全介质超构表面的光学相干控制研究

The ever-increasing demand for exotic electromagnetic responses from optical materials drives efforts to exploit strong light-matter interactions at the nanoscale. Much progress has been seen recently in advancing and engineering the science of metasurfaces. However, the static and passive nature of matasurface building blocks restrict their responses to be single-purpose. In addition, most metasurfaces are based on metallic nanostructures which provide extraordinary interaction with light via plasmonic resonances, but at the inevitable cost of significant energy dissipation and reduced device efficiency. In this proposal, we attempt to design low-loss and active metasurfaces based on optical coherent control and all-dielectric materials. We shall divide our study into three parts. First, we will develop a theoretical understanding of coupled metaatoms that are of interest. Coupled mode theory and finite-difference time-domain method will be used together to show the dependences of radiation, polarization, spectra and nearfield enhancement of metaatoms on input beams. The results will be extended to design metasurfaces. Then, we will use our recently constructed coherent angle- and polarization-resolved microscopy to experimentally realize the coherent control as well as to characterize the radiation patterns and polarization. Finally, we attempt to demonstrate a multifunctional metasurface that exhibit electromagnetic induced transparency, Fano resonance and superscattering as well as a high performing all-dielectric biosensor in a controllable manner. We expect this project will point to a new direction in controlling light with light without nonlinearity.

超构表面着眼于光与材料的相互作用，是纳米光子学的前沿领域，备受人们关注。超构表面通常是固定和无源的，所以其光电响应往往只具备单一的功能。此外，超构表面通常由金属构成，以借助表面等离激元共振效应来增强其与光的相互作用，因此具有较高热损耗和较低的工作效率。本申请项目结合我们前期的研究基础，提出基于以硅为代表的低损耗全介质材料体系，在可见光及近红外波段通过相干控制，即利用多束相干准直光作用于样品，实现低损耗、具有动态响应功能的超构表面。具体内容包括：理论上探索超构原子在相干控制下的辐射方向、远场偏振、光谱、近场增强等物理现象的机制，并将其应用至超构表面的设计中；实验上制备可控散射方向、可控手性以及可控近场增强超构表面，并通过相干光角分辨显微成像系统表征与验证。基于实验结果，我们将制备以相干控制为基础的电磁感应透明、Fano共振、超级散射、高灵敏度生物传感器等动态可调超构表面应用。

本项目聚焦以硅为代表的低损耗全介质材料体系，在可见光及近红外波段通过相干调控实现低损耗、具有动态响应功能的超构表面。项目主要开展以下三个方面的研究：1. 超构表面光学相干控制的设计与实现；2. 片上定向传播光源设计；3. 手性超构表面的本征模式分析。重要研究结果包括：1. 提出了硅纳米盘超构表面体系，通过双光束相干调制，实现了单个纳米结构360°横向散射以及超构表面衍射级相干调控，为高速、多功能光学调制提供新思路；2. 利用介质单极子共振模式、PB相位，实现自由空间光和偶极光源的片上定向耦合发射，为片上光互联场景的应用奠定了理论基础；3. 在非厄米光学框架下通过准正则模理论和耦合模理论研究复合结构超构表面基元的电磁响应，系统解析了多纳米谐振腔耦合的手性超表面的物理成因，同时成功设计极限手性超构表面，为快速、高灵敏手性分子检测奠定理论基础。

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