Corrosion at the surface of chalcogenide glass microspheres

Glasses used in photonics research and industry are required to be homogeneous and stable. Our study of chalcogenide microspheres indicates that significant deterioration can take place at the surface of such micro-optics in a few years at normal environmental conditions. Chalcogenide glass (Ga ₂S ₃:La ₂S ₃, 70:30 (GLS)) microspheres of order one hundred microns in diameter have been focused ion beam (FIB) milled and imaged to show material and morphological changes at the surface. Such microspheres are used as whispering gallery mode cavities for micro-sensors, for devices in optical communications and, with rare earth doping, for micro-lasers. It is the optical quality of the glass at, and near, the surface, that is most important in these applications. With the surface corrosion shown, the Q of a whispering gallery mode resonator based on such a microsphere will reduce dramatically over time. More generally, the result may have significant implications for the production, storage, and usage of uncoated chalcogenide micro-optics. The FIB technique emerges as an additional tool for characterizing glass morphology and homogeneity.