Tunable optical bandstop filter enabled by bilayer metasurface

This study presents a bilayer metasurface consisting of coupled metallic nanorod pairs exhibiting tunable stop-band filtering in the optical frequency range. The stop-band originates from plasmon hybridization, producing symmetric and antisymmetric resonances. Numerical simulations and equivalent RLC circuit analysis reveal that decreasing inter-rod spacing or increasing rod dimensions enhances coupling, broadens the stop band, and shifts its central wavelength. The filtering characteristics are additionally influenced by variations in the dielectric permittivity and the choice of rod material. Metasurfaces employing noble metals such as silver or gold provide the most favorable performance, yielding a central stop band around 953 nm (spanning 600-1305 nm) with a shape factor of 1.6 and an insertion loss below 0.01. Theoretical and numerical analyses provide a comprehensive understanding of the coupling mechanisms in the bilayer metastructure and offer clear design guidelines for high-performance nanophotonic stop-band filters.