Surface‐Plasmon‐Polariton Diode by Asymmetric Plano‐Concave Nanocavities

Abstract High‐efficiency and direction‐controllable launching of surface plasmon polaritons (SPPs) is highly desired in plasmonic devices and photonic circuits. Here, a heteroplasmonic device is reported consisting of an array of asymmetric nanocavities with each nanocavity constructed by an asymmetric Ag nanoshell (AgNS) and a planar gold film (AuFilm). A photoresist grating is used both as a template for fabricating the AgNS array and as the dielectric filling medium of the nanocavities. Interaction between localized surface plasmon resonance in the asymmetric AgNSs and SPPs in the AuFilm has enhanced the propagating surface modes along the gold film. A phase modulation induced by the asymmetry and interference between the SPP modes have been the main physics supporting the directional propagation of the surface waves or the in‐plane optical diode effect at normal incidence. The SPP diode works in different directions at different wavelengths, which can be controlled by adjusting the asymmetry of the AgNSs.