Dielectric travelling wave antennas for directional light emission

Abstract

We present a combined experimental and numerical study of the far-field emission properties of optical travelling wave antennas made from low-loss dielectric materials. The antennas considered here are composed of two simple building blocks, a director and a reflector, deposited on a glass substrate. Colloidal quantum dots placed in the feed gap between the two elements serve as internal light source. The emission profile of the antenna is mainly formed by the director while the reflector suppresses backward emission. Systematic studies of the director dimensions as well as variation of antenna material show that the effective refractive index of the director primarily governs the far-field emission pattern. Below cut off, i.e., if the director’s effective refractive index is smaller than the refractive index of the substrate, the main lobe results from leaky wave emission along the director. In contrast, if the director supports a guided mode, the emission predominately originates from the end facet of the director.

Optimization of optical waveguide antennas for directive emission of light

“…We use a dipole with dipole moment oriented perpendicular to the antenna axis, i.e. along y-axis, that ensures the strongest coupling to the antenna modes, as demonstrated in our previous work [38]. The light emission assisted by excitation of leaky and guided waves excited by the dipole emitter in the dielectric antenna is directed towards the glass substrate (depicted in red).…”

“…We start our study by analysing a simple antenna consisting of a dielectric reflector and a rectangular-shaped director both made of HfO 2 with refractive index n = 1.9 deposited on a SiO 2 substrate. In recent works, we have experimentally and numerically demonstrated that this kind of antenna is capable of high directivity of 29.2 in magnitude [37,38]. Aiming to further improve the directivity, we firstly identify seven vital geometric parameters influencing the optimization problem: the antenna height (H), director length (DL), director width (DW), reflector length (RL), reflector width (RW), distance of the field source from the director (DD) and the reflector (RD).…”

“…They typically produce an axially symmetrical shape in their radiation pattern and maintain an adequate directivity over a broad frequency range. Also, leaky-wave antennas have been emerging as a vital subset of the traveling wave antennas [29,30] that allow power to be leaked over the whole length of a non-resonant guiding structure by the virtue of leaky modes [31][32][33][34][35][36][37][38]. The earliest illustration of such a structure was a rectangular waveguide with a continuous slit to its side [39], followed by a plethora of recent advancements in such structures, successfully demonstrating the highly directive emission furnished by them [37,[40][41][42][43][44].…”

“…Actually, these kind of dielectric structures can support both, leaky and guided-wave propagation, depending on the modes excited, and the resulting interference between them can lead to highly directed radiation patterns. In particular, our previous work demonstrates a complex interplay between leaky and guided modes in broadband waveguide-like optical nanoantennas made from low-loss dielectric materials that are able to shape the emission pattern of quantum dot emitters in the far-field with high directivity [38].…”

The Recent Advancement in Unmanned Aerial Vehicle Tracking Antenna: A Review

“…The primary radiating mechanism of the travelling antenna is based on a travelling wave in the form of a guiding structure. A travelling antenna is different from others because the radio waves are generated by the radio frequency current in a single direction [ 50 , 51 ]. They are non-resonant and, as such, their bandwidth is wider than their resonant antennas counterpart [ 52 ].…”