Single/Dual Fano Resonance Based on Plasmonic Metal-Dielectric-Metal Waveguide

A plasmonic metal-dielectric-metal (MDM) waveguide structure is proposed by placing a slot cavity below or above a groove. The groove and the slot cavity can act as a reflector and a resonator, respectively. Due to the interactions between the broad dark mode and the narrow bright mode caused by the groove and the side-coupled slot cavity, single Fano resonance with sharp asymmetric spectral profile is achieved. Interestingly, dual Fano resonances can also be obtained by using two different slot cavities, which are simultaneously distributed on both sides of the groove. The line shape can be transformed by changing the length of the groove, while the wavelength of the resonance peak can be manipulated linearly with the length of the slot cavity. The proposed structure yields a highest sensitivity of ∼1131 nm/RIU and a figure of merit of ∼1.6 × 107, and thus, we believe that it can serve as an on-chip nanosensor.