High-Precision Adjustment of the Refractive Index in High-Power Laser Fibers

A manufacturing chain that revolutionizes the production of fibers with highly precise refractive index matching is presented. By integrating iterative refractive index adjustments using reference fibers, a remarkable improvement in homogeneity, reaching 1E-5, was achieved. Conventional methods, such as the MCVD process, are limited to ~1E-4. This enhanced precision was demonstrated through meticulous measurements of core materials and validated in the final fiber. Importantly, the presented manufacturing method considers that the refractive index of fused silica is not a fixed property of the material. It depends on the thermal treatment history and the exact conditions during fiber drawing. This breakthrough manufacturing process ensures the reproducible manufacturing of fibers with fundamental mode guiding properties and mode field diameters exceeding 100µm. These specialized fibers play a pivotal role in scaling the power of fiber lasers for ultrashort pulse applications.