A C-type PCF-SPR probe based on grapefruit air holes

Abstract

The present application relates to a kind of C-type PCF-SPR probe based on grapefruit air hole, belong to optical fiber sensing application technical field, probe cross section is symmetrically arranged multiple groups C-type opening along horizontal and vertical direction, form the sensing area of structural isolation: the inner surface of upper and lower opening is deposited AZO film and gold film respectively, constitute birefringence sensing channel;The inner surface of left and right opening is deposited gold film and filled with PDMS, constitute temperature sensing channel.The cladding region is provided with asymmetric grapefruit type air hole, enhances evanescent field localization and SPR coupling efficiency.The present application realizes the accurate decoupling of refractive index and temperature, and the double-peak displacement sensitivity reaches 15000 nm / RIU, the refractive index sensitivity is highest 35000 nm / RIU, temperature sensitivity-17 nm / ℃, cross sensitivity coefficient is less than 0.8%, with high sensitivity, high stability and multi-parameter synchronous detection ability.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing application technology, and in particular relates to a C-type PCF-SPR probe based on a grapefruit air hole. Background Technology

[0002] Photonic crystal fiber (PCF), with its advantages of precisely tunable dispersion characteristics and high degree of freedom in microstructure design, provides an important platform for surface plasmon resonance (SPR) sensing technology. In PCF-SPR sensors, the fiber microstructure parameters directly determine the phase matching condition and mode field overlap integral of the SPR mode at the core guided mode and metal-dielectric interface, which are core factors affecting coupling efficiency and sensing performance. C-shaped PCF structures, due to their ability to significantly enhance the interaction between the optical field and the external medium, are gradually becoming an important form of high-performance SPR probes. Existing research shows that by increasing the polishing depth, adjusting the aperture angle, and introducing graphene-gold composite structures into the sensing layer, the sensitivity and related performance indicators of the sensor can be improved to some extent. However, the sensing mechanism of the above sensors still mainly relies on a single SPR resonance peak as a characteristic quantity.

[0003] The single-resonant-peak mechanism has certain limitations in high-precision detection applications. Firstly, its response is typically discrete, with a significant shift in the resonant wavelength only occurring when external environmental changes reach a certain critical point. Therefore, its sensitivity is insufficient when refractive index changes are small or environmental changes are slow, making high-precision detection difficult. Secondly, the single-resonant-peak mechanism also exhibits limitations in complex sensing environments, especially when the analyte possesses complex physicochemical properties or multiple interactions. The sensor cannot fully reflect the mutual influences between various factors, thus affecting its performance. Furthermore, in practical detection environments, temperature changes often simultaneously cause changes in the refractive index of the analyte, making it difficult for a single refractive index sensing channel to distinguish the contributions of both. The cross-sensitivity problem between refractive index and temperature has not yet been effectively resolved.

[0004] To address the shortcomings of traditional C-type PCF-SPR sensors in terms of detection resolution, cross-sensitivity, and adaptability to complex environments, a dual-resonance peak sensing mechanism is introduced, providing an effective approach to further improve detection performance. Simultaneously, the influence of the geometry and arrangement of the cladding air holes on the SPR coupling efficiency warrants further investigation. Existing PCF claddings often employ circular air hole arrays, resulting in a relatively loose structure. This leads to insufficient coupling efficiency between the core fundamental mode and the surface plasmon polariton modes, resulting in low resonant loss peak intensity and limiting signal discriminability and stability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a C-type PCF-SPR probe based on grapefruit air pores. Through structural innovation, it can achieve precise decoupling of refractive index and temperature, possessing high sensitivity and good structural reliability, and has significant engineering application value.

[0006] A C-type PCF-SPR probe based on grapefruit air holes, wherein multiple sets of C-type openings are symmetrically arranged in the cross-section of the fiber optic cable along the horizontal and vertical directions, forming multiple structurally isolated sensing regions.

[0007] The outer surfaces of the two C-shaped openings arranged symmetrically along the vertical direction are respectively deposited with a first plasma active material film and a second plasma active material film, forming two independent refractive index sensing channels; the outer surfaces of the two C-shaped openings arranged symmetrically along the horizontal direction are deposited with a metal conductive film, and a temperature-sensitive polymer material is filled on top of the metal conductive film to form a temperature sensing channel.

[0008] Multiple grapefruit-shaped air holes are arranged asymmetrically within the cladding region of the optical fiber. These grapefruit-shaped air holes are used to enhance the localization intensity of the evanescent field and improve the surface plasmon resonance coupling efficiency.

[0009] The first plasma active material is aluminum-doped zinc oxide, and the second plasma active material is gold.

[0010] The conductive metal film in the temperature sensing channel is a gold film, and the thermosensitive polymer material is polydimethylsiloxane.

[0011] The matrix material of the optical fiber is fused silica, and the photonic crystal fiber is a refractive index guided type.

[0012] The number of C-shaped openings is four, which are symmetrically arranged along the horizontal and vertical directions, respectively.

[0013] The grapefruit-shaped air pores are four in number and are symmetrically distributed in the four quadrants of the cladding region.

[0014] The depth of the C-shaped opening is 12 μm to 14 μm, and the cladding radius of the photonic crystal fiber is 16 μm to 20 μm; the length of the grapefruit-shaped air hole is 12 μm to 14 μm, and the angle of the grapefruit-shaped air hole is 40° to 50°.

[0015] The thickness of the first plasma-active material film is 30 nm to 50 nm, and the thickness of the second plasma-active material film is 40 nm to 60 nm.

[0016] The two refractive index sensing channels have a refractive index detection range of 1.31–1.43 for the test medium. The maximum wavelength sensitivities of the two channels are 24,500 nm / RIU and 35,000 nm / RIU, respectively, and the minimum resolutions are 2.27 × 10⁻⁶ and 2.27 × 10⁻⁶, respectively. -6 RIU and 1.47×10 -6 RIU.

[0017] The temperature sensing channel has a temperature detection range of -40℃ to 60℃ and a maximum wavelength sensitivity of -17 nm / ℃.

[0018] By employing the above technical solution, the present invention has at least the following beneficial effects:

[0019] The upper and lower refractive index channels of this invention are made of aluminum-doped zinc oxide thin film and gold film, respectively, with a sensitivity of up to 35,000 nm / RIU. The wavelength difference between the two peaks can also respond to the refractive index change by 15,000 nm / RIU, which is more reliable than the single-peak scheme.

[0020] The structure of the gold-thermosensitive polymer in the left and right channels of this invention measures temperature separately and is physically isolated from the refractive index channel, resulting in minimal cross-interference and truly separating the effects of temperature.

[0021] The asymmetric arrangement of grapefruit-shaped air holes in this invention makes the light field more concentrated, improves SPR coupling efficiency, and makes the spectral peaks more stable.

[0022] The bimodal drift values ​​of this invention can be cross-checked, and interference can be automatically identified, making the measurement results more reliable.

[0023] Overall, the probe of this invention has high sensitivity, strong anti-interference ability, and is suitable for simultaneous detection of multiple parameters. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of the C-type PCF-SPR probe based on grapefruit air holes according to the present invention;

[0025] Figure 2 The loss spectrum curve of the upper refractive index sensing channel in the C-type PCF-SPR probe based on grapefruit air holes of this invention is shown under the condition of the refractive index range of 1.31 to 1.41.

[0026] Figure 3 The loss spectrum curve of the lower refractive index sensing channel in the C-type PCF-SPR probe based on grapefruit air holes of this invention is shown under the condition of the refractive index range of 1.31 to 1.43.

[0027] Figure 4The loss spectrum curve of the temperature sensing channel in the grapefruit-based C-type PCF-SPR probe of this invention is shown in the temperature range of -40°C to 60°C.

[0028] Figure 5 This is the curve showing the relationship between the bimodal displacement sensitivity and the refractive index to be measured in the C-type PCF-SPR probe based on grapefruit air pores of this invention.

[0029] In the picture:

[0030] 1. Fiber matrix boundary; 2. Thermosensitive polymer; 3. Right C-shaped opening; 4. Gold film; 5. Lower C-shaped opening; 6. Grapefruit-shaped air hole; 7. Left C-shaped opening; 8. Fiber matrix; 9. Aluminum-doped zinc oxide film; 10. Upper C-shaped opening. Detailed Implementation

[0031] To better explain and facilitate understanding of the present invention, the technical solution and effects of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] A C-type PCF-SPR probe based on grapefruit-shaped air holes has four C-shaped openings symmetrically arranged in the horizontal and vertical directions in the cross-section of an optical fiber, forming four structurally isolated sensing regions. Specifically, the upper C-shaped opening 10 and the lower C-shaped opening 5 constitute a refractive index sensing channel: the inner surface of the upper C-shaped opening 10 is deposited with an aluminum-doped zinc oxide thin film 9, which is the upper refractive index sensing channel, and the inner surface of the lower C-shaped opening 5 is deposited with a gold film 4, which is the lower refractive index sensing channel. Aluminum-doped zinc oxide, as a transparent conductive oxide, has strong plasmon response characteristics in the near-infrared band, and also has the advantages of high chemical stability and low cost. While maintaining high sensitivity, it can partially replace precious metals, significantly improving the economic efficiency and environmental adaptability of the sensor. Furthermore, the left C-shaped opening 7 and the right C-shaped opening 3 constitute a temperature sensing channel: the outer surface of both is deposited with a gold film 4, and a temperature-sensitive polymer 2 is filled on top of the gold film 4. In this embodiment, polydimethylsiloxane is used to form a gold-polydimethylsiloxane composite temperature sensing channel, which is used to achieve precise decoupled monitoring of temperature parameters. Four C-shaped openings are symmetrically arranged in the four directions of the fiber cross section. This structural isolation design not only effectively avoids optical crosstalk between different sensing areas, but also allows each sensing channel to work independently, laying a reliable structural foundation for subsequent decoupled measurement of refractive index and temperature.

[0033] The fiber substrate 8 is made of high-purity fused silica, and the fiber substrate boundary 1 has a circular outline in cross-section, forming an overall refractive index-guided photonic crystal fiber. The cladding region consists of four grapefruit-shaped air holes 6, which are asymmetrically arranged. Compared with traditional circular air holes, the grapefruit-shaped air holes 6 have a unique concave-convex profile, enabling the formation of more complex optical field modulation effects in the cladding. Specifically, the asymmetric array of grapefruit-shaped air holes 6 can significantly enhance the localization intensity of the evanescent field, concentrating more optical energy near the interface between the metal thin film deposited on the inner surface of each C-shaped opening and the medium under test, thereby improving the surface plasmon resonance (SPR) coupling efficiency. Simultaneously, its structural asymmetry effectively suppresses crosstalk between modes of different polarization directions, contributing to improved wavelength separation of the double resonant peaks and overall spectral stability under environmental disturbances. The grapefruit-shaped air holes 6 have a length of 12 μm to 14 μm and an angle of 40° to 50°. The cladding radius of the photonic crystal fiber, corresponding to the fiber matrix boundary 1, is 16 μm to 20 μm, and the depth of the C-shaped opening is 12 μm to 14 μm. The thickness of the aluminum-doped zinc oxide film 9 is 30 nm to 50 nm, and the thickness of the gold film 4 is 40 nm to 60 nm. This reasonable matching of parameters allows the evanescent field of the core guiding mode to extend sufficiently to the metal-dielectric interface at the bottom of each C-shaped opening, achieving efficient optical-plasma coupling while ensuring the fiber's mechanical strength.

[0034] In a preferred preparation process, specifically:

[0035] First, a PCF preform is constructed using a precision capillary stacking method, and then a PCF substrate with a pre-defined air hole structure is obtained through a high-temperature wire drawing process. Subsequently, C-shaped microgrooves are sequentially etched in four symmetrical directions of the optical fiber using a femtosecond laser micromachining system. Femtosecond laser micromachining offers advantages such as high precision and a low heat-affected zone, ensuring the dimensional consistency and positional symmetry of the four C-shaped openings, which is crucial for achieving balanced performance across all sensing channels.

[0036] An aluminum-doped zinc oxide thin film 9 was deposited on the inner surface of the upper C-shaped opening using a magnetron sputtering process. Magnetron sputtering enables precise control of the film thickness at the nanoscale, ensuring the uniformity and density of the aluminum-doped zinc oxide thin film 9, thereby guaranteeing the consistent response of the refractive index sensing channel.

[0037] By combining chemical reduction and solution impregnation techniques under vacuum-assisted permeation conditions, gold ions are uniformly deposited on the outer surfaces of the remaining three C-shaped openings—the lower C-shaped opening 5, the left C-shaped opening 7, and the right C-shaped opening 3—forming a dense and highly conductive gold functional layer. The vacuum-assisted permeation process ensures that gold ions fully penetrate deep into each C-shaped opening and form a continuous, pinhole-free metal film on the inner wall, which directly affects the intensity and stability of the SPR signal. Furthermore, a polydimethylsiloxane precursor is injected into the left C-shaped opening 7 and the right C-shaped opening 3 via vacuum permeation, and then thermosetting to form a temperature-sensitive response layer. Polydimethylsiloxane has a high thermo-optic coefficient and a high coefficient of thermal expansion; when the ambient temperature changes, its refractive index and volume change significantly, thereby modulating the dielectric environment on the surface of the gold film 4 and causing a measurable shift in the resonant wavelength of the temperature sensing channel.

[0038] Finally, the optical fiber is cut to a predetermined length and its end face is polished to complete the preparation of the PCF-SPR probe.

[0039] In practical applications, the probe is placed in the solution environment to be tested, and the broadband optical signal is coupled into the fiber core through a lens. The evanescent field of the core guided mode extends towards the cladding. Under the coordinated modulation of the four grapefruit-shaped air holes 6, the light energy is effectively guided and localized near the metal film on the inner surface of each C-shaped opening, and interacts with the metal-dielectric interface in each sensing channel. Under specific wavelength conditions, when the propagation constant of the core guided mode and the wave vector of the surface plasmon wave at the metal-dielectric interface satisfy the phase matching condition, evanescent field coupling occurs between the core guided mode and the surface plasmon mode, and the light energy is transferred from the core to the metal interface, resulting in corresponding resonance attenuation characteristics in the transmission spectrum. Due to the difference in the real and imaginary parts of the dielectric constant between the aluminum-doped zinc oxide film 9 and the gold film 4, the upper and lower refractive index sensing channels excite resonance responses in different wavelength bands, and the resonance wavelengths of the two drift at different rates with the change of the refractive index of the medium under test. By simultaneously detecting the resonant wavelengths of the upper and lower channels, high-precision measurement of the refractive index can be achieved, and the data from the two channels can be cross-checked, improving measurement reliability. Meanwhile, the gold-polydimethylsiloxane composite temperature sensing channels in the left C-shaped opening 7 and the right C-shaped opening 3 utilize the thermal expansion effect and thermo-optic effect of polydimethylsiloxane to cause a stable unidirectional drift of the resonant wavelength of the temperature sensing channel with changes in ambient temperature. During the detection process, by simultaneously acquiring the resonant wavelengths of the two refractive index channels and the temperature channel, the changes in refractive index and temperature can be calculated using a pre-calibrated sensitivity matrix, thus enabling real-time detection of multiple parameters without interference under complex media conditions.

[0040] To verify the technical effectiveness of the C-type PCF-SPR probe for grapefruit air pores, the following three specific embodiments are described in detail.

[0041] Example 1

[0042] like Figure 1 As shown, in this embodiment, the cladding radius of the photonic crystal fiber is 16 μm; the depth of the C-shaped opening is 12 μm; the thickness of the aluminum-doped zinc oxide film 9 is 30 nm; the thickness of the gold film 4 is 40 nm; the length of the grapefruit-shaped air hole 6 is 12 μm; and the angle of the grapefruit-shaped air hole 6 is 40°. Finite element simulation analysis using the above parameters shows that, within the detection range of refractive index 1.31–1.43, the maximum wavelength sensitivity of the upper refractive index sensing channel (aluminum-doped zinc oxide film 9) reaches 24,500 nm / RIU, corresponding to a minimum refractive index resolution of 2.27 × 10⁻⁶. -6 The maximum wavelength sensitivity of the lower refractive index sensing channel (gold film 4) reaches 35,000 nm / RIU, corresponding to a minimum refractive index resolution of 1.47 × 10⁻⁶. -6 RIU. Within a temperature measurement range of -40℃ to 60℃, the wavelength sensitivity of the temperature sensing channel reaches -17 nm / ℃. This embodiment features a compact structure, making it suitable for space-constrained integrated sensing applications, such as in-line detection in microfluidic chips.

[0043] Example 2

[0044] In this embodiment, the cladding radius of the photonic crystal fiber is 18 μm; the depth of the C-type aperture is 13 μm; the thickness of the aluminum-doped zinc oxide film 9 is 40 nm; the thickness of the gold film 4 is 50 nm; the length of the grapefruit-shaped air hole 6 is 13 μm; and the angle of the grapefruit-shaped air hole 6 is 45°. Compared with Embodiment 1, this embodiment increases the cladding radius and aperture depth, which is beneficial to increasing the penetration depth of the evanescent field and the interaction volume between the optical field and the medium under test, thereby improving the signal-to-noise ratio. Finite element simulation analysis was performed using the above parameters. The simulation results show that the refractive index sensitivity of the upper refractive index sensing channel and the lower refractive index sensing channel remain at 24,500 nm / RIU and 35,000 nm / RIU, respectively, the temperature sensitivity is -17 nm / ℃, and the double-peak shift sensitivity reaches 15,000 nm / RIU. When the above key geometric parameters are varied within the range of Examples 1 to 2, the fluctuation of refractive index sensitivity is less than 5%, which indicates that the structure proposed in this invention has strong tolerance to common processing deviations and is beneficial for engineered mass production.

[0045] Example 3

[0046] In this embodiment, the cladding radius of the photonic crystal fiber is 20 μm; the depth of the C-shaped opening is 14 μm; the thickness of the aluminum-doped zinc oxide film 9 is 50 nm; the thickness of the gold film 4 is 60 nm; the length of the grapefruit-shaped air hole 6 is 14 μm; and the angle of the grapefruit-shaped air hole 6 is 50°. This embodiment employs a larger cladding radius and opening depth, allowing the evanescent field to extend more fully into the analyte outside the metal film. This results in higher detection sensitivity for analytes with low concentrations or weak refractive index changes, making it suitable for applications with extremely stringent sensitivity requirements, such as trace biomolecule detection or environmental trace pollutant monitoring.

[0047] All three embodiments described above can achieve synchronous and decoupled measurement of refractive index and temperature. Furthermore, the overall sensor adopts a fused silica matrix and a sealed encapsulation process, with no external moving parts. It can maintain signal stability even in extreme environments such as low temperature, strong corrosion, and strong electromagnetic interference, and has good environmental adaptability.

[0048] Taking the parameters listed in Example 2 as an example, a two-dimensional cross-sectional sensing model of the probe is constructed using the finite element method, and the loss spectrum characteristics of each sensing channel are obtained through numerical simulation.

[0049] Figure 2 The image shows the loss spectrum curves of the upper refractive index sensing channel (aluminum-doped zinc oxide thin film 9) under the condition of the measured refractive index range of 1.31 to 1.41. It can be seen that as the refractive index increases, the resonant wavelength shifts towards longer wavelengths, while the intensity of the loss peak remains well maintained. The relationship between the resonant wavelength and the refractive index is obtained through data fitting as follows:

[0050] ;

[0051] Where: λ1 is the upper channel resonant wavelength, in nm. n1 is the refractive index of the analyte in the upper channel.

[0052] Figure 3 The loss spectrum curve of the lower refractive index sensing channel (gold film 4) under the condition of the measured refractive index range of 1.31 to 1.43 is shown in the following fitting equation:

[0053] ;

[0054] Where: λ2 is the lower channel resonant wavelength, and n2 is the refractive index of the material to be measured in the lower channel.

[0055] Figure 4 The loss spectrum curve of the temperature sensing channel (gold-polydimethylsiloxane composite temperature sensing channel) is shown in the temperature range of -40℃ to 60℃. The resonant wavelength shifts linearly towards shorter wavelengths with increasing temperature. The fitting relationship is as follows:

[0056] ;

[0057] Where: λ3 is the resonant wavelength of the temperature channel, in nm. T1 is the temperature to be measured in the temperature sensing channel.

[0058] Wavelength sensitivity can be calculated using the following formula:

[0059] ;

[0060] Where: S is the wavelength sensitivity, in nm / RIU, and Δλ k Δn represents the wavelength peak shift. a This indicates the change in the refractive index of the analyte.

[0061] According to this formula, the upper and lower refractive index sensing channels achieve maximum wavelength sensitivities of 24,500 nm / RIU and 35,000 nm / RIU, respectively, within the refractive index range of 1.31–1.43; the gold-polydimethylsiloxane composite temperature sensing channel exhibits a temperature sensitivity of -17 nm / ℃ within the range of -40℃ to 60℃. The unit of temperature sensitivity is nm / ℃, and the negative sign indicates a blue shift of the resonant wavelength with increasing temperature.

[0062] To address the dual-resonance peak response characteristics excited by the two refractive index detection channels, this invention further defines a dual-peak displacement sensitivity parameter, the calculation formula of which is as follows:

[0063] ;

[0064] in: S DPSS This represents the biphasic shift sensitivity parameter, with units of nm / RIU; Δ( λ 2- λ 1) Indicates the upper channel resonant wavelength λ 1 and the resonant wavelength of the lower channel λ The change in the interval of 2, that is, the change in the distance between the two peaks under different refractive index conditions; Δ X This represents the change in refractive index; X 1 indicates the refractive index value corresponding to the upper refractive index sensing channel. X 2 indicates the refractive index value corresponding to the lower refractive index sensing channel; λ 2- λ 1)1 and ( λ 2- λ 1) and 2 represent the refractive index, respectively. X 1 and X 2 o'clock upper channel resonant wavelength λ 1 and the resonant wavelength of the lower channel λ The interval is 2.

[0065] This parameter characterizes the degree to which the relative displacement between two resonance peaks responds to changes in refractive index. Compared to traditional single-peak wavelength sensitivity, dual-peak displacement sensitivity utilizes the differential response characteristics of two peaks to effectively counteract the co-directional interference caused by environmental fluctuations (such as temperature drift and external vibrations) on a single spectral peak, thereby improving the stability and detection accuracy of peak identification. In practical measurements, this parameter can serve as a supplement to conventional sensitivity indicators for signal redundancy verification and abnormal interference identification.

[0066] like Figure 5 The curves showing the relationship between the dual-peak shift sensitivity and the refractive index being measured are illustrated. Within the refractive index range of 1.31–1.43, the sensitivity of the dual-peak wavelength difference to the refractive index reaches 15,000 nm / RIU. This auxiliary indicator can provide redundancy verification at the signal processing level: when the drift direction or amplitude of the two peaks is inconsistent, abnormal interference can be identified, thereby triggering an alarm or data rejection, improving the reliability of the system.

[0067] Within the detection range of refractive index 1.31–1.43, the upper and lower refractive index sensing channels of the C-type PCF-SPR probe of this invention achieve maximum wavelength sensitivities of 24,500 nm / RIU and 35,000 nm / RIU, respectively, corresponding to minimum refractive index resolutions of 2.27 × 10⁻⁶. -6 RIU and 1.47×10 -6 The refractive index (RIU) is measured over a temperature range of -40℃ to 60℃, with a sensitivity of -17 nm / ℃. The dual-peak shift sensitivity reaches 15,000 nm / RIU. These superior performance characteristics stem from the C-shaped groove structure isolation design, the light field modulation of the asymmetric grapefruit-shaped air-hole array, and the complementary properties of the aluminum-doped zinc oxide and gold dual-material system. The dual resonant peaks operate within differentiated wavelength windows, effectively expanding the dynamic range of refractive index detection; simultaneously, the sensitivity difference between the two refractive index channels further enhances the refractive index resolution.

[0068] Furthermore, since the two refractive index sensing channels use aluminum-doped zinc oxide and gold as plasma active materials respectively, their sensitivity to refractive index changes has a fixed proportional relationship: 24,500 nm / RIU for the upper channel and 35,000 nm / RIU for the lower channel, with a ratio of approximately 1:1.43. During actual measurements, by simultaneously acquiring the resonant wavelengths of both channels, the ratio of the wavelength shifts of the two peaks can be calculated in real time. When this ratio deviates from the preset allowable range, it can be determined that the measurement process has been interfered with, thereby triggering data rejection or an alarm. This self-checking mechanism based on dual-peak data comparison effectively avoids misjudgments that may occur when relying on a single spectral peak.

[0069] Furthermore, the two refractive index channels can be configured with different demodulation methods depending on the measurement requirements. For minute refractive index changes in the measured medium, single-peak demodulation can be performed directly using the resonant wavelength shift of the lower refractive index sensing channel with higher sensitivity to obtain precise measurement results. For samples with a wider refractive index detection range or those with complex matrix interference, dual-peak wavelength difference demodulation can be used. Since dual-peak wavelength difference has a natural suppression effect on common-mode interference (such as ambient temperature fluctuations and light source power drift), this method can provide more stable output in dynamic measurement environments. Users can flexibly choose between these two demodulation strategies based on the actual signal quality.

[0070] Regarding temperature parameters, the gold-polydimethylsiloxane composite temperature sensing channel and refractive index sensing channel in the left C-shaped opening 7 and the right C-shaped opening 3 are physically isolated from each other. Furthermore, the thermo-optical effect and thermal expansion effect of polydimethylsiloxane are only sensitive to temperature and are essentially unresponsive to changes in refractive index. Experimental measurements show that the cross-sensitivity coefficient between the temperature channel and the refractive index channel is less than 0.8%, thus enabling accurate decoupled measurement of refractive index and temperature without the need for additional correction algorithms.

[0071] Based on the above structural design, this probe can simultaneously provide high-sensitivity refractive index detection and temperature compensation functions in applications with stringent requirements for accuracy and reliability, such as biomolecular specific recognition, trace chemical composition analysis, and real-time monitoring of industrial processes. The all-fiber integrated structure, the hermetically sealed packaging process without moving parts, and the high tolerance to typical processing deviations further ensure the sensor's engineered mass production capabilities and long-term service stability.

[0072] In summary, the C-type PCF-SPR probe based on grapefruit air holes proposed in this invention provides a new technical path and theoretical support for the development of multi-dimensional, high-precision optical sensing, thanks to its unique structure-material-function synergistic design, excellent multi-parameter synchronous detection performance, good stability, and strong engineering applicability.

Claims

1. A C-type PCF-SPR probe based on grapefruit air pores, characterized in that: The probe's optical fiber cross-section has multiple sets of C-shaped openings symmetrically arranged along the horizontal and vertical directions, forming multiple structurally isolated sensing regions; the number of C-shaped openings is four, symmetrically arranged along the horizontal and vertical directions respectively; The outer surfaces of the two C-shaped openings symmetrically arranged along the vertical direction are respectively deposited with a first plasma active material film and a second plasma active material film, forming two independent refractive index sensing channels; the first plasma active material is aluminum-doped zinc oxide, and the second plasma active material is gold; the thickness of the first plasma active material film is 30 nm to 50 nm, and the thickness of the second plasma active material film is 40 nm to 60 nm; the maximum wavelength sensitivities of the two refractive index sensing channels are 24,500 nm / RIU and 35,000 nm / RIU, respectively. Two C-shaped openings symmetrically arranged in the horizontal direction have a metal conductive film deposited on their outer surfaces, and a temperature-sensitive polymer material is filled on top of the metal conductive film to form a temperature sensing channel; the temperature sensing channel has a temperature detection range of -40℃ to 60℃ and a maximum wavelength sensitivity of -17 nm / ℃. The cross-sensitivity coefficient between the temperature sensing channel and the refractive index sensing channel is less than 0.8%; Multiple grapefruit-shaped air holes are provided in the cladding region of the optical fiber. The grapefruit-shaped air holes are used to enhance the localization intensity of the evanescent field and improve the surface plasmon resonance coupling efficiency. There are four grapefruit-shaped air holes, which are symmetrically distributed in the four quadrants of the cladding region. The length of the grapefruit-shaped air holes is 12 μm to 14 μm. The depth of the C-shaped opening is 12μm~14μm, and the cladding radius of the photonic crystal fiber is 16μm~20μm.

2. The C-type PCF-SPR probe based on grapefruit air pores according to claim 1, characterized in that: The conductive metal film in the temperature sensing channel is a gold film, and the thermosensitive polymer material is polydimethylsiloxane.

3. The C-type PCF-SPR probe based on grapefruit air pores according to claim 1, characterized in that: The matrix material of the optical fiber is fused silica, and the photonic crystal fiber is a refractive index guided type.

4. The C-type PCF-SPR probe based on grapefruit air pores according to claim 1, characterized in that: The two refractive index sensing channels have a refractive index detection range of 1.31~1.43 for the medium under test, and the minimum resolution of the two refractive index sensing channels is 2.27×10⁻⁶. -6 RIU and 1.47×10 -6 RIU.

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