Unidirectional scattering of Si ring-Au split ring nanoantenna excited by tightly focused azimuthally polarized beam

Abstract

Unidirectional scattering of various plasmonic nanoantennas has been extensively studied, giving birth to applications such as in optical sensors, solar cells, spectroscopy and light-emitting devices. The directional scattering of magnetic nanoantenna is still unexplored, though it is beneficial to artificial magnetism applications including metamaterials, cloaking and nonlinear optical resonance. In this work, we numerically investigate the far-field scattering properties of the Si ring-Au split ring nanoantenna (Si R-Au SRN) excited by a tightly focused azimuthally polarized beam (APB) through using the finite-difference time-domain (FDTD) method. The results show that the magnetic resonant peaks with different widths can be deterministically excited in Si ring and Au split ring by tightly focusing APB. Owing to the plasmon hybridization effect, the two magnetic resonant modes form antibonding mode and bonding mode in the Si R-Au SRN. At a wavelength of <i>λ</i>=1064 nm, the destructive interference between the antibonding mode and bonding mode of nanostructure results in unidirectional far-field scattering in the transverse plane, which is affected dramatically by changes of geometrical parameters. Furthermore, the directional scattering of a dipole source is realized by the designed nanostructure, and its scattering directionality is superior to that excited with APB. Our work provides a flexible way to control the far-field scattering of nano-photon structures. We expect that this study can provide an avenue to the nano-light sources and optical sensors.