Femtosecond mode-locking and soliton molecule generation based on a GaAs saturable absorber

In the last few years, research on advanced ultrafast photonic devices has attracted great interest from laser physicists. As a semiconductor material with excellent nonlinear saturation absorption characteristics, GaAs has been used in solid-state and fiber lasers as a mode-locker. However, the pulse widths that have been reported in the searchable published literature are all long and the shortest is tens of picoseconds. Femtosecond pulse widths, desired for a variety of applications, have not yet been reported in GaAs-based pulsed lasers. In this work, we further explore the nonlinear characteristics of GaAs that has been magnetron sputtered onto the surface of a tapered fiber and its application in the generation of femtosecond lasing via effective dispersion optimization and nonlinearity management. With the enhanced interaction between evanescent waves and GaAs nanosheets, mode-locked soliton pulses as short as 830 fs are generated at repetition rates of 4.64 MHz. As far as we know, this is the first time that femtosecond-level pulses have been generated with a GaAs-based saturable absorber. In addition, soliton molecules, including in the dual-pulse state, are also realized under stronger pumping. This work demonstrates that GaAs-based photonic devices have good application prospects in effective polymorphous ultrashort pulsed laser generation.