类石墨烯零折射率特异材料中光子输运行为研究

Recently, the zero- index metamaterial (ZIM) has become one of the most exciting areas in the photophysics and condensed physics fields, due to their unique electromagnetic response and potential applications. A ZIM can modify the transport properties of electromagnetic waves significantly, for example, a ZIM can tailor the radiation patterns and squeeze electromagnetic waves. In an impedance-matched ZIM, both phases and amplitudes of the electromagnetic fields are homogeneous. And recent research indicate that there is a zero-refractive-index point at the Dirac point of graphene-like photonic crystal in the center of the Brillouin zone. In this research program, we will explore the novel peroperties of the photon transport in the graphene-like ZIM by theoretical analysis, numerical simulation and experiments. Firstly, we utilize different methods to characterize the ZIM, for instance, realize the ZIM by choosing the appropriate structure parameters of the photonic crystals and metamaterials. Many approaches have been proposed to implement the metamaterials. The applicable one is the microwave transmission line approach loaded with series capacitor (C) and shunt inductor (L), known as composite right/left-handed transmission line (CRLH TL), with which we can realize the one and two dimensional ZIM. The other one is split rings and metal lines, and we can design a photonic crystal with a Dirac cone at the center of the Brillouin zone, it can be mapped to a ZIM system. Secondly, we investigate the properties of photon transport at the Dirac point in the center of the Brillouin zone of the graphene-like photonic crystal. A Dirac point with the characteristic of zero refractive index can be identified in the graphene-like photonic crystals. There are many extraordinary physical phenomena which are similar but different from the graphene at that point, such as, "pseudo-diffusive" transport regime, "Zitterbewegung" effect, and phase shift vanishing , and so on. Then, the transport regime of the photon at the Dirac point with zero-index properties are worth probing into very much. Thirdly, we design a zero-refractive-index optical microcavity. We know that the conventional cavity modes are all in the form of standing waves and the localized fields are inhomogeneous. But the electromagnetic fields within the zero-refractive-index optical microcavity are largest and uniform. The results of the above-mentioned problems not only open up the possibility to study the condensed matter analogies in optical ways, but also have guidance significance for the application of ZIM.

近年来，零折射率特异材料由于对电磁波特殊的操控能力以及潜在的应用前景，已成为相关领域一个新的研究热点。本项目拟采用理论分析、数值仿真及实验研究相结合的方法，研究类石墨烯零折射率特异材料中光子的奇异输运行为。主要包括以下三个方面：零折射率特异材料的表征，即通过设计类石墨烯光子晶体和特异材料的结构参数实现零折射率特性；类石墨烯光子晶体布里渊区中心位置狄拉克点处光子输运行为的研究，类石墨烯光子晶体中存在具有零折射率特性的狄拉克点，在该点附近会存在许多与电子石墨烯相似而又不同的奇特物理现象；利用类石墨烯光子晶体构造电磁场均匀且局域的零折射率光学微腔。上述问题的研究不仅为用光学的方法研究凝聚态物质提供了可能性，而且对零折射率特异材料的各种潜在应用具有指导意义。

光子晶体和特异材料拥有众多新奇光调控效应，国内外对这类效应的研究很重视。光子晶体能带结构中存在一种拓扑非平庸的狄拉克点，在狄拉克点附近的光子能带是线性的，从而在狄拉克频率处发生了奇特的光调控性。特异材料是通过局域共振机制实现任意的有效介电常数和有效磁导率，从而导致新奇的光调控能力。我们针对基于狄拉克点和特异材料微结构单元的的新型光调控机制进行了深入研究。.首先，我们利用氧化铝高介电介质棒设计出微波段光子石墨烯，并测试了其传输性，研究发现在狄拉克频率点处的“赝扩散”行为，而且透射系数随无序度的增加反而会增加；在布里渊区中心位置也会出现光子狄拉克点而且是三重简并态，在狄拉克频率附近具有近零折射率性质，微波实验发现了“赝扩散”，而且由于零折射率性质其场分布是接近均匀的；进一步分析布里渊区中心位置狄拉克频率处的能带模式，研究发现三重简并能带模式中平坦的纵模横穿狄拉克锥，当纵模被激发时, 由于受其干扰,狄拉克频率处的透射率随着无序度的增加而减小,而在狄拉克点频率偏上不受其干扰的地方, 其透射率几乎不受无序的影响；在狄拉克点附近存在两个简并且不等价的谷，实验研究发现在分别从armchair界面和zigzag界面入射的光波发生了自聚焦和分束的现象；另外在单轴扭曲的光子石墨烯中观察到了赝磁场作用下谷依赖的光子束弯曲传播行为，由于两个谷中的光子受到大小相等、方向相反的赝磁场作用，导致两个谷中光子束的运动路径类似于电子束在相反方向磁场控制下的传播路径。另外采用二维微带线构建了零折射率材料，用“电路等效”的方法研究了零折射率材料的零相移、群速度为零的特性；利用特异材料实现了微结构单元的光子调控，首次发现，亚波长尺度的特异材料结构单元的方位角与响应效率有一定的对应关系，实现了相位无关的振幅连续调控，增加了光子调控的自由度，解决了目前只能相位调控的难题，在特殊光学器件领域具有重要的应用价值，在国内外被大量引用。.上述研究成果将有利于探索光子微结构中光子调控的新机理和新手段，并揭示出光子石墨烯中重要的物理机制，对深入理解石墨烯及其它人工石墨烯中的物理现象提供了一个新的视角。利用特异材料实现了电磁波的振幅和相位调控，为高质量计算机全息术提供了技术支持。