The physical and optical properties of glasses in the As 40 S ((60 ‐ x:) Se x system where x = 0, 5,10,15, and 20 at. % Se have been investigated. The changes in the glass transition temperature, density, hardness, IR edge, and refractive index can be attributed to the presence of Se, which simply replaces S in these glasses. The glasses do not exhibit crystallization under the conditions used in this study, which is a desirable property from the viewpoint of flberization. Appropriate core and cladding glass compositions have been identified for fabrication of optical fibers with known numerical apertures. Furthermore, it has been shown that these glasses will not impart additional thermal or mechanical stresses in optical fibers made from these compositions.