基于改进二次多项式拟合的布里渊频移快速高精度提取算法

为了在保证测量准确性的基础上提高基于布里渊散射的光纤分布式传感的实时性,对布里渊频移的快速、高精度提高算法进行了研究。实现了基于二次多项式拟合的布里渊频移提取算法和典型的基于洛伦兹、高斯、伪Voigt和Voigt模型的算法,采用光时域反射计(BOTDR)实测了一段长光纤上的布里渊谱,采用以上算法提取了对应的布里渊频移。计算结果表明,二次多项式拟合算法的计算速度明显快于以上经典算法,其计算耗时仅分别为以上经典算法的1.15%,1.80%,1.51%和0.51%,但计算误差明显大于经典算法,影响了其实际应用。以上结果与对应数值产生布里渊谱的计算结果吻合。为了提高该算法的计算准确性,系统研究了扫频范围、扫频点数、信噪比、线宽和扫频范围偏差对基于二次多项式的布里渊频移提取准确性的影响。结果表明:当扫频点数固定时随扫频范围增加布里渊频移误差先减少到最小值后逐渐增加,扫频点数固定时最佳扫频范围为1个线宽;扫频范围不变时随扫频点数和信噪比的增加布里渊频移误差分别成幂和指数规律减少;扫频范围与线宽比值不变及扫频点数不变时随线宽增加布里渊频移误差线性增大;随扫频范围偏差增加误差逐渐增大,实际用于拟合的谱信号尽量围绕布里渊频移左右对称。根据以上研究结果提出了一种用于布里渊频移快速提取的改进二次多项式拟合算法,该算法从测量得到布里渊谱中截取1倍线宽且关于最大增益对称的谱信号用于后续拟合,较之经典的谱拟合算法,改进算法不仅能大幅提高计算速度且计算准确性与经典算法相似。采用数值产生及实测布里渊谱的计算结果验证了所提出算法的有效性。提出的算法不仅能有效提高基于布里渊散射的光纤分布式传感的实时性。

Fast and Highly Accurate Brillouin Frequency Shift Extracted Algorithm Based on Modified Quadratic Polynomial Fit

To improve real-time performance of fiber distributed sensing based on Brillouin scattering,and at the same time,ensure high measurement accuracy,the topic about Brillouin frequency shift extraction with high accuracy and less computational burden is investigated.The computer programs about Brillouin frequency shift extraction algorithms are based on quadratic polynomial fit and typical Lorentz,Gaussian,pseudo-Voigt and Voigt models are written.Brillouin spectra in a single-mode fiber are measured by the BOTDR(Brillouin Optical Time Domain Reflectometry).The Brillouin frequency shift about these spectra is extracted by the above algorithms.The results reveal that the computational burden of the algorithm based on quadratic polynomial fit is much less than those of the typical algorithms.Its computation time is only 1.15%,1.80%,1.51%and 0.51%of those of the typical algorithms.However,its error is much larger than that of the typical algorithms which will obstruct its application.The above results are consistent with the results of the corresponding numerically generated Brillouin spectra.To improve the accuracy in the quadratic polynomial fit algorithm,the influences of frequency sweep span,number of frequency sweep,signal to noise ratio(SNR),linewidth and deviation of frequency sweep span on the error in the extracted Brillouin frequency shift.The results reveal that if the number of frequency sweep is fixed,the error initially decreases with increasing frequency scanning range.Once the minimum error is reached,it may do the very opposite.The optimal frequency scanning scope equals to linewidth.The error varies as a power of the number of frequency sweep.The error also reduces exponentially with SNR(dB).The error is proportional to linewidth.The error increases with increasing deviation of frequency sweep span.Therefore,the spectra used for Brillouin frequency shift extraction should be symmetric about Brillouin frequency shift.According to the above results,a modified Brillouin frequency shift extraction algorithms based on quadratic polynomial fit is proposed.The algorithm selects Brillouin spectra with one linewidth and symmetric about maximum Brillouin gain and used to extract Brillouin frequency shift.The proposed algorithm can considerably decrease computation time relative to the typical algorithm,and at the same time,the accuracy is similar to that of the typical algorithms.The proposed algorithm is validated by the measured spectra and numerically generated spectra.The proposed algorithm not only can significantly improve real-time performance of fiber distributed sensing based on Brillouin scattering.