In this presentation the
research activities in the Photonics Group of Aalto
University will be summarized. Our research focuses on
specialty fibers and planar nanophotonics on glass and Si.
On specialty fibers, the
photo darkening effect in ytterbium-doped fibers will be
discussed. Photo darkening is a
detrimental
light-induced effect that poses a threat to the reliability
of high-power fiber lasers through progressive growth of
loss, which degrades the laser performance. Our
recent results on studies of the photo darkening effect in commercially
available cladding-pumped ytterbium-doped fibers will be
presented. Progress
of the photo darkening and thermal recovery of the induced
losses have both been measured in-situ by monitoring a weak
core-propagating probe signal.
On planar Si-nanophotonics
our recent theoretical and experimental results on Si-slot
waveguides will be presented. In our approach we combine
the Si-nanophotonics platform with atomic layer deposition (ALD).
This provides some interesting new possibilities, since ALD
can be used to fill the narrow slots as
the ALD grown films are
extremely conformal over the surfaces. Our target
applications are in all-optical signal processing devices.
In our glass based
nanophotonics we focus
on silver
nanoparticles embedded in glass, e.g., for biomedical
applications.
Glass-embedded silver nanoparticle patterns have been
fabricated by masked silver-sodium ion-exchange process
followed by etching to partially reveal the particles for
surface-enhanced Raman scattering (SERS). The intensity of
the enhanced Raman signal is comparable to that of the
fluorescence, and the detection limit of 1 nM for Rhodamine
6G has been achieved. Nanoparticles can be formed in a
glass of high optical quality and have potential to be
integrated with optical waveguides for a guided-wave sensor
chip.