PROCEEDINGS ARTICLE | February 19, 2009
Proc. SPIE. 7195, Fiber Lasers VI: Technology, Systems, and Applications
KEYWORDS: Optical fibers, Optical properties, Glasses, Ultraviolet radiation, Luminescence, Ions, Oxygen, Ytterbium, Aluminum, Absorption
In the last years, photodarkening in ytterbium doped silica based laser fibers turned out to be a critical factor for high
power laser action. Several investigations have been carried out in order to characterize the time dependent increase of
the fiber loss and to understand and model the complex optical phenomenon. Despite of progress in this field, there is
still a lack of data concerning the detailed influence of fiber composition and preparation process parameters as well as
concerning the role of atomic defects in the core glass.
Here we report on investigations about the photodarkening in dependence on the glass composition of the fiber laser
core. By MCVD, fibers with different codopants (additional to the active ytterbium doping) have been prepared in a
well-defined manner, regarding process parameters and glass composition, and comprehensively characterized. In
addition to the photodarkening measurements, further optical properties have been measured on the fibers and fiber
performs, which are related to the photodarkening effect: intensity and spectral behaviour of the Yb<sup>3+</sup> absorption and
emission in the NIR, cooperative visible fluorescence, UV absorption and UV excited visible emission. The concentration
of codopants which are commonly used for active and passive lightguide fibers (aluminium, germanium, phosphorus)
was systematically varied and correlated with the optical properties.
