Intertwined Fano resonances in sub-wavelength metallic gratings: omnidirectional and wideband optical transmission

Abstract: Metallic gratings can be used as infrared filters, but their performance is often limited by bandwidth restrictions due to metallic losses. In this work, we propose a metallic groove-slit-groove (GSG) structure that overcomes these limitations by exhibiting a large bandwidth, angularly independent, extraordinary optical transmission. Our design achieves high transmission efficiency in the longwave infrared range, driven by Fano-type resonances created through the interaction between the grooves and the central slit. This mechanism results in a tunable 2 $\mu$m transmission window with high rejection rate. We extend the concept to a two-dimensional GSG array, exhibiting a polarization insensitive 80% transmission window for incident angles up to 50{\deg}, offering significant potential for infrared filtering applications.