Ytterbium fiber system using a dispersion compensating fiber stretcher

Abstract

Ytterbium doped fiber amplifiers (YDFA) delivering high-fidelity sub 200-fs pulses are very attractive scalable sources for seeding and pumping of CEP stable DFG OPAs [1]. Replacing the grating stretcher optics by a fiber-stretcher in YDFA is of key importance for achieving a robust turn-key alignment-free all-fiber integrated design. A major problem when designing a fiber stretcher is to match the dispersion requirements of the compressor unit in the whole spectral range of the pulses. Two main approaches have been used in all-fiber integrated YDFA. One relies on nonlinear CPA [2] and uses a standard single mode fiber (SMF) stretcher in combination with a pair of gratings. The main disadvantage of this scheme is that the pulse fidelity is strongly degraded with a considerably portion of the pulse energy in the pulse pedestal [3]. The other approach uses a longer polarization maintaining (PM) SMF stretcher in combination with a grism compressor, while keeping the nonlinearities low throughout the amplifier, allowing for the generation of high-fidelity µJ level pulses [1,4]. In this contribution we report on a simplified monolithic YDFA scheme that uses a non-PM dispersion compensating fiber (DCF) stretcher [5] specially designed to match the dispersion of a compressor unit consisting of a pair of 1480 lines/mm gratings. The system delivers high fidelity >5 µJ sub-165 fs pulses. The experimental setup is shown in Fig. 1. It consists of an Yb-fiber oscillator, two PM SMF preamplifiers and a PM large mode area (LMA) fiber amplifier. The seed pulses are stretched in a hybrid fiber-pulse stretcher which consists of ∼8 m of PM980 fiber (pre-stretcher) followed by 100m DCF. After the stretcher a polarization controller and inline polarizer are used to ensure linear polarization in the amplifier.