在基于半导体光放大器的激光器中，观察到了自锁模现象，得到了脉宽分别为30 ns和50 ns的重复频率分别为19.34 MHz和9.67 MHz的光脉冲。激光器采用环形腔结构，半导体光放大器为自锁模的关键器件，当其抽运电流为200 mA时，调整偏振控制器开始出现自锁模脉冲。实验调试过程中，还观察到了重复频率的二分频现象，即激光器输出的光脉冲的重复频率是激光器基频的1/2。半导体光放大器的偏振旋转导致了输出激光功率的变化，出现了高功率和低功率脉冲交替出现的现象，即重复频率二分频现象。

In experiment of semiconductor optical amplifier based laser, the phenomenon of self-mode locking is observed. Pulse duration of 30 ns and 50 ns are achieved with repetition frequencies of 19.34 MHz and 9.67 MHz, respectively. The laser adopts a ring cavity configuration, with semiconductor optical amplifier used as key device of the self-mode locking. When the pump current adds to 200 mA, self-mode locking pulse is observed after adjusting the polarization controller. In addition, the phenomenon of dimidiate frequency is abserved, that is the repetition frequency of the pulses is equal to half of the cavity fundamental frequency. The effect of polarization rotation caused by the semiconductor optical amplifier leads to the change in output power, which is, the alternation of pulses with high power and low power, which is called the phenomenon of dimidiate frequency.