Multichannel‐Independent Information Encoding with Optical Metasurfaces

Optical metasurfaces, as an emerging platform, have been shown to be capable of effectively manipulating the local properties (amplitude, phase, and polarization) of the reflected or transmitted light and have unique strengths in high‐density optical storage, holography, display, etc. The reliability and flexibility of wavefront manipulation makes optical metasurfaces suitable for information encryption by increasing the possibility of encoding combinations of independent channels and the capacity of encryption, and thus the security level. Here, recent progress in metasurface‐based information encoding is reviewed, in which the independent channels for information encoding are built with wavelength and/or polarization in one‐dimensional/two‐dimensional (1D/2D) modes. The way to increase information encoding capacity and security level is proposed, and the opportunities and challenges of information encoding with independent channels based on metasurfaces are discussed.     

Spin-Selective Full-Dimensional Manipulation of Optical Waves with Chiral Mirror

Realizing arbitrary manipulation of optical waves, which still remains a challenge, plays a key role in the implementation of optical devices with on-demand functionalities. However, it is hard to independently manipulate multiple dimensions of optical waves because the optical dimensions are basically associated with each other when adjusting the optical response of the devices. Here, the concise design principle of a chiral mirror is utilized to realize the full-dimensional independent manipulation of circular-polarized waves. By simply changing three structural variables of the chiral mirror, the proposed design principle can arbitrarily and independently empower the spin-selective manipulation of amplitude, phase, and operation wavelength of circular-polarized waves with a large modulation depth. This approach provides a simple solution for the realization of spin-selective full-dimensional manipulation of optical waves and shows ample application possibilities in the areas of optical encryption, imaging, and detection.     

全金属超表面在电磁波相位调控中的应用及进展

全金属超表面是由亚波长金属单元所组成的结构阵列,其在调控电磁波相位方面展现出了效率高、带宽大等特点,并且相较于金属-介质混合型超表面,全金属超表面具有优良的热学和机械性能,如耐高温、强度大、延展性好等,这使得其可以应用于高温高压等极端复杂环境中。本文对近年来全金属超表面取得的研究进展进行了简要的归纳总结,主要介绍了其在构建高效、多功能平面光学器件以及多频谱电磁隐身中的应用,并对其未来的发展方向进行了展望。

     

Complementary bilayer metasurfaces for enhanced terahertz wave amplitude and phase manipulation

Manipulation of terahertz wave by metasurfaces has shown tremendous potential in developing compact and functional terahertz optical devices. Here, we propose complementary bilayer metasurfaces for enhanced terahertz wave amplitude and phase manipulation. The metasurfaces are composed of one layer of metal cut-wire arrays and one layer of their complementary aperture arrays separated by a dielectric spacer. Through the near-field coupling between transverse magnetic resonances in the metal apertures and electric resonances in the metal cut-wires, the structures can manipulate the cross polarization conversion and phase dispersion of terahertz wave. Particularly, the designed metasurfaces demonstrate a phase delay of 180° between two orthogonal axes with the same transmission amplitude between 0.70 and 1.0 THz, enabling a 45° broadband polarization conversion. When the metal cut-wires are rotated with respect to the apertures or the thickness of the dielectric spacer is changed, the amplitude and phase dispersion of the transmitted terahertz wave can be tuned. Such complementary coupled bilayer metasurfaces offer a new method to control the amplitude and phase dispersion of terahertz wave and promise great potential for applications in terahertz meta-devices.     

动态可调谐超表面的研究进展与应用

超表面能够对电磁波的偏振、振幅和相位等物理参量进行前所未有的调控,微纳加工技术的发展进一步推动了超表面在显示、成像、传感、防伪、光场调控等领域的应用前景。然而,大多数超表面缺乏动态调控,限制了其应用范围。近年来超表面的动态调控研究也取得了一些重要进展,本文将主要介绍当前超表面动态调控的主要机制,包括电调控、热调控、光调控、机械调控、化学调控等,综述了国内外学者在超表面动态调控方面的研究进展。此外,本文还对动态超表面在成像、显示、光场调控等领域的应用进行了概述,阐述了其重要意义和应用前景。最后本文总结了当前可调超表面的主要问题及未来发展方向。

     

Quasicrystal Photonic Metasurfaces for Radiation Controlling of Second Harmonic Generation

Photonic metasurfaces, a kind of 2D structured medium, represent a novel platform to manipulate the propagation of light at subwavelength scale. In linear optical regime, many interesting topics such as planar meta‐lenses, metasurface optical holography, and so on have been widely investigated. Recently, metasurfaces have gone into the nonlinear optical regime. While it is recognized that the local symmetry of the meta‐atoms plays a vital role in determining the polarization, phase, and intensity of the nonlinear waves, much less attention has been paid to the global symmetry of the nonlinear metasurfaces. According to the Penrose tiling and the newly proposed hexagonal quasicrystalline tiling, nonlinear optical quasicrystal metasurfaces are designed and fabricated based on the geometric‐phase‐controlled plasmonic meta‐atoms with local rotational symmetry. It is found that the far‐field radiation behavior of second harmonic generation waves are determined by both the tiling schemes of quasicrystal metasurfaces and the local symmetry of meta‐atoms they consist of. The proposed concept may open new avenues for designing nonlinear optical sources with metasurface crystals.     

铌酸锂超构表面：制备及光子学应用

作为三维超构材料的衍生物,具有亚波长厚度的人工超构表面结构能够在紧凑的平台上灵活操纵光与物质的相互作用,有利于多功能、超紧凑光子器件的研发,对于微纳光子学和集成光子学具有重要意义。铁电晶体铌酸锂凭借其跨越可见光至中红外波段的宽透明窗口以及较大的非线性光学、电光系数,被认为是最有前途的多功能集成光子平台之一。近年来,基于铌酸锂薄膜(lithium-niobate-on-insulator,LNOI)的集成光子学器件研究也得到了迅猛发展。本文总结了几种有潜力制备高质量铌酸锂超构表面的微纳加工技术,同时介绍了近年来铌酸锂超构表面结构的研究进展,并对其未来的研究方向进行了展望。

     

Energy‐Tailorable Spin‐Selective Multifunctional Metasurfaces with Full Fourier Components

Compact integrated multifunctional metasurface that can deal with concurrent tasks represent one of the most profound research fields in modern optics. Such integration is expected to have a striking impact on minimized optical systems in applications such as optical communication and computation. However, arbitrary multifunctional spin‐selective design with precise energy configuration in each channel is still a challenge, and suffers from intrinsic noise and complex designs. Here, a design principle is proposed to realize energy tailorable multifunctional metasurfaces, in which the functionalities can be arbitrarily designed if the channels have no or weak interference in k‐space. A design strategy is demostrated here with high‐efficiency dielectric nanopillars that can modulate full Fourier components of the optical field. The spin‐selective behavior of the dielectric metasurfaces is also investigated, which originates from the group effect introduced by numerous nanopillar arrays. This approach provides straightforward rules to control the functionality channels in the integrated metasurfaces, and paves the way for efficient concurrent optical communication.     

电磁超表面对辐射波的调控与应用

电磁超材料由亚波长尺寸的人工单元结构周期或非周期排列组成,可以实现天然材料不具备的奇特性质。超表面作为二维特殊形式超材料,具有剖面低、易集成、低成本等优点。随着有源器件、传感元件与智能算法的引入,超表面进一步实现了对电磁波的实时可编程与智能调控。目前多数电磁超表面研究致力于反射波或透射波调控,事实上,电磁超表面对辐射波同样具有强大的调控能力。本文系统介绍电磁超表面调控辐射波幅度、相位、极化等维度的相关研究进展,以超表面与馈源的集成方式和超表面对辐射波的调控原理为分类依据,重点介绍折叠阵超表面、法布里-珀罗超表面、漏波超表面和辐射式超表面,对应空间馈电、表面波馈电、缝隙耦合馈电、同轴馈电等方式,从无源与有源两个角度介绍这四类超表面对辐射波的调控机理与应用,最后对电磁超表面调控辐射波的未来研究方向进行展望。

     

基于硫属化物相变材料的可重构太赫兹超表面器件的研究进展

超表面在控制电磁波的强度、相位、偏振和复杂波前等方面发挥了重要的作用,通过与各种主动调控手段结合可实现动态可调谐器件。本文分析总结了近期基于Ge₂Sb₂Te₅ (GST)的太赫兹超表面器件的研究进展,介绍了GST在太赫兹波段的光谱特性和可逆相变条件,重点回顾了GST与超表面设计相结合用于实现对太赫兹波的振幅、偏振以及波前的非易失、可重构、和多级操纵的前沿研究工作,并讨论展望了未来的发展前景和需要解决的问题。

     

基于轻薄硬质超表面的空气声波反射场操控

对反射声波的复杂操控是声学研究的基础问题之一,并广泛应用于房间声学设计及噪声能量消除等重要场合。近年来出现的声学超表面为声学功能器件的小型化提供了新的启示,因此如何进一步缩减其尺寸和重量具有重要的物理意义与应用价值。展示了一种轻薄超表面结构对低频空气声波所产生反射声场的高效、精准操控。通过理论计算证明了利用简单的扁平中空结构,可在不显著牺牲能量反射率及结构强度的前提下,通过调控单个结构参数产生0~2π范围内的反射相位,同时避免了制备难度高和增加器件重量的复杂内部结构,因此具有尺寸超薄(λ₀/20)、重量轻盈、反射率高及制备简单等优势。通过实现任意角度的异常反射、基于超薄平面透镜的可调声聚焦、构建平面棱锥镜产生类贝塞尔声束3个典型例子展示了该器件对反射声波的丰富操控性能。实现基于轻薄超表面对反射声场的操控,有助于新型平面声学器件的研究与应用,并有望在建筑声学、噪声控制、扬声器设计等领域中产生重要价值。     

Imaging through Nonlinear Metalens Using Second Harmonic Generation

The abrupt phase change of light at metasurfaces provides high flexibility in wave manipulation without the need for accumulation of propagating phase through dispersive materials. In the linear optical regime, one important application field of metasurfaces is imaging by planar metalenses, which enables device miniaturization and aberration correction compared to conventional optical microlens systems. With the incorporation of nonlinear responses into passive metasurfaces, optical functionalities of metalenses are anticipated to be further enriched, leading to completely new application areas. Here, imaging with nonlinear metalenses that combine the function of an ultrathin planar lens with simultaneous frequency conversion is demonstrated. With such nonlinear metalenses, imaging of objects with near infrared light while the image appears in the second harmonic signal of visible frequency range is experimentally demonstrated. Furthermore, the functionality of these nonlinear metalenses can be modified by switching the handedness of the circularly polarized fundamental wave, leading to either real or virtual nonlinear image formation. Nonlinear metalenses not only enable infrared light imaging through a visible detector but also have the ability to modulate nonlinear optical responses through an ultrathin metasurface device while the fundamental wave remains unaffected, which offers the capability of nonlinear information processing with novel optoelectronic devices.     

Aligned,Ultralong Single‐Walled Carbon Nanotubes: From Synthesis,Sorting, to Electronic Devices

Aligned, ultralong single‐walled carbon nanotubes (SWNTs) represent attractive building blocks for nanoelectronics. The structural uniformity along their tube axis and well‐ordered two‐dimensional architectures on wafer surfaces may provide a straightforward platform for fabricating high‐performance SWNT‐based integrated circuits. On the way towards future nanoelectronic devices, many challenges for such a specific system also exist. This Review summarizes the recent advances in the synthesis, identification and sorting, transfer printing and manipulation, device fabrication and integration of aligned, ultralong SWNTs in detail together with discussion on their major challenges and opportunities for their practical application.     

Embedded Metal Oxide Plasmonics Using Local Plasma Oxidation of AZO for Planar Metasurfaces

New methods for achieving high-quality conducting oxide metasurfaces are of great importance for a range of emerging applications from infrared thermal control coatings to epsilon-near-zero nonlinear optics. This work demonstrates the viability of plasma patterning as a technique to selectively and locally modulate the carrier density in planar Al-doped ZnO (AZO) metasurfaces without any associated topographical surface profile. This technique stands in strong contrast to conventional physical patterning which results in nonplanar textured surfaces. The approach can open up a new route to form novel photonic devices with planar metasurfaces, for example, antireflective coatings and multi-layer devices. To demonstrate the performance of the carrier-modulated AZO metasurfaces, two types of devices are realized using the demonstrated plasma patterning. A metasurface optical solar reflector is shown to produce infrared emissivity equivalent to a conventional etched design. Second, a multiband metasurface is achieved by integrating a Au visible-range metasurface on top of the planar AZO infrared metasurface. Independent control of spectral bands without significant cross-talk between infrared and visible functionalities is achieved. Local carrier tuning of conducting oxide films offers a conceptually new approach for oxide-based photonics and nanoelectronics and opens up new routes for integrated planar metasurfaces in optical technology.     

Metasurface-Empowered Optical Multiplexing and Multifunction

Metasurfaces are planar photonic elements composed of subwavelength nanostructures, which can deeply interact with light and exploit new degrees of freedom (DOF) to manipulate optical fields. In the past decade, metasurfaces have drawn great interest from the scientific community due to their profound potential to arbitrarily control light. Here, recent developments of multiplexing and multifunctional metasurfaces, which enable concurrent tasks through a dramatic compact design, are reviewed. The fundamental properties, design strategies, and applications of multiplexing and multifunctional metasurfaces are then discussed. First, recent progress on angular momentum multiplexing, including its behavior under different incident conditions, is considered. Second, a detailed overview of polarization-controlled, wavelength-selective, angle-selective, and reconfigurable multiplexing/multifunctional metasurfaces is provided. Then, the integrated and on-chip design of multifunctional metasurfaces is addressed. Finally, future directions and potential applications are presented.     

可调谐手征超表面电磁特性研究进展

手征超表面是由具有特定电磁响应的平面手征单元结构构成的超薄超材料,由于其具有自由控制电磁波的奇异能力而引起了极大的关注.通过在超表面设计中加入可调谐材料,可以实现其功能受外部激发控制的可调谐或可重构的超器件,为动态调谐电磁波开辟了新的道路.本文介绍了可调/可重构手征超表面电磁特性的一些理论基础,当线偏振光进入可调谐手征...     

A Monolithic Force‐Sensitive 3D Microgripper Fabricated on the Tip of an Optical Fiber Using 2‐Photon Polymerization

Microscale robotic devices have myriad potential applications including drug delivery, biosensing, cell manipulation, and microsurgery. In this work, a tethered, 3D, compliant grasper with an integrated force sensor is presented, the entirety of which is fabricated on the tip of an optical fiber in a single‐step process using 2‐photon polymerization. This gripper can prove useful for the interrogation of biological microstructures such as alveoli, villi, or even individual cells. The position of the passively actuated grasper is controlled via micromanipulation of the optical fiber, and the microrobotic device measures approximately 100 µm in length and breadth. The force estimation is achieved using optical interferometry: high‐dimensional spectral readings are used to train artificial neural networks to predict the axial force exerted on/by the gripper. The design, characterization, and testing of the grasper are described and its real‐time force‐sensing capability with an accuracy below 2.7% of the maximum calibrated force is demonstrated.     

Self‐Assembly of Functional Molecules into 1D Crystalline Nanostructures

Self‐assembled functional nanoarchitectures are employed as important nanoscale building blocks for advanced materials and smart miniature devices to fulfill the increasing needs of high materials usage efficiency, low energy consumption, and high‐performance devices. One‐dimensional (1D) crystalline nanostructures, especially molecule‐composed crystalline nanostructures, attract significant attention due to their fascinating infusion structure and functionality which enables the easy tailoring of organic molecules with excellent carrier mobility and crystal stability. In this review, we discuss the recent progress of 1D crystalline self‐assembled nanostructures of functional molecules, which include both a small molecule‐derived and a polymer‐based crystalline nanostructure. The basic principles of the molecular structure design and the process engineering of 1D crystalline nanostructures are also discussed. The molecular building blocks, self‐assembly structures, and their applications in optical, electrical, and photoelectrical devices are overviewed and we give a brief outlook on crucial issues that need to be addressed in future research endeavors.     

超表面的电磁特性研究进展

超表面由于具有自然界不存在的独特电磁特性而引起了人们极大的兴趣,它是占有更少物理空间,提供更小损耗,更容易被制造的一类超材料。简要介绍了超表面的概念和背景,并着重阐述了超表面结构在微波段、太赫兹波段以及光频段的模拟计算及实验研究进展。这些超表面在微波、光波、光电子器件中具有潜在的应用价值。     

One‐Dimensional Dielectric/Metallic Hybrid Materials for Photonic Applications

Explorations of 1D nanostructures have led to great progress in the area of nanophotonics in the past decades. Based on either dielectric or metallic materials, a variety of 1D photonic devices have been developed, such as nanolasers, waveguides, optical switches, and routers. What's interesting is that these dielectric systems enjoy low propagation losses and usually possess active optical performance, but they have a diffraction‐limited field confinement. Alternatively, metallic systems can guide light on deep subwavelength scales, but they suffer from high metallic absorption and can work as passive devices only. Thus, the idea to construct a hybrid system that combines the merits of both dielectric and metallic materials was proposed. To date, unprecedented optical properties have been achieved in various 1D hybrid systems, which manifest great potential for functional nanophotonic devices. Here, the focus is on recent advances in 1D dielectric/metallic hybrid systems, with a special emphasis on novel structure design, rational fabrication techniques, unique performance, as well as their wide application in photonic components. Gaining a better understanding of hybrid systems would benefit the design of nanophotonic components aimed at optical information processing.