Nanodisk-Induced Modification of Plasmon Coupling and Appearance of Fano Resonance Without Symmetry Breaking in Concentric Ag Nanoring-Nanodisk

Simulation based on the finite-difference time-domain (FDTD) has been performed, and theoretical models comprising concentric Ag nanoring-nanodisk of different parameters have been constructed to research their plasmon properties. According to unique electronic properties of concentric nanoring-nanodisk, abundant plasmon properties could be obtained at their interfaces, including dipole, quadrupole, and octupole plasmon resonance modes. Complex field distributions which are induced by concentric nanoring-nanodisk support the possibility to create dark resonance mode. This can lead to Fano-like resonance combining with bright resonance mode by predominantly dipole resonance. A concentric nanoring-nanodisk system has been proved to support Fano-like resonance without symmetry breaking. At the frequency of the Fano resonance, strong localized optical fields can be obtained. Narrow spectral features with high local fields of Fano resonances make it possible to achieve many applications based on surface plasmon property.