Passively Q-switched Nd-doped fiber laser based on PbS/CdS core/shell quantum dots as a saturable absorber

In our work, PbS/CdS core/shell quantum dots with an absorption peak of 1043 nm were successfully employed as a modulator for achieving a passively Q-switched Nd-doped fiber laser. The saturation intensity and modulation depth of the film-type modulator were 7.6 MW/cm² and 4.1%, respectively. Due to the protection of the CdS shell, the PbS core exhibited good photo-chemical stability, which led to the generation of stable passively Q-switched operation. The maximum average output power was 7.88 mW with a minimum pulse width of 235.7 ns. To our knowledge, this was the first demonstration focusing on the combination of quantum dot and Nd-doped fiber laser; in addition, 235.7 ns was the narrowest pulse width of a passively Q-switched Nd-doped fiber laser. Our results highlighted the excellent nonlinear absorption properties of PbS/CdS core/shell quantum dots and give significant guidance for future optical applications of quantum dots and demonstrations of pulsed Nd-doped fiber lasers.