Design of a Refractive Index Plasmonic Sensor Based on a Ring Resonator Coupled to a MIM Waveguide Containing Tapered Defects

In this paper, a novel nanoscale refractive index sensor topology, which incorporates a ring resonator containing circular tapered defects coupled to a metal-insulator-metal (MIM) plasmonic waveguide with tapered defects, is proposed. For the proposed design, the effect of introduction of defects on transmittance value, shape of magnetic field, and sensor parameters such as sensitivity (S) and figure of merit (FOM) are investigated numerically and simulated using finite-difference time-domain (FDTD) method. By optimizing the ring radius and selecting the appropriate waveguide width, we have achieved a maximum sensitivity of 1295 nm per refractive index unit (RIU) and a fairly high FOM equal to 159.6 RIU-1. The structure can be used as a high accuracy refractive index sensor for refractive indices ranging from 1 to 1.65. Due to the small size, wide detection range, and the high detection resolution of the proposed sensor, it is a good choice for integrated bio-sensing applications.