掺镱光纤激光器自脉冲与自脉冲内的自锁模研究

采用单端连续抽运方式, 对自由运转的双包层掺镱光纤激光器的输出特性进行了详细的实验研究. 实验中不但观察到了自脉冲, 而且首次在自由运转的光纤激光器中观察到自锁模现象, 对它们产生的物理机理进行了相应的理论分析. 分析表明: 增益光纤的弱(未) 抽运部分对信号光的吸收导致光纤激光器内自脉冲的出现, 轴向模之间的拍频和自相位调制导致自锁模现象的出现, 而受激拉曼散射、 受激布里渊散射等非线性效应使它们进一步增强. 当抽运光功率略高于阈值时, 自脉冲宽度比较宽, 随抽运光功率增加自脉冲的脉宽变窄; 自脉冲包络面内的自锁模脉冲的宽度随抽运光功率增加也变窄, 进一步增加抽运光功率, 自脉冲和自脉冲包络面内的自锁模现象消失. 实验测得自锁模脉冲的间隔为224 ns, 最大(小) 自锁模脉冲的半高全宽约为35.0 ns (6.3 ns); 测得信号光的中心波长为1090 nm, 谱线半高全宽的最大(小) 值约为7.05 nm (2.01 nm).

Investigation of self-pulsing and self-mode-locking in ytterbium-doped fiber laser

The output characteristics of a continuous-wave diode pumped free-running double-clad ytterbium-doped fiber laser are investigated. In the experiment, not only self-pulsing is observed, but also self-mode-locking is observed for the first time in the free-running fiber laser. The physical mechanism responsible for these phenomena is analyzed. The analysis reveals that the signal is absorbed in the weakly pumped or non-pumped part of the active fiber, which leads the self-pulsing to be present, and self-mode-locking is induced by axial mode beating and self-phase modulation, which are enhanced by nonlinear effects, stimulated Raman scattering, and stimulated Brillouin scattering. The pulse width of self-pulsing decreases as pump power increases. The pulse width of self-mode-locking pulses becomes narrow with the increase of the pump power. When the pump power is higher than 8 W, self-pulsing and self-mode-locking disappear. The interval between adjacent self-mode-locking pulses is 224 ns, corresponding to the cavity round-trip time. The maximum and the minimum durations (full width at half maximum) of self-mode locked pulses are about 35.0 ns and 6.3 ns respectively, and the maximum and minimum spectral widths (full width at half maximum) of signal light are about 7.05 nm and 2.01 nm respectively.