Abstract
In a recent work [J. Opt. Soc. Am. A 28, 738 (2011)], Lifeng Li and Gerard Granet investigate nonconvergence cases of the Fourier modal method (FMM). They demonstrate that the nonconvergence is due to the irregular field singularities at lossless metal-dielectric right-angle edges. Here we make further investigations on the problem and find that the FMM surprisingly converges for deep sub-wavelength gratings (grating period being much smaller than the illumination wavelength). To overcome the nonconvergence for gratings that are not deep sub-wavelength, we approximately replace the lossless metal-dielectric right-angle edges by a medium with a gradually varied refraction index, so as to remove the irregular field singularities. With such treatment, convergence is observed as the region of the approximate medium approaches vanishing.
© 2014 Optical Society of America
Full Article | PDF ArticleMore Like This
Junda Zhu, Haitao Liu, and Ying Zhong
J. Opt. Soc. Am. A 33(5) 845-853 (2016)
Lifeng Li and Gérard Granet
J. Opt. Soc. Am. A 28(5) 738-746 (2011)
Lifeng Li
J. Opt. Soc. Am. A 29(4) 593-604 (2012)