Tilted Chiral Liquid Crystal Gratings for Efficient Large-Angle Diffraction
Tilted Chiral Liquid Crystal Gratings for Efficient Large-Angle Diffraction
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DOI：
10.1002/adom.201901364
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发表时间：
2019-09-10
影响因子：
9
通讯作者：
Neyts, Kristiaan
中科院分区：
文献类型：
--
作者：
Nys, Inge;Stebryte, Migle;Neyts, Kristiaan
利用薄的光学元件在大角度上高效地偏转光是具有挑战性的，但为诸如可穿戴显示器和光通信系统的应用提供了巨大的潜力。与超颖表面的复杂生产相比，液晶（LC）超结构的自组织提供了一种优雅而灵活的方式来生产高质量的薄光学元件。短节距手性液晶中周期性变化的介电张量产生光子带隙，可以利用光子带隙实现可见光范围内的高效衍射镜。然而，大角度衍射器件需要小的面内周期，导致体中复杂的自组装行为。这项工作表明，通过图案化的光致取向层的表面与周期相媲美的手性间距，LC自组装成一个倾斜的，无缺陷的螺旋结构。通过有限元模拟计算的导演配置，它是实验证明，一个单一的光对准基板是足够的模板在散装的倾斜手性结构。这种结构有效地（88%）衍射光在大角度（约46度），并使新的微米薄（约3 μ m）的光学元件，可以生产一个优雅的制造工艺。由于光对准的灵活性，该过程可以很容易地在新兴的光子应用中实现。
Deflecting light with high efficiency over large angles with thin optical elements is challenging but offers tremendous potential for applications, such as wearable displays and optical communication systems. Compared to the complex production of metasurfaces, the self-organization of liquid crystal (LC) superstructures provides an elegant and flexible way to produce high-quality thin optical components. The periodically varying dielectric tensor in short-pitch chiral LC gives rise to a photonic bandgap, which can be exploited to realize efficient diffractive mirrors in the visible wavelength range. However, large-angle diffractive devices require a small in-plane period, leading to complex self-assembly behavior in the bulk. This work demonstrates that by patterning photoalignment layers at the surfaces with a period comparable to the chiral pitch, the LC self-assembles into a tilted, defect-free helical structure. The director configuration is calculated by finite element simulations and it is experimentally demonstrated that a single photoaligned substrate is sufficient to template the tilted chiral structure in the bulk. This structure effectively (88%) diffracts light over large angles (approximate to 46 degrees) and enables novel micrometer-thin (approximate to 3 mu m) optical components that can be produced with an elegant manufacturing process. Due to flexibility of photoalignment, this process could easily be implemented in emerging photonic applications.