Plasmonic nano‐slits assisted polarization selective detour phase meta‐hologram

Traditional detour‐phase hologram is a powerful optical device for manipulating phase and amplitude of light, but it is usually not sensitive to the polarization of light. By introducing the light‐metasurface interaction mechanism to the traditional detour phase hologram, we design a novel plasmonic nano‐slits assisted polarization selective detour phase meta‐hologram, which has attractive advantages of polarization multiplexing ability, broadband response, and ultra‐compact size. The meta‐hologram relies on the dislocations of plasmonic slits to achieve arbitrary phase distributions, showing strong polarization selectivity to incident light due to the plasmonic response of deep‐subwavelength slits. To verify its polarization sensitive and broadband responses, we experimentally demonstrate two holographic patterns of an optical vortex and an Airy beam at p‐ and s‐polarized light with wavelengths of 532nm, 633nm and 780nm, respectively. Furthermore, we realize an application example of the meta‐hologram as a polarization multiplexed photonic device for multi‐channel optical angular momentum (OAM) generation and detection. Such meta‐holograms could find widespread applications in photonics, such as chip‐level beam shaping and high‐capacity OAM communication.

     

Functional and nonlinear optical metasurfaces

Optical metasurfaces are thin‐layer subwavelength‐patterned structures that interact strongly with light. Metasurfaces have become the subject of several rapidly growing areas of research, being a logical extension of the field of metamaterials towards their practical applications. Metasurfaces demonstrate many useful properties of metadevices with engineered resonant electric and magnetic optical responses combined with low losses of thin‐layer structures. Here we introduce the basic concepts of this rapidly growing research field that stem from earlier studies of frequency‐selective surfaces in radiophysics, being enriched by the recent development of metamaterials and subwavelength nanophotonics. We review the most interesting properties of photonic metasurfaces, demonstrating their useful functionalities such as frequency selectivity, wavefront shaping, polarization control, etc. We discuss the ways to achieve tunability of metasurfaces and also demonstrate that nonlinear effects can be enhanced with the help of metasurface engineering.

     

基于十字变形结构的高效超宽带线性极化转换超表面

提出了一种基于十字变形结构超表面的极化转换器,在反射模式下获得了高效超宽带的交叉极化反射.在8.4到20.7GHz频段内交叉极化反射率大于-0.2dB,而共极化反射率小于-12dB,在谐振频率点处交叉极化反射率大于-0.03dB,而共极化反射率达到-60dB,即在谐振点处几乎可实现完全的交叉极化转换;相对带宽达84.5%,交叉极化的平均转换效率为96.7%;此外,利用电路板刻蚀制备了此极化转换器样品,实验测试其交叉极化反射率在工作频段内大于-1dB,而共极化反射率小于-10dB,实验结果与模拟结果吻合,验证了此超表面可以在超宽的频带内实现线极化电磁波的交叉极化转换.本文设计的超宽带极化转换超表面具有转换效率高和几何结构简单的优点,可被扩展到太赫兹甚至是可见光频段.     

Helicity Multiplexed Spin‐Orbit Interaction in Metasurface for Colorized and Encrypted Holographic Display

The photonic spin‐orbit interaction (PSOI) in inhomogeneous anisotropic metasurface has drawn much attentions recently due to its superior ability to manipulate light wave in the deep‐subwavelength scale. Traditional methods involving PSOI are limited to operational spectral bandwidth owing to the intrinsic dispersion of the constitutive materials. In this paper, a helicity‐multiplexing scheme is proposed to achieve independent control of the PSOI in both the spectral and spatial domains by combining the broadband characteristic with polarization dependence of the metasurface. Two simultaneous functions of multicolor holographic display and polarization encryption are experimentally demonstrated with a single metasurface perforated with nanoholes. Although the optical response of the nanoholes themselves are almost independent of the light wavelength, the obtained image can have abundant spectral information. The approach proposed here is promising for realizing multifunction optical device, multicolor display, optical storage and information encryption.     

基于超表面的多光谱成像系统设计

超表面是一种人工制造的亚波长结构阵列平面,重量轻,易集成,可实现多种功能,被广泛应用于诸多领域。传统光谱成像系统依赖于色散元件及光程累积相位差实现不同波长的色散与聚焦,无法满足系统集成化需求。不同于传统光学元件依赖电磁波在介质中传播累积相位差,超表面依靠界面相位变化来进行相位调控,可实现十分轻薄的光学系统。研究传输相位型超表面,使用时域有限差分算法(FDTD算法)优化单元结构。将超表面引入光谱成像系统中,通过优化亚波长结构尺寸,进行结构排布,开展超表面光谱成像系统研究,实现多波长色散与聚焦独立调控。利用该方法,扫描不同单元结构参数对相位的影响,依照聚焦的相位分布针对不同波长设计对应的位相分布,仿真实现了一个波段范围为510～720 nm,焦距为2 mm,谱段数为八个的超表面多光谱成像系统。通过电磁仿真软件FDTD solutions和数据处理软件计算全模结构电场的远场分布,并分析了系统的成像性能。相比于传统光栅或棱镜分光结构,超表面光谱成像系统可有效减小系统体积,其超轻、超薄、便携特点解决了现有光谱成像系统的应用局限性,为小型化、轻量化光谱成像系统的研制提供了一种新的解决方案。     

Metasurface aided intelligent reflecting surfaces for indoor GSSK-VLC downlink

To provide high-quality communication in the indoor generalized space shift keying (GSSK) aided visible light communications (VLC) downlink transmission, especially when the line-of-sight (LoS) link is blocked, a metasurface aided intelligent reflecting surfaces (mIRS) scheme is proposed. By controlling the reflection characteristics of incident light in a deliberate manner provided in this paper, the proposed mIRS-assisted indoor GSSK-VLC downlink can significantly enhance the signal quality at the receiver end. Furthermore, the maximum likelihood (ML) and efficient preprocessing enabled sparsity orthogonal matching pursuit (OMP) detectors are respectively presented for the considered system. Finally, simulations are demonstrated to verify the effectiveness of the proposed mIRS-assisted indoor GSSK-VLC downlink transmission.     

一种具有异常透射功能的新型惠更斯超表面

提出了一种具有独立调控透射幅值与相位能力的新型惠更斯单元结构,能够实现透射幅值在0~0.9、透射相位在0~2π的任意调控。基于广义斯涅耳定理对惠更斯单元进行排列,设计并制备出具有异常透射功能的超表面结构。全波仿真结果表明超表面能够使频率为10 GHz的正入射电磁波产生约60°的偏折。近场测试结果与仿真结果基本一致,进一步证实了超表面结构设计的正确性。     

基于相位调控的超高透射声学超表面及其应用*

声学超表面可以灵活有效地对声波进行调控,实现多种新颖的现象和功能,在诸多声波调控领域有潜在的应用前景。该文引入了一种镀膜型迷宫结构单元,可以提供全范围(0~2π)的突变相位,具有高效的透射率(~100%)和较好的鲁棒性。基于相位调控,可利用镀膜型迷宫结构单元构建出超高透射超表面,实现异常声折射、声聚焦、声束沿任意凸轨迹弯曲传播以及声成像等应用。     

金属-介质-金属渔网超表面结构调控的荧光辐射：空间选择性激发和双增强

增强荧光辐射在生物成像、高灵敏探测、集成光源等方面都具有重要的应用价值.金属纳米颗粒的周围或者金属纳米结构的间隙都可以产生强的电磁场,相应的,这些结构附近的局域态密度也被极大地增强.虽然增强荧光辐射已经在多种金属纳米颗粒和颗粒对中被证明,但是利用金属纳米结构对荧光分子的吸收和辐射过程同时进行调制仍然是一个有挑战的问题.本文研究了金属-介质-金属超表面对荧光辐射的调控,其中局域表面等离激元(LSP)和磁等离激元(MPP)分別与于分子的吸收和辐射过程发中耦合相互作用.对于吸收过程,LSP的耦合作用使得可以通过旋转泵浦激光的偏振态来实现荧光分子的空间选择激发.此外,MPP模式的偏振依赖特性使得矩形渔网结构中的荧光分子的辐射波长和偏振态也受到调控.实验观测结果经过了时域有限差分模拟的验证.本文报道的纳米结构在光辐射器件和纳米尺度集成光源等方面都具有潜在的应用价值.     

Fluorescence Emission Mediated by Metal-Dielectric-Metal Fishnet Metasurface: Spatially Selective Excitation and Double Enhancement

Enhancement of fluorescent radiation is of great importance for applications including biological imaging, high-sensitivity detectors, and integrated light sources. Strong electromagnetic fields can be created around metallic nanoparticles or in gap of nanostructures, where the local state density of radiating mode is then dramatically enhanced. While enhanced fluorescent emission has been demonstrated in many metallic nanoparticles and nanoparticle pairs, simultaneous mediation of absorption and emission processes of fluorescent emitters remains challenging in metallic nanostructures. Here, we investigate fluorescent emission mediated by metal-dielectric-metal fishnet metasurface, in which localized surface plasmon (LSP) and magnetic plasmon polaritons (MPPs) modes are coupled with absorption and emission processes, respectively. For absorption process, coupling of the LSP mode enables spatially-selective excitation of the fluorescent emitters by rotating the polarization of the pump laser beam. In addition, the polarization-dependent MPP mode enables manipulation of both polarization and wavelength of the fluorescent emission by introducing a rectangular fishnet structure. All the experimental observations are further corroborated by finite-difference time-domain simulations. The structure reported here has great potentialfor application to color light-emitting devices and nanoscale integrated light sources.