Tunable directional beaming assisted by asymmetrical SPP excitation in a subwavelength metallic double slit

Abstract

We present a design for tunable directional beaming through asubwavelength metallic double slit surrounded by dielectricsurface-relief gratings. On-axis and off-axis beaming can be switched bycontrolling the incident angle to asymmetrically excite surface plasmonpolaritons (SPPs) that are subsequently coupled out to propagating beamsby the two gratings on the left and the right sides of the double slit.Furthermore, the division of optical power into two off-axis beamingdirections can be tuned smoothly by varying the incident angle whilekeeping the total power almost unchanged. The mechanism of this effectis analyzed theoretically and verified using rigorous numericalsimulations.