Modelling of photodarkening in Yb glass

Fiber lasers are known to suffer from induced optical losses at visible and lasing wavelengths (near 1.1µm), when operated at high powers. The phenomenon is commonly called photodarkening. Photodarkening can typically reduce the output power of a fiber laser with about 10% over 1000 hours.

Acreo and NKT Photonics (Crystal Fibre) carried out a joint research project to determine the nature of photodarkening, and on a longer perspective minimize the effect by optimizing fiber design and material composition.

The project was concluded in May 2008 when the PhD student Magnus Engholm presented his thesis at Mid Sweden University. Several mechanisms related to the formation of induced color centers were identified, which has paved the way to more efficient and power tolerant glasses.

Please refer to the publications below for project results. A 'popular' summary can be found in Aperturen.

In 2010, Magnus Engholm started the company Raybium AB, to provide high performance fibers to the laser industry.

Selected publications

(Invited) Engholm, M., Norin, L., "Ytterbium-doped fibers co-doped with Cerium: Next generation of fibers for high power fiber lasers?". Photonics West, Fiber Lasers. SPIE, San Fransisco, USA. January 2010.
Engholm, M. and Norin, L., "The role of charge transfer processes for the induced optical losses in ytterbium-doped fiber lasers". Photonics West, Laser Source Engineering. SPIE, San Jose, USA. January 2009.
Engholm, M., Materials Optimization for Optical Fiber Amplifiers and Fiber Lasers. PhD thesis. Mid Sweden University, Sundsvall, Sweden, 2008.
Engholm, M. and Norin, L., "Preventing photodarkening in ytterbium-doped high power fiber lasers; correlation to the UV-transparency of the core glass.", Optics Express, 16, 1260–1268. 2008.
Engholm, M. and Norin, L., "Reduction of Photodarkening in High Power Fiber Lasers". Photonics West, Proc. SPIE, San Jose, USA. January 2008.