Near-field properties of spin, Huygens and Janus sources in a narrow sandwiched structure

Abstract

Near-field photonics has attracted extensive attention for its applications from classical to quantum fields, and near-field directionality is the core of many applications. Here, we use a sandwich structure to investigate the effects of waveguide width and source position on the behavior of spin, Huygens and Janus sources. Although the structure is very simple, the conclusions obtained through it can be extended to more complex structures. In a narrow waveguide, the surface modes on each interface can be coupled together to form symmetric and antisymmetric surface plasmon polaritons (SPPs) modes, connecting the evanescent fields at the two interfaces. The width of the waveguide determines the propagation constants of the two SPPs modes and will affect the near-field directional emission of the three sources. We find that the directionality of the three sources in the narrow waveguide is no longer perfect, but related to the position of the source. In addition, we also discuss the possibility of realizing near-field directional emission of three sources with only one electric dipole in different structures by selectively exciting the special SPPs mode. Our result increases the flexibility of controlling the direction of near-field emission of evanescent waves, having potential applications in nanophotonic propagation and multifunctional nanophotonic devices.