Dynamic beam steering from a subwavelength slit by selective excitation of guided modes.

Dynamic control of the direction of radiation of the light emanating from a subwavelength slit carved out of a thin metal film is experimentally demonstrated. This is achieved by selective excitation of the individual guided modes in the slit by setting the phase of three coherent laser beams. By changing the voltage across a piezoelement, we obtain unprecedented directional steering, without relying on any mechanical alignment of optical elements. The angular range over which this maximum can be swept is determined by the intensity setting of one of the incident beams. Through simulations, we show that this method can also be applied to steer the radiation from a square hole in two independent directions. Our method can be applied to create a directional nanoemitter which can selectively address one or more detectors, or as an optical switch in photonic circuits.