We report, for the first time, generation of J-shaped pulses in figure-eight type ultra-long, all-normal dispersion Ytterbium-doped fiber laser mode locked by the combined effect of nonlinear polarization evolution and nonlinear optical loop mirror. Cavity birefringence based spectral filtering introduced by polarization controllers is used for the formation of J-shaped as well as step-like and flat-top pulses. The shape and duration of generated pulse is found to depend on applied birefringence as well as pump power. J-shaped pulses of 180 ns duration and 332 nJ pulse energy at 201.45 kHz fundamental repetition rate are generated at 200 mW pump power. Experimentally, a strong correlation between spectral and temporal profile of the generated pulse shapes is established where it has been shown that asymmetric spectral filtering is responsible for generation of J-shaped and step-like pulses. Numerically, the spectral transmission of figure-eight type resonator under different cav...

中文翻译：

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超长掺do锁模光纤激光器中J形脉冲的产生

我们首次报告了由八种类型的超长，全正态色散掺Y光纤激光器模式产生的J形脉冲的产生，该模式由非线性偏振演化和非线性光学环镜的组合作用锁定。由偏振控制器引入的基于腔双折射的光谱滤波用于形成J形以及阶梯状和平顶脉冲。发现产生的脉冲的形状和持续时间取决于所施加的双折射以及泵浦功率。以200 mW的泵浦功率产生180 ns持续时间的J形脉冲和201.45 kHz基本重复频率的332 nJ脉冲能量。实验上，在已产生的脉冲形状的频谱和时间轮廓之间建立了很强的相关性，其中已经表明，不对称频谱滤波是产生J形和阶梯状脉冲的原因。从数值上讲，八腔型谐振器在不同空腔下的光谱透射率。