Fast modal method for subwavelength gratings based on B-spline formulation

We present a B-spline modal method for analyzing a stack of complex structured layers. Thanks to a B-spline approximation of the field, we solve the Maxwell equations. Diffraction calculation is based on the scattering matrices algorithm. We prove a good convergence of this method. Moreover, B-spline approximation results in very sparse matrices, which are used to hasten the computation of eigenmodes. A method for cleaning the inverted sparse matrix is also presented. (c) 2010 Optical Society of America