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

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 µm 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°, offering significant potential for infrared filtering applications.