Broadband Absorption in Mid-Infrared via Trapezoidal Gratings Made of Anisotropic Metamaterial

Broadband absorption of electromagnetic energy plays an important role in energy harvesting and stealth. Here, we present and demonstrate an absorber with a wide bandwidth of 2.1 μm in mid-infrared. The trapezoidal metamaterial consists of alternating silicon carbide and dielectric films. We have numerically demonstrated that an ultrahigh absorption energy efficiency higher than 97.7% can be calculated from 10.6 μm to 12.7 μm. The proposed absorber has high absorption efficiency at a wide-angle range. The simulation results are consistent with the theoretical calculation based on effective medium theory. The theoretical model simplifies the multilayer structure into an effectively homogeneous metamaterial with hyperbolic dispersion. In addition, the distributions of magnetic field depict that different wavelengths can be trapped at structures with various widths. The mechanism of this phenomenon is attributed to the slowlight modes. Furthermore, a dual-sized absorber is designed to achieve high efficiency and broadband absorption, which is easy to manufacture. Our study has potential applications in the areas of energy harvesting materials, thermal emitters and photovoltaic devices in the mid-infrared.