Mixed finite element numerical mode matching method for designing infrared broadband polarization-independent...

Conventional numerical methods have found widespread applications in the design of metamaterial structures, but their computational costs can be high due to complex three-dimensional discretization needed for large complex problems. In this work, we apply a recently developed numerical mode matching (NMM) method to design a black phosphorus (BP) absorber. NMM transforms a complex three-dimensional (3D) problem into 2D numerical eigenvalue problems plus a 1-D analytical propagation solution, thus it can save a lot of computational costs. BP is treated as a 2D surface and represented by the anisotropic surface conductance. With a realistic simulation study, we show that our method is more accurate and efficient than the standard finite element method (FEM). Our designed absorber can achieve an average absorption of 97.4% in the wavelength range of 15 to 23 μm under normal incidence. Then, we investigate the physical mechanism of the absorber, tuning the geometric parameters and electron doping to optimize the performance. In addition, the absorption spectra under oblique incidence and arbitrary polarization are studied. The results confirm that our absorber is polarization-independent and has high absorption at large incident angles. Our work validates the superiority of NMM and provides a new simulation platform for emerging metamaterial device design.