A WS-based 2 All-fiber fluorescence intensity temperature sensor and its fabrication method, temperature monitoring system

Abstract

This invention belongs to the field of fiber optic sensing and relates to a method based on WS 2 A temperature sensor based on all-fiber fluorescence intensity comprises a single-mode fiber, a three-hole grapefruit fiber, and a multimode fiber connected in sequence; the three-hole grapefruit fiber has three air holes, in which WS is deposited. 2 The multimode fiber output end is equipped with a mounting base, on which a filter is mounted. This invention utilizes WS... 2 Assembled within a three-hole optical fiber, with single-mode and multi-mode fibers fused together at both ends, this sealed structure effectively isolates the sensor from external air, preventing contact between the outside air and the two-dimensional material on the inner wall of the fiber during heating. This slows down the decomposition of transition metal sulfides, significantly improving the fluorescent sensor's ability to detect high temperatures and extending its lifespan. The sensor itself and its detection system are coupled and output via optical fiber, eliminating the need for external spatial light or optical modulation.

Description

A temperature sensor based on WS2 all-fiber fluorescence intensity, its fabrication method, and temperature monitoring system. Technical Field

[0001] This invention belongs to the field of fiber optic sensing, specifically relating to a temperature sensor based on WS2 all-fiber fluorescence intensity, its preparation method, and a temperature monitoring system. Background Technology

[0002] In harsh environments such as metallurgy, oil extraction, and nuclear energy, measurements under extreme high temperature and pressure conditions require a certain range and accuracy. Industrial electrical temperature sensors are not only susceptible to electromagnetic interference but can also generate electrical sparks, leading to measurement errors and potential hazards. In contrast, optical fiber, as a device that uses light as the information carrier, offers advantages over electrical high-temperature sensors, including smaller size, lower cost, stronger corrosion resistance, immunity to electromagnetic interference, ease of reuse and networking, ultra-long-distance temperature detection, and distributed sensing.

[0003] Currently, commercially available fiber optic temperature sensors work by modulating the effective refractive index and optical path difference of the fiber using the thermo-optic coefficient and the coefficient of thermal expansion, thereby shifting the spectral wavelength. The measured temperature is then demodulated using a linear temperature-wavelength curve. Industrially, germanium-doped silica fiber has a coefficient of thermal expansion and a thermo-optic coefficient of 0.55 × 10⁻⁶. -6 8.3×10 -6 Therefore, temperature sensors made simply by changing the fiber structure, such as FBG and FP cavities, have low temperature sensitivity. To improve temperature sensitivity, materials with high thermo-optical coefficients or coefficients of thermal expansion must be combined with different fiber structures. This method requires not only building a laser-written experimental stage to fabricate the fiber but also complex processes to tightly bond the high-temperature-sensitive material to the fiber. Furthermore, temperature sensors with FBG and FP cavity structures are sensitive to both temperature and strain, requiring a series of complex demodulation techniques to separate the two measurands.

[0004] It is worth noting that fluorescent materials produce fluorescence through stimulated emission after being excited by pump light. Temperature changes affect the lattice, band gap, and transition rate, thereby altering the fluorescence intensity, center wavelength, full width at half maximum (FWHM), and lifetime. Utilizing these characteristics of fluorescent materials, their ambient temperature can be measured accurately and rapidly. Furthermore, optical fiber serves only as the carrier for fluorescence transmission; no complex fabrication techniques are required to bond the fluorescent material to the fiber core to create the sensing unit. Stress on the optical fiber does not affect the intensity of the fluorescent material, and demodulation techniques are unnecessary to separate temperature and strain.

[0005] Patent CN115200739A discloses a calibration-free fiber optic temperature sensor and sensing device based on fluorescence wavelength demodulation. It utilizes the fluorescence properties of semiconductor quantum dots for temperature measurement, achieving a range from 20°C to 70°C. However, this document has a limited temperature range and cannot be used at high temperatures. Furthermore, using fluorescence wavelength demodulation requires a relatively complex demodulation system and an expensive spectrometer.

[0006] Patent CN114935414A discloses a bismuth-erbium co-doped fiber point temperature sensor based on the principle of rare earth ion fluorescence intensity detection. Although it can measure a wide temperature range from -200℃ to 350℃, the manufacturing process of this specially made bismuth-erbium co-doped fiber is difficult and expensive, making it unsuitable for large-scale use.

[0007] In 2015, Du Xinchao, Zhou Libin, and others published an article in the *Chinese Journal of Lasers* on a fiber optic temperature sensor based on a dual fluorescence ratio method. This article utilizes plastic optical fibers to excite and transmit the fluorescence signals of the fluorescent dyes Rhodamine B (RHB) and Rhodamine 110 (RH110). Since the two fluorescent dyes have different temperature sensitivities, the temperature is calibrated by calculating the ratio of their fluorescence intensities. Because plastic optical fibers are not heat-resistant, this temperature sensor can only be used in the range of 20℃ to 60℃. Rhodamine B is not only biotoxic but also decomposes at 210℃, making it unsuitable for sensing temperatures up to 600℃. Furthermore, using the fluorescence intensity ratio to measure temperature requires certain calculations and conversions, further complicating the detection method.

[0008] In 2020, Sun Yunyun, He Wei, and others used MoS2 quantum dots to fabricate fluorescent probes for measuring temperature and rutin concentration, with a temperature measurement range from 20°C to 80°C. However, because this sensing method utilizes spatial light measurement, its integration and portability are insufficient, requiring complex optical paths to measure the MoS2 quantum dots. Furthermore, high-temperature measurements in air are prone to the decomposition of transition metal sulfides, preventing the achievement of the desired measurement temperature.

[0009] In summary, current fiber optic temperature sensors have a small temperature measurement range and complex manufacturing processes. Summary of the Invention

[0010] The purpose of this invention is to provide a temperature sensor based on WS2 all-fiber fluorescence intensity, its preparation method, and a temperature monitoring system, which solves the problems of small temperature measurement range and complex manufacturing process of current fiber optic temperature sensors.

[0011] This invention is achieved through the following technical solution:

[0012] A temperature sensor based on WS2 all-fiber fluorescence intensity includes a single-mode fiber, a three-hole grapefruit fiber, and a multimode fiber connected in sequence.

[0013] The three-hole grapefruit fiber has three air holes, and a WS2 layer is deposited in each air hole.

[0014] The output end of the multimode fiber is equipped with a mounting base, on which a filter is installed.

[0015] Furthermore, the filters are two 600nm long-pass filters used to filter out the 532nm excitation light.

[0016] Furthermore, the temperature sensor has a temperature measurement range of -100℃ to 600℃.

[0017] The present invention also discloses a method for preparing the temperature sensor, comprising the following steps:

[0018] S1. Cut out a three-hole grapefruit fiber of a preset length, and then use vapor deposition to grow a single layer of WS2 in the air holes of the three-hole grapefruit fiber. After annealing at a high temperature of 300-350℃ to eliminate residual stress, a temperature sensing unit is made.

[0019] S2. Fiber fusion of one end of the temperature sensing unit to a single-mode fiber and the other end to a multimode fiber.

[0020] S3. Connect the mounting base to the output end of the multimode fiber, and pre-install a filter on the mounting base to obtain a temperature sensor based on the fluorescence intensity of the WS2 all-fiber.

[0021] Furthermore, the welding parameters in S2 are as follows: discharge power -80bit, discharge time 3500ms, secondary discharge power -60bit, discharge time 20sec, overlap 55μm.

[0022] The present invention also discloses a temperature monitoring system for the temperature sensor, comprising a temperature sensor, a photodetector, a data acquisition card, and a host computer connected in sequence;

[0023] The output side of the temperature sensor's mounting base is connected to a photodetector to detect fluorescence intensity;

[0024] The data acquisition card is used to collect fluorescence intensity data, and the host computer is used to process the fluorescence intensity data to obtain temperature data.

[0025] Furthermore, the host computer stores the conversion formula between fluorescence intensity and temperature, specifically:

[0026]

[0027] In the above formula, Φ0 represents the integrated intensity of the WS2 fluorescence band at 0K temperature, Φ T The measured fluorescence intensity is denoted by α, the process rate parameter is denoted by α, and K represents the Boltzmann constant.

[0028] ln((Φ0-Φ T ) / Φ T ) is the independent variable of the function, and the reciprocal of temperature 1 / T is the dependent variable.

[0029] Furthermore, the host computer is equipped with a display for showing temperature data.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] This invention discloses a temperature sensor based on the fluorescence intensity of WS2 in an all-fiber optic cable. WS2, a two-dimensional transition metal sulfide, is selected as the temperature sensing material. Compared to rare earth materials, semiconductor quantum dots, and fluorescent dyes, WS2 offers advantages such as high temperature resistance, low toxicity, a wide temperature range, and low cost, making it more suitable for high-temperature measurements. The all-fiber temperature sensor's optical path is entirely composed of optical fibers and fiber optic components. Compared to spatial optical paths, the entire optical path of the all-fiber temperature sensor is enclosed within the fiber waveguide, preventing interference from the external environment. Because optical fibers are thin and flexible, temperature measurement can be achieved in narrow gaps and complex pipes. Since the excitation light intensity of 532nm is much greater than the fluorescence light intensity, a filter is installed at the output end of the multimode fiber to filter out the 532nm excitation light and avoid measurement errors caused by the excitation light affecting the fluorescence intensity detection.

[0032] This invention proposes assembling transition metal sulfides within a three-hole optical fiber, with both ends fused together using single-mode and multi-mode optical fibers, respectively. This sealed structure effectively isolates the fiber from external air, preventing contact between the outside air and the two-dimensional material on the inner wall of the fiber during heating. This slows down the decomposition rate of the transition metal sulfides, significantly improving the fluorescence sensor's ability to detect high temperatures and extending its lifespan. The sensor itself and its detection system are coupled and output via optical fiber, eliminating the need for external spatial light or optical modulation.

[0033] This invention measures temperature by utilizing changes in the fluorescence intensity of two-dimensional materials. The optical fiber serves only as a light carrier; applying axial stress to the fiber does not alter the fluorescence intensity of the two-dimensional material. This method requires only a photodetector to receive the fluorescence intensity, and the demodulation tool is inexpensive and easy to use. Furthermore, there is no strain cross-sensitivity coefficient, simplifying the demodulation method.

[0034] This invention discloses a method for fabricating a temperature sensor based on WS2 all-fiber fluorescence intensity. A monolayer of WS2 is grown within a three-hole grapefruit-shaped optical fiber using vapor deposition. This method enables the growth of a large-area, high-quality monolayer of WS2 within air holes without damaging the internal structure of the fiber. The monolayer WS2 can be tightly bonded to the fiber core without etching or grinding, making fluorescence excitation and collection easier, and the fabrication process is simple.

[0035] Furthermore, the reason for using single-mode fiber fusion splicing at the end closer to the light source is that the core diameter of the grapefruit fiber is only 6.2μm, while the core diameter of the single-mode fiber is 9μm. The difference in core diameter causes core mismatch, resulting in a large area of ​​evanescent waves on the fiber surface. The reason for using multimode fiber fusion splicing at the end closer to the acquisition card is to collect as much fluorescence as possible. Attached Figure Description

[0036] Figure 1 is a schematic diagram of the connection principle of the temperature sensor of the present invention;

[0037] Figure 2 is a schematic diagram of the temperature sensor of the present invention;

[0038] Figure 3 is a schematic cross-sectional view of the three-hole grapefruit-shaped optical fiber in which WS2 is grown in the air hole according to the present invention;

[0039] In the diagram: 1. Light source; 2. Three-hole grapefruit-shaped optical fiber; 3. Photodetector; 4. Data acquisition card; 5. Host computer; 6. Single-mode optical fiber; 7. Multimode optical fiber; 8. Air hole; 9. WS2 layer; 10. Cladding. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0041] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in a variety of different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0042] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0043] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0044] This invention selects two-dimensional transition metal sulfides as the temperature sensing material. Compared with temperature sensing materials such as semiconductor quantum dots and fluorescent dyes, two-dimensional transition metal sulfides have advantages such as a large temperature detection range, low toxicity, and high stability.

[0045] WS2 exhibits similar properties to MoS2. Monolayer WS2 possesses the largest direct bandgap and typically exhibits the strongest photoluminescence. It also demonstrates high thermal stability; while MoS2 undergoes rapid oxidation at 349℃, WS2 begins to decompose at 510℃ and completely decomposes at 650℃ in air, and begins to decompose at 1100℃ and completely decomposes at 2000℃ in a vacuum. The room-temperature photoluminescence (PL) spectrum of WS2 is dominated by the A exciton peak, which arises from the transition between the lowest conduction band and the highest valence band. As temperature increases, lattice expansion and photoluminescence quenching occur, leading to a decrease in emitted fluorescence intensity. Temperature detection is achieved by utilizing the temperature dependence of fluorescence intensity. In comparison, the all-fiber temperature sensor formed by growing a monolayer of WS2 in a three-hole fiber offers advantages such as strong resistance to external interference, a large temperature detection range, a simple optical path, and portability.

[0046] As shown in Figure 2, the present invention proposes a temperature sensor based on WS2 all-fiber fluorescence intensity, comprising a single-mode fiber 6, a three-hole grapefruit-shaped fiber 2 and a multimode fiber 7 connected in sequence; the three-hole grapefruit-shaped fiber 2 has three air holes 8, and a WS2 layer 9 is deposited in each air hole 8; the output end of the multimode fiber 7 is provided with a mounting base, and a filter is installed on the mounting base.

[0047] The optical fiber used in this invention is a three-hole grapefruit-shaped optical fiber 2, and the cross-section of the optical fiber is shown in Figure 3. The diameter of the air hole 8 is 24.8±1.5μm. The distance from the center point of the SiO2 region (hereinafter referred to as the fiber core) enclosed by the three air holes 8 to the outer edge of the air hole 8 is 3.1±1.0μm. The diameter of the cladding 10 is 125±5μm, the wall thickness is 1.92μm, and the refractive index of both the fiber core and the cladding 10 is 1.457. Three-hole grapefruit-shaped optical fibers of 5-10cm length are cut with an optical fiber cleaver, and then a single layer of WS2 is grown in the three-hole grapefruit-shaped optical fiber 2 using a vapor deposition method. After high-temperature annealing to eliminate residual stress, a temperature sensing unit is made. The left and right ends of the temperature sensing unit are manually fused together with single-mode optical fiber 6 and multimode optical fiber 7 using a fusion splicer.

[0048] The reason for splicing single-mode fiber 6 at the end closest to light source 1 is that the core diameter of the grapefruit-shaped fiber is only 6.2μm, while the core diameter of the single-mode fiber 6 is 9μm. The different core diameters of the two fibers cause core mismatch, resulting in a large area of ​​evanescent waves on the fiber surface.

[0049] The end near the acquisition card is fused with multimode fiber 7 to collect as much fluorescence as possible. This creates a closed area, preventing the WS2 from contacting the outside air, reducing environmental interference, and thus greatly improving the fluorescence sensor's ability to detect high temperatures.

[0050] The result after fusion is shown in Figure 2. The fusion parameters of the fusion machine are as follows: discharge power -80bit, discharge time 3500ms, secondary discharge power -60bit, discharge time 20sec, overlap 55μm.

[0051] As shown in Figure 1, this invention obtains the relationship between fluorescence band intensity and temperature by designing a temperature monitoring method in advance, specifically including the following steps:

[0052] Step 1: The 532nm pump light source 1 is connected to the temperature sensing unit through a single-mode fiber 6. Since the core diameter of the grapefruit fiber is 6.2±1.0μm and the core diameter of the single-mode fiber 6 is 9μm, this mismatch between the fiber cores will cause the overlapping area between the evanescent wave and the WS2 grown in the air hole 8 to increase, thereby making the fluorescence more fully excited.

[0053] Since the excitation light intensity at 532nm is much greater than the fluorescence light intensity, to avoid measurement errors caused by the excitation light affecting the fluorescence intensity detection, a mounting base is connected to the output end of the multimode fiber 7. The mounting base contains two 600nm long-pass filters to filter out the 532nm excitation light. The output end of the mounting base is connected to the photodetector 3 to detect the fluorescence light intensity. The collected data is then transmitted to the data acquisition card 4, and finally to the host computer 5 for data processing.

[0054] Photodetector 3 detects the integrated intensity of the fluorescence band. As temperature increases, charged excitons in WS2 undergo thermal dissociation, simultaneously increasing the probability of non-radiative transitions and decreasing the probability of radiative transitions that produce fluorescence. This is macroscopically manifested as a decrease in the integrated intensity of the fluorescence band. The relationship between fluorescence band intensity and temperature is as follows:

[0055]

[0056] Where Φ(T) represents the integrated intensity of the fluorescence band, Φ0 represents the integrated intensity of the WS2 fluorescence band at 0K, and a is the process rate parameter, which can be obtained by fitting experimental data with the formula. K represents the Boltzmann constant K = 1.380649 × 10 -23 E a The activation energy is typically E, which is the thermal activation energy of WS2 on a SiO2 substrate. a It is 0.53 eV.

[0057] Step 2: Place the temperature sensor in low-temperature and high-temperature environments for measurement, with a temperature range of -100℃ to 600℃. Increase the temperature by 50℃ every 15 minutes and maintain this temperature for 10 minutes. After the temperature stabilizes, measure the fluorescence intensity. Collect the fluorescence intensity at different temperature points using the acquisition card. Fit the experimental data using the formula for fluorescence intensity versus temperature to obtain a correlation curve. Through fitting, obtain the values ​​of the integrated intensity Φ0 of the WS2 fluorescence band and the process rate parameter a at 0K. Substituting these values ​​into the above formula yields a fluorescence intensity Φ. T The correspondence between temperature T and temperature.

[0058] To facilitate more convenient and intuitive temperature detection, a mathematical transformation is performed on the formula for fluorescence intensity versus temperature, yielding:

[0059]

[0060] In the above formula, ln((Φ0-Φ T ) / Φ T Let be the independent variable of the function, and the reciprocal of temperature (1 / T) be the dependent variable. All other values ​​in the function were obtained from the previous fitting of the fluorescence intensity versus temperature curve and are constants independent of temperature. According to the equation, ln((Φ0-Φ) T ) / Φ T It has a linear relationship with 1 / T.

[0061] Furthermore, to test the sensor's application in temperature sensing, a two-dimensional material fiber optic temperature sensor and a thermocouple were simultaneously placed in the environment under test. The fluorescence intensity Φ of the two-dimensional material fiber optic temperature sensor was collected by a photodetector 3. T Then, the reciprocal of temperature 1 / T can be obtained from the above formula. After a simple mathematical transformation, the temperature T measured by the temperature sensor can be obtained. This temperature is compared with the temperature measured by the thermocouple. By changing the ambient temperature from -100℃ to 600℃, the parameters of the function in the above formula can be adjusted to achieve the minimum measurement error.

[0062] In actual temperature measurement, simply place the temperature sensor in the environment to be measured, and use formula (2) to obtain the temperature of the environment based on the fluorescence intensity collected by the photodetector 3. The temperature is then displayed on the interface to achieve real-time temperature monitoring.

[0063] The temperature sensor based on two-dimensional transition metal sulfide all-fiber fluorescence intensity proposed in this invention has a simple fabrication process and strong thermal stability. Compared with sensors made of rare earth materials, semiconductor quantum dots, and fluorescent dyes, it has the advantages of low toxicity, wide temperature measurement range, and low cost. Therefore, the method described in this invention has greater application potential in the field of temperature measurement.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A temperature sensor based on WS2 all-fiber fluorescence intensity, characterized in that, It includes a single-mode fiber (6), a three-hole grapefruit fiber (2) and a multimode fiber (7) connected in sequence; the three-hole grapefruit fiber (2) has three air holes (8) inside, and a WS2 layer (9) is deposited in each air hole (8); the output end of the multimode fiber (7) is provided with a mounting base, and a filter is installed on the mounting base.

2. The temperature sensor based on WS2 all-fiber fluorescence intensity according to claim 1, characterized in that, The filters are two 600nm long-pass filters used to filter out the 532nm excitation light.

3. A temperature sensor based on WS2 all-fiber fluorescence intensity according to claim 1, characterized in that, The temperature sensor has a temperature measurement range of -100℃ to 600℃.

4. A method for preparing the temperature sensor according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Cut out a three-hole grapefruit-shaped optical fiber (2) of a preset length, and then grow a single layer of WS2 in the air hole (8) of the three-hole grapefruit-shaped optical fiber (2) by vapor deposition. After annealing at a high temperature of 300-350℃ to eliminate residual stress, a temperature sensing unit is made. S2. Fusion one end of the temperature sensing unit to a single-mode optical fiber (6) and the other end to a multimode optical fiber (7). S3. Connect a mounting base to the output end of the multimode optical fiber (7), and pre-install a filter on the mounting base to obtain a temperature sensor based on the fluorescence intensity of the WS2 all-fiber.

5. The method for preparing the temperature sensor according to claim 4, characterized in that, In S2, the welding parameters are as follows: discharge power -80bit, discharge time 3500ms, secondary discharge power -60bit, discharge time 20sec, overlap 55μm.

6. A temperature monitoring system comprising the temperature sensor according to any one of claims 1-3, characterized in that, It includes a temperature sensor, a photodetector (3), a data acquisition card (4), and a host computer (5) connected in sequence; the output side of the mounting base of the temperature sensor is connected to the photodetector (3) for detecting fluorescence intensity; the data acquisition card (4) is used to collect fluorescence intensity data, and the host computer (5) is used to process the fluorescence intensity data to obtain temperature data.

7. The temperature monitoring system according to claim 6, characterized in that, The host computer (5) stores the conversion formula between fluorescence intensity and temperature, specifically: In the above formula, This represents the integrated intensity of the WS2 fluorescence band at 0 K. The measured fluorescence intensity is denoted by α, the process rate parameter is denoted by α, and K represents the Boltzmann constant. It is the activation energy; The independent variable of the function is the reciprocal of temperature. As a dependent variable.

8. The temperature monitoring system according to claim 6, characterized in that, The host computer (5) is equipped with a display for displaying temperature data.

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