Single-groove type photonic crystal fiber sensor based on surface plasma resonance

Abstract

The invention discloses a single-groove type photonic crystal fiber sensor based on surface plasma resonance. The single-groove type photonic crystal fiber sensor structurally comprises a fiber core and a perfect matching layer wrapping the fiber core, and circular air holes which are arranged periodically and are different in size are formed in the fiber core; the fiber core is provided with a groove channel, and the lower surface of the groove channel is coated with a gold film and a titanium dioxide film. A loss spectrum is obtained through calculation, and then the wavelength of the surface plasma formant and the sensitivity of the sensor are calculated. The refractive indexes of the to-be-detected analysis liquid sample are different, and the wavelengths of the resonance peaks of the transmission loss spectrum are also different. The refractive index range of a to-be-detected analysis liquid sample of the sensor is 1.39-1.4, the sensitivity of 11000 nm / RIU and the resolution of 9.09 * 10 <-6 > RIU can be obtained, the sensitivity and the resolution of the sensor are superior to those of an existing sensor, and the sensor is simple in structure and easy to operate and has great application prospects in the fields of biosensing, environmental monitoring and the like.

Description

Technical Field

[0001] The invention belongs to the field of optical fiber sensors, and in particular relates to a surface plasma photonic crystal optical fiber sensor for refractive index sensing. Background Art

[0002] SPR is a physical phenomenon that occurs at the metal-dielectric interface. When light passes from an optically dense medium into an optically rare medium, an evanescent wave is generated under certain conditions. This evanescent wave interacts with the free electrons on the metal surface, exciting a surface plasmon wave (SPW). When the wave vector of the light matches that of the SPW, resonant coupling occurs, causing a sharp decrease in the energy of the reflected light and the appearance of a resonant loss peak in the reflection spectrum. This loss peak is extremely sensitive to changes in the refractive index of the surrounding medium. Even slight changes in the refractive index will cause the loss peak position to shift, and detecting the shift allows for detection of the refractive index. PCF also features periodically arranged air holes, with adjustable structural parameters and flexible design. In SPR-PCF sensors, the unique structure of the PCF can enhance the SPR effect, improving the sensitivity and performance of the sensor.

[0003] The SPR-PCF refractive index sensor boasts high sensitivity, real-time detection, immunity to electromagnetic interference, long-distance measurement capabilities, and ease of miniaturization and integration. It rapidly responds to changes in refractive index and is suitable for complex electromagnetic environments and long-distance measurement scenarios. This sensor has broad applications in biomedical applications, such as detecting biomolecule concentrations; environmental monitoring for water pollutants and harmful air gases; food safety testing for harmful substances such as food additives; and chemical analysis for analyzing the purity of chemical substances. Therefore, improving the sensitivity of the sensor, making it valuable for research in biomedical and environmental monitoring applications, and providing precise detection methods for these applications, remains a long-standing technical challenge in this field. Summary of the Invention

[0004] The present invention addresses the shortcomings of existing photonic crystal fiber technologies and provides a single-groove photonic crystal fiber sensor based on surface plasmon resonance. Unlike conventional PCF structures, the SPR effect stimulated by the present invention is stimulated by coating the lower surface of the groove channel with a gold film and a titanium dioxide film, which can effectively enhance the resonance effect and make the SPR more sensitive to changes in the solution being measured.

[0005] The technical solution adopted in the present invention is:

[0006] A single-groove photonic crystal fiber sensor based on surface plasmon resonance includes a fiber core and a perfectly matched layer covering the outside of the fiber core. The fiber core is provided with periodically arranged circular air holes of different sizes. The fiber core is provided with a groove channel, and the lower surface of the groove channel is coated with a gold film layer and a titanium dioxide film layer.

[0007] In the above solution, the material of the fiber core is fused silica with a refractive index n=1.45.

[0008] In the above solution, the radius of the perfect matching layer is r pml =7um; the radius of the fiber core is r0=5.5um.

[0009] In the above solution, the analyte layer is located between the core and the perfect matching layer, and the radius of the analyte layer is r bio =6um.

[0010] In the above scheme, the circular air holes are distributed in the fiber core, the period between the large circular air holes is Λ=2um, the period between the small circular air holes and the distance between the small circular air holes and the center of the fiber core are both Λ s =1.75um.

[0011] In the above scheme, the large circular air holes are arranged in a hexagonal array, and the air refractive index n of the large circular air holes is air =1, aperture size d = 1.55um; the small circular air hole is located below the groove channel, and the air refractive index n of the small circular air hole is air =1, aperture size d s =0.7um.

[0012] In the above solution, the depth of the groove channel is H=2.8um, and the width of the groove channel is d w =2.1um.

[0013] In the above solution, the thickness of the gold film coated on the lower surface of the groove channel is t Au =30nm, the thickness of the titanium dioxide film coated on the gold film is t Tio2 =11nm.

[0014] In the above solution, the refractive index of the solution to be tested in the analyte layer ranges from 1.39 to 1.4.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) By adding two small circular air holes of the same size in the inner layer of the core, the coupling direction of the core mode and the SPP mode is guided. The presence of the small circular air holes reduces the n of the core mode. eff , which improves the coupling degree between the core mode and the SPP mode.

[0017] (2) By coating the lower surface of the groove channel with gold film and titanium dioxide film, the coupling result between the core mode and the SPP mode is improved.

[0018] (3) Through the single groove structure design, under the action of Y polarization, the refractive index range of the medium to be measured is 1.39 to 1.4, the maximum wavelength sensitivity is 11000nm / RIU, and the maximum resolution is 9.09×10 -6 RIU. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic cross-sectional view of an embodiment of the present invention.

[0020] Figure 2 4 is a mode field distribution diagram of the fundamental mode according to an embodiment of the present invention.

[0021] Figure 3 4 is a mode field distribution diagram of the SPP mode according to an embodiment of the present invention.

[0022] Figure 4 is a mode field distribution diagram at the phase matching point in an embodiment of the present invention.

[0023] Figure 5 This is a loss diagram when the refractive index of the analyte changes from 1.39 to 1.4 in an embodiment of the present invention.

[0024] Explanation of the accompanying figures: 1. groove channel; 2. titanium dioxide film layer; 3. gold film layer; 4. small circular air hole; 5. large circular air hole; 6. perfectly matched layer; 7. analyte layer; 8. cladding. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific examples.

[0026] like Figure 1 Figure 2 shows a schematic diagram of the two-dimensional interface structure of a single-groove photonic crystal fiber sensor based on surface plasmon resonance. The core material is fused silica with a refractive index of n = 1.45, and the radius of the perfect matching layer is r pml =7um, the radius of the fiber core is r0=5.5um, the period between the large circular air holes is Λ=2um, the period between the small circular air holes and the distance between the small circular air holes and the center of the fiber core are both Λ s =1.75um. The large circular air holes are arranged in a hexagonal array. The refractive index of the air in the large circular air holes is n air =1, aperture size d = 1.55um; the small circular air hole is located below the groove channel, and the air refractive index n of the small circular air hole is air =1, aperture size ds = 0.7um. The depth of the groove channel H = 2.8um, the width of the groove channel d w =2.1um.

[0027] By coating the groove channel with a film thickness of tAu =30nm gold film layer and film thickness t Tio2 =11nm titanium dioxide film layer for excitation, which can enhance the resonance effect and make SPR more sensitive to changes in the analyte solution.

[0028] like Figure 4 As shown in Figure 1, when the phase matching condition is met, the energy in the fiber core couples to the plasma on the metal surface, causing the core energy to decrease. The excitation of the surface plasmon at this point can be characterized by calculating the confinement loss of the core mode. The wavelength corresponding to this point is the resonant wavelength.

[0029] like Figure 5 As shown in the figure, when the refractive index of the measured liquid changes from 1.39 to 1.4, the resonance loss peak shifts toward longer wavelengths as the refractive index increases, red-shifting and decreasing. When the refractive index of the measured liquid changes by Δn = 0.01, the loss absorption peak shifts by Δλ. The sensitivity S and resolution R of the sensor can be calculated by calculation.

[0030] Depend on Figure 5 It can be seen that the position of the loss absorption peak changes by Δλ = 110 nm. The calculated sensitivity S = 11000 nm / RIU corresponds to a resolution R = 9.09 × 10 -6 RIU.

Claims

1. A single-groove photonic crystal fiber sensor based on surface plasmon resonance, characterized by: Its structure includes a fiber core and a perfectly matched layer covering the outside of the fiber core. The fiber core is provided with periodically arranged circular air holes of different sizes. The fiber core is provided with a groove channel, and the lower surface of the groove channel is coated with a gold film and a titanium dioxide film.

2. A single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 1, characterized in that: The material of the fiber core is fused silica with a refractive index n=1.

45.

3. The single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 1, characterized in that: The radius of the perfectly matched layer is r pml =7um; the radius of the fiber core is r0=5.5um.

4. The single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 1, characterized in that: The analyte layer is located between the core and the perfect matching layer, and the radius of the analyte layer is r bio =6um.

5. The single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 1, characterized in that: The circular air holes include 16 large circular air holes and 2 small circular air holes, and the circular air holes are symmetrically distributed in the fiber core; the period between the large circular air holes is Λ=2um, the period between the small circular air holes and the distance between the small circular air holes and the center of the fiber core is Λ s =1.75um.

6. The single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 5, characterized in that: The large circular air holes are arranged in a hexagonal array, and the air refractive index n of the large circular air holes is air =1, aperture size d = 1.55um; the small circular air hole is located below the groove channel, and the air refractive index n of the small circular air hole is air =1, aperture size d s =0.7um.

7. The single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 1, characterized in that: The depth of the groove channel is H=2.8um, and the width of the groove channel is d w =2.1um.

8. The single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 1, characterized in that: The thickness of the gold film coated on the lower surface of the groove channel is t Au =30nm, the thickness of the titanium dioxide film coated on the gold film layer is t Tio2 =11nm.

9. The single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 1, characterized in that: The refractive index of the solution to be tested in the analyte layer ranges from 1.39 to 1.

4.

10. The single-groove photonic crystal fiber sensor based on surface plasmon resonance according to claim 1, characterized in that: The gold film layer and the titanium dioxide film layer generate surface plasmon resonance under the action of Y polarization, which is used to detect the refractive index of the analyte to be measured.

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