Thermally Matched Chalcogenide Glasses with High Refractive Index Contrast for Infrared Graded-Index Lenses

Abstract

Infrared graded-index (GRIN) lenses are desirable for realizing miniaturization and lightweight of infrared imaging systems. Chalcogenide glasses have excellent infrared transparency, good rheological property, and large refractive index range, making them preferred materials for infrared GRIN lenses. In this work, aiming to find thermally matched chalcogenide compositions with high refractive index contrast for preparing GRIN glasses by the stacking diffusion approach, we investigated characteristic temperature, thermal expansion coefficient and refractive index of Ge-As-Se and Ge-As-Se-Te glasses, optimized the glass compositions, and evaluated the feasibility of preparing GRIN glass using the optimized chalcogenide glass powders. It is found that Ge20As20Se20Te40 and Ge12As22Se66 glasses have similar softening temperature (247oC vs 249 oC), reasonably difference of thermal expansion coefficient (3.8 ppm/K), and large refractive index contrast (~0.48). The glass powders with composition xGe20As20Se20Te40-(1-x) Ge12As22Se66 can be hot-pressed into glass disks with good transmittance at the same temperature and pressure. Graded refractive index profile is formed near the interface between the layers after the co-pressed glass is thermally treated. These results demonstrate the prospect of the compositions for preparing infrared GRIN glasses.

Keywords: Graded-index lens, Chalcogenide glass, Hot pressing, infrared imaging