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首页> 外文期刊>Nanotechnology >Electrically tunable terahertz polarization converter based on overcoupled metal-isolator-metal metamaterials infiltrated with liquid crystals
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Electrically tunable terahertz polarization converter based on overcoupled metal-isolator-metal metamaterials infiltrated with liquid crystals

机译：基于液晶渗透渗透的过耦金属 - 隔离物金属超材料的电调谐太极光转换器

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摘要

Large birefringence and its electrical modulation by means of Freedericksz transition makes nematic liquid crystals (LCs) a promising platform for tunable terahertz (THz) devices. The thickness of standard LC cells is in the order of the wavelength, requiring high driving voltages and allowing only a very slow modulation at THz frequencies. Here, we first present the concept of overcoupled metal-isolator-metal (MIM) cavities that allow for achieving simultaneously both very high phase difference between orthogonal electric field components and large reflectance. We then apply this concept to LC-infiltrated MIM-based metamaterials aiming at the design of electrically tunable THz polarization converters. The optimal operation in the overcoupled regime is provided by properly selecting the thickness of the LC cell. Instead of the LC natural birefringence, the polarization-dependent functionality stems from the optical anisotropy of ultrathin and deeply subwavelength MIM structures. The dynamic electro-optic control of the LC refractive index enables the spectral shift of the resonant mode and, consequently, the tuning of the phase difference between the two orthogonal field components. This tunability is further enhanced by the large confinement of the resonant electromagnetic fields within the MIM cavity. We show that for an appropriately chosen linearly polarized incident field, the polarization state of the reflected field at the target operation frequency can be continuously swept between the north and south pole of the Poincare sphere. Using a rigorous Q-tensor model to simulate the LC electro-optic switching, we demonstrate that the enhanced light-matter interaction in the MIM resonant cavity allows the polarization converter to operate at driving voltages below 10 Volt and with millisecond switching times.
机译：通过FreederickSz转换的大型双折射及其电气调节使得向列液晶（LCS）进行可调谐太赫兹（THz）器件的有希望的平台。标准LC电池的厚度是波长的顺序，需要高驱动电压并仅在THz频率下进行非常慢的调制。在这里，我们首先介绍过量的金属隔离器 - 金属（MIM）空腔的概念，其允许同时实现正交电场分量和大反射率之间的非常高相位差。然后，我们将此概念应用于LC渗透的基于MIM的超材料，旨在设计电动调谐THz偏振转换器。通过适当地选择LC电池的厚度来提供超瓜型制度中的最佳操作。代替LC自然双折射，偏振依赖性功能源于超薄和深度亚波长MIM结构的光学各向异性。 LC折射率的动态电光控制使得谐振模式的光谱偏移能够调谐两个正交场分量之间的相位差。通过MIM腔内的谐振电磁场的大限制进一步增强了这种可调谐性。 We show that for an appropriately chosen linearly polarized incident field, the polarization state of the reflected field at the target operation frequency can be continuously swept between the north and south pole of the Poincare sphere.使用严格的Q张量模型来模拟LC电光切换，我们证明了MIM谐振腔中的增强的灯具相互作用允许偏振转换器在低于10伏以下的驱动电压和毫秒切换时间下操作。

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