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 similar to 550 mu m(2). With a bend diameter of 600 mm, the bending loss of fundamental mode LP01 was measured to be < 10(-3) dB/m, in agreement with the corresponding simulation results, while that of higher order mode LP11 is >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-2 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. (C) 2016 Optical Society of America