Rise of amplified spontaneous emission in high-power thulium-doped fiber lasers and amplifiers due to self-heating

The performance of high-power fiber lasers is limited by different thermal mechanisms such as a variation of spectroscopic quantities with temperature. In this paper, the effect of temperature dependent thulium cross sections on high-power thulium-doped fiber lasers and amplifiers pumped at 790 nm and operating above 1900 nm is investigated by means of numerical simulations and use of analytical models. The most significant self-heating effect was identified as an output signal power drop associated with increased amplified spontaneous emission caused by the temperature induced shift of the transparency wavelength of the single pass gain spectra.