GHz-Rate, Watt-Level Femtosecond All-Fiber MOPA System Based on Optoacoustically Mode-locked Soliton Fiber Laser With Apodization Filtering

High-power ultrafast fiber lasers are essential tools for a wide range of advanced applications. We report in this paper a GHz-rate, Watt-level all-fiber master oscillator power amplifier (MOPA) femtosecond laser system, seeded by an optoacoustically mode-locked soliton fiber laser. We show both in experiments and numerical simulations that the ubiquitous Kelly sidebands could lead to detrimental splitting of laser pulses at the compression stage through causing some distortions of the seed pulse envelope, and the use of an apodization filter can highly mitigate this impact of Kelly sidebands, resulting in improved output-pulse quality of the MOPA system. The system can deliver ultrafast pulses at 2.56-W average power and 1.879-GHz repetition rate, each pulse being of ∼97-fs duration and 1.4-nJ energy. This work provides an effective spectral engineering strategy for MOPA systems seeded by soliton fiber lasers.