Vernier effect-based high-sensitivity double-dislocation optical fiber temperature sensor

Abstract

The invention discloses a vernier effect-based high-sensitivity double-dislocation optical fiber temperature sensor, which comprises an input optical fiber, a first dislocation optical fiber, a second dislocation optical fiber, an output optical fiber and a polymer microsphere which are connected in a dislocation manner, one end of the input optical fiber and one end of the first staggered optical fiber are welded in a staggered manner, and a first staggered welding surface is formed therebetween; the other end of the first staggered optical fiber and one end of the second staggered optical fiber are welded in a staggered manner to form a second staggered welding surface; the other end of the second dislocation optical fiber is in dislocation welding with one end of the output optical fiber to form a third dislocation welding surface; and the polymer microspheres are wrapped on a staggered cavity between the second staggered welding surface and the third staggered welding surface. According to the optical fiber temperature sensor, the staggered optical fiber pairs of the two Mach-Zehnder interferometers are formed, one staggered optical fiber is coated with the polymer, and therefore the vernier effect is achieved, and the optical fiber temperature sensor has the advantages of being high in temperature measurement sensitivity, easy to prepare and low in cost.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensor technology, and particularly relates to a highly sensitive double misaligned fiber optic temperature sensor based on the vernier effect. Background Technology

[0002] Temperature plays a crucial role in fields such as smart devices, materials research, and cancer treatment. For example, hyperthermia is an effective treatment for cancer, making accurate temperature measurement and control particularly important. Currently, fiber optic temperature sensors offer many advantages, including high sensitivity, resistance to electromagnetic interference, and good biocompatibility, leading to their widespread application across various fields. Fiber optic Mach-Zehnder interferometers (MZIs) have attracted significant attention due to their simple fabrication and low cost. For instance, fused taper technology can be used to fabricate cone-sphere, micro-air-hole, D-shaped, and misaligned structures, thereby achieving Mach-Zehnder interferometry. The materials for these MZI sensing units are typically silicon or air. However, due to the relatively low thermo-optical coefficients and thermal expansion coefficients of air and silicon dioxide, the temperature sensitivity of these MZIs is still limited by their material properties.

[0003] Recently, some novel temperature-sensitive materials have been used in MZI integration, which significantly improves temperature sensitivity compared with pure fiber MZI. For example, in 2024, Tian et al. (“A temperature sensor based on multi-beamcapture and interference”, T. Tian et al. Sensors and Actuators: A. Physical 375 (2024) 115526) proposed an MZI structure that forms three cascaded cavities through six consecutive offset fusions and is prepared by adsorbing polymethyl methacrylate (PMMA) microspheres into the cavities, achieving high-sensitivity temperature detection. However, its preparation process involves multiple delicate operation steps, which is complex, and the filling of multiple cavities can easily lead to a decrease in spectral contrast.

[0004] Currently, the vernier effect is widely used to improve temperature sensitivity. In 2021, Sigifredo et al. (“In-Line Mach–Zehnder Interferometers Based on a Capillary Hollow-Core Fiber Using Vernier Effect for a Highly Sensitive Temperature Sensor”, MGSigifredo et al. Sensors and Actuators: A. Physical 2021, 21, 5471) constructed a dual (MZI) cascaded interferometer based on the Vernier effect by connecting capillary hollow-core fiber (CHCF) with multimode optical fiber (MMF); however, its reference arm requires isothermal control, limiting its applicability. In 2023, Li et al. (“Simultaneous measurement of strain and temperature based on fiber sensor with Vernier effect”, L. Zhao et al. Optics & Laser Technology 157 (2023) 108670) developed an interferometer based on the vernier effect that can simultaneously measure strain and temperature. This interferometer was fabricated by connecting an MZI and a Fabry-Perot interferometer (FPI) through a 3dB coupler. The sensor achieved highly sensitive dual-parameter measurement sensing; however, the structure relies on the coupler connection, which increases the complexity of the system and makes it less compact. Summary of the Invention

[0005] To address the aforementioned technical issues, this invention provides a highly sensitive double misaligned fiber optic temperature sensor based on the vernier effect. The fiber optic temperature sensor achieves the vernier effect by forming two misaligned fiber pairs of Mach-Zehnder interferometers, with one of the misaligned fibers being polymer-coated. It has the advantages of high temperature sensitivity, simple fabrication, and low cost, and has broad application prospects in the biomedical field.

[0006] The present invention proposes a high-sensitivity dual misaligned fiber optic temperature sensor based on the vernier effect, comprising an input fiber, a first misaligned fiber, a second misaligned fiber, and an output fiber connected by misalignment, as well as polymer microspheres; One end of the input optical fiber is fused to one end of the first misaligned optical fiber in a misaligned manner, forming a first misaligned fusion surface between them; the other end of the first misaligned optical fiber is fused to one end of the second misaligned optical fiber in a misaligned manner, forming a second misaligned fusion surface between them; the other end of the second misaligned optical fiber is fused to one end of the output optical fiber in a misaligned manner, forming a third misaligned fusion surface between them; polymer microspheres are wrapped around the misaligned cavity between the second misaligned fusion surface and the third misaligned fusion surface.

[0007] Preferably, the misalignment distance between the input optical fiber and the first misaligned optical fiber, the first misaligned optical fiber and the second misaligned optical fiber, and the second misaligned optical fiber and the output optical fiber is 40-60 μm.

[0008] Preferably, the length of the first misaligned fiber is 800-900 μm, and the length of the second misaligned fiber is 500-600 μm.

[0009] Preferably, the input optical fiber, the first misaligned optical fiber, the second misaligned optical fiber, and the output optical fiber are all multimode optical fibers; Preferably, the multimode optical fiber has a core diameter of 100-110 μm and a cladding diameter of 120-130 μm.

[0010] Preferably, the polymer microspheres are elliptical in shape, with a maximum radial diameter of 250-300 μm and an axial length of 600-650 μm; Preferably, the polymer microspheres are formed by photocuring SU-8 photoresist.

[0011] This invention also proposes a method for fabricating the above-mentioned high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect, comprising the following steps: S1. Align the two fiber segments, which serve as the input fiber and the first misaligned fiber, axially and then misalign them radially by a certain distance to perform the first fusion splice and form the first misaligned fusion splice surface. S2. After cutting the first misaligned fiber along the end away from the first misaligned fusion splice surface, align it with the axial direction of a fiber segment that serves as the second misaligned fiber, then misalign it radially by a certain distance, and perform a second fusion splice to form the second misaligned fusion splice surface. S3. After cutting the second misaligned fiber along the end away from the second misaligned fusion splice surface, align it with the axial direction of a section of fiber that serves as the output fiber, then misalign it radially by a certain distance, and perform a third fusion splice to form the third misaligned fusion splice surface. S4. Coat the misaligned cavity between the second misaligned fusion surface and the third misaligned fusion surface with a polymer, and after curing to form polymer microspheres, the double misaligned fiber optic temperature sensor is obtained.

[0012] The present invention also proposes a temperature sensing system, including the above-described double misaligned fiber optic temperature sensor or the double misaligned fiber optic temperature sensor prepared by the above-described preparation method.

[0013] Preferably, the temperature sensing system further includes a broadband light source and a spectrum analyzer; Preferably, the broadband light source is connected to the input fiber of the dual misaligned fiber optic temperature sensor, and the spectrometer is connected to the input fiber of the dual misaligned fiber optic temperature sensor.

[0014] Compared with the prior art, the present invention proposes a high-sensitivity dual misaligned fiber temperature sensor based on the vernier effect. The sensor first uses fiber fusion technology to prepare two cascaded misaligned fiber structures, which are defined as the first misaligned fiber (MMF1) and the second misaligned fiber (MMF2). Then, photoresist is applied to the microcavity of MMF2 to completely encapsulate the misaligned microcavity of MMF2. Finally, ultraviolet exposure technology is used to solidify the photoresist in the microcavity.

[0015] When the light beam passes through the input fiber (input-MMF) and reaches the first misaligned fusion splice, the optical path is split into two parts. One part of the beam enters the offset MMF1, while the other part leaks into the air. The beam entering the offset MMF1 propagates forward and is split into two beams again at the second misaligned fusion splice. One beam, I1, propagates in the photoresist (SU-8), while the other beam, I2, propagates in MMF2. The beams meet at the third misaligned fusion splice of MMF2 and the output fiber (output-MMF) and are coupled into the output-MMF. Similarly, the beam that leaked into the air is also split into two beams, I3 and I4. These two beams propagate in the photoresist (SU-8) and MMF2, respectively. Finally, the two beams are coupled into the output-MMF, and the four beams interfere and superimpose in the output-MMF. During propagation, I1 and I2 form the first MZI interference spectrum, and I3 and I4 form the second MZI interference spectrum. Since the free spectral ranges of the first and second MZI spectra are similar but not identical, the superposition of the two interference spectra creates a vernier effect. The photoresist (SU-8) has a high thermo-optic coefficient and a high coefficient of thermal expansion; the thermo-optic coefficient of SU-8 is negative, while that of silicon is positive, resulting in a significant change in the effective refractive index difference with temperature variations. Furthermore, the high coefficient of thermal expansion of SU-8 photoresist increases the effective interference length of the structure with increasing temperature. Therefore, the sensitivity of the proposed misaligned structure is significantly improved without requiring an excessively long sensing area. Within a temperature range of 30°C to 55°C, by monitoring the movement of the vernier envelope, the temperature sensitivity of the sensor described in this invention reaches 1.3533 nm / °C. Therefore, the sensor described in this invention has a compact structure, high sensitivity, and low cost, and has broad application prospects in fields such as smart devices, materials research, and tumor treatment. Attached Figure Description

[0016] Figure 1This is a schematic diagram illustrating the fabrication process of the dual misaligned fiber optic temperature sensor described in this invention. Figure 2 The following are the spectra of the dual-misaligned fiber optic temperature sensor before and after coating with SU-8 photoresist according to the present invention: (a) is the spectrum of the dual-misaligned fiber optic temperature sensor before coating with SU-8 photoresist; (b) is the spectrum of the dual-misaligned fiber optic temperature sensor after coating with SU-8 photoresist; (c) is the spectrum of the dual-misaligned fiber optic temperature sensor after coating with SU-8 photoresist and after Fourier transform; (d) is the spectrum of the dual-misaligned fiber optic temperature sensor after coating with SU-8 photoresist and after filtering. Figure 3 This is a schematic diagram of the temperature sensing system described in this invention; Figure 4 The following are transmission spectra of the double misaligned fiber optic temperature sensor of the present invention at different temperatures: (a) is the transmission spectrum of the double misaligned fiber optic temperature sensor at different temperatures; (b) is a linear fitting graph of the transmission spectrum of the double misaligned fiber optic temperature sensor at different temperatures. Figure 5 This is a temperature response stability test diagram of the dual misaligned fiber optic temperature sensor described in this invention. Detailed Implementation

[0017] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0018] Example

[0019] Reference Figure 1 This embodiment proposes a high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect, which is prepared by the following method: (1) Reference Figure 1a) Remove the coating from the ends of two 30 cm long multimode optical fibers (core diameter 106.075 μm, cladding diameter 125 μm) using Miller pliers. Clean the end faces with lens paper soaked in 75% alcohol, then cut the end faces flat with a fiber cleaver. Place the two flattened multimode optical fibers in the pressure plates at both ends of the fiber fusion splicer (KL-300T), with the ends close to the discharge electrodes but not exceeding the position where the pointers of the two discharge electrodes are directly opposite. Cover with the windproof cover. Select the left fiber using the manual splicing program of the fusion splicer and adjust its position to create a misalignment with the right fiber. Control the misalignment distance between the two multimode optical fibers to be approximately one-third of the fiber diameter, i.e., 47 μm. Set the discharge intensity of the fusion splicer to 40 bits and the discharge time to 2750 seconds. After the two misaligned optical fibers are fused together for the first time, forming the first misaligned fusion splice surface, manual additional discharge is performed 2-3 times to make the weld between the misaligned optical fibers more secure. The optical fiber located on one side of the first misaligned fusion splice surface is used as the input fiber, and the optical fiber on the other side is used as the first misaligned fiber. Figure 1 As shown in b; (2) Reference Figure 1 c. Open the windproof cover and take out the misaligned optical fiber obtained in step (1). Fix the misaligned optical fiber in the precision cutting system (XDC-10A-530HS). Place the two-dimensional moving platform and the cutting knife side by side below the precision cutting system. The misaligned optical fiber is fixed in the clamp of the cutting knife and the two-dimensional moving platform. Move the reflector to adjust it to the brightest field of view without shadows. Rotate the coarse / fine screw knob so that the optical fiber misalignment structure can be clearly seen. Adjust the two-dimensional moving platform to adjust the misalignment structure to the center of the field of view and to be near the blade of the optical fiber cutting knife. Precisely control the position of the cutting point through the two-dimensional moving platform and reserve the blade distance. Cut the first misaligned optical fiber along the end away from the first misaligned fusion splice surface and form an optical fiber misalignment cantilever on one side of the first misaligned fusion splice surface. (3) Reference Figure 1 d. Following the operation of step (1), place the fiber misalignment cantilever obtained in step (2) into one side of the fiber fusion splicer and fix it. Place another multimode fiber with a flat end face as the second misalignment fiber into the fiber fusion splicer and fix it so that it is aligned with the first misalignment fiber on one side of the fiber misalignment cantilever. Adjust its position so that it is misaligned with the first misalignment fiber. Control the misalignment distance to be 47 μm. After the second fusion splice, it is fused together with the fiber misalignment cantilever to form the second misalignment fusion surface, and obtain the misalignment convex fiber. (4) Reference Figure 1 e. Following the operation of step (2), the second misaligned fiber in the misaligned convex structure fiber obtained in step (3) is cut along the end away from the second misaligned fusion splice surface, and a fiber misaligned cantilever is formed again on one side of the second misaligned fusion splice surface. (5) Reference Figure 1f, following the operation of step (1), place the fiber misalignment cantilever obtained in step (4) into one side of the fiber fusion splicer and fix it. Place another multimode fiber with a flattened end face into the fiber fusion splicer and fix it, aligning it with the second misaligned fiber on one side of the fiber misalignment cantilever. Adjust its position so that it forms a misalignment with the second misaligned fiber, controlling the misalignment distance to be 47 μm. After the third fusion splice, it is fused together with the fiber misalignment cantilever to form the third misaligned fusion surface, and once again a misaligned convex fiber is obtained. Its physical form is as follows: Figure 1 As shown in h; (6) Reference Figure 1 g. Place the misaligned convex fiber obtained in step (5) above a hollowed-out support, so that the misaligned part of the fiber is located exactly in the center of the hollowed-out support. Apply SU-8 photoresist to the short arm of the misaligned structure. Place the support below the precision cutting system, and while adjusting the objective lens and the support, slightly rotate the misaligned convex fiber until the misaligned structure is clearly seen in the center of the field of view. Take an appropriate amount of SU-8 photoresist on the glass slide and let it stand for 5 minutes. The solvent in the photoresist is allowed to evaporate fully, improving its viscosity. A small amount of SU-8 photoresist is then applied using a syringe needle, and the needle tip is slowly moved to the misaligned cavity region corresponding to the second misaligned fiber. The needle position is monitored in real time using a precision cutting system to ensure accurate application of the photoresist to the misaligned cavity region. The application speed should be fast and the pressure light to ensure uniformity and consistency of the coating. Due to the self-leveling function of the photoresist, the applied photoresist forms a uniform ellipsoid in the misaligned cavity region. The coated region is then exposed to an ultraviolet (UV) light source (XP104) for pre-curing for 20 seconds. After exposure, the fiber optic sensing structure is placed in a temperature-controlled chamber for baking, first at 65°C for 15 minutes, then at 95°C for 45 minutes. Baking rapidly cross-links and cures the acid-catalyzed monomers in the SU-8 photoresist, forming polymer microspheres on the misaligned cavity between the second and third misaligned fusion surfaces, thus obtaining the dual misaligned fiber optic temperature sensor.

[0020] Physical reference of the above-mentioned double misaligned fiber optic temperature sensor Figure 1 As shown in i, the dual misaligned fiber optic temperature sensor includes an input fiber, a first misaligned fiber, a second misaligned fiber, and an output fiber connected in a misaligned manner, as well as SU-8 photoresist microspheres. One end of the input optical fiber is fused to one end of the first misaligned optical fiber in a misaligned manner, forming a first misaligned fusion surface between them; the other end of the first misaligned optical fiber is fused to one end of the second misaligned optical fiber in a misaligned manner, forming a second misaligned fusion surface between them; the other end of the second misaligned optical fiber is fused to one end of the output optical fiber in a misaligned manner, forming a third misaligned fusion surface between them; polymer microspheres are wrapped around the misaligned cavity between the second misaligned fusion surface and the third misaligned fusion surface; The misalignment distance between the input optical fiber and the first misaligned optical fiber, and between the first misaligned optical fiber and the second misaligned optical fiber, is 47 μm; the length of the first misaligned optical fiber is 847.22 μm, the length of the second misaligned optical fiber is 532.41 μm, the maximum radial diameter of the SU-8 photoresist microsphere is 269.23 μm, and the axial length is 615.38 μm.

[0021] The aforementioned double-misaligned fiber optic temperature sensor can achieve temperature response, and the specific principle is as follows: In the above-mentioned double misaligned fiber optic temperature sensor, the two multimode fiber segments on the left and right sides are designated as the input and output ends of the signal, respectively, and are called input-MMF and output-MMF; the misaligned fibers at both ends are MMF1 and MMF2 from left to right; the first misaligned fusion splice surface between input-MMF and MMF1 is called M1, the second misaligned fusion splice surface between MMF1 and MMF2 is called M2, and the third misaligned fusion splice surface between MMF2 and output-MMF is called M3.

[0022] The incident light beam propagates forward in the input-MMF. When it reaches M1, the beam is split into two parts. One part enters the offset MMF1, while the other part leaks into the air. The beam entering MMF1 is split into two beams at interface M2. One beam propagates in the SU-8 photoresist, and the other beam propagates in MMF2. These two beams are coupled into the output-MMF at interface M3, with intensities I1 and I2, respectively. The beam leaking into the air is also split into two beams when it reaches interface M2. These two beams propagate in the SU-8 photoresist and MMF2, respectively, and are coupled into the output-MMF at interface M3, with intensities I3 and I4, respectively. The four beams interfere and superimpose in the output-MMF. The interference superposition of I1 and I2 forms the first MZI interference spectrum, and the interference superposition of I3 and I4 forms the second MZI interference spectrum. Since the free spectral range of the first MZI spectrum is similar to but not the same as that of the second MZI spectrum, the superposition of the two interference spectra forms a vernier effect.

[0023] According to the MZI principle, I 1 and I 2 and I 3 and I 4. The interference superposition of each component results in an MZI interference spectrum, and its light field distribution is shown. I out1 and I out2 The following are given in formulas (1) and (2):

[0024] Δ and Δ They are I 1 andI 2 and I 3 and I A phase difference of 4, Δ and Δ They are represented as follows;

[0025] in, and n MMF λ is the refractive index of the SU-8 photoresistor and MMF, L is the interference length of MMF2, and λ is the wavelength of the incident light. The lengths of MMF1 and MMF2 are approximately 847.22 μm and 532.41 μm, respectively. The refractive index of air is 1, the refractive index of SU-8 photoresist is 1.58, and the refractive index of silicon is 1.47. Since SU-8 photoresist has a high thermo-optical coefficient and a high coefficient of thermal expansion, and the thermo-optical coefficient of SU-8 photoresist is negative while that of silicon is positive, the effective refractive index difference changes significantly with temperature. Furthermore, the free spectral ranges of MMF1 and MMF2 are similar but not the same, thus a vernier effect occurs.

[0026] A vernier envelope can be observed in the spectrum of the dual-misaligned fiber optic temperature sensor. The envelope is given in formula (4). By detecting the movement of the envelope, accurate temperature detection can be achieved.

[0027] in, F C It represents the light intensity distribution of the envelope, where m is the order. λ It is the wavelength of light To further improve the temperature response characteristics of the double misaligned fiber optic temperature sensor, SU-8 photoresist was applied to the fiber misalignment to enhance its temperature response characteristics, as described above. Figure 1 As can be seen, the photoresist completely encapsulates MMF2 but not MMF1. Due to the large coefficient of thermal expansion of the photoresist, the temperature sensitivity of the fiber misalignment structure is effectively enhanced. In addition, the encapsulation of the photoresist significantly improves the mechanical strength of the misalignment structure.

[0028] Reference Figure 2 Spectroscopic tests were performed on the double misaligned fiber optic temperature sensor before and after coating with SU-8 photoresist. The spectra at room temperature are shown in [the image / image / etc.]. Figure 2 a and 2b. From Figure 2As observed in a and 2b, the spectral insertion loss of the double-misaligned fiber temperature sensor before coating with SU-8 photoresist is -35 dBm, while the spectral insertion loss after coating with SU-8 photoresist is -15 dBm, showing a significant reduction in loss. Multiple characteristic peaks exist within the test wavelength range of 1250-1650 nm; however, the interference peaks have high frequencies and are close together, which limits the temperature measurement range. Since this structure is fabricated by cascading two MZIs together, and the frequencies of these two MZIs are extremely close, a vernier effect is easily generated when their spectral lines are superimposed. Figure 2 The vernier envelope was not observed in b because multiple modes exist in the spectrum. To extract the vernier envelope, we performed a Fourier transform on the spectrum. The spectrum after the Fourier transform is shown below. Figure 2 As shown in c, according to Figure 2 The spectrum of c is obtained by filtering the spectrum of the structure at 30 °C. The filtered spectrum is then... Figure 2 As given in d, from Figure 2 The appearance of the vernier envelope can be clearly observed, thus allowing for detailed monitoring of how the envelope of the structure changes with temperature.

[0029] Reference Figure 3 To investigate the temperature response characteristics of the aforementioned double-misaligned fiber optic temperature sensor, a temperature sensing system was constructed. This system mainly consists of several key components, including a broadband light source capable of providing incident light with a wavelength range of 600 nm to 1700 nm; a spectrometer with a resolution of 0.02 nm; and a temperature control chamber (CK-80G) for precise temperature control. The double-misaligned fiber optic temperature sensor was connected to the broadband light source and spectrometer via fiber optic cables. After connection, the double-misaligned fiber optic temperature sensor was placed in the temperature control chamber for calibration of its temperature response characteristics.

[0030] Figure 4 Display a shows the transmission spectra of the dual-misaligned fiber optic temperature sensor at different temperatures. The temperature detection range is from 30℃ to 55℃, and data is recorded every 5℃. After the temperature control chamber reaches the predetermined value, a 1-minute wait is taken before recording the transmission spectrum to avoid the influence of ambient temperature fluctuations on the measurement results. A total of six sets of data were recorded. Figure 4 As can be seen from point a, the transmission spectrum of the dual-misaligned fiber optic temperature sensor contains multiple interference peaks, with the peak near 1375 nm exhibiting the highest contrast. Therefore, the temperature response characteristics of this interference peak are detailed. From Figure 4As shown in Figure a, with the gradual increase in temperature, the center wavelength of the interference peak gradually shifts from 1377.48 nm to 1412.37 nm, a total redshift of 34.89 nm. This is because both the photoresist and the optical fiber exhibit thermo-optical and thermal expansion effects with increasing temperature. Since the thermal expansion coefficients of both the optical fiber and the photoresist are positive, the effective interference length of the optical fiber misalignment structure increases with increasing temperature, resulting in a redshift of the center wavelength of the interference peak. Simultaneously, the optical fiber and the photoresist have positive and negative thermo-optical coefficients, respectively, which reduces the effective refractive index difference of the optical fiber misalignment structure, corresponding to a blueshift of the center wavelength of the interference peak. Based on the experimental results, the thermal expansion effect of the optical fiber and the photoresist plays a major role in the optical fiber misalignment structure.

[0031] Plot the minimum value of the filtered vernier envelope spectrum at each temperature, draw the vernier envelope line, observe the shift of the envelope node near 1375 nm with temperature changes, and record the center wavelength position of this node at each temperature. The center wavelength positions of the interference peaks at 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃, and 55 ℃ are all within... Figure 4 As shown in section b, a linear fit was performed on these data points, and the slope and correlation coefficient of the linear fit were 1.3533 nm / ℃ and 0.9967, respectively. Based on the fitting results, the temperature sensitivity is approximately 1.3533 nm / ℃ within the detection range of 30 ℃ to 55 ℃. Experimental results indicate that the dual-misaligned fiber optic temperature sensor described in this invention has high sensitivity and good linear response characteristics within the measured temperature range.

[0032] To test the stability of the sensor, it was continuously tested in a constant temperature environment of 35℃. The exact number of the center wavelength of the envelope node was repeatedly recorded in 5-minute increments to ensure the accuracy and reliability of the data. Sixty sets of data on the change of the center wavelength over time under constant temperature conditions were obtained, and the results are as follows: Figure 5 As shown, the fluctuation range of the center wavelength can be observed to be controlled within ±0.279125 nm, indicating that the structure has high precision and stability.

[0033] This invention successfully yields a highly sensitive double misaligned fiber temperature sensor based on the vernier effect. First, two misaligned fibers are cascaded using fiber fusion technology. The misalignment size of both fibers is 47 μm, and the misalignment lengths are 847.22 μm (misaligned fiber 1) and 532.41 μm (misaligned fiber 2), respectively. Second, SU-8 photoresist with high thermo-optic coefficient and high thermal expansion coefficient is coated into the microcavity formed by misaligned fiber 2. Ultraviolet curing technology is used to expose the SU-8 photoresist, and the exposed SU-8 photoresist completely encapsulates the microcavity of misaligned fiber 2. Each of the two cascaded misaligned fibers forms a Mach-Zender interferometer (MZI). Because the free spectral ranges of the two cascaded MZI interferometers are different but similar, the vernier envelope was obtained. Within a temperature range of 30 °C to 55 °C, the temperature sensitivity was monitored, with the node changes of the vernier envelope near 1375 nm exhibiting a sensitivity of 1.3533 nm / °C, achieving highly sensitive temperature sensing. The proposed temperature sensor is simple to fabricate, low in cost, and highly sensitive, showing broad application prospects in the biomedical field.

[0034] Table 1 below records a comparison of the relevant performance of existing misaligned fiber optic temperature sensors, as follows:

[0035] In the table above: DOI number of reference 1: doi 10.1007 / s10946-021-09995-w; DOI number of reference 2: doi.org / 10.1016 / j.optlastec.2021.107174; DOI number of reference 3: doi.org / 10.1016 / j.optcom.2014.08.065; DOI number of reference 4: doi.org / 10.1016 / j.optlastec.2022.108670.

[0036] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect, characterized in that, It includes an input optical fiber with misaligned connections, a first misaligned optical fiber, a second misaligned optical fiber, and an output optical fiber, as well as polymer microspheres; One end of the input optical fiber is fused to one end of the first misaligned optical fiber in a misaligned manner, forming a first misaligned fusion surface between them; the other end of the first misaligned optical fiber is fused to one end of the second misaligned optical fiber in a misaligned manner, forming a second misaligned fusion surface between them; the other end of the second misaligned optical fiber is fused to one end of the output optical fiber in a misaligned manner, forming a third misaligned fusion surface between them; polymer microspheres are wrapped around the misaligned cavity between the second misaligned fusion surface and the third misaligned fusion surface.

2. The high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect according to claim 1, characterized in that, The misalignment distance between the input optical fiber and the first misaligned optical fiber, the first misaligned optical fiber and the second misaligned optical fiber, and the second misaligned optical fiber and the output optical fiber is 40-60 μm.

3. The high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect according to claim 1 or 2, characterized in that, The length of the first misaligned fiber is 800-900 μm, and the length of the second misaligned fiber is 500-600 μm.

4. The high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect according to any one of claims 1-3, characterized in that, The input fiber, the first misaligned fiber, the second misaligned fiber, and the output fiber are all multimode fibers; Preferably, the multimode optical fiber has a core diameter of 100-110 μm and a cladding diameter of 120-130 μm.

5. The high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect according to any one of claims 1-4, characterized in that, The polymer microspheres are elliptical in shape, with a maximum radial diameter of 250-300 μm and an axial length of 600-650 μm.

6. The high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect according to claim 5, characterized in that, The polymer microspheres are formed by photocuring SU-8 photoresist.

7. A method for fabricating a high-sensitivity double-misaligned fiber optic temperature sensor based on the vernier effect as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Align the two fiber segments, which serve as the input fiber and the first misaligned fiber, axially and then misalign them radially by a certain distance to perform the first fusion splice and form the first misaligned fusion splice surface. S2. After cutting the first misaligned fiber along the end away from the first misaligned fusion splice surface, align it with the axial direction of a fiber segment that serves as the second misaligned fiber, then misalign it radially by a certain distance, and perform a second fusion splice to form the second misaligned fusion splice surface. S3. After cutting the second misaligned fiber along the end away from the second misaligned fusion splice surface, align it with the axial direction of a section of fiber that serves as the output fiber, then misalign it radially by a certain distance, and perform a third fusion splice to form the third misaligned fusion splice surface. S4. Coat the misaligned cavity between the second misaligned fusion surface and the third misaligned fusion surface with a polymer, and after curing to form polymer microspheres, the double misaligned fiber optic temperature sensor is obtained.

8. A temperature sensing system, characterized in that, Includes the double misaligned fiber optic temperature sensor according to any one of claims 1-6 or the double misaligned fiber optic temperature sensor prepared by the preparation method according to claim 7.

9. The temperature sensing system according to claim 8, characterized in that, The temperature sensing system also includes a broadband light source and a spectrum analyzer; The broadband light source is connected to the input fiber of the dual misaligned fiber optic temperature sensor, and the spectrometer is connected to the input fiber of the dual misaligned fiber optic temperature sensor.

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