超构光栅调控衍射光场的物理及应用

基于局域表面等离激元或电介质微纳结构米氏散射的超构光栅对衍射通道的直接调制为高效率、大角度光场调控提供了优良平台.对超构光栅调控衍射光场的物理机理及应用开发进行了概述.首先,从高衍射效率超构光栅的构建机理出发,分别介绍了反射式、透射式、对称型、非对称型及可重构超构光栅的典型实现方式;其次,介绍了通过结合高衍射效率超构光...     

超构器件的设计、制造与成像应用

超构光学为平面光学器件的发展提供了新的思路与方向。超构器件由亚波长人工纳米结构组成,能在二维平面上实现对入射光的振幅、相位和偏振的操纵。研究人员已经发展了多种超构表面技术,将其用于满足各式各样的光学需求。本文首先回顾了超构器件的前沿研究与技术发展现状,介绍了超构器件的广义设计流程,并以连续宽带消色差超构透镜为例进行逐步说明,帮助读者理解;然后,展示了多种超构器件加工方法,包括直写刻蚀、图案转移刻蚀和混合图案刻蚀等,进一步讨论了超构器件在成像应用中的发展,包括偏振成像、光场成像、光学感测以及生物成像等;最后,进行了总结,并对超构器件未来的发展提出了见解与展望。     

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...     

超构透镜的色差调控应用

超构表面是由精心设计和排布的亚波长纳米单元组成的平面元件,其可以在微观尺度下调制电磁场,从而实现波前的任意调控.目前,它已被用来灵活地操纵相位、偏振、振幅等各种光学参数.超构透镜是超构表面中相当重要且非常活跃的一个研究方向,由于其厚度在波长量级,与传统光学透镜相比,能够显著增加光学器件的集成度并且降低结构复杂度.但是,...     

基于复合超构表面的宽带圆极化双功能器件设计

多功能器件的设计是推动新一代电磁系统发展的重要力量,而超构表面因其对电磁波的幅度、相位和极化等特性的灵活调控在多功能器件领域备受关注.传统的多功能超构表面是利用各向异性单元对相互正交的线极化波具有不同响应的特性,从而设计出适用于线极化的多功能器件.本文提出了一种缝隙加载的环I形复合超构表面单元,通过单元臂长和旋转角度的...     

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.     

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。     

晶圆级超构表面平面光学研究进展(特邀)

超构表面是由亚波长结构单元组成,它可以利用微纳制造工艺在平面上制造出来。通过改变超构单元的形貌以及排列方式可以实现对光的精确控制,从而使超构表面实现多种光学器件的功能。超构表面平面光学器件具有超薄、超轻、可芯片级集成、易于大规模量产等优点,近些年来成为了微纳光子学里最热门的研究领域之一。基于紫外光刻工艺的晶圆级加工技术是未来实现超构表面光学器件大规模量产最可行的路线之一。本文综述了近些年来基于紫外光刻技术的晶圆级超构表面光学所取得的进展。这些研究工作在不同尺寸和材料的晶圆上实现了超透镜、偏振带通滤波器、半波片、完美吸收体、光束偏转器等光学器件。     

基于相变与悬链线连续相位调控的超构光子开关

针对超表面相位调控中的无源及离散特性,本文拟将等宽悬链线超构单元与非易失性相变介质结合,探索研究一种高效连续相位调制的双稳态相变有源波前超构开关.首先在9—10μm之间的宽带中红外波段实现了可动态切换的波前偏转开关;当相变层在非晶态和晶态之间切换时,入射光波前分别呈现异常反射和正常的镜面反射,即"开"或"关"两个偏转状态.其次展示了一种可动态切换的高阶贝塞尔光束开关:非晶态时,9.6μm波长垂直入射下交叉极化转换效率接近100%,产生正常的几何相位调控与二阶贝塞尔聚焦,即"开"态;而相变至晶态时,交叉极化与几何相位调控被"关"闭.本质上,自旋-轨道相互作用具有无色散的相位调控保证了该类器件的宽波段工作特性,在未来的有源光电子集成、光通讯等应用领域中具有重大潜力.     

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。     

电磁超表面

光学是认识光和控制光的科学,其中光相位的调控扮演着重要角色。最近人们提出了电磁超表面的概念,通过设计非均匀人工微结构来实现亚波长尺度下的任意电磁相位分布,根据惠更斯原理进而实现任意波前调控。     

超构平面的色散关系研究

本文研究超构平面的光-物质相互作用机理。以13 nm Ge/20 nm Al₂O₃/Ag结构为例,建立色散方程、计算色散关系曲线。研究表明:超构平面支持Brewster共振模式,满足波矢匹配条件时可由从空气中入射的电磁波激发,使共振波长处吸收率接近100%(厚度只有13 nm的Ge薄膜中吸收率超过96%)。还表明:在很宽水平方向波矢量范围内,超构平面TM和TE偏振色散关系曲线近似为水平线,因而具有广角度和偏振不敏感吸收特性(结构对60°入射的两种偏振光的吸收率仍超过90%)。     

All-Dielectric Multichannel Terahertz Metasurface Empowering Independent Wavefront Manipulation

Metasurfaces have demonstrated unprecedented capabilities in modulating the polarization and phase of electromagnetic waves and formed an emerging field of research, driving the exploitation of versatile compact devices. In this work, one transmission-mode, multichannel all-silicon metasurface platform that can implement functionalities separately in two orthogonally polarized output fields under linearly polarized incidences is proposed, which can effectively promote the design flexibility. Specifically, a single metasurface can realize multiple independent target phase distributions carrying specific phase relationships, thus enabling different information processing in different linear polarization states. For proof-of-principle experimental exhibitions, a monolayer metasurface composed of silicon pillars is designed, fabricated, and characterized to demonstrate the ability of multi-dimensional light field control, such as polarization-switchable focusing beam. Moreover, the other designed metasurface can generate polarization-switchable Bessel vortex beams under linearly polarized incidences, which also verifies the flexibility and practicality of such platform. This metasurface platform may lead to new optical components, involving multichannel singular beam generators, information encoders, and holographic encryption devices.     

Characteristic Attributes of Multiple Cascaded Terahertz Metasurfaces with Magnetically Tunable Subwavelength Resonators

The characteristics of multiple cascaded metasurfaces comprising H‐shaped, magnetostatically controllable, subwavelength terahertz (THz) resonators made of InAs were systematically investigated, using a commercial solver based on the finite‐integration method, for the design of tunable filters. Three configurations of the biasing magnetostatic field were compared with each other as well as with the bias‐free configuration for filtering of normally incident linearly polarized plane waves. A close study of only one metasurface was found sufficient to broadly determine the sensitivity to the direction of the magnetostatic field and the bandwidth of a stopband. Furthermore, the effects of metasurface geometry and biasing field can be considered separately for initial design purposes. All features in the transmittance spectra for the bias‐free configuration that are related to the number of cascaded metasurfaces are also observed when the biasing magnetostatic field is applied. The coupling of adjacent metasurfaces in a cascade is strongly affected by the relative permittivity and the thickness of the spacer between the two metasurfaces. The spectral locations of stopbands scale with respect to the spacer's relative permittivity, the scaling rule being different from a classical one. The stopbands are redshifted when the spacer thickness is increased, with the redshift dependent on the polarization of the incident plane wave. Inter‐metasurface coupling and inter‐resonator coupling on the same metasurface affect the spectral location of a stopband in opposite ways. On‐off type switching can be obtained by changing the orientation of magnetostatic field. The elucidated characteristics are expected to be important for not only filters but also other tunable THz devices.     

一种光可调的多功能太赫兹几何相位超表面北大核心CSCD

基于金属-光敏硅组合圆环提出了一种光可调太赫兹超表面,可用于实现多功能的波前操控。该超表面单元由正反两面的结构层和中间介质层组成,其中结构层是开口方向相反的金属环,开口处由光敏硅进行填充。在光照强度较低时,超表面可以将入射的圆极化波转换为交叉极化的透射波;随着光照强度升高,透射波将逐渐被完全抑制。根据几何相位原理,通过旋转金属-光敏硅组合圆环,透射的交叉极化波会携带额外的相位因子,并可实现完全的2π范围相位覆盖。通过合理排列超表面单元结构,可以对透射波的波前实现任意操控。利用提出的光可调超表面,在较低光照条件下实现了高效的异常折射、透镜以及轨道角动量产生器;在较高光照条件下,抑制了其透射效率,可有条件地选择应用功能,表现出较好的灵活性。提出的光可调超表面在太赫兹成像、通信、雷达等方面具有较大的潜在应用价值。     

基于交叉极化旋转相位梯度超表面的宽带异常反射

设计实现了一种基于双圆弧形金属结构的宽带反射型极化旋转超表面, 在7.9–20.1 GHz的宽频带范围内交叉极化转换率达到99%, 通过改变其结构参数可实现在保持高效的交叉极化转换率的条件下对交叉极化反射相位的自由调控. 基于六种不同结构参数极化旋转超表面结构单元的空间排布设计实现了一维宽带相位梯度超表面, 在宽频带内, 实现了异常反射. 测试了其镜面交叉极化反射率, 与仿真结果基本一致. 仿真计算了x-极化波入射时的电磁场分布和异常反射角度, 与理论计算结果基本一致. 仿真与测试结果均表明这种相位梯度超表面在8.9–10 GHz 和10.0–18.1 GHz的两个宽带频率范围内可分别实现高效的表面波耦合和异常反射.     

Dynamic polarization rotation and vector field steering based on phase change metasurface

Polarization rotation and vector field steering of electromagnetic wave are of great significance in modern optical applications. However, conventional polarization devices are bulky, monofunctional and lack of tunability, which pose great challenges to the miniaturized and multifunctional applications. Herein, we propose a meta-device that is capable of multi-state polarization rotation and vector field steering based on phase change metasurface. The supercell of the meta-device consists of four Ge₂Sb₂Te₅ (GST) elliptic cylinders located on a SiO₂ substrate. By independently controlling the phase state (amorphous or crystalline) of each GST elliptic cylinder, the meta-device can rotate the polarization plane of the linearly polarized incident light to different angles that cover from 19.8° to 154.9° at a wavelength of 1550 nm. Furthermore, by merely altering the phase transition state of GST elliptic cylinders, we successfully demonstrated a vector field steering by generating optical vortices carrying orbital angular momentums (OAMs) with topological charges of 0, 1 and −1, respectively. The proposed method provides a new platform for investigating dynamically tunable optical devices and has potential applications in many fields such as optical communications and information processing.     

基于电磁超表面的透镜成像技术研究进展

电磁超表面属于超材料的一种,是由许多亚波长纳米结构单元组成的二维功能性平面结构.根据惠更斯原理,超表面阵列可以任意调控光波的相位、振幅和偏振.与传统器件相比,基于这种超材料设计的光学功能器件最大的优势是其具有极薄的厚度.本文首先介绍了广义斯涅耳定律以及纳米单元结构调控相位的基本原理,重点归纳了电磁超表面在透镜成像技术方面的研究进展,包括等离子体超表面、全介质超表面以及金属/介质混合式超表面在成像方面的应用,最后指出了超表面在成像方面尚未解决的前沿问题以及与实际应用接轨的重要问题,希望能为以后的深入研究提供一定的参考和借鉴.     

Multiple bottle beams based on metasurface optical field modulation and their capture of multiple atoms

Compared to conventional devices, metasurfaces offer the advantages of being lightweight, with planarization and tuning flexibility. This provides a new way to integrate and miniaturize optical systems. In this paper, a metasurface capable of generating multiple bottle beams was designed. Based on the Pancharatnam-Berry (P-B) phase principle, the metasurface lens can accurately control the wavefront by adjusting the aspect ratio of the titanium dioxide nanopillars and the rotation angle. When irradiated by left-handed circularly polarized light with a wavelength of 632.8 nm, the optical system can produce multiple micron bottle beams. Taking two bottle beams as examples, the longitudinal full widths at half-maximum of the optical tweezers can reach 0.85 μ and 1.12 μ, respectively, and the transverse full widths at half-maximum can reach 0.46 μ and 0.6 μ. Also, the number of generated bottle beams can be varied by controlling the size of the annular obstacle. By changing the x-component of the unit rotation angle, the metasurface can also change the shape of the bottle beam — the beam cross-section can be changed from circular to elliptical. This paper also analyzes the trapping of ytterbium atoms by the multi bottle beam acting as optical tweezers. It is found that the multi bottle beam can cool and trap multiple ytterbium atoms.