Observation of Various Bound States of Solitons in a Fiber Laser Based on GIMF-SIMF-GIMF Saturable Absorber

We report on the experimental observation of various bound states of solitons in an erbium-doped fiber laser mode-locked by a graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) saturable absorber (SA). Based on the nonlinear multimode interference (NL-MMI) effect of the GIMF-SIMF-GIMF SA, not only various bound single-pulse solitons (BSSs) can be obtained, but various bound twin-pulse solitons (BTSs) can also be achieved by adjusting the pump power and PC. The BSSs are formed by single soliton bound together, the BTSs are formed by multiple second-order tightly bound state of solitons.