Generation of 30-Femtosecond Pulses with an Energy of 6.3 nJ and an Average Power of 238 mW at 1.56-µm Wavelength in an All-Fiber Two-Stage Nonlinear Amplification Scheme

A compact, all-fiber source of few-cycle pulses at a wavelength of 1.56 μm has been created, based on a two-stage nonlinear amplification scheme in active erbium-doped fibers. Subsequent pulse compression in a silica-glass optical fiber with a large-mode-area (LMA) is demonstrated. The pulse spectrum undergoes coherent broadening due to self-phase modulation sequentially in the first and second amplification stages, based on a highly nonlinear erbium-doped fiber with positive group velocity dispersion. The final pulse compression occurs in a silica-glass LMA fiber with a core diameter of 39 μm, having negative second-order dispersion and lower nonlinearity. The low second-order and third-order dispersion in the active erbium-doped fiber enables effective compression of positively chirped pulses from its output to a duration of 30 fs, corresponding to approximately six wave cycles, in a 10 cm long LMA optical fiber. A maximum compressed pulse energy of 6.3 nJ at an average power of 238 mW is achieved by increasing the pump power of the second amplification stage to 1.2 W, while their peak power is about 100 kW.