The overall aim of this project is the fabrication of high-quality mid-infrared glasses and fibers for systematic investigation of the high power laser durability of mid-infrared glass types at AFRL. The findings advance the knowledge of the chemical processes during raw material thermal treatment and glass melting, which provides guidance for future experimental and theoretical investigations of high-quality and reproducible glass fabrication. The project focused on heavy metal oxide glasses such as zinc-tellurite and lead-germanate as they exhibit a combination of attractive properties such as high rare earth solubility, high refractive index and high crystallization stability, and are therefore promising candidates for mid-infrared laser and nonlinear optical processing applications. The challenge for the fabrication of these glasses is to achieve low hydroxyl group content while preventing the formation of lower valency heavy metals such as metallic tellurium and lead as both hydroxyl groups and metallic species cause detrimental absorption in the glasses, diminishing performance in particular under high power laser conditions. Another challenge is the fabrication of coreclad fibers with superior interface quality in a process that is suitable for high degree of automation for future manufacture. A new die design for dual-glass extrusion was investigated using zin-tellurite glasses. Using undoped zinc-tellurite core and cladding glass pair, the new dual-glass extrusion technique resulted in a unique combination of preform features such as complete fusion of the two glasses at the coreclad interface within the preform, small coreclad diameter ratio and consistent core diameter along the preform length.