Employment of cascaded coupled resonators for resolution enhancement in plasmonic refractive index sensors

A very high resolution refractive index optical sensor is proposed in this paper. It is based on metal–insulator–metal plasmonic waveguides. The structure is numerically simulated using finite difference time domain method. The suggested plasmonic topology is conceived upon a waveguide which is laterally coupled with cascaded coupled concentric ring and disk resonators. It acts as a filter with a quality factor of 298.6. The sensor provides a sensitivity equal to 640.6 nm/RIU and a maximum figure of merit (FoM) of 287.9 RIU −1 which is the highest FoM reported for plasmonic refractive index sensors. It is observed that a ± 0.001 change in refractive index of the analyte for index the range of 1–1.13 can easily be detected by this sensor. The small required footprint, simple, modular topology and its good resolution are the benefits of the proposed structure.