Photodarkening (PD) is a critical issue for the lifetime and modal stability of high-power Yb-doped fiber (YDF) lasers. Despite extensive investigation in last decade, the physical origin of the pump-induced losses remains a subject of discussion. Currently, though PD-resistance can be improved via doping with P and/or Al, or co-doped Ce or other means, each mean has its own disadvantage. Therefore, higher stability of YDF laser requires further upgrading the PD-resistance of YDF. 
    Recently, researchers led by Professor HU Lili at Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, have provided a more effective method, i.e., the sol-gel method combined with high-temperature sintering, for preparing PD-resistant YDF. The results showed a better PD-resistance of Yb³⁺ /Al ³⁺ co-doped silica fibers. 
    In their experiment, the PD-induced loss of YDFs prepared by the sol-gel is lower than that of YDFs prepared by MCVD method under the same experimental conditions. The mechanism of the PD-resistance enhancement caused by the sol-gel preparation method was studied using cooperative luminescence spectra of Yb³⁺ ions, electron paramagnetic resonance (EPR) spectroscopy, and electron probe microanalysis (EPMA). A model of the color-center generation in the PD process was proposed to explain the mechanism of PD resistance improvement for the YDF fabricated via the sol-gel method. 
    Obviously, this work suggests that the sol–gel method may be effective for preparing PD-resistant YDFs. 
    This research, entitled "Photodarkening-resistance improvement of Yb³⁺ /Al ³⁺ co-doped silica fibers fabricated via sol-gel method" has been published in Optics Express. 
    This work was supported by Advanced Electronic Materials of the Ministry of Science and Technology, China (Grant No. 2016YFB0402201); National Natural Science Foundation of China (Grant No.61775224); National Natural Science Foundation of China (Grant No. 61505232).

Fig. (a) Schematic of the PD measurement. (b) Experimental setup for core-pumped fiber lasers.

Article website:
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-22-28506&origin=search

Contact:

Mr. Cao Yong
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: caoyong@siom.ac.cn