Insights into directional scattering: from coupled dipoles to asymmetric dimer nanoantennas

Abstract

Strong and directionally specific forward scattering from optical nanoantennas is of utmost importance for various applications in the broader context of photovoltaics and integrated light sources. Here, we outline a simple yet powerful design principle to perceive a nanoantenna that provides directional scattering into a higher index substrate based on the interference of multiple electric dipoles. A structural implementation of the electric dipole distribution is possible using plasmonic nanoparticles with a fairly simple geometry, i.e. two coupled rectangular nanoparticles, forming a dimer, on top of a substrate. The key to achieve directionality is to choose a sufficiently large size for the nanoparticles. This promotes the excitation of vertical electric dipole moments due to the bi-anisotropy of the nanoantenna. In turn, asymmetric scattering is obtained by ensuring the appropriate phase relation between the vertical electric dipole moments. The scattering strength and angular spread for an optimized nanoantenna can be shown to be broadband and robust against changes in the incidence angle. The scattering directionality is maintained even for an array configuration of the dimer. It only requires the preferred scattering direction of the isolated nanoantenna not to be prohibited by interference.

A Metalens with a Near-Unity Numerical Aperture

“…The diffractive and non-diffractive periods of the square lattice are, respectively, P d = 721 nm and P nd = 260 nm. The asymmetric dimer nanoantennas have been previously shown to generate asymmetric radiation patterns even in the simplest case in which the interacting particles support just a single dipole mode [39][40][41][42][43] . Figs.…”

“…The latter is chosen to be small enough to avoid diffraction in air in this direction and keep a high array density. The asymmetric dimer nanoantennas have been previously shown to generate asymmetric radiation patterns even in the simplest case in which the interacting particles support just a single dipole mode. − Panels C and D of Figure show the simulated field distribution when the array is illuminated by s- or p-polarized plane waves normally incident at the operating wavelength from the substrate side. We define the s (p) polarization as that with the magnetic (electric) field directed along the axis of the dimer.…”

Design of plasmonic directional antennas via evolutionary optimization

“…Another optical functionality that is in the focus of the plasmonics community is the directional routing of light. Not only individual nanostructures were demonstrated for directional scattering of far-field light [11][12][13], color-routing [14], quantum emitter radiation steering [9,[15][16][17][18][19], electro-luminescence [20,21] or directional non-linear emission [22]. Also metasurfaces for directional scattering and color-routing have been proposed [23,24].…”

The Influence of the Emission Source on Outcoupling and Directivity of Patterned Perovskite Light-Emitting Diodes

“…Nevertheless, particularly worth mentioning is that the approaches to achieving the directional PeLED have rarely been studied. It is also an essential topic to manipulate the radiation and directivity of the lighting devices, which has various application prospects in daily life such as visible light wireless communication [18], biological sensors [19] and autostereoscopic naked-eye 3D displays [20]- [21] etc. The typical strategies to achieve directional emission include, e.g., embedment of scatters at the top of light emitting devices [22], adoption of optical cavities such as the distributed Bragg reflector (DBR) [23] and photonic crystals into the organic layers [24].…”