Generally, broadband absorbers has much non-saturable loss and low laser damage threshold, which limits the average output power of the fiber lasers mode locked by broadband absorbers. Exceptions are the absorbers in evanescent wave mode locking, in which way only weak laser passes through the absorber section. However, evanescent wave mode locking method needs to change the original structure of the fiber. Most of the commercial fiber-lasers adopt face-to-face passive mode-locking. Therefore, it is important to increase the damage threshold of the broadband absorbers. In this study, for the first time, a single-walled carbon nanotube (SWNT)-doped sol-gel glass composite absorber is fabricated using a low-temperature sol-gel method. The main component of the sol-gel glass is compact amorphous inorganic silicon-dioxide, which has high laser-damage threshold. The SWNT-doped sol-gel glass is integrated into the erbium-doped fiber (EDF) laser and mode-locking occurs at 1559 nm. The shortest pulse duration is 456 fs, and the maximum average output power is 110.65 mW. Compared to most EDF lasers based on broadband absorbers, the average output power is one of the highest values. The results indicate that encapsulating absorber in the inorganic sol-gel matrix is a promising method for fabricating high power ultrafast fiber laser type absorbers.

Characterization of SWNTs. (Image by XIOPM)