Researchers have developed a novel tunable optical filter for smart IR night vision imaging systems. They used a new phase changing material (PCM) – GSST, that undergoes a phase transition at a higher transition temperature (approx. 300°C). It is synthesized by partially substituting selenium for tellurium, resulting in a composition of Ge2Sb2Se4Te1.
The phase changing material has a lower optical loss and a larger index contrast between the two states compared to Ge2Sb2Te5, making it better suited for optical applications. It is possible to implement a pixelated version of the proposed filter in smart IR systems to enable real-time reconfigurability.
The proposed filter design is a Metal-Insulator-Metal (MIM) cavity that can be easily fabricated as stratified layers without any complex patterning processes. Even though MIM has been used previously in tunable optical filter designs with phase changing material, none of them presented a systematic approach for designing these structures. The researchers introduce a well-formed theory for designing MIM and incorporating PCMs that can be easily adapted to other wavelengths, configurations, and applications.