Monolithic thulium-doped fiber laser

In this contribution we report and discuss the results of laser characterizations of experimental thulium-doped optical fibers. These active fibers were fabricated in house and were tested in two laser systems to verify their characteristics. The first one, a monolithic fiber laser, was of great interest to us due to its potentially lower overall resonator losses, improved laser lifetime and better robustness. The compact laser cavities with a Bragg gratings inscribed directly into the active optical fiber differs to the second laser system where the Bragg gratings were inscribed into a passive fiber which had to be spliced to the active fiber. The tested fibers were manufactured by the modified chemical vapor deposition method and a solution-doping of thulium ions with Al₂O₃ or alumina nanoparticles, respectively. We focused on comparison of laser output powers, slope efficiencies, and laser thresholds for particular thulium-doped fiber in different laser configurations.