Chen Chun-Wei, Khoo Iam Choon
Department of Electrical Engineering, School of Electrical Engineering and Computer Science, The Pennsylvania State University, University Park, PA 16802.
Department of Electrical Engineering, School of Electrical Engineering and Computer Science, The Pennsylvania State University, University Park, PA 16802
Proc Natl Acad Sci U S A. 2021 Apr 20;118(16). doi: 10.1073/pnas.2021304118.
State-of-the-art nanostructured chiral photonic crystals (CPCs), metamaterials, and metasurfaces have shown giant optical rotatory power but are generally passive and beset with large optical losses and with inadequate performance due to limited size/interaction length and narrow operation bandwidth. In this work, we demonstrate by detailed theoretical modeling and experiments that a fully developed CPC, one for which the number of unit cells is high enough that it acquires the full potentials of an ideal ( → ∞) crystal, will overcome the aforementioned limitations, leading to a new generation of versatile high-performance polarization manipulation optics. Such high- CPCs are realized by field-assisted self-assembly of cholesteric liquid crystals to unprecedented thicknesses not possible with any other means. Characterization studies show that high- CPCs exhibit broad transmission maxima accompanied by giant rotatory power, thereby enabling large (>π) polarization rotation with near-unity transmission over a large operation bandwidth. Polarization rotation is demonstrated to be independent of input polarization orientation and applies equally well on continuous-wave or ultrafast (picosecond to femtosecond) pulsed lasers of simple or complex (radial, azimuthal) vector fields. Liquid crystal-based CPCs also allow very wide tuning of the operation spectral range and dynamic polarization switching and control possibilities by virtue of several stimuli-induced index or birefringence changing mechanisms.
先进的纳米结构手性光子晶体（CPC）、超材料和超表面已展现出巨大的旋光能力，但通常是无源的，且由于尺寸/相互作用长度有限和工作带宽窄而存在较大的光学损耗和性能不足。在这项工作中，我们通过详细的理论建模和实验证明，一个充分发展的CPC，即其晶胞数量足够多以至于能够发挥理想（→∞）晶体的全部潜力的CPC，将克服上述限制，从而带来新一代多功能高性能偏振操纵光学器件。这种高CPC是通过胆甾型液晶的场辅助自组装实现的，达到了前所未有的厚度，这是其他任何方法都无法实现的。表征研究表明，高CPC表现出宽的透射最大值并伴有巨大的旋光能力，从而能够在大的工作带宽上以接近单位的透射率实现大（>π）的偏振旋转。已证明偏振旋转与输入偏振方向无关，并且同样适用于简单或复杂（径向、方位角）矢量场的连续波或超快（皮秒到飞秒）脉冲激光。基于液晶的CPC还由于几种由刺激引起的折射率或双折射变化机制而允许对工作光谱范围进行非常宽的调谐以及实现动态偏振切换和控制。
