分析了在大模场面积双包层光纤(LMA-DCF)上刻写光栅的技术要求和难点，采用相位掩模法在20/400 μm 的LMA-DCF上刻写了高反射率光纤布拉格光栅。针对大模场光纤中存在高阶模的可能性，通过调整单模光纤(SMF)入射光场和LMA-DCF芯径的相对偏移量，对LMA-DCF光栅中的传输模式特性进行了理论分析和模拟计算，并在实验研究中测量了偏移量不同时光栅的反射谱，观测到了相应的LP01模和LP11模的模场光斑分布。对LMA-DCF光栅的几种光谱测试方法进行了对比研究，分析了各种方法的优缺点。研究结果将为LMA-DCF光栅在高功率激光系统中的应用提供依据和参考。

High-reflectivity fiber Bragg grating (FBG) is successfully inscribed on the 20/400 μm large-mode-area double-clad fiber (LMA-DCF) by the phase-mask method, and the relevant technical requirements and difficulty of the inscription technology are analyzed. Considering the possibility of existence of the high-order mode in LMA-DCF, the mode characteristics are theoretically simulated by altering the relative displacement between the fiber core of SMF and LMA-DCF. The grating reflection spectra of different relative displacements are experimentally measured and the corresponding light spots are obtained. Besides, the frequently-used measuring methods of spectrum of LMA-DCF Bragg grating are compared and their respective characteristics are analyzed. Research results will provide theoretical and experimental basis for the application of LMA-DCF in high-power laser systems.