Phase-Modulation Metasurface-Based Visible Broadband Absorbers with Polarization Sensitivity or Independence

Metasurface-based broadband absorbers have attracted widespread attention due to the advantages of ultra-thin, lightweight, flexible design. Currently, the main design principle depends on the amplitude modulation for the incident beam, which requires high-loss material and multiplex resonances, with fabrication duplication and severe crosstalk. Herein, two kinds of visible broadband metasurface absorbers are proposed based on the phase-modulation principle. The first is composed of a staggered Al trapezoidal array on the SiO2/Al substrate, where adjacent units have a phase difference of pi for the y-polarized beam to generate the destructive interference, leading to a high average measured absorptivity of 73.37% for the whole visible band. On the contrary, this absorber reflects the x-polarized beam with a reflectivity of 51.65%. To achieve polarization-independent absorption, a 3x3 supercell metasurface is proposed, consisting of two groups of quasi-trapezoidal interlaced arrangements in the x- and y-directions separately. The measured spectra exhibit perfect polarization independence and excellent absorption (84.13%). Besides, both have angle robustness within 60 degrees and refractive index robustness within 1.49. In theory, the influence of diffraction on the absorption effect is emphasized systematically. This research proposes a novel strategy to achieve broadband absorption, which can serve as a platform for polarizers, solar batteries, etc.