Photonic Crystal Fiber Refractive Index Sensor Based On Two-Layer Composite Film

In recent decades,optical sensing technology has advanced by leaps and bounds with the development of optoelectronic technology.In particular,Optical fiber sensing technology plays especially an increasingly important role in various industrial precision instruments,detection and related scientific research fields.Compared with the traditional fiber optical sensor,the photonic crystal fiber structure is flexible in design and has a multi-layer air hole structure,which is of great significance for the integration and miniaturization of the sensor.A novel photonic crystal fiber refractive index sensor is proposed in this paper,the air holes of the photonic crystal fiber arrange in a spiral track.Double coating is on the outer surface of photonic crystal fiber,silver was coated on the outer surface of the photonic crystal fiber as a surface plasmon resonance material,and a 15nm thin ZnO film was coated on the silver film to prevent the metal from being oxidized.Under the condition of anisotropic perfect matching layer boundary conditions,the effects of air hole size,sensing area length and silver film thickness on the sensing performance were optimized by using the full vector finite element method.The optimal structure was obtained and the numerical results were obtained.Results show that the maximal sensitivities of the sensor reach 5200nm/RIU and the resolution reach 1.92×10^-5RIU when refractive index is in the range of 1.30 to 1.36.In addition,in order to expand the measurement range of the refractive index sensor,a refractive index sensor based on gold film plus TiO₂ material was designed,the full vector finite element method was used to simulate and analyze the influence of structural parameters of the sensor and plasma materials on the sensing characteristics,and the optimal structure was obtained.The simulating results show that the maximal sensitivities of the sensor reach 9000nm/RIU and the resolution reach 1.11×10^-5RIU when refractive index is in the range of 1.36 to 1.41.The proposed sensors have simple structure and high sensitivity.It can detect liquids with refractive index ranging from 1.30 to 1.41 after combination,and has wide application in environmental,biological and biochemical analyte detection and detection.