  Electrically-driven optical antennas can serve as compact sources of
electromagnetic radiation operating at optical frequencies. In the most widely
explored configurations, the radiation is generated by electrons tunneling
between metallic parts of the structure when a bias voltage is applied across
the tunneling gap. Rather than relying on an inherently inefficient inelastic
light emission in the gap, we suggest to use a ballistic nanoconstriction as
the feed element of an optical antenna supporting plasmonic modes. We discuss
the underlying mechanisms responsible for the optical emission, and show that
with such a nanoscale contact, one can reach quantum efficiency orders of
magnitude larger than with standard light-emitting tunneling structures.
