30/900 Yb-doped Aluminophosphosilicate Fiber Presenting 6.85-kW Laser Output Pumped With Commercial 976-nm Laser Diodes

To incorporate sufficient pumping power, a large-scale Yb-doped aluminophosphosilicate (Al
₂
O3 -P
₂
O
₅
-SiO
₂
, APS) fiber with 30-μm core and 900-μ m inner clad in diameter, i.e., a 30/900 Yb-APS fiber, was theoretically designed and experimentally fabricated by using modified chemical vapor deposition system combining with chelate precursor doping technique. Analyzed by an electron probe microanalyzer, the dopant concentration of Yb
₂
O
₃
, Al
₂
O
₃
, and P
₂
O
₅
was estimated to be 0.14 mol%, 1.1 mol%, and 1.4 mol%, respectively. Based on an all-fiberized master oscillator power-amplifier laser setup directly forward pumped by commercial 976-nm laser diodes, 6.85-kW laser output at 1079.79 nm was achieved with an optical-to-optical efficiency of 67.1%, and the beam factor of M
²
was 2.38. The results indicate that large-scale Yb-APS fiber is quite competitive for high-power fiber laser development.