中文摘要：

准确的双折射特性测量对于液晶的实际应用具有重要意义。研究了液晶材料的工作原理，以激光回馈效应为基础，搭建了各向异性外腔回馈双折射测量系统，对不同驱动电压下液晶的双折射特性进行测量。测量结果表明，各向异性外腔回馈双折射测量系统测量精度在0.3°之内；通过施加0~24V交流电压，液晶材料双折射率在2.74×10-1~2.39×10-3范围内变化，对应各向异性呈现出460°~5°的大范围位相延迟值。电压范围在0.7~2V时，电压-双折射率关系表现出较好的线性度，通过线性拟合对该范围内电压-双折射率关系进行计算，其线性度优于95.5%。液晶材料可以提供稳定的位相延迟，同一电压值下的位相延迟短期重复性优于0.52°，长期重复性优于4.5°。

英文摘要：

The precise measurement of the birefringence in the liquid crystals has significant meaning for practical applications. The working principles of the liquid crystals were analyzed. The laser anisotropy external cavity feedback system was built based on the laser feedback effect. The anisotropy of the liquid crystals under different voltages was measured. The measurement results show that the accuracy of the laser anisotropy external cavity feedback system is within 0.3°; By imposing different voltage from 0 to 24 V, the birefringence changes from 2.74×10-1 to 2.39×10-3, corresponding to the large range phase retardation of 460° to 5°. With the voltage in the range of 0.7 V to 2 V, the relationship between the voltage and the birefringence is linear and its linearity is better than 95.5%. The liquid crystals can provide stable phase retardation, the short-term repeatability is better than 0.52° and the long-term repeatability is better than 4.5°.