Experimental investigation on optimal pump wavelength and efficiency thermal drifting in erbium-ytterbium co-doped fiber amplifier

The optimization selection of gain fiber length is an important step in designing fiber amplifiers. The influence of pump wavelength, fiber length, and temperature-induced wavelength drift on amplification efficiency and ytterbium-band amplified spontaneous emission (Yb-ASE) suppression of the erbium-ytterbium co-doped fiber amplifiers (EYDFAs) is experimentally analyzed in this work. Three commercial laser diodes (LDs) are thermal modulated to use as the wavelength tunable pump source. Results reveal that the optimal pump wavelength blue-shifts with increasing fiber length. The 940-nm LD demonstrates superior thermal stability, with efficiency fluctuations ≤0.1% under temperature variations (20°C to 30°C), significantly lower than other LDs. In addition, longer fiber lengths (>6 m) enhance efficiency for 940 nm pumping while suppressing Yb-ASE. An empirical formula is derived to predict the optimal pump wavelength for varying fiber lengths. The study identifies a total absorption range of 14 to 15 dB as critical for engineering optimization. These results provide practical insights for designing high-power EYDFAs with improved thermal management and efficiency in achieving stable, high-performance amplification systems.