Compact GMN amplification system based on an all-PM SESAM-assisted figure-9 Er:fiber laser

Typical all-polarization-maintaining (PM) figure-9 fiber lasers are promising for generating high-repetition-rate pulses due to their excellent long-term stability, but their development is limited by the cavity length. Herein, we propose a semiconductor saturable absorber mirror (SESAM)-assisted figure-9 Er:fiber laser that operates in the harmonic mode-locking (HML) regime to generate high-repetition-rate ultrashort pulses. By leveraging the intrinsic nonlinear reflectivity of the SESAM for pulse shaping and optimizing the pump power, the repetition rate of the pulses can be adjusted from 43.478 MHz to 645.16 MHz (15th harmonic). Notably, pump-induced gain competition stabilizes the central wavelength near 1532 nm for the 13th and higher-order harmonics. In addition, the joint gain-managed nonlinear (GMN) amplification delivers pulses with an energy of 8.65 nJ and a duration of 102 fs, achieving a spectral coverage exceeding 100 nm, which corresponds to a 3 dB bandwidth of 67.54 nm. To our knowledge, 645.16 MHz and 102 fs represent, respectively, the highest repetition rate and the shortest pulse duration in the GMN amplification within the 1.5 µm region. Our results establish a foundation for investigating high-energy, broadband pulses in 1.5 µm GMN systems.