Collision and dissociation of soliton molecules triggered by gain perturbation in passively mode-locked fiber laser.

Soliton molecule has the properties that similar to those of matter molecule, which brings great research value. The rich dynamics of soliton molecules depend on the complex interactions between pulses. As one of the important factors, gain dynamics has multi-dimensional effects on the interactions of soliton molecules. We here study the interaction process of soliton molecules under gain perturbation, and find the oscillation and collision behaviors of pulses within soliton molecules induced by gain perturbation, as well as the pulses recombination through interactions between soliton molecules. We believe that the energy change in the cavity and the energy transfer based on the continuous wave component play an important role in the evolution process of the dissociation of soliton molecules into three-pulses bunch and single pulse. These findings reveal the effects of gain on the motion of soliton molecules and provide a basis for exploring the control dynamics of soliton molecules.

Spatiotemporal mode-locked fiber laser based on dual-resonance coupling long-period fiber grating.

Spatiotemporal mode-locked (STML) fiber lasers have become an excellent platform in nonlinear optics research due to the rich nonlinear evolution process. In order to overcome modal walk-off and realize phase locking of different transverse modes, it is usually crucial to reduce the modal group delay difference in the cavity. In this paper, we use long-period fiber grating (LPFG) to compensate the large modal dispersion and differential modal gain in the cavity, realizing the spatiotemporal mode-locking in step-index fibers cavity. The LPFG inscribed in few-mode fiber could induce strong mode coupling, which has wide operation bandwidth based on dual-resonance coupling mechanism. By using dispersive Fourier transform involved intermodal interference, we show that there is a stable phase difference between the transverse modes constituting the spatiotemporal soliton. These results would be beneficial for the study of spatiotemporal mode-locked fiber lasers.

Dynamics of pulsating solitons derived from asymmetrical dispersive waves.

Pulsating soliton (PS) as a local structure of nonlinear systems has induced substantial interest in nonlinear photonics and ultrafast lasers. However, the interaction mechanism between PSs has not been fully studied. Here, the vital role of the asymmetric dispersive wave (DW) in PSs interaction is investigated for the first time. Based on the complex Ginzburg-Landau equation (CQGLE), we find that the asynchronous pulsating soliton molecule (PSM) composed of strong PSs and weak PSs will produce frequency shift due to the asymmetric DW, and the state of the PS can be transferred through the DW during the collision between PSs and PSM. Moreover, we firstly characterize the PS with asymmetric DW in experiment, and observe the drift of PSM, which agree with our simulation that the asymmetric DW can cause the frequency shift of PSMs. Our results provide new insights into the multi soliton interaction of nonlinear systems.

Transition between noise-like pulses and Q-switching in few-mode mode-locked lasers.

Spatiotemporal mode-locked lasers have attracted extensive attention of researchers due to the complex nonlinear evolution process. Compared to single-mode mode-locked lasers, intermodal interactions greatly affect the pulses evolution in spatiotemporal mode-locked lasers. Here, we experimentally investigate the transition process between noise-like pulses and Q-switching pulses in few-mode mode-locked laser by rotating the plates, where a transition state is greatly broadened in the time domain. By means of spectral filtering, we verify that the process is the reconstruction of Q-switching between different modes to noise-like pulses. Furthermore, during the evolution of noise-like pulses, soliton collisions are detected using dispersive Fourier transform technology. Our research contributes to revealing the transient evolution process in few-mode mode-locked lasers, and enriches the study of nonlinear process.

Elastic and inelastic collision dynamics between soliton molecules and a single soliton.

Dissipative systems form various self-organized states owing to the abundant attractor structures. The study of the response of different self-organized states under collision perturbation is of great significance for understanding the dissipative nonlinear systems. The collision dynamics of single soliton and soliton molecules can not only assist the stability analysis of attractors, but also reveal the rich physical connotations of soliton interactions. Here, for the first time, the collision processes of single soliton and soliton molecules in different excited states are detected using the dispersive Fourier transform technology. The collision processes include the disintegration and rebuilding of soliton molecules as well as chaotic oscillating evolution, accompanied by the emergence of transition states such as triple binding state, soliton fusion and acceleration. According to whether the soliton molecule can return to its initial excited state, the collisions are classified as elastic and inelastic. The different interaction strength between solitons is an important condition for rebuilding stable soliton molecules. Numerical simulations show that the gain dynamics are the main physical origin of collisions. Our research will stimulate in-depth research on the interaction of self-organized states in nonlinear systems such as chemical molecules, and have potential applications in optical logic gates.