CN110702148B - Preparation method and application of optical fiber sensing device capable of simultaneously distinguishing and measuring three parameters - Google Patents

Abstract

A three-parameter simultaneous differential measurement optical fiber sensor preparation method and application, a section of standard single mode fiber Bragg grating with the total length of a grid region about 15mm, which is inscribed by 193nm excimer laser, is cut into two small sections in the grid region by an optical fiber cutter, so that the grating with uniform refractive index modulation is damaged; respectively fixing two small sections of gratings on a left optical fiber fixing clamp and a right optical fiber fixing clamp of a fusion splicer, and aligning the two sections of gratings in a manual adjusting mode of the fusion splicer and adjusting the two sections of gratings to a proper interval; another section of optical fiber is taken, the tail end of the optical fiber is stripped off a distance coating layer and cleaned by alcohol, and then a small drop of photosensitive glue is dipped and dropped into the gap between the two fixed sections of optical gratings; and irradiating the photosensitive glue by using an ultraviolet curing lamp to cure the photosensitive glue to form a photosensitive glue cavity, thereby introducing structural phase shift. The invention can effectively realize the distinguishing measurement of temperature, pressure and refractive index according to the spectral characteristics of the structural phase shift, and the method has simple operation process and lower cost.

Description

A preparation method and application of a three-parameter simultaneous differential measurement optical fiber sensor device

technical field

The invention relates to the technical field of optical fiber sensor devices, in particular to a preparation method and application of a three-parameter simultaneous differential measurement optical fiber sensor.

Background technique

When an optical fiber is used as a sensing device, it can directly or indirectly measure several physical quantities, such as tension, pressure, temperature, refractive index, humidity, and so on. However, with the increasingly complex and changeable surrounding environment, the detection of changes in a single physical quantity can no longer meet people's measurement needs. Therefore, designing and fabricating a sensor device that can realize multi-parameter and multi-function has become a research hotspot of optical fiber sensing technology.

Interferometric fiber optic sensors based on the principle of optical interference, especially fiber Fabry-Perot interferometers (FPI), are widely used in fiber optic sensing and detection due to their flexible and diverse structures, high reflectivity, and low loss. field. The methods of fabricating optical fiber interference Fabry-Perot structures can be divided into: Intrinsic Interferometer (IFPI) with all-fiber F-P cavity structure and F-P cavity with the help of other materials or objects (such as capillaries, ceramic cores, etc.) Structural Extrinsic Interferometer (EFPI). At present, the technology of using the integrated structure sensor based on all-fiber FPI and fiber grating to realize the simultaneous differential measurement of temperature and pressure, temperature and refractive index, temperature and displacement, temperature and humidity is very mature, but its response sensitivity It is also limited to the optical fiber level, and the production cost is high. The principle of the above two-parameter differential measurement is mostly the temperature compensation method, that is, the structure in the integrated sensor, the fiber grating, is not sensitive to pressure, refractive index, etc., and can be used as temperature compensation during measurement. At the same time, dual or multi-parameter discriminating measurement, cross-sensitivity effect is an intrinsic problem.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the purpose of the present invention is to provide a preparation method and application of a three-parameter simultaneous differential measurement optical fiber sensor, by using photoreceptor in the middle position of the fiber grating to make an F-P cavity, introducing a structural phase shift, according to the spectrum of the structural phase shift The characteristics can effectively realize the differential measurement of temperature, pressure and refractive index, and the method is simple in operation and low in cost.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A preparation method of a three-parameter simultaneous differential measurement optical fiber sensor, comprising the following steps;

Step 1: a standard single-mode fiber Bragg grating with a grating region total length of 15mm written by a 193nm excimer laser is cut into two small sections with a fiber cutter in the grating region, resulting in the destruction of the grating with uniform refractive index modulation;

Step 2: Fix the two small sections of gratings on the left and right optical fiber clamps of the fusion splicer respectively, then align the two sections of gratings through the manual adjustment mode of the fusion splicer, and adjust the spacing to be 50 to 100um in order to obtain a better interference spectrum;

Step 3: Take another piece of optical fiber, strip the end of the coating for a distance and clean it with alcohol, and then dip a small drop of photosensitive glue into the gap between the two fixed gratings (as described in step 2) middle;

Step 4: Irradiate the photoresist with an ultraviolet curing lamp to cure the photoresist to form a photoresist cavity, thereby introducing a structural phase shift, and obtaining an integrated sensor based on extrinsic FPI and phase shift grating.

The ultraviolet curing lamp irradiates the photosensitive adhesive for 5 minutes, so as to improve the strength of the photosensitive adhesive cavity.

The fiber cutter is cut into two small sections at about the middle of the grid region.

An application of a three-parameter simultaneous differential measurement of an optical fiber sensor, the device is applied to the simultaneous differential measurement of the three parameters of temperature, pressure and refractive index;

The optical fiber sensor has two reflective surfaces, namely reflective surface 1 and reflective surface 2, which are the interface between the optical fiber and the photosensitive adhesive. The incident light is partially reflected by the fiber grating, and the remaining light continues to propagate forward, reaching the reflection. The surface 1 is reflected again, and the remaining light continues to propagate forward, and then passes through the photosensitive glue cavity with a refractive index of about 1.5 and a length of about 57um. Part of the light is reflected by the reflective surface 2, and the remaining light continues to propagate forward and is captured by the fiber grating here. Partial reflection, after the light is reflected by the two reflective surfaces of the airtight EFPI, the phase delay caused by different optical path differences is different, and an interference pattern is generated at the output end. Due to the low reflectivity of the reflective surface, multi-beam reflection can be ignored. Therefore, the output light The strong approximation is the interference formed in these two cavities, and the output light intensity is:

为干涉的初始相位；n为密闭EFPI腔的折射率；λ为光学波长；L为密闭EFPI的腔 长，因此，腔体的光学长度可以计算为:Among them, I is the output light intensity; I ₁ and I ₂ are the reflected light intensity of the incident light at the end face of the closed EFPI cavity, respectively;

is the initial phase of interference; n is the refractive index of the sealed EFPI cavity; λ is the optical wavelength; L is the cavity length of the sealed EFPI, so the optical length of the cavity can be calculated as:

where λ ₁ and λ ₂ are the wavelengths of two adjacent valleys in the sealed EFPI interference spectrum, and the free spectral range (FSR) in the sealed EFPI spectrum can be expressed as:

The transmission matrix method is widely used in the calculation of the optical wave field of non-uniform fiber gratings such as phase-shifted fiber gratings. Therefore, this method is used to analyze the spectral characteristics of the phase shift of the structure introduced by making a closed EFPI in the grating region. When the structure is phase shifted, the phase is relatively delayed, and a negative sign needs to be added before the phase shift of the grating. The phase shift matrix is:

表示相移量的大小；in the formula

Indicates the magnitude of the phase shift;

By measuring the wavelength shift (Δλ _EFPI ), the power change (ΔK _PS ), and the wavelength shift (Δλ _PS ) of the structural phase-shift spectrum in the confinement EFPI spectrum, the sensitivity coefficient matrix can be used to realize the three parameters of temperature, pressure and refractive index. At the same time, the measurement is distinguished, and the changes of temperature, pressure and refractive index are set as ΔT, ΔP and Δn, then the sensitivity matrix can be expressed as:

In the formula, S _1n , S _1T and S _1P are the sensitivities of the sealed EFPI wavelength drift with the change of refractive index, temperature and pressure; S _2n , S _2T and S _2P are the sensitivities of the structural phase shift wavelength drift with the measured change; , S _3n , S _3T and S _3P are the sensitivities of the structural phase shift power drift to the measured value. Through the inverse operation of the matrix, the changes of the three physical quantities to be measured can be obtained as:

in the formula

is the determinant of the sensitivity coefficient matrix;

Substituting the above experimental measurement results into formula (6), we can get:

So far, the simultaneous differential measurement of the three parameters of temperature, pressure and refractive index can be effectively achieved.

Beneficial effects of the present invention:

First, the airtight EFPI made by the present invention is formed by curing with photosensitive glue, which breaks through the problem that the sensitivity of the optical fiber sensor is limited to the optical fiber; A new idea is proposed for production; thirdly, the length of the F-P cavity is determined by adjusting the gap between the two small gratings fixed at the left and right ends of the welding machine clamp, so the cavity length can be flexibly and precisely controlled. Fourth, it can realize the simultaneous differential measurement of the three parameters of temperature, pressure and refractive index, with high sensitivity and low cost, which has very important research significance in the field of optical fiber sensing and detection.

Description of drawings

Figure 1 is a schematic diagram of a standard single-mode fiber grating cut at about the middle of the grating region.

Fig. 2 is a schematic diagram of fixing the cut-off two-segment grating on the optical fiber fixing clip of the fusion splicer.

Figure 3 is a schematic diagram of taking another single-mode optical fiber and dipping the photosensitive glue into the gap of two gratings.

FIG. 4 is a schematic diagram of a photosensitive adhesive for curing two grating gaps by irradiation with an ultraviolet curing lamp.

Figure 5 is a microscopic image of the integrated sensor.

Figure 6 is a schematic diagram of the integrated sensor measurement experimental setup.

Figure 7 is a spectral graph of the response of the integrated sensor to temperature.

Figure 8 is an enlarged reflection spectrum of the structured phase-shift grating at 25°C.

Figure 9 is an enlarged reflection spectrum of the structured phase-shift grating at 40°C.

Figure 10 is an enlarged reflection spectrum of the structured phase-shift grating at 50°C.

Figure 11 is a linear fit plot of the wavelength drift of a sealed EFPI as a function of temperature.

FIG. 12 is a linear fitting graph of the wavelength shift of the structural phase shift as a function of temperature.

FIG. 13 is a linear fit curve of structural phase shift power drift as a function of temperature.

Figure 14 is a spectral graph of the response of the integrated sensor to pressure.

Figure 15 is an enlarged reflection spectrum of a structured phase-shift grating with increasing pressure.

Figure 16 is a linear fit plot of the wavelength drift of a sealed EFPI as a function of pressure.

Figure 17 is a spectral graph of the response of the integrated sensor to the refractive index.

Figure 18 is an enlarged reflection spectrum of a structured phase-shift grating with a refractive index of 1.3342.

Figure 19 is a magnified reflection spectrum of a structured phase-shift grating with a refractive index of 1.3388.

Figure 20 is a magnified reflection spectrum of a structured phase-shift grating at a refractive index of 1.3478.

Figure 21 is a linear fit plot of the wavelength shift of a sealed EFPI as a function of refractive index.

FIG. 22 is a linear fitting graph of the power drift of a structured phase-shift grating as a function of refractive index.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings.

The technical scheme of sensor preparation includes the following four steps:

Step 1: A standard single-mode fiber Bragg grating with a total length of about 15mm in the gate region written by a 193nm excimer laser is cut into two small sections by a fiber cutter (FITEL S326) at about the middle of the gate region, resulting in a uniform refractive index The modulated grating is destroyed, as shown in Figure 1. ;

Step 2: Fix the two small gratings on the left and right optical fiber clips of the fusion splicer (Furukawa FITELS177), then align the two gratings with the manual adjustment mode of the fusion splicer and adjust the distance to a suitable distance. Because the free general range of FPI is inversely proportional to the cavity length, the smaller cavity length is adjusted to be about L=57um, as shown in Figure 2;

Step 3: Take another piece of optical fiber, strip the end of the coating for a distance and clean it with alcohol, then dip a small drop of photosensitive glue (AUSBONDA332) on the two fixed gratings (as described in step 2). ) in the gap, as shown in Figure 3;

Step 4: Irradiate the photosensitive adhesive with a UV curing lamp for about 5 minutes, so that the photosensitive adhesive is cured to form a photosensitive adhesive cavity, and a structural phase shift is introduced, as shown in FIG. 4 . Figure 8 shows a micrograph of the integrated sensor seen under an optical microscope, where the structural phase-shift image is not visible.

The invention provides a preparation method of a three-parameter simultaneous differential measurement optical fiber sensor. The optical fiber used is an ordinary standard single-mode fiber; the writing grating device is a 193nm excimer laser; the function of the fusion splicer is to align the two small sections of grating that are cut off and adjust the length of the F-P cavity, which acts as a micro-displacement adjustment platform without welding. The fiber grating is used; in the experiment, the airtight EFPI is made of high-transparency and high-strength photosensitive adhesive AUSBONDA332; the demodulation equipment in the experiment is SM125 demodulator, which is produced by Micron Optics International Company.

The sensitivity of the all-fiber type FPI is limited to the level of the optical fiber. Therefore, the invention can effectively improve the measurement sensitivity of the fiber F-P cavity by curing the photosensitive adhesive to form the EFPI; It is made in the middle position, which breaks the uniform refractive index modulation of the grating and introduces the structural phase shift, which has certain significance for the research and manufacture of the phase-shift grating; the fiber sensor prepared by the invention has low cost, but the produced sensing spectrum has high quality , which is equivalent to the standard F-P cavity spectrum; the invention provides the preparation technology of EFPI integrated optical fiber sensor in the gate area, and conducts a preliminary high sensitivity test on temperature, pressure and refractive index, and then realizes the simultaneous differential measurement of these three physical quantities, This provides a certain technical support for the development of a fiber-optic sensor device with high sensitivity that can realize the simultaneous differential measurement of three parameters.

In the preparation process of the integrated sensor proposed by the present invention, special attention should be paid to: (1) The photoresist has high transparency, that is, high reflectivity. Therefore, in order to successfully introduce a better structural phase shift spectrum, the grating should be about the middle of the gate area. The position is cut off to make the photosensitive glue cavity; ②The photosensitive glue can be cured quickly, but in order to improve its curing strength, the curing time can be appropriately increased, about 5 minutes; When the gap distance is the length of the cavity, on the premise that the F-P interference spectrum can be obtained, the spacing should not be too long, so as not to damage the photosensitive glue cavity;

Sensing principle and discriminating measurement:

The basic working principle of the sensor is that due to changes in external environmental parameters, such as changes in physical parameters such as temperature, pressure and refractive index, the length of the sealed EFPI cavity changes, which in turn affects the position of the phase shift point or the magnitude of the phase shift of the structure. , the final result is that the reflection spectrum of the closed EFPI reflected by the experimental spectrum drifts, and the wavelength and power of the structural phase shift also produce a certain linear change, which achieves the sensing effect and realizes the three-parameter discrimination measurement.

The integrated optical fiber sensor prepared by the invention is that after a complete optical fiber grating is cut into two small gratings at about the middle position of the grating area, it is fixed on the fusion splicer, and the mode between the two small gratings can be easily controlled by manually adjusting the mode. The gap is the length of the cavity, so as to achieve the number of free spectra required for the experiment, and the gap is filled with photosensitive adhesive to form a closed EFPI after curing.

The following laboratory data are all based on the sensor shown in Figure 5,

The optical fiber sensor has two reflective surfaces, both of which are the interface between the optical fiber and the photosensitive glue. The incident light is partially reflected by the fiber grating, the remaining light continues to propagate forward, reaches the reflecting surface 1 and is reflected again, the remaining light continues to propagate forward and then passes through the photosensitive glue cavity with a refractive index of about 1.5 and a length of about 57um. The reflection surface 2 reflects part of the light, and the remaining light continues to propagate forward and is partially reflected by the fiber grating. After the light is reflected by the two reflective surfaces of the sealed EFPI, the phase delay caused by different optical path differences is different, and an interference pattern is generated at the output end. Due to the low reflectivity of the reflective surface, multi-beam reflections can be ignored. Therefore, the output light intensity is approximated by the interference formed in these two cavities, and the output light intensity is:

为干涉的初始相位；n为密闭EFPI腔的折射率；λ为光学波长；L为密闭EFPI的腔 长。因此，腔体的光学长度可以计算为:Among them, I is the output light intensity; I ₁ and I ₂ are the reflected light intensity of the incident light at the end face of the closed EFPI cavity, respectively;

is the initial phase of interference; n is the refractive index of the sealed EFPI cavity; λ is the optical wavelength; L is the cavity length of the sealed EFPI. Therefore, the optical length of the cavity can be calculated as:

In the formula, λ ₁ and λ ₂ are the wavelengths of two adjacent valleys in the closed EFPI interference spectrum. The free spectral range (FSR) in a confined EFPI spectrum can be expressed as:

The transmission matrix method is widely used in the calculation of the optical wave field of non-uniform fiber gratings such as phase-shifted fiber gratings. Therefore, this method is used to analyze the spectral characteristics of the phase shift of the structure introduced by making a closed EFPI in the grating region. When the structure is phase shifted, the phase is relatively delayed, and a negative sign needs to be added before the phase shift of the grating. The phase shift matrix is:

表示相移量的大小。in the formula

Indicates the magnitude of the phase shift.

The integrated sensor measurement device is shown in Figure 6. One end of the SM125 demodulator with a measurement accuracy of 1pm is connected to the computer, and the other end is connected to the sensor. When the sensor is placed in different measurement environments, its spectral changes can be acquired by a computer.

Figure 10 shows the reflectance spectra of the sensor under normal pressure with temperature changes of 25°C, 30°C, 35°C, 40°C, 45°C and 50°C, where the red shift of the closed EFPI spectrum can be clearly seen. In order to clearly observe the effect of temperature change on the phase shift of the structure, several representative spectra at 25 °C, 40 °C and 50 °C were selected and enlarged, as shown in Figures 11, 12 and 13, the structure can be seen The wavelength of the phase-shifted transmission window is shifted to the right and the power is reduced. As shown in Figures 14, 15 and 16, the spectral drift at different temperatures is linearly fitted, and the sensitivity of the spectral wavelength drift of the sealed EFPI to temperature response is 0.3076nm/℃, compared with the temperature response of the bare fiber F-P The sensitivity is improved by more than 30 times, and the wavelength shift and power change of the structural phase shift also show a response sensitivity of 6.2pm/℃ and -0.2299dB/℃ to temperature.

As shown in Figure 17, it is the reflectance spectrum of the sensor when the pressure varies from 0 MPa to 1.2 MPa. The inset is a zoomed-in spectrum of the confined EFPI, where the spectrum can be seen to gradually shift towards longer wavelengths, proving that the sensor works well under high pressure. Figure 18 is an amplified spectrum of the structural phase shift after the sensor is applied to pressure. It can be seen that when pressure is applied to the sensor, the phase shift spectrum of the structure has almost no change, because the change in the refractive index caused by the applied pressure does not cause a change in the amount of phase shift. The wavelength shift of the sealed EFPI spectrum under different pressures was linearly fitted, and the response sensitivity to pressure was obtained as 0.81 nm/MPa, as shown in Figure 19.

The change in the structural phase shift is ultimately due to the change in the refractive index, so the integrated sensor was again subjected to refractive index experiments. The sensor was placed in a series of sucrose solutions with refractive index values of 1.3342, 1.3360, 1.3373, 1.3388, 1.3408, 1.3418, 1.3438, 1.3438, 1.3450, 1.3466, and 1.3478, respectively. The response spectrum of the sensor obtained is shown in Figure 20. The inset is the magnified spectrum of the confined EFPI, and it can be seen that its reflection spectrum also shifts to the longer wavelength. In addition, in order to clearly observe the effect of different concentrations of sucrose solution on the structural phase shift spectra, the representative structural phase shift spectra at refractive indices of 1.3342, 1.3388 and 1.3478 were selected and enlarged, as shown in Figures 21 and 22 shown. It can be seen that the power of the structural phase-shift spectrum gradually decreases, but its wavelength hardly shifts. The wavelength shift of the sealed EFPI spectrum when the solution with different refractive index changes was linearly fitted, and the response sensitivity to the solution with different refractive index was obtained as 355.03 nm/RIU. In addition, the response sensitivity of the power change of the structural phase shift to the refractive index is 319.82 dB/nm.

By measuring the wavelength shift (Δλ _EFPI ), the power change (ΔK _PS ), and the wavelength shift (Δλ _PS ) of the structural phase-shift spectrum in the confinement EFPI spectrum, the sensitivity coefficient matrix can be used to realize the three parameters of temperature, pressure and refractive index. Also differentiate measurements. Assuming that the changes of temperature, pressure and refractive index are ΔT, ΔP and Δn, the sensitivity matrix can be expressed as:

In the formula, S _1n , S _1T and S _1P are the sensitivities of the sealed EFPI wavelength drift with the change of refractive index, temperature and pressure; S _2n , S _2T and S _2P are the sensitivities of the structural phase shift wavelength drift with the measured change; , S _3n , S _3T and S _3P are the sensitivities of the structural phase shift power drift to the measured value. Through the inverse operation of the matrix, the changes of the three physical quantities to be measured can be obtained as:

in the formula

is the determinant of the sensitivity coefficient matrix.

Substituting the above experimental measurement results into equation (6), we can get:

So far, the simultaneous differential measurement of the three parameters of temperature, pressure and refractive index can be effectively achieved.

On the basis of the conventional manufacturing method of the dual-parameter measuring sensor, the invention uses photosensitive glue to manufacture a closed F-P cavity at about the middle position of an optical fiber grating. Thus, the fiber grating with uniform index modulation is destroyed, introducing a structural phase shift. Experiments verify the response characteristics of the integrated sensor to temperature, pressure and refractive index. The results show that the sensitivity of the hermetic FPI fabricated from photoresist is significantly improved compared to the all-fiber FPI. More importantly, during the experiment, the structural phase shift also showed a certain regular response characteristics to temperature, pressure and refractive index, so it can effectively solve the problem of cross-sensitivity and realize the simultaneous and differentiated measurement of three parameters.

Claims (1)

1. A method for preparing a three-parameter measurement optical fiber sensor is characterized in that, comprising the following steps; Step 1: Divide a standard single-mode fiber Bragg grating with a total length of 15mm in the grating region written by a 193nm excimer laser into two small sections with a fiber cutter in the grating region, resulting in the destruction of the grating with uniform refractive index modulation; Step 2: Fix the two small sections of grating on the left and right optical fiber fixing clips of the fusion splicer respectively, and then align the two sections of the grating through the manual adjustment mode of the fusion splicer and adjust the distance to a distance of 50 to 100um; Step 3: Take another piece of optical fiber, strip the end of the coating for a distance and clean it with alcohol, and then dip a small drop of photosensitive glue into the gap between the two fixed gratings (as described in step 2) middle; Step 4: Irradiate the photosensitive adhesive with a UV curing lamp, so that the photosensitive adhesive is cured to form a photosensitive adhesive cavity, and a structural phase shift is introduced; The ultraviolet curing lamp irradiates the photosensitive glue for 5 minutes, so as to improve the strength of the photosensitive glue cavity; The optical fiber cutter is cut into two small sections at about the middle position of the gate area; The device prepared by this method is applied to the simultaneous differential measurement of the three parameters of temperature, pressure and refractive index; The optical fiber sensor has two reflection surfaces, namely a first reflection surface (1) and a second reflection surface (2), both of which are the interface between the optical fiber and the photosensitive adhesive. The incident light is partially reflected by the fiber grating, and the remaining The light continues to propagate forward and reaches the first reflecting surface (1) to be reflected again. The remaining light continues to propagate forward and then passes through the photosensitive glue cavity with a refractive index of about 1.5 and a length of about 57um and is reflected by the second reflecting surface (2). Part of the light is reflected, and the remaining light continues to propagate forward and is partially reflected by the fiber grating. After the light is reflected by the two reflecting surfaces of the sealed EFPI, the phase delay caused by different optical path differences is different, and an interference pattern is generated at the output end. The surface reflectivity is low, and multi-beam reflections can be ignored, so the output light intensity is approximated by the interference formed in these two cavities, and the output light intensity is:

Among them, I is the output light intensity; I ₁ and I ₂ are the reflected light intensity of the incident light at the end face of the closed EFPI cavity, respectively;

is the initial phase of interference; n is the refractive index of the sealed EFPI cavity; λ is the optical wavelength; L is the cavity length of the sealed EFPI, so the optical length of the cavity can be calculated as:

where λ ₁ and λ ₂ are the wavelengths of two adjacent valleys in the sealed EFPI interference spectrum, and the free spectral range (FSR) in the sealed EFPI spectrum can be expressed as:

The transmission matrix method is widely used in the calculation of the optical wave field of non-uniform fiber gratings such as phase-shifted fiber gratings. Therefore, this method is used to analyze the spectral characteristics of the structural phase shift introduced by making a closed EFPI in the grating region. When the structure is phase shifted, the phase is relatively delayed, and a negative sign needs to be added before the phase shift of the grating. The phase shift matrix is:

in the formula

Indicates the magnitude of the phase shift; By measuring the wavelength shift (Δλ _EFPI ), the power change (ΔK _PS ), and the wavelength shift (Δλ _PS ) of the structural phase-shift spectrum in the confinement EFPI spectrum, the sensitivity coefficient matrix can be used to realize the three parameters of temperature, pressure and refractive index. At the same time, the measurement is distinguished, and the changes of temperature, pressure and refractive index are set as ΔT, ΔP and Δn, then the sensitivity matrix can be expressed as:

In the formula, S _1n , S _1T and S _1P are the sensitivities of the sealed EFPI wavelength drift with the change of refractive index, temperature and pressure; S _2n , S _2T and S _2P are the sensitivities of the structural phase shift wavelength drift with the measured change; S _3n , S _3T and S _3P are the sensitivities of the structural phase shift power drift with the change of the measured value. Through the inverse operation of the matrix, the changes of the three measured physical quantities can be obtained as follows:

in the formula

is the determinant of the sensitivity coefficient matrix; Substituting the above experimental measurement results into formula (6), we can get:

Simultaneous and differentiated measurement of the three parameters of temperature, pressure and refractive index is achieved.

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