Manufacturing and calibration system of double nested and sensitized optical fiber F-P cavity pressure sensor

Abstract

The application provides a double-nested sensitization type optical fiber F-P cavity pressure sensor manufacturing and calibration system and belongs to the technical field of optical fiber sensing. The single-mode optical fiber is partially inserted into the first hollow optical fiber for fusion splicing; the hollow end face of the first hollow optical fiber after fusion splicing is ground to obtain a single-mode optical fiber with a flat end face and a nested structure; then the single-mode optical fiber with the nested structure is inserted into the second hollow optical fiber for fusion splicing to obtain a single-mode optical fiber after secondary fusion splicing; the hollow end of the second hollow optical fiber is ground to obtain a fiber with a double-layer nested structure; the fiber with the double-layer nested structure is fusion spliced with a multi-mode optical fiber; the other end face of the multi-mode optical fiber after fusion splicing is ground to reduce the length of the multi-mode optical fiber, and a solid cavity is obtained as a diaphragm; and the diaphragm is subjected to etching and thinning treatment.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a manufacturing and calibration system for a double-nested enhanced fiber optic FP cavity pressure sensor. Background Technology

[0002] Fiber optic FP cavity pressure sensors, based on the principle of optical interferometry, measure pressure by acquiring the change in the FP cavity length caused by external pressure. These sensors possess outstanding advantages such as high sensitivity, resistance to electromagnetic interference, corrosion resistance, and small size, making them valuable for applications in biomedicine, earthquake monitoring, industrial equipment condition monitoring, and underwater exploration. In particular, the human pressure monitoring scenario in the biomedical field demands extremely high sensor sensitivity. For example, the normal range of central venous pressure is only 2-15 cmH2O, equivalent to approximately 0.196-1.47 kPa, requiring sensors with ultra-high sensitivity to accurately capture minute pressure signals.

[0003] According to the theory of small deflection deformation in thin plates, the pressure sensitivity of fiber optic FP pressure sensors is closely related to the geometric and material parameters of the sensitive diaphragm. To obtain fiber optic FP pressure sensors with ultra-high sensitivity, it is necessary to fabricate ultra-thin, uniformly thick, and structurally intact sensitive diaphragms. Currently, the main methods for thinning fiber optic FP sensor diaphragms include mechanical grinding, femtosecond laser processing, and chemical etching. Mechanical grinding uses a precision grinding machine to physically grind the diaphragm. This method has the advantage of being relatively mature and producing a good surface quality after grinding. However, when the diaphragm thickness is ground to below 5 μm, the mechanical strength of the fiber decreases sharply, making it extremely sensitive to processing stress. At this point, the axial runout of the grinding disc itself, the minute vibrations of the feed mechanism, and the uncertainty of manual operation can all easily lead to diaphragm breakage. Furthermore, it is difficult to achieve real-time accurate monitoring and control of the diaphragm thickness during grinding; it usually relies on experience or post-grinding measurements, making closed-loop feedback adjustment during processing impossible. Femtosecond laser processing utilizes ultrafast laser pulses to precisely remove material, offering advantages such as high processing accuracy and a small heat-affected zone. However, femtosecond laser processing equipment is expensive, with high maintenance costs, resulting in high manufacturing costs for individual sensors. Furthermore, laser pulses can induce defects within the fiber material, affecting the long-term reliability of the sensor. Chemical etching typically uses hydrofluoric acid solution to etch the main component of the fiber, SiO2. This method removes material through a chemical reaction, theoretically without introducing mechanical stress, achieving nanoscale precision material removal. Its manufacturing cost is far lower than femtosecond laser processing, making it one of the ideal methods for obtaining ultrathin films. However, traditional chemical etching processes suffer from poor etching uniformity, uncontrollable etching processes, and difficulty in real-time monitoring.

[0004] Therefore, a manufacturing and calibration system for a double-nested enhanced fiber optic FP cavity pressure sensor is provided. This system enables high-precision chemical etching to thin the fiber optic FP sensor diaphragm. It can monitor the sensitivity of the fiber optic FP cavity pressure sensor in real time during the etching process and quickly stop the etching to achieve thickness control. Temperature calibration, pressure calibration, and temperature-pressure coupling tests can be performed without the need for transportation. Summary of the Invention

[0005] In view of this, the present invention proposes a manufacturing and calibration system for a double-nested enhanced fiber FP cavity pressure sensor, which improves upon the existing fiber optic FP sensor diaphragm thinning technology, which suffers from the problems of easy breakage of mechanically ground diaphragms, high cost of femtosecond laser processing, and uneven and uncontrollable traditional chemical etching.

[0006] This invention provides a manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor, comprising: The dual-station corrosion thinning and dynamic calibration module is used to perform corrosion reaction or interrupt the corrosion reaction on the diaphragm of the pre-prepared double-nested enhanced fiber optic FP cavity pressure sensor, and to perform temperature calibration, pressure calibration and temperature-pressure coupling experiment during the corrosion process. The pressurization module is used to apply pressure to the dual-station etching and thinning and dynamic calibration module, and to collect the pressure change data of the dual-nested enhanced fiber optic FP cavity pressure sensor in real time. The control module is connected to the dual-station corrosion thinning and dynamic calibration module and the pressurization module respectively. It is used to change the corrosion state of the diaphragm of the double-nested enhanced fiber optic FP cavity pressure sensor or interrupt the corrosion, and also control the start or stop of the pressurization module. The demodulation module is used to receive the spectral information of the double-nested enhanced fiber optic FP cavity pressure sensor during the corrosion process, and obtain the cavity length information of the sensor through demodulation. The real-time sensitivity display module is used to acquire pressure change data collected by the pressurization module and cavity length information of the sensor obtained by the demodulation module. Based on the pressure change data and cavity length change, it calculates and outputs the sensitivity of the double-nested enhanced fiber optic FP cavity pressure sensor at the current diaphragm thickness in real time. When the sensitivity reaches the expected value, it sends a trigger signal to the control module to interrupt the corrosion reaction.

[0007] Based on the above technical solutions, the preferred method for pre-fabricating a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor includes the following steps: Step 1: Fix the single-mode fiber and the first hollow fiber to the two clamping ends of the fiber optic fusion splicer, respectively. Insert the single-mode fiber into the first hollow fiber. Use the high temperature generated by the electrode discharge of the fiber optic fusion splicer to achieve the fusion connection between the single-mode fiber and the first hollow fiber. Step 2: Under the observation of a microscope, grind the hollow end face of the first hollow fiber after fusion splicing until the hollow part of the first hollow fiber is completely ground to obtain a single-mode fiber with a flat end face and a nested structure. Then, use an ultrasonic cleaner to clean the end face of the single-mode fiber with the nested structure after grinding to remove the powder residue generated during the grinding process. Step 3: Fix the single-mode fiber with nested structure obtained in Step 2 and the second hollow fiber to the two clamping ends of the fiber optic fusion splicer, respectively. Insert the single-mode fiber with nested structure into the second hollow fiber. Use the high temperature generated by the electrode discharge of the fiber optic fusion splicer to achieve the fusion connection between the single-mode fiber with nested structure and the second hollow fiber, and obtain the single-mode fiber after secondary fusion splicing. Step 4: Under the observation of a microscope, the hollow end of the second hollow fiber is ground to obtain an optical fiber with a double-layer nested structure. Then, an ultrasonic cleaner is used to clean the end face of the ground double-layer nested structure optical fiber to remove the powder residue generated during the grinding process. Step 5: Fix the optical fiber with double-layer nested structure and the multimode optical fiber obtained in Step 4 to the two clamping ends of the optical fiber fusion splicer, and use the high temperature generated by the electrode discharge of the optical fiber fusion splicer to achieve the fusion connection of the optical fiber with double-layer nested structure and the multimode optical fiber. Step 6: Under the observation of a microscope, grind the other end face of the fused multimode fiber to reduce the length of the multimode fiber. The resulting solid cavity is a diaphragm. The diaphragm is then etched and thinned to obtain a double-nested enhanced fiber FP cavity pressure sensor.

[0008] Preferably, the inner diameter of the first hollow fiber is adapted to the outer diameter of the single-mode fiber, the inner diameter of the second hollow fiber is adapted to the outer diameter of the first hollow fiber, and the outer diameter of the second hollow fiber is adapted to the outer diameter of the multimode fiber.

[0009] Based on the above technical solutions, preferably, the dual-station corrosion thinning and dynamic calibration module includes a hose, a station switching device, an HF solution bottle, a water bottle, two double clamping mechanisms, an electric heating rod, and a hot water tank. The station switching device has a corrosion station and a calibration station respectively at its two ends. The HF solution bottle is positioned at the corrosion station, and the water bottle at the calibration station. The station switching device clamps a double-nested enhanced fiber optic FP cavity pressure sensor and inserts the diaphragm into the HF solution bottle corresponding to the corrosion station for corrosion, or inserts the diaphragm into the water bottle corresponding to the calibration station to interrupt corrosion. A hot water tank is located below the water bottle, and an electric heating rod is installed inside the hot water tank. The hot water tank is also connected to the area where the water bottle is located via a hose. The electric heating rod is used to heat the medium in the hot water tank, and the medium in the hot water tank circulates through the hose to achieve heat exchange with the medium in the water bottle. The two double clamping mechanisms are used for bidirectional sealing and clamping of the HF solution bottle and the water bottle. When the double-nested enhanced fiber optic FP cavity pressure sensor is at the calibration station, temperature calibration, pressure calibration, and temperature-pressure coupling experiments are performed.

[0010] Preferably, the workstation switching device includes a fixed base, an arc-shaped slide rail, a cam follower mechanism, an X-axis sliding guide rail, an X-axis slider, a Y-axis sliding guide rail, and an optical fiber clamping mechanism. The fixed base is fixedly set relative to the ground. The HF solution bottle, the water bottle, the double clamping mechanism, the electric heating rod, and the hot water tank are all set on one side of the fixed base. An arc-shaped slide rail is provided through the top of the fixed base. One end of the cam follower mechanism is hinged to the fixed base, and the other end is embedded in the arc-shaped slide rail. The non-hinged end of the cam follower mechanism is also provided with a Y-axis sliding guide rail. The guide rail is equipped with an optical fiber clamping mechanism and an X-axis slider. The optical fiber clamping mechanism is used to clamp the double-nested enhanced optical fiber FP cavity pressure sensor. The X-axis slider is embedded in the X-axis sliding guide rail and slidably connected to it. The X-axis sliding guide rail and the Y-axis sliding guide rail extend along the width and height directions of the fixed base, respectively. The extreme position on one side of the arc-shaped slide rail corresponds to the etching station, and the extreme position on the other side of the arc-shaped slide rail corresponds to the calibration station. The X-axis slider is used to limit the attitude stability of the Y-axis sliding guide rail and the optical fiber clamping mechanism when they follow the cam follower mechanism.

[0011] A further preferred embodiment of the cam follower mechanism includes a connecting rod, a stepped shaft, a top plate connector, and a guide rail connector. One end of the connecting rod is hinged to a fixed base, and the other end of the connecting rod is provided with a stepped shaft. One end of the stepped shaft is embedded in an arc-shaped slide rail, and the other end of the stepped shaft extends outward through the connecting rod and is connected to the top plate connector. The top plate connector extends radially and is connected to the guide rail connector, which is used to connect with the Y-axis sliding guide rail. The hinged end of the connecting rod is also connected to the output shaft of the stepper motor.

[0012] More preferably, the fiber optic clamping mechanism includes a pressure plate, a flexible sheath, a fiber optic protective sleeve, and threaded fasteners. The pressure plate is mounted on a Y-axis sliding guide rail and extends horizontally away from the Y-axis sliding guide rail. A hollow annular boss is provided on the pressure plate, extending away from the pressure plate. A tapered hole is provided inside the annular boss. The fiber optic protective sleeve and the flexible sheath are sequentially disposed within the tapered hole. A stepped portion is provided on the side of the fiber optic protective sleeve away from the flexible sheath, and the diameter of the stepped portion is larger than the diameter of the non-stepped portion. The fiber optic protective sleeve is arranged around the non-stepped portion and abuts against the end face of the stepped portion and the inner surface of the tapered hole respectively. The fiber optic protective sleeve is provided with a through first hole, and the threaded fastener is provided with a through second hole. The first hole and the second hole are coaxially arranged, and the threaded fastener is threadedly connected to the annular boss. The double-nested enhanced fiber optic FP cavity pressure sensor passes through the second hole and the first hole in sequence and makes the diaphragm extend out of the fiber optic protective sleeve. The size of the diaphragm is adapted to the first hole and the second hole so that the diaphragm can be inserted into the top-open HF solution bottle or water bottle.

[0013] In a further preferred embodiment, both double clamping mechanisms include a base, a lever mechanism, several compression springs, several spring shafts, a transmission pin, a pin, and an elastic washer. The base is parallel to and spaced apart from the pressure plate. Several spring shafts are provided on the base, extending towards the pressure plate. Compression springs are sleeved on the spring shafts. The end of the spring shaft away from the base is connected to the side surface of the HF solution bottle or water bottle via a lug, and the lug is slidably connected to the spring shaft. The upper surface of the HF solution bottle or water bottle abuts against the surface of the pressure plate via an elastic washer. The lever mechanism includes a hinge shaft, a lever arm, a first platform, and a second platform. The platform has a hinge shaft that is hinged to the base. The hinge shaft passes through the center of the lever arm and is fixedly connected to the lever arm. The lever arm has a first platform and a second platform at its two ends, which are hinged to the lever arm. The end face of the first platform abuts against the lower surface of the HF solution bottle or water bottle. A drive pin is provided on the pressure plate, which extends towards the base and abuts against the end face of the second platform. By abutting the upper surface of the HF solution bottle or water bottle and the end face of the second platform respectively, the pressure plate and the drive pin can achieve bidirectional clamping of the HF solution bottle or water bottle.

[0014] In a further preferred embodiment, a buffer elastic pad is provided between the end face of the first platform and the lower surface of the HF solution bottle or water bottle.

[0015] Based on the above technical solutions, preferably, the real-time sensitivity display module is used to acquire pressure change data collected by the pressurization module and cavity length information of the sensor obtained by the demodulation module. It calculates and outputs the sensitivity of the double-nested enhanced fiber optic FP cavity pressure sensor at the current diaphragm thickness in real time based on the pressure change data and cavity length change, according to the following algorithm steps: Step S1: Initialize the sliding window that adapts to the pressure fluctuation cycle, receive the raw cavity length and pressure values ​​collected by the fiber optic FP sensor at the corresponding time in real time, and store the data in the sliding window; the sliding window only retains the latest data segment, and when a new set of data is obtained and the total amount of data exceeds the length of the sliding window, the oldest set of old data is automatically removed. Step S2: Based on the pressure value sequence in the sliding window in Step S1, the pressure values ​​are analyzed in the frequency domain using the continuous wavelet transform method; the sym5 wavelet is selected as the basis function to perform a one-level wavelet decomposition on the pressure value sequence to obtain the approximation coefficients and detail coefficients, and the modulus of the detail coefficients is calculated; based on the local mean and local standard deviation of the pressure values ​​within the window, an adaptive threshold is set, and points with modulus values ​​lower than the threshold and pressure values ​​that are the local minimum values ​​are selected as pressure minimum points. The time and pressure value corresponding to the minimum point are recorded, and pressure maximum tracking is enabled; Step S3: For the pressure minimum point detected in step S2, the same continuous wavelet transform method is used again to track the pressure maximum point immediately adjacent to the minimum point, forming a minimum-maximum pressure extreme point pair, and the time and pressure corresponding to the pressure maximum point are recorded. Step S4: Extract the original cavity length value corresponding to the minimum-maximum pressure extreme point pair from the sliding window, and the cavity length values ​​of the three adjacent cavity length values ​​before and after the extreme point pair together form the cavity length value sequence to be fitted. Step S5: Perform Fourier fitting on the cavity length value sequence to be fitted, obtain the Fourier fitted cavity length value, and calculate the goodness of fit R corresponding to the cavity length value sequence. 2 If the goodness of fit R 2 If the value is greater than or equal to 0.98, the calculated cavity length is obtained by subtracting the Fourier-fitted cavity length from the original cavity length value; if the goodness of fit R... 2 If the value is less than 0.98, then the cavity length value sequence extracted in step 4 is fitted with a fifth-order Chebyshev orthogonal polynomial to obtain the fifth-order Chebyshev fitted cavity length value. The original cavity length value is subtracted from the fifth-order Chebyshev fitted cavity length value to obtain the calculated cavity length value. Step S6: Calculate the difference between the calculated cavity length value and the pressure value at the corresponding time for the pressure extreme point. The ratio of the difference in cavity length value to the difference in pressure value is the sensitivity of the extreme point at the corresponding time.

[0016] The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor provided by this invention has the following advantages compared to the prior art: 1. To address the issue of delayed diaphragm corrosion termination in existing fiber optic FP sensor technologies, a dual-station integrated system for dynamic calibration of corrosion thinning was designed. The system automatically switches between the HF acid corrosion station and the clean water station for the dual-nested enhanced-sensitivity fiber optic FP cavity pressure sensor via a station switching device. When the actual sensitivity reaches the desired sensitivity, the system can quickly switch to the clean water station to terminate the reaction, thus preventing diaphragm rupture caused by residual corrosion solution.

[0017] 2. To address the issues of unstable fiber clamping and easy shaking and breakage during the corrosion process, an optimized fiber clamping mechanism and a double clamping mechanism were designed. The fiber clamping mechanism can achieve axial bidirectional positioning of the fiber optic FP sensor, and the double clamping mechanism can achieve bidirectional sealing and clamping of the solution bottle, thereby ensuring the stability and safety of the corrosion process.

[0018] 3. To address the issues of low corrosion accuracy and inability to monitor sensitivity in real time in existing technologies, a corrosion-monitoring closed-loop control system was constructed. This system uses a demodulation system and a pressurization device to collect real-time data on the cavity length and pressure changes of the fiber optic FP sensor, calculates and provides feedback on sensitivity in real time, and automatically terminates corrosion when a threshold is reached. This ensures that the diaphragm thickness and sensitivity of the fiber optic FP sensor are precisely matched. A corresponding sensitivity calculation algorithm is also provided.

[0019] 4. To address the issues of existing equipment having limited functionality and requiring additional sensor transport, a multi-functional station integrating precision etching, termination, calibration, and coupling experiments has been developed. Subsequent experimental operations can be completed without the need for transport, reducing diaphragm damage and positioning deviation of fiber optic FP sensors and improving the efficiency of preparation and testing.

[0020] 5. To address the issue of insufficient sensitivity in traditional fiber optic FP sensors, a double-nested structure design is adopted to enhance sensitivity. This structure increases the effective radius of the diaphragm in the fiber optic FP sensor, thereby enhancing the diaphragm's response sensitivity to pressure and improving the measurement accuracy of the fiber optic FP sensor. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the overall structure of the equipment for manufacturing and calibrating the double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor of the present invention. Figure 2This is a perspective view of the dual-station etching and thinning and dynamic calibration module of the manufacturing and calibration system for the dual-nested enhanced-sensitivity fiber optic FP cavity pressure sensor of the present invention. Figure 3 This is a schematic diagram of the workstation switching device in the manufacturing and calibration system for the double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor of the present invention. Figure 4 This is a schematic diagram of the fiber clamping mechanism in the manufacturing and calibration system for the double-nested enhanced-sensitivity fiber FP cavity pressure sensor of the present invention. Figure 5 This is a schematic diagram of the dual clamping mechanism of the manufacturing and calibration system for the dual-nested enhanced-sensitivity fiber optic FP cavity pressure sensor of the present invention. Figure 6 This is a flowchart illustrating the fabrication process of the double-nested enhanced-sensitivity fiber FP cavity pressure sensor in the manufacturing and calibration system of the present invention. Figure 7 This is a flowchart of the sensitivity calculation algorithm during the corrosion thinning process of the manufacturing and calibration system of the double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor of the present invention. Figure 8 This is a flowchart of the control system for the manufacturing and calibration system of the double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor of the present invention. Figure 9 This is a schematic diagram of the overall system operation flow of the manufacturing and calibration system for the double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor of the present invention.

[0023] Figure label: 101. Dual-station etching and thinning and dynamic calibration module; 102. Control module; 103. Pressurization module; 104. Demodulation module; 105. Sensitivity real-time display module; 106. Double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor; 201. Single-mode fiber; 202. First hollow-core fiber; 203. Nested single-mode fiber; 204. Second hollow-core fiber; 205. Double-layer nested fiber; 206. Multimode fiber; 207. Solid cavity; I. Hoses; II. Station switching device; III. HF solution bottle; IV. Clear water bottle; V. Double clamping device; VI. Electric heating rod; VII. Hot water tank; 1. Arc-shaped slide rail; 2. Cam follower mechanism; 2.1 Connecting rod; 2.2 Stepped shaft; 2.3 Top plate connector; 2.4 Guide rail connector; 3. Fixed base; 4. X-axis sliding guide rail; 5. X-axis slider; 6. Y-axis sliding guide rail; 7. Fiber optic clamping mechanism; 7.1 Pressure plate; 7.2 Flexible sheath; 7.3 Fiber optic protective sleeve; 7.4 Threaded fasteners; 51. Spring shaft; 52. Compression spring; 53. Base; 54. Lever structure; 55. Transmission pin; 56. Pin; 57. Elastic washer; 4.1. Second platform; 4.2. Buffer elastic pad; 4.3. First platform; 4.4. Support seat; 4.5. Hinge shaft; 4.6. Lever arm. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Currently, the main methods for thinning diaphragms in fiber optic FP sensors include mechanical polishing, femtosecond laser processing, and chemical etching. Mechanical polishing uses a precision polishing machine to physically grind the diaphragm. Its advantage lies in its relatively mature technology and good surface quality after polishing. However, when the diaphragm thickness is ground to below 5 μm, the mechanical strength of the fiber decreases sharply, making it extremely sensitive to processing stress. At this point, axial runout of the polishing disc itself, minute vibrations of the feed mechanism, and uncertainties in manual operation can easily lead to diaphragm breakage. Furthermore, it is difficult to achieve real-time and accurate monitoring and control of the diaphragm thickness during polishing; it usually relies on experience or post-polishing measurements, making closed-loop feedback adjustment during processing impossible. Femtosecond laser processing utilizes ultrafast laser pulses to precisely remove material, offering advantages such as high processing accuracy and a small heat-affected zone. However, femtosecond laser processing equipment is expensive, with high maintenance costs, resulting in high manufacturing costs per sensor. Moreover, laser pulses may induce defects within the fiber material, affecting the long-term reliability of the sensor. Chemical etching typically uses hydrofluoric acid solution to etch SiO2, the main component of optical fibers. This method removes material through a chemical reaction, theoretically without introducing mechanical stress, and can achieve material removal with nanometer-level precision. Furthermore, its production cost is far lower than femtosecond laser processing, making it one of the ideal methods for obtaining ultrathin films. However, traditional chemical etching processes suffer from problems such as poor etching uniformity, uncontrollable etching processes, and difficulty in real-time monitoring.

[0026] In view of this, such as Figure 6 As shown, the present invention provides a method for pre-fabricating a double-nested enhanced fiber optic FP cavity pressure sensor, comprising the following steps: Step 1: Fix the single-mode fiber 201 and the first hollow fiber 202 to the two clamping ends of the fiber optic fusion splicer, respectively. Partially insert the single-mode fiber 201 into the first hollow fiber 202. Utilize the high temperature generated by the electrode discharge of the fiber optic fusion splicer to achieve the fusion connection between the single-mode fiber 201 and the first hollow fiber 202; see [link / reference] Figure 6 ① in the middle.

[0027] Step 2: Under a microscope, the hollow end face of the first hollow fiber 202 after fusion splicing is ground until the entire hollow portion of the first hollow fiber 202 is ground off, resulting in a single-mode fiber 203 with a flat end face and a nested structure, with an end face diameter of 200 μm. Then, an ultrasonic cleaner is used to clean the end face of the ground nested single-mode fiber 201 to remove powder residue generated during the grinding process; see [link to relevant documentation]. Figure 6 ② in the middle.

[0028] Step 3: Fix the single-mode fiber 203 with nested structure obtained in Step 2 and the second hollow fiber to the two clamping ends of the fiber optic fusion splicer, respectively. Part of the single-mode fiber 203 with nested structure is inserted into the second hollow fiber 204. The high temperature generated by the electrode discharge of the fiber optic fusion splicer is used to achieve the fusion connection between the single-mode fiber 203 with nested structure and the second hollow fiber 204, resulting in a second-fusion spliced ​​single-mode fiber 201; see [link to previous steps]. Figure 6 ③ in the middle.

[0029] Step 4: Under a microscope, the hollow end of the second hollow fiber 204 is ground to obtain an fiber 205 with a double-layer nested structure and an end face diameter of 330 μm. Then, an ultrasonic cleaner is used to clean the end face of the ground double-layer nested fiber 205 to remove powder residue generated during the grinding process; see [link to relevant documentation]. Figure 6 ④ in the middle.

[0030] Step 5: Fix the double-nested optical fiber 205 and multimode optical fiber 206 obtained in Step 4 to the two clamping ends of the optical fiber fusion splicer, respectively. Utilize the high temperature generated by the electrode discharge of the optical fiber fusion splicer to achieve the fusion connection between the double-nested optical fiber 205 and the multimode optical fiber 206. (See also...) Figure 6 ⑤ in the middle.

[0031] Step 6: Under microscope observation, grind the other end face of the fused multimode fiber 206 to reduce its length. The resulting solid cavity 207 is a diaphragm. The diaphragm is then thinned by etching to obtain the double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor 106 for later use. (See [link to relevant documentation]). Figure 6 ⑥ and Figure 1 .

[0032] like Figure 6As shown, the inner diameter of the first hollow fiber 202 is adapted to the outer diameter of the single-mode fiber 201, the inner diameter of the second hollow fiber 204 is adapted to the outer diameter of the first hollow fiber 202, and the outer diameter of the second hollow fiber 204 is adapted to the outer diameter of the multimode fiber 206.

[0033] On the other hand, such as Figure 1 As shown, the present invention provides a calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor, comprising: The dual-station corrosion thinning and dynamic calibration module 101 is used to perform corrosion reaction or interrupt corrosion reaction on the diaphragm of the pre-prepared double-nested enhanced fiber optic FP cavity pressure sensor 106, and to perform temperature calibration, pressure calibration and temperature-pressure coupling experiment during the corrosion process. The pressurization module 103 is used to apply pressure to the dual-station etching and thinning and dynamic calibration module 101, and to collect the pressure change data of the dual-nested enhanced fiber optic FP cavity pressure sensor 106 in real time. The control module 102 is communicatively connected to the dual-station corrosion thinning and dynamic calibration module 101 and the pressurization module 103, respectively. It is used to change the corrosion state of the diaphragm of the double-nested enhanced fiber optic FP cavity pressure sensor 106 or interrupt the corrosion, and also control the start or stop of the pressurization module 103. The demodulation module 104 is used to receive the spectral information of the double-nested enhanced fiber optic FP cavity pressure sensor 106 during the corrosion process, and obtain the cavity length information of the sensor through demodulation. The real-time sensitivity display module 105 is used to acquire pressure change data collected by the pressurization module 103 and cavity length information of the sensor obtained by the demodulation module 104. Based on the pressure change data and cavity length change, it calculates and outputs the sensitivity of the double-nested enhanced fiber optic FP cavity pressure sensor 106 at the current diaphragm thickness in real time. When the sensitivity reaches the expected value, it sends a trigger signal to the control module 102 to interrupt the corrosion reaction. The real-time sensitivity display module 105 has a built-in sensitivity calculation algorithm.

[0034] like Figure 2As shown, the dual-station etching and dynamic calibration module 101 includes a flexible tube I, a station switching device II, an HF solution bottle III, a water bottle IV, two double clamping mechanisms V, an electric heating rod VI, and a hot water tank VII. The station switching device II has an etching station and a calibration station respectively at its two ends. The HF solution bottle III is positioned at the etching station, and the water bottle is positioned at the calibration station. The station switching device II clamps a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor 106 and either inserts the diaphragm into the HF solution bottle III corresponding to the etching station for etching, or inserts the diaphragm into the calibration station. Corrosion is interrupted in the corresponding water bottle IV; a hot water tank VII is installed below the water bottle IV, and an electric heating rod VI is installed inside the hot water tank VII. The hot water tank VII is also connected to the area where the water bottle IV is located through a hose I. The electric heating rod VI is used to heat the medium in the hot water tank VII. The medium in the hot water tank VII circulates through the hose I to achieve heat exchange with the medium in the water bottle IV; two double clamping mechanisms V are used to perform bidirectional sealing clamping on the HF solution bottle III and the water bottle IV; the double-nested enhanced fiber optic FP cavity pressure sensor 106 performs temperature calibration, pressure calibration, and temperature-pressure coupling experiments at the calibration station.

[0035] The working process of the dual-nested enhanced fiber optic FP cavity pressure sensor calibration system is as follows: The dual-station corrosion thinning and dynamic calibration module 101 clamps the dual-nested enhanced fiber optic FP cavity pressure sensor 106 and automatically sends it into the HF solution bottle in the left corrosion station. Under the corrosion action of the HF solution, the diaphragm thickness of the dual-nested enhanced fiber optic FP cavity pressure sensor 106 is reduced to the desired thickness. At this time, the dual-station corrosion thinning and dynamic calibration module 101 is activated again, and the dual-nested enhanced fiber optic FP cavity pressure sensor 106 is automatically sent into the water bottle in the right calibration station, realizing the rapid interruption of the corrosion reaction. Pressure calibration, temperature calibration and temperature-pressure coupling experiments of the dual-nested enhanced fiber optic FP cavity pressure sensor 106 can be carried out in the water bottle.

[0036] like Figure 8 and Figure 9 The diagram shown illustrates the overall calibration process and the overall structure of the equipment.

[0037] The overall working process is described as follows: First, the double-nested enhanced fiber optic FP cavity pressure sensor is installed and clamped in the initial position of the workstation switching device. The microcontroller sends a pulse signal to control the stepper motor to rotate and drive the workstation switching device to move along the preset guide rail, thereby realizing the switching between different workstations. The microcontroller establishes serial communication with the host computer software through a USB to serial port module. The host computer software receives the sensor measurement data demodulated by the demodulation system in real time. At the same time, the microcontroller controls the pressurization pump to work through a relay and switches the coil state of the three-position three-way solenoid valve through the output level signal, thereby pressurizing the HF acid solution bottle and the water bottle in the corrosion workstation and calibration workstation, respectively. When the double-nested enhanced fiber optic FP cavity pressure sensor is placed in the HF solution bottle, the system is in the etching position. At this time, the pressurization pump is controlled to pressurize the HF solution bottle III. The reference pressure sensor measures the pressure change in the HF solution bottle in real time and feeds it back to the host computer. The demodulation system demodulates the interference spectrum signal returned by the double-nested enhanced fiber optic FP cavity pressure sensor, extracts the cavity length value, and transmits it synchronously to the host computer. Subsequently, the host computer software uses the sensitivity calculation algorithm proposed in this embodiment to calculate the sensitivity of the double-nested enhanced fiber optic FP cavity pressure sensor in real time. The calculated sensitivity value is displayed in real time on the sensitivity real-time display module and compared with the expected sensitivity. When the calculated sensitivity value reaches the expected sensitivity, the microcontroller controls the stepper motor to rotate, thereby driving the position switching device to switch to the calibration position.

[0038] When the double-nested enhanced fiber optic FP cavity pressure sensor is placed in water bottle IV, corrosion is immediately stopped; this is the calibration stage. The reference pressure sensor and reference temperature sensor collect real-time pressure and temperature values ​​inside the water bottle, respectively. The host computer software, based on preset different temperature and pressure combinations, sequentially completes temperature calibration, pressure calibration, and temperature-pressure coupling experiments. The specific process is as follows: First, temperature calibration is performed. Under a stable pressure, the host computer software sends a temperature control command to the microcontroller according to the preset temperature adjustment range and adjustment step size. The microcontroller controls the start and stop of the electric heating rod through a relay closed loop to stabilize the temperature in the hot water tank and the water bottle at the target point. After the temperature stabilizes for a period of time, the host computer synchronously collects the cavity length data of the double-nested enhanced fiber optic FP cavity pressure sensor. The data is collected three times at each temperature point and the average value is taken to obtain the temperature response model of the double-nested enhanced fiber optic FP cavity pressure sensor. Next, pressure calibration is performed. Under a stable temperature, the host computer software sends a pressure control command to the microcontroller according to the preset pressure adjustment range and adjustment step size. The microcontroller adjusts the start and stop of the pressurization pump through a relay closed loop to stabilize the pressure in the water bottle at the target point. After the pressure stabilizes for a period of time, the host computer synchronously collects the cavity length data of the double-nested enhanced fiber optic FP cavity pressure sensor. The data is collected three times at each pressure point and the average value is taken to obtain the pressure response model of the double-nested enhanced fiber optic FP cavity pressure sensor. Finally, a temperature-pressure coupling experiment was conducted. The host computer preset multiple sets of temperature-pressure cross-coupling working conditions. The temperature and pressure inside the water bottle were adjusted sequentially according to the working condition sequence to reach the target value. After the temperature and pressure parameters stabilized for a period of time, the host computer synchronously collected the cavity length data of the double-nested enhanced fiber optic FP cavity pressure sensor. Based on the collected multiple sets of temperature-pressure-cavity length coupling data, a multivariate regression algorithm was used to quantify the degree of cross-interference between temperature and pressure on the cavity length response and to establish a temperature-pressure coupling compensation model to improve the measurement accuracy of the double-nested enhanced fiber optic FP cavity pressure sensor under complex temperature and pressure environments. After the temperature and pressure calibration and coupling experiments are completed, the microcontroller sends a pulse signal again to control the stepper motor to rotate, which drives the station switching device to move the double-nested enhanced fiber optic FP cavity pressure sensor to the initial position.

[0039] like Figure 3 As shown, the workstation switching device II includes a fixed base 3, an arc-shaped slide rail 1, a cam follower mechanism 2, an X-axis sliding guide rail 4, an X-axis slider 5, a Y-axis sliding guide rail 6, and an optical fiber clamping mechanism 7. The fixed base 3 is fixedly set relative to the ground. The HF solution bottle III, the clear water bottle IV, the double clamping mechanism V, the electric heating rod VI, and the hot water tank VII are all set on one side of the fixed base 3. The arc-shaped slide rail 1 is provided through the top of the fixed base 3. One end of the cam follower mechanism 2 is hinged to the fixed base 3, and the other end is embedded in the arc-shaped slide rail 1. The non-hinged end of the cam follower mechanism 2 is also provided with a Y-axis sliding guide rail 6. The sliding guide rail 6 is equipped with an optical fiber clamping mechanism 7 and an X-axis slider 5. The optical fiber clamping mechanism 7 is used to clamp the double-nested enhanced-sensitivity optical fiber FP cavity pressure sensor 106. The X-axis slider 5 is embedded in the X-axis sliding guide rail 4 and slidably connected to it. The X-axis sliding guide rail 4 and the Y-axis sliding guide rail 6 extend along the width and height directions of the fixed base 3, respectively. The extreme position on one side of the arc-shaped slide rail 1 corresponds to the etching station, and the extreme position on the other side of the arc-shaped slide rail 1 corresponds to the calibration station. The X-axis slider 5 is used to limit the attitude stability of the Y-axis sliding guide rail 6 and the optical fiber clamping mechanism 7 when they follow the rotation of the cam follower mechanism 2.

[0040] Similarly, Figure 3 As shown, the cam follower mechanism 2 includes a connecting rod 2.1, a stepped shaft 2.2, a top plate connector 2.3, and a guide rail connector 2.4. One end of the connecting rod 2.1 is hinged to the fixed base 3, and the other end of the connecting rod 2.1 is provided with a stepped shaft 2.2. One end of the stepped shaft 2.2 is embedded in the arc-shaped slide rail 1, and the other end of the stepped shaft 2.2 extends outward through the connecting rod 2.1 and connects to the top plate connector 2.3. The top plate connector 2.3 extends radially and connects to the guide rail connector 2.4, which is used to connect to the Y-axis sliding guide rail 6. The hinged end of the connecting rod 2.1 is also connected to the output shaft of the stepper motor. The clockwise or counterclockwise rotation of the stepper motor's output shaft is used to switch between the corrosion station and the calibration station.

[0041] In this embodiment, the control module 102 includes a microcontroller, a driver, a stepper motor, a relay, a pressurizing pump, a three-position three-way solenoid valve, a reference pressure sensor, and a reference temperature sensor. When the microcontroller outputs a pulse signal to the driver, the driver controls the stepper motor to feed at a constant speed. The stepper motor drives the linkage of the station switching device II to rotate at a certain angle to achieve the purpose of switching stations. The relay is connected between the microcontroller and the pressurizing pump, and the microcontroller can control the operation of the pressurizing pump and the electric heating rod through the relay. The pressurizing pump is connected to the three-position three-way solenoid valve. When the double-nested enhanced fiber optic FP cavity pressure sensor 106 is in the corrosion station, the pressurizing pump and the reference pressure sensor can act on the HF solution bottle. When the double-nested enhanced fiber optic FP cavity pressure sensor 106 is in the calibration station, the pressurizing pump and the reference pressure sensor can act on the clear water bottle. The electric heating rod is connected to the hot water tank, thereby controlling the water temperature in the hot water tank and the clear water bottle.

[0042] The dual-nested enhanced fiber optic FP cavity pressure sensor 106 is used to acquire cavity length change data during the corrosion and calibration process. The reference pressure sensor is connected between the three-position three-way solenoid valve and the pressurization pump to measure the pressure change in the HF solution bottle or water bottle. The reference temperature sensor is connected to the water bottle for temperature calibration and temperature measurement during the temperature-pressure coupling experiment.

[0043] like Figure 4 As shown, the fiber optic clamping mechanism 7 includes a pressure plate 7.1, a flexible sheath 7.2, a fiber optic protective sleeve 7.3, and a threaded fastener 7.4. The pressure plate 7.1 is mounted on the Y-axis sliding guide rail and extends horizontally away from the Y-axis sliding guide rail. A hollow annular boss is provided on the pressure plate 7.1, extending away from the pressure plate 7.1. The outer surface of the annular boss has external threads, and a tapered hole is provided inside the annular boss. The fiber optic protective sleeve 7.3 and the flexible sheath 7.2 are sequentially disposed within the tapered hole. A stepped portion is provided on the side of the fiber optic protective sleeve 7.3 away from the flexible sheath 7.2, with a diameter of... The diameter of the non-stepped portion is larger than that of the non-stepped portion. The flexible sheath 7.2 surrounds the non-stepped portion and abuts against the end face of the stepped portion and the inner surface of the tapered hole, respectively. The fiber optic protective sleeve 7.3 is provided with a through first hole, and the threaded fastener is provided with a through second hole. The first hole and the second hole are coaxially arranged. The threaded fastener 7.4 is threadedly connected to the annular boss. The double-nested enhanced fiber optic FP cavity pressure sensor 106 passes through the second hole and the first hole in sequence and makes the diaphragm extend out of the fiber optic protective sleeve 7.3. The size of the diaphragm is adapted to the first hole and the second hole so that the diaphragm can be inserted into the top-opening HF solution bottle or water bottle.

[0044] The fiber optic protective sleeve 7.3 encloses the double-nested, enhanced-sensitivity fiber optic FP cavity pressure sensor 106, protecting the fiber optic cable. When the threaded fastener 7.4 is tightened, it presses downwards against the flexible sleeve 7.2, causing the lower end of the fiber optic protective sleeve 7.3 to tighten and tightly adhere to the outer wall of the double-nested, enhanced-sensitivity fiber optic FP cavity pressure sensor 106, ultimately achieving reliable axial fixation and clamping seal of the double-nested, enhanced-sensitivity fiber optic FP cavity pressure sensor 106. Furthermore, the compression fit between the flexible sleeve 7.2 and the threaded fastener 7.4 enables bidirectional axial positioning of the fiber optic protective sleeve 7.3, reducing the shaking of the double-nested, enhanced-sensitivity fiber optic FP cavity pressure sensor 106 during station switching.

[0045] like Figure 5 As shown, both double clamping mechanisms V include a base 53, a lever mechanism 54, several compression springs 52, several spring shafts 51, a transmission pin 55, a pin 56, and an elastic washer 57. The base 53 is parallel to and spaced apart from the pressure plate 7.1. Several spring shafts 51 are provided on the base 53, extending towards the pressure plate 7.1. Compression springs 52 are sleeved on the spring shafts 51. The end of the spring shaft 51 away from the base 53 is connected to the side surface of the HF solution bottle III or the water bottle IV through a lug, and the lug is slidably connected to the spring shaft 51. The upper surface of the HF solution bottle III or the water bottle IV abuts against the surface of the pressure plate 7.1 through the elastic washer 57. The lever mechanism 54 includes a support base 4.4, a hinge shaft 4.5, a lever arm 4.5, and a first platform 4.3. The second platform 4.1 is hinged to the base, and the hinge shaft 4.5 passes through the center of the lever arm 4.6 and is rotatably connected to the support 4.4. The hinge shaft 4.5 is fixedly connected to the lever arm 4.6. The two ends of the lever arm 4.6 are respectively provided with the first platform 4.3 and the second platform 4.1. The first platform 4.3 and the second platform 4.1 are respectively hinged to the lever arm 4.6. The end face of the first platform 4.1 abuts against the lower surface of the HF solution bottle or the water bottle. The pressure plate 7.1 is provided with a transmission pin 55, which extends towards the base 53 and abuts against the end face of the second platform 4.1. By abutting the upper surface of the HF solution bottle or the water bottle and the end face of the second platform, the HF solution bottle or the water bottle is clamped in both directions.

[0046] When the transmission pin 55 moves downward to abut against the second platform 4.1, the second platform 4.1 descends, causing the lever arm 4.6 to rotate, which in turn drives the first platform 4.3 to rise, thereby lifting the lower surface of the HF solution bottle or water bottle and achieving a bidirectional double clamping effect.

[0047] In a preferred embodiment, to reduce bottom deformation and prevent platform crushing due to excessive compression, a buffer elastic pad 4.2 is provided between the end face of the first platform 4.3 and the lower surface of the HF solution bottle or water bottle. Each hinge position of the lever arm 4.6 is provided with a retaining ring to axially limit the position of each hinge shaft 4.5.

[0048] like Figure 7 As shown, the real-time sensitivity display module 105 is used to acquire pressure change data collected by the pressurization module 103 and cavity length information of the sensor obtained by the demodulation module 104. Based on the pressure change data and cavity length change, it calculates and outputs the sensitivity of the double-nested enhanced fiber optic FP cavity pressure sensor 106 at the current diaphragm thickness in real time. This is based on the following sensitivity calculation algorithm steps: Step S1: Initialize the sliding window that adapts to the pressure fluctuation cycle, receive the original cavity length value and pressure value collected by the fiber optic FP sensor at the corresponding time in real time, and store the data in the sliding window; the sliding window only retains the latest data segment, and when a new set of data is obtained and the total amount of data exceeds the length of the sliding window, the oldest set of old data is automatically removed.

[0049] Step S2: Based on the pressure value sequence in the sliding window of Step S1, the pressure values ​​are analyzed in the frequency domain using the continuous wavelet transform method; the sym5 wavelet is selected as the basis function to perform a one-level wavelet decomposition on the pressure value sequence to obtain the approximation coefficients and detail coefficients, and the modulus of the detail coefficients is calculated; based on the local mean and local standard deviation of the pressure values ​​within the window, an adaptive threshold is set, and points with modulus values ​​lower than the threshold and pressure values ​​that are the local minimum values ​​of the three points are selected as pressure minimum points. The time and pressure value corresponding to the minimum point are recorded, and pressure maximum tracking is enabled.

[0050] Step S3: For the pressure minimum point detected in step S2, the same continuous wavelet transform method is used again to track the pressure maximum point immediately adjacent to the minimum point, forming a minimum-maximum pressure extreme point pair, and the time and pressure corresponding to the pressure maximum point are recorded.

[0051] Step S4: Extract the original cavity length value corresponding to the minimum-maximum pressure extreme point pair from the sliding window, and the cavity length values ​​of the three adjacent cavity length values ​​before and after the extreme point pair together form the cavity length value sequence to be fitted.

[0052] Step S5: Perform Fourier fitting on the cavity length value sequence to be fitted. The fitting formula is: ,in The Fourier fit cavity length value, k Index for cavity length data points, A 0 represents the DC component. They are respectively n Sine and cosine amplitudes of subharmonics They are respectively n The initial phase of the second harmonic is obtained; the Fourier fit cavity length is obtained, and the goodness of fit R corresponding to the cavity length sequence is calculated. 2 If the goodness of fit R 2 If the value is greater than or equal to 0.98, the calculated cavity length is obtained by subtracting the Fourier-fitted cavity length from the original cavity length value; if the goodness of fit R... 2 If the value is less than 0.98, then perform a fifth-order Chebyshev orthogonal polynomial fitting on the cavity length value sequence extracted in step 4: ,in The cavity length is the result of a fifth-order Chebyshev fit. a 0、 a 1. a 2. a 3. a 4. a 5 is the fitting coefficient. x k The x-coordinate of the normalized cavity length data point. for m The following Chebyshev orthogonal polynomials satisfy the recurrence relation: The fifth Chebyshev fitted cavity length value is obtained, and the calculated cavity length value is obtained by subtracting the fifth Chebyshev fitted cavity length value from the original cavity length value.

[0053] Step S6: Calculate the difference between the calculated cavity length value and the pressure value at the corresponding time for the pressure extreme point. The ratio of the difference in cavity length value to the difference in pressure value is the sensitivity of the extreme point at the corresponding time.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor, characterized in that, include: The dual-station corrosion thinning and dynamic calibration module is used to perform corrosion reaction or interrupt the corrosion reaction on the diaphragm of the pre-prepared double-nested enhanced fiber optic FP cavity pressure sensor, and to perform temperature calibration, pressure calibration and temperature-pressure coupling experiment during the corrosion process. The dual-station corrosion thinning and dynamic calibration module includes a hose, a station switching device, an HF solution bottle, a water bottle, two double clamping mechanisms, an electric heating rod, and a hot water tank. The station switching device has a corrosion station and a calibration station at its two ends, respectively. The HF solution bottle is positioned at the corrosion station, and the water bottle at the calibration station. The station switching device clamps a double-nested enhanced fiber optic FP cavity pressure sensor and either inserts the diaphragm into the HF solution bottle corresponding to the corrosion station for corrosion, or inserts the diaphragm into the water bottle corresponding to the calibration station to interrupt corrosion. A hot water tank is located below the water bottle, and an electric heating rod is installed inside the hot water tank. The hot water tank is also connected to the area where the water bottle is located via a hose. The electric heating rod heats the medium in the hot water tank, and the medium in the hot water tank circulates through the hose to achieve heat exchange with the medium in the water bottle. The two double clamping mechanisms provide bidirectional sealing clamping for the HF solution bottle and the water bottle. When the double-nested enhanced fiber optic FP cavity pressure sensor is at the calibration station, temperature calibration, pressure calibration, and temperature-pressure coupling experiments are performed. The pressurization module is used to apply pressure to the dual-station etching and thinning and dynamic calibration module, and to collect the pressure change data of the dual-nested enhanced fiber optic FP cavity pressure sensor in real time. The control module is connected to the dual-station corrosion thinning and dynamic calibration module and the pressurization module respectively. It is used to change the corrosion state of the diaphragm of the double-nested enhanced fiber optic FP cavity pressure sensor or interrupt the corrosion, and also control the start or stop of the pressurization module. The demodulation module is used to receive the spectral information of the double-nested enhanced fiber optic FP cavity pressure sensor during the corrosion process, and obtain the cavity length information of the sensor through demodulation. The real-time sensitivity display module is used to acquire pressure change data collected by the pressurization module and cavity length information of the sensor obtained by the demodulation module. Based on the pressure change data and cavity length change, it calculates and outputs the sensitivity of the double-nested enhanced fiber optic FP cavity pressure sensor at the current diaphragm thickness in real time. When the sensitivity reaches the expected value, it sends a trigger signal to the control module to interrupt the corrosion reaction.

2. The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor according to claim 1, characterized in that, A method for pre-fabricating a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor includes the following steps: Step 1: Fix the single-mode fiber and the first hollow fiber to the two clamping ends of the fiber optic fusion splicer, respectively. Insert the single-mode fiber into the first hollow fiber. Use the high temperature generated by the electrode discharge of the fiber optic fusion splicer to achieve the fusion connection between the single-mode fiber and the first hollow fiber. Step 2: Under the observation of a microscope, grind the hollow end face of the first hollow fiber after fusion splicing until the hollow part of the first hollow fiber is completely ground to obtain a single-mode fiber with a flat end face and a nested structure. Then, use an ultrasonic cleaner to clean the end face of the single-mode fiber with the nested structure after grinding to remove the powder residue generated during the grinding process. Step 3: Fix the single-mode fiber with nested structure obtained in Step 2 and the second hollow fiber to the two clamping ends of the fiber optic fusion splicer, respectively. Insert the single-mode fiber with nested structure into the second hollow fiber. Use the high temperature generated by the electrode discharge of the fiber optic fusion splicer to achieve the fusion connection between the single-mode fiber with nested structure and the second hollow fiber, and obtain the single-mode fiber after secondary fusion splicing. Step 4: Under the observation of a microscope, the hollow end of the second hollow fiber is ground to obtain an optical fiber with a double-layer nested structure. Then, an ultrasonic cleaner is used to clean the end face of the ground double-layer nested structure optical fiber to remove the powder residue generated during the grinding process. Step 5: Fix the optical fiber with double-layer nested structure and the multimode optical fiber obtained in Step 4 to the two clamping ends of the optical fiber fusion splicer, and use the high temperature generated by the electrode discharge of the optical fiber fusion splicer to achieve the fusion connection of the optical fiber with double-layer nested structure and the multimode optical fiber. Step 6: Under the observation of a microscope, grind the other end face of the fused multimode fiber to reduce the length of the multimode fiber. The resulting solid cavity is a diaphragm. The diaphragm is then etched and thinned to obtain a double-nested enhanced fiber FP cavity pressure sensor.

3. The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor according to claim 2, characterized in that, The inner diameter of the first hollow fiber is adapted to the outer diameter of the single-mode fiber, the inner diameter of the second hollow fiber is adapted to the outer diameter of the first hollow fiber, and the outer diameter of the second hollow fiber is adapted to the outer diameter of the multimode fiber.

4. The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor according to claim 1, characterized in that, The workstation switching device includes a fixed base, an arc-shaped slide rail, a cam follower mechanism, an X-axis sliding guide rail, an X-axis slider, a Y-axis sliding guide rail, and an optical fiber clamping mechanism. The fixed base is fixed relative to the ground. The HF solution bottle, water bottle, double clamping mechanism, electric heating rod, and hot water tank are all located on one side of the fixed base. An arc-shaped slide rail is provided through the top of the fixed base. One end of the cam follower mechanism is hinged to the fixed base, and the other end is embedded in the arc-shaped slide rail. The non-hinged end of the cam follower mechanism is also provided with a Y-axis sliding guide rail. The device is equipped with an optical fiber clamping mechanism and an X-axis slider. The optical fiber clamping mechanism is used to clamp the double-nested enhanced-sensitivity optical fiber FP cavity pressure sensor. The X-axis slider is embedded in the X-axis sliding guide and slidably connected to it. The X-axis sliding guide and the Y-axis sliding guide extend along the width and height directions of the fixed base, respectively. The extreme position on one side of the arc-shaped slide rail corresponds to the etching station, and the extreme position on the other side of the arc-shaped slide rail corresponds to the calibration station. The X-axis slider is used to limit the attitude stability of the Y-axis sliding guide and the optical fiber clamping mechanism when they follow the cam follower mechanism.

5. The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor according to claim 4, characterized in that, The cam follower mechanism includes a connecting rod, a stepped shaft, a top plate connector, and a guide rail connector. One end of the connecting rod is hinged to the fixed base, and the other end of the connecting rod is provided with a stepped shaft. One end of the stepped shaft is embedded in the arc-shaped slide rail, and the other end of the stepped shaft extends outward through the connecting rod and is connected to the top plate connector. The top plate connector extends radially and is connected to the guide rail connector, which is used to connect with the Y-axis sliding guide rail. The hinged end of the connecting rod is also connected to the output shaft of the stepper motor.

6. The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor according to claim 5, characterized in that, The fiber clamping mechanism includes a pressure plate, a flexible sheath, a fiber protective sleeve, and threaded fasteners. The pressure plate is mounted on a Y-axis sliding guide rail and extends horizontally away from the Y-axis sliding guide rail. A hollow annular boss is provided on the pressure plate, extending away from the pressure plate. A tapered hole is provided inside the annular boss. The fiber protective sleeve and the flexible sheath are sequentially positioned within the tapered hole. A stepped portion is provided on the side of the fiber protective sleeve away from the flexible sheath, with the diameter of the stepped portion being larger than the diameter of the non-stepped portion. The flexible sheath surrounds the non-stepped portion. A stepped portion is provided and abuts against the end face of the stepped portion and the inner surface of the tapered hole respectively. A through first hole is provided on the optical fiber protective sleeve, and a through second hole is provided on the threaded fastener. The first and second through holes are coaxially arranged, and the threaded fastener is threadedly connected to the annular boss. The double-nested enhanced-sensitivity optical fiber FP cavity pressure sensor passes through the second and first through holes in sequence and makes the diaphragm extend out of the optical fiber protective sleeve. The size of the diaphragm is adapted to the first and second through holes so that the diaphragm can be inserted into the top-opening HF solution bottle or water bottle.

7. The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor according to claim 6, characterized in that, Both double clamping mechanisms include a base, a lever mechanism, several compression springs, several spring shafts, a transmission pin, a pin, and an elastic washer. The base is parallel to and spaced apart from the pressure plate. Several spring shafts are mounted on the base, extending towards the pressure plate. Compression springs are fitted onto the spring shafts. The end of the spring shaft away from the base is connected to the side surface of the HF solution bottle or water bottle via a lug, and the lug is slidably connected to the spring shaft. The upper surface of the HF solution bottle or water bottle abuts against the surface of the pressure plate via an elastic washer. The lever mechanism includes a hinge shaft, a lever arm, a first platform, and a second platform. The shaft is hinged to the base, and the hinge shaft passes through the center of the lever arm. The hinge shaft is fixedly connected to the lever arm. The lever arm has a first platform and a second platform at its two ends, which are hinged to the lever arm. The end face of the first platform abuts against the lower surface of the HF solution bottle or water bottle. A transmission pin is provided on the pressure plate, which extends towards the base and abuts against the end face of the second platform. By abutting the upper surface of the HF solution bottle or water bottle and the end face of the second platform respectively, the pressure plate and the transmission pin can achieve bidirectional clamping of the HF solution bottle or water bottle.

8. The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP cavity pressure sensor according to claim 7, characterized in that, A buffer elastic pad is also provided between the end face of the first platform and the lower surface of the HF solution bottle or water bottle.

9. The manufacturing and calibration system for a double-nested enhanced-sensitivity fiber optic FP-cavity pressure sensor according to claim 1, characterized in that, The real-time sensitivity display module is used to acquire pressure change data collected by the pressurization module and cavity length information of the sensor obtained by the demodulation module. Based on the pressure change data and cavity length change, it calculates and outputs the sensitivity of the double-nested enhanced fiber optic FP cavity pressure sensor at the current diaphragm thickness in real time, based on the following algorithm steps: Step S1: Initialize the sliding window that adapts to the pressure fluctuation cycle, receive the raw cavity length and pressure values ​​collected by the fiber optic FP sensor at the corresponding time in real time, and store the data in the sliding window. The sliding window only retains the latest data segment. When a new set of data is obtained and the total amount of data exceeds the length of the sliding window, the oldest set of old data is automatically removed. Step S2: Based on the sequence of pressure values ​​in the sliding window in step S1, the pressure values ​​are analyzed in the frequency domain using the continuous wavelet transform method; the sym5 wavelet is selected as the basis function to perform a one-level wavelet decomposition on the pressure value sequence to obtain the approximation coefficients and detail coefficients, and the modulus of the detail coefficients is calculated. Based on the local mean and local standard deviation of the pressure value within the window, an adaptive threshold is set to filter points with a modulus value lower than the threshold and a pressure value that is the local minimum of three points as pressure minimum points. The time and pressure value corresponding to the minimum point are recorded, and pressure maximum tracking is enabled. Step S3: For the pressure minimum point detected in step S2, the same continuous wavelet transform method is used again to track the pressure maximum point immediately adjacent to the minimum point, forming a minimum-maximum pressure extreme point pair, and the time and pressure corresponding to the pressure maximum point are recorded. Step S4: Extract the original cavity length value corresponding to the minimum-maximum pressure extreme point pair from the sliding window, and the cavity length values ​​of the three adjacent cavity length values ​​before and after the extreme point pair together form the cavity length value sequence to be fitted. Step S5: Perform Fourier fitting on the cavity length value sequence to be fitted, obtain the Fourier fitted cavity length value, and calculate the goodness of fit R corresponding to the cavity length value sequence. 2 If the goodness of fit R 2 If the value is greater than or equal to 0.98, the calculated cavity length value is obtained by subtracting the Fourier fitted cavity length value from the original cavity length value. If the goodness of fit R 2 If the value is less than 0.98, then the cavity length value sequence extracted in step 4 is fitted with a fifth-order Chebyshev orthogonal polynomial to obtain the fifth-order Chebyshev fitted cavity length value. The original cavity length value is subtracted from the fifth-order Chebyshev fitted cavity length value to obtain the calculated cavity length value. Step S6: Calculate the difference between the calculated cavity length value and the pressure value at the corresponding time for the pressure extreme point. The ratio of the difference in cavity length value to the difference in pressure value is the sensitivity of the extreme point at the corresponding time.

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