Broadband, Polarization-Insensitive, and Wide-Angle Optical Absorber Based on Fractal Plasmonics

In this letter, a plasmonic absorber consisting of a metal-dielectric-metal stack with a top layer of Sierpinski nanocarpet is theoretically investigated. Such a compact absorber depicts broadband angle-independent behavior over a wide optical wavelength range (400-700 nm) and a broad range of incidence angles (0 degrees-80 degrees). Including several feature sizes, such a fractal-like structure shows an average simulated extinction response of 0.85 for either transverse electric or magnetic polarization states under normal incidence. Underlying mechanisms of absorbance due to excited surface plasmon modes as well as electric/magnetic dipole resonances are well revealed by investigating electric field, magnetic field, and current distributions. The proposed absorber opens a path to realize high-performance ultrathin light trapping devices.