Transmitted interference effect of double metallic nanoslits composed of a slit and a square-funnel slit

The transmitted interference characteristics for double metallic nanoslits, which are composed of a slit and a square funnel, are investigated by the finite-difference time-domain method. Two types of interference patterns, i.e., the periodic single peak or the periodic double peaks profile, are observed by varying the geometric parameters of the square-funnel slit. The fringe period crucially depends on the exit layer thickness of the square-funnel slit. The near-field field intensity can be enhanced three times that in symmetric slit-doublet structure by selecting specific parameters. We also find that surface plasmon waves can creep along the interface between metal and dielectric, even though the interface possesses orthogonal corners.