Large angle directional beaming control by metal aperture-corrugation structures

The beaming effect of subwavelength holes and slits has attracted more and more attention since it was first observed. A subwavelength metal aperture with symmetric periodic surface corrugations has an effect of on-axis... [ view full abstract ]

The beaming effect of subwavelength holes and slits has attracted more and more attention since it was first observed. A subwavelength metal aperture with symmetric periodic surface corrugations has an effect of on-axis directional beaming and the effect is attributed to the excitation of surface plasmon polariton (SPP) and its diffraction by the corrugations. Correspondingly, breaking the symmetry of the structure will lead to the off-axis directional beaming effect. But it is difficult to achieve larger angle directional beaming because the radiation field of a subwavelength aperture is not consistent with spherical distribution and the energy is confined to a limited divergence angle. However, the previous reports on the angle control are confined in ±30° and seldom approach the limited angle of about ±60°. 

To control the beaming angle, a mathematic model of a metal slit–grating structure is built and calculated with Finite-Difference Time-Domain method. A design methodology is proposed in terms of two aspects: the phase modulation of the light radiated from the surrounding gratings and the reverse process of the SPP wave coupling. The corrugation spacing can be modulated to generate the constructive interference of a specific beaming angle or destructive interference of the angle needed to be weaken. With the designed asymmetric structures, the beaming angle varied in ±60° can be achieved, as is shown in the attached figure.