Tapered waveguide mode converters for metal-insulator-metal waveguide plasmonic sensors

Herein a numerical analysis is performed to explore the conversion efficiency of mode converters for a plasmonic waveguide (WG). The major concern of metal-insulator-metal (MIM) WG devices is the efficient coupling of light to the sub-nano scale WG from an external source. In previous studies, this issue has not been usually investigated. As a result of which the experimental demonstration of MIM WG-based devices is not advanced so far. We proposed a dielectric-to-plasmonic mode converter (DPMC) in the form of a tapered WG to couple the light into the MIM WG and a plasmonic-to-dielectric mode converter (PDMC) to collect the light out of the plasmonic WG. The overall conversion efficiency of the 5000 nm long device is similar to -1.6 dB. Furthermore, a MIM WG-based sensor is designed by integrating a circular hollow cavity for refractive index sensing applications. The sensitivity and figure of merit of the proposed device are 1132.14 nm/RIU and 48.17 RIU-1, respectively. We consider this study will pave a way for the accomplishment of highly integrated plasmonic sensors based on MIM WGs.