Crank-Nicolson Reformulation of ADI-FDTD PML Extensions

The usual approach found in the literature to extend the perfectly matched layers (PMLs) absorbing technique to the alternating direction implicit finite-difference time-domain (ADI-FDTD) method employs the so-called ADI-FDTD procedure. In this letter, we show that these extensions can also be systematically reformulated as perturbations of Crank-Nicolson schemes