Abstract: A method of molding low-temperature glass into a preform for formation by drawing into glass fiber, especially for transmission of mid-IR, involves casting a cladding glass into a mold cavity in the shape of the desired preform to form a cladding layer, and forming a glass core within the cladding layer, wherein the molten cladding glass is drained from the bottom of the mold cavity, forming an annular coating of cladding glass as an annular layer, and the core glass is quickly added within the annular cladding layer to form the glass core with the cladding layer thereabout.

Abstract: High optical quality glass windows, particularly of low melting and low viscosity glasses and substantially free of defects, particularly adapted for high energy laser applications, are made by stirring the molten glass during cooling without the use of a mechanical stirrer within the glass, by rotating the mold or crucible in which the glass is cooling, using a motion which is not entirely a circular and rotary motion.