Tunable soliton molecules in mode-locked fiber laser based on GeBi4Te7 saturable absorber

•The GeBi4Te7-based saturable absorber has been obtained.•Different soliton molecules have been recorded in three fiber cavities.•Pulse-tunable soliton molecules have reached by adjusting pump power. As a member of 2D materials, GeBi4Te7 (GBT) nanoflakes about 3 nm thickness were fabricated using liquid-phase exfoliation. The GBT-SA has excellent nonlinear optical effects that the modulated depth and saturation power are 6.6 % and 1.07 mW measured by the double-balance detection method. The single-, dual-, triple-, fifth-, sixth-, and tenth-pulses molecules have been recorded under different pump power in the cavity length of 26.5 m, 16.7 m and 13.5 m cavities. These multiple soliton molecules are state-tunable by only adjusting pump power. The experimental results demonstrate the GBT has excellent nonlinear optics effects and broad application prospects in fiber communication and ultrafast lasers.