▎ 摘　　要

Plasmonic effects can be used in high sensitivity sensors, which have attracted widespread attention. However, most of the previously reported refractive index sensors can no longer be adjusted once fabricated, and their figure of merit (FOM) is undesirable. Concerning this, we propose a refractive index sensor consisting of a graphene waveguide and a graphene elliptical cavity working in the mid-infrared range. Its performance can be adjusted in real time by applying a bias voltage to the graphene patterns. The sensitivity of the proposed sensor can reach 2850 nm/refractive index unit and FOM up to 633, respectively. Owing to its excellent sensing properties of high sensitivity and high FOM, the proposed sensor can be applied in gas sensing.