Properties of omnidirectional gap and defect mode of one-dimensional graphene-dielectric periodic structures

We theoretically investigate the optical response of one-dimensional graphene based photonic crystal (1D-GPC) structures with and without defect layer in the low terahertz (THz) frequency region. The 1D-GPC is composed of alternated layers of isotropic dielectric material (SiO₂) and graphene monolayer sheets. Using the transfer matrix method (TMM), the effects of several parameters such as the incidence angle, width, thickness, and refractive index of the defect layer and the chemical potential of graphene sheets on the device response will be explored in detail for both TE and TM polarizations. Our simulation results indicate that when a defect layer is introduced, the structure may support two kinds of defect modes. One kind is created in the Bragg gap and the other one is created in the graphene-induced photonic band gap (GIPBG). Our results reveal that a defect mode can appear within the GIPBG only for an optical thickness of the defect layer greater than that of the alternated dielectric layers of the 1D-GPC. While, the defect modes in the Bragg gap may be created by simply breaking of the periodicity of the dielectric lattice. In addition, the resonance frequency of defect mode in the GIPBG is found to be almost insensitive to the incident angle for both polarizations. Moreover, we show that an effective Brewster angle for our structure can be deduced from the variation of the amplitude of defect mode with the incident angle. Our analysis has shown an innovative idea for the realization of tunable broadband reflectors and narrowband filtering devices.