A method for preparing a fiber polymer grating temperature sensing unit and a sensor system

Abstract

The application discloses a kind of optical fiber polymer grating temperature sensing unit preparation method and sensor system, it is related to the technical field of optical fiber sensing, the method comprises: providing double opening capillary, into the capillary alternately pump into solidifiable polymer precursor and air, to form the periodic arrangement structure of polymer precursor and air section inside capillary;Transmission optical fiber is inserted from the both ends opening of the capillary, and the transmission optical fiber end extends into the capillary inside, and is optically coupled with the periodic arrangement structure;Solidify the polymer precursor to form solidified polymer section, and the polymer section and the air section jointly constitute optical fiber polymer grating structure;The relative position of the transmission optical fiber and the capillary is fixed, to obtain optical fiber sensing unit by preparation.The application has simple process, low cost, and can effectively inhibit the effect of stress-strain cross sensitivity.

Description

Technical Field

[0001] This application relates to the technical field of fiber optic sensing, and in particular to a method for fabricating a fiber optic polymer grating temperature sensing unit and a sensor system. Background Technology

[0002] Fiber optic sensing technology has been widely used in industry, scientific research, and environmental monitoring due to its advantages such as strong anti-interference capability and ability to achieve remote real-time monitoring. Among these applications, temperature, as a key physical quantity, has attracted particular attention due to its fiber optic sensing technology. Currently, common fiber optic temperature sensors mainly include fiber optic grating temperature sensors, fiber optic fluorescence temperature sensors, fiber optic interferometer temperature sensors, and fiber optic distributed temperature sensors.

[0003] Various types of fiber optic temperature sensors have their own limitations in fabrication: fiber optic fluorescent temperature sensors are complex to fabricate, some materials are biotoxic, and have limited lifespans; fiber optic interferometer temperature sensors have extremely high manufacturing requirements, making mass production difficult; while fiber optic distributed temperature sensors have been put into practical use, their system cost is high and their spatial resolution is limited. Fiber Bragg grating temperature sensors utilize the principle of temperature-induced wavelength shift in grating reflection to achieve sensing, exhibiting good stability and repeatability, and are currently the most promising type of fiber optic temperature sensor for industrialization. However, their fabrication mainly relies on precision processes such as laser etching, which not only results in expensive equipment and high fabrication costs, but also makes the fabricated fiber gratings susceptible to interference from mechanical factors such as stress and strain, exhibiting significant cross-sensitivity issues that affect the accuracy and reliability of temperature detection.

[0004] Therefore, there is an urgent need for a fiber optic temperature sensor and its fabrication method that is simple to manufacture, low in cost, and can effectively suppress stress-strain cross-sensitivity. Summary of the Invention

[0005] The purpose of this application is to provide a method for fabricating a fiber optic polymer grating temperature sensing unit and a sensor system to solve the problems of high fabrication cost and cross-sensitivity of fiber optic sensing units in fiber optic temperature sensors.

[0006] To achieve the above objectives, this application provides the following solution:

[0007] In a first aspect, this application provides a method for fabricating a fiber optic polymer grating temperature sensing unit, comprising: S110, providing a double-opening capillary tube, and alternately pumping a curable polymer precursor and air into the capillary tube to form a periodic arrangement structure of the polymer precursor and air segments inside the capillary tube; S120, inserting a transmission optical fiber from both ends of the capillary tube, and extending the end of the transmission optical fiber into the capillary tube to optically couple with the periodic arrangement structure; S130, curing the polymer precursor to form a cured polymer segment, wherein the polymer segment and the air segment together constitute a fiber optic polymer grating structure; and S140, fixing the relative position of the transmission optical fiber and the capillary tube to fabricate the fiber optic sensing unit.

[0008] For example, the method pumps the polymer precursor and air into the capillary via a peristaltic pump and a silicone tube to form the periodic arrangement structure.

[0009] For example, the polymer precursor is a polydimethylsiloxane precursor, the pumped volume ratio of the polymer to air is 1:1, and the coefficient of thermal expansion of the polymer segment is less than that of air.

[0010] For example, curing the polymer precursor includes: placing the transmission optical fiber and the capillary in an environment of 60°C for heating and curing, so that the polymer precursor forms a cured polymer segment.

[0011] For example, fixing the relative position of the transmission optical fiber and the capillary tube includes: applying ultraviolet glue to the connection between the capillary tube opening and the transmission optical fiber for sealing, and then irradiating with ultraviolet light for 5-10 minutes to achieve a fixed connection between the transmission optical fiber and the capillary tube.

[0012] For example, the double-opening capillary is any one of a quartz capillary, a stainless steel capillary, or a polytetrafluoroethylene capillary.

[0013] Secondly, this application also provides a fiber optic polymer grating temperature sensor system, comprising: a light source module for generating an incident light signal; a fiber optic sensing unit prepared using any of the methods described above; a fiber optic circulator including a first port, a second port, and a third port, the first port being connected to the light source module, the second port being connected to the fiber optic sensing unit, for guiding the incident light signal to the fiber optic sensing unit and exporting the reflected light signal from the fiber optic sensing unit from the third port; and a signal acquisition and processing module connected to the third port for receiving and demodulating the reflected light signal to obtain reflection spectral data; wherein, the polymer segment in the fiber optic sensing unit has thermal expansion properties, and the grating period formed by the polymer segment and the air segment changes with temperature, causing a drift in the characteristic wavelengths of the reflection spectral data, and temperature sensing is achieved by detecting the amount of the drift.

[0014] For example, the signal acquisition and processing module includes a spectrum analyzer, and the system also includes a computer module. The computer module is communicatively connected to the signal acquisition and processing module and is used to receive the reflectance spectrum data, extract the characteristic wavelengths of the reflectance spectrum data, and calculate and output the temperature value according to a pre-stored wavelength-temperature calibration relationship.

[0015] For example, the transmission optical fiber is a germanium-doped silica single-mode optical fiber with a germanium content of less than 5%, and the core refractive index of the transmission optical fiber matches the refractive index of the polymer segment after curing.

[0016] For example, the system includes multiple fiber optic sensing units with different grating periods. The fiber optic sensing units are connected to the same light source module and the signal acquisition and processing module through fiber optic couplers or cascading, forming a quasi-distributed temperature sensing network.

[0017] According to the specific embodiments provided in this application, the following technical effects are disclosed:

[0018] This application provides a method for fabricating a fiber optic polymer grating temperature sensing unit and a sensor system. In this method, the grating structure is formed by alternately pumping a polymer precursor and air into a capillary, eliminating the need for expensive laser etching equipment and significantly reducing the fabrication threshold and cost. The polymer solidifies in situ within the capillary, bonding firmly to the capillary wall. The grating period is precisely controlled by the pumped volume, resulting in good structural consistency and overcoming the problem of stress-strain cross-sensitivity. By adjusting the pumped volume ratio of polymer to air or selecting polymer materials with different refractive indices, the grating period and optical properties can be flexibly adjusted to meet different sensing requirements. In the sensor system, temperature detection is achieved based on wavelength demodulation, resulting in fast response and real-time monitoring. The polymer precursor has good elasticity, allowing the grating period to recover after temperature changes, making the sensor reusable. This application provides a simple, low-cost, reusable, and cross-sensitive fiber optic grating temperature sensor. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the fabrication method of the fiber polymer grating temperature sensing unit in this embodiment of the application.

[0021] Figure 2 This is a flowchart illustrating the fabrication method of the fiber polymer grating temperature sensing unit in this application embodiment.

[0022] Figure 3 This is a schematic diagram of the fiber polymer grating temperature sensor system in the embodiments of this application.

[0023] Figure 4 This is a schematic diagram illustrating the detection principle of the fiber polymer grating temperature sensor in this embodiment of the application.

[0024] Reference numerals: 1. Computer module; 2. Signal acquisition and processing module; 3. Light source module; 4. Fiber optic circulator; 5. Transmission fiber; 6. Fiber optic sensing unit; 7. UV adhesive; 8. UV lamp; 9. Polymer precursor; 10. Capillary tube; 11. Silicone tube; 12. Peristaltic pump; 13. Polymer segment; 14. Air; 15. Incident light signal; 16. Reflected light signal; 17. Transmitted light signal. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown in the figure, this application provides a method for fabricating a fiber polymer grating temperature sensing unit, including the following steps:

[0028] S110, a capillary tube 10 with two openings is provided, and a curable polymer precursor 9 and air 14 are alternately pumped into the capillary tube 10 to form a periodic arrangement structure of polymer precursor 9 and air 14 segments inside the capillary tube 10.

[0029] S120. Insert the transmission optical fiber 5 into the openings at both ends of the capillary tube 10, and extend the end of the transmission optical fiber 5 into the interior of the capillary tube 10 to optically couple with the periodic arrangement structure.

[0030] S130, the cured polymer precursor 9 is used to form a cured polymer segment 13, and the polymer segment 13 and the air segment 14 together constitute the fiber polymer grating structure.

[0031] S140. Fix the relative positions of the transmission optical fiber 5 and the capillary tube 10 to prepare the optical fiber sensing unit 6.

[0032] The fiber optic polymer grating temperature sensing unit provided in this application embodiment can form a grating structure by alternately pumping polymer precursor 9 and air 14 into a capillary 10, without relying on expensive laser etching equipment, which greatly reduces the fabrication threshold and cost. The polymer is cured in situ in the capillary 10 and is firmly bonded to the inner wall of the capillary 10. The grating period is precisely controlled by the pumping volume, resulting in good structural consistency and overcoming the problem of stress-strain cross-sensitivity. By adjusting the pumping volume ratio of polymer to air 14 or by selecting polymer materials with different refractive indices, the grating period and optical characteristics can be flexibly adjusted to adapt to different sensing requirements.

[0033] like Figure 2 The diagram shown is a flowchart illustrating the fabrication process of the fiber optic sensing unit 6 of the fiber optic polymer grating temperature sensor based on capillary 10 in this embodiment of the application. The fabrication process of the fiber optic sensing unit 6 consists of multiple steps:

[0034] First, a double-opening capillary tube 10 is provided, into which a curable polymer precursor 9 and air 14 are alternately pumped. A structure using a silicone tube 11 and a peristaltic pump 12 is employed when pumping in the precursor and air 14. Before starting, the peristaltic pump 12 is securely connected to one end of the double-opening capillary tube 10 via the silicone tube 11, and the airtightness is checked to prevent leakage.

[0035] A peristaltic pump 12 alternately pumps 1 μL of PDMS precursor (polymer precursor 9) and air 14 (in a 1:1 volume ratio) into a double-opening capillary 10 to ensure the formation of a periodic grating structure. This process is repeated multiple times until the entire double-opening capillary 10 is filled.

[0036] The transmission optical fiber 5 is inserted through the double opening of the capillary tube 10 and placed in an environment of 60°C for heating and curing, so that the polymer precursor 9 is transformed into a cured polymer segment 13, which together with air 14 forms a stable fiber grating structure with a fixed period, which can achieve the cutoff of optical signals of a specific wavelength.

[0037] Finally, to ensure that the transmission optical fiber 5 can be completely fixed to the optical fiber sensing unit 6, UV glue 7 is used to encapsulate the double-opening connection of the capillary 10, and the connection is completed by irradiating with UV lamp 8 for 5-10 minutes. This completes the fabrication process of the optical fiber sensing unit 6.

[0038] The entire preparation process utilizes a peristaltic pump 12 to pump in the polymer precursor 9 and gas for curing, resulting in low cost, simple operation, and fast preparation speed, enabling mass production. The polymer is cured in situ within the capillary 10, bonding firmly to the inner wall of the capillary 10. The grating period is precisely controlled by the pumped volume, resulting in good structural consistency.

[0039] For example, the polymer precursor 9 is a polydimethylsiloxane precursor, and the pumped volume ratio of the polymer precursor 9 to air 14 is 1:1. In some embodiments, grating structures with different periods can be constructed by adjusting the volume ratio and volume amount (e.g., adjusting the volume ratio of polymer precursor 9 to air 14 to 2:1 or 3:1), and the performance of the fiber optic sensing unit 6 can also be adjusted by adjusting the refractive index of the polymer segment 13 (increasing loss, improving contrast, etc.). In some embodiments, the material of the polymer precursor 9 can be replaced with a material with similar properties, such as hydrogel or epoxy resin, as a substitute filler. In some embodiments, the elasticity of the finally cured polymer segment 13 can be improved by doping the polymer precursor 9 with substances such as silica nanoparticles, carbon nanotubes, or graphene, thereby increasing its compressibility and improving the sensitivity to temperature detection.

[0040] The polymer precursor 9 in the capillary 10, as a temperature-sensitive flexible material, possesses excellent thermal expansion coefficient and elasticity. The thermal expansion coefficient of air 14 is much greater than that of the polymer precursor 9 (and the polymer segment 13 obtained by curing the polymer precursor 9). Increased temperature causes the air gaps in 14 to widen, compressing the polymer segment 13 and thus altering the period of the fiber polymer grating. This results in corresponding changes in the wavelengths of the transmission loss peak and reflection peak, enabling real-time temperature detection by the sensor. The excellent elasticity allows the polymer segment 13 to contract back to its original position and restore the initial period after the temperature decreases, enabling repeated detection. The structure of the capillary 10 not only protects the fiber optic sensing unit 6 but also protects the entire sensor from deformation caused by stress and strain, exhibiting good structural consistency and overcoming the problem of cross-sensitivity to stress and strain. For example, the double-opening capillary 10 is any one of a quartz capillary, a stainless steel capillary, or a polytetrafluoroethylene capillary. In this embodiment, a quartz capillary is preferred. Considering that the application location may be a harsh environment, such as a factory or substation, replacing it with stainless steel or polytetrafluoroethylene can significantly improve its mechanical properties or corrosion resistance, extend the service life of the fiber optic sensing unit 6, and broaden the application fields and scenarios of the fiber optic grating polymer temperature sensor.

[0041] The entire fiber polymer grating sensing unit based on capillary 10 can be fabricated using a simple and novel mold forming method. The temperature-sensitive fiber polymer grating in the fiber sensing unit 6 is formed by using a polymer precursor 9 with excellent mechanical and optical properties in combination with air 14. It has advantages such as simple fabrication, low cost, high reusability and long service life. Compared with the traditional fiber grating fabrication achieved by laser etching, it greatly reduces the dependence on equipment and manufacturing cost, and provides a new reference method and idea for the fabrication of fiber grating temperature sensors.

[0042] like Figures 3-4 As shown in the figure, this application embodiment also provides a fiber polymer grating temperature sensor system, the system including: a light source module 3, a fiber optic sensing unit 6, a fiber optic circulator 4, and a signal acquisition and processing module 2.

[0043] The light source module 3 generates the incident light signal 15. The fiber optic sensing unit 6 is fabricated using the method described above. The fiber optic circulator 4 includes a first port, a second port, and a third port. The first port is connected to the light source module 3, the second port is connected to the fiber optic sensing unit 6, and the fiber optic circulator 4 guides the incident light signal 15 to the fiber optic sensing unit 6 and outputs the reflected light signal 16 from the fiber optic sensing unit 6 through the third port. The signal acquisition and processing module 2 is connected to the third port and is used to receive and demodulate the reflected light signal 16 to obtain reflection spectral data.

[0044] Among them, the polymer segment 13 in the fiber optic sensing unit 6 has thermal expansion properties. The grating period formed by the polymer segment 13 and the air segment 14 changes with temperature, causing a shift in the characteristic wavelength in the reflection spectrum. Temperature sensing is achieved by detecting the amount of shift.

[0045] This application provides a fiber optic polymer grating temperature sensor system that achieves temperature detection based on wavelength demodulation. It features a fast response speed and real-time monitoring. The polymer precursor 9 exhibits good elasticity, allowing the grating period to recover after temperature changes, thus enabling the sensor to be reusable. This application provides a fiber optic grating temperature sensor that is simple to fabricate, low-cost, reusable, and cross-insensitive.

[0046] For example, the light source module 3 is a broadband light source that generates broadband light in the range of 1200-1700nm to provide the incident light signal 15 for the entire sensor. The fiber optic circulator 4 is a commercially available fiber optic device that transmits optical signals in one direction. It can transmit the incident light signal 15 generated by the light source module 3 to the fiber optic sensing unit 6 in one direction, and it can also transmit the reflected light signal 16 generated by the fiber optic sensing unit 5 to the signal acquisition and processing module 2 in one direction for processing, thus preventing signal crosstalk.

[0047] The signal acquisition and processing module 2 includes a spectrum analyzer, capable of receiving and identifying reflected light signals 16 and transmitted light signals 17, converting them into spectral information, and transmitting the spectral information as electrical signals to the computer module 1 via a data cable for analysis and processing. The system also includes a computer module 1, which is communicatively connected to the signal acquisition and processing module 2. The computer module 1 receives reflected spectral data and extracts characteristic wavelengths from the reflected spectral data. The computer module 1 also calculates and outputs temperature values ​​based on a pre-stored wavelength-temperature calibration relationship. In some embodiments, the signal acquisition and processing module 2 can achieve spectral information acquisition and demodulation extraction using an integrated small fiber optic grating demodulator, achieving the goal of spectral information extraction, thereby reducing costs and improving economic efficiency.

[0048] For example, the computer module 1 is connected to a display screen. The computer module 1 can visualize the spectral information transmitted by the signal acquisition and processing module 2 on the screen, and draw a spectral image through a dedicated application. It can extract the wavelengths of the reflection peak and the transmission peak, calculate the relationship between the wavelength shift of the reflection peak and the transmission peak and the temperature change, and complete the calibration of the sensor. In actual detection, the current temperature can be calculated by the wavelength shift of the reflection peak and the transmission peak to achieve real-time monitoring.

[0049] For example, the transmission optical fiber 5 is a germanium-doped silica single-mode optical fiber with a germanium content of less than 5%, and the core refractive index of the transmission optical fiber 5 matches the refractive index of the polymer segment 13 after curing. Specifically, the core refractive index of the transmission optical fiber 5 is 1.43-1.46, and the refractive index of the polymer segment 13 after curing is 1.40-1.45, and the two refractive indices match.

[0050] For example, the double-opening capillary 10 can be improved into a cross-shaped four-way capillary 10 (changing its mechanical structure without changing its material), with air 14 introduced into the intersection of the cross, and different kinds of liquids or gases introduced into other parts, thereby generating additional transmission loss peaks and reflection peaks to achieve refractive index detection, without generating stress cross-sensitivity. This structure can enhance the detection function of the fiber optic sensing unit 6.

[0051] like Figure 4 The diagram shown illustrates the detection principle of the fiber polymer grating temperature sensor in this embodiment. During detection, the light source module 3 generates a broadband incident light signal 15, which is input to the fiber sensing unit 6 via the transmission fiber 5. Since the refractive index of the cured polymer segment 13 is 1.41-1.45, which is close to the refractive index of the fiber core of the transmission fiber 5 (1.45-1.46), the incident light signal 15 can pass through with low loss. When the incident light signal 15 propagates to the interface between the cured polymer segment 13 and the air 14, a certain degree of total internal reflection occurs due to the large refractive index difference. Furthermore, the periodic grating structure cuts off and reflects the incident light signal 15 at a specific wavelength. The cutoff wavelength of the reflection can be calculated using the Bragg condition formula, as shown below:

[0052]

[0053] in The cutoff wavelength, For effective refractive index, The grating period is defined as follows: When the temperature rises, both polymer segment 13 and air 14 undergo thermal expansion. However, due to the higher coefficient of thermal expansion of air 14, it compresses polymer segment 13, which has a lower coefficient of thermal expansion and good elasticity. This leads to a decrease in the grating period (the axial length of a single polymer segment 13), but the effective refractive index does not change significantly. Therefore, the cutoff wavelength undergoes a significant blue shift, resulting in a blue shift in the reflection peak wavelength of reflected light signal 16 and a similar blue shift in the loss peak wavelength of transmitted light signal 17. When the temperature returns to normal, the good elasticity and plasticity of polymer segment 13 allows it to recover its original shape. The grating period and effective refractive index will return to their initial values, meaning the reflection peak wavelength of reflected light signal 16 and the loss peak wavelength of transmitted light signal 17 will return to their original positions. This allows for repeated temperature detection. Since the wavelength shift and temperature change are correlated, the wavelength shift-temperature relationship can be calibrated by establishing the relationship between wavelength shift and temperature change. Subsequent detection can calculate the temperature change by calculating the wavelength shift, enabling real-time quantitative monitoring of the temperature.

[0054] The fiber optic polymer grating temperature sensing unit fabrication method and sensor system provided in this application embodiment have at least the following advantages compared to related technologies:

[0055] 1. This application uses a double-opening capillary tube 10 as the substrate of the fiber polymer grating temperature sensor. Its inner wall not only adheres tightly to the polymer segment 13 after curing without displacement, but the UV adhesive 7, cured on both ends of the capillary tube 10, also fixes the relative position of the optical fiber and the grating structure, preventing axial strain caused by external forces. This ensures that the fiber polymer grating temperature sensor is unaffected by stress and strain during temperature detection, improving its resistance to stress-strain cross-sensitivity and effectively protecting the grating structure from external environmental influences and interference. It can significantly reduce or even avoid cross-sensitivity issues caused by stress and strain without using additional compensation fiber gratings or fiber components, achieving accurate detection of a single temperature parameter.

[0056] 2. This application utilizes a peristaltic pump 12 to pump the polymer precursor 9 and air 14 into the capillary 10 at a 1:1 volume ratio and then solidify them to fabricate a grating structure. This method is simple and cost-effective. It allows for precise control of the grating period and enables fabrication using low-cost equipment. The process is short and allows for standardized batch production. The fabrication cost is lower, the process is shorter and more efficient, and it does not rely on expensive and sophisticated equipment such as lasers.

[0057] 3. This application uses a grating structure composed of polymer segment 13 and air 14. During temperature changes, the expansion and compression of the elastic-plastic polymer segment 13 by air 14 causes a change in the grating period, thus achieving temperature sensing. The characteristic that the thermal expansion coefficient of air 14 is much greater than that of polymer segment 13 is used to control the grating period. Compared with existing fiber optic grating temperature sensors, the temperature-sensitive unit is composed of air 14 and polymer segment 13. Its expansion coefficient affected by temperature is higher, and its response to temperature changes will be more sensitive, thus improving the sensitivity and measurement resolution of fiber optic grating for temperature sensing.

[0058] It should be noted that the data involved in this application (including but not limited to data used for analysis, data stored, data displayed, etc.) are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of the relevant data must comply with relevant regulations.

[0059] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0060] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0061] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for fabricating a fiber optic polymer grating temperature sensing unit, characterized in that, The method for fabricating the fiber polymer grating temperature sensing unit includes: S110, providing a double-opening capillary (10), and alternately pumping a curable polymer precursor (9) and air (14) into the capillary (10) to form a periodic arrangement of the polymer precursor (9) and air (14) segments inside the capillary (10). S120. Insert the transmission optical fiber (5) into the openings at both ends of the capillary (10) and extend the end of the transmission optical fiber (5) into the interior of the capillary (10) to optically couple with the periodic arrangement structure. S130. The polymer precursor (9) is cured to form a cured polymer segment (13), the polymer segment (13) and the air segment (14) together constitute a fiber polymer grating structure. S140. Fix the relative position of the transmission optical fiber (5) and the capillary (10) to prepare an optical fiber sensing unit (6).

2. The method for fabricating the fiber polymer grating temperature sensing unit according to claim 1, characterized in that, The method pumps the polymer precursor (9) and air (14) into the capillary (10) via a peristaltic pump (12) and a silicone tube (11) to form the periodic arrangement structure.

3. The method for fabricating the fiber polymer grating temperature sensing unit according to claim 1, characterized in that, The polymer precursor (9) is a polydimethylsiloxane precursor. The pumping volume ratio of the polymer precursor (9) to air (14) is 1:

1. The coefficient of thermal expansion of the cured polymer segment (13) is less than that of air (14).

4. The method for fabricating the fiber polymer grating temperature sensing unit according to claim 1, characterized in that, Curing the polymer precursor (9) includes: placing the transmission optical fiber (5) and the capillary (10) in an environment of 60°C for heating and curing, so that the polymer precursor (9) forms a cured polymer segment (13).

5. The method for fabricating the fiber polymer grating temperature sensing unit according to claim 1, characterized in that, Fixing the relative position of the transmission optical fiber (5) and the capillary tube (10) includes: applying UV adhesive (7) to the connection between the opening of the capillary tube (10) and the transmission optical fiber (5) for encapsulation, and then irradiating with UV light for 5-10 minutes to achieve a fixed connection between the transmission optical fiber (5) and the capillary tube (10).

6. The method for fabricating the fiber polymer grating temperature sensing unit according to claim 1, characterized in that, The double-opening capillary (10) is any one of a quartz capillary, a stainless steel capillary, or a polytetrafluoroethylene capillary.

7. A fiber optic polymer grating temperature sensor system, characterized in that, The fiber polymer grating temperature sensor system includes: The light source module (3) is used to generate the incident light signal (15); The fiber optic sensing unit (6) is prepared by the fiber polymer grating temperature sensing unit preparation method according to any one of claims 1-6. The fiber optic circulator (4) includes a first port, a second port and a third port. The first port is connected to the light source module (3), and the second port is connected to the fiber optic sensing unit (6). The circulator is used to guide the incident light signal (15) to the fiber optic sensing unit (6) and to export the reflected light signal (16) from the fiber optic sensing unit (6) from the third port. The signal acquisition and processing module (2) is connected to the third port and is used to receive and demodulate the reflected light signal (16) to obtain the reflection spectrum data. The polymer segment (13) in the fiber optic sensing unit (6) has thermal expansion properties. The grating period formed by the polymer segment (13) and the air segment (14) changes with temperature, causing a shift in the characteristic wavelength in the reflection spectrum data. Temperature sensing is achieved by detecting the amount of the shift.

8. The fiber optic polymer grating temperature sensor system according to claim 7, characterized in that, The signal acquisition and processing module (2) includes a spectrum analyzer, and the system also includes a computer module (1). The computer module (1) is communicatively connected to the signal acquisition and processing module (2) and is used to receive the reflection spectrum data and extract the characteristic wavelengths of the reflection spectrum data. It is also used to calculate and output the temperature value according to the pre-stored wavelength-temperature calibration relationship.

9. The fiber optic polymer grating temperature sensor system according to claim 7, characterized in that, The transmission optical fiber (5) is a germanium-doped silica single-mode optical fiber with a germanium content of less than 5%, and the core refractive index of the transmission optical fiber (5) matches the refractive index of the polymer segment (13) after curing.

10. The fiber optic polymer grating temperature sensor system according to claim 7, characterized in that, The system includes multiple fiber optic sensing units (6) with different grating periods. The fiber optic sensing units (6) are connected to the same light source module (3) and the signal acquisition and processing module (2) through fiber optic couplers or cascading, forming a quasi-distributed temperature sensing network.

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