Defect modes of one-dimensional graphene based photonic crystals
Photonic crystal is a kind of functional band gap material with periodical units and arrays. Due to its unique electromagnetic properties, such as photonic band gap and photonic localization, photonic crystal has become one of key research area across the world. Recently, it is observed that the multilayer structure of a stack of monolayer graphene sheets separated by dielectric slabs at low-terahertz frequencies possesses band-gap properties and supports a series of bandpass and band-stop regions. In this paper, considering a one-dimensional photonic crystal formed by a stack of graphene sheets and dielectric slabs, we introduce a single and dual layers defects by replacing graphene layer by another dielectric material. By using the transfer matrix method, the tunable filtering properties are discussed both for the graphene photonic crystal with a single defect or dual defects. It is found that a very narrow and two narrow transmission peaks appear for the single-layer defect or the dual-layer defect structures, respectively. Furthermore, influence of parameters, and the voltage on the defect modes are discussed. Figure 1 shows our the graphene photonic crystal with a single-layer defect and dual-layer defect. Figure 2 shows the transmission curves of the photonic crystals with no defect, single-layer defect and dual-layer defect. We can see that there are two gaps at the center frequencies of 0.6, 0.7 and 0.8 THz, respectively. For a single-layer defect, a narrow filter appears among the three gaps, and two narrow filters will appear to form dual-band narrow filters for the dual-layer defect. In the further study, we also find that all the narrow filters have a red shift with decreasing of external voltages. These properties of the defect structure would provide potential applications in tunable multi-band filters.