TBC and PML conditions for 2D and 3D BPM: a comparison

Any implementation of the beam propagation method, when used to analyse ope n problems, requires a procedure allowing radiation to leave the computatio nal window. In this paper we present the results of a case study on the eff ectiveness of the classical Hadley's Transparent Boundary Conditions (TBC) and the Perfectly Matched Layer (PML) to handle strong radiation at the bou ndaries. A polished fibre coupler will be studied both in 2D and in 3D conf igurations using, in the former case, a scalar method and, in the latter, a full vectorial approach. Numerical results show that simple TBC can be use d in 2D simulations also when high radiation occurs but they easily fail in 3D structures. Therefore, in these cases, the more complicated PML conditi ons should be preferred.