Temperature Dependence of Ytterbium-Doped Tandem-Pumped Fiber Amplifiers

The experimental results of a high power 1080-nm ytterbium-doped fiber amplifier (YDFA) tandem-pumped by a 1018-nm fiber laser for different temperatures have been reported. For a 1.64 m of active fiber, the power conversion efficiency (PCE) of our YDFA has reached 91.1% at room temperature. And for a 0.82 m of active fiber, i.e., half-length of 1.64-m active fiber, the PCE has been improved from 58.7% to 81.3% by increasing the heating temperature from room temperature to 302 °C. In other words, we have traded off $\sim 10$ % PCE for a 50% reduction of active fiber length. The temperature-dependent signal amplification model simulations agree well with the experiments. Our experimental and theoretical studies confirm that the temperature-dependent absorption and emission cross sections and the long-wavelength pump source are the physical causes of the improved PCE.