Numerical investigation into splicing mismatch in a large mode area double clad fiber for high power lasers

In the present work, we conducted a numerical simulation to investigate the impact of fiber core misalignment on the output beam quality of large mode area double-clad fiber (DCF), which is commonly used in high-power laser systems. By employing the beam propagation method, we analyzed the influence of higher-order core modes and cladding modes on beam quality resulting from axial offset in the fiber core alignment. Specifically, we assessed beam quality using the M² factor as a function of core misalignment for two kinds of DCFs with core and inner cladding diameters of 25/395 μm and 20/395 μm. Our findings reveal that beam quality degradation emerged as a result of the significant influence of cladding modes with increasing splicing mismatch. We also identified acceptable tolerances of approximately 1.6 μm and 1.1 μm for 25/395 μm and 20/395 μm DCF, respectively, which correspond to around 6.4 % and 5.5 % of the core diameter.