This Yb-doped phosphosilicate fiber is designed for multimode operation in the 1 μm region. Manufactured under a carefully control process, the refractive index profile and core chemical composition allow high reproducibility. This ensures a reliable batch-to-batch consistency. With its output power of up to 4kw in multimode, this fiber allows the design of laser cavity without being limited by non-linear effects and transverse mode instabilities (TMI). It is ideal for industrial applications requiring high power output.