斜入射下液晶偏振光栅衍射特性研究

Research on diffraction characteristics of liquid crystal polarization grating under oblique incidence

为了表征光束倾斜入射下液晶偏振光栅的衍射特性,提出了液晶偏振光栅斜入射角度-驱动电压-衍射效率的三维模型建模方法。该方法利用吉布斯自由能方程,求解液晶分子指向矢,得到驱动电压与液晶分子倾斜角的表达式,推导出斜入射角度与相位延迟量之间的关系,结合扩展琼斯矩阵表征不同入射角度下液晶偏振光栅的透过率,通过矢量衍射理论,建立了斜入射角度-驱动电压-衍射效率的三维模型。该模型不仅可以定量求解不同斜入射角度下液晶偏振光栅衍射效率,而且能够实现衍射效率最优时驱动电压的标定。通过仿真分析和实验对该模型的有效性进行了验证,结果表明:光束入射角度从0°倾斜到10°时,最优驱动电压由2.2 V降低到2.0 V,液晶偏振光栅衍射效率从85%下降到78%;光束入射角度从0°倾斜到-10°时,最优驱动电压由2.2 V升高到2.4 V,液晶偏振光栅衍射效率从85%下降到74%。

To characterize the diffraction characteristics of the liquid crystal polarization grating when the beam is incident obliquely,a three-dimensional model modelling method of liquid crystal polarization grating oblique incident angle-driving voltage-diffraction efficiency was proposed.This method uses the Gibbs free energy equation to solve the director of the liquid crystal molecule,obtains the expression of the driving voltage and the tilt angle of the liquid crystal molecule,derives the relationship between the oblique incident angle and the phase retardation,and combines the extended Jones matrix to characterize different incident angles.The transmittance of the lower liquid crystal polarization grating,through the vector diffraction theory,establishes a threedimensional model of oblique incident angle-driving voltage-diffraction efficiency.This model can not only quantitatively solve the diffraction efficiency of liquid crystal polarization gratings at different oblique incident angles,but also realize the calibration of the driving voltage when the diffraction efficiency is optimal.The effectiveness of the model was verified by simulation analysis and experiments.The results show that when the beam incident angle is tilted from 0° to 10°,the optimal driving voltage is reduced from 2.2 V to 2.0 V,and the diffraction efficiency of the liquid crystal polarization grating is reduced from 85% to 78%;when the beam incident angle is tilted from 0° to-10°,the optimal driving voltage is increased from 2.2 V to 2.4 V,and the diffraction efficiency of the liquid crystal polarization grating drops from 85% to 74%.