  Controlling directionality of optical emitters is of utmost importance for
their application in communication and biosensing devices. Metallic
nanoantennas have been proven to affect both excitation and emission properties
of nearby emitters, including directionality of their emission. In this regard,
optical directional nanoantennas based on a Yagi-Uda design have been
demonstrated in the visible range. Despite this impressive proof of concept,
their overall size and considerable number of elements represent obstacles for
the exploitation of these antennas in nanophotonic applications and for their
incorporation onto photonic chips. In order to address these challenges, we
investigate an alternative design. In particular, we numerically demonstrate
unidirectionality of an ultracompact optical antenna based on two parallel gold
nanorods (side-by-side dimer). Our results show that exciting the antiphase
mode by an emitter placed in the near-field can lead to unidirectional
emission. Furthermore, in order to verify the feasibility of this design, we
study the effect on the directionality of several parameters such as shape of
the nanorods, possible defects in dimer assembly, and different position and
orientation of the emitter. We conclude that this design is robust to changes,
making it experimentally achievable.
