Experimental revealing of fiber laser soliton build-up activated by shaking-soliton triplets

•A new route to generate conventional solitons.•Orthogonal shaking-soliton molecules are firstly experimentally analyzed.•Simultaneous spectral beating and binding.•Chaos internal-motion of shaking soliton triplets. Optimization of self-starting in passively mode-locked optical soliton fiber laser resonators results from a complex transient dynamic involving soliton molecules, soliton-based complexes and supramolecular structures, with particle-like properties. By means of time-stretch dispersive Fourier transform based real-time spectroscopy, we identify a new route to the passive mode-locking of fiber laser solitons. A raised relaxation oscillation stage is followed by the generation of shaking-soliton molecular triplets. The relative phase between satellite and main pulses of shaking soliton triplets evolves chaotically, while the two satellite pulses are orthogonal to each other in their state of polarization. These results provide new perspectives into the soliton formation and the internal dynamics of soliton molecules with higher degrees of freedom.