  An optical signal that propagates along a conventional waveguide is back
reflected at waveguide terminations. If the waveguide permits only one-way
propagation, this back reflection cannot take place; the optical signal
undergoes a nearly 100% conversion to radiation modes. Hence, a terminated
one-way waveguide may serve as a matched nano-antenna with a natural guiding
and feeding mechanism. We examine the termination effect in a recently
suggested nano-scale one-way plasmonic waveguide, and its properties as a
matched nano antenna are shown. Since one-way structures are inherently
non-reciprocal, our antenna possesses different transmitting and receiving
patterns, and a dynamic beam-forming functionality. These unique properties
offer new possibilities for dynamic directional selectivity that differ in
transmit and receive operations. Finally, the new concept offers nano-antennas
as yet another important field of application for non-reciprocal
nano-photonics, accelerating research of both the former and the latter fields
of activity.
