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.

Automated summary

In this study, numerical analysis is conducted to investigate the conversion efficiency of mode converters for plasmonic waveguides. The efficient coupling of light to the sub-nano scale waveguide from an external source is a major concern for metal-insulator-metal waveguide devices, which has not been extensively studied before. The proposed dielectric-to-plasmonic and plasmonic-to-dielectric mode converters demonstrate an overall conversion efficiency of approximately -1.6 dB for a 5000 nm long device. Additionally, a MIM waveguide-based sensor with a circular hollow cavity is designed for refractive index sensing applications, exhibiting a sensitivity of 1132.14 nm/RIU and a figure of merit of 48.17 RIU-1. This study is expected to pave the way for highly integrated plasmonic sensors based on MIM waveguides.