We report a broadband polarization-independent perfect absorber with wide-angle near unity absorbance in the visible regime. Our structure is composed of an array of thin Au squares separated from a continuous Au film by a phase change material (Ge2Sb2Te5) layer. It shows that the near perfect absorbance is flat and broad over a wide-angle incidence up to 80[deg] for either transverse electric or magnetic polarization due to a high imaginary part of the dielectric permittivity of Ge2Sb2Te5. The electric field, magnetic field and current distributions in the absorber are investigated to explain the physical origin of the absorbance. Moreover, we carried out numerical simulations to investigate the temporal variation of temperature in the Ge2Sb2Te5 layer and to show that the temperature of amorphous Ge2Sb2Te5 can be raised from room temperature to > 433[emsp14]K (amorphous-to-crystalline phase transition temperature) in just 0.37[emsp14]ns with a low light intensity of 95[emsp14]nW/[mgr]m2, owing to the enhanced broadband light absorbance through strong plasmonic resonances in the absorber. The proposed phase-change metamaterial provides a simple way to realize a broadband perfect absorber in the visible and near-infrared (NIR) regions and is important for a number of applications including thermally controlled photonic devices, solar energy conversion and optical data storage.

We present the design of a polarization-independent tunable absorbing metamaterial (MM) in the mid-infrared wavelength regime. Our structure is composed of an array of thin gold (Au) squares separated from a continuous Au film by a phase-change material (PCM) layer. It is shown that a 10% tuning of the absorbance peak can be obtained by switching the PCM between its amorphous and crystalline states. The strong absorbance shows a substantial overlap between TE and TM polarization states over a wide range of incident angles. The electric field, magnetic field, and current distributions in the absorber are investigated to further explain the physical origin of the absorption. The study provides a path toward the realization of tunable absorbers for applications, such as selective thermal emitters, sensors, and bolometers.

Giant chiroptical responses routinely occur in three dimensional chiral metamaterials (MMs), but their resonance elements with complex subwavelength chiral shapes are challenging to fabricate in the optical region. Here, we propose a new paradigm for obtaining strong circular conversion dichroism (CCD) based on extrinsic 2D chirality in multilayer achiral MMs, showing that giant chiroptical response can be alternatively attained without complex structures. Our structure consists of an array of thin Au squares separated from a continuous Au film by a GaAs dielectric layer, where the Au squares occupy the sites of a rectangular lattice. This structure gives rise to a pronounced extrinsically 2D-chiral effect (CCD) in the mid-infrared (M-IR) region under an oblique incidence, where the 2D-chiral effect is due to the mutual orientation of the Au squares array and the incident light propagation direction; the large magnitude of CCD due to the large difference between left-to-left and right-to-right circularly polarized reflectance conversion efficiencies.

A metal/phase-change material/metal tri-layer planar chiral metamaterial in the shape of a gammadion is numerically modelled. The chiral metamaterial is integrated with Ge₂Sb₂Te₅ phase-change material (PCM) to accomplish a wide tuning range of the circular dichroism (CD) in the mid-infrared wavelength regime. A photothermal model is used to study the temporal variation of the temperature of the Ge₂Sb₂Te₅ layer and to show the potential for fast switching the phase of Ge₂Sb₂Te₅ under a low incident light intensity of 0.016mW/μm².