Asymmetry-Enabled Dual-Resonant Mid-Infrared Absorption in Subwavelength Perforated Metal Structures

The ability to engineer multiresonant absorption response in the midwave infrared provides spectral information critical for detection and sensing. We design and fabricate thin metal absorbers with a polarization-dependent, multiresonant, and spectral response. Our approach exploits the coexistence of a conventional Fabry-Peròt (FP) resonance and a geometry-enabled resonance arising from symmetry breaking within a single, dilute-metal structure. The resulting anisotropic geometry produces a polarization-dependent response with a single resonance for x-polarized light and dual resonances for the orthogonal polarization. The resonances correspond to two fundamentally distinct physical mechanisms (i.e., cavity- and symmetry-driven); we experimentally verify our findings and achieve dual-resonant thin metal structures. These findings are promising for independently tailoring spectral position and line width within a single compact structure.