Ultrafast thulium-doped fiber lasers and their applications

Various studies have been reported on pulse generation via mode-locking in recent years due to their wide applications in several areas including remote sensing, material processing, medicine, range finding, and telecommunications. Here, mode-locked pulse trains operating in a 2-μm wavelength region were demonstrated using two types of newly developed saturable absorbers (SAs). Bismuth (III) telluride (Bi2Te3) and spent coffee ground (SCG)-based SAs were developed based on the liquid exfoliation technique. Both compounds were embedded into polyvinyl alcohol to form an SA film with a modulation depth of 30%. The mode-locked operations were successfully realized with the use of both types of SA in the thulium-doped fiber laser (TDFL) cavity. For instance, by incorporating the SCG-based SA into the TDFL cavity, the mode-locked pulse train operating at 1954nm was realized within a pump power range from 455 to 748mW. At the maximum pump power, the average output power and repetition rate were 8.0mW and 8.2MHz, respectively. It is also shown that SCG performed better than Bi2Te3 in terms of output power and pulse energy. These results show that both SAs can be an alternative SA material for generating a reliable and stable pulsed fiber laser, particularly in the 2.0μm wavelength region.