Compact plasmonic lens based on gradually decreasing size and separation nanohole cluster

Abstract

A novel nanohole cluster configuration that consists of nine holes with gradually decreasing sizes and interspace distances for light focusing purposes in a plasmonic regime is proposed. The hole size and separation are correlated with each other by introducing a scaling factor (k). A similar arrangement has already been investigated in nanoparticle cases. For some values of k, the light propagating through the holes extraordinarily transmit, constructively interfere and strongly localize at a point under the metallic layer. The physics behind the focusing is attributed to the optical diffraction and surface plasmon effects. A numerical approach is used to illustrate the focusing features. The results show that the best focusing features occur when the largest hole size is in the order of incident light wavelength and scaling factor is between 0.35 and 0.45. The calculated enhancement factor of the light intensity at focal point is approximately 2.6. Notably, the proposed structure scales down the plasmonic lens size. The fabrication process is in accordance with typical fabrication techniques used in plasmonic chips integration.