Broadband and Polarization-Insensitive Absorption Based on a Set of Multi-Sized Fabry-Perot-Like Resonators

We experimentally and theoretically demonstrate a broadband, and polarization-insensitive truncated-cone-type multilayer metamaterial absorber in the near-IR to mid-IR range. Its fabrication process combines lithography and ion beam etching techniques, which have the advantages of both high throughput and nanoscale feature size. The absorption band could be experimentally tuned from near-IR to the mid-IR range by tailoring the geometric parameters, that is, bevel angle and bottom diameter. In theory, this multilayer structure can support the gap surface plasmon-polariton (G-SPP) mode to confine the electric field in all dielectric layers. Because of counter-propagating G-SPPs forming standing waves, the stronger electric field is confined in the dielectric layers like Fabry-Perot resonators. These multisized Fabry-Perot-like resonators can trap multiwavelength incident light, giving rise to high and broadband absorption. With the separation between two adjacent nanostructures decreasing, the leakage fields of G-SPP modes can couple with each other in the air gap, leading to a stronger field and higher absorption. This broadband metamaterial absorber could lead to various advanced applications, and its fabrication method provides a straightforward and mass-production strategy to fabricate multilayer metamaterials.