We experimentally demonstrate a passively mode-locked all-fiber Tm laser with an all-fiber saturable absorber (SA) which operates based on the nonlinear multimode interference (NL-MMI) effect in a tapered graded-index multimode fiber (GIMF). The tapered GIMF SA demonstrates the nonlinear characteristics of modulation depth of 21.15%, and saturation fluence of $89.04~\mu \text{J}$ /cm2. We obtain stable fundamentally mode-locking operation at a pump threshold of 120 mW. The output soliton pulses have a center wavelength, spectral width, pulse duration and repetition rate of 1935 nm, 2.1 nm, 1.9 ps and 18.79 MHz, respectively. This is a simple, low-cost, stable, and convenient laser oscillator with many potential applications in eye-safe ultrafast photonics.

中文翻译：

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基于非线性多模干涉效应的锥形 GIMF SA 锁模 Tm 光纤激光器

我们通过实验证明了一种具有全光纤可饱和吸收器 (SA) 的被动锁模全光纤 Tm 激光器，该激光器基于锥形渐变折射率多模光纤 (GIMF) 中的非线性多模干涉 (NL-MMI) 效应工作。锥形 GIMF SA 表现出 21.15% 调制深度和 $89.04~\mu\text{J}$ /cm2 饱和注量的非线性特性。我们在 120 mW 的泵阈值下获得了稳定的基本锁模操作。输出孤子脉冲的中心波长、光谱宽度、脉冲持续时间和重复频率分别为 1935 nm、2.1 nm、1.9 ps 和 18.79 MHz。这是一种简单、低成本、稳定且方便的激光振荡器，在人眼安全的超快光子学中有许多潜在的应用。