Castles F, Morris S M, Coles H J
Electrical Engineering Division, Department of Engineering, Centre of Molecular Materials for Photonics and Electronics, University of Cambridge, 9 JJ Thomson Avenue, Cambridge CB3 0FA, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Sep;80(3 Pt 1):031709. doi: 10.1103/PhysRevE.80.031709. Epub 2009 Sep 18.
The flexoelectro-optic effect describes the rotation of the optic axis of a short-pitch chiral nematic liquid crystal under the application of an electric field. We investigate the effect in the uniform standing helix, or "Grandjean" configuration. An in-plane electric field is applied. The director profile is determined numerically using a static one-dimensional continuum model with strong surface anchoring. The Berreman method is used to solve for plane-wave solutions to Maxwell's equations, and predict the optical properties of the resulting structure in general cases. By using a chiral nematic with short pitch between crossed polarizers an optical switch may be generated. With no applied field the configuration is nontransmissive at normal incidence, but becomes transmissive with an applied field. For this case, numerical results using the Berreman method are supplemented with an analytic theory and found to be in good agreement. The transmitted intensity as a function of tilt, the contrast ratio, and the tilt required for full intensity modulation are presented. The angular dependence of the transmission is calculated and the isocontrast curves are plotted. For typical material and cell parameters a switching speed of 0.017 ms and contrast ratio of 1500:1 at normal incidence are predicted, at a switch-on tilt of 41.5 degrees. Experimental verification of the analytic and numerical models is provided.
挠曲电 - 光效应描述了在施加电场时短节距手性向列型液晶光轴的旋转。我们研究了均匀驻波螺旋或“Grandjean”构型下的这种效应。施加了面内电场。使用具有强表面锚定的静态一维连续介质模型通过数值方法确定指向矢分布。采用Berreman方法求解麦克斯韦方程组的平面波解，并预测一般情况下所得结构的光学性质。通过在交叉偏振器之间使用短节距的手性向列型液晶，可以产生一个光开关。在没有施加电场时，该构型在正入射下是不透光的，但施加电场后变为透光。对于这种情况，使用Berreman方法的数值结果辅以解析理论，发现两者吻合良好。给出了透射强度作为倾斜度的函数、对比度以及全强度调制所需倾斜度的相关结果。计算了透射的角度依赖性并绘制了等对比度曲线。对于典型的材料和盒参数，预测在正入射下开关速度为0.017 ms，对比度为1500:1，开启倾斜度为41.5度。提供了对解析模型和数值模型的实验验证。
