液晶光取向制备偏振衍射光学元件

Diffractive optical element is fundamental requirement in optical field. This kind of element is commonly based on amplitude or phase modulation of light, inducing a limited diffraction efficiency (＜40.5%). Recently, research on polarization diffractive optical element becomes a hot topic and attracts intensive attentions and wide investigations of scientists, due to their potential of 100% efficiency for single diffraction order. Unfortunately, owing to the fabrication technique limitation, to date, only such elements with simple structures such as gratings and Fresnel zone plate have been demonstrated and investigated. In this project, we try to develop a simple and high efficient method to accomplish arbitrary fabrication of director-varying liquid crystal structures, via combining our home-made DMD based microlithography setup with photoalignment, which facilitates the multi-domain patterning of liquid crystals. Based on this technique, we will develop two novel kinds of diffractive optical element, polarization fork gratings and polarization Airy masks. In this research, we want to understand the rule for the design and fabrication of micro-structured liquid crystals, know their actions on light and explain the mechanism of electro-optical tunability. Furthermore, we will optimize the general performance of these optical elements towards merits of fast tunability, arbitrary reconfigurability and insensitive to both polarization and wavelength. Finally, we will achieve practical optical vortex generators and Airy masks, thus opens a door towards optical field control.

衍射光学元件是光学领域的重要内容，该类元件常基于对光强或位相的调制实现，衍射效率较低（＜40.5%）。偏振衍射光学元件因其单衍射级效率可达100%成为近年的研究热点，吸引了科研人员的强烈关注和广泛研究。受制备技术限制，现有的研究还主要集中于光栅、菲涅尔波带片等结构简单的元件。本项目拟依托课题组创新设计的数控微镜阵缩微投影装置，结合光控取向技术在液晶多畴取向图案化方面的独特优势，设计完善一种简单、高效的制备任意指向矢连续变化的微结构取向液晶的技术方法。依托该技术，围绕偏振叉形光栅和偏振艾里模板这两类全新的人工微结构光学元件进行研究，掌握偏振衍射光学元件液晶取向结构的设计原则和取向控制规律，阐明该类元件对光的独特作用机制及其电光调控规律，进而优化元件综合性能，实现电光可调、可任意重构、偏振和波长不敏感的光涡旋产生器和艾里模板的开发，为光场操控带来全新的手段。

通信技术的蓬勃发展正促使万物互联引发新的生产力革命。调光技术在这场革命中处于关键位置。传统衍射光学元件多基于二元光强或位相调制来实现，衍射效率偏低。偏振衍射光学元件效率可达100%，因而成为研究热点。但受制备技术限制，先前研究主要集中在光栅、菲涅尔波带片等简单元件。通过该项目，我们开发了一种光控液晶图案化取向技术，其基于数字微镜阵缩微投影装置点对点多步曝光写入不同偏振信息，利用光配向剂的偏振敏感特性来记录取向，进而操控液晶方位角实现微结构图案的灵活制备。该技术充分利用液晶光学各向异性对取向的依赖性，通过高精度液晶指向矢分布控制实现特定光轴分布，基于几何相位调制实现复杂化和精细化的波前控制。项目面向液晶调光技术在材料和元件层面的挑战，针对液晶微结构精细操控和液晶微结构光子元件的设计开发，从液晶人工微畴的形成机制、制备工艺与外场调控机制，原理性器件的设计，光学性质与器件性能优化等多个方面进行了系统研究。通过合理设计取向微结构，实现了偏振叉形光栅和偏振艾里模板等全新的人工微结构光学元件，掌握了偏振衍射光学元件液晶取向结构的设计原则和取向控制规律，阐明该类元件对光的独特作用机制及其电光调控规律，进而优化元件综合性能，实现电光可调、可任意重构、偏振/波长不敏感的光涡旋产生器和艾里模板的开发，为光场操控带来全新的手段。这些元件较比传统的电寻址空间光调制器体现出空间分辨率、开孔率、透过率高，响应速度快、工作波段宽、耐光损伤阈值高等优势，打开了液晶应用的一条全新的通道。项目研究探索了液晶材料设计开发、液晶微结构形成机制与控制规律、光与液晶微结构相互作用的新效应与新规律，有助于促进我国光通讯关键材料、元件、设备和工艺的协同创新，可望在光通讯、强激光整形调制等方面催生出产业的硕果。