Rigorous electromagnetic analysis of resonant sub-wavelength metallic gratings by parametric Fourier modal method

Electromagnetic TM modes of metallic lamellar reflection or transmission gr atings are analyzed by means of the parametric fourier modal method. We sho w that the resonant optical response of such devices is due to the excitati on of guided waves inside the slits. Our rigorous methods allows us to defi ne a resonance condition number and to calculate the field everywhere insid e the grating layer.