Highly sensitive refractive index sensor based on a D-shaped few-mode fiber with silver and graphene film

Abstract

A D-shaped few-mode optical fiber sensor based on surface plasmon resonance (SPR) is proposed. Compared with photonic crystal fiber, the few-mode fiber (FMF) as a sensor has many advantages, such as, the polishing direction and the collapse of air holes can be ignored in the polishing process. The polished surface is coated with silver film to generate the surface plasmon mode. Furthermore, the Graphene coating on silver film can not only enhance the SPR effect, but also prevent the silver from being oxidized. Then the dispersion characteristics and loss spectrum of the designed fiber are studied by the finite-element method (FEM). Higher sensitivity can be selected with few-mode fiber that can transmit several modes. Numerical results reveal that the maximum wavelength interrogation sensitivity of LP01 mode and higher-order mode (LP31 mode) can reach at 9000 nm/RIU and 14,500 nm/RIU. In addition, the maximum figure of merit is 232. The designed sensor is a potential candidate for the further biochemical application on account of its simple structure, high sensitivity and promising sensing performance.