One-way optical waveguides for perfectly matched non-reciprocal nano-antennas with dynamic beam tuning

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.