Design and Simulation of a Plasmonic Refractive Index Nano-Sensor Based on Tunable Fano Resonance

Abstract In this paper, a nano-scaled surface plasmon-polariton (SPP) refractive index sensor based on metal-insulator-metal (MIM) waveguide is proposed and evaluated numerically by finite-difference time-domain (FDTD) method. Polygonal cavities, that are coupled to a disk resonator cavity, are attached to this sensor's MIM bus waveguide. Fano resonance and its characteristics are utilized to improve the essential parameters of the sensor, such as full width at half maximum (FWHM), quality factor, and sensitivity. Figure of merit (FOM) of the sensor can be increased by tuning its geometrical parameters. In optimized conditions, which are concluded in this work, the sensor shows a FWHM of 1.15 nm, a quality factor of 604.1, a sensitivity of 687.9 nm/RIU and a FOM of 598.1 RIU−1 in the visible light region. A sensor with such a high resolution can be used in highly integrated photonic circuits and biosensors. The effects of incorporating metal patches inside the disk cavity are also discussed in this paper.