挠曲电效应对液晶微波相位调制的影响

摘要

液晶微波调制器件的相位调制取决于液晶分子指向矢的分布.液晶指向矢的分布不仅会受基板表面处液晶分子预倾角和锚定能等因素的影响,液晶材料的挠曲电特性同样会影响液晶指向矢分布.基于液晶弹性理论和差分迭代方法,研究了挠曲电效应对平行排列向列相(PAN)液晶微波相位调制的影响,理论推导得到弱锚定PAN液晶盒的平衡态方程,数值模拟给出了不同的预倾角、锚定能和液晶材料的挠曲电特性条件下单位长度微波相移(MPSL)随电压的变化.结果表明MPSL随锚定能系数的减小而增大,A0=Ad=5×10-5J/m2时,挠曲电效应e11+e33=5×10-11C/m对MPSL最大可调范围为20°,0°预倾角对MPSL最大可调范围为17°,MPSL差值最大增加均为9°;预倾角为3°时,MPSL可调范围随挠曲电系数的增大而增大,相对于忽略挠曲电效应情形,强锚定A0=Ad=10-3J/m2条件下MPSL始终减小,弱锚定A0=Ad=5×10-5J/m2条件下MPSL先减小后增大然后再减小,MPSL差值最大增加为9°.此项研究对液晶微波调制器件设计有一定的指导意义.%The phase modulation of the liquid crystal microwave modulator depends on the distribution of the liquid crystal molecular director.The distribution of liquid crystal director is not only affected by these factors such as the pretilt angle of the liquid crystal molecules and the anchoring energy on the surface of the substrate.The flexoelectric effect of the liquid crystal material also affects the liquid crystal director distribution.Based on the elastic theory of liquid crystal and the finite-difference itera-tive method,the influence of flexoelectric effect on the microwave phase modulation of parallel aligned nematic (PAN ) liquid crystal is studied.We get the equilibrium equations of the weak anchoring PAN cell.The numerical simulation shows the variation of microwave phase shift per unit length (MPSL ) with voltage under different pretilt angles, anchoring energies and flexoelectric coefficients of the liquid crystal material.The results show that the MPSL increases with the decrease of anchoring ener-gy.The maximum adjustable range of MPSL is 20° under A0 = Ad = 5 ×10- 5 J/m2 when e11+e33 =5×10-11C/m.Due to the flexoelectric effect,the maximum adjustable range of MPSL is 17° when the pretilt angle is 0°,and the maximum difference increase of MPSL is 9°.When the pretilt angle is 3°,the adjustable range of MPSL increases with the increase of e11+e33,and the MPSL always decreases under A0=Ad=10-3J/m2,while the MPSL first decreases,then increases,and eventually decreases under A0=Ad=5×10-5J/m2.The maximum difference increase of MPSL is 9° relative to ignoring the flexoelectric effect.This study has some guiding significance for the design of liquid crystal micro-wave modulator.