Internal dynamics in bound states of unequal solitons

The bound states (BSs) of solitons are found to have intriguing internal dynamics in ultrafast lasers. Here, we explore the binding mechanism and internal motions of asymmetric bound state (ABS) solitons constituted by unequal solitons at short-range with their tails directly overlapped. Experiments and simulations show that the periodic energy flux between two solitons, mediated by their overlapped tails, gives rise to a balanced separation and energy distribution across the ABS. The motion mechanisms of strong and weak solitons are discussed in detail. This work provides insights into the binding mechanism and internal dynamics of BSs.