Soliton interaction in a SnBi4Te7-based mode-locked fiber laser: From soliton molecules to harmonic soliton

The two-dimensional (2D) ternary topological insulator SnBi4Te7, due to its unique layered van der Waals heterostructure and exceptional properties, holds significant potential in thermoelectric and optoelectronic devices. This paper investigates the nonlinear optical properties of SnBi4Te7 nanosheets. SnBi4Te7-based saturable absorber (SA) was prepared using liquid phase exfoliation (LPE). The modulation depth of SnBi4Te7-SA was measured to be 8 %, with an unsaturation loss of 28.35 % and a saturation intensity of 8.66 MW/cm2. SnBi4Te7-SA was integrated into a resonator using the direct-coupling technique. By adjusting the pump power and the polarization controller (PC), conventional soliton, 2nd, 3rd-order soliton molecules, and 2nd, 3rd-order harmonic mode-locking were achieved within the same laser system. The pulse width of the conventional soliton was measured to be 1.03 ps, with a signal-to-noise ratio (SNR) reaching up to 72 dB. The supermode suppression ratio (SMSR) for both the 2nd and 3rd-order harmonic mode-locking exceeded 40 dB. These diverse phenomena indicate that SnBi4Te7 nanosheets exhibit outstanding nonlinear optical properties. •SnBi4Te7 nanosheets dispersion was obtained by liquid phase exfoliation. And, with the help of the direct-coupling technique, we successfully prepared SnBi4Te7-SA.•Using a dual-arm detection technique, the modulation depth of the SnBi4Te7-SA was measured to be 8 %, with an unsaturation loss of 28.35 % and a saturation intensity of 8.66 MW/cm2.•We developed a fiber laser based on SnBi4Te7-SA for the first time (with reference to current literature).•By adjusting the pump power and the polarization controller (PC), conventional soliton, 2nd, 3rd-order soliton molecules, and 2nd, 3rd-order harmonic mode-locking were achieved within the same laser system.•Analyzed the formation mechanisms of soliton molecules and harmonic mode-locking in fiber lasers, as well as the interactions between solitons.