Passively mode-locked laser using HfSe2 as saturable absorber at 1.5 μm and 2.0 μm

This research demonstrates mode-locked erbium-doped fiber laser (EDFL) and thulium-holmium doped fiber laser (THDFL) using hafnium diselenide (HfSe2) as saturable absorber (SA). The Kelly's sidebands were observed in both spectra, showing that both lasers operated in an anomalous dispersion region. A polarization controller was used to achieve reliable mode-locking operation at a threshold power of ∼46 mW and ∼254 mW for the EDFL and THDFL respectively. The center wavelengths obtained for the EDFL and THDFL were 1557 nm and 1912 nm, respectively. In EDFL, the output soliton generates 0.75 ps of pulse width and a repetition rate of 14.8 MHz, while THDFL has a pulse width of 1.15 ps and a repetition rate of 12.5 MHz. The pulses were highly stable for both gain mediums, verified by the signal-to-noise ratio (SNR) of 68 dB and 63 dB for EDFL and THDFL, respectively. In addition, there were no significant changes during the three-hour stability test, suggesting a long-term stability. This work shows a low-cost laser with possible application in C-band and near the 2.0 μm region.