Fibre amplifier based on an ytterbium-doped active tapered fibre for the generation of megawatt peak power ultrashort optical pulses

Abstract

We report a new ytterbium-doped active tapered fibre used in the output amplifier stage of a fibre laser system for the generation of megawatt peak power ultrashort pulses in the microjoule energy range. The tapered fibre is single-mode at its input end (core and cladding diameters of 10 and ) and multimode at its output end (diameters of 45 and ), but ultrashort pulses are amplified in a quasi-single-mode regime. Using a hybrid Er/Yb fibre system comprising an erbium master oscillator and amplifier at a wavelength near , a nonlinear wavelength converter to the range and a three-stage ytterbium-doped fibre amplifier, we obtained pulses of energy and duration, which were then compressed by a grating-pair dispersion compressor with 60 % efficiency to a duration, approaching the transform-limited pulse duration. The present experimental data agree well with numerical simulation results for pulse amplification in the three-stage amplifier.