Evolution of Plasmonic Modes in a Metal Nano-Wire Studied by a Modified Finite Element Method

A finite width thin metal film plasmonic nanowire with its unique feature of subwavelength light guiding is finding many applications in compact integrated nanophotonic circuits and sensors. Full-vectorial finite element method (FV-FEM) is becoming an important simulation tool for the analyses of such exotic waveguides. Instead of a penalty approach reported earlier, a more direct divergence formulation considering each discretized element's optical properties to eliminate nonphysical modal eigenvectors has been exploited and is reported here. Long and short-range fundamental and higher order plasmonic modes and supermodes of a pure metal nanowire and their evolutions with waveguide geometry, surrounding identical, and nonidentical dielectric cladding materials and operating wavelength are thoroughly studied. Interesting long-range modal properties such as, supermode formation, complex phase matching, and mode evolution in identical and non-identical clad metal nanowires have been observed and explained in detail including supermode profiles. This study is expected to help in understanding the evolution of plasmonic guided modes in compact active and passive integrated photonic devices containing metal narrow strips.