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光纤光栅的相位谱对光纤光栅法布里-珀罗(F-P)腔的光谱特性有重要影响。对光纤布拉格光栅(FBG)光谱,特别是FBG相位谱进行了深入分析,推导了低反射率FBG的线性相位谱的一般表达式,提出了高反射率FBG的三段线性相位近似方法,得到了简洁直观的相位谱数学表达式。然后采用和普通F-P腔对比的方式,以等效腔长的概念分析了FBG构成的F-P(FBG-FP)腔相位谱特性,并讨论了拟合法、周期法和傅里叶变换法这3种常用的FBG-FP腔长估计算法。设计了FBG-FP腔光谱测量方案,得到了高精度的光谱曲线,对比分析了前述3种腔长估计方法的计算结果,验证了理论分析的正确性。
The phase spectrum of FBG has an important influence on the spectral characteristics of fiber grating Fabry-Perot (F-P) cavity. The FBG spectrum, especially the FBG phase spectrum, is analyzed in depth. The general expression of the linear phase spectrum of low reflectivity FBG is deduced, and the three-phase linear phase approximation method of high reflectivity FBG is proposed. Simple and intuitive mathematical expression of phase spectrum. Then, compared with the conventional FP cavity, the phase characteristic of the FBG-FP (FBG-FP) cavity was analyzed with the concept of equivalent cavity length. Three methods of fitting, periodic method and Fourier transform were discussed Common FBG-FP cavity length estimation algorithm. The scheme of FBG-FP cavity spectroscopy was designed and the high-precision spectral curve was obtained. The calculation results of the three cavity length estimation methods were compared and analyzed, which verified the correctness of the theoretical analysis.