Highly sensitive refractive index sensor based on D-shaped PCF with gold-graphene layers on the polished surface

D-shaped photonic crystal fiber (PCF) sensor in the infrared spectrum is proposed to detect the analytes/liquids of different refractive indices (RIs) ranging from 1.32 to 1.40. To observe the effect of surface plasmon a thin layer of gold was deposited on the D-shaped PCF. Then a flake of graphene was deposited on the layer of gold. Graphene improves the detection capability of PCF sensors because of its excellent molecule adsorption property. Its large surface area and rich π conjugation make it a suitable dielectric layer for sensing. The proposed sensor is designed and numerically analyzed using finite element method. The thickness of the gold, graphene layer and the diameter of the two large air holes of PCF are varied to study its effect on the sensing characteristics of the proposed SPR-based PCF sensor. It is observed that the sensitivity improved to 33,500 nm RIU⁻¹ with effective RI resolution of 2.98 × 10^-5 RIU which makes the device more competitive among various plasmonic sensors.