Invisibility Dips of Near-Field Energy Transport in a Spoof Plasmonic Metadimer

TL;DR

This paper demonstrates near-field invisibility dips in spoof plasmonic resonators, revealing strong coupling effects and Fano-like line-shapes useful for sensing and on-chip optical applications.

Contribution

It introduces the use of spoof surface plasmons to observe near-field invisibility dips, overcoming the experimental challenges of narrow gaps in optical frequencies.

Findings

Observation of Fano-like transmission dips in near-field energy transport

Enhanced coupling between stacked SLSP resonators causes spectral dips

Field maps confirm mode interference and localization

Abstract

Invisibility dips, minima in scattering spectrum associated with asymmetric Fano-like line-shapes, have been predicted with transformation optics in studying strong coupling between two plasmonic nanoparticles. This feature of strongly coupled plasmonic nanoparticles holds promise for sensor cloaking. It requires an extremely narrow gap between the two nanoparticles, though, preventing its experimental observation at optical frequencies. Here, the concept of spoof surface plasmons is utilized to facilitate the strong coupling between two spoof-localized-surface-plasmon (SLSP) resonators. Instead of observing in far field, the near-field energy transport is probed through the two SLSP resonators. By virtue of enhanced coupling between the two resonators stacked vertically, a spectral transmission dip with asymmetric Fano-like line-shape, similar to the far-field invisibility dips predicted by transformation optics, is observed. The underlying mode interference mechanism is further demonstrated by directly imaging the field maps of interfered waves that are tightly localized around the resonators. These near-field invisibility dips may find use in near-field sensing, on-chip switching, filters and logical operation elements.