Time-domain flexible pulse fiber laser generation and high-power evolution based on inter-band excitation of lead sulfide nanoflakes

Ultrafast photonics has become an interdisciplinary topic of great significance owing to the spectacular development of compact and efficient ultrafast pulse generation. Saturable absorbers (SAs) are the kernel for ultrafast pulse generation. However, the conventional SAs performance is plateauing owing to the complex preparation process, the diversification of demand for pulse width, and the relatively low laser output at mill watt level. Herein, high-quality comprehensive vertical Lead Sulfide (PbS) nanoflakes were synthesized by the physical vapor deposition (PVD), and a home-build handy dry-transfer system was used to simplify the fabrication process of PbS saturable absorbers device (PbS-SAs). Total-energy calculations by the density functional theory (DFT) were performed to further understand the saturable absorption characteristic of PbS. A time-domain flexible erbium-doped fiber pulse laser has obtained Q-switched, mode-locked, and highest 14th order harmonic mode-locked pulse. Based on a selected mode-locked operation, an all-fiber master oscillator power amplifier (MOPA) pulse laser system was proposed and demonstrated. The integrated system based on PbS-SAs achieved a time-domain flexible fiber pulse laser, high order harmonic mode-locked pulse, and a picosecond pulse (∼287 ps) with high average power of ∼57.5 W and peak power of ∼13.7 kW at the central wavelength of 1562 nm. This research not only provides a simple manufacturing process for high uniformity SAs devices but also greatly improves output power, which would attract interest in exploring the unique properties of nanocomposite SAs for photonic applications.