Quadruple Fano resonances in MIM waveguide structure with ring cavities for multisolution concentration sensing.

In this paper, a metal-insulator-metal (MIM) waveguide structure is proposed to produce quadruple Fano resonances, which is composed of a side-coupled elliptical cavity, a half-ring cavity, a half-ring cavity with an opening, and a bus waveguide with a circular barrier. The simulation results show that the resonant wavelengths of the quadruple Fano resonances can be almost independently tuned by changing the structural parameters of the three cavities. The refractive index sensing based on different cavities is discussed, and the maximum sensitivity is 1048.6 nm/RIU with an excellent linear-sensing relationship. Finally, the simultaneous multisolution concentration sensing is demonstrated, and the sensitivities are 0.138n m L -1 g -1 for the plasma concentration, 0.120n m L -1 g -1 for the glucose solution concentration, and 0.180n m L -1 g -1 for the N H 4 C l solution concentration. The results are conducive to promoting the applications of MIM waveguide structures in integrated optical sensing.