A comparison of mode instability in Yb- and Tm-doped fiber amplifiers

We use a detailed numerical model of stimulated thermal Rayleigh scattering to compare mode instability thresholds in cladding pumped Tm3+-doped and Yb3+-doped fiber amplifiers. The Tm-doped fiber amplifies 2040 nm light using a 790 nm pump; the Yb-doped fiber amplifies 1060 nm light using a 976 nm pump. The predicted instability threshold of the Tm-doped fiber is found to be higher than that of the Yb-doped fiber, even though its heat load is much higher. We attribute the higher threshold in part to its longer signal wavelength, and in part to stronger gain saturation.