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Effective photodarkening suppression in Yb-doped fiber lasers by visible light injection

: Piccoli, Riccardo; Robin, Thierry; Brand, Thomas; Klotzbach, Udo; Taccheo, Stefano

Postprint (1 MByte; PDF; )

Optics Express 22 (2014), No.7, pp.7638-7643
ISSN: 1094-4087
Journal Article, Electronic Publication
Fraunhofer IWS ()
aluminum; excited states; fiber laser; silicates

Al-silicate fibers have excellent manufacturing quality. Unfortunately, high-Yb doping concentration may be limited by severe losses induced by photodarkening phenomenon. In this paper we demonstrate for the first time that Al-silicate Yb-doped fibers with highinversion and doping concentration above 1 wt% can be successfully used by implementing a simple optical bleaching scheme. A co-injection into the active fiber of a few mW of light at around 550 nm wavelength successfully eliminates almost all photodarkening induced losses. We demonstrate operation at above 90% of the pristine output power level in several lasers with up to 30% Yb ions in the excited state. These results may allow to use Yb-doped Al-silicate fibers with doping level increased by one order of magnitude. Finally, we provide a comprehensive picture of main parameters affecting photobleaching performance and, to the best of our knowledge, we report the first quantitative measurement of the Ytterbium excited state absorption cross-section in the visible range.