A side-polished fiber temperature sensor and a method of making

Abstract

The application discloses a side-polished fiber temperature sensor and a preparation method, and relates to the technical field of optical fiber sensing. The method comprises the following steps: providing a single-mode-multimode-single-mode optical fiber structure formed by fusing a multimode optical fiber and two single-mode optical fibers; manually grinding the sidewall of the multimode optical fiber to form a polishing surface; during the grinding process, connecting the optical fiber structure to a light source and a spectrum analyzer to monitor the transmission spectrum in real time, and determining the grinding endpoint according to preset characteristic changes of the transmission spectrum; and coating a temperature-sensitive polymer material on the polishing surface and curing. The application introduces real-time spectrum monitoring as a closed-loop feedback control means, converts subjective manual operation into objective and quantitative index control, solves the problem of uncontrollable precision of traditional manual grinding, and can stably and repeatedly prepare a high-performance sensor in a low-cost manner.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a side-thrown fiber optic temperature sensor and its fabrication method. Background Technology

[0002] Fiber optic temperature sensors have been widely used in industry, medicine, and scientific research due to their advantages such as resistance to electromagnetic interference, small size, and remote measurement capabilities. Among them, fiber optic sensors based on the single-mode-multimode-single-mode (SMS) structure have attracted much attention due to their simple structure and ease of fabrication. However, the temperature sensitivity of traditional SMS sensors based on pure quartz materials is limited by the inherent thermo-optical coefficient and thermal expansion coefficient of quartz, resulting in typically low sensitivity that is difficult to meet the requirements of high-precision measurement.

[0003] To improve sensor sensitivity, various enhancement schemes have been explored in existing technologies. One scheme involves side polishing of the optical fiber to expose the evanescent field near the fiber core, followed by coating with a thermo-optical material with a high thermo-optical coefficient. This interaction between the evanescent field and the thermo-optical material significantly improves sensitivity.

[0004] However, the side-polishing process itself has significant technical bottlenecks. While using precision wheel-type polishing equipment offers high accuracy, the equipment is expensive, the process is complex, and production efficiency and yield are unsatisfactory, making it unsuitable for low-cost, large-scale production. Manual grinding, on the other hand, is low-cost and flexible, but its production process heavily relies on the operator's experience and feel, making it difficult to precisely control the polishing depth and uniformity, resulting in poor sensor performance consistency and low yield. Therefore, how to accurately fabricate a side-polished structure in a low-cost, highly controllable manner and effectively combine it with temperature-sensitive materials to obtain a high-performance fiber optic temperature sensor is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a side-polished fiber optic temperature sensor and its preparation method, aiming to solve the technical problems of low precision, poor repeatability, and high cost of precision equipment processing in existing side-polishing methods.

[0006] To achieve the above objectives, this application provides the following solution: In a first aspect, this application provides a method for fabricating a side-thrown fiber optic temperature sensor, comprising: Provide a single-mode-multimode-single-mode fiber structure formed by sequentially splicing a section of multimode fiber and two sections of single-mode fiber; The sidewalls of the multimode fiber are manually polished to form a polished surface along the fiber axis. During the manual polishing process, the single-mode-multimode-single-mode fiber structure is connected to a light source and a spectrum analyzer to monitor its transmission spectrum in real time, and the polishing endpoint is determined based on the preset characteristic changes of the transmission spectrum. A temperature-sensitive polymer material is coated onto the polished surface, and then the temperature-sensitive polymer material is cured.

[0007] In some embodiments, determining the grinding endpoint based on a preset characteristic change in the transmission spectrum includes: The contrast of the interference valley in the transmission spectrum is monitored, and the grinding endpoint is determined to be reached when the contrast decays to a preset threshold.

[0008] In some embodiments, the temperature-sensitive polymer material is polydimethylsiloxane.

[0009] In some embodiments, during the manual grinding step, polyester film sandpaper is used for grinding, and alcohol is added as a lubricating medium during the grinding process.

[0010] In some embodiments, the core diameter of the multimode optical fiber is 105 μm and the length of the multimode optical fiber is 3 cm.

[0011] In some embodiments, the polydimethylsiloxane is prepared by mixing a prepolymer and a curing agent in a volume ratio of 10:1.

[0012] In some embodiments, the curing process includes: heating the thermosensitive polymer material at a constant temperature of 100°C for 60 minutes.

[0013] Secondly, this application provides a side-thrown fiber optic temperature sensor, comprising: A single-mode-multimode-single-mode fiber structure, wherein the multimode fiber has a D-shaped cross-section polished surface formed by side grinding; A temperature-sensitive polymer coating is cured on the polished surface.

[0014] In some embodiments, the temperature-sensitive polymer coating is a polydimethylsiloxane coating.

[0015] In some embodiments, the core diameter of the multimode optical fiber is 105 μm and the length of the multimode optical fiber is 3 cm, and the polishing depth of the polished surface is 30 μm.

[0016] According to the specific embodiments provided in this application, the following technical effects are disclosed: By side-polishing the optical fiber to expose the evanescent field and coating it with a thermosensitive polymer material (such as polydimethylsiloxane) with a high negative thermo-optic coefficient, the temperature sensitivity of the sensor is significantly improved, and the response linearity is high. For example, the sensitivity can be increased from approximately +0.023 nm / ℃ in the conventional structure to approximately -0.178 nm / ℃, and the linear correlation coefficient R0 is significantly improved. 2 The response intensity can reach as high as 0.992, and the response direction reverses from redshift to blueshift, exhibiting distinct characteristics and ease of demodulation. Furthermore, this invention replaces expensive precision machining equipment with a low-cost manual grinding method, and creatively introduces real-time spectral monitoring as a closed-loop feedback control mechanism. By monitoring characteristic changes in the transmission spectrum (such as the attenuation of interference valley contrast), the grinding endpoint is accurately determined, solving the fundamental problem of traditional manual grinding relying on personal experience and having uncontrollable precision. This allows for the stable and repeatable fabrication of high-performance sensors at low cost. The entire manufacturing process is clear and requires minimal equipment. By transforming subjective "feel" control into objective, quantifiable spectral indicators to guide manual operation, the reliance on operator skills is greatly reduced, significantly improving the success rate and consistency of finished product performance. Attached Figure Description

[0017] 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.

[0018] Figure 1 This is a schematic flowchart of the fabrication method of a side-thrown fiber optic temperature sensor in one embodiment of this application.

[0019] Figure 2 This is a temperature-wavelength relationship diagram of a side-thrown fiber optic temperature sensor in one embodiment of this application. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] This application provides a method for fabricating a side-sprayed fiber optic temperature sensor, aiming to address the technical pain points of low precision, poor repeatability, and high cost of precision equipment processing in existing technologies. The core idea of ​​this method is to combine a low-cost manual grinding process with high-precision real-time spectral monitoring to form a closed-loop feedback control system, thereby enabling the fabrication of a high-performance fiber optic temperature sensor in an economical, efficient, and controllable manner.

[0023] Reference Figure 1 The method for fabricating the side-thrown fiber optic temperature sensor provided in this application embodiment specifically includes: Step S110: Provide a single-mode-multimode-single-mode fiber structure formed by sequentially splicing a multimode fiber segment and two single-mode fibers.

[0024] Step S120: The sidewalls of the multimode fiber are manually polished to form a polished surface along the fiber axis. During the manual polishing process, the single-mode-multimode-single-mode fiber structure is connected to the light source and the spectrum analyzer to monitor its transmission spectrum in real time, and the polishing endpoint is determined based on the preset characteristic changes of the transmission spectrum.

[0025] Step S130: Coat the polished surface with a temperature-sensitive polymer material and cure the temperature-sensitive polymer material.

[0026] First, a single-mode-multimode-single-mode (SMS) fiber structure is required, consisting of a multimode fiber segment and two single-mode fiber segments sequentially fused together. This step is fundamental to constructing the multimode interferometric sensing unit. By axially fusion-splitting the single-mode and multimode fibers, when light propagates from the input single-mode fiber to the multimode fiber, the abrupt change in core diameter excites multiple higher-order modes in the multimode fiber due to the fundamental mode. These modes interfere as they propagate through the multimode fiber, forming a specific interference spectrum at the output. This structure provides the physical basis for the subsequent sensing mechanism.

[0027] Subsequently, the sidewalls of the multimode fiber need to be manually polished to form a polished surface along the fiber axis. The purpose of this step is to allow the evanescent field, originally confined within the fiber core, to leak to the outside of the fiber by controllably removing a portion of the fiber cladding. The evanescent field is a key medium for sensing; its strength and distribution directly affect the efficiency of the sensor's interaction with the external environment. Compared to existing wheel-based processing methods that rely on expensive and precise equipment, manual polishing significantly reduces equipment costs and process complexity. However, the inherent uncontrollable precision problem is the core challenge that this invention aims to address.

[0028] To address the precision control challenges of manual polishing, this method connects a single-mode-multimode-single-mode fiber structure to a light source and a spectrometer during the manual polishing process. This allows for real-time monitoring of the transmission spectrum, and the polishing endpoint is determined based on preset characteristic changes in the transmission spectrum. This step is the core innovation of this invention, transforming an open, experience-dependent "manual operation" into a "closed-loop control process" with objective data feedback. By monitoring spectral changes in real time, the operator can intuitively understand the real-time impact of the polishing process on the optical waveguide performance, thus enabling precise stopping of polishing when the target polishing depth is reached. This avoids under- or over-polishing, achieving a balance between low cost and high precision.

[0029] After the polishing process reaches its end point, a temperature-sensitive polymer material needs to be coated onto the polished surface. The purpose of this step is to introduce temperature sensitivity. By coating the area exposed to the evanescent field with this material, the refractive index of the material changes when the ambient temperature changes. This change, in turn, modulates the effective refractive index of the guided wave mode in the optical fiber through evanescent field coupling, ultimately causing a measurable shift in the transmission spectrum. Through this design, temperature changes are converted into changes in the spectral signal, achieving the function of temperature sensing.

[0030] Finally, the temperature-sensitive polymer material undergoes a curing process. This step aims to transform the liquid or semi-solid temperature-sensitive material into a stable, firmly adhered solid coating on the polished surface of the optical fiber. A stable and reliable coating is crucial for ensuring the long-term operational stability and measurement repeatability of the sensor. The curing process ensures a stable optical and mechanical coupling between the temperature-sensitive coating and the optical fiber, thereby guaranteeing the sensor's performance.

[0031] In a preferred embodiment, the grinding endpoint is determined based on a preset characteristic change in the transmission spectrum. Specifically, this includes monitoring the contrast of interference valleys in the transmission spectrum and determining that the grinding endpoint has been reached when the contrast decays to a preset threshold. This step provides a specific and quantifiable physical indicator for the aforementioned "preset characteristic change." As the grinding depth increases, evanescent field leakage intensifies, transmission loss increases, leading to a decrease in the contrast of interference fringes. By setting a clear contrast decay threshold (e.g., decaying to 50% of the initial value), the determination of the grinding endpoint can be transformed from the operator's subjective "feel" or vague observation into an objective and repeatable data indicator. In this way, the stability and yield of the manual grinding process are greatly improved, solving the core pain point of uncontrollable precision in traditional manual grinding.

[0032] In another preferred embodiment, the temperature-sensitive polymer material is polydimethylsiloxane (PDMS). PDMS was chosen as the temperature-sensitive material based on its excellent optical properties. PDMS has a very high negative thermo-optic coefficient, and its refractive index decreases significantly with increasing temperature. Compared to the weak positive thermo-optic effect of silica optical fiber itself, the introduction of PDMS can greatly amplify the temperature response of the sensor. By coating PDMS onto a polished surface and utilizing its significant change in refractive index to modulate the evanescent field, an order-of-magnitude improvement in temperature sensitivity is achieved, solving the problem of low sensitivity in traditional SMS sensors.

[0033] Furthermore, polydimethylsiloxane is prepared by mixing prepolymer and curing agent at a volume ratio of 10:1. This ratio is an optimized formulation verified through extensive experiments. PDMS prepared using this ratio can form a coating with moderate crosslinking density, good mechanical properties, and stable thermo-optical characteristics during the subsequent curing process. Excessively high or low curing agent ratios can lead to incomplete curing, excessively brittle or soft coatings, or poor long-term stability. Therefore, by precisely controlling the ratio, the high quality of the temperature-sensitive coating itself is ensured, providing material-level protection for the overall performance of the sensor.

[0034] In one optional embodiment, the manual polishing step involves using polyester film sandpaper and adding alcohol as a lubricant during the polishing process. Polyester film sandpaper offers advantages such as uniform abrasive particles and a smooth substrate, enabling the production of a polished surface with low surface roughness while maintaining polishing efficiency. Adding alcohol as a lubricant effectively removes heat generated during polishing, preventing damage to the optical fiber due to localized overheating; it also washes away quartz micro-shavings produced during polishing, preventing scratches on the polished surface or impacting polishing efficiency. This combination achieves effective control over the quality of the polished surface.

[0035] In another preferred embodiment, the multimode fiber has a core diameter of 105 μm and a length of 3 cm. These geometric parameters are optimized based on theoretical simulations and experimental optimization. For the SMS structure, the length of the multimode fiber directly affects the self-image effect of the multimode interference. A length of 3 cm allows for a clear and stable self-image to be formed in a multimode fiber with this core diameter, resulting in high contrast and sharp characteristic peaks and valleys in the output interference spectrum, providing a high-quality raw signal for subsequent spectral monitoring and demodulation. By optimizing the geometric parameters of the SMS structure, the signal-to-noise ratio and measurement accuracy of the sensor are fundamentally improved.

[0036] Furthermore, the curing process includes isothermal heating of the temperature-sensitive polymer material at 100°C for 60 minutes. This step provides optimized process parameters for PDMS curing. The temperature of 100°C effectively promotes the hydrosilylation reaction between the PDMS prepolymer and the curing agent, ensuring full cross-linking and curing of the coating. The 60-minute duration ensures complete reaction, avoiding problems such as coating stickiness, insufficient mechanical strength, or long-term performance drift caused by incomplete curing. By precisely controlling the curing process, a strong bond and long-term stability between the temperature-sensitive coating and the optical fiber surface are ensured.

[0037] This application also provides a side-polished fiber optic temperature sensor. This sensor is a product directly fabricated using any of the aforementioned methods. The sensor includes a single-mode-multimode-single-mode fiber structure, wherein the multimode fiber has a D-shaped cross-section polished surface formed by side polishing, and a temperature-sensitive polymer coating cured on the polished surface. The core of this structure lies in exposing the evanescent field through the D-shaped cross-section polished surface and achieving a sensitive response to temperature through the temperature-sensitive polymer coating, thereby forming a complete high-sensitivity sensing unit.

[0038] In a preferred embodiment, the temperature-sensitive polymer coating is a polydimethylsiloxane (PDMS) coating. This limitation corresponds to the preferred materials in the aforementioned method, clarifying the core material for achieving high-performance sensing. Because PDMS has a high negative thermo-optic coefficient, sensors using PDMS coatings can achieve extremely high temperature sensitivity and excellent linearity, which is a key structural feature for realizing the beneficial effects of this invention.

[0039] In another preferred embodiment, the multimode fiber in the single-mode-multimode-single-mode fiber structure has a core diameter of 105 μm, a length of 3 cm, and a polishing depth of 30 μm. This definition dictates the preferred geometry of the sensor. As previously stated, the 105 μm core diameter and 3 cm length are chosen to achieve optimal self-image effect and high-quality interference spectrum. The 30 μm polishing depth represents the optimal balance between evanescent field coupling efficiency and transmission loss, determined through simulation and experimentation. By combining these optimized geometric parameters, the resulting sensor structurally ensures excellent overall performance.

[0040] The following exemplary embodiment will provide a more detailed description of the fabrication method of the side-thrown fiber optic temperature sensor provided in this application.

[0041] In an exemplary embodiment, the method for fabricating a side-sprayed fiber optic temperature sensor involves constructing a real-time monitoring system consisting of a broadband light source, a V-groove fixture for fixing the SMS fiber structure to be processed, and a spectrometer. The system guides the manual grinding process by analyzing the real-time changing transmission spectrum curve.

[0042] The specific process for fabricating a side-thrown fiber optic temperature sensor is as follows: First, a single-mode-multimode-single-mode (SMS) fiber structure is fabricated. Specifically, a segment of multimode fiber is selected, and its two ends are fused to the end faces of a single-mode fiber to form a series SMS fiber structure. This structure is the physical basis for realizing the multimode interference effect.

[0043] Next, manual side polishing is performed. The prepared SMS fiber structure is fixed on a V-groove fixture to ensure its stability during the polishing process. Then, using a suitable polishing tool, such as sandpaper, the multimode fiber portion of the SMS fiber structure is manually polished back and forth to form a flat polished surface on its sidewalls. The purpose of this polished surface is to expose the evanescent field inside the fiber so that it can interact with the subsequently coated temperature-sensitive material.

[0044] Simultaneously, real-time spectral monitoring and process control are implemented during the polishing process. One end of the SMS fiber structure is connected to a broadband light source, and the other end is connected to a spectrometer. The spectrometer displays the transmission spectrum curve through the fiber in real time. As polishing progresses, the fiber cladding thins, and the evanescent field leakage intensifies, causing changes in the transmission spectrum curve. The operator observes these preset spectral characteristic changes, such as a decrease in the overall power or a reduction in contrast of the interference fringes, to determine whether the polishing is close to or has reached the target depth. When the polishing endpoint is determined to have been reached, polishing is stopped; if not, polishing continues. This closed-loop feedback mechanism transforms the invisible changes in polishing depth into visible changes in spectral data, enabling the operator to precisely control the endpoint of manual polishing and solving the problem that traditional manual polishing relies entirely on "feel" and experience.

[0045] After grinding, a layer of temperature-sensitive polymer material is coated onto the resulting polished surface. This material should have the characteristic of a significant change in refractive index with temperature variations. The material is uniformly applied to the polished surface using methods such as drop coating, spin coating, or other techniques. The preferred temperature-sensitive polymer material is polydimethylsiloxane (PDMS).

[0046] Finally, the coated temperature-sensitive polymer material undergoes a curing process. Depending on the properties of the selected material, methods such as constant-temperature heating or ultraviolet light irradiation can be used to transform the liquid polymer into a solid coating, which then firmly bonds to the surface of the optical fiber. At this point, a complete side-projected optical fiber temperature sensor is fabricated.

[0047] By using the above method, low-cost manual grinding tools combined with high-precision real-time spectral feedback, high-performance sensors can be fabricated in an economical and controllable manner, balancing cost and performance.

[0048] In an example process: First, the SMS fiber structure is fabricated. A 3cm long multimode fiber with a core diameter of 105μm is selected, and its end faces are precisely processed using a fiber cleaver. Then, using a fiber fusion splicer, its two ends are fused to two standard single-mode fibers respectively to form the SMS structure.

[0049] Next, a real-time monitoring system was set up. The prepared SMS fiber structure was carefully fixed in a V-groove fixture, ensuring that the area to be polished was flat and stable. One end of the SMS fiber structure was connected to a broadband light source (e.g., an ASE light source), and the other end was connected to a spectrometer. At this time, the initial transmission spectrum curve of the SMS fiber structure would be displayed on the screen of the spectrometer. A clear, high-contrast interference valley was selected, and its initial contrast value was recorded.

[0050] Next, precise manual polishing is performed. Take a sheet of 800-grit polyester film sandpaper and drop a small amount of 95% alcohol onto the area to be polished. The operator holds the sandpaper and, with uniform pressure and speed, reciprocates along the fiber axis to polish the multimode fiber section, controlling the polishing length to approximately 2.5 cm. Throughout the polishing process, the operator needs to observe the changes in the transmission spectrum curve on the spectrometer in real time, especially the attenuation of the contrast of the target interference valley. When the contrast attenuation reaches approximately 50% of the initial value, polishing is immediately stopped. In this way, the polishing depth can be precisely controlled to approximately 30 μm, forming a high-quality polished surface.

[0051] After polishing, the PDMS coating is prepared and applied. The PDMS prepolymer and curing agent are thoroughly mixed in a clean container at a volume ratio of 10:1. After stirring evenly, the mixture is allowed to stand for 30 minutes to eliminate air bubbles generated during mixing. Then, using a pipette, an appropriate amount of the PDMS mixture is carefully dripped onto the polished surface of the optical fiber, ensuring that the mixture completely and evenly covers the entire polished area.

[0052] Finally, a curing process is performed. The PDMS-coated optical fiber, along with its support (such as a glass slide), is placed on a precision heating stage. The stage temperature is set to 100°C and maintained at that temperature for 60 minutes. After heating, it is allowed to cool naturally to room temperature, at which point the PDMS coating is fully cured and firmly bonded to the optical fiber. At this point, a high-performance optical fiber temperature sensor is complete.

[0053] The sensor, fabricated in this manner, was tested for performance using the following procedure: The sensor was placed in a temperature-controlled environment and connected to a light source and spectrometer. When the ambient temperature changed, the spectrometer detected the shift in the wavelength of the interference valleys in the transmission spectrum. For example... Figure 2As shown, experimental results indicate that the characteristic wavelength exhibits a regular blue shift when the temperature increases from 50℃ to 75℃. The temperature sensitivity of the sensor can be obtained by linearly fitting the temperature and wavelength data points. The sensor fabricated in this embodiment has a temperature sensitivity as high as -0.178 nm / ℃, and the linear correlation coefficient R0 is [missing value]. 2 The value reached 0.992. In contrast, the conventional SMS structure without polishing and coating had a sensitivity of only +0.023 nm / ℃ and poor linearity (R0). 2 =0.96).

[0054] This embodiment achieves a nearly 8-fold increase in the absolute value of sensor temperature sensitivity and significantly improves linearity by synergistically combining multiple technical features, including closed-loop control for real-time spectral monitoring, optimized SMS geometry, high-quality polishing process, and high-performance PDMS temperature-sensitive material. This fully demonstrates that the synergistic effect of the various technical features of this invention brings about significant technical results, thereby solving the technical challenges of manufacturing high-precision sensors in a low-cost manner.

[0055] The side-projectile fiber optic temperature sensor provided by this invention can be widely used in various scenarios requiring precise, distributed, or remote temperature monitoring. In practical applications, a typical temperature measurement system consists of a broadband light source, one or more sensors of this invention, and a spectral demodulation device (which can be a spectral analyzer or a more compact fiber Bragg grating demodulator). During operation, the light emitted by the broadband light source passes through the sensor, and its transmission spectrum is received and analyzed by the spectral demodulation device.

[0056] The specific workflow is as follows: First, the sensor is calibrated, that is, the wavelength of its characteristic interference valley is measured at different known temperature points to establish a model. Figure 2 The temperature-wavelength relationship curve or lookup table is shown. In actual measurements, the spectral demodulation equipment tracks the wavelength position of this characteristic interference valley in real time. Once a wavelength drift is detected, the system can calculate the corresponding temperature value in real time based on the pre-calibrated relationship. Due to its small size, corrosion resistance, and electromagnetic interference resistance, the sensor is particularly suitable for temperature monitoring in harsh or special environments where traditional electrical sensors are difficult to apply, such as power transformer windings, large bridge structures, and minimally invasive surgical instruments.

[0057] 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.

[0058] 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 side-thrown fiber optic temperature sensor, characterized in that, include: Provide a single-mode-multimode-single-mode fiber structure formed by sequentially splicing a section of multimode fiber and two sections of single-mode fiber; The sidewalls of the multimode fiber are manually polished to form a polished surface along the fiber axis. During the manual polishing process, the single-mode-multimode-single-mode fiber structure is connected to a light source and a spectrum analyzer to monitor its transmission spectrum in real time, and the polishing endpoint is determined based on the preset characteristic changes of the transmission spectrum. A temperature-sensitive polymer material is coated onto the polished surface, and then the temperature-sensitive polymer material is cured.

2. The method for fabricating a side-thrown fiber optic temperature sensor according to claim 1, characterized in that, The step of determining the grinding endpoint based on the preset characteristic changes in the transmission spectrum includes: The contrast of the interference valley in the transmission spectrum is monitored, and the grinding endpoint is determined to be reached when the contrast decays to a preset threshold.

3. The method for preparing the side-thrown fiber optic temperature sensor according to claim 1, characterized in that, The temperature-sensitive polymer material is polydimethylsiloxane.

4. The method for fabricating a side-thrown fiber optic temperature sensor according to claim 1, characterized in that, In the manual grinding step, polyester film sandpaper is used for grinding, and alcohol is added as a lubricating medium during the grinding process.

5. The method for fabricating a side-thrown fiber optic temperature sensor according to claim 1, characterized in that, The multimode fiber has a core diameter of 105 μm and a length of 3 cm.

6. The method for preparing the side-thrown fiber optic temperature sensor according to claim 3, characterized in that, The polydimethylsiloxane is prepared by mixing a prepolymer and a curing agent in a volume ratio of 10:

1.

7. The method for fabricating a side-thrown fiber optic temperature sensor according to claim 1, characterized in that, The curing process includes heating the thermosensitive polymer material at a constant temperature of 100°C for 60 minutes.

8. A side-thrown fiber optic temperature sensor, characterized in that, include: A single-mode-multimode-single-mode fiber structure, wherein the multimode fiber has a D-shaped cross-section polished surface formed by side grinding; A temperature-sensitive polymer coating is cured on the polished surface.

9. The side-thrown fiber optic temperature sensor according to claim 8, characterized in that, The temperature-sensitive polymer coating is a polydimethylsiloxane coating.

10. The side-thrown fiber optic temperature sensor according to claim 8 or 9, characterized in that, The multimode fiber has a core diameter of 105μm and a length of 3cm, and the polishing depth of the polished surface is 30μm.

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