基于光控取向的铁电液晶高通量偏振转换技术研究

The light sources of optical systems are mostly unpolarized or partially polarized, including skylight, lasers, reflected light by objects and so on. However, polarized light is required in the majority of optical instruments. Thus, the polarizers, which are normally with transmission of 40% to 50%, is the main reason of low efficiency, leading to the limit of signal noise ratio, detection precision, and effective length. In this project, to solve this problem we proposed to explore the high efficient polarization conversion system using ferroelectric liquid crystal with nano-scale structure as polarization grating arrays and quarter wave plate arrays. In this approach, polarization grating is utilized to separate unpolarized light into left handed and right handed circular polarized light with efficiency near 100%, and then quarter wave plate arrays convert circular polarized light to linearly polarized light respectively. Considering applied in passive source system, the compact polarization conversion system will be optimized for visible and short wavelength infrared light and efficiency up to 90%.

光学系统中绝大多数光源是非偏振或部分偏振的，而多数光学仪器系统需要偏振光入射，因此起偏器大量存在于光路中，且其引入的光通量损失在50%-60%以上，是光通量损失最为严重的器件之一，限制了信噪比等仪器关键指标的提高，是亟待解决的重要问题。本项目针对此问题，开展高通量偏振转换技术研究：采取非偏振光分离转换循环利用的思想，将非偏振光通过偏振光栅阵列转化并分离后，经微结构波片阵列进行分别转换成线偏振光均匀输出；开发高衍射效率（接近100%）液晶偏振光栅阵列，并利用光控取向手段使其呈微纳尺寸的有序性排列，打破偏振态分光后不同光路的限制，将偏振光栅阵列与波片阵列优化配准集成；提出基于快响应铁电液晶的宽波段偏振光栅相位匹配方法，建立铁电液晶电控折射率匹配精确模型；针对被动式光子探测系统，实现覆盖整个可见光至近红外波段的入射非偏光到线偏光的90%以上的高效率转换，提高光学仪器系统的总体能量利用率。

本项目针对凝视型声光可调谐滤波（Acoustic optical tunable filter-AOTF）光谱成像系统的偏振减损问题，开展高通量偏振转换技术研究。传统的基于AOTF的光谱成像系统采用正交偏振片结构，利用前置偏振片进行衍射单色偏振光选通，利用后置偏振片进行全色杂散光抑制，正交偏振片带来了系统大部分的光通量损失。针对此问题，本项目采用偏振复用方案，开发了高衍射效率（接近100%）液晶偏振光栅，并利用光控取向手段使其呈微纳尺寸的有序性排列，采用液晶偏振光栅对合像的色差进行补偿，实现了两束单色o/e衍射光的合像，提升了系统能量利用率。