Q-Switching Pulse Generation with Thulium-Doped Fiber Saturable Absorber

A simple Q-switched erbium-doped fiber laser (EDFL) is proposed and demonstrated by using a 2-m-long thulium-doped fiber (TDF) as a passive saturable absorber (SA). The EDFL generates a Q-switching pulse operating at 1557.6 nm at a threshold pump power as low as 20.0 mW. The Q-switching operation is maintained before disappearance when the pump power is above 33.7 mW. This is due to the fact that the TDF SA could not fully recover in time after a pulse and less gain population is excited before the next pulsing. With the SA, the laser produces a stable pulse train with repetition rate ranging from 3.9 to 12.7 kHz and the pulse width reduces from 20.6 to 7.4 μs while varying the 1480 nm pump power from 20 mW to 33.7 mW. The maximum pulse energy of 22.8 nJ is obtained at a pump power of 20.0 mW. The laser is perspective for technology processes and medicine.