Rare-earth doped silica bers have already shown their huge potential in the telecom and sensing industry. The most successful of all rare-earths today is erbium, well known for its ideal characteristics for optical amplication in the telecommunications frequency window. Yet, interest is growing in the utilization of other rare-earth doped bers to reach wavelengths outside the standard telecom range of 1525 nm - 1565 nm. Other rare-earths include ytterbium, neodymium and thulium. Thulium has potential applications in optical amplication, remote sensing, optical radar (aka. lidar), spectroscopy and frequency conversion. Thulium has a primary emission band from 1700-2100 nm, depending the chemical compounds of the silica ber. The primary absorption bands are centered around 790 nm and 1560-1600 nm which oers the opportunity of high-power pumps. This ph.d. project is devoted to characterization of thulium in silica and the fabri- cation, design and characterization of coherent Distributed Feed-Back (DFB) ber lasers incorporating thulium as the active laser medium. Our recent results have proved that single-frequency, single-polarization, narrow-linewidth (tens of kHz) operation of thulium doped DFB ber lasers is possible. Demonstrations of single-frequency lasers have, until now, been achieved at 1740 nm, 1984 nm and at a record-breaking 2090 nm. The 1740 nm laser has been boosted to 60 mW of output power with a linewidth of only 3 kHz and implemented in a plug-and-play turnkey system with SMF28-APC output in collaboration with Koheras A/S (www.koheras.dk).