Generation of harmonic mode-locking of bound solitons in the ultrafast fiber laser with Sb₂Te₃ saturable absorber on microfiber

We report on the observation of the harmonic mode-locking of bound solitons in an erbium-doped fiber laser with an Sb₂Te₃ topological insulator saturable absorber (SA) on a microfiber. In the regime, there are two solitons in the bound-state pulses and the soliton separation is almost constant at different pump powers. When changing the pump power from 108 mW to 520 mW, the repetition rate of the bound-soliton mode-locking increases from 8th harmonic (105.6 MHz) to 46th harmonic (607.2 MHz). Our experiment results show that the Sb₂Te₃ topological insulator SA on microfiber could be not only used as an excellent mode locker, but could also provide a highly nonlinear effect for effectively exploring the multiple pulses in the fiber lasers. (letter)