The concept of laser glasses relates to the doping of a glass with rare-earth (RE) ions. These materials have been developed since 1961, when Nd3+ ions were first considered for laser applications. Rare earth doped glasses are attractive materials for the engineering of photonic devices, due to their easy processing, good thermal stability, excellent optical properties and high rare-earth ions solubility. If the rare-earth ions are located in crystalline phase of desired nature and structure, the spectroscopic properties of the glasses can be enhanced. Therefore, efforts have been focused on the development of new glass-ceramics (GCS) obtained from the heat treatment of glasses, as these engineered materials possess some of the glass properties (large flexibility of composition and geometry) but also some advantages of the RE-doped single crystals (high absorption and emission as well as long lifetimes). As the growth of crystals with specific crystalline phase cannot be controlled in glass, the other technique consists of adding RE doped crystals in the glass batch prior to or after the melting using the direct doping method.
In this presentation, we will review our work on the development of new glass-ceramics and composites suitable for the fabrication of optically active fibers. We will show that the heat treatment does not necessarily lead to the bulk precipitation of rare-earth doped crystals. We will explain all the challenges related to the addition of crystals in glass matrix. Finally, we will also discuss the challenges related to drawing these glass-based materials into fiber.