Tunable Mid-Infrared Refractive Index Sensor Composed of Asymmetric Double Graphene Layers

An enhanced graphene-based refractive index sensor with high sensitivity composed of two vertical layers, asymmetric double graphene layers, that act as a resonator and also two horizontal layers that act as input/output waveguides is designed and proposed. Performance of the sensor is based on the alternation of the resonance wavelength of the resonator. The two-dimensional-finite difference time-domain (2D-FDTD) simulation results show a linear relation between the resonance wavelengths and the refractive index of the material under sense (MUS). This feature makes it easy to identify the injected material in the resonator. The mid-infrared (MIR) wavelength range of the sensor structure can be tuned by applying the bias voltage to graphene to change its chemical potential. The sensitivity value can be obtained as high as 1900 nm per refractive index unit (nm/RIU). The performance of the proposed sensor is studied theoretically and confirmed numerically. The proposed plasmonic refractive index sensor would have useful applications in nano devices and circuits in MIR.