用于FBG信号解调的Sagnac环双差动滤波特性研究

Investigation on the filter properties of dual-differential Sagnac loop for FBG demodulator with high temperature stability

采用高双折射光纤Sagnac环作为布拉格光栅(FBG)波长解调器,为消除温度变化引起的测量误差,研究了一种基于参考光的Sagnac环双差动滤波器。介绍了Sagnac环双差动滤波器工作原理,给出了滤波器输出双差动信号的数学表达式。理论分析了双差动滤波器的传输特性和波长解调特性,并进行实验验证。理论分析和实验测试的结果均表明,与常规Sagnac环边缘滤波解调方法相比,本文的双差动滤波解调方法具有更高的灵敏度、更好的线性特性和温度稳定性,温度引起解调装置的测量误差从1.38nm/℃降低到1×10-3 nm/℃,温度稳定性提高了3个数量级。

A high birefringence fiber Sagnac loop is used as wavelength demodulator for FBG signals. For the purpose of reducing the measurement error from temperature changes, a dual-differential edge filter demodulation method based on reference light is proposed. The mathematical expression of the dual-differential edge filter output signal is given. The transmission light intensity and reflected light intensity output from Sagnac loop are detected differentially, and then the differential detection is operated to these processed signals once again. Transmission characteristics of this dual-differential filter and the properties of this filter when it is used as wavelength demodulator for FBG sensor are analyzed theoretically and e- valuated experimentally,and the experimental results agree with the＇ theoretical results. They all show that compared with the conventional Sagnac loop edge filter demodulator for FBG signals, this method makes higher sensitivity and the measurement results have much better linearity. Furthermore,the measurement error from temperature changes of this demodulator decreases from 1.38 nm/℃ to 1 × 10-3 nm/℃ and the stability of this FBG demodulator is improved by three orders of magnitude. The final re- suits show that this dual-differential edge filter demodulation method can eliminate the temperature effect of high birefringence fiber Sagnac loop effectively and improve the stability of this demodulator.