Enhanced propagation in a plasmonic chain waveguide with nanoshell structures based on low- and high-order mode coupling.

We studied the performance of a plasmonic chain waveguide by employing an array of nanoshell structures. The optical properties of the proposed structures are discussed in detail with respect to the mode coupling for both low-order resonances and high-order multipolar modes. We show (a) that the choice of nanoshell particles allows an easy tuning of the structure's resonances according to given wavelength specifications and (b) that the resonances are insensitive to the chain length when high-order multipolar modes are involved. Moreover, chain waveguides that are operated on resonant multipolar modes provide propagation lengths up to 1.88 microm, which is beyond what is maximally achieved by conventional solid particle chains. This is attributed to the large field enhancement within metallic nanoshell structures, as well as to far-field effects, which play an important role in low-loss light guiding along nanoshell chains.