利用锗酸铋晶体的电光补偿型光学应力传感器

Optical Stress Sensor Based on Single Bismuth Germanate Crystal and Electrooptic Compensation

利用锗酸铋(BGO)晶体的弹光双折射与电光双折射可以相互补偿的特性,设计并研究了一种新型光学应力传感器。折射率椭球分析结果表明,在垂直于BGO晶体的(111)晶面方向上同时施加应力和电场,晶体的弹光双折射能够被电光双折射所补偿,因而可以实现应力的闭环光学测量。光学传感单元主要包括两个棱镜偏振器和一块平行四边形的BGO晶体,该晶体自身能够通过对光波的两次全反射产生0.5π的光学相位偏置,因而不需要附加四分之一波片。实验测量了30kPa以内的压缩应力,被测压缩应力与补偿电压之间具有较好的线性关系,且每1kPa压缩应力所需要的补偿电压约为4.26V。

An optical stress sensor is proposed and demonstrated in experiment based on single bismuth germanate （BGO） crystal and electrooptic compensation. The sensing principle is mainly based on the mutual compensation property between photoelastic birefringence and electrooptic birefringence existing in the BGO crystal. According to the index ellipsoid analysis method, when external stress and electric field are simultaneously applied to the （111） crystalline surface, photoelastic birefringence of the BGO crystal can be compensated by its electrooptic birefringence, thus it is possible to perform the closed-loop measurement of external stress by the method of electrooptic compensation. The proposed optical stress-sensing unit is only composed of two prism polarizers and single parallelogramic BGO crystal. Additional quarter waveplate is not needed for the proposed stress sensor since the optical phase bias of 0.5π is produced by two times of total inner reflection of light wave in the BGO crystal itself. Compression stress is measured in the range of 30 kPa and experimental data demonstrated a good linear relationship between compensating voltage and measurand stress. The compensating voltage is about 4.26 V corresponding to the applied stress of 1 kPa.