Multiple Fano resonances in a triangular–T-shaped coupled MIM waveguide for refractive index sensing

Abstract

Abstract In this work, a metal–insulator–metal (MIM) plasmonic sensor based on a triangular resonator coupled to a T-shaped waveguide is proposed. Existing MIM plasmonic sensors are generally limited by single-resonance operation or significant cross-sensitivity between multiple resonances, restricting their capability for reliable multi-parameter sensing. In this work, we propose a compact plasmonic sensor plateform based on a hybrid triangular–T-shaped resonator that generates three Fano resonances operating in the near-infrared domain (1050–1450 nm) with partially decoupled sensing channels, providing enhanced selectivity and high refractive index (RI) sensitivity. Numerical simulations were performed using the finite element method in COMSOL Multiphysics. The transmission characteristics, magnetic field distribution, and sensing performance were systematically analyzed. The obtained sensitivities reach 1010, 1180, and 1260 nm RIU − 1 for the three resonances, with corresponding figures of merit ranging from 21 to 49 (1/RIU). In addition, the sensing capability of the structure is explored for RI variations associated with biochemical analytes. The results indicate that the proposed design can provide multi-resonance responses with potential applicability in RI sensing. These findings highlight the capability of the proposed structure for plasmonic sensing applications, although further investigations are required to assess its robustness and practical implementation.