中文摘要：

摘要：为了在大模场平顶基模光纤激光器中实现单模单偏振运转，提出一种获得单模单偏振平顶基模信号光的方法。在平顶基模光纤的包层中引入两个带有椭圆空气孔的无源纤芯，无源纤芯对称地置于直径为20um的有源芯区的两侧，椭圆空气孔用来引入双折射。通过数值仿真发现，在上述有源光纤作为平顶基模光纤激光器的增益介质的情况下，可以使得光纤激光器在不采用其他模式选择方法的情况下只输出x方向偏振基模。

英文摘要：

For performing single mode （SM） single polarization （SP） operation in fiber lasers with flattened fundamental （FM） mode in large-mode-area, a method for obtaining SMSP signals with FM mode is presented. Two passive fiber cores with elliptical air holes are inserted into layers of fibers with FM mode. The cores are placed on both sides of an active core region with 20 p.m diameter symmetrically and elliptical air holes are used to import birefringence. According to numerical simulation, when the active fiber is used as the gain medium of fiber lasers with FM mode, only polarization fundamental mode in x direction will be output by fiber lasers without choosing other modes.