对自行研制的主振荡功率放大结构短脉冲双包层光纤激光系统(2 W，30 ps)的偏振特性进行了研究.分别研究了种子源激光和经过包层泵浦放大后输出激光在连续工作和脉冲输出情况下的偏振特性，结果表明在不加偏振控制措施情况下，系统输出为椭圆偏振光，偏振度和偏振角都容易受到光纤扰动的影响；在激光腔内加入起偏器后，输出线偏振光，偏振态相对比较稳定，但是偏振角度仍然容易受到光纤扰动的影响.实验证明：经过高功率放大后，输出激光的偏振态稳定性有一定程度的下降，在进行激光相干合成前需进一步加以控制.

Based on the master oscillator power amplifier(MOPA) system including a single mode erbium-doped fiber laser used as the master oscillator,and a large-mode-area Erbium/Ytterbium double-clad fiber used as the amplifier gain medium,the polarization states of the seeding laser and the amplified laser are experimentally investigated.The results show that the polarization degree of the output laser of the amplifier is very low without any polarization control device;after inserting a polarizer in the loop of the signal source,the degree of polarization is improved evidently and the stability of the polarization state becomes better,both for continuous wave operation and for mode-locked operations.The mode-locked operation has a little lower polarization degree and a better stability than the continuous wave operation of the amplifier.When a polarizer introduced in the loop of the signal,the instability of the polarization state of the output of amplifier is mainly caused by the polarization parameter azimuth.As a result,the combination use of a polarizer and a polarization controller is supposed to improve the polarization degree and the stability of the output of the amplifier,furthermore,polarization-maintaining gain fiber is recommended to be used to avoid the random perturbation of the environment.The work offers an important experimental basis for the control of the polarization state in the laser beam coherent combination.