the refractive index signal.

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