High sensitivity plasmonic sensing based on Fano interference in a rectangular ring waveguide

We investigate a plasmonic waveguide system using 2-dimension finite element method, which consists of a rectangular ring metal–insulator–metal waveguide and a baffle. Numerical simulations results show that the sharp and asymmetric Fano-line shapes can be created by the proposed structure, because of the interaction between the strong trapped resonance in the FP resonator and the weak resonance in the stub resonator. An analytic model based on the scattering matrix theory is utilized to describe and explain this phenomenon. The physical features contribute to a highly efficient plasmonic nanosensor for refractive index sensing with the sensitivity of 1300 nm/RIU and a figure of merit of 6838. This plasmonic structure with such high figure of merits may find important applications in the on-chip nanosensors.