FMM / RCWA [S-Matrix]

The FMM/RCWA solver works in the spatial frequency domain (k domain). It consists of

• an eigenmode solver for each periodically modulated layer and
• an S-matrix for matching the boundary conditions between the layers.

The eigenmode solver computes the field solution in the k domain for the periodically modulated medium in each layer. The S-matrix algorithm calculates the response of the whole layer system by matching the boundary conditions in a recursive manner. It is well-known for its unconditional numerical stability since, unlike the traditional transfer matrix, it avoids the exponentially growing functions in the calculation steps.