报道了一个被动锁模线性腔皮秒光纤激光器，实验中利用半导体可饱和吸收镜(SESAM)和光纤光栅构成了激光器的线性腔结构，利用SESAM实现了激光器的被动锁模，激光器内光纤结构采用保偏光纤实现了激光器的线性偏振态输出，研制光纤式SESAM实现了光纤激光器的全光纤密闭结构。得到的锁模脉冲的重复频率为40 MHz，脉冲宽度为25 ps，3 dB光谱宽度为0.12 nm，激光器锁模阈值输出功率为8 mW，可以实现稳定锁模的最大平均功率为19 mW。通过射频谱仪对锁模脉冲的检测可以证明锁模脉冲序列中没有掺杂调Q锁模。

This paper reports a passively mode locked fiber laser from a linear cavity. It consists of semiconductor saturable absorption mirror (SESAM) and fiber Bragg grating. Another function of the SESAM is to achieve passive mode locking based on saturable absorption. The polarization of picosecond pulses is maintained by polarization maintaining fiber. All-fiber structure of fiber laser is achieved by a homemade fiber coupled SESAM. Repetition rate of mode locked trains of 40 MHz, pulse width of 25 ps, spectral width of 0.12 nm, mode locked threshold average laser power of 8 mW, and the maximum laser power of 19 mW are obtained. Mode locked train without Q-switched mode locking is proved by radio frequency (RF) spectrometer.