Optical absorption engineering in dispersive band structure of MWCNTs array:design and optimization of total absorber for NIR to MIR regime

Abstract:

In this paper, we design a total infrared (IR) absorber based on a dispersive band structure of two-dimensional (2D) multiwall carbon nanotube (MWCNTs) square array working from near IR (NIR) to mid IR (MIR) regime. The absorption characteristics have been investigated by the 2D finite-difference time domain (FDTD) method in square lattice photonic crystal (PC) of the multipole Drude-Lorentz model inserted to the dispersive dielectric function of MWCNTs. Dispersive photonic band structure and scattering parameters for the wide range of lattice constants from 15 nm to 3 500 nm with various filling ratios have been calculated. The results show that for large lattice constant (>2 000 nm), the Bragg gap moves to the IR regime and leads to MWCNTs arrays acting as a total absorber. For a structure with lattice constant of 3 500 nm and filling factor of 12%, an enhanced absorption coefficient up to 99% is achieved in the range of 0.35 eV (λ=3.5 μm) nominated in the MIR regime. Also, the absorption spectrum peak can be tuned in the range of 0.27—0.38 eV (λ=4.59—3.26 μm) with a changing filling factor. Our results and methodology can be used to design new MWCNTs based photonic devices for applications like night-vision, thermal detector, and total IR absorbers.