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)10.1103/PhysRevLett.83.2845]. 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 nonradiative 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.