Ultrashort Pulse Generation With a Black Phosphorus Thin Film Absorber

This paper presents a mode-locked fiber laser incorporating a black phosphorus (BP) thin film as a saturable absorber (SA), with polyvinyl alcohol (PVA) serving as the host material for BP compound integration in the thin film fabrication. The fiber laser's resonant cavity spans a total length of 114 m, yielding a soliton pulse train operating at a repetition rate of 1.78 MHz. Integration of the SA, featuring a modulation depth of 2.8%, into the Erbium-doped fiber laser (EDFL) cavity results in the emission of stable mode-locked pulses working at 1572.62 nm, with pumping power ranging from 149.8 to 217.6 mW. The laser system produces a pulse train characterized by a pulse duration of 3.36 ps, reaching a maximum pulse energy of 3.0 nJ, average power of 5.33 mW, and peak power of 0.88 kW at 217.6 mW pump power. These results underscore the efficacy of the proposed BP-based SA, demonstrating properties comparable to the conventional SAs. The effective mode-locking operation and favorable optical properties exhibited by the BP thin film establish a robust foundation for their prospective utilization in the field of ultrafast photonics.