掺铒光纤环形激光器中饱和吸收光栅瞬态特性引发跳模的实验研究

Experimental study on mode hopping triggered by transient characteristics of saturable absorber gratings in Er-doped fiber ring lasers

在掺铒光纤环形激光器中插入饱和吸收光栅是获得稳定单纵模激光的常用方法,但跳模难以完全避免.通过干涉仪动态相移解调法将光频跳变实时转化为相位变化,发现了一种由饱和吸收动态光栅的瞬态响应特性导致的跳模新机理.实验测量了由腔长快调触发的规则跳模,获得了跳模规律及成因.此种跳模发生在调制曲线斜率最大值附近区域,通常在相邻模式之间出现,跳模前移频量约为纵模间隔.在同等调制振幅下,抽运功率越高,触发跳模所需的光频调制频率越大,所需的最小移频量也越大.实验结果给出了振动和调制条件下激光器稳定工作的条件,这为设计激光器的隔振封装和确定频率调制工作模式下的调制范围提供了实验依据.

It is preferred to insert a saturable absorber grating in Er-doped fiber ring lasers for obtaining a stable single-longitudinal-mode laser operation;however, mode hopping is hardly avoided in various applications. A new mode hopping mechanism is found by utilizing the interferometric phase-demodulation method to transfer the optical frequency hops to the phase changes in real time. The regular mode hops triggered by fast cavity-length modulation are measured, and the characteristics and the origin of the mode hopping are obtained. Experimental results show that this kind of mode hopping, usually occurring between two neighboring longitudinal modes, may appear near the maximum slope of the modulation curve, and the laser frequency with shift about the space of the longitudinal modes before mode hopping. In addition, both the threshold frequency of the optical frequency modulation and the minimal frequency shift, which can triggered a mode hop, increase with the pump power at the same modulation amplitude. These experimental results can provide the stable operation condition if vibration or modulation exists, and they are helpful for optimal designing of the isolated assemblage or determining the operation range under the modulation condition.