Passive tunable and polarization-insensitive fan-like metamaterial absorber in the visible spectrum

We numerically study a fan-like metamaterial absorber (FMMA) composed of an Au-TiO2-Au multilayer with a 3-D finite-difference-time-domain method (FDTD) and verify it experimentally. Our proposed design shows high absorbance, >98% numerically, in the visible spectrum, which is due to the excitation of both localized surface plasmons (LSPs) and propagating surface plasmons (PSPs). In particular, the TiO2 dielectric spacer sandwiched between the top fan-like nanopatterned structure and the bottom planar Au-film is identified as playing a crucial role in the spectral response of the FMMA. Its introduction excites the PSP mode, which first enhances the absorbance of the FMMA and subsequently redshifts the spectral absorbance with a further increase in the thickness. Moreover, the proposed FMMA, numerically and experimentally, also shows polarization and angle insensitivity in the visible spectrum under normal and selected oblique incidence. These results offer unique potential in sensing applications and devices requiring selective absorption in the visible spectral region. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement