Fano resonance in metallic ring-ellipse nanostructures

Using the finite-difference time-domain (FDTD) method, we investigate the Fano resonance in a silver ring-ellipse nanostructure. The symmetry of the ellipse is lower than a disk, and thus enables the excitation of higher order dark mode in the outer ring. The excitation of Fano resonance can be understood as the coupling of the octupole mode of the ring and the dipole mode of the ellipse. By changing the structure parameters, we study the variation of the optical resonance of the proposed structure.