基于Lissajous曲线拟合的EFPI光纤传感器腔长解调

为提高非本征光纤珐珀传感器(Extrinsic Fabry-Perot Interferometric, EFPI)腔长解调的精度，基于EFPI传感器反射光谱近似余弦函数的特性，设计了一种基于李萨如图形(Lissajous-Figure)与标准形式椭圆曲线拟合的解调方法。将两组光强信号经过坐标变换拟合为标准椭圆曲线，以减少求解参数；并通过经验模态分解对数据进行分析，去余项后将得到的极值点代入椭圆曲线求解。将离散数据点分别移动5、10、15、20、25个点测试五组不同相移对解调结果的影响并选取其中误差最小的一组对EFPI传感器进行横向负载实验，分别施加5~25 N的应力，通过拟合椭圆曲线的解调方法将计算腔长差与理论腔长差相对比。结果表明，实际腔长差随负载成正比，平均误差值为5.690%左右，可以准确获取 EFPI 的腔长。

Cavity length demodulation of EFPI optical fiber sensor based on Lissajous curve fitting

In order to improve the accuracy of cavity length demodulation of Extrinsic Fabry-Perot Interferometric (EFPI), a demodulation method based on the approximate cosine function of the reflection spectrum was designed based on Lissajous-Figure and standard elliptic curve fitting. The two sets of light intensity signals were fitted into standard elliptic curves by coordinate transformation to reduce the required parameters; The empirical mode decomposition was used to analyze the data. The extreme point obtained after the baseline was taken into the elliptic curve to solve the problem. The discrete data points were moved by 5, 10, 15, 20 and 25 points respectively to test the influence of five groups of different phase shifts on the demodulation results, and the group with the smallest error was selected for the transverse load experiment of EFPI sensor. The stress of 5-25 N was applied respectively, the calculated cavity length difference was compared with the theoretical cavity length difference by the demodulation method of fitting elliptic curve. The results show that the actual cavity length difference is proportional to the load, the average error is about 5.690%, and the cavity length of EFPI can be obtained accurately.