Theoretical Analysis of a Simultaneous Graphene-Based Circular Plasmonic Refractive Index and Thickness Bio-Sensor

Abstract

A simultaneous plasmonic refractive index and thickness bio-sensor has been investigated theoretically and numerically to detect DNA hybridization and biomolecules attached to the inner wall of nano-ring resonators. The finite element method has been used to better appreciate the derived transmission formula based on both transfer matrix and coupled mode theories. For the first time, by applying a monolayer of graphene around the nano-ring resonators and introducing a MIM circular coupled waveguide, the power coupling coefficient, figure of merit and efficiency of the bio-sensor have been enhanced. Also, the coupling distance and optical properties including the chemical potential of graphene have been considered and studied to obtain optimal results. The maximum attained sensitivity and figure of merit of the bio-sensor are 1100 nm/RIU and 200 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , respectively. By employing a strong coupling condition, the full-width at half-maximum and extinction ratio have been obtained as 5 nm and 40 dB, respectively. Finally, the potential of the proposed structure as simultaneous AND and NOR logic gates have been studied with the intensity contrast ratios of 57 and 102.6 dB, respectively. Due to the excellent performance of the graphene-based circular plasmonic structure, it can find significant applications in photonic integrated circuits and on-chip nano-sensors.