| In 2004, Andre and Constantine succeeded in separating graphene from graphite for the first time, proving that it could exist alone, and winning the prize for. Graphene has a very high electron mobility at room temperature. The conductivity of graphene is tunable with voltage,temperature and so on. In this paper, we study the dispersion properties and defect mode properties of one-dimensional graphene photonic crystals, and design two types of tunable broadband polarization insensitive terahertz absorbers based on graphene.The main work of this paper is as follows:(1) Based on the Maxwell equation, the transfer matrix equation of one-dimensional anisotropic graphene photonic crystals is derived, and the complex dispersion relation is obtained. The study found that as the dielectric constant of graphene complex characteristics, the corresponding dispersion can be divided into two parts, one is the transmission curve corresponding to the real part of the wave vector, and a loss characteristics corresponding to the imaginary part of the wave vector.Finally, the simulation software is used to build the model, which further verifies the correctness of the theoretical derivation.(2) By introducing multiple defects in two layer and three layer graphene in one-dimensional photonic crystal, we found that due to the introduction of multilayer defects, a number of defect modes emerges in the original band gaps, and the frequency and amplitude of the defect modes can be tuned by external voltage. It is also found that the frequency, amplitude and number of defect modes are affected by the number of layers, defects numbers. When the number of defects increases,the amplitude of defect mode decreases. The peak value of the defect mode is not changed obviously, but the position of the defect mode moves to the center of the band gap with the increase of the number of cycles. When the number of photonic crystals in the defect layer increases to a threshold value,the double defect modes combine together. When the defect layer is changed from symmetry to irregularity, the peak of defect mode increases.(3) Most absorbing structures based on graphene are usually narrow and polarization sensitive. two types of wideband and polarization insensitive THz absorber are designed. And the physical mechanism of broadband absorption filter is analyzed by using mode superposition principle and impedance matching principle. These tunable absorbers have important applications. Finally, the influence of the conductivity of graphene on the absorption characteristics of graphene absorber is discussed.Graphene based photonic crystals have important applications in terahertz functional devices, this study may further promote the development of terahertz multi band tunable narrowband filter and polarization insensitive broadband absorbers in the future. |
