Single-mode large-mode-area laser fiber with ultralow numerical aperture and high beam quality

By using the chelate precursor doping technique, we report on an ytterbium-doped aluminophosphosilicate (APS) large-mode-area fiber with ultralow numerical aperture of 0.036 and effective fundamental mode area of ∼550 μm . With a bend diameter of 600 mm, the bending loss of fundamental mode LP was measured to be 100 dB/m at 1080 nm. Measured in an all-fiber oscillator laser cavity, 592 W single-mode laser output was obtained at 1079.64 nm with high-beam quality M of 1.12. The results indicate that the chelate precursor doping technique is a competitive method for ultralow numerical aperture fiber fabrication, which is very suitable for developing single-mode seed lasers for high power laser systems.