Complex propagation constants of surface plasmon polariton rectangular waveguide by method of lines.

A numerical study on the complex propagation constants of the surface plasmon polariton (SPP) rectangular hollow waveguide by the method of lines (MoL) is performed. New cut-off conditions are proposed for the SPP waveguide. A SPP rectangular hollow waveguide constructed of gold is first considered. The dependences of complex propagation constants on the sizes of the waveguide and on the wavelength are investigated. Fundamental and unusual characteristics of the SPP waveguide are revealed. The validity and limitations of effective index method (EIM) are examined by comparing the numerical results obtained by the MoL with the approximate results obtained by EIM. The differences in the propagation characteristics among the various metals are then shown.