基于石墨烯超材料的可调电磁诱导透明的研究

发布时间：2018-10-26 19:59

【摘要】：近年来,THz技术得到了巨大的发展。由于在电磁波谱中的特殊位置,THz波在医疗诊断、环境监测、移动通讯和军用雷达等方面具有非常广阔的应用前景。然而,有效材料的缺乏限制了 THz技术的深入发展和实际应用。石墨烯作为新兴的二维半导体材料,具有超高的载流子迁移率和优异的光电性能,在THz器件的研制中具有独特的优势。本文主要针对基于石墨烯超材料结构的可调电磁导透明进行了研究。本文的主要研究内容及结论概括如下:1.基于石墨烯电导率的可调性,研究了 T型石墨烯纳米结构。通过研究我们发现,当亮模式与暗模式互相靠近时,可以产生电磁诱导透明(EIT)现象。讨论了不同几何尺寸情况下,EIT效应随频率的变化情况。结果表明当两个石墨烯条中心距离由Onm增加到20nm时,透明窗口由3THz变为1.5THz,且窗口的右侧出现了第二个透明窗口。当入射偏振角由垂直入射变为斜60度入射时,透射由0.7变为0.85,耦合强度大大减弱。讨论了费米能级对EIT效应的影响,证实了改变石墨烯费米能级可以调节窗口频率大小,并实现光速减慢。2.研究了具有非对称性的级联兀型石墨烯纳米结构,模型中竖直放置的石墨烯条作为暗模式,水平石墨烯条作为亮模式。在入射光的激励下,亮模式和暗模式发生耦合,实现了 EIT效应。讨论了模型尺寸参数对EIT的影响并得出结论。在该模型的基础上研究了更为紧凑的超材料结构,以实现将电场集中在更小的模式体积上。讨论了石墨烯费米能级的变化对EIT及慢光效应的影响,为慢光效应的按需调节提供了另一种思路。3.基于两个亮模式之间的弱杂化,研究了一种新型平面石墨烯超材料结构,可以在THz波段实现EIT效应。该结构由一个石墨烯圆环和一个石墨烯长条组成,结构的透射强度很高,可以从5%调节到95%。由于圆环和长条都可以被外电场单独激发,因此二者都视为亮模式。两模式之间的弱杂化和频率失谐产生了 EIT现象,出现了透明窗口。改变石墨烯的费米能级,可实现对EIT效应的动态调谐。透明窗口附近可观察到较大的群速率延迟,窗口处达到0.5ps。
[Abstract]:In recent years, THz technology has been greatly developed. Because of its special position in electromagnetic spectrum, THz wave has a very broad 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. As a new two-dimensional semiconductor material, graphene has a unique advantage in the development of THz devices because of its ultra-high carrier mobility and excellent optoelectronic properties. In this paper, the adjustable electromagnetic conductivity transparency based on graphene supermaterial structure is studied. The main contents and conclusions of this paper are summarized as follows: 1. Based on the adjustable conductivity of graphene, T-type graphene nanostructures were studied. It is found that electromagnetically induced transparent (EIT) can occur when the bright and dark modes approach each other. The variation of EIT effect with frequency under different geometric dimensions is discussed. The results show that when the central distance of two graphene strips increases from Onm to 20nm, the transparent window changes from 3THz to 1.5THZ, and a second transparent window appears on the right side of the window. When the incident polarization angle changes from vertical incidence to oblique 60 degree incident, the transmission is changed from 0.7 to 0.85, and the coupling strength is greatly weakened. The effect of Fermi level on EIT effect is discussed. It is proved that the window frequency can be adjusted by changing the Fermi level of graphene, and the speed of light can be slowed down. The cascaded unsymmetrical graphene nanostructures with vertical graphene strips as dark mode and horizontal graphene strips as bright modes are studied. The EIT effect is realized by coupling the bright mode with the dark mode under the excitation of the incident light. The influence of model size parameters on EIT is discussed and the conclusion is drawn. On the basis of this model, a more compact structure of metamaterials is studied in order to concentrate the electric field on a smaller mode volume. The effect of the change of Fermi level of graphene on EIT and slow light effect is discussed, which provides another way of thinking for the adjustment of slow light effect on demand. 3. Based on the weak hybrid between two bright modes, a novel planar graphene supermaterial structure is studied, which can realize the EIT effect in THz band. The structure consists of a graphene ring and a graphene strip. The transmission intensity of the structure is very high and can be adjusted from 5% to 95%. Since both the ring and the strip can be excited by the external electric field, both are considered as bright modes. The weak hybrid and frequency detuning between the two modes lead to EIT phenomenon and transparent window. The EIT effect can be dynamically tuned by changing the Fermi level of graphene. A large group rate delay can be observed near the transparent window, which reaches 0.5 ps.
【学位授予单位】：山东科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O613.71;O441

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