Abstract

Recently, Lalanne and Morris¹, and Granet and Guizal² numerically achieved dramatic improvement in the convergence rate of the modal method by Fourier expansion (MMFE, also called the coupled-wave method) for metallic gratings in TM polarization by reformulating the algebraic eigenvalue problem. Figure 1 shows a numerical comparison between the old and new formulations for a case studied in Ref. 3. Their work convincingly proved that the cause of the slow convergence of the MMFE is not the use of the Fourier series but the way in which the Fourier series of the permittivity and reciprocal permittivity functions are used.

© 1996 Optical Society of America