基于石墨烯超表面的宽带电磁诱导透明研究

Wide band electromagnetically induced transparency in graphene metasurface of composite structure

提出了一种新的基于石墨烯超表面的复合结构,该结构由带有空气槽的石墨烯条、氮化镓、二氧化硅和二氧化钛组成.通过时域有限差分法研究了该结构的电磁特性,研究结果表明,该结构具有更宽频带的电磁诱导透明特性.从结构参数、电磁场分布等方面研究了电磁诱导透明的物理机理.在该结构中,石墨烯条作为明模存在,耦合作为暗模的空气槽和氮化镓侧板,即存在两种明暗模耦合的现象,因此产生宽带的电磁诱导透明现象.从研究结果发现该结构可以产生多个频点的慢光效应和传感效应,因此在光存储、红外波段的传感器设计中具有一定的指导意义和潜在的应用.

The electromagnetic induction transparency （EIT） is a phenomenon m wnlcn ~ne or,grumpy Ul~ transparent under certain resonant electromagnetic fields. It has been seen in applications ranging from nonlinear optics, slow light and optical storage. From the viewpoint of single-frequency, researchers have paid much attention to the realization of broadband electromagnetic induction transparency in recent years. In this paper, a broadband electromagnetic induction transparency effect is investigated theoretically by the finite difference time-domain method. A composite structure based on graphene metasurface which consists of graphene strip with air groove, gallium nitride, silica and titanium dioxide is designed in infrared range. A broadband electromagnetically induced transparency effect could be found in the designed composite structure compared with those in several similar structure. The electromagnetically induced transparency window can be tuned gently by the width of air groove and gallium nitride dielectric slabs. The results show that a wideband electromagnetically induced transparency window of 4 terahertz is found in the infrared frequency range. By comparison with the existing research results, a wider band of eleetromagnetically induced transparency is found in our structure. We study the physical mechanism of broadband electromagnetically induced transparency from the aspects of structural parameters and electromagnetic field distribution. The thickness Wl of gallium nitride, the width w~ and depth h of air groove on graphene strip are discussed in this article. The smaller the length w~ or depth h, the wider the EIT band is. The peak of high frequency at which the transmission is near to zero is blue-shifted as h increases. However, red-shift is found as width w~ increases. It is found that graphene strip exists as a bright mode. coupling action acts as air groove and gallium nitride slabs function as dark mode, resulting in broadband electromagnetic induced transparency. That is to say, the principle of broadband electromagnetically induced transparency is due to a bright mode coupling in two different forms of dark mode, thus widening the transmission band. This work provides a kind of structure and a design way, to gain the broadband of electromagnetically induced transparency effect. Moreover, it is found that changing the refractive index of background medium, the frequency of high frequency band has a red-shift, the greater change of the refractive index can lead to smaller frequency range. It can be seen that the values of group index ng of three frequency peaks exceeding 25 are observed. The results also show that the slow-light effect and the sensing effect in several frequency ranges are obtained in the proposed structure and potential applications in the optical storage and highly sensitive infrared-band sensor, infrared optical switching, etc.