Off-axis directional beaming of optical field diffracted by a single subwavelength metal slit with asymmetric dielectric surface gratings

The authors propose a method for the off-axis directional beaming of optical field diffracted by a single subwavelength metal slit with dielectric surface gratings. In the proposed method, dielectric gratings are optimally designed to directionally couple the surface plasmon polariton modes induced by the metal slit into surrounding medium along a specific off-axis direction. Design of the gratings and the analysis are conducted based on the rigorous coupled wave analysis method. Their simulation shows the off-axis directional beaming of the oblique angle, 20.2°, with respect to the on axis by the proposed method. The beaming angle can be changed by adjusting the grating periods.