Micro-fluidic temperature and salt double-parameter optical fiber sensor based on anti-resonant effect, preparation method and test system thereof

Abstract

The present application relates to the technical field of optical fiber sensing, and proposes a microfluidic temperature and salt double-parameter optical fiber sensor based on anti-resonance effect, a preparation method thereof and a test system. The optical fiber sensor comprises: an input single-mode optical fiber, a hollow tubular optical fiber, a side single-hole double-core optical fiber and an output single-mode optical fiber which are connected in sequence; a micro groove is etched on the cladding layer of the fusion end of the input single-mode optical fiber and the hollow tubular optical fiber; a micro channel penetrating through the cladding layer of the hollow tubular optical fiber is etched on the side wall of the hollow tubular optical fiber; the side single-hole double-core optical fiber is located between the hollow tubular optical fiber and the output single-mode optical fiber, and has an air hole parallel to the axial direction in the inside, forming a fluid outflow channel; through the scheme, the response speed and the detection sensitivity are improved.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect, its fabrication method, and testing system. Background Technology

[0002] Anti-resonant reflective optical waveguides (ARROW), as a novel optical guiding mechanism, have gained widespread attention in the field of fiber optic sensing in recent years. Unlike traditional total internal reflection optical guiding mechanisms, the anti-resonant effect utilizes a high-refractive-index cladding structure as a reflector to confine the light field to a low-refractive-index hollow core. When the cladding thickness satisfies a specific anti-resonance condition, destructive interference occurs at the cladding interface, resulting in extremely high reflectivity at the hollow-cladding boundary, thereby achieving low-loss optical transmission. Because the anti-resonance condition is highly sensitive to changes in the refractive index of the waveguide interface, this type of structure naturally possesses the potential to become a high-sensitivity fiber optic sensing platform, capable of converting minute perturbations in the surrounding medium into significant spectral feature shifts.

[0003] Among various optical fibers based on the anti-resonance (AR) principle, hollow-core tube fiber (HCTF) is highly favored due to its simple structure, controllable fabrication, and ease of integration with microfluidic functions. HCTF utilizes a thin-walled silica cladding to support anti-resonance light guiding. Its large hollow structure not only accommodates gaseous or liquid analytes but also significantly enhances the interaction area between the light field and matter, effectively overcoming the limitation of traditional solid-core fiber sensors that rely solely on weak evanescent fields for detection. Currently, related research has utilized HCTF to achieve high-resolution measurements of biomolecular layers, liquid levels, and refractive indices. Some schemes, by combining HCTF with single-mode fibers or embedding it into specific optical structures, have developed sensors capable of measuring single or dual parameters such as liquid level, curvature, and temperature. Some designs theoretically exhibit extremely high refractive index and temperature response sensitivity, but some conceptual designs have not yet been transformed into practically testable physical devices.

[0004] Despite the theoretically superior performance of anti-resonant fiber optic sensors, significant technical bottlenecks remain in practical applications. First, most existing designs employ surface contact measurement, where the liquid only contacts the outer surface of the fiber. This results in the optical energy being concentrated primarily in the hollow core, leading to extremely low overlap with the external liquid and severely limiting measurement sensitivity. Second, while some solutions attempt to fill the fiber with liquid, they lack a continuous microfluidic circulation mechanism. Liquid replacement relies on slow natural diffusion or capillary action, resulting in extremely long response times (typically exceeding 90 seconds) to environmental changes. Furthermore, air bubbles easily accumulate within the fiber core, causing unstable measurement signals. Additionally, in multi-parameter measurements of liquids such as seawater, the refractive index is simultaneously affected by both temperature and salinity. A single spectral characteristic change cannot distinguish the contributions of both parameters, leading to severe cross-sensitivity. Existing solutions often rely on complex cascaded structures or expensive demodulation equipment and lack efficient data decoupling algorithms for high-precision synchronous measurement. Summary of the Invention

[0005] This invention provides a microfluidic temperature-salt dual-parameter fiber optic sensor based on the anti-resonance effect, its fabrication method, and testing system. It aims to solve technical problems in related technologies, such as the low overlap factor between the optical field and the liquid under test, which limits the measurement sensitivity; the lack of a through-microfluidic circulation mechanism, which leads to long response time and easy bubble retention; and the serious cross-sensitivity in temperature-salt multi-parameter measurement, which lacks an efficient single-probe decoupling scheme.

[0006] In a first aspect, embodiments of the present invention provide a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect, the microfluidic temperature-controlled salt dual-parameter fiber optic sensor comprising: a single-mode fiber for introduction, a hollow tubular fiber, a dual-core fiber with a single hole on the side, and a single-mode fiber for extraction, cascaded in sequence;

[0007] The fusion splice end of the single-mode fiber and the hollow tubular fiber is etched with a first microgroove. The first microgroove is located in the first cladding of the single-mode fiber and does not contact the core of the single-mode fiber.

[0008] The hollow tubular optical fiber has microchannels etched vertically through its second cladding on its sidewalls.

[0009] The side-mounted single-hole dual-core optical fiber is located between the hollow-core tubular optical fiber and the lead-out single-mode optical fiber. It has an air hole parallel to the axial direction inside, forming a fluid outflow channel.

[0010] The fusion splice end of the side-hole dual-core fiber and the lead-out single-mode fiber is etched with a second microgroove. The second microgroove is located in the third cladding of the lead-out single-mode fiber and does not contact the core of the side-hole dual-core fiber.

[0011] The seawater to be tested flows into the interior of the hollow tubular fiber through the first microgroove of the single-mode fiber and the microchannel of the hollow tubular fiber, and is discharged to the single-mode fiber through the air hole of the side single-hole dual-core fiber, forming a through-loop microfluidic circuit. The hollow tubular fiber filled with seawater excites the anti-resonance effect, and the position of the characteristic valley of the transmission spectrum drifts with the change of seawater temperature and salinity.

[0012] In one embodiment, optionally, the depth of the first microgroove is greater than the second cladding thickness of the hollow tubular optical fiber.

[0013] In one embodiment, optionally, the width of the microchannel is a preset width, and the distance between the microchannel position and the fusion splice point of the introduced single-mode fiber and the hollow tubular fiber is a preset distance, and the cladding wall thickness of the hollow tubular fiber satisfies the anti-resonance light guiding condition.

[0014] In one embodiment, optionally, after the hollow tubular optical fiber is excited with anti-resonance effect, the center wavelength of the characteristic valley in the transmission spectrum is... Satisfy the following formula:

[0015]

[0016] in, This indicates the thickness of the annular cladding in a hollow-core optical fiber. This indicates the refractive index of the quartz material used to make the second cladding layer. This represents the refractive index of the liquid filling the interior of a hollow tubular optical fiber. Indicates the order of the resonant mode.

[0017] In one embodiment, optionally, the wavelength dip position corresponding to the sidelobe in the transmission spectrum Satisfy the following formula:

[0018]

[0019] in, This represents the effective refractive index of the hollow tubular optical fiber core. and These represent the diameter of the second cladding and the length of the hollow tubular optical fiber, respectively. The self-imaging order is represented by the order of the self-imaging effect produced by multimode interference when light is transmitted in the anti-resonant guided wave mode in a hollow tubular optical fiber. Different orders correspond to sidelobe wavelength depressions at different positions in the transmission spectrum. p=0 corresponds to the depression corresponding to the basic self-imaging, and p=1,2,… corresponds to a series of sidelobe depressions corresponding to higher-order self-imaging.

[0020] In one embodiment, optionally, the wavelength displacement of the characteristic trough and the change in seawater refractive index satisfy the following equation:

[0021]

[0022] in, Indicates the center wavelength of the characteristic trough. This indicates the refractive index of the quartz material used to make the second cladding layer. This represents the refractive index of the liquid filling the interior of a hollow tubular optical fiber. The order of the resonant mode is represented by S, and the salinity of the seawater to be measured is represented by S.

[0023] Based on the fact that seawater temperature simultaneously modulates the refractive index of seawater and the cladding through the thermo-optic effect, the theoretical temperature sensitivity is derived by differentiation, satisfying the following equation:

[0024]

[0025] in, The value represents the second cladding thickness of the hollow-core optical fiber, and T represents the temperature of the seawater being measured.

[0026] In one embodiment, optionally, the refractive index of the seawater filling the hollow tubular optical fiber satisfies the following equation:

[0027]

[0028] Where S represents the salinity of the seawater to be measured, T represents the temperature of the seawater to be measured, λ represents the wavelength of the incident light, and k0 to k9 represent constant coefficients.

[0029] Secondly, embodiments of the present invention provide a method for fabricating a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect, the method comprising:

[0030] A femtosecond laser was used to etch the first and second microgrooves in the cladding near the close end faces of the single-mode fiber and the single-mode fiber, and airflow was used to remove debris during the etching process.

[0031] The single-mode fiber with the first microgroove etched on it is aligned and fused with the hollow tubular fiber.

[0032] Hollow-core tubular optical fibers are cut to a fixed length, and their cladding wall thickness is made to meet the anti-resonance light guiding conditions.

[0033] The cut end of the hollow tubular optical fiber is fused to one end of the single-hole dual-core optical fiber on the side.

[0034] Cut the fused side single-hole dual-core optical fiber to the predetermined length;

[0035] The other end of the single-hole dual-core fiber on the side is fused to the single-mode fiber with a second microgroove etched on it to form the microfluidic temperature-salt dual-parameter fiber sensor.

[0036] Thirdly, embodiments of the present invention provide a test system composed of a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect. The test system includes: a supercontinuum light source, a jumper, a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect, and a jumper-connected spectrometer connected in sequence. After the light signal emitted by the supercontinuum light source enters the microfluidic temperature-controlled salt dual-parameter fiber optic sensor, the anti-resonance effect is excited in the hollow tubular fiber optic cable filled with the seawater to be tested. The transmitted light signal is transmitted to the spectrometer through the single-mode fiber optic cable. The spectrometer collects the transmission spectrum and extracts the parameters of the characteristic valleys.

[0037] In one embodiment, optionally, the testing system further includes:

[0038] The data decoupling module establishes a three-dimensional mapping relationship between wavelength, temperature, and salinity based on polynomial surface fitting. It achieves simultaneous calculation of temperature and salinity by simultaneously solving the inverse function. The three-dimensional mapping relationship satisfies the following equation:

[0039]

[0040] in, and These represent the center wavelengths of two distinct characteristic troughs in the transmission spectrum, respectively; T and S represent the temperature and salinity of the seawater being measured, respectively; and p nm and q nm p represents the surface fitting coefficient obtained through experimental calibration. nm and q nm The subscripts "n" and "m" are assigned the following values: n represents the power of temperature T (n=0 corresponds to the constant term, n=1 corresponds to the first-order term of T, and n=2 corresponds to the quadratic term of T), and m represents the power of salinity S (m=0 corresponds to the constant term, and m=1 corresponds to the first-order term of S). For example... For the coefficients of the constant term, The coefficient of the linear term T, The coefficient of the linear term S, for coefficient of quadratic term, q is the cross term coefficient of TS. nm The subscript rules and p nm Consistent.

[0041] The above technical solution utilizes a core structure that cascades a single-mode fiber, a hollow tubular fiber, a side-hole dual-core fiber, and an exiting single-mode fiber. Combined with a microgroove in the cladding of the single-mode fiber fusion splice and a vertically penetrating microchannel in the sidewall of the hollow tubular fiber, and an axial air hole in the side-hole dual-core fiber to form a continuous microfluidic loop, efficient flow of seawater within the hollow tubular fiber is achieved. This significantly improves the overlap factor of the interaction between the light field and the liquid, reducing the response time to the second level, while preventing bubble retention and ensuring stable measurement signals. Furthermore, by leveraging the anti-resonance effect excited by the seawater-filled hollow tubular fiber and considering the differentiated sensitivity of different characteristic troughs to temperature and salinity parameters, a three-dimensional mapping relationship is established through polynomial surface fitting to achieve efficient data decoupling and effectively eliminate cross-sensitivity interference from temperature and salinity. This single structure enables high-precision synchronous measurement of temperature and salinity parameters in a marine environment. The overall structure is simple and highly integrated, providing a reliable technical solution for in-situ real-time monitoring of the ocean. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A schematic diagram of a microfluidic temperature-salt dual-parameter fiber optic sensor based on the anti-resonance effect according to an embodiment of the present invention is shown.

[0044] Figure 2 A flowchart illustrating a method for fabricating a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect according to an embodiment of the present invention is shown.

[0045] Figure 3 A schematic diagram of a method for fabricating a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect according to an embodiment of the present invention is shown. (a) is step S201, (b) is step S202, (c) is step S203, (d) is step S204, (e) is step S205, and (f) is step S206.

[0046] Figure 4 A schematic diagram of a test system consisting of a microfluidic temperature-salt dual-parameter fiber optic sensor based on the anti-resonance effect is shown according to an embodiment of the present invention.

[0047] Figure 5The Comsol numerical simulation analysis of a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect according to an embodiment of the present invention is shown. (a) Dispersion curves of HCTF coatings HE1,20, HE1,21 and HE1,22, and electric field vector distribution of the NCF model. (b) Evolution of the beam envelope field.

[0048] Figure 6 The transmission spectrum salinity response of a microfluidic temperature-controlled dual-parameter fiber optic sensor based on the anti-resonance effect according to an embodiment of the present invention is shown. (a)-(c) Transmission spectra measured under different salinity conditions during the salinity rising, falling, and rising phases. (d) Linear fitting curves of the wavelengths of dip 1 and dip 2 as a function of salinity.

[0049] Figure 7 The transmission spectrum temperature response of a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect according to an embodiment of the present invention is shown. (a)-(c) Transmission spectra measured under different temperature conditions during the temperature rise, fall, and rise phases. (d) Linear fitting curves of the wavelengths of dip 1 and dip 2 as a function of temperature.

[0050] Figure 8 A schematic diagram of a three-dimensional nonlinear temperature-salinity fitting surface of a microfluidic temperature-salinity dual-parameter fiber optic sensor based on the anti-resonance effect according to an embodiment of the present invention is shown. (a) Fitted three-dimensional surface of dip1 wavelength as a function of temperature and salinity. (b) Fitted three-dimensional surface of dip2 wavelength as a function of temperature and salinity.

[0051] Explanation of the labels in the diagram:

[0052] Introducing single-mode fiber 11, hollow tubular fiber 12, side-hole dual-core fiber 13, outgoing single-mode fiber 14, first microgroove 111, fiber core 112, microchannel 121, air hole 131, second microgroove 141, and microfluidic circuit 15. Detailed Implementation

[0053] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0054] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0055] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0056] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0057] Please see Figure 1 , Figure 1 A schematic block diagram of a microfluidic temperature-salt dual-parameter fiber optic sensor based on the anti-resonance effect according to an embodiment of the present invention is shown.

[0058] like Figure 1 As shown, this embodiment of the invention provides a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect. The microfluidic temperature-controlled salt dual-parameter fiber optic sensor includes: a single-mode fiber 11 for introduction, a hollow tubular fiber 12, a dual-core fiber 13 with a single hole on the side, and a single-mode fiber 14 for extraction, which are cascaded in sequence.

[0059] The fusion splice end of the single-mode fiber 11 and the hollow tubular fiber 12 is etched with a first microgroove 111. The first microgroove 111 is located in the first cladding of the single-mode fiber 11 and does not contact the core 112 of the single-mode fiber.

[0060] The hollow tubular optical fiber 12 has microchannels 121 etched vertically through its cladding on its sidewalls;

[0061] The side-mounted single-hole dual-core optical fiber 13 is located between the hollow tubular optical fiber 12 and the lead-out single-mode optical fiber 14, and has an air hole 131 parallel to the axial direction inside to form a fluid outflow channel.

[0062] The fusion splice end of the side-hole dual-core optical fiber 13 and the lead-out single-mode optical fiber 14 is etched with a second microgroove 141. The second microgroove 141 is located in the third cladding of the lead-out single-mode optical fiber 14 and does not contact the core of the side-hole dual-core optical fiber.

[0063] The seawater to be tested flows into the interior of the hollow tubular fiber through the microgroove of the single-mode fiber and the microchannel of the hollow tubular fiber, and is discharged to the single-mode fiber through the air hole of the side single-hole dual-core fiber, forming a through-loop microfluidic circuit 15. The hollow tubular fiber filled with seawater excites the anti-resonance effect, and the position of the characteristic valley of the transmission spectrum drifts with the change of seawater temperature and salinity.

[0064] This invention breaks away from the conventional structure of directly splicing single-mode optical fibers to hollow-core optical fibers, innovatively introducing a Side-Single-Hole Fiber (SSF) at the output end. The SSF utilizes an internal air hole parallel to the fiber core as a dedicated channel for fluid outflow, working in conjunction with the front-end structure to solve the problems of flow path blockage and difficult liquid replacement in traditional hollow-core optical fiber sensors. By etching microgrooves in the single-mode fiber cladding as a liquid inlet, etching microchannels on the sidewall of the hollow-core optical fiber to enhance lateral flow, and combining this with the SSF as a liquid outlet, a continuous microfluidic circulation loop is constructed. This design ensures that the seawater under test can flow smoothly through and completely fill the hollow core of the hollow-core optical fiber under pressure, eliminating the risk of air bubble retention. Unlike surface contact sensors that rely on weak evanescent fields for detection, this invention achieves full coupling between the liquid under test and the transmitted optical field. The liquid directly acts as the low-refractive-index fiber core for light transmission, and combined with the high-reflectivity interface of the quartz cladding, it excites a strong anti-resonance effect, thereby significantly improving the sensitivity of spectral characteristics to changes in refractive index.

[0065] In one embodiment, optionally, the depth of the first microgroove is greater than the second cladding thickness of the hollow tubular optical fiber.

[0066] In one embodiment, optionally, the width of the microchannel is a preset width, and the distance between the microchannel position and the fusion splice point of the introduced single-mode fiber and the hollow tubular fiber is a preset distance, and the cladding wall thickness of the hollow tubular fiber satisfies the anti-resonance light guiding condition.

[0067] In one embodiment, optionally, after the hollow tubular optical fiber is excited with anti-resonance effect, the center wavelength of the characteristic valley in the transmission spectrum is... Satisfy the following formula:

[0068]

[0069] in, This indicates the thickness of the annular cladding in a hollow-core optical fiber. This indicates the refractive index of the quartz material used to make the second cladding layer. This represents the refractive index of the liquid filling the interior of a hollow tubular optical fiber. Indicates the order of the resonant mode.

[0070] In one embodiment, optionally, the wavelength dip position corresponding to the sidelobe in the transmission spectrum Satisfy the following formula:

[0071]

[0072] in, This represents the effective refractive index of the hollow tubular optical fiber core. and These represent the diameter of the second cladding and the length of the hollow tubular optical fiber, respectively. This indicates the self-imaging order.

[0073] In one embodiment, optionally, the wavelength displacement of the characteristic trough and the change in seawater refractive index satisfy the following equation:

[0074]

[0075] in, Indicates the center wavelength of the characteristic trough. This indicates the refractive index of the quartz material used to make the second cladding layer. This represents the refractive index of the liquid filling the interior of a hollow tubular optical fiber. The order of the resonant mode is represented by S, and the salinity of the seawater to be measured is represented by S.

[0076] Based on the fact that seawater temperature simultaneously modulates the refractive index of seawater and the cladding through the thermo-optic effect, the theoretical temperature sensitivity is derived by differentiation, satisfying the following equation:

[0077]

[0078] in, The value represents the second cladding thickness of the hollow-core optical fiber, and T represents the temperature of the seawater being measured.

[0079] In one embodiment, optionally, the refractive index of the seawater filling the hollow tubular optical fiber satisfies the following equation:

[0080]

[0081] Where S represents the salinity of the seawater to be measured, T represents the temperature of the seawater to be measured, λ represents the wavelength of the incident light, and k0 to k9 represent constant coefficients.

[0082] Furthermore, the hollow tubular optical fiber has a length of 1.0mm-2.0mm, an outer diameter of 120µm-130µm, and an inner diameter of 70µm-80µm; the cladding wall thickness of the hollow tubular optical fiber satisfies the anti-resonance light guiding condition.

[0083] Furthermore, the microgroove is a groove structure with a depth of 40µm-50µm; the microchannel is a through-hole structure processed by femtosecond laser.

[0084] Furthermore, the length of the side-mounted single-hole dual-core optical fiber is 3cm-5cm, and the diameter of its internal air hole is 35µm-45µm.

[0085] like Figure 2 and Figure 3As shown, in a second aspect, embodiments of the present invention provide a method for fabricating a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect, the method comprising:

[0086] Step S201, as follows Figure 3 As shown in (a), a femtosecond laser is used to etch the first and second microgrooves in the cladding near the close end faces of the single-mode fiber and the single-mode fiber, and airflow is used to remove debris during the etching process.

[0087] Specifically, the microgroove is a cubic defect with a depth of 50μm and a microchannel width of 50μm, which vertically penetrates the quartz cladding of the hollow fiber and is located 150μm away from the single-mode fiber-hollow fiber fusion splice point.

[0088] Step S202, as follows Figure 3 As shown in (b), the SMF (Single-Mode Fiber) with the first microgroove etched on it is aligned and fused with the HCTF (Hollow-Core Tube Fiber).

[0089] Step S203, as follows Figure 3 (c) shows the hollow tubular optical fiber being cut to a fixed length;

[0090] Step S204, as follows Figure 3 As shown in (d), the cut end of the hollow tubular optical fiber is fused to one end of the SSF (Side-Single-Hole Fiber).

[0091] Step S205, as follows Figure 3 As shown in (e), the fused side single-hole dual-core optical fiber is cut to a predetermined length;

[0092] Step S206, as follows Figure 3 As shown in (f), the other end of the single-hole dual-core fiber on the side is fused to the single-mode fiber with the second microgroove etched on it to form the microfluidic temperature-controlled salt dual-parameter fiber sensor.

[0093] Furthermore, in step S202, the cutting length of the hollow tubular optical fiber is preferably 1.4 mm; in step S204, the cutting length of the side-hole dual-core optical fiber is preferably 4 cm.

[0094] like Figure 4As shown, this embodiment of the invention provides a test system composed of a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect. The test system includes: a supercontinuum light source 41, a microfluidic temperature-controlled salt dual-parameter fiber optic sensor 42 based on the anti-resonance effect, and a spectrometer 43 connected in sequence. After the light signal emitted by the supercontinuum light source 41 enters the microfluidic temperature-controlled salt dual-parameter fiber optic sensor 42, the anti-resonance effect is excited in the hollow tubular fiber optic cable filled with the seawater to be tested. The transmitted light signal is transmitted to the spectrometer 43 through the single-mode fiber optic cable. The spectrometer 43 collects the transmission spectrum and extracts the parameters of the characteristic valleys.

[0095] In one embodiment, optionally, the testing system further includes:

[0096] The data decoupling module establishes a three-dimensional mapping relationship between wavelength, temperature, and salinity based on polynomial surface fitting. It achieves simultaneous calculation of temperature and salinity by simultaneously solving the inverse function. The three-dimensional mapping relationship satisfies the following equation:

[0097]

[0098] in, and These represent the center wavelengths of two distinct characteristic troughs in the transmission spectrum, respectively; T and S represent the temperature and salinity of the seawater being measured, respectively; and p nm and q nm This represents the surface fitting coefficient obtained through experimental calibration.

[0099] The microfluidic fiber optic sensor proposed in this invention operates based on the ARROW principle. In this structure, the quartz cladding of the HCTF acts as a Fabry-Perot (FP) etalon. When light propagates in the hollow core, the quartz cladding of the HCTF acts as a reflective layer. Light waves that meet specific phase-matching conditions undergo destructive interference within the cladding walls, leading to energy leakage; while light waves that do not meet these conditions undergo constructive interference at the core-cladding interface, resulting in extremely high reflectivity and thus being confined to the low-refractive-index liquid core for propagation. According to the anti-resonance theory, the center wavelength of the transmission trough (i.e., the high-loss point) corresponding to the FP resonance in the spectrum can be determined by the following equation:

[0100] (1)

[0101] in, The thickness of the annular cladding of the hollow-core optical fiber. The refractive index of the quartz material used to make the second cladding layer, The refractive index of the liquid filling the HCTF. This represents the order of the resonant mode.

[0102] When light propagates through the AR waveguide mode in an HCTF, it undergoes a self-imaging process due to multimode interference, resulting in side lobes in the output spectrum. The corresponding wavelength dips can be represented as:

[0103] (2)

[0104] in, Indicates the effective refractive index of the HCTF core. and These represent the cladding diameter and HCTF length, respectively. This represents the self-imaging order.

[0105] The characteristic resonance depression of the SHSS cascade structure exhibits spectral shift under changes in temperature and salinity. Since the thermo-optic coefficient and thermal expansion coefficient of silica are much lower than those of seawater, the changes in cladding thickness d and refractive index ncladding are negligible. According to equation (1), the relationship between the concave wavelength shift and the change in seawater refractive index can be expressed as:

[0106] (3)

[0107] Furthermore, considering that temperature modulates the refractive index of both seawater and the silica cladding through the thermo-optic effect, the theoretical temperature sensitivity can be derived by differentiation:

[0108] (4)

[0109] For this sensor structure, the complementary design of integrating sidewall microchannels in the HCTF and cladding microgrooves in the SMF enables unimpeded circulation of liquid within the sensing region and promotes efficient optical field coupling. The refractive index of seawater is determined by both temperature and salinity, and its empirical expression is as follows:

[0110] (5)

[0111] in and These represent seawater salinity and temperature, respectively. to is a constant coefficient. Equations (3) and (4) characterize the dependence of the refractive index of the liquid core on temperature and salinity. By explicitly quantifying the refractive index term in equation (1), the model bridges the gap between environmental measurements and optical resonance conditions, verifying the applicability of the polynomial surface fitting method. Changes in seawater temperature and salinity will cause changes in the refractive index inside the microfluidic sensing platform, thereby inducing the displacement of the characteristic anti-reflection transmission valley.

[0112] In this invention example, the Comsol software was used to perform numerical simulation analysis of a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect using the finite element method, and the transmission and reflection spectrum curves were obtained as follows: Figure 5 As shown, where, Figure 5 (a) shows the dispersion curves of HCTF coatings HE1,20, HE1,21, and HE1,22, and the electric field vector distribution of the NCF model. Figure 5 (b) shows the evolution of the light field envelope of the beam. It can be seen that the sensor in this invention achieves multifunctional integration and simultaneously excites the anti-resonance effect.

[0113] The sensing region of the HCTF was numerically simulated using frequency-domain electromagnetic analysis. The fiber geometry was consistent with the previously described design, with a 3 μm thick perfectly matched layer applied externally to simulate open boundary conditions. The refractive indices of the seawater and silica cladding were set to 1.3313 and 1.46, respectively. Figure 5 As shown, the effective refractive index of the guided mode in HCTF decreases in a stepwise manner with increasing wavelength. The decreasing segment perfectly matches the resonant wavelength predicted by equation (1). The intensity transmitted through the antireflection mechanism originates from the superposition of all HE1 and N modes, and can be quantitatively described as:

[0114] (6)

[0115] Furthermore, the optical field evolution in the SHSS composite structure was analyzed using the beam propagation method. Simulation results in Figure [Figure Number] show a distinct transmission intensity distribution at different incident wavelengths, forming a continuous output spectrum. The spectral concave region corresponds to the region of maximum transmission loss, where the resonance effect is most significant; conversely, the peak position exhibits the strongest anti-reflection effect, thus achieving the highest transmission efficiency.

[0116] Sensor performance test:

[0117] like Figure 6 As shown, Figure 6 (a)- Figure 6 (c) shows the transmission spectra measured under different salinity conditions during the rising, falling and rising phases of salinity. Figure 6(d) shows the linear fitting curves of the wavelengths of dip 1 and dip 2 as a function of salinity. Specifically, under a constant temperature of 20°C, the refractive index of the liquid inside the sensor was changed by sequentially injecting standard seawater with different salinities (0‰, 5‰, 20‰, 30‰, 35‰, and 40‰) into the microfluidic channel of the sensor. The changes in the transmission spectrum curves acquired by the spectrometer show that as the salinity of the seawater increases, the refractive index of the seawater increases, causing the anti-resonance characteristic valleys (dip 1 and dip 2) to drift towards shorter wavelengths (blue shift). The wavelength shift of the characteristic valleys was linearly fitted with salinity, and the results show that the two have extremely high linearity (R2>0.999). Tests conducted at different temperature environments from 10°C to 40°C show that the sensor maintains excellent salinity response characteristics, with the highest salinity sensitivity of 1.152 nm / ‰ measured at 10°C. Furthermore, dynamic response tests showed that the sensor reached a stable state within 15 seconds when the injected salinity underwent a step change, demonstrating an extremely fast response speed.

[0118] like Figure 7 As shown, Figure 7 (a)- Figure 7 (c) shows the transmission spectra measured under different temperature conditions during the rising, falling and rising phases of temperature. Figure 7 (d) shows the linear fitting curves of the wavelengths of dip 1 and dip 2 as a function of temperature. Specifically, with a fixed salinity of 0‰, the temperature around the sensor was varied from 10°C to 40°C (in 5°C steps). As the temperature increased, the refractive index of the seawater changed, causing the characteristic trough of the hollow tube fiber anti-resonant structure to shift towards longer wavelengths (redshift). The fitting results of the transmission spectrum curve changes and the characteristic wavelength show that the shift of the characteristic wavelength follows a quadratic polynomial function relationship with temperature. In multiple heating-cooling cycle tests, the sensor exhibited good repeatability, with a highest measured temperature sensitivity of 1.316 nm / °C.

[0119] Based on the above test results, and considering the differences in sensitivity responses of different characteristic valleys to temperature and salinity, this invention establishes the following data decoupling function based on polynomial surface fitting:

[0120] (6)

[0121] in, and These represent the center wavelengths of two distinct characteristic troughs in the transmission spectrum, respectively; T and S represent the temperature and salinity of the seawater being measured, respectively; and p... nm and q nmThese are the surface fitting coefficients obtained through experimental calibration. The model constructs a three-dimensional mapping relationship between wavelength, temperature, and salinity, such as... Figure 8 As shown, Figure 8 (a) shows the fitted three-dimensional surface of dip1 wavelength as a function of temperature and salinity. Figure 8 (b) shows the fitted three-dimensional surface of dip2 wavelength as a function of temperature and salinity.

[0122] Based on the wavelength positions of the two characteristic valleys in the collected spectral data, the salinity and temperature values ​​of the seawater under test can be obtained by simultaneously solving the inverse function in equation (1). Experimental points with different temperature-salinity combinations were selected for verification, and the root mean square error (RMSE) of temperature was calculated to be 0.063°C, and the root mean square error (RMSE) of salinity was 0.044‰. This result demonstrates that the decoupling method proposed in this invention can effectively eliminate the cross-sensitivity of temperature and salinity, achieving high-precision simultaneous measurement of two parameters.

[0123] To address the issue of temperature-salinity cross-sensitivity, this invention abandons the complex cascaded sensing element scheme. Instead, it utilizes the differences in sensitivity to temperature and salinity at different characteristic valleys (dip 1 and dip 2) within a single sensing probe to construct a three-dimensional wavelength-temperature-salinity mapping model. By solving the inverse function using a polynomial surface fitting algorithm, temperature and salinity values ​​can be simultaneously retrieved in a single measurement, effectively eliminating measurement errors.

[0124] In this invention, HCTF is used as the research object. A cascaded structure is constructed, consisting of an introduced single-mode fiber, a hollow tubular fiber, a side-hole fiber, and an exiting single-mode fiber. Femtosecond laser micromachining technology is used as the main means to etch microgrooves and microchannel structures on the fiber. Combined with the flow-guiding characteristics of SSF, a through-type microfluidic circulation path is constructed, realizing the efficient excitation of the anti-resonance effect under the condition of full filling of the liquid to be measured. By establishing a data decoupling model based on polynomial surface fitting, the problems of response hysteresis and cross-sensitivity of temperature and salinity in traditional fiber optic sensors are effectively solved. A sensing unit integrating microfluidics and high-sensitivity detection is established, realizing high-precision synchronous measurement of seawater temperature and salinity parameters, providing a new technical idea and solution for in-situ real-time monitoring of the marine environment.

[0125] Compared with existing technologies, the present invention has the following significant advantages:

[0126] 1) Order-of-magnitude improvement in response speed: Thanks to the low-resistance microfluidic pathway constructed by the synergistic construction of microgrooves, microchannels, and side-hole optical fibers, this invention completely solves the problem that liquid exchange inside traditional hollow-core optical fiber sensors mainly relies on natural diffusion. Experiments show that this microfluidic temperature-salt dual-parameter optical fiber sensor based on the anti-resonance effect responds to salinity step changes in only 15 seconds, while similar existing technologies typically require more than 90 seconds. This characteristic enables the microfluidic temperature-salt dual-parameter optical fiber sensor based on the anti-resonance effect to capture rapid dynamic changes in the marine environment, meeting the needs of real-time profile monitoring.

[0127] 2) Significantly Enhanced Detection Sensitivity: This invention employs a fully filled mode to excite the anti-resonance effect, maximizing the efficiency of light-matter interaction. Within the measurement ranges of 10-40°C and 0-40‰, the microfluidic temperature-salinity dual-parameter fiber optic sensor based on the anti-resonance effect achieves a maximum temperature sensitivity of 1.316 nm / °C and a maximum salinity sensitivity of 1.152 nm / ‰. These performance indicators outperform most current fiber optic sensors based on the evanescent field principle, enabling precise capture of minute temperature and salinity changes.

[0128] 3) High-precision dual-parameter decoupling capability: By introducing a polynomial surface fitting decoupling algorithm, this invention effectively solves the problem of cross-sensitivity between temperature and salinity to refractive index modulation, significantly improving measurement accuracy. Experimental verification shows that the root mean square error (RMSE) of temperature measurement after decoupling is as low as 0.063°C, and the RMSE of salinity is as low as 0.044‰, proving the metrological reliability of this method in complex marine environments.

[0129] 4) Excellent long-term stability and reusability: The microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect adopts a fully fused, all-glass structure, which has good mechanical strength and corrosion resistance. In continuous testing for up to 60 minutes and repeated testing after 2 months, the fluctuation of the spectral characteristic wavelength is minimal, indicating that the sensor has excellent long-term stability and repeatability, making it suitable for long-term in-situ deployment in harsh marine environments.

[0130] It should be noted that the functions or steps that can be implemented by the computer-readable storage medium or computer device described above can be referred to the relevant descriptions in the foregoing method embodiments. To avoid repetition, they will not be described one by one here.

[0131] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0132] It should be understood that although the terms "first," "second," etc., may be used to describe the setting units in the embodiments of this application, these setting units should not be limited to these terms. These terms are only used to distinguish the setting units from each other. For example, without departing from the scope of the embodiments of this application, the first setting unit may also be referred to as the second setting unit, and similarly, the second setting unit may also be referred to as the first setting unit.

[0133] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0134] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0135] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in a combination of hardware and software functional units.

[0136] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0137] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect, characterized in that, The microfluidic temperature-controlled salt dual-parameter fiber optic sensor includes: a single-mode fiber for introduction, a hollow tubular fiber, a dual-core fiber with a single hole on the side, and a single-mode fiber for extraction, which are cascaded in sequence. The fusion splice end of the single-mode fiber and the hollow tubular fiber is etched with a first microgroove. The first microgroove is located in the first cladding of the single-mode fiber and does not contact the core of the single-mode fiber. The hollow tubular optical fiber has microchannels etched vertically through its second cladding on its sidewalls. The side-mounted single-hole dual-core optical fiber is located between the hollow-core tubular optical fiber and the lead-out single-mode optical fiber. It has an air hole parallel to the axial direction inside, forming a fluid outflow channel. The fusion splice end of the side-hole dual-core optical fiber and the lead-out single-mode optical fiber is etched with a second microgroove. The second microgroove is located in the third cladding of the lead-out single-mode optical fiber and does not contact the core of the side-hole dual-core optical fiber. The seawater to be tested flows into the interior of the hollow tubular fiber through the first microgroove of the single-mode fiber and the microchannel of the hollow tubular fiber, and is discharged to the single-mode fiber through the air hole of the side single-hole dual-core fiber, forming a through-loop microfluidic circuit. The hollow tubular fiber filled with seawater excites the anti-resonance effect, and the position of the characteristic valley of the transmission spectrum drifts with the change of seawater temperature and salinity.

2. The microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect according to claim 1, characterized in that, The depth of the first microgroove is greater than the thickness of the second cladding of the hollow tubular optical fiber.

3. The microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect according to claim 1, characterized in that, The width of the microchannel is a preset width, and the distance between the microchannel and the splice point of the single-mode fiber and the hollow tubular fiber is a preset distance. The cladding wall thickness of the hollow tubular fiber satisfies the anti-resonance light guiding condition.

4. The microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect according to claim 1, characterized in that, After the hollow tubular optical fiber is excited to exhibit anti-resonance, the center wavelength of the characteristic valley in the transmission spectrum is... Satisfy the following formula: in, This indicates the thickness of the second cladding layer of the hollow tubular optical fiber. This indicates the refractive index of the quartz material used to make the second cladding layer. This represents the refractive index of the liquid filling the hollow tubular optical fiber. Indicates the order of the resonant mode.

5. The microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect according to claim 1, characterized in that, The wavelength depression position corresponding to the side lobes in the transmission spectrum Satisfy the following formula: in, This represents the effective refractive index of the hollow tubular optical fiber core. and These represent the diameter of the second cladding and the length of the hollow tubular optical fiber, respectively. This indicates the self-imaging order.

6. The microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect according to claim 1, characterized in that, The relationship between the wavelength displacement of the characteristic trough and the change in the refractive index of seawater satisfies the following equation: in, Indicates the center wavelength of the characteristic trough. This indicates the refractive index of the quartz material used to make the second cladding layer. This represents the refractive index of the liquid filling the hollow tubular optical fiber. The order of the resonant mode is represented by S, and the salinity of the seawater to be measured is represented by S. Based on the fact that seawater temperature simultaneously modulates the refractive index of seawater and the cladding through the thermo-optic effect, the theoretical temperature sensitivity is derived by differentiation, satisfying the following equation: in, The thickness of the second cladding layer of the hollow tubular optical fiber is indicated by T, and the temperature of the seawater to be measured is indicated by T.

7. The microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect according to claim 1, characterized in that, The refractive index of the seawater filling the hollow tubular optical fiber satisfies the following equation: Where S represents the salinity of the seawater to be measured, T represents the temperature of the seawater to be measured, λ represents the wavelength of the incident light, and k0 to k9 represent constant coefficients.

8. A method for fabricating a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on the anti-resonance effect as described in any one of claims 1-7, characterized in that, The method includes: A femtosecond laser was used to etch the first and second microgrooves in the cladding near the close end faces of the single-mode fiber and the single-mode fiber, and airflow was used to remove debris during the etching process. The single-mode fiber with the first microgroove etched on it is aligned and fused with the hollow tubular fiber. The hollow tubular optical fiber is cut to a fixed length. The cut end of the hollow tubular optical fiber is fused to one end of the side-hole dual-core optical fiber. Cut the fused side single-hole dual-core optical fiber to a predetermined length; The other end of the side-hole dual-core optical fiber is fused to the lead-out single-mode optical fiber with a second microgroove etched thereon to form the microfluidic temperature-salt dual-parameter optical fiber sensor.

9. A testing system based on a microfluidic temperature-controlled salt dual-parameter fiber optic sensor according to any one of claims 1-7, characterized in that, The testing system includes: a supercontinuum light source, a microfluidic temperature-controlled salt dual-parameter fiber optic sensor based on anti-resonance effect, and a spectrometer connected in sequence; after the light signal emitted by the supercontinuum light source enters the microfluidic temperature-controlled salt dual-parameter fiber optic sensor, it excites the anti-resonance effect in the hollow tubular fiber optic cable filled with seawater to be tested, and the transmitted light signal is transmitted to the spectrometer through the lead-out single-mode fiber, and the spectrometer collects the transmission spectrum and extracts the parameters of the characteristic valleys.

10. The testing system according to claim 9, characterized in that, Also includes: The data decoupling module establishes a three-dimensional mapping relationship between wavelength, temperature, and salinity based on polynomial surface fitting. It achieves simultaneous calculation of temperature and salinity by simultaneously solving the inverse function. The three-dimensional mapping relationship satisfies the following equation: in, and These represent the center wavelengths of two distinct characteristic troughs in the transmission spectrum, respectively; T and S represent the temperature and salinity of the seawater being measured, respectively; and p... nm and q nm This represents the surface fitting coefficient obtained through experimental calibration.

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