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

摘要

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 3500 nm with various filling ratios have been calculated.The results show that for large lattice constant(>2000 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 3500 nm and filling factor of 12%,an enhanced absorption coefficient up to 99%is achieved in the range of 0.35 eV(λ=3.5μm)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—3.26μm)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.