10 kW-level Output power from a Tandem- pumped Yb-doped aluminophosphosilicate fiber amplifier

• A large-scale Yb 3+ doped aluminophosphosilicate fiber was theoretically designed and experimentally fabricated. • The characteristics of active fiber for amplifier stage is reported. • A 10 kW-level output power fiber amplifier with domestic fiber based on tandem-pumping was obtained. In this paper, we present a 10 kW-level output power fiber amplifier based on tandem-pumping. The characteristics of active fiber for amplifier stage is reported. To ensure adequate absorption of tandem pumping light in relatively short fiber length, a large-scale Yb 3+ doped aluminophosphosilicate (Al 2 O 3 -P 2 O 5 -SiO 2 , APS) fiber with 50 μm core and 400 μm inner-clad in diameter, i.e., a 50/400 Yb-APS fiber, was theoretically designed and experimentally fabricated by using modified chemical vapor deposition system combined with chelate precursor doping technique. The measurements showed that the dopant concentration of Yb 2 O 3 , Al 2 O 3 , and P 2 O 5 was estimated to be 0.17 mol%, 1.4 mol%, and 1.5 mol%, respectively, and the absorption coefficient of the fiber was about 0.77 dB/m at 1018 nm. The amplifier stage with this 40 m Yb-APS fiber tandem-pumped by 1018 nm fiber laser, delivered 9.82 kW laser output at 1080.08 nm with an optical-to optical efficiency of 86.8%. The knowledge of the characteristics of the Yb 3+ doped APS fiber can usefully guide future design of high output power fiber amplifier based on tandem pumping.