Nearly Perfect Fano Transmission Resonances through Nanoslits Drilled in a Metallic Membrane

We report nearly perfect optical transmission (87%) through freestanding metallic gratings with narrow slits, as the experimental demonstration of the theoretical prediction by Porto et al. [Phys. Rev. Lett. 83, 2845 (1999)]. In addition, we show that the Fano line shape of transmission spectra reveals the interplay between localized and propagating surface plasmon resonances, and allows us to determine the non-radiative losses. It provides the limits for the transmission efficiency and resonance quality factor. As an illustration, a mosaic of various bandpass filters has been achieved in a single membrane.