Controllable directive radiation from dipole emitter coupled to dielectric nanowire antenna with substrate-mediated tuna
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Research Letter
Controllable directive radiation from dipole emitter coupled to dielectric nanowire antenna with substrate-mediated tunability Mohammad M. Salary, Ali Forouzmand, and Hossein Mosallaei, Metamaterials Lab, Electrical and Computer Engineering Department, Northeastern University, Boston, Massachusetts 02115, USA Address all correspondence to Hossein Mosallaei at [email protected] (Received 31 December 2017; accepted 19 March 2018)
Abstract The present work demonstrates controllable directive radiation of a dipolar emitter coupled to a substrate-supported dielectric nanowire antenna. Nanoactuators, transparent-conducting oxides, and graphene are integrated into the substrate, respectively, to establish tunable antenna platforms in visible, near-infrared (IR), and far-IR frequency regimes. We exploit the substrate-induced interference effects and tunability mechanisms in each antenna system to achieve directive radiation with real-time steering capability. The design and modeling are rigorously carried out using an efficient and accurate semi-analytical framework based on transition matrix formulation. Each configuration is optimized to achieve maximal steering range while attaining a proper gain. Owing to subwavelength footprint, enhanced directionality, real-time tunability, and fairly simple geometry, the proposed platforms are ideal candidates for nanoantenna synthesis.
Introduction The rapid progress in electronics and wireless communications over the past decades has led to a growing demand for wireless devices with the ability to operate at visible and infrared (IR) regimes. This enables miniaturization of devices and circuits usually operating at much lower frequencies. The optical wireless nanolinks offer a better performance in sending optical signals from one point to the other as they do not suffer from the losses associated with the waveguide interconnect counterparts, especially when the propagation distance is of the order of several wavelengths.[1,2] They can also provide simpler and ultracompact network architectures. The high directionality of antennas is a key parameter in the performance of such wireless links and networks. In nanophotonics, highly directional antennas have been realized using arrays of plasmonic and dielectric nanoantennas as well as impedance sheets arranged based on the phased array,[3] Yagi-Uda,[4] and holographic design[5] approaches. In these cases, while individual elements of the arrays are subwavelength, the overall size of the antenna system becomes greater than the radiation wavelength. As such, downscaling of the whole radiative system to subwavelength footprints is a challenge that needs to be tackled. Semiconductor quantum dots as point-like dipole sources of spontaneous emission are promising candidates to surmount this challenge, but achieving a high radiation efficiency and directionality require nanoantennas in order to effectively match the impedance of a quantum source to that of free
space. Plasmonic and high-index semiconductor nanoantennas ca
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