Spatial filtering by using cascading plasmonic gratings

In this study, the optical properties of a plasmonic multilayer structure, consisting of tw6o 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 3o. The angular dispersion of the cascading plamonic gratings is about d?/d=0.15o/nm. The cascading plasmonic gratings can be used as a spatial filter to improve the spatial coherence of a light source.