Modulation of ultrafast soliton molecules enabled by plasmonic metafibers

Abstract Soliton molecules (SMs) are bound states of two or more fundamental solitons arising from the balance between nonlinear interactions and dispersion effects. SMs are the focus of intense research and have sparked numerous applications in optical communication, including coding, storage, and exchange. However, it remains challenging to experimentally produce SMs with the required pulse number and temporal separation in mode-locked fiber lasers owning to the gap between the theoretical prediction and the experimental results. Here, we achieve controllable output of SMs by utilizing a plasmonic metafiber and external manipulation techniques. Plasmonic metafibers with superior nonlinear performance are used as saturable absorbers to realize soliton mode-locking operation with femtosecond pulse duration. Regulation of pump power and polarization enables switching of pulse number from one to five and temporal separation from 4 ps to 10 ps, respectively. An analytical model based on the nonlinear Schrödinger equation is well established, effectively bridging the gap between experimental results and theoretical predictions. Our results shed light on the understanding of the formation mechanism, transport properties, and free regulation of SMs.