The modal method is well adapted for the modeling of deep-groove, high-contrast gratings of short period, possibly involving metal parts. Yet problems remain in the case of the TM polarization in the presence of metal parts in the corrugations: whereas most of the diffraction features are explained by the interplay of an astonishingly small number of true propagating and low-order evanescent modes, the exact solution of the diffraction problem requires the contribution of two types of evanescent modes that are usually overlooked. We investigate the nature and the role of these modes and show that metal gratings can be treated exactly by the modal method.
© 2006 Optical Society of America
Diffraction and Gratings
Original Manuscript: February 6, 2006
Revised Manuscript: April 14, 2006
Manuscript Accepted: April 18, 2006
Maud Foresti, Ludivine Menez, and Alexander V. Tishchenko, "Modal method in deep metal-dielectric gratings: the decisive role of hidden modes," J. Opt. Soc. Am. A 23, 2501-2509 (2006)