Effect of P-to-Rare Earth Atomic Ratio on Energy Transfer in Er-Yb-Doped Optical Fiber

Erbium (Er)- and Ytterbium (Yb)-doped optical fibers (EYDFs) have been used in various industrial fields as the only technology suitable for >1 W high-power amplifiers in the 1550-nm band. The output power is mainly limited by unwanted 1-mu m band amplified spontaneous emissions from excited Yb3+; however, the factors affecting the output performance remain unclear. Here, we quantitatively and systematically reveal that the Phosphorus (P)-to-rare earth atomic ratio in the EYDFs has an optimal value for achieving the best output performance of EYDFs. We experimentally evaluated the quantitative relationship among co-dopants by fabricating preforms, drawing them as fibers, and measuring the amplification characteristics. At an appropriate Er concentration (0.3-0.5 wt%), a pump-to-signal conversion efficiency of 45.4% was obtained when the P/(Yb + Er) atomic ratio was around 25. This study paves the way for energy saving in high-power applications, such as high-speed optical wireless communication and long-distance optical ranging.