Topology of the near field in enhanced transmission through subwavelength apertures

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.

Figures (5)

• Figure 1: Near-field energy flow through a subwavelength slit under TM illumination. Streamlines represent the time-averaged Poynting vector $\langle \bm{S}\rangle$ across a wavelength scan. The resonant regime exhibits pronounced energy funneling, localized backflow, and nontrivial streamline organization.
• Figure 2: Correlation between energy-flow topology and phase structure near a subwavelength slit. The resonant regime exhibits strong phase gradients and singular features associated with the excited modal field, which organize $\langle \bm{S}\rangle$ into vortical and saddle-type patterns.
• Figure 3: Evolution of the transverse electric-field component $E_y$ under TM illumination. Resonant transmission is accompanied by strong localization near the slit edges, providing a direct near-field mechanism for polarization selectivity within the modal picture.
• Figure 4: Near-field energy flow in a subwavelength channel under TM illumination. The resonant regime again exhibits strong funneling and localized backflow/recirculation near the channel entrances, consistent with resonant excitation of the dominant TM guided mode.
• Figure 5: Representative channel field evolution across the wavelength scan. Enhanced localization at resonance accompanies the energy-flow reorganization and is consistent with modal buildup inside the channel.