Near-Field Microscopy of Plasmonic Waveguides and Tight-Binding Lattices

Abstract

Electronic computing has dominated data processing for decades, but we are reaching a point where fundamental physical limitations motivate the exploration of alternative approaches. Photonic and plasmonic systems provide promising routes toward compact, high-speed, and low-energy information processing by enabling strong light–matter interactions at the nanoscale. In particular, plasmonic waveguides allow optical confinement below the diffraction limit, making them attractive building blocks for integrated nanophotonic circuits. Furthermore, many fundamental condensed matter or quantum effects can be investigated with coupled waveguide arrays. However, their characterization and control require advanced experimental techniques capable of resolving optical fields at subwavelength scales. This thesis investigates plasmonic waveguides with a focus on their fabrication, near-field characterization, and functional coupling schemes. After an introduction to surface plasmon polaritons and their excitation, the thesis describes the fabrication methods used to realize plasmonic nanostructures and discusses the associated challenges. As a key tool for nanoscale optical characterization, the principles and experimental implementation of scattering-type scanning near-field optical microscopy are then presented. These techniques are used to investigate three distinct plasmonic waveguide systems. First, metal strip waveguides with chiral couplers are studied, demonstrating spin-dependent directional excitation of surface plasmon polaritons based on the polarization of incident light. Second, dielectric-loaded plasmonic waveguides are investigated, including a detailed analysis of their electromagnetic field components. Building on this, coupled dielectric-loaded surface plasmon polariton waveguides are explored as a platform for studying coupling dynamics and analogies to solid-state systems. By implementing a plasmonic analogue of the Su–Schrieffer–Heeger model, topological edge states are experimentally realized and directly visualized using near-field microscopy.