Evanescent field boundary conditions for modelling of light propagation

In this work, we introduce a straightforward and original approach for evanescent field boundary conditions (EBCs), which can be, in principle, applied in both Beam Propagation Method (BPM) and Finite Difference Time Domain Method (FDTD) numerical simulations. Importantly, suggested method may serve as an efficient alternative to typically applied ones, such as transparent boundary conditions (TBCs), absorbing boundary conditions (ABCs) or perfectly matched layer (PML) boundary conditions, giving comparable or even better results in terms of smaller reflections and of shorter computation time. Definition of proposed evanescent function, a way of its practical implementation, as well as an influence of its parameters on the light beam propagation in the free-space and in exemplary photonic structures are described in detail. In addition, results of EBCs application are compared with those achieved for Dirichlet, TBC and PML boundary conditions used in analogous arrangement of the physical systems.