Resonant sensor based on dual-core dual-channel photonic crystal fiber and measurement method

Abstract

The application provides a resonance sensor based on a double-core double-channel photonic crystal fiber and a measuring method, and relates to the technical field of resonance sensors. The application discloses a resonance sensor based on a double-core double-channel photonic crystal fiber and a measuring method, and relates to the technical field of resonance sensors. The application discloses a resonance sensor based on the double-core double-channel photonic crystal fiber and the measuring method. The application discloses a resonance sensor based on the double-core double-channel photonic crystal fiber, and the measuring method. The application discloses a resonance sensor based on the double-core double-channel optical crystal fiber and the measuring method. The application discloses a resonance sensor based on the double-core optical crystal fiber and the measuring method. The application discloses a resonance sensor based on the double-channel optical crystal fiber and the measuring method. The application discloses a resonance sensor based on a double-core double-channel photonic crystal fiber, and the measuring method. The application discloses a double-core double-channel photonic crystal fiber resonance sensor and a measuring method. The application discloses a resonance sensor based on the double-core double-channel optical crystal optical fiber and the measuring method. The application discloses a resonance sensor based on the double-core double channel optical crystal fiber and the measuring method. The application discloses a resonance sensor based on the double core double channel optical crystal fiber and the measuring method. The application discloses a resonance sensor based on a double core double channel optical crystal fiber and a measuring method. The application discloses a resonance sensor based on the double-core double-channel photonic optical crystal fiber and the measuring method. The application discloses a resonance sensor based on the double channel optical crystal fiber and the measuring method. The application discloses a resonance sensor based on double-core double-channel photonic crystal fiber and a measuring method. The application discloses a resonance sensor based on the double-core optical crystal fiber and a measuring method. The application discloses a resonance sensor based on the double-channel optical crystal fiber and a measuring method. The application discloses a resonance sensor based on the double core double channel optical crystal optical fiber and the measuring method. The application discloses a resonance sensor based on the optical crystal fiber and the measuring method. The application discloses a resonance sensor based on the double optical crystal fiber and the measuring method. The application discloses a resonance sensor based on the double-optical crystal fiber and the measuring method. The application discloses a resonance sensor based on the double-core photonic crystal fiber and the measuring method. The application discloses a resonance sensor based on the optical crystal fiber, and the measuring method. The

Description

Technical Field

[0001] This invention relates to the field of resonant sensor technology, and in particular to a resonant sensor and measurement method based on a dual-core dual-channel photonic crystal fiber. Background Technology

[0002] Surface plasmon resonance (SPR) photonic crystal fiber (PCF) sensors have attracted much attention in the field of biochemical sensing due to their high sensitivity and compact structure. However, existing dual-channel or multi-channel PCF-SPR sensors often face the problem of cross-sensitivity between channels, and the design of their structural parameters (such as lattice period, pore diameter, and channel position) often relies on empirical stacking or conventional finite element parameter scanning, lacking guidance from design methods based on strict physical constraints. This causes the core mode to easily undergo unexpected Bragg resonance with the cladding mode in the operating wavelength range, generating stray loss peaks that severely interfere with the accurate extraction of sensing signals. At the same time, in traditional dual-channel structures, the air holes between the sensing channels and the core often constitute a refractive index abrupt barrier on the evanescent wave propagation path, severely weakening the energy of the core mode reaching the metal film surface. This results in insufficient SPR excitation efficiency, broadened and weak resonant loss peaks, making it difficult to meet the application requirements of high precision and independent measurement of multiple parameters. Summary of the Invention

[0003] To address the aforementioned technical problems, the technical solution adopted by this invention is as follows: According to a first aspect of this application, a resonant sensor based on a dual-core, dual-channel photonic crystal fiber is provided, comprising: a fiber core using fused silica as a substrate; a periodic array of air holes arranged in a hexagonal lattice within the substrate; a first analyte channel and a second analyte channel symmetrically arranged in a D-shape on both sides of the fiber core; and metal coating layers respectively deposited on the inner wall surfaces of the first analyte channel and the second analyte channel; wherein at least one adjacent air hole is removed from the light propagation path between the first analyte channel, the second analyte channel and the fiber core, thereby constructing a continuous, low-loss silica medium path without abrupt changes in air refractive index between the fiber core and the corresponding metal coating layer; The preset structural parameters of the sensor are determined by the following method: Based on the Bragg resonance suppression condition of the fundamental mode transverse wave vector by the periodic structure of the photonic crystal cladding, combined with the working wavelength range of the sensor and the machinability of the fiber drawing process, the parameters that make the dual-channel loss spectrum curve smooth, free of stray peak interference and have the best separation of the two resonance peaks are selected by finite element analysis scanning, and used as the arrangement lattice period of the periodic air hole array. The ratio range of the air hole diameter to the period of the arranged crystal lattice is set, and the resonance peak intensity and loss peak wavelength shift under different ratios are compared by finite element analysis. The value that can make the dual-channel loss spectrum have high coupling strength and keep the resonance peak spacing optimal is selected as the air hole diameter. The vertical distance between the inner wall surfaces of the first analyte channel and the second analyte channel and the corresponding fiber core center axis is set, and the vertical distance is gradually increased in micrometer increments for finite element analysis scanning. The position displacement of the loss peak and the coupling loss intensity are tracked and observed. The value corresponding to the point where the vertical distance increases to the point where the position of the loss peak no longer moves and the coupling loss values ​​of both channels remain within a reasonable range is selected as the optimal channel vertical distance.

[0004] According to another aspect of this application, a dual-parameter independent sensing measurement method based on a resonant sensor based on a dual-core dual-channel photonic crystal fiber as described in the first aspect is also provided, comprising: The first and second external physical quantities to be measured are changed independently, and the center wavelength shift of the corresponding resonant loss peaks of the first and second analyte channels is recorded respectively. The sensitivity response matrix of the wavelength change with respect to the two external physical parameters is constructed. A first functional liquid sensitive to a first external physical quantity is injected into the first analyte channel, and a second functional liquid sensitive to a second external physical quantity is injected into the second analyte channel. In a complex physical field environment, the real-time wavelength values ​​of the resonant loss peaks of the two current channels are simultaneously acquired by a spectrometer, and the real-time wavelength drift relative to the initial reference wavelength is calculated. By substituting the real-time wavelength drift data into the sensitivity response matrix and solving the simultaneous equations, the specific values ​​of the first and second external physical quantities are calculated synchronously, thus achieving crosstalk-free synchronous online measurement of the two physical fields.

[0005] The present invention has at least the following beneficial effects: The resonant sensor based on a dual-core, dual-channel photonic crystal fiber of this invention firstly constructs a low-loss path of continuous silica medium without abrupt changes in refractive index by removing adjacent air holes in the light propagation path between the fiber core and the metal coating layer. This effectively reduces the energy attenuation caused by crossing the air / quartz interface during evanescent wave propagation, significantly enhances the evanescent field intensity reaching the metal film surface, and thus greatly improves the coupling efficiency of the SPR mode. This results in a sharper resonant loss peak with higher peak intensity, providing a good signal-to-noise ratio for accurate wavelength demodulation. Secondly, the structural parameter determination method based on Bragg resonance suppression conditions and finite element analysis scanning proposed in this application can fundamentally avoid Bragg resonance interference caused by the cladding periodic structure. It accurately selects structural parameters that make the dual-channel loss spectrum curve smooth, free of stray peak interference, and have optimal separation between the two resonance peaks. This fundamentally solves the problems of blind parameter selection and the easy generation of stray modes in the working band leading to measurement errors in traditional design methods. Finally, through the above-mentioned optimized symmetrical D-type dual-channel structure, the two channels can independently excite surface plasmon resonance to form a dual-loss peak with excellent separation. When the refractive index of the analyte in either channel changes, it only causes the wavelength shift of the corresponding loss peak without interfering with the response of the other channel. This achieves absolute independent decoupling of the two channels in the wavelength domain, enabling high-precision synchronous sensing and measurement of multiple physical quantities (such as temperature and magnetic field) simultaneously and without interference. Attached Figure Description

[0006] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0007] Figure 1 A schematic diagram of the structure of a resonant sensor based on a dual-core, dual-channel photonic crystal fiber provided in an embodiment of the present invention; Figure 2 A schematic diagram illustrating the parameter annotations of a resonant sensor based on a dual-core, dual-channel photonic crystal fiber, provided in an embodiment of the present invention; Figure 3 A schematic diagram of the physical field simulation of dual-core PCF-SPR provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of the electric field distribution of the dual-channel fundamental mode provided in an embodiment of the present invention. Detailed Implementation

[0008] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0009] It should be noted that, based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Furthermore, this device and / or practice the method can be implemented using other structures and / or functionalities besides one or more of the aspects set forth herein.

[0010] The following will refer to Figure 1 The schematic diagram shown illustrates the structure of a resonant sensor based on a dual-core, dual-channel photonic crystal fiber, which introduces a resonant sensor based on a dual-core, dual-channel photonic crystal fiber.

[0011] The resonant sensor based on a dual-core, dual-channel photonic crystal fiber includes: a fiber core using fused silica as a substrate; a periodic array of air holes arranged in a hexagonal lattice within the substrate; a first analyte channel and a second analyte channel symmetrically arranged in a D-shape on both sides of the fiber core; and metal coatings respectively deposited on the inner wall surfaces of the first analyte channel and the second analyte channel; wherein, at least one adjacent air hole is removed from the light propagation path between the first analyte channel, the second analyte channel and the fiber core, thereby constructing a continuous, low-loss silica medium path without abrupt changes in air refractive index between the fiber core and the corresponding metal coating.

[0012] like Figure 1 As shown, the physical structure of this sensor is based on a fused silica substrate. Within the cross-section of the substrate, a dense array of periodic air holes (Air) arranged in a standard hexagonal lattice structure forms the cladding of the photonic crystal fiber. The fiber core is composed of a high-refractive-index silica medium lacking air holes in the central region. D-shaped microfluidic analyte channels (analyte A channel and analyte B channel, respectively) are symmetrically formed above and below the fiber core. To achieve the metal layer required for exciting surface plasmon resonance (SPR), a gold film (Au) is deposited on the straight inner wall of each D-shaped channel near the fiber core.

[0013] The core technical feature of this structure lies in the localized microscopic modification of the pore array: during microfabrication or drawing, at least one pair of adjacent air holes on the light propagation path between the first and second analyte channels and the central fiber core are selectively and completely removed or destroyed. This is achieved in the attached... Figure 1 The cross-section shows that there are no air pore units in the region between the fiber core and the straight edge of the D-shaped channel. After this removal operation, a physical region consisting only of continuous solid silica medium is formed between the fiber core and the metal coating layer, without the abrupt change in refractive index interface of air / silica. In actual fabrication, this structure can be fabricated by first creating a preform using the "capillary stacking method," inserting solid rods at predetermined positions on both sides of the fiber core, and then fabricating the D-shaped channel in subsequent micromachining; if post-grooving is used, femtosecond laser micromachining or precision mechanical cutting is used to directly open the geometric space of the continuous channel while removing the corresponding material, and then gold film is deposited on the inner wall of the D-shaped channel by directional magnetron sputtering or chemical plating. In addition, at the level of physical field setting in the simulation modeling stage, such as Figure 1 As shown in the outermost dark gray ring, a perfect matching layer (PML) is set around the fiber body to construct an infinitely large spatial environment. This layer is used to completely absorb the outwardly leaking light waves in the simulation calculation, ensuring the accuracy of the boundary conditions for the mode calculation.

[0014] The beneficial effects of the above structural design in practical applications are that, by removing the refractive index abrupt change barrier between the fiber core and the metal film, the evanescent wave leaking outward during light transmission in the fiber core can directly reach the gold film surface without additional attenuation along the continuous quartz medium channel. This significantly improves the excitation efficiency and coupling strength of surface plasmon polaritons (SPP), resulting in a steeper loss peak and higher peak intensity on the resonant loss spectrum. This provides a stable and excellent signal foundation for subsequent high-precision wavelength demodulation. Simultaneously, this symmetrical and uniform D-shaped channel layout, combined with local spatial modification... The design allows the fundamental mode energy in the fiber core to be efficiently coupled to two independent channels when the phase matching condition is met, forming clear and well-separated dual-loss peaks in the spectrum. Since the two optical paths do not interfere with each other in physical space, when only the refractive index of the analyte in a single channel is changed, the corresponding loss peak will experience wavelength shift, while the position of the loss peak in the other channel will remain stable. This directly ensures that the dual channels have absolutely independent decoupling characteristics at the physical structure level, meeting the requirement of synchronous and highly sensitive sensing of various external physical parameters such as temperature and magnetic field on the same optical fiber simultaneously and without crosstalk.

[0015] The preset structural parameters of the sensor are determined by the following method: Based on the Bragg resonance suppression condition of the fundamental mode transverse wave vector by the periodic structure of the photonic crystal cladding, combined with the working wavelength range of the sensor and the processability of the fiber drawing process, the parameters that make the dual-channel loss spectrum curve smooth, free of stray peak interference and have the best separation of the two resonance peaks are selected by finite element analysis scanning, and used as the arrangement lattice period of the periodic air hole array.

[0016] A range of ratios between the air hole diameter and the period of the arranged crystal lattice is defined. The intensity of the resonance peak and the wavelength shift of the loss peak under different ratios are compared by finite element analysis. The value that enables the dual-channel loss spectrum to have high coupling strength and the resonance peak spacing to be optimal is selected as the air hole diameter.

[0017] The vertical distance between the inner wall surfaces of the first analyte channel and the second analyte channel and the corresponding fiber core center axis is set, and the vertical distance is gradually increased in micrometer increments for finite element analysis scanning. The position displacement of the loss peak and the coupling loss intensity are tracked and observed. The value corresponding to the point where the vertical distance increases to the point where the position of the loss peak no longer moves and the coupling loss values ​​of both channels remain within a reasonable range is selected as the optimal channel vertical distance.

[0018] In this embodiment, the specific implementation of the above method is as follows: Step 1: Determine the lattice period (Λ) of the crystal arrangement. In finite element simulation software (such as COMSOL Multiphysics), a two-dimensional cross-sectional geometric model of the photonic crystal fiber is established. Then, elements such as... are added to the outermost periphery of the model. Figure 1 The perfectly matched layer (PML) shown is used to eliminate boundary reflections. To achieve single-mode transmission of the fundamental mode and avoid unintended Bragg resonances caused by the cladding periodic structure, the lattice period Λ needs to be initially constrained. Physically, it must be ensured that the effective transverse wave vector of the fundamental mode avoids the reciprocal lattice vector corresponding to the boundary of the first Brillouin zone of the hexagonal lattice; engineeringly, the limits of the actual fiber drawing process must be considered (too small a period will lead to porosity collapse and a sharp increase in process difficulty). Based on this, the initial scan range of Λ is usually set between 1.5 and 2.5 μm, with a small step size of 0.05 μm. The transmission loss spectrum of the core fundamental mode is calculated at each Λ value, focusing on the loss characteristics within the working wavelength range of 550 to 1050 nm. By comparing the scan spectra, Λ values ​​with smooth loss spectrum curves, no stray "spicules" or interference peaks introduced by cladding mode coupling, and sufficient separation between the resonance peaks of the two channels are selected.

[0019] Step 2: Determine the diameter (d) of the air vent. Based on a selected lattice period Λ, the ratio of the air hole diameter d to Λ (i.e., the duty cycle d / Λ) is parametrically scanned as an independent variable. In actual finite element simulation settings, this ratio is usually set in the range of 0.3 to 0.5 (corresponding to d values ​​of approximately 0.6 to 1.0 μm), and the air hole diameter is gradually increased in steps of 0.05 μm or 0.1 μm. After each calculation, the resonant loss peak value and its center wavelength position corresponding to the two channels are extracted and recorded. In this step, two physical quantities need to be observed: first, whether the evanescent field in the fiber core fundamental mode can effectively penetrate the cladding to reach the gold film surface (reflected in the peak loss magnitude, i.e., coupling strength); and second, whether the wavelength position of the resonant peak remains stable. After comprehensive comparison, the d value that can take into account the high-loss resonant peak intensity (ensuring sufficient signal-to-noise ratio) and does not show crosstalk reduction in the distance between the resonant peaks of the two channels is selected as the final design value.

[0020] Step 3: Determine the vertical distance (H) of the channel. The channel distance H refers to the vertical distance from the straight line segment of the inner wall of the D-type analyte channel to the central axis of the corresponding fiber core. Based on the determined Λ and d, H is used as the third layer parameter for fine-tuning scanning. During actual scanning, H is gradually increased from 6.0 μm to 6.4 μm in 0.1 μm increments. For each calculated H value, the peak intensity and center wavelength of the loss peaks of the upper and lower channels are recorded simultaneously. Simulation results show that when the H value is too small (too close), the coupling between the fiber core and the metal film is too strong, leading to waveform distortion of the loss peak and a drastic shift in the resonant wavelength with slight changes in H. However, when H gradually increases to a specific value, the loss peak enters a gradual decreasing range, and at this point, the resonant wavelength hardly shifts with small changes in H. The H value at which the "displacement stops" and the "coupled loss values ​​of both channels are at suitable detection intensities" is selected as the optimal vertical distance. In engineering terms, this process is equivalent to finding the position with the largest processing tolerance in order to avoid uncontrollable drift of the center wavelength due to tiny dimensional deviations during actual fiber drawing.

[0021] The aforementioned method for determining structural parameters effectively avoids clutter interference caused by Bragg resonance from a physical mechanism perspective, providing designers with clear parameter selection rules. This avoids the inefficiencies and deviations caused by relying solely on manual experience or blind modeling and simulation in traditional designs. Furthermore, in engineering and manufacturing, the progressive parameter scanning process and tolerance window evaluation accurately select the parameter combination with the highest tolerance for process fluctuations (especially the selection of channel distance H). This not only ensures the yield of the sensor in actual manufacturing but also guarantees that the final packaged device has highly consistent dual-peak separation and stable coupling energy, fundamentally improving the reliability and mass production feasibility of this dual-channel SPR sensor in complex multi-parameter measurement scenarios.

[0022] Furthermore, the first analyte channel and the second analyte channel are physically isolated independent microcavity structures, which are respectively filled with a first functional liquid that is sensitive to a first external physical quantity and a second functional liquid that is sensitive to a second external physical quantity, so as to realize independent measurement of different external physical parameters by the two channels.

[0023] In this embodiment, during the fiber drawing stage, solid rods are inserted at predetermined positions on both sides of the fiber core in the preform to reserve space for subsequent micromachining, or two D-shaped microgrooves are symmetrically etched on both sides of the fiber core using a femtosecond laser after drawing. These two D-shaped channels are physically isolated from each other, forming independent, closed microcavities. To inject functional fluid into the channels and achieve long-term physical isolation, fiber end-face microfluidic encapsulation technology can be used: at the cut ends of the fiber, the inlet and outlet of the two channels are independently sealed using UV-curable adhesive or epoxy resin, and two independent capillary tubes are connected to each. Using an external micro-injection pump, functional fluid can be independently injected into the first and second analyte channels without concern about cross-mixing of the two fluids inside the fiber. This process ensures the physical independence of the two microcavities throughout the entire fiber lifecycle.

[0024] To make the two channels sensitive to different external physical parameters, liquids with specific physicochemical properties need to be selected. For the first analyte channel, a liquid with a large thermo-optic coefficient (a refractive index that changes linearly with temperature) is typically chosen, such as an ethanol-water mixture or a glycerol solution with a specific ratio. When the ambient temperature changes, the refractive index of this liquid changes, thereby causing a linear shift in the loss peak of this channel. For the second analyte channel, a magnetorheological fluid (i.e., a colloidal solution in which Fe3O4 nanoparticles are uniformly dispersed in a carrier liquid) with magneto-optical refraction effect is typically chosen. When a magnetic field is present, the nanoparticles in the magnetorheological fluid will align and aggregate in a chain under the influence of the magnetic field, causing its macroscopic equivalent refractive index to change systematically with the increase of the magnetic field strength.

[0025] In practical applications, this fiber optic sensor operates in a combined environment of the temperature and magnetic field to be measured. Because the functional fluids in the first and second channels are physically isolated and confined within their respective independent microcavities, the temperature-sensitive fluid in the first channel is only affected by ambient temperature fluctuations, and its refractive index change is entirely temperature-driven. Therefore, the resonant loss peak shift in this channel is only temperature-dependent. Similarly, the magnetohydrodynamic fluid in the second channel is only affected by magnetic field fluctuations, and its loss peak shift is only related to the magnetic field strength. By simultaneously reading the real-time wavelengths of the two loss peaks on the spectrometer, even if both external physical quantities change simultaneously, the wavelength shift can be directly extracted from the two independent resonant spectral lines, achieving high-precision simultaneous measurement of temperature and magnetic field without complex cross-demodulation calculations.

[0026] In this embodiment, by setting the two channels as physically isolated independent microcavity structures and injecting them with special functional liquids sensitive to different physical quantities, the possible material exchange between the two sensing units is completely eliminated at the structural level, effectively avoiding cross-sensitivity interference caused by the simultaneous action of different measured physical quantities. In actual field testing, by matching functional liquids with different sensitivity characteristics, a single optical fiber can have the ability to independently sense multiple physical parameters such as temperature and magnetic field at the same time. Moreover, this physical isolation and decoupling mechanism allows the sensor to accurately separate the measurement signal without relying on complex demodulation algorithms in practical applications, greatly reducing the design and computational burden of the subsequent signal processing system, while ensuring the measurement reliability and long-term stability of the sensor in complex coupled field environments.

[0027] Furthermore, the lattice period of the periodic air hole array is [value]; the diameter of the air hole is [value].

[0028] Furthermore, the optimal vertical distance between the inner wall of the first analyte channel and the central axis of the corresponding fiber core is [value missing]; both the first analyte channel and the second analyte channel are D-type microfluidic channels, and the diameter of the circumscribed circle of their cross-section is [value missing].

[0029] Furthermore, the metal coating layer is a gold film with a thickness of [missing information].

[0030] Furthermore, the optical fiber is also surrounded by a perfectly matched layer with a thickness of [thickness value missing], which is used to absorb light waves leaking to the cladding boundary in finite element simulation, thereby eliminating the influence of external boundary reflections on the physical field of the sensor simulation.

[0031] According to the appendix Figure 2 The structural parameter setting first requires fabricating a cladding air-hole array for the photonic crystal fiber, controlling the actual arrangement of the lattice period within the range of 1.8 to 2.0 micrometers, while setting the diameter of a single air hole to 0.6 to 1.0 micrometers. During the actual drawing process, precise control of the wall thickness and drawing speed of each capillary in the preform is necessary to ensure that the matching of these two parameters meets the requirement of equal-spaced close-packing of the hexagonal lattice. Following this, the attached... Figure 2The core D-shaped microfluidic channel is directionally fabricated so that the vertical distance between the flat inner wall of the channel and the center of the fiber core is between 6.0 and 6.4 micrometers. Furthermore, the diameter of the circumscribed circle corresponding to the cross-section of the microcavity containing the channel is precisely adjusted to 5.29 micrometers. This dimension takes into account both the flow resistance of the injected functional fluid and the control of the H-value over the evanescent field penetration depth. Subsequently, a gold film with a thickness ranging from 40 to 55 nanometers is uniformly deposited on the flat inner wall of the fabricated D-shaped channel near the fiber core using magnetron sputtering. This thickness range effectively balances the excitation efficiency of the metal film on the incident light field with ohmic absorption loss. Finally, when performing physical field simulation verification of the sensing structure, a perfect matching layer (PML) with a thickness of 3 micrometers needs to be constructed on the outer ring of the optical fiber. This layer is given a special complex dielectric constant in the finite element mesh to absorb the residual electromagnetic waves that diffuse outward from the central fiber core and reach the truncation boundary of the model. This allows for the realistic reproduction of the physical process of light wave leakage in an infinite space within the simulation environment, avoiding the distortion of the loss calculation results of the internal real mode due to the superposition of boundary reflections.

[0032] According to the appendix Figure 2 The sensor was actually fabricated using the structural parameters specified above. By strictly controlling the pore lattice period and aperture, the unintended Bragg scattering interference caused by the cladding air hole array on the core guided mode could be eliminated from the physical level. Combined with a core-to-channel distance of 6.0 to 6.4 micrometers, it ensured that the evanescent wave could penetrate the continuous quartz channel without air hole obstruction to reach the metal surface, while preventing mode shift instability caused by excessive coupling. Furthermore, with an optimal gold film thickness of 40 to 55 nanometers, the core mode and SPP mode could achieve a dramatic energy transfer at the phase-matching wavelength. At the same time, the 5.29-micrometer outer circular channel diameter ensured the smoothness of liquid flow and the matching of the optical action section. The boundary protection of the 3-micrometer perfect matching layer verified the effectiveness of the above parameter combination in the simulation. This ensured that the micro-nano structure device not only had good manufacturing tolerance and processing repeatability in the actual fabrication process, but also exhibited excellent sensing characteristics in the final loss spectrum, with a sharp main peak and no stray secondary peak interference between the two peaks.

[0033] In an exemplary embodiment, a dual-parameter independent sensing measurement method based on a resonant sensor using a dual-core, dual-channel photonic crystal fiber as described in the above embodiments is provided, comprising: S100, the first and second external physical quantities to be measured are changed independently, and the center wavelength shift of the corresponding resonant loss peaks of the first and second analyte channels is recorded respectively, so as to construct the sensitivity response matrix of the wavelength change with respect to the two external physical parameters.

[0034] In this embodiment, before formal application in measurement, the sensor's sensing characteristics need to be calibrated in a laboratory environment. The prepared dual-channel sensor is fixed on a precision temperature control platform, and Helmholtz coils are arranged around the sensor probe to generate a controllable uniform magnetic field. While keeping one physical quantity constant, the other physical quantity is changed unidimensionally. For example, the magnetic field strength is first fixed at zero, and the temperature is gradually increased in fixed steps. The center wavelength of the loss peak in the first analyte channel (temperature-sensitive channel) of the spectrometer is recorded and extracted, and the wavelength drift coefficient of this channel with temperature is fitted. Then, keeping the temperature constant, the excitation current of the Helmholtz coil is increased in fixed steps, the center wavelength of the loss peak in the second analyte channel (magnetic-sensitive channel) is recorded, and the wavelength drift coefficient of this channel with magnetic field is fitted. Based on the results of the two univariate calibration experiments, a 2×2 sensitivity matrix mathematical model from the dual-channel wavelength drift to the dual physical parameters is constructed in the experimental data recording table.

[0035] S200, inject a first functional liquid sensitive to a first external physical quantity into the first analyte channel, and inject a second functional liquid sensitive to a second external physical quantity into the second analyte channel.

[0036] For the D-shaped dual-microcavity structure of this sensor, fiber optic end-face encapsulation technology and a microfluidic injection system were used to independently connect each channel to two different capillary tubes. Channel 1 is slowly injected with a temperature-sensitive liquid via a micro-injection pump, while channel 2 is similarly injected with a magnetic field-sensitive fluid via an independent injection pump. During injection, the flow must be smooth to expel any tiny air bubbles within the microcavities. After injection, the inlet and outlet of each channel are sealed. This physically isolated filling operation provides a basis for two non-interfering sensitive media for subsequent simultaneous measurement of dual parameters.

[0037] In a complex physical field environment, the S300 synchronously acquires the real-time wavelength values ​​of the resonant loss peaks of the two current channels using a spectrometer, and calculates the real-time wavelength drift relative to the initial reference wavelength.

[0038] After completing the S200 filling operation, connect the sensor probe to the actual detection environment. Set the spectral output range of the broadband light source (e.g., 550~1050nm), and scan the resonant loss spectra of the two current channels in real time using a spectrometer. Set the initial reference wavelength in the system software (i.e., the dual-channel starting wavelength recorded during the S100 calibration process). In the actual composite field environment, the system continuously captures the real-time center wavelengths corresponding to the two loss peaks at this moment, and the software automatically performs difference calculations to obtain the real-time wavelength drift of the first and second channels relative to the initial reference value.

[0039] S400, the real-time wavelength drift data is substituted into the sensitivity response matrix, and the specific values ​​of the first and second external physical quantities are calculated synchronously by solving the simultaneous equations, so as to realize crosstalk-free synchronous online measurement of the two physical fields.

[0040] The system's backend data processing module directly uses the two real-time wavelength drift values ​​calculated in step S300 as known variables, substituting them into the sensitivity matrix equations constructed in step S100. Since the dual-channel sensor is designed to ensure absolute physical isolation between the channels, the wavelength drift values ​​of the two channels in step S300 have independent properties that do not interfere with each other. Therefore, the above simultaneous equations must have a unique solution. The computer performs calculations according to a preset inverse matrix algorithm or numerical iteration method, thereby calculating the temperature and magnetic field values ​​in real time under the current environment. These two physical parameters are then output to the terminal display, completing the synchronous, crosstalk-free measurement of the two physical fields.

[0041] The method in this embodiment relies on a pre-sequence dual-core dual-channel structure design, combined with a closed-loop process of simultaneous solution of prior matrix calibration and real-time wavelength drift data, which breaks through the limitations of traditional single-variable sensing in actual measurement. Without introducing complex digital demodulation algorithms, the objective uniqueness of the simultaneous equation calculation is ensured by the physical isolation structure, enabling a single optical fiber to output the values ​​of the measured temperature and magnetic field simultaneously, synchronously and without interference. This significantly reduces the signal processing difficulty in external multi-physics field measurement environments and effectively improves the online measurement accuracy and long-term operational reliability of the optical fiber sensor in complex field environments.

[0042] Furthermore, the first external physical quantity is temperature, and the first functional liquid is a temperature-sensitive liquid; the second external physical quantity is a magnetic field, and the second functional liquid is a magnetohydrodynamic fluid; the first analyte channel and the second analyte channel are physically isolated and do not contact each other; the resonant loss peak of the first analyte channel only produces a wavelength response to temperature changes, and the resonant loss peak of the second analyte channel only produces a wavelength response to magnetic field changes; by synchronously reading the real-time wavelengths of the two loss peaks on the spectrometer, absolute physical decoupling of the two sensing channels in the wavelength domain is achieved without the need for additional demodulation algorithms; in the sensitivity response matrix, the mapping relationship between wavelength drift and the two physical quantities is described by a nonlinear fitting formula, and the goodness-of-fit determination coefficient is not less than 0.999.

[0043] In this embodiment, considering the practical application requirements of the dual-channel sensor for temperature and magnetic field measurements, a functional liquid matching the channel characteristics needs to be configured first in the specific engineering implementation. For the first analyte channel, the thermosensitive liquid filled inside is generally a mixed solution with a high thermo-optic coefficient (e.g., a glycerol-water mixture or ethanol solution prepared in a specific ratio). This liquid exhibits extremely high sensitivity and linearity in its macroscopic refractive index as it changes with ambient temperature. For the second analyte channel, the magnetic fluid filled inside is typically a colloidal solution formed by uniformly dispersing iron(III) oxide nanoparticles coated with surfactants in a base carrier liquid. When a magnetic field of a certain strength is applied externally, the particles will aggregate in a chain along the direction of the magnetic field, resulting in a regular change in the equivalent refractive index of the magnetic fluid.

[0044] At the physical level of the measurement device, microfluidic encapsulation technology on the fiber end face allows the inlet and outlet ends of the first and second channels to be led out and sealed through independent capillary tubes, ensuring that the two sensitive liquids do not physically contact each other inside the microcavity. In actual composite environment measurements, a broadband light source (covering the 550nm~1050nm operating wavelength band) is connected to the input of the PCF-SPR sensor, while a spectrometer is connected to the output. Because the two functional liquids are physically isolated, and the fiber core fundamental mode independently excites surface plasmon resonance in the two D-type channels, the double loss peaks captured synchronously by the spectrometer are naturally separated in the wavelength domain. Changes in ambient temperature only directly cause fluctuations in the refractive index of the temperature-sensitive liquid in the first channel, leading to a drift of the first loss peak. Meanwhile, the magnetofluid in the second channel is unaffected by temperature disturbances, and the wavelength position of its second loss peak remains absolutely stationary. Similarly, changes in the spatial magnetic field only affect the refractive index of the magnetofluid, causing a shift in the second loss peak, while the first loss peak remains completely unaffected by the magnetic field.

[0045] In the actual data calibration and application phase, to achieve extremely high measurement accuracy, it is necessary to pre-determine the nonlinear correspondence between the two physical quantities and the two wavelength drift. Specifically, in practical operation, operators record the initial reference wavelength of the two channels under a constant temperature / zero magnetic environment. Then, they independently adjust the temperature or magnetic field step by step, recording a large number of real discrete data points of the two wavelength shifts caused by the two physical quantities. Because the physical properties of real refractive index-sensitive media (temperature-sensitive solutions or magnetic fluids) often lead to a high-order polynomial relationship between wavelength drift and physical quantities, a second-order or higher-order nonlinear fitting formula must be used to curve-fit the discrete data points when establishing the sensitivity response matrix. When the fitting result reaches 0.999 or higher, it proves that the response matrix basically coincides with the change curve of the actual physical quantity. Subsequently, in actual measurement, the wavelength drift values ​​of the two channels captured in real time by the spectrometer are substituted into the nonlinear response matrix as known conditions, and the specific temperature and magnetic field values ​​under the current composite environment can be calculated simultaneously.

[0046] In this embodiment, by employing the aforementioned specific medium filling and calibration process, the sensor's most prominent advantage in actual measurement lies in its inherent dual-channel physical isolation structure. This completely eliminates the traditional practice of relying on complex mathematical stripping algorithms or subsequent signal processing demodulation for multi-parameter fiber optic sensors, enabling absolute physical decoupling of temperature and magnetic field in the wavelength domain, ensuring they operate independently and without confusion. In any complex working environment, the shift of the first loss peak on the spectrometer directly reflects the current ambient temperature, while the shift of the second loss peak directly reflects the current magnetic field strength. Operators can intuitively obtain the dual-parameter values ​​without performing additional matrix inversion or complex calculations. Simultaneously, relying on the ultra-high goodness of fit (not less than 0.999) obtained through the nonlinear fitting process, the accuracy of the single-channel refractive index-wavelength response curve is raised to its limit. This ensures that the sensor not only possesses intrinsic decoupling characteristics in complex physical field environments but also achieves online real-time monitoring of dual physical quantities with extremely high measurement repeatability and accuracy.

[0047] Furthermore, the wavelength range for the wavelength scanning is set as follows; in the prior matrix calibration step, the change step size of the first external physical quantity and the second external physical quantity is 0.01 RIU.

[0048] In the actual implementation of this sensing measurement, the operating wavelength of the hardware system must first be configured. The output spectral range of the broadband light source is set to 550 to 1050 nm, ensuring a high power flatness within this band. This wavelength range is chosen because the gold film (Au) exhibits significant and stable plasmon resonance absorption characteristics within this spectral range. Furthermore, this band effectively avoids the significant material absorption loss that may occur in the near-infrared band (e.g., >1100 nm) of the molten silica substrate, ensuring that the weak resonance peak signal will not be masked by background noise on the final received loss curve. After the hardware configuration is complete, the sensor is integrated into a dual-physics-field composite calibration system consisting of a temperature control platform and a Helmholtz coil.

[0049] Regarding the fine-grained step size of physical quantities in the calibration process, to achieve high-precision step control of 0.01 RIU (refractive index unit), the actual operation does not involve directly and manually increasing or decreasing the Celsius temperature or magnetic induction intensity value. Instead, the calibration object is converted into the refractive index of the sensitive liquid being measured. The specific technical means are as follows: For the temperature-sensitive liquid in the first channel, it is placed in a precision thermostatic bath with PID closed-loop feedback. By fine-tuning the temperature control module, the net increase in the equivalent refractive index of the liquid caused by temperature is precisely controlled at 0.01 RIU. For the magnetofluid in the second channel, it is placed at the axial center of a Helmholtz coil driven by a high-precision current source. By fine-tuning the excitation current, the equivalent refractive index of the magnetofluid is also increased in a step-like manner with a step size of 0.01 RIU. In the actual matrix calibration operation, after each increase of the equivalent refractive index of the functional liquid in one channel by 0.01 RIU, the operator needs to maintain stability for a period of time (usually tens of seconds to several minutes) until the transmission spectral lines of the spectrometer no longer drift before recording the peak-to-peak wavelength of the dual-channel loss at this steady state. Following this step size, all nodes within the range of the refractive index to be tested are traversed sequentially, and a complete discrete wavelength drift dataset is recorded, laying the experimental foundation for the subsequent construction of a high-precision nonlinear response matrix.

[0050] By strictly limiting the band matching and calibration accuracy of the aforementioned hardware, the scanning band is set from 550 to 1050 nm, effectively ensuring the efficient coupling of the gold film-excited SPR in the hollow guided mode and the high signal-to-noise ratio output of the signal. At the same time, the refractive index change step size of the two physical quantities is precisely set to 0.01 RIU, which enables the acquisition of extremely high-density experimental sampling points during the prior matrix calibration stage. This fine-grained stepping fundamentally eliminates the measurement blind zone that may be caused by excessive calibration intervals, and can accurately capture the small displacement of the loss peak caused by slight changes in refractive index. This high-resolution acquisition of the underlying data directly ensures that the coefficient of determination of the subsequent nonlinear fitting curve can be stably maintained at an extremely high level of over 0.999, thereby effectively improving the recognition limit and long-term measurement accuracy of the dual-parameter sensor for small fluctuations of the measured physical quantity in a composite physical field.

[0051] Furthermore, in the actual decoupling measurement step, when the refractive index of the analyte in the first analyte channel changes, the corresponding resonant loss peak undergoes wavelength shift, while the position of the resonant loss peak corresponding to the second analyte channel remains unchanged; when the refractive index of the analyte in the second analyte channel changes, the corresponding resonant loss peak undergoes wavelength shift, while the position of the resonant loss peak corresponding to the first analyte channel remains unchanged; thus, absolutely independent decoupling measurement of the two sensing channels is achieved in the wavelength domain.

[0052] Before actually performing this decoupling measurement step, both ends of the optical fiber had undergone independent sealing and impregnation of dual channels (pre-injected with temperature-sensitive liquid and magnetorheological fluid), and the broadband light source and high-resolution spectrometer were connected. In the background software of the measurement instrument, the system first recorded the wavelength position of the initial resonant loss peak of the dual channels under the current composite environment as the reference value.

[0053] When the first external physical quantity (temperature) in the environment changes, the equivalent refractive index of the temperature-sensitive liquid inside the first analyte channel undergoes a substantial change. Since the fundamental mode field in the fiber core needs to exchange energy with the metal layer on the surface of the first channel via evanescent waves, this change in the liquid's refractive index directly causes the phase-matching condition of the excited surface plasmon polariton (SPP) mode to deviate from its initial state. Therefore, the resonant loss peak corresponding to the first analyte channel, read by the spectrometer, immediately undergoes a wavelength shift. During this physical process, the second analyte channel is located in a physically isolated independent microcavity, and the magnetofluid filling it does not exchange any substances with the liquid in the first channel, nor is it affected by temperature changes. Therefore, the SPP phase-matching condition corresponding to the metal film surface of the second channel remains in its original reference state, and the absolute wavelength position of the second loss peak remains fixed on the real-time scanning interface of the spectrometer.

[0054] Similarly, when the second external physical quantity (magnetic field) in the environment changes, the nanoparticles in the magnetofluid within the second channel undergo chain-like arrangement, leading to a change in the equivalent refractive index. Correspondingly, the resonant loss peak experiences wavelength shift. However, because the first channel is physically isolated and unaffected by the magnetic field, the refractive index of the temperature-sensitive liquid inside remains unchanged, and the position of the first loss peak remains absolutely stationary. In practical hardware operation, the operator only needs to simultaneously read the positions of the two independent loss peaks within the same frame display period of the spectrometer to naturally identify which physical quantity has changed. This absolute isolation characteristic in the physical structure is directly reflected in the wavelength domain, allowing the operator to directly determine the real-time independent changes of the two physical quantities based solely on a single snapshot observation without needing to call any backend software for cross-demodulation and filtering calculations.

[0055] The direct engineering value of this decoupled measurement mechanism lies in its ability to completely eliminate the wavelength domain cross-sensitivity problem, which is difficult to overcome in traditional multi-parameter fiber optic sensors, through the physical-level channel microcavity isolation structure. In actual composite field measurement, the wavelength responses of the two channels exhibit a completely uncoupled and independent state on the spectrometer. This means that on-site operators can directly judge the change of a single physical quantity based on the movement of a single loss peak, without relying on complex mathematical stripping algorithms to separate superimposed valleys. This significantly simplifies the hardware configuration and software computational load of back-end signal processing, and improves the real-time response and long-term measurement stability of the sensor in harsh industrial environments.

[0056] In an exemplary embodiment, the aforementioned sensor was simulated. Based on the finite element analysis, the boundary calculation results assumed that light would reflect upon contact with the boundary, affecting the mode simulation. However, in reality, light leaks out and never returns. Therefore, a perfectly matched layer needs to be introduced to absorb the light and ensure the correctness of the mode. The perfectly matched layer used has a PML value of 3 μm. Figure 3 The diagram shows the physical field simulation structure of the dual-core PCF-SPR.

[0057] like Figure 4 The diagram shows the fundamental mode distribution of the dual-core, dual-channel system, where channel A analyzes the refractive index n of the material. a =1.33, B-channel analysis of the material's refractive index n b =1.40. The effective mode refractive indices of channels A and B in the figure are 1.43836328-9.91090188E-5i and 1.43841465-1.065648E-4i, respectively. The optical mode energy in the figure is mainly concentrated in the fiber core and does not excite the SPP mode. Different modes will be excited as the measurement wavelength changes. The imaginary part of the effective refractive index corresponds to the coupling between the fundamental mode and the SPP mode, and the light loss is proportional to the imaginary part of the effective refractive index.

[0058] The coupling effect is most pronounced when the fundamental mode in the fiber core achieves phase matching with the surface plasmon polarization (SPP) mode, resulting in a peak in the loss of the fundamental mode. Wavelength scanning was performed in the range of 550–1050 nm. Due to the different refractive indices of the analytes in channels A and B, they achieve phase matching with the SPP mode at different wavelengths, exhibiting a double-peak phenomenon. This also shows that changes in the refractive index of the analyte cause a shift in the wavelength of the loss peak; sensing can be achieved by calculating the degree of wavelength shift.

[0059] Furthermore, although the steps of the method in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps.

[0060] While specific embodiments of the invention have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art should also understand that various modifications can be made to the embodiments without departing from the scope and spirit of the invention.

Claims

1. A resonant sensor based on a dual-core, dual-channel photonic crystal fiber, characterized in that, include: The fiber core uses fused silica as a substrate; A periodic array of air holes arranged in a hexagonal lattice within the substrate; A first and second analyte channel, symmetrically arranged in a D-shape on both sides of the fiber core; And metal coating layers respectively deposited on the inner wall surfaces of the first analyte channel and the second analyte channel; wherein, at least one adjacent air hole is removed from the light propagation path between the first analyte channel, the second analyte channel and the fiber core respectively, thereby constructing a continuous low-loss quartz medium path without abrupt changes in air refractive index between the fiber core and the corresponding metal coating layer. The preset structural parameters of the sensor are determined by the following method: Based on the Bragg resonance suppression condition of the fundamental mode transverse wave vector by the periodic structure of the photonic crystal cladding, combined with the working wavelength range of the sensor and the machinability of the fiber drawing process, the parameters that make the dual-channel loss spectrum curve smooth, free of stray peak interference and have the best separation of the two resonance peaks are selected by finite element analysis scanning, and used as the arrangement lattice period of the periodic air hole array. The ratio range of the air hole diameter to the period of the arranged crystal lattice is set, and the resonance peak intensity and loss peak wavelength shift under different ratios are compared by finite element analysis. The value that can make the dual-channel loss spectrum have high coupling strength and keep the resonance peak spacing optimal is selected as the air hole diameter. The vertical distance between the inner wall surfaces of the first analyte channel and the second analyte channel and the corresponding fiber core center axis is set, and the vertical distance is gradually increased in micrometer increments for finite element analysis scanning. The position displacement of the loss peak and the coupling loss intensity are tracked and observed. The value corresponding to the point where the vertical distance increases to the point where the position of the loss peak no longer moves and the coupling loss values ​​of both channels remain within a reasonable range is selected as the optimal channel vertical distance.

2. The resonant sensor based on a dual-core, dual-channel photonic crystal fiber according to claim 1, characterized in that, The first analyte channel and the second analyte channel are physically isolated independent microcavity structures, which are respectively filled with a first functional liquid that is sensitive to a first external physical quantity and a second functional liquid that is sensitive to a second external physical quantity, so as to realize independent measurement of different external physical parameters by the two channels.

3. The resonant sensor based on a dual-core, dual-channel photonic crystal fiber according to claim 1, characterized in that, The periodic lattice period of the periodic air hole array is [value]; the diameter of the air hole is [value].

4. The resonant sensor based on a dual-core, dual-channel photonic crystal fiber according to claim 1, characterized in that, The optimal vertical distance between the inner wall of the first and second analyte channels and the corresponding fiber core central axis is [value missing]; both the first and second analyte channels are D-type microfluidic channels with a circumscribed circle diameter of their cross-section.

5. The resonant sensor based on a dual-core, dual-channel photonic crystal fiber according to claim 1, characterized in that, The metal coating layer is a gold film with a thickness of [missing information].

6. The resonant sensor based on a dual-core, dual-channel photonic crystal fiber according to claim 1, characterized in that, The optical fiber is also surrounded by a perfectly matched layer with a thickness of [thickness value missing]. This layer is used to absorb light waves that leak to the cladding boundary in finite element simulation, thereby eliminating the influence of external boundary reflections on the physical field of the sensor simulation.

7. A dual-parameter independent sensing and measurement method based on the resonant sensor based on a dual-core dual-channel photonic crystal fiber as described in claim 1, characterized in that, include: The first and second external physical quantities to be measured are changed independently, and the center wavelength shift of the corresponding resonant loss peaks of the first and second analyte channels is recorded respectively. The sensitivity response matrix of the wavelength change with respect to the two external physical parameters is constructed. A first functional liquid sensitive to a first external physical quantity is injected into the first analyte channel, and a second functional liquid sensitive to a second external physical quantity is injected into the second analyte channel. In a complex physical field environment, the real-time wavelength values ​​of the resonant loss peaks of the two current channels are simultaneously acquired by a spectrometer, and the real-time wavelength drift relative to the initial reference wavelength is calculated. By substituting the real-time wavelength drift data into the sensitivity response matrix and solving the simultaneous equations, the specific values ​​of the first and second external physical quantities are calculated synchronously, thus achieving crosstalk-free synchronous online measurement of the two physical fields.

8. The dual-parameter independent sensing measurement method according to claim 7, characterized in that, The first external physical quantity is temperature, and the first functional liquid is a temperature-sensitive liquid; the second external physical quantity is a magnetic field, and the second functional liquid is a magnetohydrodynamic fluid; the first analyte channel and the second analyte channel are physically isolated and do not come into contact with each other; the resonant loss peak of the first analyte channel only produces a wavelength response to temperature changes, and the resonant loss peak of the second analyte channel only produces a wavelength response to magnetic field changes; by synchronously reading the real-time wavelengths of the two loss peaks on the spectrometer, absolute physical decoupling of the two sensing channels in the wavelength domain is achieved without the need for additional demodulation algorithms; In the sensitivity response matrix, the mapping relationship between wavelength drift and the two physical quantities is described by a nonlinear fitting formula, and the goodness-of-fit determination coefficient is not less than 0.

999.

9. The dual-parameter independent sensing measurement method according to claim 7, characterized in that, The wavelength range for the wavelength scan is set as follows; in the prior matrix calibration step, the change step size of the first external physical quantity and the second external physical quantity is 0.01 RIU.

10. The dual-parameter independent sensing measurement method according to claim 7, characterized in that, In the actual decoupling measurement step, when the refractive index of the analyte in the first analyte channel changes, the corresponding resonant loss peak undergoes wavelength shift, while the position of the resonant loss peak in the second analyte channel remains unchanged; when the refractive index of the analyte in the second analyte channel changes, the corresponding resonant loss peak undergoes wavelength shift, while the position of the resonant loss peak in the first analyte channel remains unchanged; thus, absolutely independent decoupling measurement of the two sensing channels is achieved in the wavelength domain.

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