Spatio-Temporal Dynamics of Pulses in Multimode Fibers

Time lenses can measure ultrafast signals but are based on single-mode fibers (SMFs). To develop multimode time lenses that are based on a four-wave mixing process, we must have full control of the nonlinear interaction between the modes. Specifically, we need to generate an idler from each mode without any cross-talk between the modes. Here, as a first step toward a multimode time lens, we study how stable a short pulse is traveling in a multimode fiber, and how pulses at different modes interact with each other. We utilize a single-mode-based time lens to measure the dynamics of these pulses in the time and spectral domains. We found that there is cross-talk between the modes and that the pulses are not stable and excite other modes, rather than staying in the same modal order. These findings indicate that developing a multimode time-lens may be more challenging than expected.