Nanoscale Control of the Radiation Properties of Coupled Nanoantennas

The peculiar properties of a pair of nanoantennas fed at a gap region have been studied. The possibility of controlling the radiation pattern at the nanoscale is demonstrated: indeed, unidirectional radiation can be obtained by placing two identical nanorods at a distance which is in the order of λ/20 (in stark contrast with the typical quarter-wavelength spacing of Yagi-Uda antennas), and scales down with increasing effective index of the plasmonic mode of the single cylindrical rod. Powerful techniques borrowed from electrical engineering have been applied in order to justify in an elegant and straightforward way the behavior of the nanostructure at optical frequencies.