Research Of Tunable Electromagnetically Induced Transparency Based On Graphene Metamaterials

In recent years, THz technology has been greatly developed. Because of its special position in the electromagnetic spectrum,THz wave has a wide application prospect in medical diagnosis, environmental monitoring, mobile communication and military radar. However, the lack of effective materials limits the further development and practical application of THz technology. Graphene, as a two-dimensional semiconductor material,owns a high carrier mobility and excellent photoelectric properties, and has unique advantages in the development of THz devices. In this paper, the structural design and characteristics of electromagnetically induced transparency based on graphene metamaterials are studied.The main contents and conclusions of this paper are summarized as follows:1. Based on the tunability of the conductivity of graphene, the T-shaped graphene nanostructures are designed. Through the investigation, we find that when the bright and dark modes are close to each other, electromagnetically induced transparency (EIT) can be produced. The change of EIT effect with frequency is discussed under different geometrical dimensions. The results show that when the distance between two graphene strips increases from Onm to 20nm,the transparency window changes from 3THz to 1.5THz, and there occurs a second transparency window on the right side of the window. When the incident angle of polarization changes from a vertical incident to an oblique 60 degree, the transmission changes from 0.7 to 0.85, and the coupling strength is weakens greatly. The effect of Fermi level on EIT effect is discussed. When the Fermi level increases from 0.3eV to 0.9eV,the resonance frequency is shifted from 24THz to 35THz, which confirms that changing the Fermi level of graphene can adjust the frequency of the window and slow down the speed of light.2. We design a cascaded ?-shaped asymmetry graphene nanostructures, the vertical graphene strips can be regarded as dark modes, the horizontal graphene strips can be viewed as bright modes. Under the excitation of the incident light, the bright and dark modes are coupled to achieve the EIT effect. The influences of dimension parameters on EIT are also discussed. In addition, based on this model,a more compact metamaterial structure is designed to focus the electric field on the smaller mode volume. Finally, the influence of the Fermi level on the EIT and slow light effect is discussed, which provides a new way for the slow light effect.3. Based on the weak hybridization between two bright modes, a no'vel planar graphene metamaterial structure is designed, which can realize the EIT effect in the THz band. The structure is composed of a graphene ring and a graphene strip, the transmission intensity of the structure is very high, which can be adjusted from 5%to 95%. Since both the ring and the strip can be individually excited by an external electric field, they are both treated as bright modes. The weak hybridization and frequency detuning between them produce the EIT phenomenon, and the transparency window appears. The dynamic tuning of the EIT effect can be achieved by changing the Fermi level of graphene without redesigning or reoptimizing the structure. In addition,a large group delay can be observed near the transparency window,which reaches 0.5ps at the transparency window.