基于范德华异质结构的纳米光学杂化体系设计与模式调控研究

Both surface plasmon polariton (SPP) and phonon polariton (PHP) can break through the optical diffraction limit and manipulate light in the nanometer scale for numerous applications. However, SPP suffers from its large Ohmic loss and relatively short lifetime, while PHP suffers from its narrow spectral bandwidth. Based on our just-published pioneering results, this project aims to design novel van der Waals heterostructures based on two-dimensional atomically-thick materials, and to realize electromagnetic hybrid modes via plasmon-phonon coupling to combine the ultra-long lifetime of PHPs and the widely tunable spectrum response of SPPs. We will study the plasmon-phonon coupling mechanism in van der Waals heterostructures, discover the correlation between the coupled and hybridized mode properties (e.g., the electrical field intensity distribution, the phase delay, the lifetime, the tunability, etc.). We will also investigate the effects of dielectric environments and substrate phonons on the hybrid modes in the ultra-thin van der Waals heterostructures. Then complex heterostructures constructed by three or more layers will be designed to explore the coupling mechanism between multi-phonons and plasmons. This project will investigate the strong coupling effect between spatially－confined electromagnetic field, free carriers and phonons for the first time, and the control of their behavior. This project will not only push the boundary in the current understanding of SPPs and PHPs in van der Waals heterostructures, but also develop a new generation of nanophotonic devices with performance unattainable previously.

等离激元与声子极化波均能突破光的衍射极限，在纳米尺度上对光进行操控和增强,是实现纳米光子学的重要途径。然而等离激元寿命短、声子极化波工作频谱窄等瓶颈限制了它们的广泛应用。在我们先导性研究基础上，本项目拟通过设计基于二维纳米材料的范德华异质结构，研究等离激元与声子极化波的相互耦合，以实现兼具超长寿命和超高带宽的光学杂化新模式。该项目将研究范德华异质结构内该杂化模式产生的物理机制；研究周边介电环境对该新型杂化模式的影响；研究复杂多元范德华异质结构中多声子-等离激元杂化模式的耦合机理；并优选出高性能异质结构以实现对电磁场模式的全方位调控（包括场强分布、相位延迟、模式寿命等）。本项目是光子学、电子学和热学三个学科的交叉，将实现在高局域化条件下电磁场、载流子和声子之间的强耦合，并对它们的特性进行有效调控。这将不仅对等离激元和声子极化波的研究有着极大拓展，而且也为今后实现高性能纳米光学器件开辟新思路。

本项目以高性能石墨烯等离激元、氮化硼声子极化激元等高性能二维极化激元为基础，通过范德华异质结构设计，研究了石墨烯/h-BN，石墨烯/云母，石墨烯/单层MoS2，二维纳米材料和金属复合结构等异致结构对二维极化激元的调控特性。实现兼具超长寿命、超高带宽、全光调制等的光学杂化新模式。分别从以下几方面取得了成果：（一）设计石墨烯/单层MoS2异质结构实现了高效全光中红外等离激元波导和自由空间调制器。借助 MoS2对可见光的高灵敏性，会形成光生电子对石墨烯掺杂，从而改变石墨烯费米能，实现对石墨烯等离激元的超快时间响应和低能耗的调控。（二）利用高灵敏电学激发方式首次直接观测到单层悬空氮化硼中的声子极化波。借助电子波长短和高动量的优势，实现对单层悬空氮化硼中的声子极化波的高效激发，解决了长期以来针对单层氮化硼上声子极化波是否存在的争议。（三）设计石墨烯和金天线的异质结构，实现石墨烯等离激元的完美吸收。通过构建石墨烯等离激元与金天线的微腔模式耦合，让石墨烯等离激元产生更高局域的电磁场增强，提高了石墨烯与自由空间光场的耦合效率，实现了石墨烯等离激元的完美吸收。（四）建立能够分析异质结中二维极化波复杂近场光学图像的表征方法。异质结构中近场光学成像是非常复杂的，因此建立了一套完整的复杂图像分析极化激元模式的解析方法，探索了各种异质结边界对极化激元模式和成像的定量分析。