A dual-parameter measurement optical fiber sensor and a manufacturing method thereof

Abstract

The application relates to the technical field of optical fiber sensing, in particular to a double-parameter measurement optical fiber sensor and a manufacturing method thereof. The double-parameter measurement optical fiber sensor comprises an optical fiber and a sensing unit arranged at one end of the optical fiber; the sensing unit is composed of a Bragg mirror and a noble metal nanometer film arranged in sequence; the noble metal nanometer film is provided with nanometer structure units arranged in an array; the sensing unit can excite two resonance modes; the refractive index variation and the temperature variation of an external medium can cause the resonance wavelength of the two resonance modes to move; and the refractive index and the temperature of the external medium can be simultaneously measured. The metal nanometer film is improved to excite the two resonance modes, the sensitivity of detection is improved, the processing difficulty is simplified, the structural stability is improved, and the precise decoupling measurement of the refractive index and the temperature is realized.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a dual-parameter measurement fiber optic sensor and its fabrication method. Background Technology

[0002] In numerous fields such as modern industrial production, environmental monitoring, and biomedicine, the accurate and real-time measurement of refractive index and temperature—two key physical parameters—is crucial. Fiber optic sensors, with their advantages of electromagnetic interference resistance, small size, light weight, and long-distance transmission capability, have gained widespread attention and application in parameter measurement. In refractive index measurement, traditional fiber optic refractive index sensors are mainly based on principles such as Mach-Zehnder interferometry, Michelson interferometry, and Fabry-Perot interferometry, or on fiber grating sensing mechanisms. For example, patent applications CN121431445A and CN121113953A both construct interferometric fiber optic sensors based on the mode mismatch principle, realizing biochemical detection based on refractive index measurement. However, these two types of fiber optic refractive index sensors focus only on a single refractive index sensing target, neglecting the significant impact of temperature changes on the fiber optic sensing system in practical applications. This leads to temperature sensitivity issues; temperature changes during measurement can significantly interfere with the refractive index measurement results, causing decreased measurement accuracy or even functional failure.

[0003] To address the cross-sensitivity issue in multi-parameter measurements, researchers have proposed a dual-parameter measurement scheme. Typically, this involves combining sensors with different sensing mechanisms and measuring the signals corresponding to different parameters to achieve dual-parameter measurement. However, this approach often suffers from structural complexity, large size, and inconvenient data analysis.

[0004] Tamm plasmon polaritons (TPPs) are localized electromagnetic modes at the interface between a metallic thin film and a distributed Bragg mirror (DBR). Compared to traditional optical mechanisms, TPPs do not require complex coupling structures, can be directly excited at the fiber end face, and have a simple structure, significant local field enhancement effect, narrow resonant peak line, and strong anti-interference, providing a new and high-quality solution for fiber optic sensing. However, the electromagnetic field of traditional TPP modes is localized within the structure, making it difficult to sense changes in the refractive index of the external environment. To address this, existing technologies introduce microcavity spacers within the multilayer film structure of TPPs. For example, patent applications CN117309812A and CN117990658A theoretically demonstrate refractive index measurement based on the characteristics of TPPs; patent application CN118425100A utilizes the influence of environmental refractive index and temperature changes in the microcavity spacer layer on different orders of TPPs, also theoretically demonstrating dual-parameter sensing of refractive index and temperature.

[0005] However, the sensing unit of this type of sensor is essentially still a TPP (Transmission-Package) model, and the integrated TPP structure is separated into three parts: a distributed Bragg mirror layer, an open microcavity spacer layer, and a metal layer. The introduction of the open microcavity spacer layer separates the distributed Bragg mirror from the metal film. This separated structure is equivalent to the combined use of two independent elements, which is difficult to fabricate and operate in practice.

[0006] Furthermore, the thickness of the open-cavity spacer layer is crucial to the mode spectrum and sensing performance of TPP, typically ranging from tens to hundreds of nanometers. In actual fabrication, controlling the thickness and uniformity of the microcavity spacer layer is extremely difficult, which is a key obstacle affecting the practical application of the above-mentioned scheme. Moreover, the electromagnetic field energy in the microcavity spacer layer is very low, resulting in low intensity of electromagnetic field interaction with the environment, leading to relatively low refractive index sensitivity and temperature sensitivity. Summary of the Invention

[0007] To address the issues of relatively low refractive index and temperature sensitivity in existing microcavity-introduced fiber optic temperature and refractive index sensors, and the difficulty in actual fabrication, this invention provides a dual-parameter measurement fiber optic sensor and its fabrication method that combines high sensitivity, high reliability, low cost, and ease of preparation.

[0008] The dual-parameter measurement fiber optic sensor provided by this invention achieves accurate decoupled measurement of refractive index and temperature by developing a stable, simple to prepare, and highly robust TPP fiber optic sensing structure, which is of great value for fields such as health monitoring and biochemical detection.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows.

[0010] This invention provides a dual-parameter measurement fiber optic sensor, comprising an optical fiber and a sensing unit disposed at one end of the optical fiber; wherein, the sensing unit is composed of a Bragg reflector and a noble metal nanofilm arranged in sequence, the noble metal nanofilm having nanostructure units arranged in an array, the sensing unit being able to excite two resonant modes, causing the refractive index change and temperature change of the external medium to cause a shift in the resonant wavelength of the two resonant modes, thereby realizing the simultaneous measurement of the refractive index and temperature of the external medium.

[0011] Preferably, the noble metal nanofilm is a gold nanofilm or a silver nanofilm, and the thickness of the noble metal nanofilm is 50 nm to 100 nm. This is because gold and silver, as noble metals, have excellent chemical stability and environmental adaptability.

[0012] Preferably, the period of the nanostructure units on the noble metal nanofilm is 400nm to 700nm to meet the resonant mode excitation of the target operating wavelength.

[0013] Preferably, the array configuration of the nanostructure units on the noble metal nanofilm is a one-dimensional periodic distribution or a two-dimensional periodic distribution; the one-dimensional periodic distribution nanostructure units are nanostrips with a width of 100 nm to 400 nm; the two-dimensional periodic distribution nanostructure units are pores with a pore size of 100 nm to 400 nm.

[0014] In this invention, the nanostructure units only need to meet the excitation requirements of the resonant mode in the target operating band, and their shape is not strictly limited. Usually, shapes that are easy to fabricate in micro-nano processes, such as circles, rectangles, or squares, are preferred. The array configuration is a one-dimensional or two-dimensional periodic distribution.

[0015] Preferably, the Bragg reflector is composed of a first material and a second material arranged alternately along the thickness direction, with the number of alternating periods being 5 to 10; the refractive index of the first material is greater than that of the second material. In this invention, the first material is a high-refractive-index material; the second material is a low-refractive-index material.

[0016] Preferably, the first material is tantalum pentoxide, titanium dioxide, or hafnium dioxide; the second material is silicon dioxide. In this invention, both the first and second materials have good optical properties and stability, and the Bragg reflector formed by their alternating arrangement can provide high reflectivity, thereby enhancing the resonance effect of the sensing unit and improving the measurement sensitivity.

[0017] Preferably, the optical fiber is a multimode optical fiber, with a core diameter of 50μm to 1000μm and a cladding diameter of 125μm to 1100μm. The larger core size of the multimode optical fiber results in a larger effective area for the sensing unit at the fiber end face, leading to a higher signal-to-noise ratio for the fiber optic sensor.

[0018] Another aspect of the present invention provides a method for fabricating a dual-parameter measurement fiber optic sensor, comprising: depositing a Bragg reflector on the end face of an optical fiber using a vacuum coating technique, and then transferring a noble metal nanofilm to the end face of the optical fiber using a metal sacrificial layer etching and transfer method to obtain a dual-parameter measurement fiber optic sensor.

[0019] This invention primarily employs a metal sacrificial layer etching-transfer method, sequentially depositing a sacrificial layer and a noble metal nanofilm on a substrate. The sacrificial layer is then removed using an etching solution to release the noble metal nanofilm, resulting in a probe-type fiber optic sensor with an integrated sensing unit at the fiber end face. This invention features high integration, repeatable fabrication process, and simple measurement methods, making it suitable for applications such as biochemical and environmental monitoring.

[0020] A preferred method for fabricating a dual-parameter measurement fiber optic sensor includes the following steps: A Bragg reflector is deposited on the end face of an optical fiber using vacuum deposition technology to obtain a composite optical fiber. A metal sacrificial layer and a noble metal nanofilm are deposited on the surface of a substrate using vacuum deposition technology to obtain a substrate containing a noble metal nanofilm. The substrate has an array of nanostructure units. The substrate containing the noble metal nanofilm is immersed in a metal etching solution to remove the metal sacrificial layer and release the noble metal nanofilm. The noble metal nanofilm is rinsed with water to remove residual metal etching solution. The noble metal nanofilm is lifted using the composite optical fiber to make contact between the noble metal nanofilm and the end face of the composite optical fiber. After evaporation to remove residual water from the end face of the composite optical fiber, the noble metal nanofilm is cut and shaped to obtain a dual-parameter measurement optical fiber sensor.

[0021] In this invention, the combined optical fiber employs ion beam assisted deposition (IBED) technology to deposit a Bragg reflector on the fiber end face. Pre-depositing a DBR on the fiber surface allows the DBR to form a unified whole with the fiber, improving the structural stability and optical performance consistency of the sensing unit. Simultaneously, the deposition process can be performed in batches, reducing manufacturing costs.

[0022] The structure of the noble metal nanofilm is the same as the surface structure of the substrate. The purpose of cutting and shaping the noble metal nanofilm is to remove excess noble metal nanofilm outside the fiber end face. The noble metal nanofilm is tightly bonded to the combined fiber end face due to strong van der Waals forces.

[0023] Preferably, the sacrificial metal layer is made of copper with a thickness of 30 nm to 50 nm. In this invention, copper has good electrical conductivity and corrosivity, can be rapidly corroded by specific metal corrosive liquids, and the corrosion products are easy to clean.

[0024] The metal etchant is a copper etchant; for example, a FeCl3 solution with a mass fraction of 20%–40%. FeCl3 solution has a good corrosive effect on copper, with a moderate corrosion rate, capable of completely corroding the copper sacrificial layer in a short time, without significantly corroding the gold nanofilm.

[0025] The area of ​​the noble metal nanofilm is larger than the end face area of ​​the composite optical fiber. The noble metal nanofilm needs to completely cover the end face of the composite optical fiber to avoid incomplete coverage, thereby ensuring the stable optical performance of the sensing unit.

[0026] The substrate is a substrate with a micro / nano structure; the structure of the noble metal nanofilm is the same as the surface structure of the substrate. Through a vapor deposition process, the noble metal nanofilm replicates the micro / nano structure of the substrate, forming a noble metal nanofilm with a corresponding micro / nano structure.

[0027] A third aspect of the present invention provides a measurement method for a dual-parameter measurement fiber optic sensor, comprising the following steps: The dual-parameter measurement fiber optic sensor was placed in a test environment, and the refractive index and temperature of the environment were changed respectively. Simultaneously, the reflection spectrum of the dual-parameter measurement fiber optic sensor was recorded, and the wavelength changes of two characteristic modes in the reflection spectrum were extracted. A sensitivity matrix was constructed based on the calibration results of the refractive index and temperature. S Based on the wavelength variation Δ of the two characteristic modes measured online. λ Substitute into the sensitivity matrix S， The refractive index change Δ is obtained by solving the problem. n With temperature change Δ T This enables the decoupled reconstruction of two parameters.

[0028] The refractive index calibration was performed using a refractive index matching liquid with refractive indices of 1.3330, 1.3418, 1.3505, 1.3594, and 1.3684. The temperature calibration was performed in increments of 10℃, within the range of 20℃ to 60℃.

[0029] Sensitivity matrix S The formula is: Among them, S 1,n S represents the sensitivity of mode 1 to changes in refractive index; 1,T The sensitivity of Mode 1 to temperature changes; S 2,n S represents the response sensitivity of mode 2 to changes in refractive index. 2,T This represents the response sensitivity of Mode 2 to temperature changes.

[0030] In this invention, changes in the refractive index of the external medium and the ambient temperature will cause the corresponding mode wavelengths in the resonant spectrum to shift. A sensitivity matrix is ​​established by segmented calibration with refractive index matching liquid and temperature, thereby achieving decoupled measurement of refractive index and temperature as dual parameters.

[0031] The beneficial effects of this invention are: 1. This invention removes the microcavity spacer layer of the prior art, improves the metal nanofilm, and modulates the nanostructure units of the metal nanofilm to excite two resonance modes, thereby improving the detection sensitivity. At the same time, it can also simplify the processing difficulty, improve the structural stability, and achieve accurate decoupled measurement of refractive index and temperature.

[0032] 2. This invention introduces periodic micro-nano structures into metal nanofilms to excite two modes: TPP and localized surface plasmon resonance (LSP). The two modes are sensitive to temperature and refractive index, respectively, thus achieving dual-parameter sensing without destroying the integration and integrity of the TPP structure. It also has good operability and the actual processing is highly standardized.

[0033] 3. The metal nanofilm of the present invention can excite two modes, and both modes have strong electromagnetic field interaction with the environment. Therefore, it can achieve a synergistic improvement in refractive index sensitivity and temperature sensitivity. The refractive index sensitivity is 347 nm / RIU and the temperature sensitivity is 0.0778 nm / K. Compared with the prior art (fiber temperature refractive index sensor with microcavity), the refractive index sensitivity is improved by 39% and the temperature sensitivity is improved by more than 1 times, and the performance is significantly improved. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the dual-parameter measurement fiber optic sensor in Embodiment 1 of the present invention. Figure 1 The two illustrations on the right are schematic diagrams of different cross-sectional orientations of noble metal nanofilms.

[0035] Figure 2 This is a schematic diagram of the fabrication process of the dual-parameter measurement fiber optic sensor in Embodiment 2 of the present invention.

[0036] Figure 3 The images show the reflection spectrum and electric field diagrams of two resonant modes of the sensing unit of the dual-parameter measurement fiber optic sensor in Embodiment 2 of the present invention in a solution with a refractive index of 1.3330. (a) is the reflection spectrum; (b) is the electric field diagram for mode 1; and (c) is the electric field diagram for mode 2.

[0037] Figure 4 This is the reflection spectrum of the response of a fiber optic sensor to solutions with different refractive indices, as measured by a dual-parameter measurement method in Embodiment 3 of the present invention.

[0038] Figure 5 This is the reflection spectrum of the dual-parameter measurement fiber optic sensor in embodiment 3 of the present invention when the temperature range changes from 20°C to 60°C in air.

[0039] Explanation of reference numerals in the attached figures: 1. High refractive index materials; 2. Low refractive index materials; 3. Fiber cladding; 4. Fiber core; 5. Noble metal nanofilms. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0042] TPP stands for Tamm Plasmon Polariton. LSP stands for Localized Surface Plasmon.

[0043] Prior art: Patent application CN118425100A discloses a fiber optic temperature refractive index sensor based on TPP dual-peak coupling. By introducing microcavities in the silver film and Bragg mirror, the integrated TPP structure is separated into three parts: a distributed Bragg mirror layer, an open microcavity spacer layer, and a metal layer, in order to enhance the contact between the TPP mode and the environment, thereby realizing the sensing of two parameters: refractive index and temperature.

[0044] From a principle and structural perspective, the sensing units of the aforementioned existing technologies are essentially still a type of TPP (Transformer-Pulse Array) model. In traditional TPP models, the electromagnetic field is localized within the TPP structure, making it difficult to sense changes in the refractive index of the external environment. Therefore, the aforementioned existing technologies introduce microcavity spacers within the multilayered film structure of the TPP to achieve the interaction between the electromagnetic field of the TPP model and the refractive index of the environment, thus realizing refractive index sensing. This is equivalent to artificially separating the integrated TPP structure into three parts: the Bragg mirror layer, the microcavity spacer layer, and the metal layer. Because of this, actual fabrication is difficult to achieve, and therefore the existing technologies are only theoretical results without empirical data to support them.

[0045] In terms of performance, existing technologies achieve sensing by introducing microcavity spacers. However, the thickness of microcavity spacers is usually only tens of nanometers. The electromagnetic field energy in the microcavity spacers is very low, resulting in low intensity of electromagnetic field interaction with the environment. The refractive index sensitivity is only 249 nm / RIU, and the temperature sensitivity is 0.03721 nm / K.

[0046] In summary, the existing technology disclosed above discloses an optical fiber temperature refractive index sensor with a microcavity, which can only realize one TPP mode, and has the problems of relatively low refractive index sensitivity and temperature sensitivity, as well as high difficulty in actual processing.

[0047] To this end, the present invention removes the microcavity spacer layer of the prior art and improves the metal nanofilm by controlling the period, pore size and material of the pore structure unit of the metal nanofilm to excite two resonance modes: LSP mode and TPP mode, thereby improving the detection sensitivity. At the same time, it can also simplify the processing difficulty, improve the structural stability, and realize the accurate decoupled measurement of refractive index and temperature.

[0048] From the perspective of principle and structure, this invention introduces one-dimensional or two-dimensional periodic micro-nano structures into the metal layer of the TPP structure, thereby exciting two modes: TPP and localized surface plasmon resonance (LSP). The two modes are sensitive to temperature and refractive index, respectively, thus realizing dual-parameter sensing without destroying the integration and integrability of the TPP structure. It also has good operability and the actual processing is highly standardized.

[0049] In terms of performance, based on the differences in structure and principle between existing technologies, this invention can excite two modes by removing the microcavity and improving the surface metal nanofilm. Both modes have strong electromagnetic field interaction with the environment, thus achieving a synergistic improvement in refractive index sensitivity and temperature sensitivity. The refractive index sensitivity is 347 nm / RIU and the temperature sensitivity is 0.0778 nm / K. Compared with existing technologies, the refractive index sensitivity is improved by 39% and the temperature sensitivity is improved by more than 100%, resulting in a significant performance improvement.

[0050] The technical solution of the present invention will be further described below through specific embodiments. Unless otherwise specified, the methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0051] Example 1 like Figure 1 As shown, the dual-parameter measurement fiber optic sensor consists of an optical fiber and a sensing unit at one end of the fiber. The sensing unit comprises a Bragg reflector (DBR) and a noble metal nanofilm 5 arranged sequentially. The noble metal nanofilm 5 includes nanostructure units arranged in an array. The sensing unit can excite two resonant modes: the LSP mode and the TPP mode. Changes in the external refractive index and temperature can cause a shift in the resonant wavelengths of these two modes, enabling simultaneous measurement of the external refractive index and temperature.

[0052] A Distributed Bragg reflector (DBR) is composed of alternating high-refractive-index material 1 and low-refractive-index material 2 (such as tantalum pentoxide and silicon dioxide, or titanium dioxide and silicon dioxide, or hafnium dioxide and silicon dioxide, etc.), with a period number of 5 to 10. The period number is set to ensure that the DBR has good reflection characteristics in the target operating band and effectively enhances the intensity of the resonant mode.

[0053] The noble metal nanofilm 5 is a gold or silver nanofilm with a thickness of 50 nm to 100 nm. Gold and silver have excellent electrical conductivity, and their nanostructures can efficiently excite resonant modes. Furthermore, choosing gold or silver as the material for the noble metal nanofilm 5 allows it to meet the target operating wavelength range of 400 nm to 700 nm. The noble metal nanofilm 5 comprises nanostructure units arranged in a one-dimensional or two-dimensional array; the period of these nanostructure units is 400 nm to 700 nm. The period of the nanostructure units affects the target operating wavelength range. By adjusting the period of the nanostructure units, the excitation requirements for resonant modes in the target operating wavelength range (visible light wavelength range of 400 nm to 700 nm) can be met. This invention does not strictly limit the shape of the nanostructure units, but generally prefers shapes that are easily fabricated in micro- and nano-scale processes, such as circles, rectangles, or squares. The array arrangement of the nanostructure units is either one-dimensional or two-dimensional periodic. The one-dimensional periodic nanostructure units are nanostrips with a width of 100 nm to 400 nm; the two-dimensional periodic nanostructure units are pores with a diameter of 100 nm to 400 nm. Therefore, by adjusting the period of the nanostructure units and selecting a suitable noble metal nanofilm 5 material, the sensitivity of the target operating wavelength can be improved. For example, in this embodiment, the noble metal nanofilm 5 used is a gold nanofilm, with a period of 400 nm to 700 nm for the nanostructure units, and circular pores with a diameter range of 100 nm to 400 nm. The size of the pores affects the intensity of the two resonant modes and the electromagnetic field intensity.

[0054] The optical fiber is a multimode fiber, consisting of a fiber core 4 and a fiber cladding 3. The fiber cladding 3 is designed with a refractive index slightly lower than that of the fiber core 4 to achieve light guidance based on total internal reflection within the fiber core 4. The diameter of the fiber core 4 in the multimode fiber is 50μm to 1000μm, and the diameter of the fiber cladding 3 is 125μm to 1100μm.

[0055] In this embodiment of the invention, different materials and structures of noble metal nanofilms 5 (e.g., continuous flat nanofilms and nanofilms with periodic structural units) and different types of optical fibers (e.g., solid optical fibers, hollow optical fibers, single-mode optical fibers or multimode optical fibers) can be flexibly selected as substrates according to different applications, which can be widely used in optical sensing, optical communication and other fields.

[0056] When broadband light is incident on the sensing unit from the end face of the optical fiber, two resonant modes are excited in the sensing unit, such as... Figure 3 These two resonance modes have different effects on the refractive index of the external medium. n With ambient temperature T Sensitive. Among them, the LSP mode is sensitive to changes in the refractive index of the external medium, while the TPP mode is sensitive to changes in ambient temperature.

[0057] In use, the dual-parameter measurement fiber optic sensor is connected to a broadband light source and a spectrometer via a circulator. The sensing unit is placed in the environment; as the refractive index of the external medium changes, the wavelength of the representative resonant mode monotonically shifts towards longer or shorter wavelengths. When the ambient temperature changes, the wavelength of the other resonant mode shifts. Through pre-calibration in a refractive index matching liquid and a constant-temperature environment, the response relationship of the fiber optic sensor to refractive index and temperature can be established. During online measurement, by selecting the two resonant modes as characteristics, the changes in refractive index and temperature can be obtained simultaneously based on their wavelength shifts, or the effect of temperature can be compensated when only the refractive index is measured.

[0058] Example 2 like Figure 2 As shown, based on Example 1, a method for fabricating a dual-parameter measurement fiber optic sensor is provided. This method first involves batch-depositing a Bragg reflector (DBR) on the fiber end face using vacuum coating technology, and then depositing a noble metal nanofilm 5 on a large-area substrate. Subsequently, the noble metal nanofilm is released by etching a metal sacrificial layer, completing the transfer. The fiber used is a 200μm core, 0.22 cladding multimode silica fiber. The specific transfer method includes the following steps:

[0059] S1. Fabrication of composite optical fiber: Using ion beam assisted deposition technology, high refractive index materials and low refractive index materials are alternately deposited on the end face of the optical fiber to form a composite optical fiber coated with a Bragg reflector (DBR).

[0060] S2. Provide a substrate: The substrate can be a substrate with a nanoarray structure (for obtaining gold nanofilms with array structures). The period of the array structure is preferably 400 nm to 700 nm, and the structure shape, parameters and array configuration can be selected according to the excitation requirements of the target band resonant mode.

[0061] S3, Deposition of sacrificial layer and noble metal nanofilm: at ~1×10 -4 Under a vacuum of mbar, copper (Cu) with a thickness of 30 nm to 50 nm and gold (Au) with a thickness of 50 nm to 100 nm were sequentially deposited onto the above-mentioned substrate using thermal evaporation technology. During thermal evaporation, the deposition rate of the metals remained at 0.1 nm / s.

[0062] S4. Release of the noble metal nanofilm: The silicon template with deposited metal is slowly immersed in a copper etching solution (FeCl3 solution with a mass fraction of 20%–40%). As the copper layer is etched, the uppermost gold nanofilm will gradually separate from the substrate, forming a self-supporting film near the liquid surface. This separation process is highly controllable, and the gold nanofilm will not exhibit structural defects such as wrinkles or tears, ultimately floating intact and flat on the surface of the etching solution.

[0063] S5. Cleaning: Use deionized water to repeatedly rinse the etching solution under the gold nanofilm until the residual etching solution is completely cleaned to avoid the influence of etching agent residue on the sensor unit structure and optical performance.

[0064] S6. Transfer: The floating gold nanofilm is slowly lifted using a composite optical fiber, bringing it into contact with the end face of the composite optical fiber and completing the transfer. Due to the excellent flexibility of the gold nanofilm and the strong van der Waals force between it and the optical fiber, the gold nanofilm can be smoothly bonded to the end face of the fiber. Simultaneously, to improve the transfer success rate, the area of ​​the gold nanofilm is preferably larger than the end face area of ​​the composite optical fiber ferrule, ensuring complete coverage of the fiber end face while allowing for trimming.

[0065] S7. Drying: After the deionized water remaining on the end face of the combined optical fiber evaporates naturally, the excess gold nanofilm on the end face is cut and shaped to remove the excess gold nanofilm outside the end face of the optical fiber, and finally an optical fiber sensor with the end face completely covered by gold nanofilm is obtained.

[0066] The substrate recovered after corrosion treatment can be reused for metal deposition and film stripping experiments after undergoing standardized cleaning processes such as deionized water rinsing, ultrasonic cleaning, and drying, while maintaining stable surface microstructure and structural integrity. This reusability significantly reduces the material consumption cost per experiment, eliminates the economic and time costs of preparing new substrates, and significantly improves the overall operational efficiency and economy of the process.

[0067] In this embodiment, the DBR (Distributed Bragg Mirror) is composed of alternating layers of SiO2 and Ta2O5, with refractive indices of 1.46 and 2.11, and thicknesses of 97 nm and 67 nm, respectively. The film thickness of each layer in the DBR satisfies the Bragg reflection condition: film thickness × material refractive index = target working wavelength / 4. The nanostructure unit is a circular aperture; specifically, the period of the nanostructure unit in the gold nanofilm is 600 nm, the diameter is 180 nm, and the thickness is 100 nm.

[0068] For the dual-parameter measurement fiber optic sensor prepared in Example 2, the fabricated dual-parameter measurement fiber optic sensor was immersed in water, and the reflectance spectrum was measured. Figure 3 As shown in (a), electromagnetic simulations were performed on the two characteristic resonant modes to obtain the electric field distribution diagrams for the corresponding modes. Among them, Figure 3 (b) is the electric field diagram for Mode 1. Figure 3(c) shows the electric field diagram for Mode 2. Mode 1 is the TPP mode; Mode 2 is the LSP mode. The electric field in Mode 1 is localized between the metal layer and the DBR layer, and is insensitive to changes in the ambient refractive index, exhibiting TPP characteristics. Therefore, Mode 1 is a TPP mode, but is sensitive to changes in ambient temperature. The electric field in Mode 2 is locally enhanced at the upper edge of the nanopore, generating a direct and strong electromagnetic interaction with the surrounding medium. Therefore, it is sensitive to changes in the ambient refractive index, and refractive index measurement can be achieved by monitoring its wavelength drift. Therefore, Mode 2 is an LSP mode, and is sensitive to changes in the refractive index of the external medium. Since the two resonant modes respond to changes in refractive index and temperature respectively, decoupling of refractive index and temperature measurements can be achieved by monitoring the wavelength shifts of these two modes affected by changes in refractive index and temperature.

[0069] In summary, the sensor in this embodiment of the invention excites two resonant modes through the sensing unit. Changes in external refractive index and temperature will cause the resonant wavelength of the corresponding modes to shift, respectively. Simultaneously, the synergistic effect of the Bragg reflector (DBR) and the noble metal nanofilm enhances the sensor's response sensitivity to changes in refractive index and temperature, improving measurement sensitivity. The sensing unit of the sensor is directly disposed at one end of the optical fiber, exhibiting high robustness, compact size, and ease of installation and use. Furthermore, all components of the sensor (such as the DBR, noble metal nanofilm, and optical fiber) possess good chemical stability and mechanical strength, enabling them to adapt to different working environments and further enhancing the sensor's reliability. In addition, the manufacturing process of this invention is simple and low-cost. The method of this invention is highly practical and possesses stable production repeatability. The optical fiber sensor used in this invention first utilizes a mature coating process to mass-produce the DBR on the end face of the optical fiber, and then transfers the noble metal nanofilm to the end face of the optical fiber using a transfer method. This eliminates the need for complex mechanical processing and splicing of the optical fiber body, reducing processing difficulty and manufacturing costs, and providing a reliable guarantee for its long-term stable operation in complex industrial scenarios.

[0070] Example 3 Based on the above embodiments, to achieve synchronous measurement of refractive index and temperature, this invention employs a decoupling strategy of "calibration-matrix solving". In the calibration phase, the response relationship between characteristic mode wavelengths and refractive index and temperature is established respectively; in the measurement phase, the real-time measured characteristic mode wavelengths are shifted and substituted into the sensitivity matrix to solve for the changes in these two parameters, refractive index and temperature.

[0071] Step 1, Spectral Line Acquisition and Feature Extraction: Establish a baseline reflection spectrum, select the wavelengths of the two resonant modes from Example 2 as the tracking targets, and fix their baseline center positions. Place the dual-parameter measurement fiber optic sensor prepared in Example 2 in the target medium environment. After the reflection spectrum stabilizes, extract the wavelength positions. Repeat the acquisition three times at each measurement point and take the average.

[0072] Step 2, Refractive Index Calibration: At a constant temperature (e.g., 25℃), change the test solution sequentially in order of increasing refractive index. After each spectral line stabilizes, record the wavelength values ​​of the two resonant modes. Establish a response curve of mode wavelength versus refractive index, and save it as refractive index sensitivity information.

[0073] Step 3, Temperature Calibration: The dual-parameter measurement fiber optic sensor prepared in Example 2 was placed in a constant temperature chamber, and the temperature was increased and decreased in 10°C increments within the range of 20°C to 60°C. After each temperature point stabilized, the wavelength values ​​of the two resonant modes were recorded, and a response curve of the mode wavelength versus temperature was established and stored as temperature sensitivity information.

[0074] Step 4, Online Decoupling: In actual measurement applications, the wavelength values ​​of the two resonant modes are tracked in real time and compared with the baseline or the most recent calibration point to obtain the displacement. The system calls up the pre-stored refractive index and temperature sensitivity information, and combines the comprehensive response of the two spectral lines to decompose the observed wavelength shift into refractive index change and temperature change.

[0075] Embodiment 3 of the present invention utilizes a dual-parameter measurement method to obtain the reflection spectra of the fiber optic sensor's response to solutions with different refractive indices, such as... Figure 4 As shown. The refractive indices were successively set to 1.3330, 1.3418, 1.3505, 1.3594, and 1.3684. Reflectance spectra were acquired under each refractive index condition. As the mass fraction of the solution increases, its refractive index increases, and mode 2 of the dual-parameter measurement fiber optic sensor will redshift accordingly, shifting by a total of 12.3 nm. According to the sensitivity calculation formula, where Δ... λ Δ n The changes in the center wavelength and refractive index of the mode, respectively, can be used to calculate the response sensitivity of the dual-parameter fiber optic sensor to changes in refractive index in mode 2.

[0076] Sensitivity calculation formula: Where S is the sensitivity; Δ λ Δ represents the change in the center wavelength of the mode. n This represents the change in refractive index.

[0077] In Embodiment 3 of this invention, the dual-parameter measurement fiber optic sensor is placed in a test environment, and the refractive index and temperature of the environment are changed respectively. Simultaneously, the reflection spectrum of the dual-parameter measurement fiber optic sensor is recorded, and the wavelength changes of two characteristic modes in the reflection spectrum are extracted. A sensitivity matrix is ​​constructed based on the calibration results of the refractive index and temperature. S Based on the wavelength variation Δ of the two characteristic modes measured online. λ Substitute into the sensitivity matrix S， The refractive index change Δ is obtained by solving the problem. n With temperature change Δ TThis achieves decoupled reconstruction of two parameters. The refractive index calibration uses a refractive index matching liquid with refractive indices of 1.3330, 1.3418, 1.3505, 1.3594, and 1.3684. Temperature calibration is performed in 10-degree increments within the range of 20℃ to 60℃.

[0078] Sensitivity matrix S The formula is: Among them, S 1,n S represents the sensitivity of mode 1 to changes in refractive index. 1,T The sensitivity of Mode 1 to temperature changes; S 2,n S represents the sensitivity of mode 2 to changes in refractive index. 2,T This represents the response sensitivity of Mode 2 to temperature changes.

[0079] Embodiment 3 of the present invention utilizes a dual-parameter measurement method to obtain the reflectance spectrum of a fiber optic sensor in response to temperature changes, such as... Figure 5 As shown. During the test, the prepared dual-parameter measurement fiber optic sensor was placed in a closed temperature-controlled test chamber, and temperature scanning was performed in 10°C increments within the range of 20°C to 60°C. As the temperature rose from 20°C to 60°C, Mode 1 underwent a blue shift, indicating that the fiber optic sensor's sensitivity to temperature changes was 0.0778 nm / K. Simultaneously, Mode 2 also shifted with temperature changes, indicating that Mode 2 exhibits cross-sensitivity to temperature, with a cross-sensitivity of 0.0913 nm / K.

[0080] Experiments show that this fiber optic sensor can simultaneously excite two resonant modes, which, as two detection signals, respond to changes in refractive index and temperature respectively. Substituting the sensor's refractive index and temperature calibration results into the cross-sensitivity matrix, the fiber optic sensor's response to changes in refractive index and temperature can be obtained.

[0081] Cross-sensitivity matrix: ; where Δ λ 1 represents the wavelength change in Mode 1; Δ λ 2 represents the wavelength change in mode 2; S 1,n This represents the sensitivity of Mode 1 to changes in refractive index. S 2,n This represents the sensitivity of Mode 2 to changes in refractive index. S 1,T This represents the response sensitivity of Mode 1 to temperature changes; S 2,T The sensitivity of Mode 2 to temperature changes; Δ n Δ is the change in refractive index. T This represents the change in temperature.

[0082] In practical applications, it is only necessary to measure the wavelengths of the two resonant modes of the fiber optic sensor. λ 1 and λ The change in 2 (Δ) λ 1 and Δ λ 2) Substituting these values ​​into the following two-parameter decoupling matrix, we can obtain the changes in temperature and refractive index relative to the base point (Δ). n and Δ T This enables the decoupled reconstruction of two parameters, completing the dual-parameter measurement of temperature and refractive index.

[0083] Two-parameter decoupling matrix: ; where Δ n Δ is the change in refractive index. T Δ represents the change in temperature. λ 1 represents the wavelength change in Mode 1; Δ λ 2 represents the wavelength change in mode 2.

[0084] In summary, the dual-parameter measurement fiber optic sensor prepared in this embodiment of the invention, through a sensing unit composed of a DBR (Draco Bragg reflector) and a noble metal nanofilm, can effectively excite different resonant modes, achieving simultaneous measurement of external refractive index and temperature. This dual-parameter measurement fiber optic sensor possesses advantages such as high measurement accuracy, compact structure, good stability, simple fabrication process, and strong anti-interference capability. It can be widely applied in various fields such as industrial production, biomedicine, and environmental monitoring, demonstrating significant practical value and broad market prospects. Furthermore, for different applications, noble metal nanofilms of different materials and structures can be transferred, and different types of optical fibers (e.g., solid optical fibers, hollow optical fibers, single-mode optical fibers, multimode optical fibers, etc.) can be used as substrates, enabling its widespread application in optical sensing, optical communication, and other fields.

[0085] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual-parameter measurement fiber optic sensor, comprising an optical fiber and a sensing unit disposed at one end of the optical fiber; characterized in that, The sensing unit is composed of a Bragg reflector and a noble metal nanofilm arranged in sequence. The noble metal nanofilm has nanostructure units arranged in an array. The sensing unit can excite two resonance modes, so that the change in refractive index and temperature of the external medium causes the resonant wavelength of the two resonance modes to shift, thereby realizing the simultaneous measurement of the refractive index and temperature of the external medium. The noble metal nanofilm is a gold nanofilm or a silver nanofilm, and the thickness of the noble metal nanofilm is 50 nm to 100 nm. The period of the nanostructure units on the noble metal nanofilm is 400nm to 700nm to meet the resonant mode excitation of the target working band. The array configuration of the nanostructure units on the noble metal nanofilm is a one-dimensional periodic distribution or a two-dimensional periodic distribution; the one-dimensional periodic distribution nanostructure units are nanostrips with a width of 100 nm to 400 nm; the two-dimensional periodic distribution nanostructure units are pores with a pore size of 100 nm to 400 nm.

2. The dual-parameter measurement fiber optic sensor according to claim 1, characterized in that, The Bragg reflector is composed of a first material and a second material arranged alternately along the thickness direction, with the number of alternating periods being 5 to 10; the refractive index of the first material is greater than that of the second material.

3. The dual-parameter measurement fiber optic sensor according to claim 2, characterized in that, The first material is tantalum pentoxide, titanium dioxide, or hafnium dioxide; the second material is silicon dioxide.

4. The dual-parameter measurement fiber optic sensor according to claim 1, characterized in that, The optical fiber is a multimode optical fiber with a core diameter of 50μm to 1000μm and a cladding diameter of 125μm to 1100μm.

5. A method for manufacturing a dual-parameter measurement fiber optic sensor as described in claim 1, characterized in that, include: A Bragg reflector is deposited on the fiber end face using vacuum coating technology, and then a noble metal nanofilm is transferred to the fiber end face using a metal sacrificial layer etching transfer method to obtain a dual-parameter measurement fiber optic sensor.

6. The method for fabricating a dual-parameter measurement fiber optic sensor according to claim 5, characterized in that, The specific production method includes the following steps: A Bragg reflector is deposited on the end face of an optical fiber using vacuum coating technology to obtain a composite optical fiber; A metal sacrificial layer and a noble metal nanofilm are deposited on the surface of a substrate using vacuum deposition technology to obtain a substrate containing a noble metal nanofilm; the substrate is a substrate with nanostructure units arranged in an array. The substrate containing the noble metal nanofilm was immersed in a metal etching solution to remove the metal sacrificial layer and release the noble metal nanofilm; the noble metal nanofilm was then rinsed with water to remove any residual metal etching solution. A noble metal nanofilm is lifted using a composite optical fiber and brought into contact with the end face of the composite optical fiber. After evaporation to remove residual water from the end face of the composite optical fiber, the noble metal nanofilm is cut and shaped to obtain a dual-parameter measurement optical fiber sensor.

7. The method for manufacturing a dual-parameter measurement fiber optic sensor according to claim 6, characterized in that, The sacrificial metal layer is made of copper and has a thickness of 30nm to 50nm; the metal etching solution is a copper etching solution; the area of ​​the noble metal nanofilm is larger than the end face area of ​​the combined optical fiber.

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