Experimental investigation on optimal pump wavelength in single frequency erbium-ytterbium co-doped fiber amplifier

Suppressing Yb-ASE to overcome the bottleneck effect is the key to optimizing the efficiency bottleneck of the Erbium-Ytterbium co-doped fiber amplifier (EYDFA). In this work, we use three typical commercial laser diodes (LDs) as pump sources to experimentally compare the efficiency with variations of pump wavelength in different fiber lengths. We found that the optimal pump wavelength of EYDFA has a blue shifting with the increment of gain fiber length. The functional relationship between the optimal pump wavelength and the length of gain fiber is predicted according to the experimental results. If the fiber length increases over 20 m, the amplification efficiency under 940 nm-LD pumping conditions is better than other pumping sources. It is necessary to consider appropriately extending the fiber length to optimal efficiency using a pump source with an offset pump wavelength (such as a commercial 940-nm LD). This work provides a reliable technical reference for the practical fabrication of high-power EYDFA.