中文摘要：

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20/400μm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。

英文摘要：

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.