Theory of linear chains of metamaterial/plasmonic particles as subdiffraction optical nanotransmission lines

Here we discuss the theory and analyze in detail the guidance properties of linear arrays of metamaterial/plasmonic small particles as nanoscale optical nanotransmission lines, including the effect of material loss. Under the assumption of dipolar approximation for each particle, which is shown to be accurate in the geometry of interest here, we develop closed-form analytical expressions for the eigenmodal dispersion in such arrays. With the material loss included, the conditions for minimal absorption and maximum bandwidth are derived analytically by studying the properties of such dispersion relations. Numerical examples with realistic materials, including their ohmic absorption and frequency dispersion, are presented. The analytical properties discussed here also provide some further physical insights into the mechanisms underlying the subdiffraction guidance in such arrays and their fundamental physical limits. The possibility of guiding beams with subwavelength lateral confinement and reasonably low decay is discussed, offering the possible use of this technique at microwave, infrared, and optical frequencies. Interpretation of these results in terms of nanocircuit concepts is presented, and possible extension to two- and three-dimensional nanotransmission line optical metamaterials is also foreseen.