Coherent proprietary rare earth doping technology is used to deliver Er/Yb co-doped fibers with industry leading performance and reliability. This fiber feature a 20 micron diameter core and a 250 micron diameter cladding with a 0.09 NA. The fiber design has been finely optimized to deliver the best performance. PLMA-EYDF-20P/250-XPH is optimized to achieve tens of Watts of output power with high efficiency and suppressed 1 µm parasitic ASE, offering unmatched stability. The large core of the fiber allows for shorter fiber lengths in amplifier and laser systems to reduce the impact of non-linear effects. The fiber utilizes the latest fiber design and NuCOAT-FA coating technology to ensure excellent preservation of beam quality and extended operating light at the high power levels demanded by today’s industrial fiber laser applications.