| Special optical fiber is an optical fiber with special performance and purpose that is different from the international communication standard optical fiber.Its material doping,structural design,process,transmission wavelength,optical performance,mechanical and environmental performance are all special and can be used in communication,sensing,electricity,petrochemical,military and other fields.The photonic crystal fiber and Solid-core fiber involved in the research of this article belong to the category of special fiber.Combining special optical fiber with surface plasmon resonance(SPR)technology can not only get a real-time telemetry sensor with high sensitivity,wide detection range,small size and easy integration,but also can get polarization filter with high extinction ratio,small size,and easy to integrate with Modern Communicate System.Based on the theory of optical waveguide and surface plasmon resonance,a photonic crystal fiber polarization filter with double-layer metal coating based on the SPR effect is designed in this paper.The outer surface of the Solid-core fiber is coated with a double-layer metal film to achieve a liquid refractive index sensor based on SPR effect.The introduction of the double-layer metal film can adjust or enhance the SPR effect and further improve the performance of the polarization filter and sensor.The main research work of this paper is as follows:First,the basic principles of evanescent wave transmission and SPR in optical fiber are given,a double-layer metal film model is proposed and the characteristics of SPR effect excitation are analyzed,It laid a theoretical foundation for the research of double-layer metal film photonic crystal fiber polarization filter and Solid-core fiber refractive index sensor based on the SPR effect.Secondly,a silver-gold double-layer metal film photonic crystal fiber polarization filter based on the SPR effect is designed.The introduction of the double-layer metal film can not only enhance the SPR effect but also adjust the wavelength corresponding to the resonance peak.In the case of keeping the structural parameters such as hole spacing and diameter,the performance of the polarization filter can be optimized only by adjusting the parameters of the double-layer metal film in the pores.Numerical simulation results show that only by changing the thickness of the double-layer metal film,the filter can achieve dual-channel filtering in the x-polarization and y-polarization directions in the wavelength range of 1420-1700 nm and 1320-1590 nm.When the thickness of the gold layer is 4.5nm and the thickness of the silver layer is 18 nm,the extinction ratio of the filter at 1430 nm is as high as 444.1d B.Finally,using the silver mirror reaction and the copper mirror reaction to deposit silver and copper films on the outside of the Solid-core fiber without air holes made in the laboratory,a double-layer metal-coated Solid-core fiber refractive index sensor based on the SPR effect was designed and prepared.Due to the particularity of the solid-core fiber structure,the light field concentrated in the ring-shaped quartz zone can easily interact with the doublelayer metal film deposited on the outside,further realizing the detection of liquid refractive index and improving its resolution.The experimental results show that in the refractive index range of 1.3328-1.3853,the maximum wavelength sensitivity is 2849nm/RIU when the Solid core fiber sensor with deposited silver film is used for detection;if other sensing conditions are kept unchanged,the maximum wavelength sensitivity of the Solid core optical fiber sensor of the membrane is 3958nm/RIU when detecting with a Solid-core optical fiber sensor deposited with a silver film.Therefore,the sensitivity of the sensor can be significantly improved by depositing a double-layer metal film. |
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