Nanofocusing of surface plasmon polaritons by a pyramidal structure on an aperture.

A numerical study of the nanofocusing of surface plasmon polaritons (SPPs) by a pyramidal structure on a rectangular aperture is performed by the volume integral equation method. It is possible to perform nanofocusing using this structure by using a linearly polarized wave as the incident wave. The focusing process of SPPs by the tip of the pyramidal structure has been demonstrated numerically. The characteristics of the focused optical field near the tip have been investigated in detail. It was found to be similar to that of monopole rather than that of a tiny dipole. The optical field at the tip is sensitive to the local shape of the tip. The enhanced intensity on the tip increases with an increase in the aperture width.