Optical Transmission through Double-Layer Metallic Subwavelength Slit Arrays

Subwavelength structures on the surface of a metal can strongly modify its interaction with light [1]. For example, periodically structured metal films display extraordinarily high optical transmission [2] and/or beaming characteristics [3]. Such metallic nanostructures have potential applications in a variety of disciplines, including miniature photonic circuits [4,5], microscopy, and high-density optical data storage [6]. While much progress has been made with subwavelength structures on a single layer of metal [7-17], coupling between the strong evanescent fields on the surfaces of two or more nanostructured metal layers in close proximity [18-20] could lead to novel optical properties and offer new functionalities. We have fabricated such double-layer metallic nanostructures and measured the far-field optical transmission as a function of the lateral shift between the two layers. Even when no direct line of sight exists through the structure due to a lateral shift between the two metal layers, the transmission remains remarkably high at resonance, comparable to the single-layer case. These findings open a new dimension in the design and operation of plasmonic devices.