分布反馈式光纤激光器动态特性的研究

为了探明分布反馈式(DFB)光纤激光器用于水声探测时，所测得的声压灵敏度高于静压条件下计算所得的声压灵敏度，且动态响应曲线不平坦的原因及其机理，对DFB光纤激光器的动态特性进行了研究。对两端固定并分别置于空气和水介质中的DFB光纤激光器的振动模态进行了数值仿真分析；设计加工了实验夹具，分别对其进行了实验研究。实验测得数据表明，两端固定的裸纤在发生振动时的第一阶固有频率与其夹持长度有关，且随着该长度的增大，固有频率降低；当夹持长度分别为50mm、55mm和60mm时，在空气和水介质中DFB光纤激光器振动的第一阶固有频率分别约为250Hz、200Hz、125Hz以及200Hz、160Hz、120Hz，实测数据与仿真分析吻合。可见当DFB光纤激光器受外界激励发生振动时，引起了激光器输出信号幅值的波动，导致其声压灵敏度出现起伏，第一阶固有频率对其具有很大的影响。

Dynamical characteristics of distributed feedback fiber laser

In the study on the application of DFB fiber laser to underwater sound detecting, it was found that the acoustic pressure sensitivity of the DFB fiber laser was higher than that calculated under hydrostatic boundary conditions, and its frequency response curve was not smooth. However, the reason and the mechanism were to be figured out. Accordingly, dynamical characteristics of the DFB fiber laser were investigated. Firstly, a DFB fiber laser, whose both ends were fixed, and the cavity was tensioned and placed in air and water respectively, was analyzed numerically. And then, with specially designed testing assemblies, experimental study on it was also conducted. And the results indicate that the first natural frequency of the DFB fiber laser is related to the length of the optical fiber between the two fixed ends, and the length increases, the frequency decreases. When the length has been specified as 50 mm, 55 mm and 60 mm respectively, the first natural frequencies have been found to be about 250 Hz, 200 Hz and 125 Hz in air, and 200 Hz, 160 Hz and 120 Hz in water, correspondingly. It shows that when vibration is taking place in the DFB fiber laser, fluctuation in its output will be resulted, and the first natural frequency is an important factor of it.