2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/17645We study electromagnetic waves scattering by a 2D photonic crystal made of a stack of diffraction gratings. In case where there are only two propagative modes in the crystal, we derive an explicit expression for the superior (resp. inferior) envelope of the reflected (resp. transmitted) energy.5 pages, 6 figures, submitted to J. Opt. A: Pure and Applied OpticsMaterials Sciencetext