A polarization-maintaining 1.5 μm mode-locked fiber laser with a fundamental repetition rate of 1.5 GHz

We report a 1.5 μm passively mode-locked fiber laser with a fundamental repetition rate of 1.56 GHz. The fiber laser is constructed by an oscillator and a single-stage fiber amplifier, with all polarization-maintaining optical components. The net dispersion of the oscillator is calculated to be approximately -1514.5 fs², enabling the generation of soliton pulses that possess a broad 3dB bandwidth of 12.9 nm. Owing to the high reflectivity of the oscillation, the threshold of soliton mode-locking pulse is reached at around 130 μW, under a pump power of 250 mW. Subsequently, the output signal power of the oscillation is efficiently amplified to around 2 mW with the suppression ratio of amplified spontaneous emissions more than 20 dB. The signal generated from this passively mode-locked fiber laser exhibits remarkable power stability, maintaining mode-locked lasing operation for nearly 22 hours. These results present a practical approach to realize a stable GHz-level repetition rate mode-locked fiber laser, which is promising to be employed in optical frequency combs, spectral diagnostics, and LIDAR etc.