Generate high repetition frequency mode-locking fiber lasers based on Nb2GeTe4 saturable absorber

Two-dimensional materials as saturable absorbers (SA) are advancing ultrafast fiber lasers. Ternary transition metal chalcogenides (TMCs) offer excellent stability and high carrier mobility, but the potential of Nb 2 GeTe 4 in high-repetition-rate mode-locking remains unexplored. In this work, Nb 2 GeTe 4 nanosheets were prepared by liquid-phase exfoliation and deposited onto tapered fibers. When incorporated into an erbium-doped fiber ring cavity, stable conventional soliton mode-locking was achieved. By precisely tuning the polarization state, multiple-order harmonic mode-locking from the 4th-8th and 22nd-26th orders was realized. Moreover, a maximum repetition rate of 319.8 MHz (52nd harmonic) was obtained at increased pump power. The Nb 2 GeTe 4 -SA exhibits excellent nonlinear modulation and long-term stability. This work provides a reliable material platform for high-repetition-rate pulsed lasers and soliton nonlinear dynamics, with promise for ultrafast light sources and high-capacity optical communications.