超构天线:原理、器件与应用

自从电磁波被发现和应用以来,利用各种材料或者结构调节电磁波的辐射行为、构造高性能的电磁辐射器件一直是研究人员的追求目标.经过百余年的发展,电磁辐射器件的方向性提高、带宽拓展等技术逐渐达到瓶颈.受自然材料电磁特性的限制,微带天线、喇叭天线等传统电磁辐射器件存在体积重量大、工作带宽窄、无法快速动态调控等缺陷,难以满足日益发展的通信技术的需求.近年来出现的亚波长结构可在深度亚波长尺度下调控电磁波的传输行为,出现了多种奇异的电磁现象,完善了传统的电磁学理论,在一定程度上突破了传统材料电磁特性的限制,形成全新的电磁辐射技术,有效解决了传统天线存在的口径大、厚度高、带宽窄等难题,促进了电磁学、光子学、材料学等领域的发展.这种基于超构材料的新型天线可以被称为超构天线,具有高方向性、低副瓣、超宽带、可重构等传统天线难以实现的功能.本文主要回顾了近年来基于亚波长超构材料的超构天线技术的发展现状和取得的成果,介绍了超构材料在亚波长尺度下对电磁波振幅、相位、偏振态等的衍射调控机理,以及在此基础上形成的新型辐射器件,例如相控阵天线、高方向性天线、低雷达散射截面天线,基于亚波长结构的多种偏振调控器件及其在天线中的应用等.在衍射极限尺度下,这种亚波长结构的调控行为可有效提升电磁辐射器件的方向性、带宽,并可重构天线的工作频率、偏振态等性能.     

“超构表面2.0”专刊序

正伴随着人工智能、5G通讯以及高端芯片等信息技术的飞速发展,大容量大带宽的光学信息传输、处理和存储技术成为必然趋势。对高性能和高集成度的光学信息技术以及轻量化、微型化和集成化的纳米光学器件的迫切需求,驱动研究人员不断开发微纳尺度下的光场调控技术。然而,自然材料远远不能满足人们对微纳尺度下光场灵活多样的调控需求。尽管超构材料(Metamaterials)展现出超越自然材料的物理特性及强大的光波调控能力,基于三维亚波长人工微结构的超构材料存在损耗高、加工难、不易集成等问题,这制约了其发展及实用。     

超颖表面原理与研究进展

超颖表面是一种特殊的二维亚波长阵列结构,具有很强的光场调控能力,兼有超薄、低损耗、易加工等优势,表现出广阔应用前景,近些年吸引了广泛的研究兴趣。本文将综述超颖表面的原理与研究进展,简要分析已报道的超颖表面类型,并重点介绍其在广义折反射、偏振转换、光束轨道角动量操控以及计算全息中的应用。超颖表面设计灵活、功能强大,有望在诸多应用中取代传统光电器件。未来基于超颖表面的新型、宽带、高效率、多功能以及主动可调功能器件等将是其重要的发展方向。     

介质超构表面的CMOS兼容制备工艺的进展

超构表面为纳米光子器件赋予了更高的自由度与灵活度，使实用的微纳米光子器件的实现成为可能。基于高折射率半导体材料的介质超构表面制备技术可以和半导体集成电路的制作工艺结合，有希望在攻克超构表面大面积和高通量制备技术难题上发挥重要的作用，因此对其光场调控性能和制备工艺的研究是该领域近年来的重要发展方向。本文从硅、氮化硅和二氧化钛等介质超构表面出发，介绍了超构表面高通量制造技术的发展。此外，介绍了基于大面积制造技术实现实际应用的基于纳米光子器件的光学器件，如显示、成像、光调控器件。     

光学超构表面中的复合相位调控

超构表面是一种二维的超构材料,能在平面上实现对光波相位、振幅、偏振等参数的灵活调控。相位型超构表面可突破经典折反射定律,使得光场调控不再依赖于曲面光学元件,为实现光学系统的平面化、集成化和多功能化提供了有效途径。特别地,通过对传输相位和几何相位协同调控,能够有效解决传统超构表面存在的功能单一、带宽受限、可调谐性差等原理性问题。文章介绍了复合相位调控的实现原理和方法,以及复合相位超构表面的典型应用及特点,最后对复合相位超构表面的未来研究方向进行了总结和展望。     

非线性光学超构表面

非线性光学超构表面是一类由空间变化的超构功能基元组成的超薄非线性光学器件。通过合理选择超构功能基元的材料组成、空间对称性,人们可以在亚波长尺度上对超构表面上产生的非线性光波的偏振、相位、振幅等自由度进行多维度光场调控。文章介绍了在非线性光学超构表面上实现谐波、四波混频、太赫兹波辐射的设计与原理,并讨论了如何在非线性光学超构表面上实现非线性光的波束调控、全息成像、光学图像加密等功能。     

超构表面在量子光学中的研究与应用

超构表面是利用二维平面微纳结构调控光场的光学元件。近年来,超构表面在量子光学中的研究和应用受到越来越广泛的关注。超构表面能够实现量子器件的小型化和集成化,提高量子光源的发光效率和光源质量。结合量子光学和超构表面两个领域,介绍了量子等离激元、运用超构表面优化量子光源、运用超构表面测量和操纵量子态、量子光学的应用,以及量子发光体的量子真空调控这5个方面的最新研究进展,最后进行总结和展望。     

多路角度复用体全息三维显示技术

为满足高分辨率真三维大数据显示的空间带宽积要求,提出一种基于多通道角度复用模式的体全息三维显示技术。通过对三维场景进行波前编码,获得相位计算全息图,并将计算全息图依次按照不同角度复用记录到掺杂金纳米颗粒体全息光致聚合物材料的同一区域,获得复用体全息图,再现时可以在不同角度观察三维场景。在体全息三维显示实验系统中,实现体全息材料记录区域的单点像素总数为120×1 920×1 080,显示的空间带宽积达到了2.5×108,相对于空间光调制器显示提升了120倍。     

非线性光学超构表面

在线性光学范畴内,人们已经通过亚波长尺度的超薄超构表面成功实现了对光的众多新颖特性的调控功能.其主要理念是通过对具有亚波长尺度且空间方向变化的超构功能基元进行特定的排列,从而实现对光的偏振、相位和振幅的有效控制.近来,超构表面上的非线性光学特性也引起了大家的广泛关注.在本综述中,我们对非线性光学超构表面的设计、超构功能单元的材料和对称性选择、非线性手性光学、非线性贝里几何相位和非线性波前整形等内容进行了总结;最后对非线性光学超构表面在调控光与物质的相互作用中面临的挑战和前景进行了展望.     

超构表面的振幅调控及其功能器件研究进展

超构表面是一种具有亚波长特征尺寸的人工平面结构材料,可以在亚波长尺度上对入射电磁波的振幅、相位、偏振、频率、光谱等参量进行精密且灵活的调控,近年来备受关注。振幅是光波的基本参量之一,本文将从振幅调控的角度出发,对基于超构表面材料的振幅调控机理进行分析,主要包括通过改变纳米结构的尺寸和方向角对振幅进行调控,同时对基于振幅调控超构表面的功能器件的研究现状及其应用场景进行总结和讨论。研究表明,振幅调控超构表面具有设计灵活、加工简单、功能强大、可与其他参量调控相融合等特点,其在高分辨率图像显示、高密度信息存储、信息加密、信息复用、光束整形、光信息处理和安全防伪等诸多领域具有重要的研究价值和广阔的应用前景。     

动态全息三维显示研究最新进展

全息三维显示是真三维显示技术, 其原理是利用光学干涉记录和衍射再现将物体或场景的三维信息全部重建出来, 所以观看全息三维图像与观看真实物体或场景的效果一样. 近期全息研究领域有一些突破性的成果被报道, 将推动全息显示的应用不断走向成熟. 本文将重点介绍基于光学材料和空间光调制器为全息图承载载体的动态全息三维显示最新发展状况. 虽然动态全息三维显示研究仍然存在挑战, 但最近研究中已经利用光学材料实现了实时动态全息三维视频显示, 这为未来实现大尺寸、高分辨率、彩色全息真三维视频显示提供了可能.     

Physically Realizable Broadband Acoustic Metamaterials with Anisotropic Density

Transformation acoustics are concentrated for the purpose of designing novel acoustic devices to tailor acoustic waves to achieve desirable characteristics. However, these devices require fluid or fluid-like materials with an anisotropic density that generally does not exist in nature. Therefore, we introduce pentamode metamaterials into an alternating multilayer isotropic medium model to build fluid-like metamaterials with an anisotropic density. A 2D acoustic bending based on transformation acoustics is established and investigated to verify our method. This idea provides a method to design broadband and physically realizable acoustic metamaterials with an anisotropic density and is meaningful for the design of acoustic metamaterials.     

Hybridization effect in coupled metamaterials

Although the invention of the metamaterials has stimulated the interest of many researchers and possesses many important applications, the basic design idea is very simple: composing effective media from many small structured elements and controlling its artificial EM properties. According to the effective-media model, the coupling interactions between the elements in metamaterials are somewhat ignored; therefore, the effective properties of metamaterials can be viewed as the “averaged effect” of the resonance property of the individual elements. However, the coupling interaction between elements should always exist when they are arranged into metamaterials. Sometimes, especially when the elements are very close, this coupling effect is not negligible and will have a substantial effect on the metamaterials’ properties. In recent years, it has been shown that the interaction between resonance elements in metamaterials could lead to some novel phenomena and interesting applications that do not exist in conventional uncoupled metamaterials. In this paper, we will give a review of these recent developments in coupled metamaterials. For the “metamolecule” composed of several identical resonators, the coupling between these units produces multiple discrete resonance modes due to hybridization. In the case of a “metacrystal” comprising an infinite number of resonators, these multiple discrete resonances can be extended to form a continuous frequency band by strong coupling. This kind of broadband and tunable coupled metamaterial may have interesting applications. Many novel metamaterials and nanophotonic devices could be developed from coupled resonator systems in the future.     

Spatiotemporal multiplexing and streaming of hologram data for full-color holographic video display

We propose a new approach to spatiotemporally multiplex sub-holograms and stream hologram data in parallel by using multiple spatial light modulators (SLMs) to increase the spatiotemporal resolution of holographic display system. With the proposed approach, we have achieved a spatiotemporal resolution of 4.5 × 10¹⁰ pixel/s, as compared with 1.89 × 10⁹ pixel/s of a single SLM. Each frame of computer-generated hologram video has a pixel count of 378 Mpixels and is divided into 288 sub-holograms, each of 1.31 Mpixels. During the playback of holographic video, these sub-holograms are spatiotemporally multiplexed and streamed in parallel to form the integrated hologram within 16.67 ms, which enables full-color holographic video display with a 10-in. diagonal at a hologram data frame rate of 60 frames per second (fps). New SLM devices with higher spatiotemporal resolution need to be developed in order to meet the data bandwidth requirement of about 10¹²–10¹⁴ pixel/s for future 3D holographic displays.     

Copper vs. iron: Microwave magnetism in the metamaterial age

It is now well established that metamaterials based on copper patterns can exhibit significant permeability levels, but can such materials outdo conventional magnetic materials? In the case where permeability levels and bandwidth are the key figures-of-merit, it is acknowledged that copper-based metamaterials can exceed the performance of ferrites at operating frequencies above 10 GHz. As for low-frequency operation, magnetic metamaterials may also be preferred to conventional magnetic materials when requirements include excellent temperature stability or immunity to external magnetic fields. However, in many cases, metamaterials need to include certain conventional magnetic constituents in order to compete with conventional magnetic materials.     

Computer generated hologram from full-parallax 3D image data captured by scanning vertical camera array (Invited Paper)

Full-parallax light-field is captured by a small-scale 3D image scanning system and applied to holographic display. A vertical camera array is scanned horizontally to capture full-parallax imagery, and the vertical views between cameras are interpolated by depth image-based rendering technique. An improved technique for depth estimation reduces the estimation error and high-density light-field is obtained. The captured data is employed for the calculation of computer hologram using ray-sampling plane. This technique enables high-resolution display even in deep 3D scene although a hologram is calculated from ray information, and thus it makes use of the important advantage of holographic 3D display.     

Fabrication of multilayer metamaterials by femtosecond laser‐induced forward‐transfer technique

A novel method based on femtosecond laser‐induced forward transfer for high‐throughput and efficient fabrication of periodic multilayer plasmonic metamaterials is demonstrated. With precisely controlling laser raster path applied on sputtered multilayer thin films, the laser‐ablated materials can be transferred to another substrate leaving the fabricated multilayer structure on the original substrate. Subsequently, three‐dimensional metamaterials can be made by multilayer structuring. Moreover, all the experimental results show that to create such multilayer split resonant rings (SRRs) with uniform profile, the laser fluence should be fine controlled under proper conditions. The optical property of fabricated multilayer SRR array is investigated by optical measurements and finite‐difference time‐domain simulations, showing various resonant modes in the middle‐IR region. The calculated induced current distributions exhibit rich resonance properties of the structures as well. This work markedly extends the laser direct writing technique to a wide application in fabricating complicated metamaterials and plasmonic devices efficiently.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H1.然后将H1作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H₁.然后将H₁作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.