Nanosensor and slow light based on quintuple Fano resonances in a metal–insulator–metal waveguide coupled with a concentric-ring resonator

In this paper, quintuple Fano resonances are produced and numerically analyzed based on a plasmonic resonator system. The system is composed of an optical metal–insulator–metal (MIM) waveguide, a side-coupled disk, and a concentric-ring resonator. Five Fano resonances can be seen, which originate from the interaction of the cavity mode between the disk resonator and the concentric-ring resonator. The transmission spectrum shows that the Fano resonance can be independently tuned by changing different geometrical parameters, such as the outer radius or inner radius of the concentric-ring resonator. The refractive index sensitivity is 1250nm/RIU for FR5, and the figure of merit is 138.9 (RIU is a refractive index unit). It can also serve as a temperature sensor with a maximum sensitivity of about 0.4nm/ ∘ C. Moreover, for slow light, the maximum delay time is about 0.12 ps at FR3. The proposed nano-scale structure has a sharp Fano line shape and effective ways of tuning independently, which may have applications in slow light and nano-biosensing; for example, we show the application of the detection of different human blood types.