Unidirectional Light Scattering With High $f/b$ at Optical Frequencies Based on Coupled Nanoantennas

Dengchao Huang,Yi Zhang,Lisheng Yang

doi:10.1109/access.2019.2937127

Abstract

We propose an optically coupled nanoantenna which contains an asymmetric dimer of core-dual shells nanoparticles, and the individual nanoparticle consisting of two identical metal strips that separated by a dielectric spacer known as the metal-dielectric-metal (MDM) structure. According to the dipole-dipole theory and the Mie theory, we theoretically and numerically demonstrate that this design can provide unidirectional forward scattering along the incident axis of light with high $f/b$ radio (known as the ratio of scattering spectra to forward and backward direction) and narrow beam-width owing to interference between electric dipole and magnetic high-order modes. We also find that all properties of this nanoantenna that the performance of it is related with the gap separation of the asymmetric dimer. Comparing with the asymmetric dimer of pure metal nanoparticles and the symmetric dimer of MDM nanoparticles, the proposed nanoantenna has higher directivity and low loss at the same time, due to effectively coupled electric dipole mode and magnetic multipole modes. The ultra-directional nanoantenna may shed new light to overcome power losses and low directivity of coupled nanoantennas, which can find various applications in bio-sensing and metamaterials.

Highlights

Nanoantennas which can control the directionality of scattered electromagnetic waves at optical frequencies have attracted tremendous attention
Liu [18]. demonstrated that a core-shell nanoparticle consisting of a dielectric shell and a metal core can allow flexible overlapping electric and magnetic multipole of high orders which were excited by a plane wave, which results in significantly narrow radiation beam-width and backward scattering suppression, and Zhang et al [19]. show that a local dipole source can efficiently excite several hybridized plasmonic modes in multilayered nanoantennas, which lead to unidirectional emissions in opposite directions at different wavelengths
These radiative properties of the asymmetric dimer are analyzed by the dipole-dipole theory [20] and the 3-D numerical calculation

Summary

Introduction

Nanoantennas which can control the directionality of scattered electromagnetic waves at optical frequencies have attracted tremendous attention. When the MDM nanoparticles are coupled together to form the asymmetric dimer, they can provide field enhancement, localization of electromagnetic energy in the gap and high forward scattering intensity with narrow beam-with.

Results

Conclusion