Theory of Linear Chains of Metamaterial/Plasmonic Particles as   Sub-Diffraction Optical Nanotransmission Lines
  Here we discuss the theory and analyze in detail the guidance properties of linear arrays of metamaterial/plasmonic small particles as nano-scale 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 eigen-modal 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 sub-diffraction guidance in such arrays and their fundamental physical limits. Possibility of guiding beams with sub-wavelength 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 2-D and 3-D nanotrasnsmission line optical metamaterials is also foreseen. 
Andrea Alu, Nader Engheta