A microstructure optical fiber temperature sensor based on Ag composite MoO2 nanofilm

Abstract

The application belongs to the technical field of optical fiber temperature sensing, and particularly relates to a microstructure optical fiber temperature sensor based on Ag composite MoO2 nanometer film, mainly comprising a fiber core, a cladding air hole, a nanometer silver film, a nanometer molybdenum dioxide film and a temperature sensitive material, the fiber core is composed of a background material, the microstructure optical fiber is a D type spherical crown structure, the D type spherical crown structure is obtained by side polishing of a cylindrical optical fiber with four air holes symmetrically arranged, the D type spherical crown structure is composed of the fiber core and a plane, a double-layer nanometer film is deposited on the plane section, the inner layer cladding air hole and the double-layer nanometer film surround the fiber core, and finally, the temperature sensitive material is coated on the double-layer nanometer film. The application provides a D type microstructure optical fiber temperature sensor with simple structure, high sensitivity and easy control of drawing parameters.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic temperature sensing technology, specifically relating to a microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm, which is a D-type microstructured fiber optic temperature sensor based on the surface plasmon resonance (SPR) effect. Background Technology

[0002] With the continuous improvement and development of microstructured fiber drawing technology, microstructured fibers have been widely used in the field of optics due to their flexible and versatile structural design and unique and novel transmission characteristics. In particular, sensing technology based on microstructured fibers has gradually become a research hotspot in the field of new sensing. Among them, microstructured fiber sensing technology that utilizes the surface plasmon resonance effect has gained particular favor.

[0003] Microstructured fiber optic sensors based on surface plasmon resonance (SPR) selectively deposit or fill metal materials onto microstructured optical fibers using methods such as magnetron sputtering and chemical deposition. By altering the fiber's structural design and the physical parameters of the metal-coated portion, the phase-matching wavelength and resonance peak intensity during SPR can be changed. Therefore, high-performance fiber optic sensors can be designed by selecting different metals and coating thicknesses on top of the traditional microstructured fiber structure. The fiber's structural design (such as the size, shape, number, location, and arrangement of air holes in the cladding, as well as the location, thickness, and type of metal coating) effectively influences the performance of metal-filled fiber optic sensors.

[0004] In 2024, Kaifeng Li et al. proposed a surface plasmon resonance (SPR) fiber optic sensor based on a Ti3C2Tx-Mxene / Ag film. A V-shaped photonic crystal fiber (V-PCF) was used as the sensing probe, and a silver film was deposited on its surface by magnetron sputtering to excite the SPR effect. The sensor's refractive index (RI) measurement range was 1.333–1.421, with a maximum sensitivity of 10015 nm / RIU. Temperature sensing was achieved by coating a gold film on the sensing probe with polydimethylsiloxane (PDMS), achieving a maximum sensitivity of 3.5 nm / ℃ in a temperature range of 10℃–100℃. Although this sensor can achieve simultaneous temperature and refractive index detection, its structure is complex, difficult to fabricate, and has a relatively low average wavelength sensitivity.

[0005] In 2025, Yuxuan Yi et al. designed a D-type elliptical open-loop photonic crystal fiber (PCF) temperature sensor based on the surface plasmon resonance (SPR) effect. The SPR effect was excited by gold plating the elliptical sidewalls, and polydimethylsiloxane (PDMS) was selected as the sensing material. The sensor achieved a sensitivity of 7.16 nm / ℃ in the -20℃ to 0℃ range and 3.13 nm / ℃ in the 0℃ to 40℃ range. However, in practical operation, it is quite difficult to deposit a uniform and appropriately thick metal film on the inner wall of the elliptical groove of the microstructured fiber, and the sensitivity of the sensor is still not very high.

[0006] In 2025, Guoning Hu et al. studied a dual-channel D-type photonic crystal fiber sensor, which simultaneously measured refractive index and temperature by depositing ZnO / Ag and WS2 / Ag / PDMS on the upper and lower polished surfaces, respectively. The maximum temperature sensitivity was 14.3 nm / ℃ in the temperature range of -10℃ to 100℃. Despite its excellent performance, this structure requires double-sided precision polishing, multilayer heterogeneous film deposition, and complex decoupling algorithms, making the fabrication process difficult and costly. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention aims to provide a microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilms. The sensor primarily comprises a fiber core, cladding air holes, a silver nanofilm, a molybdenum dioxide nanofilm, and a temperature-sensitive material. The microstructured fiber is a D-shaped spherical cap structure, obtained by side polishing of a cylindrical fiber with four symmetrically arranged air holes. It consists of a fiber core and a planar section. A double-layer nanofilm is deposited on the planar section, with the inner cladding air holes and the double-layer nanofilm surrounding the fiber core. Finally, the temperature-sensitive material is coated onto the double-layer nanofilm. This invention provides a D-shaped microstructured fiber optic temperature sensor with a simple structure, high sensitivity, and easily controllable drawing parameters, overcoming the technical defects of existing fiber optic temperature sensors.

[0008] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: This invention protects a microstructured optical fiber temperature sensor based on Ag composite MoO2 nanofilms, comprising a fiber core, cladding air holes, a nano-molybdenum dioxide film, a nano-silver film, and a temperature-sensitive material. The microstructured optical fiber is a D-shaped spherical cap structure, consisting of a fiber core and a plane. The D-shaped spherical cap structure is obtained by polishing the sidewalls of a cylindrical optical fiber with four symmetrically arranged cladding air holes to form a plane. The cladding air holes are located on the fiber core. The cladding air holes are elliptical holes. The fiber core is composed of a background material, which is the substrate matrix material constituting the main structure of the optical fiber. A nano-silver film and a nano-molybdenum dioxide film are sequentially deposited on the plane. The deposition of the nano-silver film and the nano-molybdenum dioxide film can be performed by chemical vapor deposition (CVD) or magnetron sputtering. A temperature-sensitive material, polydimethylsiloxane (PDMS), is coated on the nano-molybdenum dioxide film. The specific cross-sectional structure of the microstructure fiber optic temperature sensor based on Ag composite MoO2 nanofilm of the present invention is that four cladding air holes and a double-layer nanofilm surround the fiber core region. That is, the four cladding air holes and the double-layer nanofilm are arranged in a spatially coordinated manner to form a surrounding constraint on the fiber core region.

[0009] Furthermore, the semi-major axis of the cladding air holes is a = 1.8 μm, the semi-minor axis is b = 1.0 μm, and the rotation angles of the cladding air holes around the origin are 18°, 162°, 234°, and 306°, respectively. The theoretical design of this cladding air hole is to use five air holes arranged in a regular pentagonal distribution, with each pair of air holes spaced 72° apart. However, in the actual design, the air hole located at 90° was removed, and only the remaining four air holes were retained.

[0010] Furthermore, the background material is quartz glass. It serves as the basic medium supporting the fiber core and special functional structures (such as cladding air holes, polished surfaces, and coatings).

[0011] Furthermore, the cylindrical optical fiber has a diameter of 10 μm and a side polishing depth of h = 2.8 μm. The core reason for side polishing of photonic crystal fibers is to create physical conditions for efficient coupling between the core guided mode and the surface plasmon mode of the metal film. Its significance lies in breaking through the optical field constraint limitations of conventional PCFs, realizing the controllable excitation of the SPR effect and significantly optimizing sensing performance.

[0012] Furthermore, the thickness of the nanosilver film ranges from 10 nm to 45 nm. If the coating of the D-type SPR-PCF fiber is too thick, it will lead to defects such as deterioration of the surface plasmon resonance (SPR) effect, decreased light transmittance, and poor film stability; if it is too thin, problems such as film discontinuity, weak SPR signal, and insufficient durability will occur. The coating is designed as a nanosilver film because it can efficiently excite the SPR effect, and silver is far more economical than gold, effectively reducing the manufacturing cost of the sensor while balancing performance and practicality.

[0013] Furthermore, the thickness of the nano-molybdenum dioxide film ranges from 10 nm to 30 nm. Coating the silver coating of D-type SPR-PCF optical fiber with a nano-molybdenum dioxide film is chosen because it can improve the stability of the silver coating, modulate the surface plasmon resonance (SPR) effect, and adapt to the structural and functional requirements of the optical fiber. If the film is too thick, it will lead to SPR signal degradation, stress concentration, and decreased transmittance; if it is too thin, it cannot effectively protect the silver coating, the SPR modulation effect is weak, and the film continuity is insufficient.

[0014] Furthermore, the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm is also nested within a perfectly matched layer, which facilitates the addition of computational boundaries when performing performance simulation using the finite element method.

[0015] Furthermore, the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilms exhibits a sensitivity of 12.925 nm / ℃ in the near-infrared x-polarization direction and a high sensitivity of 13.922 nm / ℃ in the near-infrared y-polarization direction. Among existing publicly available sensors, most can only achieve sensing in a single polarization direction, and their sensitivities are generally low. For example, the surface plasmon resonance (SPR) fiber optic sensor based on Ag+Ti3C2Tx-MXene films proposed by Li et al. has a maximum temperature sensitivity of 9.33 nm / ℃.

[0016] Furthermore, the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm achieves near-infrared sensing within a temperature range of -20℃ to 40℃.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention relates to a microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilms. The sensor uses a D-type microstructured fiber with four symmetrical elliptical cladding air holes as a substrate. A double-layer structure of a silver nanofilm and a molybdenum dioxide nanofilm is deposited on the polished side surface. Polydimethylsiloxane (PDMS) is used as the temperature-sensitive material. High-sensitivity temperature detection is achieved through the coupling of the SPR effect with the temperature-sensitive layer. The SPR effect of the D-type PCF is achieved through the synergistic effect of "D-type side-polished structure constructing the coupling interface + metal nanofilm deposition providing the plasma excitation medium + regulating the phase matching conditions between the core guiding mode and the surface plasmon mode." The core structure and material elements are indispensable. The essence of the SPR effect is the resonant coupling and energy transfer process between the core guiding mode and the surface plasmon polaritons (SPPs) of the metal film.

[0018] This invention relates to a microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilms. Utilizing the surface plasmon resonance (SPR) effect, this microstructured fiber exhibits high sensitivity and excellent sensing characteristics in the near-infrared band, making it suitable for fiber-optic temperature sensing applications and system integration. The high sensitivity of this temperature sensor is driven by three factors: the synergistic effect of the composite film layers, the optical field modulation characteristics of the microstructured fiber, and the enhanced responsiveness of both to the SPR effect.

[0019] 2. Compared with the prior art, the coating process of this invention on the polished surface is simpler than coating inside the air hole of the optical fiber; in addition, the uniformity of the nanofilm coverage thickness is controllable, making the drawing parameters easier to control.

[0020] 3. By simply placing the analyte in contact with the outer surface of the microstructured optical fiber, the sensing performance can be directly detected, making the detection method more efficient and accurate, and the application range of the temperature sensor wider.

[0021] 4. In this invention, a molybdenum dioxide film is deposited on a silver film. Due to the stable structure of molybdenum dioxide, it can effectively prevent silver from being oxidized, thereby improving performance. The loss peak intensity is sharper and the efficiency is better than that of silver film alone.

[0022] 5. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm of this invention exhibits high sensing sensitivity, with a sensitivity of 12.925 nm / ℃ in the x-polarization direction of the near-infrared band and a high sensitivity of 13.922 nm / ℃ in the y-polarization direction of the near-infrared band. By adjusting the thickness of the metal film coated on the polished plane, high-sensitivity sensing characteristics in the near-infrared band can be achieved within a temperature range of -20℃ to 40℃. Attached Figure Description

[0023] Figure 1 This is a three-dimensional view of the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm of the present invention.

[0024] Figure 2 This is a cross-sectional view of the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm of the present invention after being fitted with a perfectly matched layer.

[0025] Figure 3 This is a mode field distribution diagram of the microstructured optical fiber temperature sensor based on Ag composite MoO2 nanofilm of the present invention.

[0026] Figure 4 This is a graph showing the relationship between the confinement loss and wavelength of the microstructured optical fiber temperature sensor based on Ag composite MoO2 nanofilm in Embodiment 1 of the present invention.

[0027] Figure 5 This is a graph showing the relationship between the resonant wavelength and the temperature of the analyte in Example 1 of the present invention, which is based on a microstructured fiber optic temperature sensor made of Ag composite MoO2 nanofilm.

[0028] Figure labeling: 1-Fiber core, 2-Background material, 3-Elliptical air pore, 4-Nano silver film, 5-Nano molybdenum dioxide film, 6-Perfectly matched layer, 7-Analyte. Detailed Implementation

[0029] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0030] This invention provides a microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilms. Compared with existing surface plasmon resonance (SPR) fiber optic sensors based on Ti3C2Tx-Mxene / Ag films, the maximum average wavelength sensitivity of this invention is 13.922 nm / ℃, which is much higher than the 3.5 nm / ℃ of the existing technology. Furthermore, the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilms can also achieve simultaneous detection of temperature and refractive index. It has a simple structure and easy-to-control drawing parameters, overcoming the shortcomings of existing microstructured fiber optic temperature sensors based on Ag composite MoO2 nanofilms.

[0031] Compared with the existing D-type elliptical open-loop photonic crystal fiber (PCF) temperature sensor based on surface plasmon resonance (SPR), the preparation method of the present invention deposits a double-layer nanofilm on the exposed plane, which overcomes the technical difficulty of depositing a uniform and moderately thick metal film on the inner wall of the elliptical groove, and achieves uniform deposition of the double-layer nanofilm.

[0032] Compared with existing dual-channel D-type photonic crystal fiber sensors, the technical solution of this invention does not require double-sided precision polishing, multi-layer heterogeneous thin film deposition, and complex decoupling algorithms. The fabrication steps are simple and the structure is straightforward.

[0033] The technical solution of the present invention will be studied using the following embodiments. The specific research methods and results are shown below: Example 1 A microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm, such as Figure 1As shown, the microstructured optical fiber has a D-shaped spherical crown structure. This structure is obtained by polishing the sidewalls of a cylindrical optical fiber with four symmetrically arranged cladding air holes 3 into a flat surface. After polishing, the remaining fiber portion, excluding the flat surface, forms the fiber core 1, with the cladding air holes 3 located on the core 1. The core 1 is composed of a background material 2. A nano-silver film 4 and a nano-molybdenum dioxide film 5 are sequentially deposited on the flat surface, and a temperature-sensitive material, polydimethylsiloxane, is coated onto the nano-molybdenum dioxide film 5. The four cladding air holes 3 and the double-layer nanofilm surround the core region. In this invention, the polydimethylsiloxane layer primarily serves as a temperature-sensitive medium, and its refractive index changes with temperature, causing a shift in the surface plasmon resonance wavelength. When the thickness of the polydimethylsiloxane layer reaches a level sufficient to completely cover the metal film and ensure the evanescent field's full effect, its influence on the surface plasmon resonance conditions tends to stabilize. Therefore, the thickness of the polydimethylsiloxane layer is not a key parameter affecting the technical effect of this invention, and its specific thickness is not required.

[0034] like Figure 2 The image shown is a cross-sectional view of the microstructured optical fiber of this invention. In the microstructured optical fiber, four cladding air holes 3 are symmetrically distributed. The cladding air holes 3 are elliptical, with a major semi-axis of 1.8 μm and a minor semi-axis of 1.0 μm. To obtain a microstructured optical fiber with a polished side and a deposited nanofilm, it is only necessary to polish the sides after the cylindrical optical fiber is drawn to obtain a polished surface. Two nanofilms are then coated on the polished surface: a silver nanofilm with a thickness of 10 nm and a molybdenum dioxide nanofilm with a thickness of 10 nm. The temperature of the analyte in contact with the outer surface of the microstructured optical fiber is 0 °C. Figure 2 7 in the figure represents the analyte to be tested. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm needs to be completely immersed in the analyte 7 during operation. Figure 2 The 6 in the diagram represents the perfect matching layer, which is the computational boundary added when performing performance simulation using the finite element method.

[0035] like Figure 3 The image shows the mode field distribution of the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm at 2279 nm. The arrows indicate the electric field directions in the x and y modes. Figure 3 Figure (a) shows the mode field distribution in the x-mode. It can be seen that most of the mode field energy in the core-conducting mode in the x-polarization direction is concentrated in the core within the cladding (cladding refers to the quartz glass substrate region), with a small portion coupled to the bilayer of the silver and molybdenum nanofilms and beyond (the latter refers to the liquid-filled portion). Figure 3The results in Figure (b) show that, in the core conduction mode of the y-polarization direction, only a small portion of the mode field energy is confined in the core, while most of the energy is coupled to the surface of the silver nanofilm. This results in the core mode loss (core mode) in the y-polarization mode being much higher than that in the x-polarization mode, which is more beneficial for the design and application of the sensor.

[0036] like Figure 4 The figure shows the relationship between the confinement loss of the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm and wavelength. The equation is: L = 8.686 × 2π / λ × Im(n eff )×10 4 The limiting loss for transmission at different wavelengths is calculated, where λ represents the optical wavelength, and Im(n) eff The ) represents the imaginary part of the effective refractive index. The unit for limiting loss is dB / cm, and the unit for wavelength is μm. In the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm of this invention, the change in loss peak shift is observed by changing the temperature of different analytes, and is expressed by the following equation: S λ =dλ peak / dT gives the sensor's sensitivity, where T represents the analyte temperature and λ represents the resonant wavelength. S λ dλ is usually expressed in nm / ℃. peak dT is the shift of the resonance wavelength, and dT is the change in analyte temperature. Here, the temperature range for different analytes is -20℃ to 30℃.

[0037] according to Figure 4 As shown in Figure (a), with the gradual increase of the temperature of the analyte, the resonance peak in the x-polarized fiber core conduction mode gradually redshifts (i.e., shifts to a longer wavelength), and the intensity of the loss peak gradually increases, indicating that the surface plasmon resonance intensity gradually strengthens. The resonance wavelength ranges from 2020 nm to 2730 nm. Figure 5 Figure (a) shows that the average wavelength sensitivity reaches 12.925 nm / ℃ when the temperature changes from -20℃ to +30℃. The correlation coefficient R² between temperature and resonant wavelength is 0.99732, indicating a good fit between the two.

[0038] according to Figure 4 As shown in Figure (b), with the gradual increase of the temperature of the analyte, the resonance peak in the y-polarized fiber core conduction mode gradually redshifts, and the intensity of the loss peak gradually increases, indicating that the surface plasmon resonance intensity gradually strengthens. The resonance wavelength ranges from 1990 nm to 2650 nm. Similarly, it can also be observed in... Figure 5Figure (b) shows that the average wavelength sensitivity reaches 13.922 nm / ℃ when the temperature changes from -20℃ to +30℃, which is higher than the sensitivity in the x-polarization direction. The correlation coefficient R² between temperature and resonant wavelength is 0.99765, indicating a good fit between the two.

[0039] exist Figure 5 The graph showing the relationship between the resonant wavelength and the analyte temperature in this embodiment of the invention illustrates a linear fit between the resonant wavelength and the temperature of the analyte. The linear fit equation in the x-mode is: y = 12.92541x + 2267.4864. The linear fit equation in the y-mode is: y = 13.92222x + 2316.50381. The slope in these equations represents the average wavelength sensitivity of the microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm within the corresponding analyte temperature range.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm, characterized in that, The microstructured optical fiber is a D-shaped spherical crown structure, which consists of a fiber core (1) and a plane. The D-shaped spherical crown structure is obtained by polishing the sidewall of a cylindrical optical fiber with four cladding air holes (3) symmetrically arranged to form the plane. The cladding air holes (3) are located on the fiber core (1). The cladding air hole (3) is an elliptical hole; The fiber core (1) is composed of background material (2); A nano-silver film (4) and a nano-molybdenum dioxide film (5) are sequentially deposited on the plane, and a temperature-sensitive material is coated on the nano-molybdenum dioxide film (5).

2. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm according to claim 1, characterized in that, The major semi-axis of the cladding air hole (3) is 1.8 μm and the minor semi-axis is 1.0 μm. The cladding air hole (3) rotates around the center of the cylindrical optical fiber by 18°, 162°, 234° and 306° respectively.

3. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm according to claim 1, characterized in that, The cylindrical optical fiber has a diameter of 10 μm and a polishing depth of h = 2.8 μm.

4. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm according to claim 1, characterized in that, The background material (2) is quartz glass.

5. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm according to claim 1, characterized in that, The thickness of the nanosilver film (4) is 10nm~45nm.

6. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm according to claim 1, characterized in that, The thickness of the nano molybdenum dioxide film (5) is 10 nm to 30 nm.

7. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm according to claim 1, characterized in that, The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm is also nested within the perfectly matched layer (6).

8. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm according to claim 1, characterized in that, The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm has a sensitivity of 12.925 nm / ℃ in the x-polarization direction of the near-infrared band and a sensitivity as high as 13.922 nm / ℃ in the y-polarization direction of the near-infrared band.

9. The microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilm according to claim 1, characterized in that, A microstructured fiber optic temperature sensor based on Ag composite MoO2 nanofilms achieves near-infrared sensing within a temperature range of -20℃ to 40℃.

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