A New Generation of Fibers Based on Yb³⁺-Doped Crystals Embedded in Phosphate Glass

Composites, defined here as crystals embedded in glass matrices, are promising materials for photonics applications, as they combine the properties of the crystals with the beneficial properties of glass (easy and cheap to process, drawing capability). Yb³⁺-ion doping is of particular interest for developing laser fibers emitting around 1 μm due to its simple energy levels, minimal excited-state absorption, and reduced quenching effects. Here, CaWO₄:Yb³⁺, Yb₂Si₂O₇, and LiNbO₃:Yb³⁺ crystals are prepared using a solid-state reaction and added into a phosphate glass matrix, the composition of which is selected based on its drawability. The spectroscopic properties of the composites are used to evidence the reaction of the crystals with the glass matrix during composite preparation. Partial to almost complete decomposition of the crystals occurs, depending on their composition and the composite preparation method, leading to the diffusion of the crystal elements into the glass network. The composite with embedded LiNbO₃:Yb³⁺ crystals is successfully prepared as a glass-based rod, which is drawn into a single-index fiber. Despite the presence of crystals in the fiber, light can propagate through the fiber, which emits light at ∼1 μm. This study demonstrates the potential of composite fibers for lasing applications.