Extremely Large Mode-Area Bent Hybrid Leakage Channel Fibers for Lasing Applications

In this work, we propose bent hybrid leakage channel fiber (LCF) designs to achieve effectively single-mode operation with low bending loss (BL) to overcome the limitation of mode area at the commercial packaging radius of 7.5 cm for doped fiber laser applications. Large-mode-area (LMA) designs are realized by introducing high-index rings around the low-index fluorine-doped silica rods to compensate the bend induced distortion. A full-vectorial finite-element method is used to obtain the bending characteristics of the proposed LMA hybrid LCF designs. The optimized hybrid LCF exhibits an effective mode area of 1406 μm ² for a core diameter of ~40 μm, good beam quality factor M² of 1.19 and differential BL ratio of 130 between higher-order mode (LP₁₁-like) and the fundamental mode (LP₀₁-like) at the bending radius of 7.5 cm.