Improved boundary integral equation neumann-to-dirichlet map method for diffraction gratings

The boundary integral equation (BIE) method is one of the most effective numerical methods for analyzing diffraction gratings. The recently developed BIE-Neumann-to-Dirichlet (BIE-NtD) method is particularly simple to use, since it avoids the quasi-periodic Green´s functions. In this paper, we present an improved BIE-NtD method. Numerical results indicate that our new BIE-NtD method achieves a high order of accuracy.