Spatial filtering by using cascading plasmonic gratings

In this study, the optical properties of a plasmonic multilayer structure, consisting of two longitudinally cascaded gratings with a half pitch off-set, are investigated. The proposed structure, which is a system mixing extended and localized surface plasmon, forms transversely cascaded metal/insulator/metal cavities. The angle dependent reflection spectrum of the proposed structure displays a resonance peak at a specific angle. The full-width at half maximum (FWHM) of the resonant peak is smaller than 3 degrees. The angular dispersion of the cascading plasmonic gratings is about d theta/d lambda =0.15 degrees/nm. The cascading plasmonic gratings can be used as a spatial filter to improve the spatial coherence of a light source.