Continuous harmonic mode locking in an Er-doped fiber laser based on a Ta₂NiSe₇saturable absorber

In this work, a Ta₂NiSe₇-based tapered fiber saturable absorber (SA) was fabricated and integrated into an erbium-doped fiber laser. Stable conventional soliton mode locking was achieved at a fundamental repetition rate of 6.13 MHz. By adjusting the intracavity polarization state and increasing the pump power, continuous harmonic mode locking from the fundamental state to the 40th order was realized, corresponding to a maximum repetition rate of 245.6 MHz with a supermode suppression ratio (SMSR) of 41 dB. The harmonic order increased nearly linearly with the pump power while maintaining a stable operation and a high SMSR. These results demonstrate the potential of Ta₂NiSe₇ for continuously tunable high-repetition-rate ultrafast fiber lasers.