报道了一种改进的非线性放大环形镜锁模激光器，即在传统的8 字腔和σ腔中，通过加入非互易性元件的方式，有效缩短了光纤长度，降低了非线性积累量，从而提升锁模激光器的重复频率，并且可以改善激光器的自启动特性。传统的“8”字腔保偏光纤激光器必须借助半导体可饱和吸收镜、碳纳米管等真实可饱和吸收体才能锁模运转。本文只利用非互易性元件，在改进的“8”字腔全保偏(PM)掺铒光纤激光器中，实现了重复频率为22 MHz，平均功率为23.6 mW 的孤子锁模单脉冲激光输出，直接输出脉宽为308 fs。传统的“8”字腔光纤激光器的重复频率限制在10 MHz 水平。通过加入非互易性元件，本文在改进的“σ”腔非保偏掺铒光纤激光器中，在呼吸孤子锁模域获得了重复频率为80 MHz，平均功率为36 mW 的单脉冲激光输出；在正色散域获得了重复频率为53.6 MHz，平均功率为14 mW 的单脉冲激光输出。

A modified nonlinear amplifying loop mirror mode- locked laser is demonstrated. In this setup, nonreciprocal elements are included into traditional“figure eight”and“s-like”cavities in order to decrease the length of essential fiber required to accumulate nonlinear phase shift. As a result, the repetition rate of these lasers is significantly increased. In addition, the self-starting characteristic is also improved. The passive mode-locking operation of traditional“figure eight”polarization maintaining (PM) fiber lasers requires real saturable absorbers, such as semiconductor saturable absorber mirror, or carbon nanotube. In this work, by using nonreciprocal elements, passive mode locking in a modified“figure eight”polarization maintaining Er-fiber laser is realized. The laser works in soliton regime and generates 308 fs pulses with an average power of 23.6 mW at a repetition of 22 MHz . The repetition rate of traditional“figure eight”fiber lasers is limited to 10 MHz. By using nonreciprocal elements, a non PM Er-fiber laser based on a modified“s-like”cavity working at stretched pulse regime generates pulses with an average power of 36 mW at a repetition of 80 MHz. The same laser working at normal dispersion domain generates pulse train with an average power of 14 mW at a repetition of 53.6 MHz.