调Q及连续掺Yb光纤激光器中的自锁模研究

Study of Self Mode-Locking in Q-Switched and Continuous Working Yb-Doped Fiber Laser

在用半导体激光器抽运的单包层掺Yb调Q光纤激光器中观察到了清晰稳定的自锁模脉冲序列,脉冲包络形状为调Q脉冲,每个锁模脉冲的幅值由其在调Q脉冲中的相应位置决定。经过分析,认为自相位调制是调Q光纤激光器中产生锁模的主要原因。自相位调制的存在使得光脉冲的频谱被展宽,当这种展宽和腔的模式间隔相差不多时,腔内的模式便能相互作用,直到它们之间产生一个固定的相位关系,也即形成锁模。在此基础上,去掉声光晶体,并用两个光栅作为腔镜,实现了全光纤法布里珀罗(F-P)腔锁模光纤激光器。改变腔结构,分别采用光栅和光纤反射圈作为前后腔镜,同样观察到了锁模脉冲。经过观察发现,锁模脉冲的产生和掺Yb光纤的浓度、长度、抽运功率的大小有着密切的关系,这为锁模脉冲的产生提供了一种新的方法。

A clear and stable self mode-locked pulse train was observed with Q-switched pulse envelope in diode pumped Yb-doped Q-switched fiber lasers. Self phase modulation (SPM) is regarded as the main reason to generate mode-locked pulses in this Q-switched fiber laser. The main effect of SPM is to broaden the spectrum of the optical pulses. If the width of the broadened spectrum is comparable with the cavity-mode spacing then the modes can interact with each other, and a fixed-phase relationship between different oscillating axial modes is maintained, resulting in the mode-locked operation. On this basis, the acousto-optic modulator (AOM) was removed and two gratings were used as the cavity mirrors, and an all-fiber Fabry-Perot (F-P) cavity fiber laser was realized. Similar mode-locked pulses were observed when using two ring reflectors as the cavity mirrors. It is observed that mode-locking has close relations with fiber length, Yb-doped concentration and pump power. Such kind of laser provides a new method to generate mode-locked pulses.