环磁动量主导高品质电磁谐振模式及其非线性研究

High-quality resonant mode with high Q-factor can strongly localize electromagnetic waves into a small mode volume. Electromagnetic wave-materials interactions, particularly nonlinear responses can be enhanced remarkably within the resonant mode. A new kind of fundamental electromagnetic moment, namely toroidal moment, drew considerable attentions in specially designed metamaterial strucuctures recently, for its high Q-factor response and novel localization configuration of electromagnetic fields. In this project, we will theoretically and experimentally investigate the high quality electromagnetic resonant mode dominated by toroidal moment through optimal design, its direct observation through microwave field mapping as well as its ability to enhance nonlinear electromagnetic response. The influences on the radiating properties and Q-factor of geometric parameters and symmetry will be studied with the multipole expansion method involving toroidal moment contribution; we will also implement the direct observation of toroidal mode with the assistant of near-field excitation and microwave field mapping; and toroidal metamaterial samples with nonlinear varactors and microwave-thermal-nonlinear ceramics substrate will be fabricated, the nonlinear transmission and dynamic control of the nonlinear responses will be studied for low-power nonlinear components. This proposal deserves in-depth investigations for its great significance in subwavelength-sized high-Q micro-cavities based nonlinear optics.

高品质电磁谐振模式能够束缚电磁波于很小模式体积内，并具有很高的品质因子，可以实现对电磁波与材料的相互作用尤其是非线性响应的显著增强。环磁动量(toroidal moment)作为一类基本的电磁动量最近在特殊设计的亚波长特异材料结构中得到关注，环磁动量主导的电磁谐振模式具有高品质因子和新颖局域场特性。本课题拟围绕环磁动量主导的高品质电磁谐振模式的优化设计、环磁模式的近场直接扫描观测以及环磁模式对微波非线性响应的增强进行理论和实验研究。利用含环磁项的多极矩展开方法研究结构单元的对称性和几何尺寸对环磁特异材料辐射特性及品质因子的影响；开展环磁模式的近场激励及其局域场探测实验，实现对环磁模式的直接观测；构造含有非线性变容器或具有热非线性响应陶瓷衬底的环磁特异材料，研究非线性输运特性并掌握非线性双稳态响应的动态调控方法。本项目对亚波长微腔增强光学非线性研究有重要科学意义。

本课题提出利用超材料阵列周期对称性及单元结构对称性的调控，实现环磁模式主导高品质电磁谐振的激励及调控。并在研究中，引入微波高介电陶瓷、石墨烯等新材料，从微结构阵列多极散射严格计算的高度阐释了有关超材料环磁谐振模式的新效应和电磁耦合机理。主要结果包括：系统地研究了一类平面二维周期超材料结构中环磁动量激励的影响及其各阶电磁极矩的辐射特性，掌握了获得高Q因子环磁模式的设计方法。研究了一类基于介质陶瓷块的周期非对称结构中的高品质Fano谐振行为，基于前期环磁超材料结构研究基础中环磁动量激励的影响及其各阶电磁极矩的辐射特性，理论与实验研究结合掌握了基于金属或高介电材料高品质电磁谐振超材料的设计方法与调控方法。在超材料高品质电磁谐振模式动态调控方面也开展了系列研究工作，制备了介质环磁超材料结构，实验研究了其动态调控行为。发现由于其显著不同的环磁模式场分布环磁电磁谐振行为对于超材料结构单元所处的背景极为敏感，对几何结构的对称性极为敏感，因而有可能被用于超灵敏探测、传感等方面，此外环磁模式显著的强电磁局域和高品质特性有望用于低阈值非线性光子器件，如低阈值激光等。项目执行过程中在主流光学相关期刊Physical Review A、ACS Photonics、Advanced Optical Materials、AM, PRX, Nanoscale、Optics Express上已发表SCI学术论文23 篇。发表英文专著章节1章。申请专利1 项。项目资助期间，培养毕业硕士2 人，在读硕士、博士2人。