反常色散超快光纤激光器中孤子爆炸特性研究

As ultra-short pulse sources, ultrafast fiber laser have been applied to many fields, such as laser processing, optical communication and so on. Besides, ultrafast fiber lasers are also regarded as great platforms to investigate soliton nonlinear dynamics. As one of the most interesting soliton nonlinear phenomena, the investigations of soliton explosions would not only further reveal the physical nature of solitons, but also play important role in the design of ultrafast fiber laser. However, so far the researches on soliton explosions mostly carried on in the normal dispersion regime and few works on the investigation of soliton explosions in anomalous dispersion regime have been reported. In addition, due to the limitations of measuring instruments, it is difficult to conduct the investigations of the transient phenomenon of soliton explosions. For these reasons, in this project we will investigate the characteristics of soliton explosions in ultrafast fiber laser with anomalous dispersion by using the transient detection methods of dispersive Fourier transformation and time lens technologies. The following issues will be addressed: firstly, the real-time spectral evolution in frequency domain of the soliton explosions will be detected; secondly, the pulse profiles evolution in time domain of the soliton explosions will be investigated; then the multi-soliton explosions will be studied; finally, the vector characteristics of soliton explosions will be analyzed. Carrying out this project would not only enhance the understanding of physical features of soliton explosions, but also be helpful to the developments of the fiber laser technologies.

除了作为超短脉冲光源应用于激光加工、光通信等领域外，超快光纤激光器还是研究孤子非线性动力学特性的优良平台。孤子爆炸是激光器中一种有趣的非线性现象，对孤子爆炸的研究不仅能进一步揭示孤子的物理本质，而且对于激光器系统的设计具有重要意义。然而，目前对孤子爆炸的研究主要集中在正常色散区，反常色散超快光纤激光器中的孤子爆炸研究却鲜有报道。另外，由于常规探测仪器的限制，孤子爆炸这一瞬态过程的研究工作难以进行。针对这些问题，本项目拟利用瞬态检测手段——色散傅里叶变换和时间透镜技术，在反常色散超快光纤激光器中开展孤子爆炸特性研究，项目主要内容包括：①观察孤子爆炸的频域光谱演化情况；②检测孤子爆炸的时域脉冲演化特性；③研究多孤子状态下孤子爆炸特性；④探索孤子爆炸的矢量特性。本项目的开展不仅能加深人们对孤子爆炸过程的理解，而且有助于推动光纤激光技术的发展。

本项目主要研究超快光纤激光器中非线性孤子动力学过程，并揭示其内在物理机制。在本项目的资助下，我们围绕孤子爆炸、孤子脉动及孤子启动等瞬态非线性孤子动力学过程开展了研究工作，所取得的的主要成果可以概括为以下几方面：（1）在孤子爆炸产生与特性研究方面：我们首次在反常色散超快光纤激光器中获得了孤子爆炸和脉动孤子伴随混沌行为，并研究了其光谱坍塌、瞬时孤子分子、能量增加等特性；在双波长锁模掺镱光纤激光器中发现了由于腔内孤子碰撞引起的“周期性”孤子爆炸：周期性产生但具有不同的爆炸细节；（2）在脉动孤子的产生与特性研究方面：基于改进的深度优化算法我们在光纤激光器中实现了特定参数脉动孤子的搜索和产生，脉动孤子的强度调制深度可以灵活控制；在反常色散掺铒超快激光器中发现了一种的新型孤子脉动——“隐形”孤子脉动：孤子周期性地经历峰值功率变化，但脉冲能量几乎不变，实验发现通过使用实时光谱技术记录每圈光谱可实现“隐形”孤子脉动可视化；研究了脉动孤子的矢量特性，除普通的偏振锁定和偏振旋转脉动矢量孤子之外，还发现了渐进式脉动偏振旋转矢量孤子；（3）在孤子启动过程研究方面：在全保偏掺镱光纤激光器中研究了两种极端的孤子启动过程，证实了孤子启动过程的随机性。本项目的开展不仅丰富了非线性孤子的研究，加深了对超快光纤激光器中瞬态孤子动力学过程的理解，而且对光纤激光技术的发展具有重要意义。