  Analogous to radio- and microwave antennas, optical nanoantennas are devices
that receive and emit radiation at optical frequencies. Until recently, the
realization of electrically driven optical antennas was an outstanding
challenge in nanophotonics. In this review we discuss and analyze recent
reports in which quantum tunneling-specifically inelastic electron tunneling-is
harnessed as a means to convert electrical energy into photons, mediated by
optical antennas. To aid this analysis we introduce the fundamentals of optical
antennas and inelastic electron tunneling. Our discussion is focused on recent
progress in the field and on future directions and opportunities.
