Numerical investigation of gain characteristics of Er3+/Yb3+ co-doped fiber amplifiers

In this work, a model for analyzing the gain characteristics of heavily Er³⁺/Yb³⁺ co-doped compact fiber amplifier is presented. Four-level rate equations and finite-difference beam propagation method are applied to simulate the optical field evolution along the active fiber. Based on this model, the influences of ion concentration, fiber length and pump power on the gain characteristics of Er³⁺/Yb³⁺ co-doped phosphate glass fiber amplifiers are theoretically investigated. Numerical results show that for a fiber length of 3.6 cm the internal gain can reach 27.2 dB with N _Er = 2.6 × 10²⁶ ions/m³ and N _Yb = 1.2 × 10²⁷ ions/m³ when pumped with 224 mW at 980 nm. The gain per centimeter is 7.56 dB/cm. The results can provide useful information to optimize the gain performance of these compact fiber amplifiers.