For the first time, a >10W single-mode Tm-doped amplifier is demonstrated. The all fiber format is optimized for single frequency signals in the 1800 - 2020 nm band. Natural Tm <sup>3+</sup> gain bandwidth is shifted towards the 1800nm and 2000nm region by selecting the fiber composition and length. No SBS-related issues were observed at levels of >10W of output power while using a single-frequency seed source. A simple model allowing the prediction of amplifier gain is presented.