Single-mode Er:Yb fiber solutions for power scaling in next-generation 1.5 µm fiber laser systems

High-power fiber lasers and amplifiers operating near 1.5 μm are of growing interest for applications such as LIDAR, free-space optical communications, and emerging quantum technologies, where high output power must be combined with excellent beam quality. Erbium/Ytterbium (Er/Yb) co-doped double-clad fibers are the industrial standard at this wavelength, but achieving higher power levels remains limited by thermal load, parasitic Yb emission, and photodarkening mechanisms. In this work, we report recent advances in industrial-grade Er/Yb fiber designs aimed at addressing these challenges. We first present a newly developed 10/125 µm pure single-mode fiber, which delivers more than 30 W of output power with over 700 hours of stable continuous-wave operation, establishing a new benchmark for power scalability in this geometry. We then describe the latest improvements to existing designs, including preliminary results achieved with an optimized 13/125 μm single-mode fiber demonstrating output powers exceeding 60 W. To the best of our knowledge, this represents the highest reported power for a pure single-mode Er/Yb fiber. In addition, further enhancements are demonstrated in the 25/250 μm few-mode fiber design, paving the way for 100 W-class industrial systems. Finally, we discuss complementary investigations in alternative spectral regions and operating regimes enabled by the newly developed fiber.