Optimizing Chiral Optical Response in Nanostructures Using Plasmonic Fano Resonance

This study investigates the chiral enhancement effects of plasmonic Fano resonance modes in planar metallic nanostructures. The nanostructure consists of a central Z-shaped or 卍-shaped element surrounded by six clustered gold nanorods, focusing on the coupling between these doubly rotationally symmetric structures. This coupling induces plasmonic Fano resonance, which significantly enhances the chiral response. Under normal incidence of circularly polarized light, the maximum chiral response can reach up to 41%. Finite-difference time-domain simulation and multipole expansion analysis reveal the fundamental origin of this enhanced chiral response: the selective excitation of electric dipoles and toroidal dipoles in polarization. The study demonstrates that rotationally symmetric structures and coupling effects play a crucial role in modulating the chiral response of nanostructures.