High-sensitivity methane and temperature double-parameter detection PCF sensor based on SPR effect

Abstract

The invention relates to the technical field of special optical fibers, and discloses a high-sensitivity methane and temperature double-parameter detection PCF sensor based on an SPR effect. The sensor adopts a germanium-doped silicon dioxide photonic crystal fiber with a periodic air hole microstructure as a core element, and D-shaped polished surfaces are symmetrically arranged on the outer side of the fiber. A gold film and a functional material layer are respectively deposited on polished surfaces on two sides, one side is a Cryptophane-A methane sensitive film, the other side is a PDMS temperature sensitive material, and a two-parameter independent detection channel is constructed. After the design is optimized, the methane detection range is 0-3.5%, and the highest sensitivity can reach 68nm / %; the temperature detection range is 25-120 DEG C, and the maximum temperature sensitivity is 16 nm / DEG C. According to the invention, the SPR technology, the gas sensitive effect of the methane sensitive material and the thermo-optic effect of the temperature sensitive material are combined, so that high-precision synchronous detection of two parameters is realized. The sensor overcomes the defect of single measurement of a traditional optical fiber sensor, has the advantages of electromagnetic interference resistance, simple structure, high sensitivity, multi-parameter synchronous detection and the like, and is suitable for complex environments such as underground coal mines and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of special optical fibers, and particularly to a high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect. Background Technique

[0002] The safe production of mines is an important topic in the mining field, and the temperature and methane concentration in the mine environment are two key factors directly affecting mine safety. Factors such as high geothermal gradients deep in the mine, heat generated by the operation of mechanical equipment, and poor ventilation are likely to cause temperature rises, which not only affect the health and work efficiency of miners but may also lead to accidents such as equipment aging, fires, and even gas explosions. Methane (CH4) is a common colorless and odorless flammable gas and is also the main component of natural gas. When the methane concentration in a confined area reaches 5%-15%, it is extremely likely to cause an explosion. Therefore, methane is a safety hazard during the production, storage, and transportation of natural gas. Especially in the underground coal mine environment, the control standard for methane gas concentration is more stringent. Generally, the methane concentration in underground coal mines shall not exceed 1%; the national standard stipulates that when the methane concentration in coal mines exceeds 1.25%, a warning shall be issued to workers; when the methane concentration exceeds 2%, it is a serious danger situation. Traditional mine environment monitoring systems usually use independent electrochemical temperature and methane sensors, which have problems such as independent monitoring data, low sensitivity, susceptibility to electromagnetic interference, and low system integration, making it difficult to comprehensively and timely reflect the safety status of the mine environment. Therefore, developing a high-sensitivity, multi-parameter synchronous monitoring optical fiber sensor that can real-time monitor the changes in temperature and methane concentration is of great significance for improving the mine safety guarantee level.

[0003] Surface Plasmon Resonance (SPR) is a physical and optical phenomenon that occurs at the interface between a metal and a dielectric. When the SPR phenomenon occurs, part of the energy of the incident light is transferred to the surface plasmon polaritons, forming a depression in the transmission spectrum. SPR is very sensitive to the parameters of the incident light and changes in the refractive index of the environmental medium. When the refractive index of the surrounding environment changes, the position of the resonance peak also changes. Traditional SPR sensors use the Kretschmann-Raether structure. However, this structure not only has a large size but also is complex in design, limiting its application in long-distance detection. With the rapid development of Photonic Crystal Fiber (PCF) technology, researchers have gradually combined the Surface Plasmon Resonance (SPR) technology with photonic crystal fibers. This PCF-SPR sensor can not only effectively control the mode field area and distribution but also more efficiently excite the SPR effect by optimizing the PCF structure parameters, thus providing new possibilities for the miniaturization and long-distance detection of sensors.

[0004] In recent years, fiber optic gas sensors based on surface plasmon resonance (SPR) have made significant progress in the field of methane gas detection, and the research trend is towards multi-parameter integration and high-sensitivity detection. For example, in 2022, Liu et al. designed a novel SPR sensor based on photonic quasi-crystal fiber (PQF) that can detect methane and hydrogen simultaneously. The simulation results show that in the concentration range of 0% - 3.5%, the maximum detection sensitivities of hydrogen and methane are 0.8 nm / % and 10 nm / %, respectively. In 2023, the hollow anti-resonant fiber sensor developed by Li et al. can achieve a maximum detection sensitivity of 5.54 nm / % in the methane concentration range of 0% - 3.5%. To improve the detection sensitivity of methane gas, in 2024, Liu et al. proposed a photonic quasi-crystal fiber - surface plasmon resonance (PQF-SPR) methane sensor, and the maximum wavelength sensitivity was increased to 64 nm / % in the methane concentration range of 0% - 3.5%. In the same year, Xiao et al. designed a novel anchor-shaped photonic crystal fiber (AS-PCF) multi-parameter sensor that combines SPR technology and dual-polarization interferometry and can detect methane, hydrogen, and temperature simultaneously in the concentration range of 0.5% - 3%, with sensitivities of 4.48 nm / %, 0.23 nm / %, and 0.58 nm / °C (10 - 30 °C), respectively. In addition, Gan et al. developed an SPR-based D-type open-loop micro-groove photonic crystal fiber (PCF) sensor for dual-parameter detection of methane concentration (0.5% - 3.0%) and temperature (0 - 50 °C), with average sensitivities reaching 96.57 nm / % and 6.86 nm / °C, respectively. Although the reported technical solutions have made great progress in methane gas concentration detection and temperature detection, the existing research still faces many technical challenges. For example, the early multi-parameter sensors such as the AS-PCF designed by Xiao et al. have a methane detection sensitivity of only 4.48 nm / %, which is difficult to meet the requirements of high-precision detection; although the sensor designed by Gan et al. can achieve high-sensitivity methane detection of 96.57 nm / %, its temperature detection range is only 0 - 50 °C, which cannot meet the requirements of wide-temperature applications. In addition, most high-performance solutions rely on complex micro-structure designs, such as anti-resonant tube gold plating or film coating structures inside air holes, which significantly increase the manufacturing difficulty and cost. More importantly, the existing technologies are difficult to simultaneously meet the requirements of high sensitivity and multi-parameter detection, and these limitations severely restrict the application effect of SPR fiber optic sensors in actual industrial environments. Summary of the Invention

[0005] (1) Technical problems to be solved

[0006] Aiming at the deficiencies of the existing technology, the present invention provides a high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect, a photonic crystal fiber (PCF) sensor for high-sensitivity methane and temperature dual-parameter detection based on the surface plasmon resonance (SPR) effect. It not only has high sensing sensitivity, but also can simultaneously sense methane concentration and temperature without mutual interference. At the same time, it is simple to operate during the experiment, and there is no filling of substances in the internal air holes, which also reduces the manufacturing difficulty and is easy for experimenters to manufacture.

[0007] (II) Technical Solution

[0008] To solve the above technical problems, the present invention provides the following technical solutions:

[0009] A high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect, the sensor uses a photonic crystal fiber as a functionalized optical waveguide medium, and the photonic crystal fiber has a microstructure with periodically arranged air holes and a germanium-doped substrate material;

[0010] The photonic crystal fiber includes a substrate material, the substrate material is germanium-doped silica, and two parallel D-shaped cut surfaces are provided on the outer side of the substrate material, and the two D-shaped cut surfaces are symmetrically arranged with respect to the axis of the substrate material;

[0011] A gold film is coated on the surfaces of the two D-shaped cut surfaces. After the upper cut surface of the two D-shaped cut surfaces is coated with a gold film, a methane-sensitive material for measuring methane concentration change is coated as a methane concentration sensing channel, and a temperature-sensitive material for measuring the change of the external environmental temperature is coated on the lower cut surface of the two D-shaped cut surfaces on the gold film as a temperature sensing channel;

[0012] The cladding of the photonic crystal fiber of the sensor adopts a double-layer air hole array structure. The first layer includes six inner air holes, which are divided into two sizes of air holes, namely cladding air hole one and cladding air hole two. The second layer includes ten air holes, and the air hole size is the same as that of cladding air hole two. All cladding air hole one, cladding air hole two and the cylindrical central axis of the substrate material are rotationally symmetrically distributed.

[0013] Preferably, the radius of the cladding air hole one is 0.35 μm, the radius of the cladding air hole two is 0.62 - 0.76 μm, and the distance between adjacent cladding air holes two is 2.34 - 2.5 μm; the thickness of the gold film coated on the surface of the D-shaped cut surface is 30 - 50 nm, the distance between the cladding air hole one and the core is 2.35 - 3.75 μm, and the lateral distance between the cladding air hole two of the first layer and the core is 2.4 - 2.55 μm.

[0014] Preferably, the distance between the D-shaped section and the fiber core is 4.6 - 5.5 μm.

[0015] Preferably, the methane-sensitive material coated on the upper D-shaped section surface is Cryptophane-A.

[0016] Preferably, the temperature-sensitive material coated on the lower D-shaped section surface is polydimethylsiloxane.

[0017] Preferably, the substrate material adopts a double-section structure design, where the upper section is coated with a methane-sensitive material to excite the SPR effect and couple the methane concentration signal, and the lower section is coated with a temperature-sensitive material to excite the SPR effect and couple the temperature signal, realizing the independent detection of dual parameters.

[0018] Preferably, the temperature-sensitive material modulates the surface plasmon resonance condition of the gold film through the thermally induced volume expansion effect, forming a dual-channel structure physically isolated from the methane concentration sensing channel to achieve the decoupled detection of temperature and methane concentration.

[0019] Preferably, the size optimization of the first and second cladding air holes can improve the detection sensitivity of the sensor by adjusting the phase matching condition between the fiber core mode and the surface plasmon polariton mode.

[0020] Compared with the prior art, the present invention provides a high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect, having the following beneficial effects:

[0021] The high-sensitivity methane and temperature dual-parameter detection PCF sensor of the present invention based on the SPR effect combines the SPR technology, the gas-sensing effect of the methane-sensitive material, and the thermo-optical effect of the temperature-sensitive material to achieve the high-precision synchronous detection of dual parameters, overcoming the deficiency of single measurement of traditional fiber optic sensors, and having the advantages of compact structure, anti-electromagnetic interference, stable structure, intrinsic safety, high sensitivity, and multi-parameter synchronous detection. After optimization design, the methane detection range is 0 - 3.5%, the highest sensitivity can reach 68 nm / %, the temperature detection range is 25 - 120 °C, and the maximum temperature sensitivity is 16 nm / °C. It is particularly suitable for the multi-parameter real-time monitoring requirements in harsh industrial environments such as coal mines, providing a more reliable solution for methane leakage monitoring. At the same time, the operation is simple during the experiment, and there is no filling of substances in the internal air holes, which also reduces the manufacturing difficulty and is easy for experimenters to fabricate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the overall structure of the present invention;

[0023] Figure 2 is a front view structure schematic diagram of the present invention;

[0024] Figure 3 Dispersion relationship between the core mode and the SPP mode of the methane gas concentration sensing channel of the sensor of the present invention;

[0025] Figure 4 Dispersion relationship between the core mode and the SPP mode of the temperature sensing channel of the sensor of the present invention;

[0026] Figure 5 Variation of the loss spectrum of the methane concentration sensing channel of the sensor of the present invention with methane concentration;

[0027] Figure 6 Corresponding relationship between the numerical simulation results of the resonance wavelength of the methane gas concentration sensing channel of the sensor of the present invention and methane concentration;

[0028] Figure 7 Variation of the loss spectrum of the temperature sensing channel of the sensor of the present invention with the ambient temperature T;

[0029] Figure 8 Relationship between the numerical simulation results of the resonance wavelength of the ambient temperature T in the temperature sensing channel of the sensor of the present invention and the change of the ambient temperature T;

[0030] Figure 9 Effect of the change of the gold film thickness of the sensor of the present invention on the performance of the sensor;

[0031] Figure 10(a)-10(d) Effect of the air hole radius, air hole spacing and polishing depth of the sensor of the present invention on the performance of the sensor of the present invention;

[0032] Figure 11 Loss spectrum when the temperature T is 40 °C and the methane concentration changes from 0% to 3.5%;

[0033] Figure 12 Loss spectrum when the methane concentration is 0.5% and the temperature T ranges from 25 °C to 120 °C.

[0034] Wherein: 1. Substrate material; 2. Cladding air hole one; 3. Cladding air hole two; 4. Lateral distance between the first layer of cladding air holes two and the core; 5. Methane concentration sensing channel; 6. Temperature sensing channel; 7. Spacing between adjacent cladding air holes two; 8. Spacing between the cladding air hole one and the core; 9. Gold film; 10. Methane sensitive material; 11. Temperature sensitive material. Detailed implementation mode

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] Embodiment 1:

[0037] Please refer to Figure 1-2 , a high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect. The sensor uses photonic crystal fiber as the functionalized optical waveguide medium, and the photonic crystal fiber has a microstructure with periodically arranged air holes and a germanium-doped substrate material.

[0038] The photonic crystal fiber includes a substrate material 1, and the substrate material 1 is germanium-doped silica. Two parallel D-shaped cut surfaces are provided on the outer side of the substrate material 1, and the two D-shaped cut surfaces are symmetrically arranged with respect to the axis of the substrate material 1.

[0039] The cladding of the photonic crystal fiber of the sensor adopts a double-layer air hole array structure. The first layer includes six inner air holes, which are divided into two types of air holes, namely cladding air hole 1 2 and cladding air hole 2 3. The second layer includes ten air holes, and the air hole size is the same as that of cladding air hole 2 3. All cladding air hole 1 2 and cladding air hole 2 3 are rotationally symmetrically distributed with respect to the cylindrical central axis of the substrate material 1.

[0040] Gold films 9 are coated on the surfaces of the two D-shaped cut surfaces to excite the surface plasmon resonance (SPR) effect. After the upper cut surface of the two D-shaped cut surfaces is coated with the gold film 9, a methane-sensitive material 10 for measuring the change in methane concentration is further coated as the methane concentration sensing channel 5, so as to realize the highly sensitive sensing detection of methane concentration. The methane-sensitive material 10 is Cryptophane-A. On the lower cut surface of the two D-shaped cut surfaces, a temperature-sensitive material 11 for measuring the change in the external environmental temperature is further coated on the gold film 9 as the temperature sensing channel 6. The temperature-sensitive material 11 is polydimethylsiloxane (PDMS).

[0041] Among them, the radius of the first cladding air hole 2 is 0.35 μm; the radius of the second cladding air hole 3 is 0.62 - 0.76 μm, preferably 0.62 μm; the spacing 7 between adjacent second cladding air holes 3 is 2.34 - 2.5 μm, preferably 2.5 μm. The thickness of the gold film 9 coated on the D-type section surface is 30 - 50 nm, preferably 50 nm; the spacing 8 between the first cladding air hole 2 and the core is 2.35 - 3.75 μm, preferably 3.75 μm; the lateral distance 4 from the first layer of the second cladding air hole 3 to the core is 2.4 - 2.55 μm, preferably 2.5 μm. The size optimization of the first cladding air hole 2 and the second cladding air hole 3 can improve the detection sensitivity of the sensor by adjusting the phase matching condition between the core mode and the surface plasmon polariton mode.

[0042] During detection, the upper section adsorbs methane molecules through the methane-sensitive material 10, changes the dielectric constant of the gold film 9, and thus modulates the SPR wavelength shift to achieve methane concentration detection; the lower section uses the thermally induced volume expansion effect of the temperature-sensitive material 11 to modulate the surface plasmon resonance condition of the gold film 9. Utilizing the high thermo-optic coefficient and thermal expansion characteristics of polydimethylsiloxane (PDMS), the SPR resonance angle of the gold film 9 is changed by temperature variation, causing a double modulation effect of the refractive index and thickness of PDMS, and achieving highly sensitive sensing detection of the ambient temperature. The D-type double-section structure of the photonic crystal fiber optimizes the evanescent field excitation efficiency respectively. The precise design of the spacing 8 between the first cladding air hole 2 and the core and the lateral distance 4 from the first layer of the second cladding air hole 3 to the core enhances the surface plasmon resonance effect. The physical spatial isolation of the methane-sensitive material 10 and the temperature-sensitive material 11 enables interference-free independent detection of methane concentration and ambient temperature.

[0043] The used photonic crystal fiber body (PCF) adopts germanium-doped silica as the substrate material 1, and its dispersion relation can be calculated by the Sellmeier equation. The equation is as follows:

[0044]

[0045] Where λ represents the incident wavelength in micrometers, A1 = 0.6867178, A2 = 0.4348151, A3 = 0.8956551, B1 = 0.0726752, B2 = 0.1151435, B3 = 10.002389

[0046] The dielectric constant of the gold film coated on the D-type surface is calculated using the Drud-Lorentz model, and its expression is as follows:

[0047]

[0048] In the formula, ε ∞= 5.9673 is the dielectric constant of gold at high frequencies, ω D and γ D are the plasma frequency and the damping frequency respectively, with the values ω D / 2π = 2113.6 THz, γ D / 2π = 15.92 THz. Δε is a weighting factor with a magnitude of 1.09, Γ L and Ω L are the frequency and spectral width of the Lorentz oscillator respectively, with the values Γ L / 2 = 104.86 Hz, Ω L / 2π = 650.07 THz

[0049] Polydimethylsiloxane (PDMS) is a temperature-sensitive material with a high thermo-optic coefficient. The variation relationship between its effective refractive index and temperature is as follows:

[0050] n PDMS = n0 - γΔT

[0051] where n0 = 1.4204 is the effective refractive index of PDMS at 22 °C, γ = -4.66×10 -4 °C -1 is the thermo-optic coefficient, and ΔT is the temperature change.

[0052] The methane-sensitive material 10 coated on the upper side cut surface of the D type is Cryptophane-A.

[0053] Its refractive index is linearly correlated with the methane concentration in the range of 0% - 3.5%. The specific variation relationship formula is as follows:

[0054]

[0055] In the formula, n A represents the refractive index of Cryptophane-A, represents the percentage concentration of methane gas

[0056] The calculation formula for the confinement loss at the core of a photonic crystal fiber (PCF) is as follows:

[0057]

[0058] In the formula, Im(n eff ) represents the imaginary part of the effective refractive index of the core mode.

[0059] Example 2:

[0060] Please refer to Figure 3-12 , when the methane gas concentration is 0.5% and the temperature is 40 °C, the coupling dispersion relationship between the core fundamental mode and the SPP mode is asFigure 3 and Figure 4 as shown

[0061] The schematic diagram of the loss curves of the sensor at different methane concentrations is as Figure 5 shown. Keeping the temperature at 40 °C and only changing the methane concentration, the following technical effects are comprehensively produced, effectively realizing the sensing of methane in the range of 0% - 3.5% concentration. From Figure 5 it can be obtained that the confinement loss basically increases with the decrease of the methane concentration, and the phenomenon of red shift of the resonant wavelength appears. Among them, when the methane concentration changes from 0% to 0.5%, the peak value of the loss peak in the loss spectrum moves 34 nm, and at this time, there is the maximum response sensitivity, and the sensitivity reaches 68 nm / %. The fitting result of the relationship between the resonant wavelength of the measured methane and the methane concentration is as Figure 5 shown, and the fitting degree is 0.99995.

[0062] The confinement loss spectrogram of the sensor at different temperatures is as Figure 7 shown. Under the condition of keeping the methane concentration constant at 0.5%, only changing the temperature, the following technical effects are comprehensively produced: effectively realizing the precise sensing of the temperature range from 25 °C to 120 °C. From Figure 7 it can be seen that the peak value of the confinement loss decreases with the decrease of the temperature, and the phenomenon of red shift of the resonant wavelength appears. At the same time, when the temperature changes from 25 °C to 30 °C, the peak value of the loss in the loss spectrum moves 80 nm, and at this time, the maximum response sensitivity of the temperature sensing is 16 nm / °C, Figure 7 showing the fitting equation of the relationship between the temperature resonant wavelength and the temperature, and the fitting degree is 0.99694.

[0063] Keeping the methane concentration at 0.5% and the temperature at 40 °C unchanged, while changing the thickness of the gold film coated on the upper and lower D-shaped surfaces at the same time, and the change range of the gold film thickness is 30 - 50 nm. Through calculation, the loss spectrogram of the methane concentration and temperature changes can be obtained, as Figure 9 shown. With the increase of the gold film thickness, for temperature detection, the peak value of the confinement loss decreases, and the loss curve gradually blue-shifts. For methane concentration detection, the peak value of the loss curve gradually increases, and the loss curve gradually blue-shifts. If the loss is too high, the energy reaching the detection terminal is too low in the end, which is not conducive to detection. If the loss is too high, the coupling effect between the core mode and the SPP mode is not obvious, which is also not conducive to detection. Considering comprehensively, the thickness of the gold film is finally selected as 40 nm as the gold film thickness of this sensor.

[0064] While keeping the thickness of the gold film coated on the upper and lower D-shaped surfaces at 40 nm, keeping the methane concentration at 0.5% and the temperature at 40 °C unchanged, keeping the radius of the cladding air hole -2 at 0.35 μm, keeping the pitch of the cladding air hole -2 at 2.46 μm, and keeping the polishing depth at 4.6 μm, and only changing the radius of the cladding air hole -2, the following technical effects are comprehensively produced: the variation range of the radius of the cladding air hole -3 is 0.62 μm - 0.70 μm. As can be seen from Figure 10(a), the resonance peaks of the loss spectra of the methane concentration channel and the temperature sensing channel gradually decrease with the increase of the radius of the cladding air hole -3, and a blue shift of the resonance wavelength occurs.

[0065] While keeping the thickness of the gold film coated on the upper and lower D-shaped surfaces at 40 nm, keeping the methane concentration at 0.5% and the temperature at 40 °C unchanged, keeping the radius of the cladding air hole -3 at 0.62 μm, keeping the pitch of the cladding air hole -3 at 2.46 μm, and keeping the polishing depth at 4.6 μm, and only changing the radius of the cladding air hole -2, the following technical effects are comprehensively produced: the variation range of the radius of the cladding air hole -2 is 0.30 μm - 0.50 μm. As can be seen from Figure 10(b), the resonance peaks of the loss spectra of the methane concentration channel and the temperature sensing channel first increase and then decrease with the increase of the radius of the cladding air hole -2, and a blue shift of the resonance wavelength occurs.

[0066] While keeping the thickness of the gold film coated on the upper and lower D-shaped surfaces at 40 nm, keeping the methane concentration at 0.5% and the temperature at 40 °C unchanged, keeping the radius of the cladding air hole -2 at 0.35 μm, keeping the radius of the cladding air hole -3 at 0.62 μm, and keeping the polishing depth at 4.6 μm, and only changing the pitch of the cladding air holes, the following technical effects are comprehensively produced. The variation range of the pitch of the cladding air holes is 2.42 μm - 2.50 μm. As can be seen from Figure 10(c), the resonance peak of the loss spectrum of the methane concentration sensing channel first increases and then decreases with the increase of the pitch of the cladding air holes, while the resonance peak of the loss spectrum of the temperature sensing channel gradually decreases with the increase of the pitch of the cladding air holes, and a blue shift of the resonance wavelength occurs in both cases.

[0067] While keeping the thickness of the gold film coated on the upper and lower D-shaped surfaces at 40 nm, keeping the methane concentration at 0.5% and the temperature at 40 °C unchanged, keeping the radius of the cladding air hole -2 at 0.35 μm, keeping the radius of the cladding air hole -3 at 0.62 μm, and keeping the pitch of the cladding air holes at 2.46 μm, and only changing the polishing depth, the following technical effects are comprehensively produced: the variation range of the polishing depth is 4.40 μm - 4.60 μm. As can be seen from Figure 10(d), the resonance peaks of the loss spectra of the methane concentration channel and the temperature sensing channel both increase with the increase of the polishing depth, and a red shift of the resonance wavelength occurs.

[0068] While maintaining the thickness of the gold film coated on the upper and lower D-shaped surfaces at 40 nm, the radius of the first cladding air hole at 0.35 μm, the radius of the second cladding air hole at 0.62 μm, the cladding air hole spacing at 2.46 μm, and the polishing depth at 4.6 μm, analysis was carried out by controlling a single variable, and the following technical effects were comprehensively generated: As can be seen from Figure 11 that when the temperature is controlled at 40 °C and the methane concentration changes from 0% to 3.5%, the resonant wavelength of the confinement loss spectrum in the temperature sensing channel 6 hardly moves, while the resonant wavelength of the confinement loss spectrum in the methane concentration sensing channel 5 moves with the change of the methane concentration. As can be seen from Figure 12 that when the methane concentration is 0.5% and the temperature changes from 25 °C to 120 °C, the resonant wavelength of the confinement loss spectrum in the methane concentration sensing channel 5 hardly moves, while the resonant wavelength of the confinement loss spectrum in the temperature sensing channel 6 moves with the change of the temperature. It can be seen that there is no mutual crosstalk between the methane concentration sensing channel 5 and the temperature sensing channel 6, and they have good independence.

[0069] In summary, the high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect provided by the present invention has achieved multiple breakthroughs in performance indicators and structural design. The sensor uses a germanium-doped silica photonic crystal fiber with a periodic air hole microstructure as the core element, and D-shaped polished surfaces are symmetrically arranged on the outer side of the fiber. Gold films and functional material layers are deposited on the two polished surfaces respectively. One side is a Cryptophane-A methane-sensitive film, and the other side is a PDMS temperature-sensitive material, constructing a dual-channel independent detection mechanism that can simultaneously sense the methane concentration (CCH4) and temperature (T) without mutual interference. By optimizing the structure of the Cryptophane-A / PDMS composite sensitive film, the sensor can achieve a methane concentration detection range of 0 - 3.5%, with a maximum sensitivity of up to 68 nm / %; the temperature detection range is 25 - 120 °C, and the temperature sensitivity is up to 16 nm / °C. The invention combines the SPR technology, the gas-sensing effect of the methane-sensitive material, and the thermo-optical effect of the temperature-sensitive material to achieve high-precision synchronous detection of dual parameters, and has the advantages of compact structure, anti-electromagnetic interference, stable structure, intrinsic safety, high sensitivity, and multi-parameter synchronous detection. It is especially suitable for the multi-parameter real-time monitoring requirements in harsh industrial environments such as coal mines, providing a more reliable solution for methane leakage monitoring. More importantly, an innovative all-fiber coating process is used to replace complex microstructure processing (such as open-loop microgrooves or anti-resonant tubes), significantly reducing the manufacturing complexity while maintaining high performance. These innovations have achieved simultaneous breakthroughs in the three dimensions of sensitivity, temperature adaptability, and process feasibility. At the same time, the operation is simple during the experiment, and there is no filling of substances in the internal air holes, which also reduces the production difficulty and is easy for experimenters to fabricate.

[0070] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect, characterized in that: The sensor uses a photonic crystal fiber as the functionalized optical waveguide medium, and the photonic crystal fiber has a microstructure with periodically arranged air holes and a germanium-doped substrate material; The photonic crystal fiber includes a substrate material (1), the substrate material (1) is germanium-doped silica, and two parallel D-shaped cut surfaces are provided on the outer side of the substrate material (1), and the two D-shaped cut surfaces are symmetrically arranged with respect to the axis of the substrate material (1); Gold films (9) are coated on the surfaces of the two D-shaped cut surfaces. After the gold films (9) are coated on the upper cut surface of the two D-shaped cut surfaces, a methane-sensitive material (10) for measuring the change in methane concentration is coated as a methane concentration sensing channel (5). On the surface of the lower cut surface of the two D-shaped cut surfaces, a temperature-sensitive material (11) for measuring the change in the external environmental temperature is coated on the gold film (9) as a temperature sensing channel (6); The cladding of the photonic crystal fiber of the sensor adopts a double-layer air hole array structure. The first layer includes six inner air holes, which are divided into two sizes of air holes, namely cladding air hole one (2) and cladding air hole two (3). The second layer includes ten air holes, and the air hole size is the same as that of cladding air hole two (3). All cladding air hole one (2), cladding air hole two (3) and the cylindrical central axis of the substrate material (1) are rotationally symmetrically distributed.

2. The high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect according to claim 1, wherein: The radius of the cladding air hole one (2) is 0.35 μm, the radius of the cladding air hole two (3) is 0.62 - 0.76 μm, and the distance (7) between adjacent cladding air hole two (3) is 2.34 - 2.5 μm; the thickness of the gold film (9) coated on the surface of the D-shaped cut surface is 30 - 50 nm, the distance (8) between the cladding air hole one (2) and the core is 2.35 - 3.75 μm, and the lateral distance (4) between the first-layer cladding air hole two (3) and the core is 2.4 - 2.55 μm.

3. A high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect according to claim 2, characterized in that: The distance from the D-shaped cut surface to the core is 4.6 - 5.5 μm.

4. A high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect according to claim 3, characterized in that: The methane-sensitive material (10) coated on the surface of the upper D-shaped cut surface is Cryptophane-A.

5. A high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect according to claim 4, characterized in that: The temperature-sensitive material (11) coated on the surface of the lower D-shaped cut surface is polydimethylsiloxane.

6. A high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect according to claim 5, characterized in that: The substrate material (1) adopts a double-cut surface structure design, in which a methane-sensitive material (10) is coated on the upper cut surface to excite the SPR effect and couple the methane concentration signal, and a temperature-sensitive material (11) is coated on the lower cut surface to excite the SPR effect and couple the temperature signal, realizing the independent detection of dual parameters.

7. A high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect according to claim 6, characterized in that: The temperature-sensitive material (11) modulates the surface plasmon resonance condition on the surface of the gold film (9) through the thermally induced volume expansion effect, forming a dual-channel structure physically isolated from the methane concentration sensing channel (5), realizing the decoupled detection of temperature and methane concentration.

8. A high-sensitivity methane and temperature dual-parameter detection PCF sensor based on the SPR effect according to claim 7, characterized in that: The size optimization of the cladding air hole one (2) and the cladding air hole two (3) can improve the detection sensitivity of the sensor by adjusting the phase matching condition between the core mode and the surface plasmon polariton mode.

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