Any implementation of the beam propagation method, when used to analyse open problems, requires a procedure allowing radiation to leave the computational window. In this paper we present the results of a case study on the effectiveness of the classical Hadley's Transparent Boundary Conditions (TBC) and the Perfectly Matched Layer (PML) to handle strong radiation at the boundaries. A polished fibre coupler will be studied both in 2D and in 3D configurations using, in the former case, a scalar method and, in the latter, a full vectorial approach. Numerical results show that simple TBC can be used in 2D simulations also when high radiation occurs but they easily fail in 3D structures. Therefore, in these cases, the more complicated PML conditions should be preferred. References: 16
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机译：当用于分析开放问题时，光束传播方法的任何实现都需要一个允许辐射离开计算窗口的程序。在本文中，我们介绍了经典Hadley透明边界条件（TBC）和完美匹配层（PML）在边界处处理强辐射的有效性的案例研究结果。抛光光纤耦合器将在 2D 和 3D 配置中进行研究，在前一种情况下使用标量方法，在后一种情况下使用全矢量方法。数值结果表明，当发生高辐射时，简单的TBC也可用于二维模拟，但在三维结构中很容易失效。因此，在这些情况下，应首选更复杂的 PML 条件。[参考资料： 16]
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