亚毫秒响应近红外聚合物网络液晶相位调制器及其液晶相控阵应用性能

Liquid crystal optical phased array has attracted wide research interest in nonmechanical laser beam steering and wavefront control technology for laser radar and space laser communication application. To obtain full wavelength phase modulation in the infrared region,large liquid crystal cell was required. Due to the visco-elastic limitation of nematic liquid crystal, the response time was usually on the order of 10ms, which restrained the application of liquid crystal optical phased array. In this project, polymer network liquid crystal was employed to decrease the response time to be hundreds of microseconds. But several drawbacks of current polymer network liquid crystal has limited its phase modulation effect, such as light scattering, threshold voltage, electro striction and birefringence. To solve these problems, the formation mechanism of polymer network was studied and polymer network morphology effect on the light scattering, threshold voltage and electrostriction was elucidated. To eliminate the light scattering, high voltage induced electrostriction and hysterysis effect, polymer network liquid crystal with optimized polymer network morphology was proposed. Polymer network liquid crystal with cross linked fibril bundles and small unit domain on the order of hundreds of nanometer was essential. Liquid crystal solvent with large dielectric anisotropy and birefringence was also employed to fabricate infrared phase modulator with low threshold voltage and large birefringence. UV stability of the liquid crystal solvent was concerned. UV curing source with optimized small bandwidth, liquid crystal with large viscosity and UV resitant chemical was employed to enhance the UV stability of polymer network liquid crystal.The achievement of this project would enable submillisecond response liquid crystal optical phased array.

液晶相控阵已经在激光雷达、激光通信等研究中的激光束非机械扫描、波前校正等技术中展现出巨大应用前景，然而这些应用主要位于近红外波段，受限于向列相液晶粘弹性响应，液晶相控阵响应时间通常在10ms量级，这极大限制了其应用范围。本课题拟采用聚合物网络液晶作为液晶相控阵电光材料，将近红外波段响应时间提高至百微秒量级。针对目前聚合物网络液晶相位调制时存在的主要问题，首先研究聚合物网络形成机理及其形貌特征对光散射、阈值电压和电致伸缩等缺点的影响，在控制聚合物网络形貌基础上抑制其光散射、电致伸缩、回滞线等缺点；采用大介电各向异性、高双折射率液晶溶剂，结合窄带固化波长优化、增加液晶溶剂粘度、掺杂抗紫外剂的方法，实现低阈值电压和高双折射率的近红外聚合物网络液晶相位调制器。本课题的开展将为提高液晶相控阵响应速度至百微秒量级奠定坚实基础。

本项目基本按照工作计划、研究目标与研究内容的要求，充分结合液晶相控阵技术对快响应聚合物网络液晶相位调制器的需求，从若干方面完成了对聚合物网络液晶电光材料的关键问题研究，明确了聚合物网络形貌在不同反应条件、液晶溶剂、聚合单体等的形成机理与控制方法，阐明了不同形貌聚合物网络对聚合物网络液晶光散射、回滞线、阈值电压等光电性能的影响机制，从聚合物网络形貌控制、液晶溶剂优化、聚合单体及其比例优化等若干方面，研制成功一系列聚合物网络液晶相位调制器，其光散射强度在1.55微米波段最优可达1%，最全波相位调制低阈值电压达到49V，有效的抑制了电致伸缩、回滞线等效应，在近红外波段实现了关态<500微秒的响应速度。在优化聚合物网络液晶的同时，实验研究了光寻址聚合物网络液晶相位调制的响应机理与优化方法，初步证明了聚合物网络液晶的应用潜力。在本项目工作基础上进一步优化，有望在液晶相控阵及其他空间光调制应用领域获得应用。