基于非对称多项式拟合的光谱波纹系数算法

Spectral Ripple Algorithm Based on Asymmetric Polynomial Fitting

在光纤陀螺中,常采用超辐射发光二极管(SLD)或放大自发辐射(ASE)光源,其较宽的光谱可有效抑制偏振噪声及背向反射、瑞利散射等影响。在SLD及ASE光源中,波纹系数是一项重要指标,其主要来自于宽带光源中未完全抑制掉的激射部分,会对光纤陀螺的精度产生影响。目前在国军标中对波纹系数的定义是:光谱曲线峰值波长附近的模式幅值的极差,单位为dB。目前对波纹系数还是采用人眼观察的方法,人眼观察具有一定的主观性和偶然性,不能排除人们主观因素以及外界干扰带来的测量误差,并且经过处理后得到的对数光谱不能准确反映原始光谱特性。针对宽带光源非对称光谱中的波纹系数进行分析,对比多峰高斯拟合和多项式拟合各自的优缺点,选择多项式拟合的方式;通过理论分析及实验验证,采用五次多项式拟合满足要求。基于三倍标准差原理提出了一种新的波纹系数计算方法,可以准确反映波纹系数大小。采用AQ6370D光谱仪和自制的“光谱波纹系数测试”软件对ASE光源和SLD光源进行实验,计算结果与人眼观察数据基本吻合。在此基础上进行重复性验证实验,采集同一光源的五次实验数据,分别计算其波纹系数,并与人眼观察结果比较,结果表明人眼观察只能估算到小数点后两位,而光谱波纹系数算法精度较高,分辨率可达0.0001。自制的“光谱波纹系数测试”软件可以在交互界面上得到测试光谱的平均波长、峰值波长、中心波长、谱宽、波纹系数、线性坐标和对数坐标下的光谱及其拟合曲线表达式,使实验分析更加方便快捷,大大提高了实验效率。提出的基于非对称多项式拟合的光谱波纹系数算法可以更有效地对光源波纹系数进行判断,提高了计算效率,消除了主观性和偶然性的影响,对国军标进行了补充,有较为广阔的应用前景。

Super luminescent diode(SLD)and amplified spontaneous emission(ASE)light sources are often used in fiber optic gyroscopes.Their wide spectrum can effectively suppress the influence of polarization noise,back reflection and Rayleigh scattering.Ripple,as an important index in SLD and ASE light sources,mainly coming from the laser part of broadband light source that is not completely suppressed,impacts the accuracy of fiber optic gyroscope.In the military standard,ripple is defined as the range of mode amplitude near the peak wavelength of the spectral curve,with dB as the unit.At present,ripple measurement is mainly based on the logarithmic spectrum observed by human eyes.However,in human eye observation,the subjective factors of a human and the external interference may lead to subjectivity and contingency of the results,and measurement errors cannot be ruled out.Additionally,the spectrum in logarithmic coordinates cannot accurately reflect the spectral characteristics.Because of this,the present study analyzed the ripple in the asymmetric spectrum of the broadband light source,compared the advantages and disadvantages of multi-peak Gaussian fitting and polynomial fitting.Finally,adopted the polynomial fitting method.Through theoretical analysis and experimental verification,it was revealed that the quintic polynomial fitting can meet the requirements.Besides,a new method which can precisely calculate the ripple based on the triple standard deviation principle was proposed.AQ6370D spectrometer and a self-made“Spectral Ripple Fitting”software were utilized to experiment with ASE and SLD light sources,and the results obtained were in good agreement with the observation data of human eyes.On this basis,repeated validation experiments were carried out,the five experimental data of the same light source were recorded,and their ripple coefficients were calculated respectively.Compared with the human eye observation results,the experimental results demonstrate that the spectral ripple coefficient algorithm can well eliminate the influence of subjectivity and contingency,indicating that it is feasible.With the self-made“Spectral ripple Test”software,the average wavelength,peak wavelength,center wavelength,spectral width,ripple,linear coordinates and logarithmic coordinates of the spectrum and their fitting curve expressions can be obtained on the interactive interface,which makes the experimental analysis more convenient and speedy,thus significantly improving the experimental efficiency.It has been proved that the spectral ripple algorithm based on asymmetric polynomial fitting proposed in this paper can effectively judge the light source ripple,improve the calculation efficiency,and eliminate the influence of subjectivity and contingency,showing a broad application prospect.Furthermore,it is a supplement to the national military standard as well.