Long-wavelength infrared metamaterial absorber with polarization and angle insensitivity using compact hybrid cylindrical structures

Broadband metamaterial absorbers in the long wavelength infrared region are promising in applications including thermal imaging, cloaking, radiative cooling and IR signature suppression. Although high absorption over the long wavelength infrared region has been extensively achieved, the challenge is to shrink both the thickness and lateral footprint of unit absorbing structures. Here, a compact broadband long wavelength infrared metamaterial absorber consisting of multilayered Ge/Ti/Ge/SiO₂ hybrid cylindrical structures, whose period and thickness are only ∼1.2 μm, is proposed and realized. Various surface plasmon polaritons, localized surface plasmon resonances and their hybridization modes in the long wavelength infrared region, with polarization and angle insensitivity (in the range of 0-45°), are supported by this compact absorber whose absorbing unit is ultra-thin with a small footprint, thanks to the strong redshift effect induced by high-k Ge. Paired with the loss provided by Ti and SiO₂, an experimental spectral averaged absorption of 92.7% is achieved over 8 to 14 μm, agreeing well with simulation. The absorber can be facilely fabricated by a standard photolithographic process, not requiring lengthy and costly e-beam lithography. The absorber is promising in IR signature suppression indicated by preliminary results. The structural compactness and excellent long wavelength infrared absorbing capability grant the presented absorber good potential in various applications, especially those requiring miniaturization, integration and low heat capacity.