Abstract

Surface-relief gratings made with anisotropic materials are finding more applications. An example is grooved magneto-optic disks as data storage media. The present work is a reformulation of the couple-wave method, for solving the anisotropic grating problem, that is described in Refs. 1-3. [Since the method essentially is a modal method relying on expanding both the electromagnetic fields and the permittivity function into Fourier series, here it is referred to as the Fourier modal method (FMM).] It originated from the work documented in Refs. 4-7. Recently Lalanne and Morris⁴, and Granet and Guizal⁵ simultaneously reformulated the conventional FMM for isotropic gratings in TM polarization. As a result, the convergence of the method for highly conducting metallic gratings was greatly improved. Auslender and Hava⁶ also reported the same reformulation. The findings of these authors were mathematically justified and summarized in the form of three Fourier factorization rules⁷. The use of these factorization rules has led to improvement of convergence in two other cases: the C method for gratings with sharp edges⁸ and the FMM for crossed gratings.⁹ This conference paper briefly reports yet another successful application of the factorization rules. A detailed exposition will soon appear elsewhere.¹⁰

© 1998 Optical Society of America