Researchers at State Key Laboratory of High Field Laser Physics——Shanghai Institute of Optics and Fines Mechanics (SIOM/China) have proposed an exact theoretical design for directional beaming of light from a structure composed of a nanoslit perforated in the center of silver film flanked by metal-dielectric gratings on the output surface. [Photonics and Nanostructures – Fundamentals and Applications 9 (2011) 179–183] 

There are two mechanisms that govern the beaming effect: the MDA/MDM SPP mode resonance, and its diffraction by the surface grating. The effective excitation of MDA/MDM SPP mode (TM0 mode) results in directional beaming of light just by designing the geometry parameters, according to our theoretical design scheme. The numerical simulation based on the finite-difference time-domain method has been undertaken and the results obtained match well with our prediction. We have also shown that adding a thin metal grating to the output dielectric surface grating layer makes the transmitted light more convergent. This work will be helpful for designing subwavelength optical devices and elements.

Fig. The intensity distribution generated by a nanoslit with metal dielectric composite surface grating for offset distance between the nanoslit and nearest neighbor grating bump(a)d=195nm. (b)d=390nm