Temperature-aware chalcogenide glass optical fiber evanescent wave sensor and method of making same

Abstract

The application discloses a temperature-sensing chalcogenide glass optical fiber evanescent wave sensor and a preparation method thereof. The sensor comprises a chalcogenide glass optical fiber, the chalcogenide glass optical fiber has a chemical sensing area and a temperature sensing area, the temperature sensing area is coated with a temperature response medium layer, the temperature response medium layer is composed of polydimethylsiloxane, the chemical sensing area is used for detecting chemical information of a to-be-measured substance through an infrared evanescent wave effect, and the temperature sensing area is used for modulating an optical fiber evanescent field through a thermo-optic effect of polydimethylsiloxane, so that temperature information is acquired. The application sets the chemical sensing area and the temperature sensing area on the chalcogenide glass optical fiber, utilizes the infrared evanescent wave effect and the thermo-optic effect, realizes synchronous all-optical sensing of the chemical information and the temperature information on the same optical fiber, and the sensor can be applied to complex chemical process monitoring, dangerous environment early warning, biomedical analysis and other fields, and provides a brand-new thought for development of a multifunctional optical fiber sensing technology.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a chalcogenide glass fiber evanescent wave sensor with integrated temperature sensing and its fabrication method. Background Technology

[0002] Fiber optic chemical sensing technology is a cutting-edge analytical technique that combines the advantages of remote, real-time, and in-situ detection of optical fibers with chemical identification capabilities. Its core lies in achieving qualitative and quantitative detection of target substances through optical parametric modulation caused by changes in chemical composition. It has enormous application potential in fields such as biomedical diagnostics, environmental monitoring, and public safety.

[0003] Currently, mainstream fiber optic chemical sensing technologies are mainly based on principles such as fiber gratings and surface plasmon resonance. However, these methods often rely on the specific adsorption or reaction of coatings to achieve selective identification, and are usually only effective for a specific type of substance, making it difficult to meet the complex monitoring needs of multi-component coexistence and dynamic compositional changes in practical applications. In contrast, infrared fiber optic evanescent wave sensing technology, relying on the high fingerprint response of the mid-infrared band to the fundamental frequency vibration of molecules, can directly acquire molecular fingerprint information through the interaction between the evanescent field and the analyte without a recognition coating, and is considered an ideal technical approach for achieving multi-component chemical sensing.

[0004] Among existing infrared evanescent wave sensing materials, chalcogenide glass fibers have become the core material in this field due to their wide infrared transmittance and flexible, tunable composition. Currently, research teams both domestically and internationally have achieved highly sensitive detection of various chemical substances using infrared evanescent wave sensing based on chalcogenide glass fibers, and related research has made a series of advances in fields such as gas analysis and environmental monitoring. However, as application scenarios become increasingly complex and diverse, infrared fiber evanescent wave sensing technology, due to its limited sensing information, is gradually failing to meet the comprehensive assessment needs of complex system states. Temperature, as a core physical quantity in the evolution of system states, directly affects material properties, biological activities, and environmental changes through its dynamic changes. In applications such as chemical process monitoring and biological metabolic analysis, its changes often occur synchronously and are highly coupled with the evolution of chemical composition. The lack of synchronous temperature sensing capability has become a key bottleneck restricting the further development and application of infrared fiber evanescent wave sensing technology.

[0005] Currently, the synchronous sensing of chemical and temperature information based on chalcogenide glass optical fibers mainly involves introducing the thermistor effect into infrared evanescent wave sensing, reading temperature information through changes in fiber resistance. However, this method typically relies on high tellurium (Te) content glass to obtain a stable electrical response, resulting in poor fiber thermal stability. Furthermore, the sensitivity of resistive temperature sensing decreases significantly in high-temperature regions, and the synchronous acquisition of optical and electrical signals increases system complexity, hindering its further application in wide-temperature environments. Therefore, there is an urgent need to develop novel infrared fiber evanescent wave sensing technology that integrates temperature sensing to achieve real-time and accurate monitoring of complex systems. Summary of the Invention

[0006] This invention provides a chalcogenide glass fiber evanescent wave sensor with integrated temperature sensing and its fabrication method. By setting a chemical sensing region and a temperature sensing region coated with polydimethylsiloxane (PDMS) on a chalcogenide glass fiber, and utilizing the infrared evanescent wave effect and thermo-optic effect, synchronous all-optical sensing of chemical and temperature information is achieved on the same fiber. This avoids the increased system integration complexity caused by introducing electrical signals and overcomes the shortcomings of existing infrared evanescent wave sensing technology, such as the single information requirement, and the poor thermal stability and significant sensitivity attenuation in high-temperature regions caused by thermistor-type schemes relying on high tellurium content glass. The sensor of this invention can be applied to fields such as monitoring complex chemical processes, early warning of hazardous environments, and biomedical analysis, providing a completely new approach for the development of multifunctional fiber optic sensing technology.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a chalcogenide glass fiber evanescent wave sensor with temperature sensing, wherein the evanescent wave sensor includes a chalcogenide glass fiber, the chalcogenide glass fiber has a chemical sensing region and a temperature sensing region, the temperature sensing region is covered with a temperature-responsive medium layer, the temperature-responsive medium layer is composed of polydimethylsiloxane, the chemical sensing region is used to detect the chemical information of the analyte through the infrared evanescent wave effect, and the temperature sensing region is used to modulate the evanescent field of the fiber through the thermo-optic effect of the polydimethylsiloxane, thereby obtaining temperature information.

[0008] The working principle of this invention is as follows: When light propagates inside an optical fiber, the evanescent wave generated on the fiber surface interacts with the external medium. For chemical sensing, when the chemical sensing region of the optical fiber comes into contact with the sample to be tested, the evanescent wave of a specific frequency is absorbed by the vibration of the chemical bonds in the sample, forming a corresponding infrared characteristic absorption peak in the output spectrum. By analyzing the peak shape and intensity changes of this absorption peak, the type and concentration information of the analyte can be obtained. For temperature sensing, the refractive index of the polydimethylsiloxane coating in the temperature sensing region changes with temperature. The intensity and distribution of the evanescent field in the optical fiber are modulated through the thermo-optic effect, causing the intensity of the polydimethylsiloxane characteristic absorption peak to evolve distinguishably with temperature. Temperature measurement can be achieved by monitoring the change in the intensity of this characteristic peak. Since the chemical response and temperature response are respectively reflected in the changes of infrared absorption peaks in different wavenumber regions of the spectrum, the simultaneous sensing of chemical and temperature information can be achieved by independently analyzing the corresponding regions in the output spectrum.

[0009] The sensor of this invention has a dual-sensing-area structure. By setting a chemical sensing area and a temperature sensing area on the same chalcogenide glass optical fiber, the chemical sensing area uses the infrared evanescent wave effect to obtain the molecular fingerprint information of the analyte, while the temperature sensing area uses the thermo-optic effect of polydimethylsiloxane to modulate the evanescent field of the optical fiber to obtain temperature information. This enables the synchronous sensing of chemical and temperature information on the same sensor, thereby solving the defects of existing infrared evanescent wave sensing technology, which provides only single information and is difficult to meet the comprehensive evaluation needs of complex system states. In addition, the temperature information is read optically and unified with the chemical information in the optical signal output, avoiding the increase in system integration complexity caused by the introduction of electrical signals.

[0010] In the sensor of this invention, polydimethylsiloxane is coated on the surface of the optical fiber as a temperature-responsive medium layer. Its refractive index changes with temperature, thereby modulating the intensity and distribution of the evanescent field of the optical fiber. This allows temperature changes to be directly reflected as a distinguishable evolution of the intensity of the characteristic absorption peak of polydimethylsiloxane in the infrared spectrum, without relying on the electrical response of high tellurium content glass. This overcomes the technical defects of poor optical fiber thermal stability and significant sensitivity attenuation in high-temperature regions in existing thermistor-type temperature sensing schemes.

[0011] Preferably, the chalcogenide glass optical fiber is made of chalcogenide glass material, the molar composition of which is expressed by the chemical formula (As...). x Se 100-x ) 100-z M zWherein, 10≤x≤90, 5≤z≤20, and M is one or more of Ge, Ga, Sb, Sn, S, Te, and CsCl. Chalcogenide glass fibers made from the above-described chalcogenide glass materials exhibit excellent infrared transmittance and glass formation stability. Furthermore, the glass composition ratio can be flexibly adjusted according to specific application requirements to optimize evanescent wave sensing sensitivity. Compared to existing technologies that rely on high tellurium content, this composition range effectively improves the thermal stability and processability of the optical fiber while ensuring infrared sensing performance.

[0012] Preferably, the structures of the chemical sensing region and the temperature sensing region are selected from one of the following: conical, flat, ring, and spiral. The chemical sensing region and the temperature sensing region can be flexibly selected according to the actual application scenario, providing diverse implementation solutions for sensor design under different detection requirements.

[0013] Preferably, the diameter of the chalcogenide glass fiber is 400–500 μm, and the thickness of the temperature-responsive medium layer is 0.1–2 mm. Limiting the diameter of the chalcogenide glass fiber to 400–500 μm ensures that it possesses sufficient mechanical strength to support the subsequent fabrication and coating of the sensing area, while also guaranteeing sufficient optical power transmission within the fiber to maintain effective excitation of the evanescent wave. This avoids excessive optical transmission loss due to an excessively thin fiber or insufficient evanescent field strength due to an excessively thick fiber. Limiting the thickness of the polydimethylsiloxane temperature-responsive medium layer to 0.1–2 mm avoids the drawback of an excessively thin coating causing susceptibility to interference from external fluid fluctuations, and also avoids the significant increase in heat conduction time and decreased real-time temperature sensing performance due to an excessively thick coating, thus ensuring the accuracy and timeliness of the temperature response.

[0014] Preferably, the length of the temperature-responsive dielectric layer is 7–22 mm. This 7–22 mm length range ensures a sufficiently long interaction distance between the evanescent field of the optical fiber and the temperature-responsive dielectric layer, allowing the refractive index change caused by temperature variations to accumulate into a resolvable spectral signal change. It also avoids the problems of an excessively long coating leading to a redundant overall optical fiber structure, increased optical transmission loss, and increased fabrication difficulty, thus achieving a reasonable balance between temperature response sensitivity and sensor structural compactness.

[0015] A method for fabricating a chalcogenide glass fiber evanescent wave sensor with temperature sensing as described above includes the following steps: (1) A chalcogenide glass rod was prepared by melt quenching method, and after annealing, polishing and cleaning, an optical fiber preform was obtained. The optical fiber preform was drawn into a chalcogenide glass optical fiber. (2) The chemical sensing region and the temperature sensing region are prepared on the chalcogenide glass optical fiber by means of melt tapering, hot pressing, or local heating and bending. (3) The mixture of polydimethylsiloxane prepolymer and curing agent is coated on the surface of the temperature sensing area and cured to form a temperature response medium layer, thus obtaining the evanescent wave sensor.

[0016] The sensor of this invention is simple to manufacture and the process is controllable. It can precisely control the geometric dimensions of the sensing area to achieve the required evanescent wave excitation intensity, making it suitable for mass production.

[0017] Preferably, in step (3), the preparation method of the mixture includes: mixing the polydimethylsiloxane prepolymer and the curing agent at a mass ratio of (5-15):1, stirring until homogeneous, and then performing vacuum degassing treatment at room temperature for 15-30 minutes. By limiting the mass ratio of polydimethylsiloxane prepolymer to curing agent to (5-15):1, the crosslinking density of the cured polydimethylsiloxane network can be adjusted within this ratio range. The lower the degree of crosslinking, the more significant the thermal expansion effect of the free volume of the polymer network, thereby giving the temperature-responsive medium layer a higher thermo-optic coefficient and temperature response sensitivity. In addition, removing air bubbles from the mixture through vacuum degassing treatment can avoid the problem of increased light scattering and uneven evanescent field distribution caused by pore defects inside the cured coating, ensuring the stability and consistency of the temperature sensing signal.

[0018] Preferably, in step (3), the coating method is as follows: the mixture is injected into the mold to completely cover the temperature sensing area, and then cured by heating at 80-100°C for 2-4 hours or by standing at room temperature for 24-48 hours. After demolding, the temperature-responsive dielectric layer is obtained. The above coating method is simple to operate and has good repeatability. It can effectively solve the problems of uneven coating thickness and irregular shape when directly coating the optical fiber surface, and ensure the consistency of batch preparation of temperature-responsive dielectric layers.

[0019] As a further preferred embodiment, the mold is prepared by 3D printing or machining. The mold has a groove or slot inside that matches the shape of the temperature sensing area. Before coating, the temperature sensing area is placed horizontally in the mold and fixed at both ends by clamping devices, so that the temperature sensing area is suspended or placed in the center of the groove. Then, the mixture is slowly injected along one side of the mold, so that the mixture completely covers the temperature sensing area and keeps the liquid surface flat and free of bubbles. The mold with grooves or slots prepared by 3D printing or machining can accurately match the shape of the temperature sensing area. Combined with the clamping device, slow injection of the mixture, and liquid surface control, it can ensure that the coating is free of off-center cores and bubbles, thereby improving the preparation quality of the temperature response medium layer and the signal stability of the sensor.

[0020] A chalcogenide glass fiber evanescent wave sensing system integrating temperature sensing includes a chalcogenide glass fiber evanescent wave sensor, an infrared light source, an infrared detector, and a data processing terminal for processing spectral signals. The output optical path of the infrared light source is coupled to the input end of the chalcogenide glass fiber, the infrared detector is connected to the output end of the chalcogenide glass fiber, and the data processing terminal is connected to the infrared detector. This sensing system utilizes changes in the infrared absorption peak corresponding to the chemical sensing region to obtain the type and concentration information of the analyte. Simultaneously, it uses the intensity change of the characteristic absorption peak of polydimethylsiloxane in the temperature sensing region to invert temperature information, enabling synchronous acquisition and output of both chemical and temperature parameters within the same system. This sensing system has a simple structure and uses a unified optical signal format, effectively avoiding the photoelectric signal conversion step. It is suitable for various practical applications such as chemical process monitoring, environmental monitoring, and biomedical analysis, providing a fully optical solution for the synchronous real-time monitoring of chemical composition evolution and temperature changes in complex systems.

[0021] Compared with the prior art, the present invention has the following advantages: 1. The sensor of this invention avoids dependence on high tellurium content. Temperature sensing is achieved in a fully optical manner through the thermo-optical effect of polydimethylsiloxane, without relying on the electrical response of the glass material itself. It has good thermal stability and a wider operating temperature range, and is highly processable.

[0022] 2. The sensor of this invention features a dual-sensing-area structure. By placing a chemical sensing area and a temperature sensing area on the same optical fiber, the chemical sensing area utilizes the infrared evanescent wave effect to acquire the molecular fingerprint information of the analyte, while the temperature sensing area utilizes the thermo-optical effect of polydimethylsiloxane to modulate the evanescent field of the optical fiber to acquire temperature information. Chemical and temperature information are simultaneously transmitted through a single infrared spectrum, achieving synchronous sensing of chemical and temperature information and overcoming the limitation of single-information infrared evanescent wave sensing technology. Furthermore, temperature and chemical information are unified in the optical signal output, avoiding the increased system integration complexity caused by introducing electrical signals. The sensor of this invention is simple to fabricate and the process is controllable, allowing for precise adjustment of the sensing area's geometry to achieve the required evanescent wave excitation intensity, making it suitable for mass production. The sensor's sensing area structure and polydimethylsiloxane coating parameters have a wide adjustable range, enabling applications in complex chemical process monitoring, hazardous environment early warning, and biomedical analysis, providing a novel approach for the development of multifunctional fiber optic sensing technology. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the chalcogenide glass fiber evanescent wave sensing system with temperature sensing built in Example 1. Figure 2The infrared spectra of the biconical chalcogenide glass fiber in Example 1 in saturated urea solutions at different temperatures are shown. Figure 3 The graph shows the response curve of the infrared characteristic absorption peak intensity of polydimethylsiloxane as a function of temperature in Example 2. Detailed Implementation

[0024] To better understand the present invention, the following detailed description is provided in conjunction with embodiments. However, the implementation of the present invention is not limited thereto. For process parameters not specifically described, conventional techniques can be referred to.

[0025] The chalcogenide glass fiber evanescent wave sensor of Example 1, which integrates temperature sensing, is fabricated by the following steps: (1) Preparation of matrix chalcogenide glass The chalcogenide glass material in this embodiment has the following molar composition: (As 37.5 Se 62.5 ) 80 Te 20 As 30 Se 50 Te 20 Using elemental As, Se, and Te with a purity of 5N as raw materials, they were accurately weighed and mixed uniformly according to stoichiometric ratios in a glove box filled with inert gas. The mixed raw materials were then placed into a quartz tube with an inner diameter of 15 mm, which had been pre-cleaned with aqua regia. The quartz tube was then evacuated to a vacuum of 1.0 × 10⁻⁶. -3 After Pa, the quartz tube was sealed using an oxyhydrogen flame. The sealed quartz tube was then placed in a swing furnace and slowly heated to 850°C for 10 hours, followed by cooling to 650°C and removing from the furnace. It was then air-cooled and quenched until the glass walls separated. The quartz tube was quickly transferred to an annealing furnace preheated to 120°C and held for 4 hours to relieve internal stress. After annealing, the furnace temperature was slowly lowered to room temperature, and the quartz tube was broken to remove the sample, yielding a chalcogenide glass rod.

[0026] (2) Preparation of optical fiber preform The surface of the chalcogenide glass rod obtained above was mechanically polished and then cleaned sequentially with hydrochloric acid, anhydrous ethanol and deionized water to finally obtain an optical fiber preform with a diameter of 13 mm and a length of 70 mm.

[0027] (3) Fiber drawing The fiber preform is vertically loaded into the furnace of the drawing tower, and inert gas is continuously introduced into the furnace as a protective gas. The furnace temperature is increased, and when the furnace temperature reaches the softening point of the chalcogenide glass, fiber drawing begins by precisely adjusting the drawing speed and the lowering speed of the preform. Inert gas protection is maintained throughout the drawing process, ultimately yielding chalcogenide glass optical fibers with a diameter of 500 μm.

[0028] (4) Preparation of chemical sensing area and temperature sensing area (4.1) Cut a 40cm long, 500μm diameter chalcogenide glass fiber and fix it on the fiber clamp controlled by the stepper motor, ensuring that the length of the fiber suspended at both ends of the clamp is consistent. (4.2) Move the heated copper block to the center of the optical fiber, ensuring that the optical fiber passes through the center of the heated copper block ring; (4.3) Adjust the microscope lens to be aimed at the heated area, turn on the illumination power and adjust it to a suitable magnification until a clear fiber optic morphology is observed on the monitor; (4.4) Set the drawing temperature to 185℃ using the temperature control system; (4.5) Observe the display. When the optical fiber is slightly bent due to heat, set the stretching speed of the stepper motor to 0.01 mm / s and the stretching distance to 10 mm. (4.6) After the fiber is slightly bent and held for 10 seconds, the tapering program is started. Once the set stretching target is reached, the program is stopped immediately and the heated copper block is quickly removed to obtain a tapered temperature sensing area with a waist diameter of 50 μm and a waist length of 10 mm; (4.7) After the first cone region is drawn, the optical fiber is translated to an appropriate distance, the drawing speed is changed to 0.01 mm / s, and the stretching distance is 8 mm to obtain a cone-shaped chemical sensing region with a waist diameter of 100 μm and a waist length of 8 mm.

[0029] (5) Preparation of temperature-responsive dielectric layer (5.1) The polydimethylsiloxane prepolymer and curing agent are mixed at a mass ratio of 10:1. Under this ratio, the crosslinking density of the cured polydimethylsiloxane network is low, and its free volume thermal expansion effect is more significant, resulting in a higher thermo-optic coefficient. The mixture is stirred at a constant speed with a glass rod for 8 minutes until fully mixed. Then, the mixture is placed in a vacuum drying oven and vacuum degassed at room temperature for 20 minutes until there are no obvious bubbles in the mixture, resulting in a uniform and transparent polydimethylsiloxane mixture.

[0030] (5.2) A fiber fixing mold is prepared by mechanical processing. The mold has a groove inside that matches the shape of the conical temperature sensing area. The temperature sensing area with a waist diameter of 100 μm and a waist length of 8 mm in the biconical fiber is placed horizontally in the mold and fixed at both ends by clamping devices, so that the temperature sensing area is suspended in the center of the groove. The polydimethylsiloxane mixture prepared in step (5.1) is slowly injected along one side of the mold to completely cover the temperature sensing area and keep the liquid surface flat and free of bubbles.

[0031] (5.3) Place the entire mold on a heating platform and heat at 100°C for 1 hour to cure, allowing the polydimethylsiloxane to fully crosslink and solidify. After curing, carefully demold to obtain a biconical chalcogenide glass fiber with a 0.5 mm thick polydimethylsiloxane temperature-responsive dielectric layer covering the surface of the temperature-sensing area. The uncoated chemical-sensing area is retained as the chemical substance sensing area. In this embodiment, the temperature response sensitivity of the temperature-responsive dielectric layer exhibits good performance in the range of 30–75°C.

[0032] (6) Sensor system construction Based on the biconical chalcogenide glass optical fiber prepared in step (5) above, a structure is constructed. Figure 1 The illustrated system is a chalcogenide glass fiber evanescent wave sensor system that integrates temperature sensing. For example... Figure 1 As shown, the sensing system includes: an infrared light source 1, a zinc selenide focusing objective 2, an optical fiber clamp 3, a biconical chalcogenide optical fiber 4, a reaction chamber 5, an infrared detector 6, and a data processing terminal 7. The infrared light emitted from the infrared light source 1 is focused by the zinc selenide focusing objective 2 and coupled to the input end of the biconical chalcogenide optical fiber 4 via the optical fiber clamp 3. The output end of the optical fiber is connected to the infrared detector 6, which is connected to the data processing terminal 7. The chemical sensing region of the biconical chalcogenide optical fiber 4 is placed in the reaction chamber 5, so that this region is in contact with the sample to be tested. The temperature sensing region is also placed in the reaction chamber 5 to simultaneously acquire temperature information.

[0033] (7) Temperature-substance concentration detection Infrared light was input into the aforementioned biconical chalcogenide glass fiber, and the fiber was immersed in a saturated urea solution at a temperature of 30°C to obtain... Figure 2 The infrared spectrum shown is shown (blue curve). Figure 2 As shown, when the chemical sensing region of the optical fiber comes into contact with a urea solution, the vibrations of the NH and C=O groups in the urea molecules occur between 1560 and 1700 cm⁻¹. -1 The region exhibits characteristic infrared absorption peaks, and also at 1260 cm⁻¹. -1 A characteristic absorption peak at 1.66 ppm, attributed to the vibration of the Si-CH3 group in polydimethylsiloxane, appears. Further increasing the temperature of the urea solution to 60 °C reduces the Si-CH3 absorption peak intensity to 1.56 ppm due to the high thermosensitivity of polydimethylsiloxane and modulation of the infrared evanescent field intensity and distribution in the optical fiber, while the intensity of the urea characteristic peak remains essentially unchanged (e.g., ...). Figure 2 (As shown by the red curve in the middle). The above results indicate that the chemical response and temperature response are reflected in the changes of infrared absorption peaks in different wavenumber regions of the spectrum, respectively. By independently analyzing the corresponding regions in the output spectrum, the simultaneous perception of chemical and temperature information can be achieved.

[0034] The chalcogenide glass fiber evanescent wave sensor of Example 2, which integrates temperature sensing, is fabricated by the following steps: (1) Preparation of matrix chalcogenide glass The chalcogenide glass material in this embodiment has the following molar composition: (As 20 Se 80 ) 85 Ge 10 Te 15 Using elemental Ge, As, Se, and Te with a purity of 5N as raw materials, the materials were accurately weighed and mixed uniformly according to stoichiometric ratios in a glove box filled with inert gas. The mixed materials were then loaded into a quartz distillation tube with an inner diameter of 15 mm, which had been pre-cleaned with aqua regia. The quartz tube was then evacuated to a vacuum of 1.0 × 10⁻⁶. -3 After Pa, the quartz tube was sealed using an oxyhydrogen flame. The sealed quartz tube was then placed in a swing furnace and slowly heated to 850°C for 12 hours, followed by cooling to 650°C and removing from the furnace. It was then air-cooled and quenched until the glass walls separated. The quartz tube was quickly transferred to an annealing furnace preheated to 180°C and held for 6 hours to relieve internal stress. After annealing, the furnace temperature was slowly lowered to room temperature, and the quartz tube was broken to remove the sample, yielding a chalcogenide glass rod.

[0035] (2) Preparation of optical fiber preform The surface of the chalcogenide glass rod obtained above was mechanically polished and then cleaned sequentially with hydrochloric acid, anhydrous ethanol and deionized water to finally obtain an optical fiber preform with a diameter of 13 mm and a length of 70 mm.

[0036] (3) Fiber drawing The fiber preform is vertically loaded into the furnace of the drawing tower, and inert gas is continuously introduced into the furnace as a protective gas. The furnace temperature is increased, and when the temperature reaches the softening point of the chalcogenide glass, fiber drawing begins by precisely adjusting the drawing speed and the lowering speed of the preform. Inert gas protection is maintained throughout the drawing process, ultimately yielding a chalcogenide glass optical fiber with a diameter of 450 μm.

[0037] (4) Preparation of chemical sensing area and temperature sensing area (4.1) Cut a 40cm long, 450μm diameter chalcogenide glass fiber and fix it on the fiber clamp controlled by the stepper motor, ensuring that the length of the fiber suspended at both ends of the clamp is consistent. (4.2) Place the ceramic heating rod in the center of the optical fiber, ensuring that the optical fiber is in close contact with the heating rod; (4.3) Place the two ends of the optical fiber on the optical fiber clamps above the stepper motor and straighten and fix them; (4.4) Set the winding temperature to 185℃ using the temperature control system; (4.5) When the optical fiber is slightly bent due to heat, a stepper motor at one end is set to move in a circular motion around the heating rod at a speed of 0.5 mm / s; (4.6) When the motor returns to the initial position, immediately stop the program and quickly remove the ceramic heating rod to obtain an annular temperature sensing area with a diameter of 6mm; (4.7) After the first ring region is prepared, the optical fiber is translated to an appropriate distance and steps (4.1) to (4.6) are repeated to obtain a double ring optical fiber with two ring regions having the same structure. One of them is used as a temperature sensing region and the other is used as a chemical sensing region.

[0038] (5) Preparation of temperature-responsive dielectric layer (5.1) The polydimethylsiloxane prepolymer and curing agent were mixed at a mass ratio of 8:1. Under this ratio, the cured polydimethylsiloxane network had a high crosslinking density and good resistance to swelling in organic solvents, making it suitable for monitoring polymerization reaction systems with corrosive and exothermic characteristics. The mixture was stirred at a constant speed for 10 minutes with a magnetic stirrer until fully mixed. Then, the mixture was placed in a vacuum drying oven and vacuum degassed at room temperature for 25 minutes until no obvious bubbles were found in the mixture, resulting in a uniform and transparent polydimethylsiloxane mixture.

[0039] (5.2) A fiber optic fixing mold is prepared using 3D printing. The mold has a slot inside that matches the shape of the annular temperature sensing area. The annular temperature sensing area of ​​the double-ring fiber is placed horizontally in the mold, and the two ends are fixed by clamping devices so that the temperature sensing area is placed in the center of the slot. The polydimethylsiloxane mixture prepared in step (5.1) is slowly injected along one side of the mold to completely cover the temperature sensing area and keep the liquid surface flat and free of bubbles.

[0040] (5.3) Place the entire mold on a heating platform and heat it at 100°C for 1 hour to allow the polydimethylsiloxane to fully crosslink and solidify. After curing, carefully demold to obtain a double-ring chalcogenide glass fiber with a 0.2 mm thick polydimethylsiloxane temperature-responsive medium layer on the surface of the temperature-sensing area. The other uncoated chemical-sensing area is retained as the chemical substance sensing area. In this embodiment, the mass ratio of polydimethylsiloxane prepolymer to curing agent is 8:1. The higher crosslinking density helps to enhance the resistance of the temperature-responsive medium layer to organic reaction liquids, which is beneficial to the long-term stability of the sensing interface. The thinner coating thickness of 0.2 mm shortens the heat conduction path, enabling the sensor to respond quickly to the heat released instantaneously by the polymerization reaction.

[0041] (6) Monitoring of the polymerization process of methyl methacrylate (MMA) The aforementioned double-ring optical fiber was fixed in a quartz liquid tank equipped with a water bath heating device at the bottom, and a reaction solution containing different proportions of methyl methacrylate and benzoyl peroxide (BPO) was added. By adjusting the reaction temperature, the detection sensitivity and detection limit of the optical fiber sensor for the polymerization reaction were investigated.

[0042] (7) Analysis of the polymerization reaction process The output optical path of the infrared light source is coupled to the input end of the double-ring optical fiber, the infrared detector is connected to the output end of the fiber, and the data processing terminal is connected to the infrared detector. When the light propagates to the ring region, an evanescent wave is generated on the surface of the fiber. The evanescent wave interacts with the external reaction liquid, and the vibration of the characteristic groups in the methyl methacrylate molecule occurs at 1725 cm⁻¹. -1 With 1637cm -1 Specific infrared absorption peaks were generated at certain wavelengths, with intensities of 0.55 and 0.40, respectively. As the reaction proceeded, the intensities of these two specific absorption peaks gradually decreased to 0.32 and 0.22, indicating that methyl methacrylate underwent a bulk polymerization reaction initiated by benzoyl peroxide to produce polymethyl methacrylate. By monitoring the dynamic evolution of this characteristic absorption peak, qualitative and quantitative analysis of the process of synthesizing polymethyl methacrylate from methyl methacrylate can be achieved.

[0043] (8) Real-time monitoring of reaction temperature The heat released during the polymerization of methyl methacrylate modulates the infrared evanescent field at the interface between polydimethylsiloxane and optical fiber, thereby affecting the performance of polydimethylsiloxane at 1260 cm⁻¹. -1 Changes in the characteristic absorption peaks of Si-CH3. Figure 3 This is a response curve showing the intensity of the infrared characteristic absorption peak of polydimethylsiloxane as a function of temperature in Example 2, at temperatures of 30℃, 40℃, 50℃, 60℃, and 70℃. Figure 3 As shown, within the temperature range of 30–70 °C, this characteristic absorption peak gradually decreases from 0.86 to 0.65 as the reaction proceeds. By monitoring the intensity change of this characteristic absorption peak, the temperature change during the bulk polymerization of methyl methacrylate can be deduced in real time. These results indicate that the chemical and temperature responses are reflected in the changes of infrared absorption peaks in different wavenumber regions of the spectrum, respectively. Simultaneous sensing of chemical and temperature information can be achieved through independent analysis of the corresponding regions in the output spectrum.

Claims

1. A chalcogenide glass fiber evanescent wave sensor integrating temperature sensing, characterized in that, The evanescent wave sensor includes a chalcogenide glass optical fiber, which has a chemical sensing region and a temperature sensing region. The temperature sensing region is covered with a temperature-responsive medium layer composed of polydimethylsiloxane. The structures of the chemical sensing region and the temperature sensing region are selected from one of the following: tapered, planar, toroidal, and spiral. The diameter of the chalcogenide glass optical fiber is 400–500 μm, and the thickness of the temperature-responsive medium layer is 0.1–2 mm. The chemical sensing region is used to detect the chemical information of the analyte through the infrared evanescent wave effect. The temperature sensing region is used to modulate the evanescent field of the optical fiber through the thermo-optical effect of the polydimethylsiloxane, thereby obtaining temperature information. For temperature sensing, the refractive index of the polydimethylsiloxane covering the temperature sensing region changes with temperature. By modulating the intensity and distribution of the evanescent field of the optical fiber through the thermo-optical effect, the intensity of the characteristic absorption peak of polydimethylsiloxane undergoes a distinguishable evolution with temperature. Temperature measurement can be achieved by monitoring the change in the intensity of this characteristic peak.

2. The chalcogenide glass fiber evanescent wave sensor with temperature sensing according to claim 1, characterized in that, The chalcogenide glass optical fiber is made of chalcogenide glass material, the molar composition of which is expressed by the chemical formula (As...). x Se 100-x ) 100-z M z , Where 10≤x≤90, 5≤z≤20, and M is one or more of Ge, Ga, Sb, Sn, S, Te, and CsCl.

3. The chalcogenide glass fiber evanescent wave sensor with temperature sensing according to claim 1, characterized in that, The length of the temperature-responsive dielectric layer is 7–22 mm.

4. A method for fabricating a chalcogenide glass fiber evanescent wave sensor integrating temperature sensing as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) A chalcogenide glass rod was prepared by melt quenching method, and after annealing, polishing and cleaning, an optical fiber preform was obtained. The optical fiber preform was drawn into a chalcogenide glass optical fiber. (2) The chemical sensing region and the temperature sensing region are prepared on the chalcogenide glass optical fiber by means of fused taper method, hot pressing method or local heating bending method; (3) The mixture of polydimethylsiloxane prepolymer and curing agent is coated on the surface of the temperature sensing area and cured to form a temperature response medium layer, thus obtaining the evanescent wave sensor.

5. The method for fabricating a chalcogenide glass fiber evanescent wave sensor with integrated temperature sensing according to claim 4, characterized in that, In step (3), the preparation method of the mixture includes: mixing the polydimethylsiloxane prepolymer and the curing agent at a mass ratio of (5-15):1, stirring until homogeneous, and then vacuum degassing at room temperature for 15-30 minutes.

6. The method for fabricating a chalcogenide glass fiber evanescent wave sensor with integrated temperature sensing according to claim 4, characterized in that, In step (3), the coating method is as follows: the mixture is injected into the mold so that the mixture completely covers the temperature sensing area, and then heated and cured at 80-100°C for 2-4 hours or left to stand at room temperature for 24-48 hours. After demolding, the temperature-responsive medium layer is obtained.

7. The method for fabricating a chalcogenide glass fiber evanescent wave sensor with integrated temperature sensing according to claim 6, characterized in that, The mold is prepared by 3D printing or machining. The mold has a groove or slot inside that matches the shape of the temperature sensing area. Before the coating is performed, the temperature sensing area is placed horizontally in the mold and fixed at both ends by clamping devices, so that the temperature sensing area is suspended or placed in the center of the groove. Then, the mixture is slowly injected along one side of the mold so that the mixture completely covers the temperature sensing area and keeps the liquid surface flat and free of bubbles.

8. A chalcogenide glass fiber evanescent wave sensing system integrating temperature sensing, characterized in that, The invention includes a chalcogenide glass fiber evanescent wave sensor with temperature sensing as described in any one of claims 1 to 3, an infrared light source, an infrared detector, and a data processing terminal for processing spectral signals, wherein the output optical path of the infrared light source is coupled to the input end of the chalcogenide glass fiber, the infrared detector is connected to the output end of the chalcogenide glass fiber, and the data processing terminal is connected to the infrared detector.

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