  A conformal dispersive finite-difference time-domain (FDTD) method is
developed for the study of one-dimensional (1-D) plasmonic waveguides formed by
an array of periodic infinite-long silver cylinders at optical frequencies. The
curved surfaces of circular and elliptical inclusions are modelled in
orthogonal FDTD grid using effective permittivities (EPs) and the material
frequency dispersion is taken into account using an auxiliary differential
equation (ADE) method. The proposed FDTD method does not introduce numerical
instability but it requires a fourth-order discretisation procedure. To the
authors' knowledge, it is the first time that the modelling of curved
structures using a conformal scheme is combined with the dispersive FDTD
method. The dispersion diagrams obtained using EPs and staircase approximations
are compared with those from the frequency domain embedding method. It is shown
that the dispersion diagram can be modified by adding additional elements or
changing geometry of inclusions. Numerical simulations of plasmonic waveguides
formed by seven elements show that row(s) of silver nanoscale cylinders can
guide the propagation of light due to the coupling of surface plasmons.
