Hybrid double-cladding Er/Yb co-doped fiber amplifier with Yb-ASE suppression

• The amplifier uses a hybrid fiber made up of two EYDFs with various core diameters. • The pump absorption is redistributed by hybrid fiber to avoid the Yb-ASE boosting. • The Yb-ASE is suppressed by 3 dB and the slope efficiency is enhanced by 1.6%. A single-frequency hybrid double-cladding Erbium-Ytterbium co-doped fiber amplifier (EYDFA) with Yb-band amplified spontaneous emission (Yb-ASE) suppression is demonstrated. Two segments of EYDFs, with core diameters of 6 μm and 12 μm, are fused in sequence to form a hybrid gain fiber. Theoretical analysis indicates that reducing the pump absorption in the initial part of the gain fiber is beneficial to avoid Yb-ASE boosting. A 4.79-W output laser with a linewidth of 1.67 kHz is obtained in the experiment. The Yb-ASE of the hybrid fiber amplifier is suppressed by more than 3 dB when compared to the uniform fiber amplifier with the same gain fiber length, and the slope efficiency is increased by 1.6 %. The loss characteristics of the hybrid gain fiber for backward transmitted light indicate its potential to suppress SBS effects. These results show a compact structure to suppress the Yb-ASE of the EYDF amplifier.