High Sensitivity Refractive Index Sensor Based on D-Shaped Photonic Crystal Fiber Coated with Graphene-Silver Films

A D-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor is proposed to measure the refractive index in visible and near-infrared regions. Compared with traditional PCF, the use of D-shaped PCF can avoid filling materials and coatings in the hole. The plasma material of sensors is silver, and graphene is coated on the surface of the silver film. Graphene layer can not only prevent the oxidation of the silver but also improve the performance of the sensor. Then the influence of structural parameters on the sensor performance is studied by the finite element method (FEM). Results show that the performance of the sensor is not sensitive to the structural parameters, which makes the sensor has a good manufacturing tolerance. Moreover, when the refractive index (RI) of the analyte is 1.33 similar to 1.41, the maximum wavelength sensitivity is 13,750 nm/RIU, and the corresponding RI resolution is 7.27 x 10(-6) RIU-1. In addition, the maximum figure of merit is 201 RIU-1. The proposed sensor is advanced with high sensitivity, simple structure and big fabrication tolerance, which could become a competitive candidate for water pollution monitoring, medical diagnosis, biochemical analysis, and detection fields.