在基于大模场面积的高功率光纤放大器中，随着放大激光功率的提升而出现的高阶模激发现象，将会导致放大激光的光束质量严重下降。以光纤模式的弯曲损耗特性为基础，研究了光纤弯曲半径对高功率全光纤放大器高阶模激发阈值特性的影响。搭建了掺镱全光纤窄线宽高功率主振荡放大系统，设计了不同弯曲半径的水冷光纤盘，进行了相应对比实验。通过优化光纤盘半径，成功抑制了高功率光纤放大器中的高阶模激发，得到了千瓦量级的近单模激光输出，在输出功率为1.31 kW 时光束质量因子M2约为1.4。

In high power fiber amplifier which uses large mode area (LMA) fiber, the high-order modes(HOM) appear with the increase of laser output power, and the beam quality degrades severely. The influence of fiber bending on thresholds of HOM is studied in experiments based on the fiber bending loss theory. A ytterbium-doped all- fiber narrow- linewidth and high power master- oscillator power amplifier (MOPA) system is built. Novel watering cooling plates of different sizes are designed and used in the main amplifier stage. By using these plates, a series of optimizing experiments are done with the LMA fiber bending at different radii. The threshold of highorder modes are raised successfully and kW-class nearly single mode laser output is obtained. The beam quality factor (M2) is about 1.4 at 1.31 kW.