Saturable absorption in Mg ₂ Sn _1−x Sb _x alloy for Q-switched and mode-locked erbium-doped fiber lasers

A new <i>M</i><i>g</i>₂<i>S</i><i>n</i>_1-<i>x</i><i>S</i><i>b</i>_<i>x</i>-based saturable absorber (SA), to our knowledge, was developed and incorporated into an erbium laser cavity to explore its nonlinear optical characteristics for pulse generation. The prepared SA film, positioned between two fiber ferrules, exhibited a modulation depth of approximately 18%, enabling both Q-switched and mode-locked operations. In the Q-switched regime, stable pulse emission was achieved at 1562.4 nm as the pump power was set within 62.91-169.07 mW, producing a maximum repetition rate of 43.23 kHz, a minimum pulse width of 2.13 µs, and a pulse energy of 45.57 nJ. By extending the cavity length, soliton-type mode-locked pulses were realized at 1562.2 nm, delivering a repetition rate of 1.795 MHz and a pulse duration of 3.45 ps. The time-bandwidth product of 0.334 confirmed slightly chirped pulses, while high signal-to-noise ratios of 65.1 and 64.9 dB for the Q-switched and mode-locked regimes, respectively, verified excellent operational stability. These findings demonstrate the outstanding performance, nonlinear response, and versatility of the MgSnSb-based SA, establishing it as a capable candidate for ultrafast photonic and fiber-laser applications.