偏振光干涉法消除光纤光栅解调中的交叉敏感现象

提出一种偏振光干涉的光纤光栅应变测量方法,该方法能解决光纤光栅应变和温度测量时的交叉敏感问题。对于钒酸钇晶体偏振光干涉仪,如果选择两个能使干涉仪产生180°相位差的不同中心波长的光纤光栅,一个用于应变测量,一个用于补偿温度,就能很好地解决光纤光栅应变测量时的温度交叉敏感问题。分析了构成偏振光干涉仪的晶体的厚度对应变偏差的影响。理论计算和试验结果显示,当晶体厚度为0.5 mm时温度对应变测量的交叉敏感现象被压缩到了1.6%,相当于0.13με/℃。进一步的仿真分析发现当晶体厚度为0.1 mm时交叉敏感现象将被压缩到0.08%,相当于0.0067με/℃。小的晶体厚度有利于减小交叉敏感现象,但小厚度的晶体加工困难,为此分析了双晶体结构的方案。

Reduction of Cross Sensitivity in Fiber Bragg Grating Sensor Based on the Principle of Polarized-Light Interference

An approach of fiber grating strain demodulation based on the principle of polarized-light interference is introduced, which can solve the so called cross sensitivity in the fiber Bragg grating sensor. To the yttrium vanadate (YVO4) crystal polarized-light interferometer, by choosing two different fiber Bragg gratings with a π rad phase difference, one as a strain sensor and the other for temperature compensating. The cross sensitivity can be conquered. The analysis of the strain demodulation resolution shows that with the decreasing of the crystal thickness the resolution increases. The experiment shows that when the thickness of the YVO4 crystal is 0.5mm the effect of cross sensitivity is reduced to 0.13 με/℃ which is 1.6% of the effect with only one fiber Bragg grating for strain measure and that when the thickness is 0.1 mm the cross sensitivity is reduced to 0.0067 με/℃ which is less than 0.08%. Reduced thickness of crystal benefits the resolution of strain measure but the machining of the small thickness crystal is difficult, and to solve this problem a new scheme of polarized-light interferometer with the structure of double layers crystal is analysed in the end.