High gain and output power from a novel 17/125-56/400 PM Yb-doped tapered double-clad fiber

A polarization-maintaining ytterbium-doped tapered double-cladding fiber was made from an aluminophosphosilicate glass preform, with core/cladding diameters of 17/125 mu m and 56/400 mu m at the small and large ends of the flared section, respectively. Amplifier gain exceeding 50 dB and average output power beyond 200 W were simultaneously achieved after the 1032-nm seed laser, while amplified spontaneous emission was measured < 1% of total output power. This fiber also yields an optical efficiency close to 90%, near diffraction-limited output with M-2 < 1.2 and polarization extinction ratio > 18 dB. The newly developed fiber holds the potential to combine two successive amplifier stages in a single device, with foreseen benefits for ultrafast fiber amplifiers and laser harmonics generation.