Topology of the near field in enhanced transmission through subwavelength apertures

TL;DR

This paper investigates the near-field energy flow in enhanced optical transmission through subwavelength apertures, revealing topological transitions and flow structures that govern the transmission process.

Contribution

It introduces a modal formulation to analyze the energy flow topology in enhanced transmission, providing a unified interpretation for various aperture geometries.

Findings

Resonant transmission involves a reorganization of energy flow near the aperture.

Energy transport exhibits topological transitions with vortices and saddle points.

Modal analysis explains enhanced transmission in both slit and channel geometries.

Abstract

We analyze enhanced optical transmission through subwavelength apertures using a modal formulation for the two fundamental polarizations, transverse electric (TE) and transverse magnetic (TM). Within this framework, the fields inside the aperture are described in terms of guided modes whose excitation and interference govern the transmission process. By examining the near-field energy transport through the time-averaged Poynting vector, we show that resonant transmission is accompanied by a pronounced reorganization of the energy flow in the vicinity of the aperture. As the wavelength is varied across resonance, the energy transport undergoes a topological transition characterized by vortical and saddle-type flow structures, localized backflow regions, and efficient energy funneling through the aperture. These features correlate with strong phase gradients and phase singularities associated with the excited modal fields. The modal approach provides a unified and physically transparent interpretation of enhanced transmission in both slits and channels, applicable to perfect conductors and beyond plasmonic regimes.