IMPROVED FORMULATION OF THE COUPLED-WAVE METHOD FOR 2-DIMENSIONAL GRATINGS

A new formulation of the coupled-wave method for two-dimensional grati ngs is proposed. It is based on mathematical and physical results rece ntly obtained for one-dimensional gratings. Numerical evidence obtaine d for many different diffraction problems, including dielectric, metal lic, volume, and surface-relief gratings, shows that the new formulati on outperforms the conventional one in terms of convergence rates. The specific case of gratings with very small thickness, for which opposi te conclusions on the convergence performance are obtained, is studied and explained. The methodology can be applied to other numerical tech niques that rely on Fourier expansions of the electromagnetic fields a nd on grating parameters such as the permittivity and the permeability . (C) 1997 Optical Society of America.