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Doped Nanoparticle Fibers
Liekki
(Lohja, Finland) has developed a new generation
of Direct Nanoparticle Deposition (DND) highly
doped ytterbium fibers with a significant improvement
in photodarkening performance. In a side-by-side
testing comparison, the Liekki DND fibers showed
less than half of the photodarkening degradation
of conventional fibers with similar doping density
made with the MCVD process commonly used in industry.
Photodarkening is an impairment in doped fibers
that manifests itself as increased attenuation
over time. In extreme cases, under certain pump
conditions, photodarkening results in considerable
incremental attenuation over a timeframe of minutes.
This severely limits the efficiency and lifetime
of fiber lasers and fiber amplifiers. Photodarkening
has recently been focused on ytterbium (Yb3+)
doped fibers for industrial and military lasers.
Although the underlying mechanism is not completely
understood, it is believed that the formulation
of the core composition, inhomogeneities and impurities,
the co-dopants used in conventional fiber processes
(such as MCVD), and unwanted rare earth dopants
are key factors to photodarkening.
Liekki has measured a significant improvement
in photodarkening in its new generation ytterbium
fibers with 1200 dB/meter core absorption at 976
nm. This improvement, which translates into a
significant benefit in product lifetime, was the
result of a very straightforward process improvement
that built on the flexibility of Liekki’s
DND process.
Visit www.liekki.com
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