Numerical analysis and optimization of high power single frequency co-doped erbium–ytterbium fiber amplifier

This study presents a comprehensive numerical analysis of a high-power, fully monolithic, single-frequency Erbium–Ytterbium (Er-Yb) fiber amplifier tailored for free-space optical (FSO) applications. Focusing on Erbium Doped Fiber Amplification (EDFA), the investigation aims to understand its behavior and optimize key parameters for enhancing the amplification process. The proposed design consists of four all-fiber master oscillator power amplifier (MOPA) stages, achieving over 20 W of output power at 1550 nm. Specific fiber parameters—such as fiber length, EDF pump power, and signal power—were found to be critical for significantly enhancing EDFA gain. By carefully optimizing these parameters, the performance and efficiency of the amplifier were greatly improved. The four-stage MOPA architecture effectively increases the Brillouin threshold power, allowing for higher output power levels while maintaining single mode performance. Each amplification stage was meticulously designed, with the first stage achieving 280 mW output using a $5.5\mu m$ core diameter fiber and 800 mW pump power, the second stage producing 1.55 W output with a $10\mu m$ core diameter fiber and 10 W pump power, the third stage reaching nearly 5 W output using a $12\mu m$ core diameter fiber and 20 W pump power, and the final stage delivering 20 W output with a $16\mu m$ core diameter fiber and 70 W pump power.