“…To remove the above CFL limit of time‐step size, we presented here an implicit scheme. By applying the ADI principle , we have broken up the computation of (17) in the FDTD solution marching from the k th time‐step to the ( k + 1) th time‐step into two computational sub‐advancements: the advancement from the k th time‐step to the ( k + 1/2) th time‐step and the advancement from the ( k + 1/2) th time‐step to the ( k + 1) th time‐step. For the first half‐step, using the first‐order upwind scheme for spatial derivatives, and defining Yields the following equation: …”