电控聚合物分散液晶折衍混合透镜成像系统的变焦及消像差特性研究

Study on Zoom and Aberration Characteristics of Electronically Controlled Polymer Dispersed Liquid Crystal Hybrid Lens Imaging System

摘要: 菲涅尔液晶透镜在电控变焦领域具有独特的性能，但菲涅尔透镜成像由于多级衍射的特性，会产生多个成像焦点。本文首先深入探究了菲涅尔液晶透镜厚度以及有效折射率对入射光聚焦效果的影响，实验中我们以R (λ = 700 nm)、G (λ = 546 nm)、B (λ = 450 nm)三色光入射到厚度不同单层菲涅液晶透镜中，仿真结果显示RGB同一位置聚焦能量会随着单层菲涅尔液晶层厚度的改变而出现周期性变化，且菲涅尔液晶透镜有效折射率越大，周期变化越明显。我们以此为理论基础对基于聚合物分散液晶(PDLC)材料构建的折衍射混合透镜系统做出了适当的结构优化。其次，通过电压调制，我们发现三种不同波长光焦距可以在一定的范围内发生重叠，从而成功消除了轴向色差，而且在PDLC折衍射透镜消除轴向色差的基础上，通过进一步精确控制电极，我们实现了透镜变焦范围的增长，突破了传统液晶透镜仅能在单一工作光波段内工作的局限性。并将上述原理以及模型应用到入射光源为点光源时的情境，通过改变点光源入射时的水平位置以及轴向物距，验证了点光源成像在水平方向以及竖直方向仍可以实现消色差。

Abstract: Fresnel liquid crystal lens has a unique performance in the field of electronically controlled zoom, but Fresnel lens imaging will produce multiple imaging focal points due to the characteristics of multi-stage diffraction. In this paper, the thickness of Fresnel liquid crystal lens and the effect of effective refractive index on the focusing effect of incident light were investigated in depth. In the experiment, three-color light R (λ = 700 nm), G (λ = 546 nm) and B (λ = 450 nm) were incident into the single-layer Fresnel liquid crystal lens with different thickness. The simulation results show that the focusing energy of RGB at the same position will change periodically with the change of thickness of single-layer Fresnel liquid crystal layer, and the larger the effective refractive index of Fresnel liquid crystal lens, the more obvious the periodic change. Based on this theory, we have optimized the structure of the hybrid lens system based on polymer dispersed liquid crystal (PDLC) materials. Secondly, through voltage modulation, we found that the focal lengths of three different wavelengths of light can overlap within a certain range, thus successfully eliminating the axial chromatic aberration. Moreover, on the basis of eliminating the axial chromatic aberration of the PDLC folded diffraction lens, by further accurately controlling the electrode, we achieved an increase in the lens zoom range. It breaks through the limitation that the traditional liquid crystal lens can only work in a single working light band. By changing the horizontal position and axial distance of the point light source, the point light source imaging can still achieve achromatic effect in both horizontal and vertical directions.