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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。
The technical requirements and difficulties of writing a grating on a large mode area double clad fiber (LMA-DCF) are analyzed. A high-reflectivity fiber Bragg grating is inscribed on a 20/400 μm LMA-DCF using a phase mask method. Aiming at the possibility of high-order mode in large mode field fiber, the transmission mode characteristics in LMA-DCF grating are theoretically analyzed by adjusting the relative offset of SMF incident light field and LMA-DCF core diameter. In the experiment, the reflection spectra of the grating with different offsets were measured and the mode field spot distributions of the corresponding LP01 and LP11 modes were observed. Several spectral test methods of LMA-DCF grating were compared and the advantages and disadvantages of various methods were analyzed. The research results will provide reference and reference for the application of LMA-DCF grating in high power laser system.