Influence of Pedestal Fiber Splice on Tm-Doped Fiber Laser Performance

The influence of Tm-doped pedestal fiber splice on the output performance of a large-mode-area (LMA) Tm-doped fiber laser (TDFL) has been investigated. Arc-fusion induced refractive-index deformation leads to laser leakage from the core to the pedestal, resulting in a periodic decrease in the output power of TDFL. Based on the measured refractive-index of splice with different arc-fusion parameters, the influence of the Tm-doped pedestal splice on laser propagation was analyzed using the beam propagation method (BPM). The simulation results indicate that optimizing the arc-fusion parameters can improve the efficiency of laser coupling into the fiber core at the splice. Experimental comparisons were made to assess the impact of different arc-fusion parameters on laser performance. By optimizing arc-fusion parameters of the TDFL, the near-periodic power degradation is reduced effectively. A hundred-watt-level all-fiber TDF setup was established. Compared to the initial splice, the optical conversion efficiency increased from 39.6% to 48.4% and the beam quality factor M-2 was reduced from 10.55 to 2.17 in the horizontal direction and from 11.89 to 2.26 in the vertical direction. Understanding these mechanisms behind the abnormal power fluctuations hold practical value for the design of TDF pedestal fiber and further power scaling.