High-temperature-resistant and high-pressure-resistant optical fiber cascade refractive index-temperature double-parameter integrated sensor

Abstract

The invention belongs to the technical field of optical fiber high-temperature sensing, and discloses a high-temperature-resistant and high-pressure-resistant optical fiber cascade refractive index-temperature double-parameter integrated sensor which comprises a packaging structure, an optical fiber sensing device and a transmission optical fiber. The optical fiber sensing device comprises a photonic crystal fiber, a hollow Bragg fiber, a connecting fiber and a hollow capillary fiber which are connected in sequence; the hollow capillary optical fiber at the tail end of the optical fiber sensing device is connected with the transmission optical fiber; the optical fiber sensing device is arranged in the packaging structure; an outer air hole is formed in a position, opposite to the photonic crystal fiber, of the side wall of the packaging structure; and the optical fiber sensing device transmits a sensing signal to the outside of the packaging structure through the transmission optical fiber. According to the invention, refractive index-temperature in-situ double-parameter synchronous high-precision measurement capable of resisting high temperature of 1100 DEG C can be realized, and the method has important application value in the fields of aero-engine combustion chamber combustion state monitoring, nuclear reactor coolant concentration analysis, oil exploitation component analysis and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature sensing, and particularly relates to a high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual-parameter integrated sensor. BACKGROUND

[0002] Refractive index sensing and temperature sensing have extremely important application value in many industrial fields, such as monitoring of combustion states of aerospace engine combustion chambers, analysis of nuclear reactor coolant concentrations, and analysis of oil extraction components. These industrial application scenarios are often accompanied by extreme working environments such as high temperature and high pressure, which requires the sensor to maintain good sensing performance at high temperature. In a harsh and complex environment, the changes of refractive index and temperature generally occur simultaneously, and in order to improve the accuracy of detection, it is often necessary to simultaneously detect the refractive index and the temperature and compensate for the temperature error of the refractive index.

[0003] At present, in the field of sensor technology research, there are relatively rich research results on electrical refractive index sensors and optical fiber temperature sensors, but there are still many deficiencies in the application in high-temperature environments. For example, the traditional refractive index sensor cannot work stably at high temperature, and due to the lack of temperature compensation mechanism, the measurement value is seriously affected by thermal drift; and in a high-temperature environment, refractive index measurement is affected by thermal light effect and thermal expansion effect, which easily leads to data distortion. The existing technology usually uses a discrete temperature sensor to correct the refractive index data later, but this way is difficult to realize real-time dynamic compensation and is easy to introduce additional errors. Optical fiber sensors have advantages such as anti-electromagnetic interference, corrosion resistance, small size, can withstand 1100℃ high temperature, and have stronger environmental adaptability, and become an ideal choice for high-temperature environment monitoring. However, the existing optical fiber refractive index sensor is easily affected by temperature factors in a complex environment, has a large measurement error in a high-temperature environment, and there is cross-coupling interference between temperature and refractive index, which makes it difficult to realize high-precision measurement.

[0004] Therefore, in order to realize the composite dual-parameter sensing of refractive index-temperature in a high-temperature and high-pressure harsh environment, the structure of the optical fiber sensor needs to be improved to solve the problem of high-temperature refractive index measurement in a harsh environment, which is of great significance for monitoring gas flow component, reaction state and equipment safety. SUMMARY

[0005] In order to solve the problem that the existing optical fiber sensor cannot realize synchronous in-situ accurate measurement of refractive index-temperature in a high-temperature and high-pressure harsh environment, the application provides a high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual-parameter integrated sensor, which forms a double-Fabry-Perot interference cavity structure through optical fiber cascade to realize in-situ accurate sensing of refractive index-temperature dual parameters in a high-temperature and high-pressure environment.

[0006] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows: a high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual parameter integrated sensor, comprising: a packaging structure, an optical fiber sensing device and a transmission optical fiber; The optical fiber sensing device comprises a photonic crystal fiber, a hollow Bragg fiber, a connecting optical fiber and a hollow capillary fiber connected in sequence; the hollow capillary fiber at the end of the optical fiber sensing device is connected with the transmission optical fiber; The photonic crystal fiber, the hollow Bragg fiber and the connecting optical fiber form a first Fabry-Perot interferometer for measuring refractive index, and the connecting optical fiber, the hollow capillary fiber and the transmission optical fiber form a second Fabry-Perot interferometer for measuring temperature. The optical fiber sensing device is arranged in the packaging structure, and the side wall of the packaging structure is provided with an air hole opposite to the photonic crystal fiber; the optical fiber sensing device transmits a sensing signal to the outside of the packaging structure through the transmission optical fiber.

[0007] Further, the packaging structure comprises a front-end protective cap and an outer packaging tube. The outer packaging tube is provided with a central through hole for accommodating the transmission optical fiber, and one end of the central through hole is provided with a cavity for accommodating the optical fiber sensing device; the front-end protective cap is fixedly connected with the outer packaging tube and seals the cavity; the front-end protective cap is provided with a plurality of air holes.

[0008] Further, the front-end protective cap is provided with an internal thread in the center, the outer packaging tube is provided with an external thread on the outer periphery, and the front-end protective cap is connected with the outer packaging tube through the thread and is reinforced by high-temperature resistant anaerobic inorganic glue.

[0009] Further, the hollow Bragg fiber is provided with a fiber cavity in the center, and the cylindrical wall of the fiber cavity has a Bragg structure with periodic refractive index modulation; the photonic crystal fiber is provided with a plurality of penetrating fiber air holes at the position corresponding to the fiber cavity.

[0010] Further, the hollow capillary fiber is provided with a central cavity in the center.

[0011] Further, the outer side end face of the photonic crystal fiber is a bevel or a rough end face to avoid the formation of multi-stage interference.

[0012] Further, the high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual parameter integrated sensor further comprises a fixed tube, the fixed tube is arranged in the central through hole, and the transmission optical fiber is arranged in the fixed tube; the fixed tube is provided with high-temperature resistant ceramic glue at one end close to the optical fiber sensing device, the high-temperature resistant ceramic glue is used for sealing and fixing the transmission optical fiber, the fixed tube and the outer packaging tube; the other end of the fixed tube away from the optical fiber sensing device is connected and fixed with the outer packaging tube through a rubber ring.

[0013] Further, the fixed tube is made of high-temperature resistant corundum.

[0014] Further, the photonic crystal fiber, the hollow Bragg fiber, the connecting fiber, the hollow capillary fiber and the transmission optical fiber are all made of quartz material, and the packaging structure is made of zirconia ceramic material with a temperature resistance of more than 1500 DEG C.

[0015] The high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual parameter integrated sensor further comprises a continuous white light source, a fiber amplifier, a fiber circulator, a spectrometer and a data processor, broadband light generated by the continuous white light source is first subjected to optical power amplification by the fiber amplifier, and then is transmitted to the transmission optical fiber and the optical fiber sensing device through the fiber circulator, the cascade reflection spectrum generated in the optical fiber sensing device is output again through the fiber circulator and then is transmitted to the spectrometer for spectral data acquisition, and then the spectral data is transmitted to the data processor for data processing and demodulation analysis, so that the measured refractive index and temperature are obtained; the formula for calculating the measured temperature and refractive index is as follows: ; ; Wherein, and respectively represent the temperature change and the refractive index change, represents the optical path difference change of the first Fabry-Perot interferometer; represents the optical path difference change of the second Fabry-Perot interferometer; respectively represent the refractive index sensitivity and the temperature sensitivity of the first Fabry-Perot interferometer, represents the optical path difference change of the second Fabry-Perot interferometer and the temperature change and the function relationship of a, b, c, d, m, n are all fitting parameters, and e represents the base number of natural logarithm.

[0016] Compared with the prior art, the present application has the following beneficial effects: 1. The application provides a high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual parameter integrated sensor, which is formed by optical fiber cascade to form a double-Fabry-Perot interference cavity structure, realizes in-situ refractive index-temperature dual parameter synchronous sensing in a high-temperature and high-pressure environment, and the two Fabry-Perot interferometer structures are independent of each other, so that the cross-sensitivity of refractive index and temperature is avoided in structure, and therefore the application can improve the detection precision of refractive index in a high-temperature environment through temperature compensation, and solves the problem of high-precision refractive index detection in a high-temperature environment. In summary, the application can realize in-situ refractive index-temperature dual parameter synchronous sensing and accurate sensing in a high-temperature and high-pressure environment, solves the limitation of a single physical quantity sensor of a conventional sensor, and improves the detection precision of refractive index and temperature in a harsh environment such as high temperature and high pressure.

[0017] 2. The sensor of the application is packaged by zirconium oxide ceramic, which greatly improves the protection capability of the sensor in a high-temperature and high-pressure harsh environment, and a plurality of micro external air holes are arranged on the packaging structure, which can provide a sensing environment for the first Fabry-Perot interferometer on the one hand, and can avoid the deformation of the sensing structure caused by the high-pressure environment on the other hand, greatly improving the high-pressure resistance of the sensor and the environmental adaptability. Therefore, the application can be used as an effective means for high-precision detection of gas refractive index and environmental temperature at 1100 DEG C.

[0018] 3. Moreover, the sensing structure of the application is a full-optical fiber probe structure, which has the advantages of small size and low cost, and can be arranged and applied in extremely narrow test environment according to actual application environment, which is a prominent advantage distinguishing from the larger size of traditional sensors. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Fig. 1 is a whole structure sectional view of a high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual parameter integrated sensor provided by the first embodiment of the application; Figure 2 Fig. 2 is a structure schematic view of an optical fiber sensing device in the first embodiment of the application; Figure 3 Fig. 3 is a sectional view schematic of an outer packaging tube in the first embodiment of the application; Figure 4 Fig. 4 is a sectional view schematic of a front-end protective cap in the first embodiment of the application; Figure 5 Fig. 5 is a structure schematic view of a high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual parameter integrated sensor provided by the second embodiment of the application; Figure 6 Fig. 6 is a composite cascade reflection spectrum schematic obtained in the application; Figure 7 Fig. 7 is an interference spectrum schematic corresponding to the extracted refractive index detection signal; Figure 8 a schematic diagram of an interference spectrum corresponding to the extracted temperature detection signal; Figure 9 a schematic diagram of a change in optical path difference of the first Fabry-Perot interferometer under different refractive indexes; Figure 10 a schematic diagram of a change in optical path difference of the first Fabry-Perot interferometer under different temperatures; Figure 11 a schematic diagram of a change in optical path difference of the second Fabry-Perot interferometer under different temperatures; In the figure, 1 is a front-end protective cap, 2 is a fiber sensing device, 3 is a high-temperature-resistant ceramic glue, 4 is an outer packaging tube, 5 is a fixed tube, 6 is a transmission fiber, 7 is a rubber ring, 11 is an inner thread, 12 is an outer air hole, 21 is a photonic crystal fiber, 22 is a hollow Bragg fiber, 23 is a hollow capillary fiber, 24 is a first Fabry-Perot interferometer, 25 is a second Fabry-Perot interferometer, 26 is a fiber air hole, 27 is a fiber cavity, 28 is a central cavity, 29 is a connecting fiber, 41 is a central through hole, 42 is an outer thread, 43 is a cavity, 51 is a continuous white light source, 52 is a fiber amplifier, 53 is a fiber circulator, 54 is a sensing terminal, 55 is a spectrometer, 56 is a data processor, and 57 is a computer. DETAILED DESCRIPTION

[0020] To make the purposes, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0021] As shown in Figures 1-4 The present application provides a high-temperature and high-pressure resistant fiber cascade refractive index-temperature dual-parameter integrated sensor, which comprises a packaging structure, a fiber sensing device 2, and a transmission fiber 6. The fiber sensing device 2 comprises a photonic crystal fiber 21, a hollow Bragg fiber 22, a connecting fiber 29, and a hollow capillary fiber 23 connected in sequence. The hollow capillary fiber 23 at the end of the fiber sensing device 2 is connected with the transmission fiber 6.

[0022] The photonic crystal fiber 21, the hollow Bragg fiber 22, and the connecting fiber 29 form a first Fabry-Perot interferometer 24 for measuring the refractive index. The connecting fiber 29, the hollow capillary fiber 23, and the transmission fiber 6 form a second Fabry-Perot interferometer 25 for measuring the temperature.

[0023] The optical fiber sensitive device 2 is arranged in the packaging structure, and the side wall of the packaging structure is provided with an external air hole 12 at a position opposite to the photonic crystal fiber 21; the optical fiber sensitive device 2 transmits a sensing signal to the outside of the packaging structure through the transmission optical fiber 6.

[0024] Specifically, as shown in Figure 1 、 3 , 4, in the embodiment, the packaging structure includes a front-end protective cap 1 and an outer packaging tube 4; the outer packaging tube 4 is provided with a central through hole 41 for accommodating the transmission optical fiber 6, and one end of the central through hole 41 is provided with a cavity 43 for accommodating the optical fiber sensitive device 2; the front-end protective cap 1 is fixedly connected to the outer packaging tube 4 and closes the cavity 43; the front-end protective cap 1 is provided with a plurality of external air holes 12.

[0025] Further, in the embodiment, the front-end protective cap 1 is provided with an internal thread 11 at the center, the outer packaging tube 4 is provided with an external thread 42 at the outer periphery, the front-end protective cap 1 is connected to the outer packaging tube 4 through the thread, and the effectiveness of the packaging protection is ensured by setting the high-temperature-resistant anaerobic inorganic glue reinforcement at the thread.

[0026] In the embodiment, the packaging structure composed of the front-end protective cap 1 and the outer packaging tube 4 can protect the optical fiber sensitive device 2 from being damaged, and the external air holes 12 arranged on the packaging structure can enable the external physical quantity to act on the optical fiber sensitive device 2 of the sensor.

[0027] In the embodiment, the connecting optical fiber 29 and the transmission optical fiber 6 are both single-mode optical fibers.

[0028] Further, as shown in Figure 2 , in the embodiment, the hollow Bragg fiber 22 is provided with a fiber cavity 27 at the center, and the cylindrical wall of the fiber cavity 27 has a Bragg structure with a periodic modulation of refractive index; the photonic crystal fiber 21 is provided with a plurality of penetrating fiber air holes 26 at a position corresponding to the fiber cavity 27.

[0029] Specifically, through the external air hole 12 and the fiber air hole 26 on the photonic crystal fiber 21, it can be ensured that the gas molecules can enter the first Fabry-Perot interferometer 24 and be detected by the first Fabry-Perot interferometer 24. Specifically, the diameter of the external air hole 12 should not be set too large, preferably less than 2 mm, to prevent damage to the sensor sensitive unit caused by the gas impact. In the embodiment, the diameter of the external air hole 12 is 1 mm. The number of external air holes 12 can be 3-10, preferably 8.

[0030] In the embodiment, the fiber air hole 26 on the photonic crystal fiber 21 has a diameter of about 1-5 μm, and 3 μm is used in the embodiment. The fiber air hole 26 can be provided in multiple numbers, for example, 5-20. The diameter of the fiber cavity 27 in the center of the hollow Bragg fiber 22 is 20-50 μm, and the diameter of the fiber cavity 27 used in the embodiment is 32 μm.

[0031] Specifically, as shown in Figure 2 , in the embodiment, the hollow capillary fiber 23 is provided with a central cavity 28 in the center. The hollow capillary fiber 23 and the connecting fiber 29 and the transmission fiber 6 at both ends form a closed second Fabry-Perot interferometer 25, which is not in communication with the outside and thus is not sensitive to refractive index changes; the hollow capillary fiber 23 will expand at high temperatures and is only sensitive to temperature; in order to avoid the effect of external pressure changes on the hollow capillary fiber 23 and cause measurement errors, the length of the hollow capillary fiber 23 should be less than 200 μm.

[0032] Further, in the embodiment, the central cavity 28 in the center of the hollow capillary fiber 23 has a diameter of 20-60 μm, and 50 μm or 30 μm can be selected, and increasing the thickness of the tube wall can further avoid deformation caused by pressure changes.

[0033] Further, in the embodiment, the outer end face of the photonic crystal fiber 21, i.e. Figure 2 , the leftmost end face is beveled or roughened to avoid forming multiple levels of interference. Multiple levels of interference will result in the refractive index signal and temperature signal of the sensor being unable to be effectively extracted, which is not conducive to demodulation accuracy; specifically, when processing the outer end face of the photonic crystal fiber 21, it is necessary to ensure that the fiber air hole 26 is not blocked.

[0034] Further, as shown in Figure 1 , the high-temperature and high-pressure resistant fiber cascade refractive index-temperature dual-parameter integrated sensor in the embodiment further comprises a fixing tube 5 provided in the central through hole 41, and the transmission fiber 6 is provided in the fixing tube 5; the fixing tube 5 is provided with high-temperature resistant ceramic glue 3 near one end of the fiber sensing device 2, and the high-temperature resistant ceramic glue 3 is used to seal and fix the transmission fiber 6, the fixing tube 5, and the outer packaging tube 4; the end of the fixing tube 5 away from the fiber sensing device 2 is connected and fixed with the outer packaging tube 4 through the rubber ring 7.

[0035] Further, in the embodiment, the fixed tube 5 is made of high-temperature-resistant corundum. In the embodiment, the fixed tube 5 has an inner diameter of 130 μm, which is greater than the diameter of the transmission optical fiber 6, so that the transmission optical fiber 6 can pass through; the main body of the transmission optical fiber 6 is arranged at the center of the fixed tube 5 and is used to transmit a spectrum signal, and the two have coaxial axes; the signal transmission in the transmission optical fiber 6 is bidirectional, that is, both incident light and reflected light spectrum carrying physical quantities are transmitted, and the two do not interfere with each other.

[0036] Specifically, in the embodiment, the photonic crystal fiber 21, the hollow Bragg fiber 22, the connecting fiber 29, and the hollow capillary fiber 23 are all made of quartz material. In addition, the transmission optical fiber 6 is also made of quartz material, which can ensure that the sensor can withstand a high temperature of 1100°C without coating or using a carbon coating layer. In the embodiment, the splicing between the photonic crystal fiber 21, the hollow Bragg fiber 22, the connecting fiber 29, the hollow capillary fiber 23, and the transmission optical fiber 6 can be completed by using an optical fiber fusion splicer by using arc discharge technology. By adjusting the discharge power, discharge time, discharge interval, and other parameters, the fusion splicing of different optical fibers can be well completed.

[0037] In addition, in the embodiment, the outer diameters of the photonic crystal fiber 21, the hollow Bragg fiber 22, the connecting fiber 29, the hollow capillary fiber 23, and the transmission optical fiber 6 are all 125 μm, which has good size compatibility.

[0038] Specifically, in the embodiment, the front-end protective cap 1 and the outer packaging tube 4 in the packaging structure are made of zirconia ceramic material with a temperature resistance of more than 1500°C.

[0039] The working process of the high-temperature-resistant and high-pressure optical fiber cascade refractive index-temperature dual-parameter integrated sensor in the embodiment for refractive index and temperature detection is as follows: when broadband light is input into the optical fiber sensitive device 2 through the transmission optical fiber 6, the light first passes through the second Fabry-Perot interferometer 25 and then passes through the first Fabry-Perot interferometer 24. The light will undergo double-beam interference in the second Fabry-Perot interferometer 25 and the first Fabry-Perot interferometer 24, and the superposition of the two will form a cascade composite reflection spectrum. After the reflection spectrum is received by the transmission optical fiber 6, the single interference spectrum carrying the refractive index and temperature information is extracted by the Fourier transform filtering method, and the refractive index and temperature signals to be measured can be obtained by demodulation.

[0040] The working principle of the refractive index detection is as follows: when the refractive index of the external environment where the sensor is located increases, the gas molecules enter the packaging structure, and then enter the fiber cavity 27 of the hollow Bragg fiber 22 through the fiber air hole 26 of the photonic crystal fiber 21. The increase of the gas molecules causes the increase of the air medium density and the change of the refractive index between the two interference planes of the first Fabry-Perot interferometer 24, and further causes the increase of the optical path difference of the first Fabry-Perot interferometer 24. The refractive index and the optical path difference of the first Fabry-Perot interferometer 24 are linearly related. When the external refractive index decreases, the whole process presents a reversible change, and the optical path difference of the first Fabry-Perot interferometer 24 decreases. Therefore, by using the linear relationship between the refractive index and the optical path difference of the first Fabry-Perot interferometer 24, the change of the optical path difference can be demodulated from the extracted interference spectrum carrying the refractive index information, so that the value of the refractive index can be detected in real time.

[0041] Further, in the embodiment, when the refractive index of the external environment where the sensor is located changes, the gas molecules cannot enter the inside of the second Fabry-Perot interferometer 25 because the second Fabry-Perot interferometer 25 is closed. Therefore, the second Fabry-Perot interferometer 25 is not sensitive to the change of the refractive index.

[0042] The working principle of the temperature detection is as follows: when the temperature of the external environment where the sensor is located increases, the length of the hollow capillary fiber 23 increases due to thermal expansion, that is, the physical cavity length of the second Fabry-Perot interferometer 25 increases, and further causes the increase of the optical path difference of the second Fabry-Perot interferometer 25. The temperature and the optical path difference of the second Fabry-Perot interferometer 25 are exponentially related. When the external temperature decreases, the whole process presents a reversible change, and the optical path difference of the second Fabry-Perot interferometer 25 decreases. Therefore, by using the exponential relationship between the temperature and the optical path difference of the second Fabry-Perot interferometer 25, the change of the optical path difference can be demodulated from the extracted interference spectrum carrying the temperature information, so that the value of the temperature can be detected in real time.

[0043] Further, in the embodiment, the high-temperature and high-pressure resistant fiber cascade refractive index-temperature dual-parameter integrated sensor can detect the refractive index and the temperature at the same time at high temperature. The change of the temperature causes the expansion of the gas molecules, thereby reducing the refractive index. The temperature also affects the optical path difference of the first Fabry-Perot interferometer 24. Therefore, the refractive index needs to be compensated for the refractive index error caused by the temperature in the high-temperature environment.

[0044] Specifically, in the embodiment, at high temperature, the change of the refractive index and the temperature caused by the change of the optical path difference of the first Fabry-Perot interferometer 24 can be represented as: ; (1) In formula (1), This represents the change in optical path difference of the first Fabry-Perot interferometer 24. and These represent the changes in optical path difference of the first Fabry-Perot interferometer 24 caused by changes in temperature and refractive index, respectively. and These represent the temperature sensitivity and refractive index sensitivity of the first Fabry-Perot interferometer 24, respectively. and These represent the change in temperature and the change in refractive index, respectively.

[0045] Furthermore, in this embodiment, the mechanism by which the second Fabry-Perot interferometer 25 senses the real-time temperature to compensate for the refractive index test error at high temperatures is as follows: First, through temperature calibration, the change in optical path difference caused by temperature variation in the first Fabry-Perot interferometer 24 is established. With temperature change The relationship, that is, determining the temperature sensitivity of the first Fabry-Perot interferometer 24. Furthermore, the refractive index sensitivity of the first Fabry-Perot interferometer 24 is determined through refractive index calibration. Then, the real-time temperature change was detected using a second Fabry-Perot interferometer 25. Finally, the change in optical path difference of the first Fabry-Perot interferometer 24 was measured. That is, the accurate change in refractive index can be calculated. The calculation formula is: ; (2) Therefore, the temperature compensation mechanism in this embodiment can greatly improve the accuracy of refractive index sensing under high temperature conditions.

[0046] Furthermore, such as Figure 1 , 2 As shown, in this embodiment, the first Fabry-Perot interferometer 24 for refractive index detection and the second Fabry-Perot interferometer 25 for temperature detection are connected in series in the optical path. They can work simultaneously and obtain real-time values ​​of refractive index and temperature. The temperature compensation mechanism is implemented in the demodulation algorithm and there is no time delay.

[0047] Furthermore, for the open structure of the first Fabry-Perot interferometer 24, detecting the refractive index is the most basic sensing mechanism. For coupling forms where physical quantities change the refractive index, such as sound signals and pressure signals changing the refractive index of the medium during propagation, the structure of this embodiment can, in principle, also sense sound signals and pressure signals. This embodiment can be expanded at the application level.

[0048] Example 2 like Figure 5 As shown, Embodiment 2 of the present invention provides a high-temperature and high-pressure resistant fiber optic cascaded refractive index-temperature dual-parameter integrated sensor. Similar to Embodiment 1, it includes a packaging structure, a sensing terminal 54 formed by a fiber optic sensing device 2 and a transmission fiber 6. In addition, this embodiment also includes a continuous white light source 51, a fiber optic amplifier 52, a fiber optic circulator 53, a spectrometer 55, a data processor 56, and a computer 57. The broadband light generated by the continuous white light source 51 is first amplified by the fiber optic amplifier 52, and then transmitted to the sensing terminal 54 through the fiber optic circulator 53. The cascaded reflection spectrum generated in the fiber optic sensing device 2 in the sensing terminal 54 is output again through the fiber optic circulator 53 and transmitted to the spectrometer 55 for spectral data acquisition. Then, the spectral data is transmitted to the data processor 56 for data processing and demodulation analysis to obtain the actual values ​​of the refractive index and temperature to be measured. The demodulation results are transmitted to the computer 57 for display. The spectrometer 55 can be a miniature high-precision spectrometer.

[0049] Specifically, in this embodiment, the data processor 56 calculates the refractive index and temperature to be measured using the following method: Step 1: [The following text appears to be a separate, unrelated section:] ... Figure 6 The composite cascaded reflection spectrum shown is subjected to a fast Fourier transform to convert the spectral signal from the wavelength domain to the frequency domain; then, a custom bandpass filter is used to filter and extract the refractive index detection frequency domain signal and the temperature detection frequency domain signal from the frequency domain signal.

[0050] Step 2: Perform an inverse fast Fourier transform on the refractive index detection frequency domain signal and the temperature detection frequency domain signal to obtain the interference spectrum corresponding to the refractive index detection signal and the interference spectrum corresponding to the temperature detection signal, as shown below. Figure 7 , 8 As shown.

[0051] Step 3: Using the least mean square error comparison method, calculate the real-time optical path difference between the interference spectrum corresponding to the refractive index detection signal and the interference spectrum corresponding to the temperature detection signal obtained in Step 2. Subtract the initial optical path difference of the sensor from each, and you can obtain the change in optical path difference between the first Fabry-Perot interferometer 24 and the second Fabry-Perot interferometer 25. and .

[0052] Step 4: Calculate the temperature and refractive index to be measured. The calculation formula is as follows: (3) (4) in, This represents the change in optical path difference of the second Fabry-Perot interferometer 25. a function of the temperature change amount , the real-time temperature can be demodulated, and the refractive index can be calculated by substituting formula (4).

[0053] The function relationship between the optical path difference change amount of the second Fabry-Perot interferometer 25 and the temperature change amount can be calibrated in advance. The temperature sensitivity and the refractive index sensitivity of the first Fabry-Perot interferometer 24 also need to be calibrated in advance.

[0054] As shown in Figure 6 , it is the composite cascade reflection spectrum collected by the spectrometer 55 in the embodiment; as shown in Figure 7 , it is an interference spectrum diagram corresponding to the extracted refractive index detection signal; as shown in Figure 8 , it is an interference spectrum diagram corresponding to the extracted temperature detection signal.

[0055] Figure 9 The first Fabry-Perot interferometer 24 optical path difference change amount under different refractive index conditions measured in the embodiment of the application is shown in the figure; from Figure 9 , it can be seen that the refractive index and the first Fabry-Perot interferometer 24 optical path difference change amount present a linear relationship, and the slope is determined by linear fitting, that is, the refractive index sensitivity of the first Fabry-Perot interferometer 24. Figure 10 The first Fabry-Perot interferometer 24 optical path difference change amount under different temperatures measured in the embodiment of the application is shown in the figure; from Figure 10 , it can be seen that the temperature and the first Fabry-Perot interferometer 24 optical path difference change amount present a linear relationship, and the slope is determined by linear fitting, that is, the temperature sensitivity of the first Fabry-Perot interferometer 24.

[0056] Figure 11 The second Fabry-Perot interferometer 25 optical path difference change amount under different temperatures measured in the embodiment of the application is shown in the figure; from Figure 11 , it can be seen that the temperature change amount and the second Fabry-Perot interferometer 25 optical path difference change amount present an exponential relationship, and the exponential equation is fitted by an exponential equation, that is: ; (5) Wherein, a, b, c, d, m, n are fitting parameters, and e represents the base number of natural logarithm; it can be obtained by fitting the data measured by the calibration experiment. ThroughFigure 11 The relationship obtained by data fitting can be expressed as: ; (6) Therefore, in this embodiment, after determining the fitting parameters a, b, c, d, m, n of the exponential equation through experimental calibration and fitting, the change amount of the optical path difference of the second Fabry-Perot interferometer 25 is calculated as Substituting equation (5) can directly demodulate the temperature change amount , and the refractive index change amount can be calculated by combining equation (4) .

[0057] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high-temperature and high-pressure resistant optical fiber cascade refractive index-temperature dual-parameter integrated sensor, characterized in that, It comprises a packaging structure, a fiber sensitive device (2) and a transmission fiber (6); The fiber sensitive device (2) comprises a photonic crystal fiber (21), a hollow Bragg fiber (22), a connecting fiber (29) and a hollow capillary fiber (23) connected in sequence; the hollow capillary fiber (23) at the end of the fiber sensitive device (2) is connected with the transmission fiber (6); The photonic crystal fiber (21), the hollow Bragg fiber (22) and the connecting fiber (29) form a first Fabry-Perot interferometer (24) for measuring the refractive index, and the connecting fiber (29), the hollow capillary fiber (23) and the transmission fiber (6) form a second Fabry-Perot interferometer (25) for measuring the temperature. The fiber sensitive device (2) is arranged in the packaging structure, and an air hole (12) is arranged at a position opposite to the photonic crystal fiber (21) on the side wall of the packaging structure; the fiber sensitive device (2) transmits a sensing signal to the outside of the packaging structure through the transmission fiber (6). 2.The high-temperature and high-pressure resistant optical fiber concatenated refractive index-temperature dual-parameter integrated sensor of claim 1, wherein, The packaging structure comprises a front-end protective cap (1) and an outer packaging tube (4); The outer packaging tube (4) is provided with a central through hole (41) for accommodating the transmission fiber (6), and one end of the central through hole (41) is provided with a cavity (43) for accommodating the fiber sensitive device (2); the front-end protective cap (1) is fixedly connected with the outer packaging tube (4) and seals the cavity (43); a plurality of air holes (12) are arranged on the front-end protective cap (1). 3.The high-temperature and high-pressure resistant optical fiber concatenated refractive index-temperature dual-parameter integrated sensor of claim 2, wherein, The front-end protective cap (1) is provided with an internal thread (11) in the center, the outer packaging tube (4) is provided with an external thread (42) on the outer periphery, the front-end protective cap (1) is connected with the outer packaging tube (4) through the threads, and is reinforced by high-temperature-resistant anaerobic inorganic glue. 4.The high-temperature and high-pressure resistant optical fiber concatenated refractive index-temperature dual-parameter integrated sensor of claim 1, wherein, The hollow Bragg fiber (22) is provided with a fiber cavity (27) in the center, and the cylindrical wall outside the fiber cavity (27) is provided with a Bragg structure with a periodic refractive index modulation; a plurality of fiber air holes (26) are arranged at the corresponding position of the fiber cavity (27) in the center of the photonic crystal fiber (21).

5. The high-temperature and high-pressure resistant optical fiber concatenated refractive index-temperature dual-parameter integrated sensor according to claim 1, characterized in that, The hollow capillary fiber (23) is provided with a central cavity (28) in the center.

6. The high-temperature and high-pressure resistant optical fiber concatenated refractive index-temperature dual-parameter integrated sensor according to claim 1, characterized in that, The outer side end face of the photonic crystal fiber (21) is beveled or roughened to avoid forming multiple levels of interference.

7. The high-temperature and high-pressure resistant optical fiber concatenated refractive index-temperature dual-parameter integrated sensor according to claim 1, characterized in that, It further comprises a fixing tube (5) arranged in the central through hole (41), and the transmission fiber (6) is arranged in the fixing tube (5); the fixing tube (5) is provided with high-temperature-resistant ceramic glue (3) at one end close to the fiber sensitive device (2), the high-temperature-resistant ceramic glue (3) is used for sealing and fixing the transmission fiber (6), the fixing tube (5) and the outer packaging tube (4); the other end of the fixing tube (5) away from the fiber sensitive device (2) is connected and fixed with the outer packaging tube (4) through a rubber ring (7). 8.The high-temperature and high-pressure resistant optical fiber concatenated refractive-index-temperature dual-parameter integrated sensor of claim 7, wherein, The material of the fixing tube (5) is high-temperature-resistant corundum.

9. The high-temperature and high-pressure resistant optical fiber concatenated refractive index-temperature dual-parameter integrated sensor according to claim 1, characterized in that, The photonic crystal fiber (21), the hollow Bragg fiber (22), the connecting fiber (29), the hollow capillary fiber (23) and the transmission fiber (6) are made of quartz material, and the packaging structure is made of zirconia ceramic material with a temperature resistance of more than 1500 DEG C.

10. The high-temperature and high-pressure resistant optical fiber concatenated refractive index-temperature dual-parameter integrated sensor according to claim 1, characterized in that, The continuous white light source (51), the fiber amplifier (52), the fiber circulator (53), the optical spectrum analyzer (55) and the data processor (56) are also included. The broadband light generated by the continuous white light source (51) is first amplified in optical power by the fiber amplifier (52), and then transmitted to the transmission fiber (6) and the fiber sensitive device (2) through the fiber circulator (53). The cascade reflection spectrum generated in the fiber sensitive device (2) is output again through the fiber circulator (53) and then transmitted to the optical spectrum analyzer (55) for spectral data acquisition. Then the spectral data is transmitted to the data processor (56) for data processing and demodulation analysis to obtain the refractive index and temperature to be measured. The formula for calculating the temperature and refractive index to be measured obtained by the data processor (56) is: ； ； wherein, and respectively represent a temperature change amount and a refractive index change amount, represents a change amount of an optical path difference of the first Fabry-Perot interferometer (24); represents a change amount of an optical path difference of the second Fabry-Perot interferometer (25); respectively represent a refractive index sensitivity and a temperature sensitivity of the first Fabry-Perot interferometer (24), represents a change amount of an optical path difference of the second Fabry-Perot interferometer (25) and a temperature change amount have a functional relationship, a, b, c, d, m, n are all fitting parameters, and e represents a base number of a natural logarithm.

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