Investigation of the temperature dependence of core-pumped 2 µm thulium-doped fiber lasers

We investigated the temperature dependence of a multi-watt thulium-doped fiber laser. For high-power laser operation, thulium-doped fiber lasers are often pumped in the cladding by diode lasers operating at 793 nm to take advantage of the cross-relaxation effect. However, these diode lasers have to be temperature stabilized since the 3H4 absorption band in thulium-doped fibers is narrow and, therefore, not suitable for passively cooled setups. In contrast in-band pumping into 3F4 is an alternative, benefiting from a broad absorption band. The investigated thulium-doped fiber laser is core-pumped by an in-house built erbium:ytterbium-codoped fiber laser. In order to keep the surrounding temperature defined, the thulium-doped fiber was integrated into a metal plate with grooves and embedded in a thermal interface material. In addition, the metal plate was mounted on Peltier elements to control its temperature. During the experiment, the temperature of the metal plate was changed between -20°C and 80°C while the output power, slope efficiency and electrooptical efficiency of the thulium-doped fiber laser were measured. The performance of the laser versus temperature is reported and show minor dependence over a broad temperature range.