搭建了一台主振荡功率放大(MOPA)结构的单模线偏振窄线宽纳秒脉冲全光纤放大器，理论仿真和实验结果较为吻合。通过声光调制器(AOM)对连续单频1 064 nm激光进行调制，获得了重复频率50 kHz、平均功率25 μW的脉冲激光，作为放大器的种子源。对预放大过程中非线性效应、放大自发辐射、自激振荡及泵浦饱和问题进行了仿真分析。随后对种子光进行功率放大，通过光纤内参数的有效优化，进一步抑制了自激振荡，提升了弱信号的放大倍率。实验实现了脉冲宽度64 ns、平均功率75 mW的脉冲激光输出。最后，对亚毫瓦弱信号放大器中决定系统性能的关键因素进行了总结。

A single mode, linearly polarized, narrow line-width, nanosecond pulsed fiber laser in master oscillator power amplifier(MOPA) configuration was demonstrated and the experimental results agreed with the theory. A single-frequency continuous wave laser operating at 1 064 nm was modulated by an acousto-optic modulator(AOM) to obtain pulses as the seed of the master amplifier. The repetition rate of the pulsed seed was 50 kHz and the average power was 25 μW. In the pre-amplification stage, the effect of nonlinear effect, amplified spontaneous emission(ASE), parasitic lasing and pump saturation were analyzed by simulation. By optimizing the parameters of the MOPA system, the parasitic lasing was suppressed and the enlargement factor was increased effectively. In the experiment, the laser with pulse width of 64 ns and average power of 75 mW was achieved. Finally, the key factors that affect the performance of the sub-milli-watt weak signal amplifier were discussed.