Generation and numerical simulation analysis of multisoliton bound states

We explore diverse soliton bound states within a nonlinear polarization rotation (NPR) mode-locked erbium-doped fiber laser, including both two-soliton and multisoliton configurations. Experimentally, we have achieved two-soliton bound states featuring switchable and continuously adjustable soliton intervals. The tunability of these intervals has been further validated through numerical simulations utilizing the intracavity Lyot birefringence filter model. In addition, simulations based on the experimentally observed three-soliton and four-soliton bound states demonstrate good agreement with the experimental data. Notably, we find extremely narrow soliton spacing, as small as 0.49 ps for the two-soliton state. To our knowledge, this is the smallest interval reported so far in an erbium-doped mode-locked fiber laser.