On the Effect of Low Temperatures on the Maximum Output Power of a Coherent Erbium-Doped Fiber Amplifier

The influence of low temperatures on the performance of a high-power single-frequency fiber laser amplifier is evaluated with a numerical simulation. Cooling the fiber can allow to take advantage of both higher damping of the acoustic waves in the silica glass, and higher laser efficiency. We first report on the measurement of the stimulated Brillouin scattering (SBS) threshold in a silica fiber as a function of the temperature from 300 K down to 77 K. We then present the measurements of small-signal absorption and gain spectra of an erbium(Er) doped alumino-phosphosilicate fiber, at room temperature and liquid nitrogen temperature. Based on these data, we derive a numerical study of the combined effects of cooling on the SBS threshold and the amplifier efficiency, and conclude on the interest of this technique for SBS limited high power Er-doped fiber amplifiers. The temperature increase caused by the pump laser in the fiber core is also addressed.