Erbium-ytterbium doped fiber amplifier with suppressed Yb-ASE and improved efficiency

A new design of an erbium-ytterbium doped fiber amplifier is demonstrated. The amplifier contains a wavelength-tuned loop resonator for the 1 mu m signal. The amplified spontaneous emission (ASE) from Yb ions is used to stimulate a laser emission at several wavelengths from the 1 mu m band in the 1550 nm amplifier. The wavelength of this lasing is selected by introducing a spectral filter. The results show, that the efficiency of the amplifier at nominal 1550 nm wavelength can be increased by introducing a feedback loop with 1040 nm and 1050 nm filters. This loop also protects the Er-Yb amplifier from parasitic lasing and allows output power scaling without risk of self-pulsing at 1 mu m.