Composite membrane pqf-spr methane sensor based on double-core structure

Abstract

The application relates to an optical fiber methane sensor, in particular to a composite film PQF-SPR methane sensor based on a double-core structure, wherein air holes arranged according to an eight-fold Penrose photonic quasicrystal structure are arranged in the cladding of the optical fiber, the first layer, the second layer and the fourth layer are small air holes, two small air holes of the second layer are located on the X axis, and the layer has two hole positions without air holes on the Y axis, which are the cores; two air holes of the third layer, which are located above and below the cores on the positive and negative half axes of the Y axis, are large air holes; two planes perpendicular to the Y axis are polished and ground on the cladding of the air holes of the fourth layer, a semicircular hole groove is formed on the plane located on the Y axis; a zinc oxide film and a gold film are plated in the hole groove, and a methane sensitive thin film is coated on the surface of the gold film and the plane. The sensor has high sensitivity in a measurement range, the sensor structure is simple, the inside of the optical fiber does not need to be sensed, the film plating difficulty is reduced, and the sensor is beneficial to processing.

Description

TECHNICAL FIELD

[0001] The application relates to an optical fiber methane sensor, in particular to a ZnO-Au composite film PQF-SPR methane sensor based on a double-core structure. BACKGROUND

[0002] At present, common methane sensors mainly include catalytic combustion type, thermal conductivity type of the electrical type, and absorption spectroscopy type and optical fiber sensing type of the optical type. The catalytic combustion type and the thermal conductivity type of the electrical type have a relatively high working temperature and high loss, and are difficult to achieve full coverage monitoring of the dangerous area in the mine and other special environments. The absorption spectroscopy type methane sensor is more suitable for remote measurement of methane in open environments, while the optical fiber methane sensor has the advantages of simple structure, small size and anti-electromagnetic interference, and is more suitable for working in harsh environments, and has great application potential. The existing optical fiber methane sensors mainly include microstructure optical fiber absorption spectroscopy type sensors, interference type sensors, long period fiber grating methane sensors and optical fiber surface plasmon resonance (SPR) methane sensors. Among the above optical fiber methane sensors, the optical fiber SPR technology has high sensitivity to environmental refractive index measurement, and the change of the refractive index of the methane sensitive material with the methane concentration can realize the detection of the methane concentration.

[0003] Surface plasmon resonance (SPR) is a special physical phenomenon caused by the joint action of surface plasmon wave (SPW) and evanescent wave. When light is incident from the core to the cladding and total reflection occurs, most of the light is reflected back to the dense medium, and part of the light penetrates into the metal film and generates evanescent wave. Surface plasmon wave is a kind of electromagnetic wave formed by collective oscillation of free electrons in metal. When the evanescent wave and the surface plasmon wave satisfy the phase matching condition in the wave vector component parallel to the interface, resonance phenomenon occurs, at this time, the energy of the evanescent wave and the surface plasmon polaritons (SPPs) is completely or incompletely coupled, and then the energy loss of reflected light wave occurs, the light intensity is weakened, and a trough is formed in the reflection spectrum. Surface plasmon polaritons are a new type of meta-excitation quasi-particles, which have unique dispersion and local field enhancement characteristics. SPPs devices break the traditional optical diffraction limit and have unique advantages in nanophotonic devices.

[0004] The air hole arrangement of the photonic quasi-crystal fiber (PQF) has no periodicity but long-range order, and has higher stiffness and elasticity than ordinary optical fibers and photonic crystal fibers. The photonic quasi-crystal fiber (PQF-SPR) sensor based on surface plasmon resonance has the advantages of small volume, high resolution, high sensitivity, low loss, easy coupling, etc., and has wide application prospects in many fields such as biology, chemistry, environment, medicine, etc.

[0005] In 2020, Hossain et al. disclosed a photonic crystal fiber methane gas sensor coated in the envelope hole, with a sensitivity of 1.078 nm / %. However, it is difficult to inject methane gas into the PCF; in 2023, Liu Hai et al. disclosed a PCF sensor based on tellurite as a substrate, which relies on four-wave mixing (FWM) and SPR, and simultaneously measures the concentration of hydrogen and methane, with the maximum sensitivity of methane and hydrogen reaching 4.03 nm / % and -14.19 nm / %, respectively; in 2024, Xiao et al. disclosed an SPR gas sensor of an anchor-shaped photonic crystal fiber, with an average sensitivity of -4.84 nm / % for methane. However, the existing similar sensors all use a single metal to excite SPR, and the sensitivity is not ideal. Changing the plasmonic material can adjust the excitation of evanescent waves on the plasmonic wave, and different materials have obvious differences in the peak value and line width of the loss spectrum when meeting the surface plasmon resonance condition, and mixing and coating the noble metal with the metal oxide can improve the sensitivity of the sensor. SUMMARY

[0006] To solve the above technical problems, the present application provides a double-core structure composite film PQF-SPR methane sensor, which makes up for and improves the shortcomings of the prior art. The sensor has high sensitivity in the measurement range. The sensor uses PQF to construct a double-core D-shaped structure, and uses ZnO-Au composite film coated in the hole groove to excite SPR, enhances the surface plasmon resonance effect, and improves the detection sensitivity of the sensor. The sensor structure is simple, does not need to be sensed in the optical fiber, reduces the difficulty of coating, and is beneficial to processing.

[0007] The technical scheme adopted by the present application is: a composite film PQF-SPR methane sensor based on a double-core structure, the double-core structure composite film PQF-SPR methane sensor is a photonic quasicrystal fiber, the cladding of the fiber is provided with four layers of air holes arranged according to an eight-fold Penrose type photonic quasicrystal structure, wherein the first layer, the second layer and the fourth layer are small air holes, two small air holes of the second layer are located on the X-axis, and the two hole positions without air holes on the Y-axis of this layer are cores; two air holes of the third layer, which are located above the core on the positive half axis of the Y-axis, are large air holes, two air holes of the third layer, which are located below the core on the negative half axis of the Y-axis, are large air holes, and the remaining four air holes of the third layer are small air holes; two planes perpendicular to the Y-axis are polished on the cladding of the fourth layer air hole, forming a fiber with a D-shaped plane structure, a semicircular hole groove is opened on the plane located on the Y-axis, and there is no air hole on both sides of the semicircular hole groove, that is, there is no fourth layer air hole in the horizontal direction passing through the center of the semicircular hole groove; a zinc oxide film and a gold film are plated in the semicircular hole groove, and a methane sensitive film is coated on the surface of the gold film and the plane.

[0008] The radius of the photonic quasicrystal fiber is 9 μm, the lattice constant is 3 μm, the diameter of the large air hole is 2.5 μm, the diameter of the small air hole is 2.1 μm, the radius of the semicircular hole groove is 1.075 μm, the width between the two planes is 14 μm, the thickness of the zinc oxide film is 10 nm, the thickness of the gold film is 27 nm, and the thickness of the methane sensitive film is 500 nm. L Further, the methane sensitive film is prepared from Cryptophane E and polysiloxane.

[0009] Further, the material of the photonic quasicrystal fiber is silica.

[0010] Further, the eight-fold Penrose type photonic quasicrystal structure is a scatterer from the first layer to the fourth layer.

[0011] Further, the cladding of the photonic quasicrystal fiber is composed of four layers of air holes arranged according to an eight-fold Penrose type quasicrystal structure, and six air holes of the second layer are removed to form a symmetric double-core structure. Meanwhile, four air holes of the fourth layer are removed and polished into a D-shaped structure, the diameters of the air holes above and below the core are enlarged to constrain the core mode, and the diameters of the remaining air holes are the same; a zinc oxide film and a gold film are sequentially plated in the semicircular hole groove after polishing, and finally a methane sensitive layer is coated on the D-shaped plane, so that the ZnO-Au composite film can better excite SPR, the sensitive layer has good adsorption and resolution, the sensitivity and FOM of the sensor can be improved, and the performance of the sensor can be improved.

[0012]

[0013] ​Further, the working wavelength of the methane sensor is in the near-infrared short-wave region, when the methane concentration to be measured changes, the refractive index of the corresponding sensitive film will change, thereby changing the resonance strength of the surface plasmon, and the position of the resonance peak will also change, and the concentration of methane is obtained by measuring the position change of the resonance peak.

[0014] The methane sensor of the application has the advantages that: the methane sensor can monitor in real time and has high sensitivity; compared with the previous sensor, the composite metal layer is used to excite SPR, which can not only reduce the half-width of the loss spectrum, but also significantly improve the FOM and the sensitivity of the sensor as a whole; the distance between the fiber core and the metal film is reduced by using the groove channel on the D-shaped plane of the optical fiber, and the surface plasmon resonance effect is effectively enhanced, so that the methane gas measurement with high sensitivity can be realized; the sensor is formed into a D shape by polishing the outer surface of the optical fiber, a semicircular hole groove channel is designed, a ZnO film and a gold film are coated in the hole groove channel in sequence to excite SPR, and a methane sensitive material is coated on the D-shaped plane outside the gold film to detect the methane gas.

[0015] (1) The methane sensor uses external channel sensing, has simple structure, is easy to manufacture, and can realize miniaturization of the sensor.

[0016] (2) The methane sensor uses ZnO-Au composite film as the plasmonic material to excite SPR, which enhances the SPR effect and improves the sensitivity of the sensor.

[0017] (3) The methane sensor designs a semicircular hole groove channel on the external D-shaped plane and a D-shaped channel inside the optical fiber, the D-shaped channel is used to contact the gas to be measured with the outer surface of the optical fiber, and the distance between the fiber core and the ZnO-Au composite film is reduced, which promotes the coupling strength of the optical fiber sensor.

[0018] (4) The methane sensor coats the ZnO-Au composite film and the methane sensitive material on the outer surface of the optical fiber, which directly contacts the gas to be measured, and reduces the detection difficulty.

[0019] (5) The sensitivity of the methane sensor is as high as 64 nm / % when the concentration of the methane to be measured is 0%-3.5%, and the average wavelength sensitivity can reach 41.43 nm / %. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a schematic view of the cross section of the photonic quasicrystal fiber;

[0021] Figure 2 is a schematic view of the arrangement of air holes in the cladding of the photonic quasicrystal fiber;

[0022] Figure 3 is a basic structural unit diagram of the eight-fold Penrose type quasicrystal structure.

[0023] Figure 4 is the Y-polarization confinement loss spectrum and the electric field distribution of the photonic quasicrystal fiber sensor (confinement loss spectrum when the methane concentration is 0.5%);

[0024] Figure 5 is the loss spectrum of the fundamental mode of the photonic quasicrystal fiber sensor at different methane concentrations (confinement loss spectrum when the methane concentration is 0%-3.5%);

[0025] Figure 6 is the relationship between the methane concentration and the resonance wavelength shift of the photonic quasicrystal fiber sensor (methane concentration is 0%-3.5%);

[0026] Figure 7 is the loss spectrum of the photonic quasicrystal fiber sensor at different air hole diameters d 2 (large air hole) (confinement loss spectrum when the methane concentration is 0% and 0.5%);

[0027] Figure 8 is the resonance wavelength and sensitivity diagram of the photonic quasicrystal fiber sensor under different air hole diameters d 2 (large air hole) (resonance wavelength and sensitivity when the methane concentration is 0% and 0.5%);

[0028] Figure 9 is the loss spectrum of the photonic quasicrystal fiber sensor at different semicircular hole slot radii r (confinement loss spectrum when the methane concentration is 0% and 0.5%);

[0029] Figure 10 is the resonance wavelength and sensitivity diagram of the photonic quasicrystal fiber sensor under different semicircular hole slot radii r (confinement loss spectrum when the methane concentration is 0% and 0.5%);

[0030] Figure 11 is the loss spectrum of the photonic quasicrystal fiber sensor at different air hole diameters d 1 (small air hole) (confinement loss spectrum when the methane concentration is 0% and 0.5%);

[0031] Figure 12 is the resonance wavelength and sensitivity diagram of the photonic quasicrystal fiber sensor under different air hole diameters d 1 (small air hole) (resonance wavelength and sensitivity when the methane concentration is 0% and 0.5%);

[0032] Figure 13 is the loss spectrum of the photonic quasicrystal fiber sensor at different air hole diameters t Au (confinement loss spectrum when the methane concentration is 0% and 0.5%).

[0033] Figure 14 It is a photonic quasi-crystal fiber optic sensor with different air hole diameters t Au Resonance wavelength and sensitivity plots (resonance wavelength and sensitivity at methane concentrations of 0% and 0.5%).

[0034] Figure 15 Different air hole diameters in photonic quasi-crystal fiber optic sensors t ZnO Loss spectra at methane concentrations of 0% and 0.5% (limited loss spectra).

[0035] Figure 16 It is a photonic quasi-crystal fiber optic sensor with different air hole diameters t ZnO Resonance wavelength and sensitivity plots (resonance wavelength and sensitivity at methane concentrations of 0% and 0.5%). Detailed Implementation

[0036] Referring to the figures, a composite film PQF-SPR methane sensor based on a dual-core structure is described. The dual-core composite film PQF-SPR methane sensor is a photonic quasi-crystal fiber, and the cladding of the fiber contains an eight-fold Penrose fiber. The optical fiber has four layers of air holes arranged in a D-shaped photonic quasi-crystalline structure. The first, second, and fourth layers are small air holes 4. The two small air holes in the second layer are located on the X-axis, and the two holes in this layer without air holes on the Y-axis are the fiber core 1. In the third layer, the two air holes above the fiber core on the positive Y-axis are large air holes 3, and the two air holes below the fiber core on the negative Y-axis are large air holes 3. The remaining four air holes in the third layer are small air holes 4. The cladding of the fourth layer of air holes is polished with two planes 6 perpendicular to the Y-axis, forming an optical fiber with a D-shaped planar structure. A semi-circular slot 5 is opened on the plane on the Y-axis. There are no air holes on both sides of the semi-circular slot 5, that is, there are no fourth layer air holes in the horizontal direction passing through the center of the semi-circular slot. The semi-circular slot 5 is coated with a zinc oxide film 7 and a gold film 8. The surface of the gold film 7 and the plane 6 are coated with a methane-sensitive film 9.

[0037] The photonic quasi-crystal fiber has a radius of 9 μm and a lattice constant of [missing information]. L The diameter of the large air hole 3 is 3μm. d 2 is 2.5μm, small air pore diameter 4 d 1 is 2.1 μm, the radius of the semi-circular groove. r The thickness is 1.075 μm; the width between the two planes 6 is 14 μm; the thickness of the zinc oxide film 7 is... t ZnO The thickness of the gold film 8 is 10nm. tAu is 27 nm, the thickness of the methane-sensitive thin film 9 t_CH 4 is 500 nm.

[0038] Figure 1 is a cross-sectional view of a methane sensor based on photonic quasicrystal fiber SPR, the scattering sub of the whole structure is arranged in an eight-fold Penrose type photonic quasicrystal structure, which is composed of squares and rhombuses with inner angles of 45° and 135°, as shown in the structural schematic diagram of Figure 2 and Figure 3 . The spacing (lattice constant) between adjacent air holes in the quasicrystal structure L is 3 μm, in which four large air holes in the third layer are used to limit the energy leakage. The background material of the optical fiber is silica, the refractive index of which is determined by the Sellmeier equation, and the refractive index of air is 1. The optical fiber is a refractive index guided photonic quasicrystal fiber.

[0039] The optical fiber is coated with a zinc oxide film and a gold film in the semicircular hole groove of the D plane, respectively, and then a methane-sensitive film is coated on the D surface outside the gold film. When the incident light wave passes through the optical fiber and irradiates on the metal film, the free electrons in the metal film undergo collective oscillation under the action of the electric field of the light wave, forming surface plasmon waves. When certain specific conditions (such as angle, wavelength or polarization state) of the incident light wave are met, the surface plasmon waves resonate with the incident light waves, resulting in a significant decrease in the absorption intensity of the reflected light. The loss spectrum can be drawn through the relationship between energy absorption and wavelength. This resonance phenomenon is very sensitive to the small changes in the dielectric constant of the substance outside the metal film. The refractive index of the methane gas-sensitive film coated on the D surface will change with the change of the concentration of the gas to be measured, thus affecting the resonance intensity and resonance wavelength to a certain extent, and the resonance peak will shift. By observing the shift of the loss peak of the sensor, the concentration of the gas to be measured can be detected, thereby achieving the purpose of detection.

[0040] In the detection of methane concentration, Cryptophane E is selected as the gas-sensitive material, which has physical and chemical properties that match methane molecules and can effectively adsorb methane molecules. Moreover, Cryptophane E has a special cage-like molecular structure, which forms a large hollow space inside, thereby having a high surface area to adsorb methane molecules. This adsorption process is reversible, and Cryptophane E can quickly respond and adjust its adsorption state when the methane concentration changes. Therefore, the unique cage-like molecular structure of Cryptophane E, its high selectivity and adsorption capacity for methane molecules make it have unique advantages in methane detection.

[0041] The composite film PQF-SPR methane sensor uses a methane-sensitive film prepared from Cryptophane E and polysiloxane, and the refractive index of the sensitive filmn The relationship between the methane gas concentration and the transmission loss is linear, and the relationship is n =1.448-0.0046 C_CH 4, wherein C_CH 4 represents the methane gas concentration. A simulation software is used to establish a model of the sensor, and the effective refractive index of the fundamental mode at a certain wavelength is obtained through simulation. The effective refractive index is a complex number. The sensor structure is optimized to obtain an optimal structure d 1 =2.1 μm ，d 2 =2.5 μm ，r =1.075 μm ，R =9 μm ,Λ =3 μm ，t CH4 =500 nm. When the methane concentration is 0.5%, the restriction loss spectrum and the real part of the effective refractive index of the fundamental mode and the SPP mode are as shown in Figure 4 At a wavelength of 856 nm, the real part of the effective refractive index of the fundamental mode and the SPP mode intersects, and the resonance is the strongest at this point, corresponding to the peak value of the restriction loss.

[0042] The transmission loss can be calculated by using the imaginary part of the effective mode refractive index:

[0043]

[0044] wherein, λ is the incident wavelength, in micrometers, and Im( n eff ) is the imaginary part of the effective refractive index of the fundamental mode. The restriction loss spectrum of methane and hydrogen in the concentration range of 0%-3.5% can be obtained by using the formula, as shown in Figure 5 When the concentration of methane increases, the resonance peak is blue-shifted. The relationship between the gas concentration and the resonance wavelength can be obtained by linear fitting the resonance wavelength of methane, as shown in Figure 6 When detecting the concentration of methane gas, only the resonance wavelength at the gas concentration needs to be detected, and the corresponding gas concentration value can be obtained.

[0045] The sensitivity of the sensor can be obtained by the following formula:

[0046]

[0047] wherein, Δλ peak is the difference of the resonance wavelength, and ΔC_gas is the difference of the concentration of the gas to be detected. The sensitivity of the sensor isFigure 6 The data and the formula show that the sensor's maximum methane sensitivity is 64 nm / .

[0048] (1) Large air hole d 2 Semi-circular groove r Small air holes d 1 The effect of aperture on fiber optic sensing performance

[0049] By increasing the methane concentration from 0% to 0.5% and keeping other structural parameters constant, different large air hole diameters were obtained. d Loss spectrum at 2, such as Figure 7 As shown. It can be seen that when d When 2 varies between 2.4 and 2.6, as d As the value increases by 2, the resonant wavelength exhibits a blue shift, and the loss peak gradually decreases. This is because... d The increase of 2 leads to a decrease in the effective refractive index of the core mode, so the phase matching point shifts towards shorter wavelengths, i.e., the loss peak undergoes a blue shift. Simultaneously... d The increase of 2 enhances the confinement of the core mode, which weakens the coupling between the core mode and the SPP mode, thus reducing the loss spectrum. Figure 8 Different d The resonant peak wavelength and wavelength sensitivity at 2°C are visible. d 2 has a relatively small impact on wavelength sensitivity, but... d The sensitivity is highest when 2 = 2.5 μm, which is taken as the optimal value. Figure 9 The radius of the semi-circular groove for coating metal material r The loss spectrum increases from 1.0 μm to 1.1 μm. The figure shows that when... r As the wavelength gradually increases, the loss spectrum shifts towards longer wavelengths, and the loss peak increases. This is mainly because when... r As the distance increases, the distance between the metal layer and the core mode decreases, enhancing the transfer of the core mode field from the core to the cladding, thus leading to an increase in the peak loss. The core mode is also more easily coupled with the SPP mode, enhancing the SPR effect. For example... Figure 10 For methane concentration increasing from 0% to 0.5%, the peak wavelength and wavelength sensitivity at different radii are calculated. r The wavelength sensitivity reaches its maximum at 1.075 μm. Similarly, the sensitivity of small air holes was analyzed. d 1. Impact on sensor performance, such as Figure 11 As shown, when d 1. When the wavelength increases from 2.0 μm to 2.2 μm, the resonant wavelength exhibits a redshift trend, and the loss peak gradually increases. This is because... dThe increase of 1 enhances the extrusion to the Y direction mode field, and hinders the leakage of X direction energy. It makes the fiber core more energy coupled with SPP mode along the Y polarization direction. Figure 12 The effects of different d The wavelength sensitivity of the fiber sensor with 1 increased from 0 to 0.5% when the methane concentration increased from 0 to 0.5%, and the sensitivity first increased and then decreased with the increase of 1, and the sensitivity reached the maximum when 1=2.1 μm. d The wavelength sensitivity of the fiber sensor with 1 increased from 0 to 0.5% when the methane concentration increased from 0 to 0.5%, and the sensitivity first increased and then decreased with the increase of 1, and the sensitivity reached the maximum when 1=2.1 μm. d The wavelength sensitivity of the fiber sensor with 1 increased from 0 to 0.5% when the methane concentration increased from 0 to 0.5%, and the sensitivity first increased and then decreased with the increase of 1, and the sensitivity reached the maximum when 1=2.1 μm.

[0050] (2) The thickness of zinc oxide film t ZnO and the thickness of gold film t Au The effect of the change of the thickness of gold film on the fiber sensor

[0051] For surface plasmon resonance sensor, the thickness of the film directly determines the performance of the sensor. When the sensor structure parameters are r =1.075 μm, R =9 μm, Λ =3 μm, d 1=2.1 μm, d 2=2.5 μm, t ZnO =10 nm, t_CH 4=500 nm, the loss spectrum of different gold film thickness when the concentration of the measured gas methane is 0% and 0.5% is shown in Figure 13 The loss spectrum is red-shifted with the increase of the thickness of gold film, because the effective refractive index of SPP mode increases with the increase of the thickness of gold film, while the effective refractive index of the fiber core mode is almost unchanged, resulting in the phase matching point moving to the long wavelength direction. The resonance wavelength and sensitivity under different gold film thickness are shown in Figure 14 It can be seen that with the increase of the thickness of gold film, the wavelength sensitivity first increases and then decreases, because with the increase of the thickness, the evanescent wave is difficult to penetrate the thicker metal layer, resulting in a decrease in sensitivity, and when t Au =27 nm, the wavelength sensitivity is the maximum. Similarly, when the thickness of gold film is fixed at 27 nm, Figure 15 the loss spectrum of different thickness of zinc oxide film. When t ZnO from 6 nm to 14 nm, the phase matching point of the fiber core mode and the SPP mode is changed, resulting in a blue shift of the loss spectrum. The resonance wavelength and sensitivity under different thickness of zinc oxide film are shown in Figure 16 when t ZnO =10 nm, the sensitivity shows the best value, reaching the maximum of 64 nm / %.

[0052] Through simulation and calculation,d 1 = 2.1 μm ，d 2 = 2.5 μm ，r = 1.075 μm ，R = 9 μm ,Λ = 3 μm ，t Au = 27 nm, t ZnO = 10 nm, t CH4 = 500 nm is set as the optimal structure parameter. In the range of 0%-3.5% of the concentration of the to-be-detected gas methane, the sensor can obtain the maximum sensitivity of 64 nm / % of methane.

[0053] The methane sensor is plated with ZnO-Au composite film in the semicircular hole groove of the D plane of the optical fiber, for exciting surface plasmon, and the excitation effect is better than that of the previous single metal. The semicircular hole groove sensing channel not only can realize the external sensing of the optical fiber, but also can enhance the SPR effect by shortening the distance between the two modes. The coating of the methane sensitive layer has good selectivity and adsorption for the detected gas; the methane sensor is relatively easy to manufacture in structure, and realizes high sensitivity through the structure design and the use of the new composite material.

[0054] The above is the further detailed description of the present application in combination with the specific embodiments, and the present application cannot be limited to the above specific embodiments. Without departing from the overall idea of the present application and the protection of the claims, a number of simple deductions or replacements can also be made, which should be regarded as belonging to the protection scope of the present application.

Claims

1. A composite film PQF-SPR methane sensor based on a double-core structure, characterized by: The methane sensor of the double-core structure composite film PQF-SPR is a photonic quasicrystal fiber, the cladding of the fiber is provided with four layers of air holes arranged according to an eight-fold Penrose type photonic quasicrystal structure, wherein the first layer, the second layer and the fourth layer are small air holes (4), two small air holes of the second layer are located on the X-axis, and the two hole positions of the layer without air holes on the Y-axis are cores (1); two air holes of the third layer, which are located above the core on the positive half-axis of the Y-axis, are large air holes (3), two air holes of the third layer, which are located below the core on the negative half-axis of the Y-axis, are large air holes (3), and the remaining four air holes of the third layer are small air holes (4); the cladding of the fourth layer of air holes is polished to have two planes (6) perpendicular to the Y-axis, a semicircular hole groove (5) is opened on the plane located on the Y-axis, and there is no air hole on both sides of the semicircular hole groove (5); the semicircular hole groove (5) is plated with a zinc oxide film (7) and a gold film (8), and the surface of the gold film (8) and the plane (6) are coated with a methane sensitive thin film (9); The photonic quasi-crystal fiber has a radius of 9 μm and a lattice constant of [missing information]. L The diameter of the large air hole (3) is 2.5 μm, the diameter of the small air hole (4) is 2.1 μm, and the radius of the semi-circular groove is 1.075 μm; the width between the two planes (6) is 14 μm; the thickness of the zinc oxide film (7) is 10 nm, the thickness of the gold film (8) is 27 nm, and the thickness of the methane sensitive film (9) is 500 nm.

2. The composite film PQF-SPR methane sensor based on a dual-core structure according to claim 1, characterized in that: The methane sensitive thin film (9) is prepared from Cryptophane E and polysiloxane.

3. The dual-core structure based composite film PQF-SPR methane sensor according to claim 1, wherein: The material of the photonic quasicrystal fiber is silicon dioxide.

4. The dual-core structure based composite film PQF-SPR methane sensor according to claim 1, wherein: The eight-fold Penrose type photonic quasicrystal structure is a scatterer from the first layer to the fourth layer.

Images