Near-Field Interference for the Unidirectional Excitation of Electromagnetic Guided Modes

TLDR

Wave interference is a fundamental manifestation of the superposition principle with numerous applications. The study shows that the vectorial structure of an emitter’s near field is essential for controlling its radiation through self‑interference with a mediating object. The authors mimicked a circularly polarized dipole with a single illuminated slit in a gold film and measured unidirectional surface‑plasmon excitation in a spatially symmetric structure. Near‑field interference of the dipole produces unidirectional guided electromagnetic modes with no preferred far‑field direction, and the surface‑wave direction can be switched by changing the polarization.

Abstract

Wave interference is a fundamental manifestation of the superposition principle with numerous applications. Although in conventional optics, interference occurs between waves undergoing different phase advances during propagation, we show that the vectorial structure of the near field of an emitter is essential for controlling its radiation as it interferes with itself on interaction with a mediating object. We demonstrate that the near-field interference of a circularly polarized dipole results in the unidirectional excitation of guided electromagnetic modes in the near field, with no preferred far-field radiation direction. By mimicking the dipole with a single illuminated slit in a gold film, we measured unidirectional surface-plasmon excitation in a spatially symmetric structure. The surface wave direction is switchable with the polarization.