Near-Perfect Spectral Transmission Properties for Two Cascaded Plasmonic Ultrathin Nanograting Structures

Abstract

A high-performance plasmonic transmission structure consisting of two longitudinally cascaded ultrathin metallic nanogratings with a half period lateral dislocated and separated by two heterogeneous dielectric layers is proposed and theoretically studied. Three near-unity spectral transmission peaks are observed for the cascaded plasmonic nanograting structure due to the evanescent field coupling of surface plasmon polariton waves supported by the two neighboring plasmonic nanogratings. The physical mechanism responsible for the near-perfect peak transmissions is discussed based on the corresponding spatial distributions of electromagnetic fields and is found to be two possible ways: by the excitation of hybrid anti-symmetric surface plasmon polariton leaky mode on the incident and transmission surfaces of the cascaded plasmonic nanograting structure or by the formation of localized surface plasmon polariton resonance modes within horizontally butt-jointed metal/insulator/metal coupled waveguides between the two cascaded plasmonic nanogratings. It is the two heterogeneous dielectric layers inserted between the two cascaded plasmonic nanogratings that is indispensable for the formation of the hybrid anti-symmetric surface plasmon polariton leaky mode, resulting in the near-unity transmission peak with an ultra-narrow bandwidth of 20 nm. The high-tunability of spectral transmission behaviors with varying structural parameters and dielectric layer are explored, which promise numerous potential applications in nano-optics devices, such as plasmonic filters, sensors, and nanoscale distance ruler.