The sol-gel core was formed from aluminophosphosilicate
glass-doped with erbium and ytterbium. The P O dopant
served to reduce the SC-RTA process temperature and reduce
OH contamination (as shown by both optical and FTIR
spectroscopy [9], [11]), the Al O to control the Er environment
and the Yb O to improve the pump efficiency.
Fig. 2 shows the process used to prepare the sol. The silica
precursor was a solution of tetraethyl-orthosilicate (TEOS) in
isopropanol (IPA), while the dopant precursors were solutions
of phosphorus pentaoxide and aluminum, ytterbium and erbium
salts in IPA.