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Concepts and constraints of plasmonic waveguides operating from the visible to the THz regime

A number of examples of metallic plasmon waveguides for high-confinement guiding of electromagnetic energy working in different parts of the spectrum are reviewed. While at visible frequencies, out-of-plane confinement below the diffraction limit is possible in simple planar geometries due to the efficient coupling of the electromagnetic field to the conduction electron plasma of the metal interfaces constituting the waveguide, at lower frequencies in the far-infrared a metamaterials approach is needed in order to engineer a plasmonic response through surface patterning. Additionally, an approach for efficient coupling of plasmon waveguides operating in the telecommunications window to optical fiber tapers is presented.