Strongly coupled nanoantennas: A simple route toward unidirectional radiation in optics

We analyze the radiative properties of a couple of optical nanoantennas fed at a gap region. We demonstrate that the radiation pattern can be controlled at the nanoscale, and unidirectional radiation can be obtained by placing two nanorods at a distance in the order of λ/20, in stark contrast with the λ/4 spacing which is typical of Yagi-Uda antennas. Conventional techniques commonly used at microwaves, such as theory of antenna arrays and surface integral equations, are applied in order to estimate the peculiar behavior of these nanostructures at optical frequencies.