Development of metasurfaces for wavefront modulation in terahertz waveband
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摘要: 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。Abstract: Metasurface is an ultrathin planar device composed of artificial microstructures, which can be used to manipulate the amplitude, phase, and polarization of electromagnetic (EM) waves. Metasurface has the advantages of small volume, light weight, highly integrated, flexible manipulation of EM waves, so it plays an important role in the field of EM wave spectrum and wavefront modulation. In this paper, the research progresses of metasurface for wavefront modulation in the terahertz (THz) waveband were reviewed. The amplitude and phase modulation mechanisms of three kinds of microstructure units in the metasurface, including the microstructure based on Pancharatnam-Berry (PB) phase, localized surface plasmon resonance (LSPR) and Mie resonance were summarized, and the methods for realizing metasurface with high efficiency were discussed. After that, the pure phase and complex amplitude modulation methods for designing the wavefront modulation metasurface were introduced. Specifically, the typical functions, including single function and multifunction and tunable function, of the wavefront modulation metasurfaces in the THz waveband were reviewed. In the early research, metasurfaces were used to realize beam focusing, beam deflection, holographic imaging, and special beam generation such as vortex beam, Airy beam, and Lorentz beam in the THz region. In order to improve the utilization of a THz component, multifunctional metasurfaces, such as metasurfaces with polarization and wavelength multiplexing were proposed. With the requirement of dynamic control of the THz wavefront, some active metasurfaces were proposed and demonstrated. There were two kinds of active metasurfaces. One of the active metasurfaces was formed by combining the metasurface with semiconductor or phase transition materials, and the other was the all-optical metasurface formed by a silicon wafer with pump beam. The all-optical metasurfaces can be reused without reprocessing. The THz wavefront can be modulated dynamically by adjusting the image of the metasurface projected on the silicon wafer. Thus, the all-optical metasurface had the ability to dynamically control the beam steering and focusing, and it can be applied in THz communication, THz radar and other fields. At the end, the development trend and application prospects of the metasurfaces for wavefront modulation in the THz waveband were discussed.
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Key words:
- terahertz /
- metasurface /
- wavefront modulation /
- multifunction metasurface /
- tunable metasurface
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图 2 典型太赫兹波前调制超表面。(a)太赫兹超表面透镜及其聚焦和成像性能测试结果;(b)太赫兹全息超表面及其在不同位置处重建的字母图;(c)不同拓扑数的太赫兹涡旋超表面及其产生的涡旋光场的相位分布;(d)太赫兹编码超表面及其产生的波束偏转测试结果
Figure 2. Typical terahertz (THz) metasurfaces for wavefront modulation. (a) THz metasurface lens and verification of its focusing and imaging performance; (b) THz meta-hologram and the alphabets reconstructed at different positions; (c) THz metasurfaces for generating the vortex beams with different topologies and the phase distribution of the generated vortex fields; (d) THz coded metasurfaces and the experiment results of beam deflection
图 3 功能复用的太赫兹波前调制超表面。(a)波分复用的太赫兹超表面功能示意图及其在0.5 THz和0.63 THz处重现的图像;(b)基于PB相位的偏振复用超表面透镜及其在不同偏振的太赫兹波入射时的聚焦结果;(c)用于产生涡旋/Bessel光束的基于Mie共振的全介质偏振复用超表面及其在x偏振和y偏振的太赫兹波入射时的波前调控实验结果
Figure 3. Multifunctional metasurfaces for wavefront modulation in the THz waveband. (a) Schematic diagram of a wavelength multiplexed metasurface and the images obtained at 0.5 THz and 0.63 THz, respectively; (b) Polarization multiplexed metasurface lens based on PB phase and the experimental results of the focusing results for incident wave with different polarizations; (c) Polarization multiplexed all-dielectric metasurface based on Mie resonance for vortex/Bessel beam generation and the measured intensity distributions under x- and y-polarized incidence, respectively
图 4 温控太赫兹波前调制超表面器件。(a)V形金结构超表面与VO2薄膜形成的太赫兹温控超表面透镜;(b)直接刻蚀VO2材料形成的C形狭缝结构超表面透镜及环形艾里光束发生器;(c)VO2材料填充的C形金结构形成的太赫兹全息超表面
Figure 4. Temperature-controlled metasurface device for THz wavefront modulation. (a) Tunable THz metasurface lens consisting of metasurface lens with V-shaped antennas and a VO2 film; (b) Tunable metasurface lens and ring-Airy beam generator with C-shaped slots formed by etching the VO2 film directly; (c) Tunable THz meta-hologram consisting of C-shaped gold antenna with VO2
图 5 (a)太赫兹波前调制全光等离子体超表面示意图;(b)基于PB相位的光致天线设计;(c)用CCD捕获到的投影到硅片上的光致全息图
Figure 5. (a) Schematic of the photo-induced THz plasmonic metasurface for wavefront modulation; (b) Design of photo-induced antennas based on PB phase; (c) Meta-hologram projected on the silicon wafer captured by charge-coupled device (CCD)
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