원적외선 대역 결상 렌즈용 칼코지나이드 유리의 조성 최적화

Compositional Optimization of Chalcogenide Glasses for Use as Imaging Lenses in the Long-Wavelength Infrared Range

Demand on thermal camera capable of visualizing spatial distribution of infrared radiation especially in the long-wavelength infrared (LWIR; 8-12 ㎛) range is rapidly increasing in diverse civilian sectors including, for example, mobile electronic devices like smartphone. Unlike the traditional military applications, not only size miniaturization and performance enhancement but also cost reduction becomes more crucial in these civilian applications. As such, as compared with its crystalline counterparts, chalcogenide glass turns out to be more promising as LWIR-transmitting lenses working in numerous civilian sectors in view of its inherent compositional flexibility as to adjusting thermal and optical properties. In addition, its viscoelasticity upon mechanical loading at a proper temperature makes it much more competitive in saving processing cost: Specifically, chalcogenide glass lenses can be mass-produced via precision glass molding (PGM) technique. Optical characteristics prioritized in lens performance can also be engineered via compositional finetuning over a wide glass forming region reaching far off-stoichiometric compositions. These merits enable extra degrees of freedom in designing lens assembly well-functioning to a desired level of performance. In this article, we employ ternary Ge-Sb-Se glass as a representative chalcogenide glass for the LWIR lens applications, and review its composition-dependent behaviors of thermal, mechanical and optical properties. These experimentally verified compositional dependences are then elucidated in terms of unempirical glass structure related parameters in an effort to provide guidelines for compositional engineering of other chalcogenide glasses. In addition, we present some exemplary cases of compositional optimization applied to chalcogenide glasses containing Ge and Sb, which are mainly aimed at broadening the LWIR Abbe diagram towards the high-dispersion side.