Nonlinear propagation of signals in single-mode fibers is well understood, and is typically observed by measuring the temporal profile or optical spectrum of an emerging signal. In multimode fibers, the nonlinearity has both a spatial and a temporal element, and a complete investigation of the interactions between propagating modes requires resolving the output in both space and time. We report here spatiotemporal measurements of a time-dependent mode interference effect, arising from the Kerr nonlinearity, of two selectively excited ${{\text{LP}}_{0m}}$ modes of a step-index few-mode fiber. We describe a method to selectively excite two propagating modes through the use of a phase mask directly patterned on the entrance face of the fiber. The output is resolved by raster-scanning a near-field tapered single-mode optical fiber probe that is connected to a high-speed detector. The results show that in the presence of nonlinearity, the output exhibits a spatiotemporal character that cannot be adequately characterized by a camera image or pulse shape alone.

中文翻译：

---

几模光纤的选择性激发模之间非线性模态干扰的时空特征

信号在单模光纤中的非线性传播已广为人知，通常可以通过测量新兴信号的时间轮廓或光谱来观察。在多模光纤中，非线性具有空间和时间因素，对传播模式之间相互作用的完整研究需要解析空间和时间上的输出。我们在此报告两个选择性激发的$ {{\ text {LP}} _ {0m}} $由Kerr非线性引起的时变模式干扰效应的时空测量阶跃数模光纤的各种模式。我们描述了一种通过使用直接在光纤入口面上构图的相位掩模来选择性激发两种传播模式的方法。通过光栅扫描连接到高速检测器的近场锥形单模光纤探头来解析输出。结果表明，在存在非线性的情况下，输出表现出时空特性，仅凭摄像机图像或脉冲形状无法充分表征。