Analysis of strip gratings using a parametric modal method by Fourier expansions

The combined boundary conditions method (CBCM) is one of the most versatile methods to treat diffraction from strip gratings. This method is revisited using the original concept of adaptive spatial resolution, that consists of introducing a new coordinate system in which the fields are meshed more finely in the neighbourhood of the strips. The result is a strong improvement of the convergence of the computed efficiencies and a better representation of the fields. For instance, we observe a dramatic reduction of the Gibbs phenomenon.