Fig. 1. (a) TEM image and (b) corresponding size distribution histogram of PbS QDs.

Fig. 2. (a) Linear absorption spectrum of the PbS QDs and (b) nonlinear transmission curve of the PbS QD-based SA.

Fig. 3. PbS QD mode-locked laser setup. Inset: digital photograph of the PbS QD mode locker fabricated on the fiber connector end.

Fig. 4. Mode-locked pulse characteristics. (a) Spectrum, (b) autocorrelation trace, (c) pulse train, and (d) radio frequency spectrum.

Fig. 5. (a) Average output power versus pump power in mode-locking states and (b) corresponding spectra at different pump powers.