TiO2/Ti3C2TX MXene composite as saturable absorber for passive harmonic mode-locking operation in thulium–holmium-doped fiber laser

In this work, a TiO 2 /Ti 3 C 2 T[Formula: see text] MXene composite saturable absorber (SA) in a thulium–holmium-doped fiber laser (THDFL) is used to generate harmonic mode-locked (HML) pulses. The SA demonstrated a modulation depth of 6.4%. The center wavelength of the fundamental HML pulses is 1904[Formula: see text]nm, with a repetition rate of 14.3[Formula: see text]MHz. The fundamental HML pulses exhibit excellent stability over long-term operation, with a high signal-to-noise ratio of 71[Formula: see text]dB after 4[Formula: see text]h. The laser cavity achieved up to the 17th harmonic order at 244.5[Formula: see text]MHz frequency. At the 17th harmonic mode-locking regime, bright and dark solitons coexist, exhibiting a uniform pulse spacing of 4.09[Formula: see text]ns. Spectral analysis reveals distinct peaks at 1909.4[Formula: see text]nm and 1902[Formula: see text]nm for the bright and dark solitons, respectively. The bright soliton shows a 1.62[Formula: see text]ps pulse width with a TBP of 0.317, indicating slight chirping. The bright and dark solitons exhibited a signal-to-noise ratio (SNR) of 81.5[Formula: see text]dB, demonstrating high stability attributed to the energy exchange and phase interactions between the solitons.