Cnoidal waves are a type of nonlinear periodic wave solutions of the nonlinear dynamic equations. They are well known in fluid dynamics, but it is not the case in optics. In this paper we show both experimentally and numerically that cnoidal waves could be formed in a fiber laser either in the net normal or net anomalous cavity dispersion regime, especially because, as the pump power is increased, the formed cnoidal waves could eventually evolve into a train of bright (in the net anomalous cavity dispersion regime) or dark (in the net normal cavity dispersion regime) solitons. Numerical simulations of the laser operation based on the extended nonlinear Schrödinger equation (NLSE) have well reproduced the experimental observations. The result not only explains why solitons can still be formed in a fiber laser even without mode locking but also suggests a new effective way of automatic stable periodic pulse train generation in lasers with a nonlinear cavity.

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单模光纤激光器中的椭圆曲线波及其孤子极限

余弦波是非线性动力学方程的非线性周期波解的一种。它们在流体动力学中众所周知，但在光学中却并非如此。在本文中，我们通过实验和数值证明，光纤激光器可以在净法向或净反常腔色散状态下形成椭圆形波，特别是因为，随着泵浦功率的增加，形成的椭圆形波最终可能演变成一串亮（在净异常腔色散范围内）或暗（在净正常腔色散范围内）孤子。基于扩展非线性薛定谔方程（NLSE）的激光运行数值模拟很好地再现了实验观察结果。该结果不仅解释了为什么即使没有锁模，光纤激光器中仍然可以形成孤子，而且还提出了一种在非线性腔激光器中自动稳定周期性脉冲序列生成的新有效方法。