Liquid crystal cells with subwavelength metallic gratings for transmissive terahertz elements with electrical tunability
Liquid crystal cells with subwavelength metallic gratings for transmissive terahertz elements with electrical tunability
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DOI：
10.1016/j.optcom.2018.09.013
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发表时间：
2019-01
影响因子：
2.4
通讯作者：
T. Sasaki;Hiroki Kushida;M. Sakamoto;Kohei Noda;H. Okamoto;N. Kawatsuki;H. Ono
中科院分区：
文献类型：
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作者：
T. Sasaki;Hiroki Kushida;M. Sakamoto;Kohei Noda;H. Okamoto;N. Kawatsuki;H. Ono
报道了偏振太赫兹波在具有亚波长金属光栅的液晶盒中的传播特性，以制作具有电调谐性的透射式太赫兹元件。在液晶盒的石英玻璃衬底上制作了一维金属光栅，它既可以用作透明电极，也可以用作太赫兹波段的线偏振器。对于电场平行于光栅矢量的线偏振太赫兹波，具有和不具有金属光栅的衬底表现出几乎相同的透射光谱。我们制作了一个90度扭曲的双折射液晶盒，使用两个基板与金属光栅，并检查其在太赫兹制度的透射光谱。在这些测量过程中，我们通过金属光栅向LC施加电压。基于亚波长结构的有效介质理论、扭曲双折射液晶的连续介质理论和液晶在太赫兹波段的光学常数，详细计算了其透射谱及其电压依赖性。观测到的光谱与理论模拟吻合得很好。这些结果表明，具有亚波长金属光栅的LC单元在诸如衰减器和偏振旋转器的应用中作为有源THz元件是有用的。
We report the propagation properties of polarized terahertz (THz) waves in a liquid crystal (LC) cell with subwavelength metallic gratings to produce transmissive THz elements with electrical tunability. One-dimensional metallic gratings, which can be used both as transparent electrodes and linear polarizers in the THz regime, were fabricated on the quartz glass substrates of the LC cell. The substrates with and without the metallic grating showed almost identical transmission spectra for a linearly polarized THz wave whose electric field was parallel to the grating vector. We fabricated a 90∘-twisted nematic LC cell using the two substrates with the metallic grating and examined its transmission spectra in the THz regime. During these measurements, we applied a voltage to the LC via the metallic gratings. We calculated in detail the transmission spectra and its voltage dependence based on the effective medium theory for subwavelength structures, the continuum theory of twisted nematic LCs, and the optical constants of the LC in the THz regime. The observed spectra agreed well with theoretical simulations. These results demonstrate that LC cells with subwavelength metallic gratings are useful as active THz elements in applications such as attenuators and polarization rotators.