在分析大模场双包层光纤的模式特性和测试光路中光功率分配的基础上，根据耦合波理论和传输矩阵法，对不同情况下大模场双包层光纤光栅的透射谱和反射谱进行数值分析，结果表明光谱形状取决于模式间的功率分配，通过基模的透射谱可以测量双包层光纤光栅的真实反射率。采用相位掩模法制作了基模反射率不低于99.7%的20/400 μm大模场双包层光纤光栅，测试了不同情况下的反射谱和透射谱，实验结果和理论分析的结论一致。

Based on the analysis of large-mode-area (LMA) double-clad fiber′s mode properties and optical power distribution in the measurement setup, reflection and transmission spectra of LMA fiber gratings are numerically simulated by using coupled-wave theory and transfer-matrix approach. Theoretical results indicate that the spectral shape depends on the power distribution between modes, and the reflectivity of LMA fiber grating can be calculated from the transmission spectrum of the fundamental mode. LMA fiber grating with the reflectivity of more than 99.7% has been fabricated in 20/400 μm double-clad fiber by phase mask method, the reflection and transmission spectra under different conditions are measured, and the experimental results agree well with the theoretical analysis.