YbPO₄ crystals in as-drawn silica-based optical fibers

MCVD germanosilica glass embedded with YbPO₄ crystals were for the first time drawn into optical fibers. Solution doping was used to embed the crystals in the silica soot prior to the collapsing step. We demonstrate, using scanning/transmission electron microscopes and confocal Raman microscope, that YbPO₄ crystals survive not only the MCVD process but also the drawing process despite the high temperature involved (up to 2100 °C) during fabrication processes. The fiber contains 100 nm-crystals with the same composition and structure as the as-prepared crystals. During the drawing process, these crystals tend to have a preferential orientation of their c-axis along the drawing direction. These results open a new route to fabricate glass-based composite fibers containing crystalline particles without additional post heat-treatment.