Modal Absorption in the FDTD Method: a Critical Review

This paper deals with absorbing boundary conditions for the finite difference time domain (FDTD) method applied to homogeneous lossless waveguide structures. A theoretical formulation of the so-called ‘modal absorption’ (MA) is developed. On the basis of this theory different implementations available in the literature have been derived and compared. Then, some techniques to enhance the efficiency of the method have been proposed and tested. It is demonstrated that, with the proposed methods, the high level of accuracy of the original formulations is retained, while the computational cost is strongly reduced.