Sub-100-fs 1.87 GHz mode-locked fiber laser using stretched-soliton effects

Abstract

Current pulsed fiber lasers that are capable of delivering stable sub-100-fs pulses at megahertz repetition rates require intracavity pulse energies in the nanojoule range. Scaling these lasers to gigahertz repetition rates necessitates, therefore, very high average power levels and complex cladding-pumped configurations. Here we report a type of stretched-soliton all-fiber laser that generates broadband, soliton-like pulses at 1.55 μm with intracavity pulse energies of only tens of picojoules. In the laser cavity, strong dispersion management leads to a temporal breathing ratio of ~70, while the weak residual anomalous dispersion is perfectly balanced by the low Kerr nonlinearity, resulting in the formation of temporally stretched, hyperbolic-secant pulses. A lumped wavelength-dependent attenuator compensates for the effects of the gain filtering on the pulse spectrum, ensuring intracavity pulse self-consistency. This unique stretched-soliton mechanism, combined with a harmonic mode-locking technique based on intense optoacoustic interactions in solid-core photonic crystal fiber, yields for the first time stable gigahertz-rate, sub-100-fs, dispersive-wave-free pulse trains at moderate pump powers.