Analysis of plane-wave scattering by bigratings

We present here a rigorous analysis of the plane-wave scattering by a class of bigratings, each of which consists of two separated gratings that may have different periods and different orientations. Inherently, this is a three-dimensional boundary value problem, regardless of the incidence condition. An exact formulation based on the method of mode matching is carried out, taking into account the effect of polarization couplings. Numerical results are shown for identifying physical phenomena associated with the class of bigrating structures. In particular, Wood's anomalies in the presence of a bigrating are carefully examined and the results are interpreted in terms of those well known for single gratings.