A nanosensor with ultra-high FOM based on tunable malleable multiple Fano resonances in a waveguide coupled isosceles triangular resonator

A simple plasmonic structure, which is made up of a metal baffle in the middle of the metal–insulator–metal (MIM) waveguide coupled with an isosceles triangular cavity, is reported to achieve triple Fano resonances. These Fano resonances are numerically calculated by the finite element method (FEM). Besides, the multimode interference coupled mode theory (MICMT) and the standing wave theory are used for analyzing the Fano resonances phenomenon. On the one hand, these three Fano resonances can be independently tuned by adjusting the structural parameters, which makes the design of highly integrated photonic circuits more flexible. On the other hand, the proposed structure is well malleable and can be easily extended to a quintuple Fano system by introducing a ring resonator. Furthermore, the suggested structure can act as a high efficient refractive index (RI) sensor, yielding a great sensitivity of 1200 nm/RIU and a ultra-high maximal figure of merit (FOM) value of 3.0×106. Comparing with other similar sensors, our structure has relatively good sensitivity and it is superior to other structures in the maximal FOM, which obviously demonstrates its excellent nano-sensing performance.