利用近场增强实现基于石墨烯和超材料复合结构的可调谐非线性太赫兹调制器件

Modulating terahertz waves using conductivity-adjustable graphene material has drawn enormous attention in the terahertz research. In particular, modulating terahertz waves using graphene-metamaterial hybrid structures has greatly improved the modulating performances, which is very potential in realizing next-generation active terahertz modulation devices. However, the previous research mainly rely on the linear property of graphene under low terahertz incident field, research on the nonlinear effect of graphene under strong-field terahertz incidence are seldom reported. Meanwhile, the modulation depth of the reported works in nonlinear terahertz modulation still need to be improved (~15%). In this proposal, we aim to apply the graphene-metamaterial hybrid structures to enhance the nonlinear effect of graphene by using the near-field enhancement effect of metamaterial structures, and study the interaction process between the nonlinear graphene and the metamaterials. We will reveal the inner physical mechanisms by means of numerical simulation, sample fabrication, experimental characterization and theoretical analysis. Next, based on the above research, we will further introduce external optical pump and bias voltage to control the strength of the nonlinear effect of graphene, so as to realize controllable nonlinear terahertz modulators with large modulation depth (Maximum > 80%). Our proposal will serve as a foundation of this kind of terahertz functional devices.

利用石墨烯电导率可调的特性调制太赫兹波是太赫兹领域中备受瞩目的研究方向，尤其是利用石墨烯和超材料复合结构来调制太赫兹，极大地优化了相应调制器件的性能，有望实现新一代主动式太赫兹调制器件。然而，在以往的研究中，主要用到的是低太赫兹入射场下石墨烯的线性性质，关于强太赫兹入射场下石墨烯非线性效应的研究工作还鲜有报道，且已报道的相关太赫兹调制深度也有待提高（~15%）。本项目旨在采用石墨烯和超材料复合结构，利用超材料微结构的近场增强效应增强石墨烯的非线性效应，研究强场太赫兹入射下非线性石墨烯和超材料相互作用的物理过程。通过模拟仿真、样品制备、实验测量和理论模型分析等手段，揭示内在物理规律。并在此研究基础上，引入外加光泵和偏置电压等调控方法，来进一步调谐石墨烯的非线性效应的强弱，实现大调制深度（最高> 80%）的可调谐非线性太赫兹调制器件。本项目将为推动太赫兹波段此类功能器件的发展奠定基础。

太赫兹科学与技术是近年来电磁领域的研究热点之一，相关太赫兹源、太赫兹探测器等器件层出不穷。然而，相应调控功能器件却较为匮乏，制约了太赫兹技术的发展，其中包括太赫兹非线性调制器件。超材料的出现为突破这一困难提供了有效途径，这是因为超材料微结构的谐振场增强效应，为非线性效应的产生提供了理想的场所。另外，二维材料石墨烯近年来也发展迅速，其本身在太赫兹波段具有非线性特性。鉴于此，本项目结合超材料近场增强效应和石墨烯的非线性效应，对可调谐非线性太赫兹调制器件开展了深入研究。在3年的项目实施过程中，采用三角形二聚体、小缝隙（百纳米量级）开口谐振环、电磁诱导透明耦合结构等超材料微结构与石墨烯相互作用，实现了多种对太赫兹透射谱和反射谱的非线性主动调制器件。同时，结合光泵和偏置电压两种调控手段，也实现了多种主动式的太赫兹调控器件。项目在《Advanced Materials Technologies》、《Optics Express》、《ACS Photonics》、《Nanophotonics》、《Materials》等国际高水平期刊发表SCI论文11篇。研究成果为太赫兹非线性功能器件的设计奠定了基础，在未来集成化应用方面具有应用前景。