We demonstrated an all fiber passively mode-locked fiber laser by using one single mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) structure as a saturable absorber (SA) based on the nonlinear multimode interference. The proposed SA with the modulation depth of 9.58%, saturation intensity of 36.50 MW cm−2 and nonsaturable loss of ~ 21% was inserted into an Er-doped fiber laser cavity. Then the conventional soliton laser at 1566 nm was realized at a pump threshold of 180 mW. The output pulses had a pulse duration and repetition rate of 520 fs and 33.7 MHz, respectively. And the maximum pulse energy was 256 pJ. Our results further indicated that the SMF-GIMF-SMF structure can be used as an effective SA for ultrashort pulse generation.

中文翻译：

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基于非线性多模干涉的锁模掺铒光纤激光器

我们通过使用一个单模光纤渐变折射率多模光纤-单模光纤 (SMF-GIMF-SMF) 结构作为基于非线性多模干涉的可饱和吸收器 (SA)，展示了一种全光纤被动锁模光纤激光器。将调制深度为 9.58%、饱和强度为 36.50 MW cm-2 且不饱和损耗为~21% 的 SA 插入到掺铒光纤激光器腔中。然后在 180 mW 的泵浦阈值下实现了 1566 nm 的常规孤子激光器。输出脉冲的脉冲持续时间和重复频率分别为 520 fs 和 33.7 MHz。最大脉冲能量为 256 pJ。我们的结果进一步表明，SMF-GIMF-SMF 结构可用作超短脉冲生成的有效 SA。