Bend Insensitive W-type Single Mode Fiber with 30µm Mode Field Diameter

The all-fiber platform of laser system attracts increasing attention due to possibility to achieve outstanding characteristics simultaneously combined with usage convenience. However, the latter is minimized without providing flexible laser radiation delivery by using optical fibers. Passive large mode area (LMA) fibers should deliver a high-power beam without significant quality deterioration and maintain stable performance caused by environmental vibrations, which accompanies routine operations. The proposed approaches for the LMA fibers are chirally coupled core fibers, multicore fibers, low NA all-silica fibers, photonic crystal fibers and hollow core fibers. Most outstanding results shows that hollow core fiber structure allows to achieve core diameter about 60 µm with effectively single mode (ESM) operation at 1 µm, mode field diameter (MFD) about 40 µm [1] and fundamental mode attenuation about 0.017 dB/m. However, demanding manufacturing process together with necessity to seal input and output makes industrial application of hollow core fibers less attractive comparatively to the all-silica fibers. Typical core diameter for conventional all-silica low-NA LMA fibers, does not exceed 30 µm with MFD less than 20 µm. At the same time increase of the core diameter significantly increase the bending losses.