Bismuthene quantum dots integrated D-shaped fiber as saturable absorber for multi-type soliton fiber lasers

In the present work, the uniformly sized bismuthene quantum dots (BiQDs) with an average diameter of 26 nm were fabricated via the solvothermal approach. By transferring the BiQDs onto the plane of micro-machined D-shaped fiber (DSF), a new type of saturable absorber (SA) was successfully prepared. Based on the evanescent field effect of D-shaped fiber, the prepared SA exhibits excellent saturable absorption properties with the maximum modulation depth of 5.1% at around 1.5 μm. To further investigate its potential applications in ultrafast photonics, we demonstrated passive mode-locking operation in the erbium-doped fiber laser (EDFL) with BiQDs/DSF-SA. The conventional soliton pulses with duration of 835 fs at the repetition rate of 9.23 MHz and dissipative soliton pulses with duration of 575 fs at the repetition rate of 7.83 MHz were generated successfully. In addition, stable bound state of solitons with the pulse duration of 1.04 ps and sub-pulse time interval of 15.9 ps were also obtained based on the conventional soliton state by adjusting the pump power and polarization state. Our work reveals the great potential and capacity of BiQDs/DSF-SA in soliton mode-locking operations and promotes the explorative investigation of bismuth-based optoelectronic devices.