Complex-envelope LOD-FDTD for wave propagation in dispersive metallic gratings

In this paper, a complex-envelope (CE) scheme is introduced into the locally one-dimensional finite-difference time-domain (LOD-FDTD) method for the extraordinary optical transmission (EOT) analysis of periodic metallic gratings. The dispersion of the metal, caused by the evanescent waves propagating along the interface between the metal and dielectric materials in the visible and near infrared regions, is expressed by the Drude model and solved with a generalized auxiliary differential equation (ADE) technique. With efficient preprocessing for the lower-upper (LU) decomposition, the periodic boundary condition (PBC) is applied to the two-dimensional (2-D) metallic grating structure. Numerical examples show that the proposed method provides much more accurate results than the traditional ADE-LOD-FDTD with the same CFL number.