Unveiling the advances and challenges in the development of Er³⁺-doped tellurite fiber with embedded Ag nanoparticles

Er³⁺-doped fibers are widely used as 1.55 µm broadband optical amplifiers. Tellurite glasses are particularly suitable as a gain medium due to their lower phonon energy and better rare-earth solubility compared to silica glass. Various strategies, such as reducing the OH content and co-doping with silver nanoparticles (Ag NPs), are attempted to improve the spectroscopic properties. However, maintaining the glass drawability into fibers when developing glasses with improved spectroscopic properties remains a significant challenge. Indeed, it is confirmed that NH₄HF₂ can be added into the tellurite glass batch prior to the melting to reduce OH⁻ content. However, the presence of remaining F in the glass is demonstrated to have a detrimental impact on the glass thermal properties preventing the drawing of this glass into fiber. The successful drawing of a single-index optical fiber from a tellurite glass preform heavily doped with Er³⁺ ions is reported for the first time. The Ag NPs are grown in the fiber using a thermal treatment at the glass transition temperature. The presence of the NPs is confirmed using a TEM and from the spectroscopic properties. The interaction between Er³⁺ ions and the Ag species offers potential for modifying the luminescence properties of the fiber.