为了获得稳定的谐波锁模脉冲，分析了有理数谐波锁模的理论和非线性放大环镜的传输特性。构建了包括一个外部环和一个内部环的8字形被动锁模掺铒脉冲光纤激光器，对被动锁模掺铒光纤激光器进行了相关理论分析和实验研究。实验发现，当调整泵浦功率分别为167,146和126 mW时，除了观测到了稳定的谐波锁模脉冲外，还观察到了分别类似于3阶、5阶、6阶的有理数谐波锁模脉冲产生现象，分析其脉冲重复频率，证实此类脉冲序列具有属于3阶、5阶和6阶有理数谐波锁模脉冲序列重复频率的一样的规律，认为其产生原因是8字形光纤激光器中的Sagnac环起了和主动锁模中调制器一样的作用。

To achieve a steady harmonic mode-locked pulse (HMLP), the theory of rational harmonic mode-locking and the transmission characteristics of a nonlinear amplifying loop mirror were analyzed. A figure-8 shape pulse laser including an outer ring and an inner ring was constructed to theoretically and experimentally investigate the passively mode-locked technology of an erbium-doped fiber laser. By modulating the pump power to 167 mW,146 mW or 126 mW,not only a steady HMLP,but also several rational HMLPs were observed. It is found that these pulses show the same properties as those of 3th-order,5th-order,6th-order HMLPs by analyzing the repetition rate of pulse train. The reason is that the Sagnac ring in the figure-8 shape pulse laser plays the same role as the modulator used in an actively mode-locked pulse laser.