太赫兹人工表面等离激元无源器件

Recently, spoof (or structured) surface plasmon polaritons (SPP) based on plasmonic metamaterials have attracted lots of interests due to the significant effects of electromagnetic field confinement and enhancement, and the potentials for application in sub-wavelength imaging, miniaturized devices, and highly sensitive sensors. In our previous works, we have thoroughly studied the physical mechanism of microwave SPP, and proposed a series of flexible, ultra-thin two-dimensional SPP devices. The terahertz band, since the wavelength is largely shortened, the feature size of devices also decreases, the SPP excitation way used in microwave frequencies is no longer applicable. Although the transformation between free space wave and SPP wave have been intensively reported in the literature, the efficiency is not high, and the systematic studies about plane-type terahertz SPP passive devices have not been performed yet. Therefore, the project is planned to study the terahertz passive devices based on spoof SPP. Specially, the following contents are included: the effective excitation of SPP wave, design of SPP unit, and developments of SPP devices such as waveguides, filters, and couplers, etc. We think this project is of significant importance in improving the terahertz SPP theories, developing novel terahertz passive devices, and also facilitating the research of THz circuits and communications.

近年来，人工表面等离激元（SPP）因显著的场局域和场增强效应、亚波长成像、器件小型化、高灵敏传感等而引起人们的广泛关注。在前期工作中，本课题组已深入研究了微波SPP的物理机制，并提出了一系列柔性、超薄的二维SPP器件。在太赫兹频段，由于波长大大缩短，器件特征尺寸也随之减小，因此原有的SPP激励方式已不再适用。尽管文献中已经有不少关于太赫兹空间波和SPP波转换的报道，但效率较低，而且尚未有关于平面型太赫兹SPP无源器件的系统性实验研究。本项目拟在前期工作基础上，进一步研究太赫兹人工表面等离激元无源器件，包括太赫兹空间波、导波与SPP波的有效转换、太赫兹SPP单元设计、以及典型太赫兹SPP无源器件，例如SPP波导、滤波器和耦合器等的开发。上述研究不仅对完善太赫兹SPP的理论体系具有重要意义，而且有助于开发各种新型太赫兹无源器件，促进太赫兹电路和通信的发展。

表面等离激元（SPP）是局域在金属－介质界面并沿界面传播的表面电磁波模式。因具有显著的场局域、场增强和波长压缩效应，SPP在小型化光学元件、近场成像和高灵敏度传感器等方面都有很好的应用前景，因此成为电磁学、物理学与材料科学等诸多领域的研究热点。然而，在微波和太赫兹频率区，金属表现为良导体，不能有效激励SPP波。基于等离子体超材料的人工表面等离激元器件可以模拟光频的SPP效应，在低频区获得场局域与场增强性质。目前，微波频段的SPP器件已有广泛报道，包括SPP波高效激励、SPP无源器件、SPP有源器件和柔性超薄SPP器件等。本项目在此基础上，系统研究了太赫兹空间波、导波与SPP 波的有效转换机制，并基于此设计了平面型太赫兹SPP无源器件。具体包括：通过设计维瓦尔第天线和人工结构单元，实现了太赫兹空间波与SPP 波的有效转换，优化的工作频率为0.6 THz；通过设计微带探针天线和矩形波导、SPP波导一体化设计，实现了亚太赫兹导波与SPP波的高效转换，并在220~280GHz频带范围获得了SPP波的低损耗传输（传输损耗的仿真值不高于1.5dB，实测结果不高于5dB）；基于探针馈电的亚太赫兹SPP波导有效工作带宽为0.15 THz、传输损耗小于3dB。本工作解决了空间波、导波与SPP波的动量不匹配问题，进而研制了宽带、低损耗、紧束缚的太赫兹人工表面等离激元无源器件，获得了太赫兹SPP波导原型器件。太赫兹SPP器件具有显著的场局域与场增强特性、波长压缩特性，因此在太赫兹电路与系统、生物化学传感与成像等方面均具有重要应用。