Sub-30  fs pulse generation at 1.56  µm in all-fiber single- and double-stage nonlinear pulse amplification schemes with large-mode area solid- and hollow-core fiber compressors

We demonstrate a compact source of few-cycle pulses at 1.56 µm wavelength on the basis of single- and double-stage erbium fiber schemes of nonlinear pulse amplification with large-mode area (LMA) solid- and hollow-core fiber compressors. The source is designed according to the concept of self-phase modulation-induced spectrum broadening in normal-dispersion erbium-doped fiber (EDF) followed by ultra-broadband pulse compression in passive LMA fibers with negative second-order dispersion and low nonlinearity. Due to low second- and third-order dispersion of highly nonlinear EDF, just ∼10<i>c</i><i>m</i> long LMA fiber with a 39 µm wide solid core or ∼1<i>m</i> long LMA fiber with a 34 µm wide hollow core is sufficient for high-quality compression of positively chirped wideband pulses down to few-cycle duration. The shortest pulse width of 26.5 fs (≈5 wave cycles), as well as the highest pulse energy of 4.42 nJ, and average power of 168.4 mW are achieved in the double-stage setup, while maximum peak power of 100 kW together with improved pulse quality is obtained in the single-stage scheme. We believe that the developed source may be a prospective versatile tool for nonlinear visualization in bio-photonics and other applications requiring few-cycle wideband pulses, successfully competing with various fiber and solid-state counterparts.