手性超材料圆极化波吸收特性研究进展

Research Progress of the Absorption Characteristics of Circular Polarization Wave in Chiral Metamaterials

基于亚波长单元结构的人工电磁超材料具有优异的电磁/光学特性,如负折射率、超分辨率以及极化转化等,使得超材料研究成为近年量子通信、纳米光学、材料科学、能源探测等领域的前沿研究方向,其中以手性超材料的研究尤为突出。手性超材料是指与其镜像不具有几何对称性,且不可通过旋转或平移等任意操作使其与镜像重合的一种新型电磁超材料。超材料的深入研究,极大地丰富了手性结构的建模,为许多隐晦物理现象和理论分析的研究提供了更多有效的方法。手性超材料所具备的超强光学活性、圆二色性以及不对称传输等独特的电磁/光学特性,也为电磁学、物理学、材料科学、光学、声学、纳米科学以及信息科学等领域提供了全新的研究方向。手性是手性分子的一种固有特征,也是生命体征的一种表现,在有机世界中普遍存在,诸如蛋白质、DNA、糖分子、病毒、氨基酸和液晶体等分子。然而在自然界中,手性结构十分有限,有关建模和理论分析仅停留在原始结构的表征。目前,手性超材料的研究正逐步从微波段扩展至太赫兹、红外波段,甚至光波段。基于手性微结构的电磁超材料的实现很大程度上取决于单元结构尺寸和周期阵列排布,因此吸收带宽仍然局限于较窄的频率范围,且对左旋圆极化波(LCP)和右旋圆极化波(RCP)的识别(选择性吸收)能力较弱。随着对手性超材料的进一步研究,微波频段的差异化吸收率逐步提高到90%以上,但在高频段差异化的吸收率仍然较低。此外,随着微纳技术和纳米技术的发展,利用包括半导体材料、相变材料、高电阻/电感/电容薄膜、石墨烯在内的新型功能材料,以及结合集总元件的匹配电路控制,为实现红外、可见光波段的吸波器提供了研究空间。本文介绍了手性超材料对圆极化波的吸收原理,着重阐述了内在手性结构、外在手性结构以及与包括半导体材料、石墨烯等其他新型功能材料相结合的手性超材料吸收光谱的研究进展。这种基于人工电磁微结构的手性吸波特性可应用于极化转化器、电磁能量收集器、红外成像等电磁/光学器件设计中。

Artificial electromagnetic metamaterials based on the subwavelength units structure have excellent electromagnetic/optical properties,such as negative refractive index,super-resolution and polarization conversion,making them to be the leading field in the areas of quantum communication,nano-optics,material science,energy exploration and others in recent years.Among them,the study of chiral metamaterials is particularly prominent.Chiral metamaterials refer to a new type of electromagnetic metamaterial which have no geometric symmetry and can’t be overlapped with their mirror image by rotation or translation or other operations.The further investigations of metamaterials drastically enrich the mode-ling of chiral structures,and provide more effective methods for the research of many obscure physical phenomenas and theoretical analysis.The unique electromagnetic/optical properties of chiral metamaterials,including ultra-strong optical activity,circular dichroism and asymmetric transmission,offer a fire-new research direction for electromagnetic,physics,materials science,optics,acoustics,nanoscience and information science,etc.Chirality is considered to be an inherent feature of chiral molecules and a manifestation of vital signs that are ubiquitous in the organic world,such as proteins,DNA,sugar molecules,viruses,amino acids and liquid crystals.However,the chiral structure is extremely limited in nature,and the related modeling and theoretical analysis merely stay at the characterization of the original structure.At present,the research of chiral metamaterials is gradually expanding from microwave segment to the terahertz,infrared band,and even light wave band.Since the realization of electromagnetic metamaterials based on chiral microstructures highly lies on the size of the cell structure and the arrangement of periodic arrays,thus the absorption bandwidth is still limited in a narrower frequency range,and the ability of recognizing(selective absorption)the left-handed circular polarized wave(LCP)and right-handed circular polarized wave(RCP)is relatively weak as well.With the further research on the chiral metamaterials,the differential absorptivity of microwave frequency band is gradually increased over 90%,while in high frequency band it is still low.In addition,with the development of micro-nano technology and nano technology,the utilization of new functio-nal materials,including semiconductor materials,phase change materials,high resistance/inductance/capacitance thin films and graphene,and matching circuits combined with lumped elements provide a research space for achieving infrared and visible wave band absorbers.This paper introduces the principle of absorption of circular polarized waves by chiral metamaterials,and detailedly expound the research progress in the absorption spectra of chiral metamaterials of intrinsic chiral structure,the external extrinsic chiral structure and other new functional materials,including semiconductor materials,graphene,etc.The chiral absorption characteristics based on artificial electromagnetic microstructures are available in the design of electromagnetic/optical devices such as polarization converter,electromagnetic energy collector,infrared imaging and so on.