Unidirectional Enhanced Dipolar Emission with an Individual Dielectric Nanoantenna.

Tianyue Zhang,Zi-Lan Deng,Fei Qin,Dejiao Hu,Xiangping Li,Jian Xu

doi:10.3390/nano9040629

Abstract

Light manipulation at the nanoscale is the vanguard of plasmonics. Controlling light radiation into a desired direction in parallel with high optical signal enhancement is still a challenge for designing ultracompact nanoantennas far below subwavelength dimensions. Here, we theoretically demonstrate the unidirectional emissions from a local nanoemitter coupled to a hybrid nanoantenna consisting of a plasmonic dipole antenna and an individual silicon nanorod. The emitter near-field was coupled to the dipolar antenna plasmon resonance to achieve a strong radiative decay rate modification, and the emitting plasmon pumped the multipoles within the silicon nanorod for efficient emission redirection. The hybrid antenna sustained a high forward directivity (i.e., a front-to-back ratio of 30 dB) with broadband operating wavelengths in the visible range (i.e., a spectral bandwidth of 240 nm). This facilitated a large library of plasmonic nanostructures to be incorporated, from single element dipole antennas to gap antennas. The proposed hybrid optical nanorouter with ultracompact structural dimensions of 0.08 λ2 was capable of spectrally sorting the emission from the local point source into distinct far-field directions, as well as possessing large emission gains introduced by the nanogap. The distinct features of antenna designs hold potential in the areas of novel nanoscale light sources, biosensing, and optical routing.

Highlights

Controlling light emissions from nanoemitters has key merit in many applications, such as biological sensing and imaging, surface-enhanced spectroscopy, light-emitting devices, and on-chip integrated sources [1,2]
Owing to the engineered localized density of photonic states introduced by the plasmon resonance, plasmonic nanostructures can concentrate the optical electric field, alter the de-excitation pathways, change the emission polarization, and redirect the emission intensity, leading to various functionalities like fluorescence enhancement, lifetime shortening, spectrum reshaping, and direction steering [4,5,6,7]
We theoretically demonstrate that the dipolar emission pattern can be reshaped to be highly unidirectional by placing a conventional plasmonic antenna–nanoemitter system in the vicinity of an individual silicon nanorod

Summary

Introduction

Controlling light emissions from nanoemitters has key merit in many applications, such as biological sensing and imaging, surface-enhanced spectroscopy, light-emitting devices, and on-chip integrated sources [1,2]. With the ability to manipulate the excitation and emission processes of the localized emitters, function as transducers between far- and near-field light signals working at the optical frequency known as optical nanoantennas [3]. Because of the nature of resonant enhancement, the far-field angular emission of the emitter-antenna coupling system is determined strongly by the antenna modes [8,9], whilst the most commonly used nanoantennas (e.g., metallic nanoparticles and gap antennas) possess dominant dipolar plasmon resonances with omnidirectional characteristics, which are disadvantageous for directional emission control.

Results

Conclusion