Soliton molecules in femtosecond fiber lasers: universal coupling mechanism and electronic switching

Stable arrangements of temporal solitons are reported for essentially every implementation of femtosecond fiber lasers. Their formation can be tracked with today’s real-time instrumentation. However, the underlying interaction mechanism frequently remained elusive and predictions of soliton separations in actual sources are often missing. Here, we present the experimental analysis of bound-state trajectories in a femtosecond Er:fiber laser and reveal the underlying universal coupling mechanism. We demonstrate all-electronic switching between two stable soliton molecules and the feasibility of tuning bound-state separations. The results are applicable to various ultrafast sources and may readily be adapted for generating femtosecond pulse pairs in spectroscopy and material processing.