Manipulating the Spectral-Temporal Characteristics of Multi-GHz Ultrashort Pulses by Leveraging the Nonlinear Phase Modulation and CW-Seeded Four-Wave Mixing

Ultrashort pulse fiber lasers with multi-GHz repetition rates have recently attracted significant attention in various fields. However, the parameter tunability of multi-GHz ultrashort pulse fiber lasers is inherently limited by their miniaturized design, particularly the central wavelength and transform-limited pulsewidth. To this end, here we propose a method for externally manipulating the spectral-temporal characteristics of multi-GHz ultrashort pulses by exploring continuous-wave (CW)-seeded four-wave mixing (FWM) and nonlinear phase modulation (NPM) driven by miniaturized mode-locked fiber laser with a multi-GHz fundamental repetition rate. We first conduct a theoretical investigation on the picosecond-pulse-driven CW-seeded FWM, and then study the NPM for manipulating the spectral-temporal performance of multi-GHz ultrashort pulses, i.e., associated with the CW-seeded FWM for pulsewidth tunability. Then, we perform experiments to validate the theoretical findings, and a pulsewidth tuning range of 598 fs–5.3 ps is achieved. Furthermore, a continuous wavelength tuning range from 1520 nm to 1550 nm is obtained. The experimental results show good agreement with the numerical simulation results. These efforts can provide a promising route to realize high-quality multi-GHz ultrashort pulses with flexible tunability of wavelength and pulsewidth through manipulating the spectral-temporal characteristics.