We report for the first time, rogue waves generation in a mode-locked fiber laser that worked in multiple-soliton state in which hundreds of solitons occupied the whole laser cavity. Using real-time spatio-temporal intensity dynamics measurements, it is unveiled that nonlinear soliton collision accounts for the formation of rogue waves in this laser state. The nature of interactions between solitons are also discussed. Our observation may suggest similar formation mechanisms of rogue waves in other systems.
Bibliographical note/Funding: EC Marie Curie International Incoming Fellowship (628198), ERC project ULTRALASER; H2020 project CARDIALLY; and Russian Ministry of Education
and Science (project 14.584.21.0014).