Harmonic splitting phenomenon of bright-dark pulse pairs in a passive mode-locked Thulium-Holmium co-doped fiber laser

被动锁模铥钬共掺光纤激光器亮暗脉冲对的谐波分裂现象

This study reports a passive mode-locked Thulium-Holmium co-doped fiber laser featuring a figure-9 shaped resonator structure.The laser utilizes a nonlinear amplifying loop mirror(NALM)as the mode-locking device.By increasing pump power,the laser’s output evolution was experimentally observed,showing that bright-dark pulse pairs first split into double pulses and then into a second harmonic state.Additionally,the time intervals between bright and dark pulses and between double pulses increased with higher pump power.The RF spectrum of the bright-dark pulse pairs exhibited envelope modulation,with a modulation frequency approximately equal to the reciprocal of the time interval between bright and dark pulses.When the pump power increased from 0.46 W to 0.72 W,the reciprocal of the modulation frequency showed a linear growth trend.These findings contribute to understanding the evolution patterns of bright-dark pulse pairs in passive mode-locked fiber lasers.

报道了一种具有“9”字型谐振腔结构的被动锁模铥钬共掺光纤激光器,该激光器采用非线性放大环镜作为锁模器件。实验通过增加泵浦功率观察到激光器输出的亮暗脉冲对先分裂为双脉冲,再分裂为二次谐波状态的具体演化过程;基频下亮暗脉冲之间和双脉冲之间的时间间隔随着泵浦功率增加而增加的规律。此外,实验还观察到,亮暗脉冲对的射频谱呈现包络调制现象,调制频率近似等于亮暗脉冲之间时间间隔的倒数;泵浦功率从0.46 W增加至0.72 W时,调制频率的倒数呈线性增长趋势。研究结果有助于探明被动锁模光纤激光器亮暗脉冲对的演化规律。