Er-Yb-doped double-clad fiber amplifier

We present model calculations of gain at 1550 nm for Er-Yb double clad amplifiers as a function of pump power, signal input power, fiber length and temperature. The calculated gain is ~20 dB for 6W pump for 20 mW input signal at 25 C. More than 10 W of amplified power can be obtained using 8m long fiber with ~25 W of pump power. The gain decreases with increasing input signal. We show that a high power Er-Yb co-doped double-clad fiber amplifier also exhibits high gain for Yb transition near 1060 nm. This is not unexpected since the input pump causes population inversion in Yb also. The high gain can lead to high peak power pulses at 1060 nm in the presence of small reflections.