Yb-ASE Suppression in Single-Frequency Hybrid Double Cladding Erbium-Ytterbium Co-Doped Fiber Amplifier with SMS Structure

A hybrid double cladding erbium-ytterbium co-doped fiber (EYDF) amplifier with a single-mode-multimode-single-mode (SMS) active fiber is demonstrated in this study. The hybrid gain fiber with an SMS structure is composed of two kinds of EYDFs with 6 and 12 mu m core diameters. The transmission spectra of the SMS fiber structure were theoretically analyzed and the simulation results indicated that the maximum loss in the 1 similar to 1.1 mu m band where the Yb-band amplified spontaneous emission (Yb-ASE) located, was much larger than that of the 1.5-mu m band because of the wavelength difference. The power performance and spectra properties of the hybrid fiber amplifier were theoretically and experimentally analyzed and compared with a typical uniform fiber amplifier under the same conditions. The experimental results demonstrated that this hybrid fiber amplifier can suppress the Yb-ASE by over 12 dB and increase the slope efficiency by more than 2%, but the ASE in the 1.5-mu m band increases by 2 similar to 3 dB. This work provides a possible method to enable EYDF amplifiers to suppress the Yb-ASE and overcome the pump bottleneck effect.