Development of Mid-Infrared Glass Lens based on TeO2-ZnO-La2O3 Glass System

Investigation on thermal, mechanical and optical properties is of utmost importance in designing optical glass for the development of mid-infrared camera module. In this study, two tellurite glass systems, namely the ternary TeO2−ZnO−La2O3 (TZL) system modified with various concentrations of ZnO and the quaternary TeO2−ZnO−La2O3−MoO3 (TZL-Mo) system incorporated with various concentrations of MoO3, were fabricated using the melt-quenching method for mid-infrared optical glass lens. The effects of ZnO and MoO3 contents on characteristic properties of the glasses were investigated. The thermal stabilities were found to be > 117 °C in both the glass systems. The coefficients of thermal expansion decreased from 14.26 to 12.6 and 13.91 to 13.08 (×10-6/K) with increasing the ZnO and MoO3 contents in the TZL and TZL-Mo glass systems, respectively. Notably, the thermal stability and coefficient of thermal expansion were improved considerably with the addition of MoO3 to the ternary TeO2−ZnO−La2O3 (TZL) tellurite glass composition. The Knoop hardness values increased from 339 to 384 and 326 to 371kgf/mm2 with increasing the contents of ZnO and MoO3, respectively. The glass composition of 60TeO2−30ZnO−7La2O3−3MoO3 was selected to produce molded glass lens using the glass molding process because of its attractive thermal and optical characteristics. The average transmittance of the glass in the range of 3–5 μm was found to be 91% after the anti-reflection coating process. Finally, the TZL-Mo3 aspherical lens was developed with diameter of 22mm for mid-IR camera module.