Generation of Q-switched and mode-locked pulses based on PbS/CdS saturable absorbers in an Er-doped fiber laser

Abstract

PbS/CdS quantum dots (QDs) have attracted much attention for application in photonic devices owing to their excellent saturable absorption properties. Here, highly monodisperse and perfect crystalline PbS/CdS QDs with bright infrared fluorescence emissions have been successfully synthesized by a low-temperature shell growth approach. By incorporating the PbS/CdS QDs into a thin film, sandwiched between a fiber connector as the saturable absorber (SA), stable Q-switched and mode-locked laser pulses have been observed. In the Q-switching operation, the maximum single pulse energy is measured to be 142 nJ with a pulse width of 3.3 μs and a repetition rate of 42.2 kHz, the best reported record for PbS/CdS-based SAs. With increasing pump power, we observe a stable mode-locked pulse train with a pulse width of 1.5 ps and a repetition rate of 24.2 MHz. These results prove that highly monodisperse PbS/CdS QDs prepared by low-temperature solution processes are a promising SA candidate to generate ultrafast laser pulses.