Photodarkening-Free Yb-Doped Saddle-Shaped Fiber for High Power Single-Mode 976-nm Laser

We propose a novel saddle-shaped Yb-doped fiber design for high power generation in the spectral range near 0.976 μm. The fiber has a central single-mode part with a core diameter of approximately 12 μm and an ultra-thin silica clad of approximately 49 μm. At both ends of the fiber, the core/clad diameters were adiabatically increased up to 20/80 μm to be compatible with ordinary passive fibers. A monolithic 976-nm single-mode continuous wave laser based on the proposed fiber was created. The laser's power was a record high compared with all-fiber laser schemes, with an output power of 10.6 W. Utilization of a photodarkening-free core glass matrix has allowed us to demonstrate perfect long-term stability (without any power degradation) of the developed laser over 45 h.