  Developing of new rare-earth (RE)-doped optical fibres for power amplifiers
and lasers requires continuous improvements in the fibre spectroscopic
properties (like shape and width of the gain curve, optical quantum efficiency,
resistance to spectral hole burning and photodarkening...). Silica glass as a
host material for fibres has proved to be very attractive. However, some
potential applications of RE-doped fibres suffer from limitations in terms of
spectroscopic properties resulting from clustering or inappropriate local
environment when doped into silica. To this aim, we present a new route to
modify some spectroscopic properties of RE ions in silica-based fibres based on
the incorporation of erbium ions in amorphous dielectric nanoparticles, grown
in-situ in fibre preforms. By adding alkaline earth elements, in low
concentration into silica, one can obtain a glass with an immiscibility gap.
Then, phase separation occurs under an appropriate heat treatment. We
investigated the role of three alkaline-earth elements: magnesium, calcium and
strontium. We present the achieved stabilisation of nanometric erbium-doped
dielectric nanoparticles within the core of silica fibres. We present the
nanoparticle dimensional characterisation in fibre samples. We also show the
spectroscopic characterisation of erbium in preform and fibre samples with
different compositions. This new route could have important potentials in
improving RE-doped fibre amplifiers and laser sources.
