Polarization and Holography Recording in Real- and k-Space Based on Dielectric Metasurface

The diverse design freedom and mechanisms of metasurfaces motivate the manipulation of polarization in an ultrashort distance with subwavelength resolution and make metasurfaces outperform conventional polarization optical elements. However, in order to enhance the information capability and encryption security of metasurface holograms, polarization manipulation together with multiplexing technologies are still highly desired. Here, a birefringent dielectric metasurface with the capability of encoding a grayscale image in real-space based on Malus's law by utilizing the inhomogeneous polarization distribution and realizing the reconstruction of a vectorial holographic image in k-space with the help of the phase profiles of different polarization components of output light is demonstrated. This novel functionality is realized by exploiting the manipulation of polarization and phase of output light simultaneously offered by the dielectric metasurface. The proposed method may enhance the information capability and security level of applications such as the anticounterfeiting and encryption.     

Full‐Color Complex‐Amplitude Vectorial Holograms Based on Multi‐Freedom Metasurfaces

Phase, polarization, amplitude, and frequency represent the basic dimensions of light, playing crucial roles for both fundamental light–material interactions and all major optical applications. Metasurfaces have emerged as a compact platform to manipulate these knobs, but previous metasurfaces have limited flexibility to simultaneous control them. A multi‐freedom metasurface that can simultaneously and independently modulate phase, polarization, and amplitude in an analytical form is introduced, and frequency multiplexing is further realized by a k‐space engineering technique. The multi‐freedom metasurface seamlessly combines geometric Pancharatnam–Berry phase and detour phase, both of which are frequency independent. As a result, it allows complex‐amplitude vectorial hologram at various frequencies based on the same design strategy, without sophisticated nanostructure searching of massive geometric parameters. Based on this principle, full‐color complex‐amplitude vectorial meta‐holograms in the visible are experimentally demonstrated with a metal–insulator–metal architecture, unlocking the long‐sought full potential of advanced light field manipulation through ultrathin metasurfaces.     

Colorful Metahologram with Independently Controlled Images in Transmission and Reflection Spaces

Benefiting from the excellent properties of manipulating electromagnetic waves at subwavelength scale, metasurfaces are widely used to realize metaholograms with a large viewing angle or diffraction angle. However, all previously reported holograms just utilize transmission (or reflection) space while the corresponding reflection (or transmission) space is abandoned. In this paper, combining the off‐axis illumination method and polarization dependence of geometric‐phase‐based metasurfaces, a scheme is proposed to realize colorful metaholograms with independently controlled holographic images in both the transmission and reflection spaces. With this method, the usable data capacity and imaging region are greatly expanded. As far as it is known, it is the first time that independently controlled color holographic images in both the transmission and reflection spaces using metasurfaces is demonstrated. This approach has promising applications in real 360° holographic image, multifunctional optical device, multicolor display, etc.     

High‐Performance Broadband Circularly Polarized Beam Deflector by Mirror Effect of Multinanorod Metasurfaces

Manipulation of light phase and amplitude by plasmonic metasurfaces has immensely promising applications in optical imaging, information processing, communications, and quantum optics. However, the controllability of efficiency and bandwidth is relatively low for the single‐layer metasurfaces. Here, a high efficiency and broadband circularly polarized (CP) beam deflector based on multirod single‐layer metasurfaces is presented. Each unit can be regarded as an imperfect polarizer, and the phase and amplitude induced by the mirror effect can be easily controlled. Owing to the plasmonic hybridization, the high efficiency and broadband characteristics of the proposed metasurfaces are theoretically and experimentally demonstrated. Meanwhile, an easy way to determine the polarization degree of the incident light based on Poincaré sphere is also proved by the multirod metasurfaces. Our work provides a simple alternative way to enhance the efficiency of CP anomalous light and thus has robust applications in nanophotonics and nanooptics.     

太赫兹波前调制超表面器件研究进展

超表面是一种由人工微结构组成的超薄平面器件,能够实现对电磁波振幅、相位以及偏振态的调控,具有体积小、重量轻、集成度高、可灵活操控电磁波等优势,在电磁波谱、波前调制中发挥着巨大的作用。综述了近年来基于超表面的太赫兹波前调制器件的研究进展。总结了基于Pancharatnam-Berry相位、基于局域表面等离子体共振(LSPR)、基于Mie共振的三种超表面单元结构对电磁波的振幅、相位调控机理,并讨论了实现高效率超表面的方法。之后,介绍了用于设计波前调制超表面器件的纯相位调制方法和复振幅调制方法。综述了在太赫兹波段典型的超表面波前调制器,包括单一功能、复合功能以及可调谐功能的超表面波前调制器件。在早期的研究工作中,设计的超表面可实现波束偏转、波束聚焦、全息成像、以及涡旋光束、自聚焦光束、洛伦兹光束等特殊光束产生等功能。为提高太赫兹器件的利用率,波分复用、偏振复用等功能复用的太赫兹超表面器件被提出。随着对太赫兹波前动态调控需求的增长, 一些主动的太赫兹超表面器件被提出并在实验上被验证。共有两种主动的超表面器件。其中一种主动超表面是通过将超表面结构与半导体材料或相变材料结合形成的,另一种是通过光泵浦硅片形成的全光器件。全光超表面在不用重新加工的前提下能够被重复使用。通过调整投影在硅片上的超表面图像即可动态操控太赫兹波前。全光超表面具有动态控制波束扫描和波束聚焦的能力,将来可应用于太赫兹通信、太赫兹雷达等领域。最后,对太赫兹波前调制超表面器件的发展趋势与应用前景进行了展望。     

多维度超表面及其在信息加密防伪上的应用

超表面是一种厚度在亚波长或波长量级的人工层状材料。可通过调控超表面单元结构上的大小、形状、转角、位移量等自由度，实现对电磁波频率、振幅、相位、偏振等特性的灵活有效调控。超表面具有超薄、宽带、低损耗、易加工、灵活设计，功能强大等特点。文中综述了具有单维度、双维度、多维度光场调控功能的超表面及其在外部激励作用下具有主动可调特性超表面的发展历程，并特别介绍了这些超表面用于信息加密防伪领域的实现方式与优势特点。相比于传统的信息加密防伪技术，超表面信息加密防伪术具有亚波长像素，精密控制，安全系数高等特点，展现了全新视角，拥有广阔的发展前景。     

新型功能超颖表面波前调制技术的发展与应用(特邀)

超颖表面作为一类智能表面,通常由特殊设计、加工而得到的特征尺寸接近或小于波长的亚波长纳米天线阵列构成。超颖表面能够实现光场的振幅、相位和偏振的人为调控,具有超薄、超小像素、宽带、低损耗、易加工等优势,设计灵活,功能强大。文中针对超颖表面在全息显示、波前调制和偏振转换、主动可调、非线性波前调控等方向进行综述,并展望未来发展趋势。超颖表面作为一种超薄的、微型化的波前调制器件,具有极大的信息容量,且更能适应未来高度集成的微型光电系统的发展要求,在全息显示、光束整形、涡旋光束的产生、数据存储、加密与防伪、超透镜与色散控制、彩色印刷、非对称传输、非线性光学、光的自旋霍尔效应、光通信与集成光电子学等应用领域提供了潜在的可行性和新的视角,有望取代传统光电器件,展现出了广阔的发展前景。     

宽带消色差红外光学超构透镜研究进展（特邀）

超构透镜是由亚波长散射单元结构排列而成的具有聚焦功能的平面二维超构表面。超构表面能够在亚波长尺度上操控光场的振幅、相位、色散和偏振态,是近年来迅速发展起来的新型光场调控载体。亚波长共振纳米结构使得高阶衍射被抑制,入射光场可以完美地被调制到设计的衍射级次上,从而确保了超构表面器件具有高的光子调控效率。同时,超构单元在设计上的灵活性及其特定的电磁响应使得超构表面可以实现对光场多个维度的定制化操控。不同于传统光学透镜依赖光传播的相位累积效应,宽带消色差超构透镜通过对光场相位和相位色散的同时独立调控解决了传统通过级联多个透镜修正色差造成的光学系统复杂和体积庞大限制,为发展小型化片上集成光学提供了全新的思路。文中围绕超构透镜的相关研究,首先介绍了超构表面调控光场振幅、相位和偏振态的基本原理,在此基础上,重点回顾了近年来关于超透镜的研究发展,包括通过单一参量调控的单波长超透镜的实现,以及通过对光场偏振、相位及相位色散的多参量联合调控的多功能宽带消色差超构透镜的发展现状,最后讨论其进一步发展的可能挑战与应用前景。     

Simultaneous Control of Light Polarization and Phase Distributions Using Plasmonic Metasurfaces

Harnessing light for modern photonic applications often involves the control and manipulation of light polarization and phase. Traditional methods require a combination of multiple discrete optical components, each of which contributes to a specific functionality. Here, plasmonic metasurfaces are proposed that accomplish the simultaneous manipulation of polarization and phase of the transmitted light. Arbitrary spatial field distribution of the optical phase and polarization direction can be obtained. The multifunctional metasurfaces are validated by demonstrating a broadband near‐perfect anomalous refraction with controllable linear polarization through introducing a constant phase gradient along the interface. Furthermore, the power of the proposed metasurfaces is demonstrated by generating a radially polarized beam. The new degrees of freedom of metasurfaces facilitate arbitrary manipulation of light and will profoundly affect a wide range of photonic applications.     

基于任意偏振态的数字全息散斑去噪

数字离轴全息图重建的物体图像会有明显的散斑噪声,本文利用降低相干度的方法来实现散斑去噪。具体方法是通过任意偏振态的物光和线偏振态参考光实现干涉记录,通过这些光场进行平均处理可以有效减少数字全息中产生的散斑噪声。通过控制三个波片的旋转实现任意偏振态,得到多种偏振态下的全息图,多偏振态下重建物体图像的散斑对比度各有不同,对各个重建图像进行对比分析得到最优结果。之后再将各偏振态下的全息图叠加进行重建,重建图像中的散斑噪声得到很好的抑制且比单偏振态下效果更好。从实验结果的分析中能看到这种方法对抑制散斑噪声的有效性。     

Multistate Tuning of Third Harmonic Generation in Fano-Resonant Hybrid Dielectric Metasurfaces

Hybrid dielectric metasurfaces have emerged as a promising approach to enhancing near field confinement and thus high optical nonlinearity by utilizing low loss dielectric rather than relatively high loss metallic resonators. A wider range of applications can be realized if more design dimensions can be provided from material and fabrication perspectives to allow dynamic control of light. Here, tunable third harmonic generation (THG) via hybrid metasurfaces with phase change material Ge₂Sb₂Te₅ (GST) deposited on top of amorphous silicon metasurfaces is demonstrated. Fano resonance is excited to confine the incident light inside the hybrid metasurfaces, and an experimental quality factor (Q-factor ≈ 125) is achieved at the fundamental pump wavelength around 1210 nm. Not only the switching between a turn-on state of Fano resonance in the amorphous state of GST and a turn-off state in its crystalline state are demonstrated, but also gradual multistate tuning of THG emission at its intermediate states. A high THG conversion efficiency of η = 2.9 × 10⁻⁶% is achieved, which is 32 times more than that of a GST-based Fabry–Pèrot cavity under a similar pump laser power. Experimental results show the potential of exploring GST-based hybrid dielectric metasurfaces for tunable nonlinear optical devices.     

利用超表面的涡旋光束产生进展（特邀）

涡旋光束因为携带轨道角动量,在光通信、粒子操纵及量子信息等领域都具有重要的应用前景。目前有很多方法可用于产生涡旋光束,如利用螺旋相位板、模式转换、空间光调制器等。然而,传统的方法需要搭建体积相对较大的光学系统,限制了其在集成光学等领域中的应用。不同于传统方法中通过传输效应来获得相位变化,超表面可以通过纳米结构使入射光产生相位突变,在纳米尺度上独立控制动态或几何相位以产生涡旋。超表面具有强大光控制能力的同时,还具有体积小、易于集成等特点,因此成为了产生涡旋光的理想方法。文中在介绍产生涡旋光束基本原理的基础上,回顾了近年来利用超表面产生涡旋光束的研究进展。首先介绍了利用动力学相位、Pancharatnam-Berry (P-B)相位以及混合相位产生光学涡旋的方法。随后,对利用全息与编码超表面产生涡旋及通过多路复用产生多个涡旋等不同方法进行了综述。最后,对基于超表面产生涡旋的一些亟待解决的问题和应用前景作了简单总结与讨论。     

水下目标自然光偏振成像的研究

采用白炽灯作光源、面阵CCD作探测器,用圆偏振和线偏振技术并且改变光源能量对水下目标进行成像。通过比较图像清晰表明用自然光照明无论是采用圆偏振技术还是采用线偏振技术都可提高水下目标成像的清晰度和成像距离,且当偏振条件一定时适应提高光源强度能使图像变得更清晰。     

基于随机森林的红外图像超分辨力算法

为提高低分辨力红外图像的分辨力,提出了一种红外图像超分辨力算法。该算法训练2个随机森林模型：红外图像训练第1个模型、配准的多传感器图像训练第2个模型。采用自适应边缘提取算法提取红外图像与可见光图像的边缘,计算输入的低分辨力红外图像块与对应的高分辨力可见光图像块之间的相关系数。根据相关性选择合适的重建模型,用选择的模型重建高分辨力红外图像块,并整合为高分辨力红外图像。实验结果表明,与超分辨力随机森林算法相比,算法重建的高分辨力红外图像具有更高的客观指标,峰值信噪比(PSNR)平均提升了0.09 dB,并且获得更为清晰的主观视觉效果,更接近原始图像。     

Hybrid Metasurfaces of Plasmonic Lattices and 2D Materials

Plasmonic metasurfaces can significantly enhance the interaction between light and 2D materials. Hybrid structures of plasmonic lattices and 2D materials show great promise for both fundamental and practical studies because of their unprecedented ability for precise manipulation of light at the nanoscale. This review starts with an overview of the basic concepts of plasmonic lattices and optical properties of 2D materials, as well as fabrication strategies for hybrid metasurfaces. Then, the enhanced photoluminescence, quantum emission, optoelectronic detection, nonlinear process, and valleytronics in hybrid metasurfaces are summarized, and their development for nanophotonic functional devices are reviewed. Further, several compelling topics are also outlined that provide outlooks for future directions of hybrid metasurfaces such as novel structural design and high-quality fabrication, all-dielectric metasurfaces, dynamic metasurfaces, and plasmonic mediation of chemical reactions and physical processes. It is believed that hybrid metasurfaces of plasmonic lattices and 2D materials can open prospects for versatile platforms for light-matter interactions and contribute to the revolutions on nanophotonic devices.     

时空复用法实现傅里叶计算全息图的彩色显示

为实现傅里叶计算全息图的真彩色显示,本文提出了一种时空复用方法。首先对一幅彩色场景进行红绿蓝分色,并按照一定的比例对三色场景进行缩放处理,实现真彩色再现像的色差补偿;然后制作3幅具有特定结构的全息图,将3幅全息图轮流加载到空间光调制器上,通过时空复用保证了彩色再现像信息的完整性;最后通过使用滤光片,实现以白光LED作为再现光源的真彩色全息显示。结果验证了所提出方法的可行性。     

空间分集光通信的信标光切换设计

为了解决空间分集激光通信中信标光同步快速切换的问题,提出一种使用FPGA实现阵列信标光同步转换设计,解决了基于分集激光通信中多路信标光同步快速切换的问题。在此使用卡诺图编程方式,生成电机驱动时序,通过原理图编程方式设计多路粗精信标切换电路。实验结果表明,该方法实现了分集激光通信中多光路的协同工作,并有效地简化了传统信标光切换复杂的系统结构。     

基于电介质超表面的双频带双偏振通道波前调控

随着微纳加工技术的发展,超表面在亚波长尺度对电磁波的多维度调控展现出传统光学器件难以比拟的优势。基于电介质硅纳米柱结构构建了具有双频带响应的超表面,利用微结构对不同偏振入射光反射系数的差异,通过构建梯度几何相位实现了双波长下的异常反射;同时设计了超表面灰度成像阵列,在近红外波段实现了对正交偏振态和双波长入射具有不同响应的正负灰度图像。文中提出的超表面设计为基于超表面的多功能集成技术的发展奠定了基础。     

Code Division Multiplexing Inspired Dynamic Metasurface Holography

Metasurface holography is attracting increasing attention owing to its numerous advantages over conventional holography techniques, such as precise control of phase profiles, compact sizes, and multiple information channels via a single optical element. Metasurfaces provide a flexible platform for incorporating various multiplexing techniques. Inspired by code division multiplexing (CDM), which is widely employed in networking and wireless digital communications, metasurface holography for generating dynamic holographic images controlled by both the patterned beam profiles and polarization states is designed and realized in this study. Specifically, two orthogonal polarization states and 16 code bases of light illumination are combined to generate 32 independent channels. Only the correct code reference can decode the target image for a specific channel, providing encryption for information transportation. Meanwhile, the demonstrated metasurface holography with CDM can realize active modulation via a digital micromirror device. The proposed metasurface can be utilized to achieve dynamic information display, data storage, optical encryption, and other applications in optics.     

基于多波束GEO卫星的大容量互联网接入系统

针对大容量地球同步轨道（GEO）卫星系统目的关口站距用户远、同步耗时长、下行传输效率低等问题,提出基于多波束GEO卫星的大容量互联网接入系统。所提方案星上进行非再生式信号处理、基带程控交换、闭环同步控制、信令信息处理和信道调度管理以及下行链路采用时分复用传输方式。对于支持大量分散或移动用户接入互联网的应用,业务质量显著改善,且因信道利用率大大提高,实际运行时的用户容量、数据吞吐率也可能更大。仿真结果表明多频-准正交时分复用传输方式的性能更好,且根据我们已进行过的有关单元的现场可编程门阵列设计实现经验,所提系统现实可行。