为了实现多芯光纤激光器的单模输出，提出一种新的选模机制，即利用单模光纤进行选模。采用单模光纤和全反镜相结合作为选模器件，可以使6芯光纤激光器中同相位超模的耦合效率远远大于其他高阶超模，从而使高阶超模得到有效的抑制，实现高亮度的同相位超模单模输出。为了提高同相位超模的耦合效率，可以进一步优化单模光纤纤芯尺寸，同时调节单模光纤和6芯光纤之间的间隙距离。将同相位超模的耦合效率代入速率方程进行理论模拟，证明输出功率和耦合效率之间的必然联系，结果显示同相位超模输出功率随着耦合效率的增大而增大，得到单模输出的最大光光转换效率为63.7%。

A multi-core fiber laser with single-mode output is reported, which is mode selected by the proposed mechanism based on single-mode fiber. Using single-mode fiber combined with a total reflection mirror as mode selection element, the in-phase supermode always has much higher coupling coefficient than that of the other higher-order supermodes. As a result, high brightness single in-phase supermode output is obtained while higher-order supermodes are suppressed. The coupling coefficient can be optimized by choosing proper single-mode fiber core radius and adjusting the gap distance between multi-core fiber and single-mode fiber. The relationship between coupling coefficient and single-mode output power is investigated. The simulation results got from rate equation show that the output power increases with coupling coefficient, and the maximum optical-optical conversion efficiency is calculated to be 63.7%.