Effect of thermal history on the material structure and optical performance of Yb-doped fibres

To investigate the effect of thermal history on the material structure and optical performance of Yb-doped fibres, Ybdoped preforms were subjected to annealing. Revealed by EPMA , the composition of the fibre core becomes more uniform after annealing. In addition, the Si–O–Si bond angle continues to decrease, accompanied by an increase in the content of Si–Al, Si–P and Si–Yb bonds. Laser experimental results indicate that the attenuation of 20/400-μm fibres at 1080 nm decreases from 63 to 40 dB/km after annealing at 900°C for 3 h. The annealed fibres exhibit improved beam quality, with the M2 parameter decreasing from 1.37 to 1.24 and the slope efficiency increasing from 75% to 77%, as observed in a Master Oscillator Power Amplifier fiber laser setup. This study comprehensively shows that suitable annealing can change the internal structure of the fiber, reduce the fiber atttenuation, improve the beam quality and the slope efficiency.