Limitation on Effective Area of Bent Large-Mode-Area Leakage Channel Fibers

We investigate the bending characteristics of leakage channel fibers (LCFs) to achieve large mode area (LMA) and effectively single-mode operation with a practically allowable bending radius for compact Yb-doped fiber applications. Through numerical simulations, carried by the full-vectorial finite-element method, we present the limitations on the effective area of LCFs under bent condition and compare their limits with that of conventional step-index LMA fibers. Due to a better controllability of the low numerical aperture and a large value of the differential bending loss (~20 dB/m) between the fundamental and higher order modes in LCFs, the LMA of ~500 μm² (core diameter of ~36 μm) at 1064 nm can be achieved when the optimized LCF is bent into a 10 cm bending radius.