A polarization insensitive infrared filter based on a liquid-crystal Fabry-Perot for electrically tunable spectral imaging

This paper presents a polarization insensitive infrared filter based on a liquid-crystal Fabry-Perot (LC-FP) developed for electrically tunable spectrum and performing high efficient imaging detection. Generally, the LC-FP filters are polarization sensitive optical devices, which means that filtering effect will be enormously influenced by ray polarization so as to lead to a low utilizing efficiency of incident energy. Therefore, it is of great significance to find an approach to improve or even solve the problem. The new type of infrared filter designed by us is mainly consists of a FP resonant cavity with a layer of zinc selenide (ZnSe) material as its substrate and a thin film of nano-aluminum (Al) material acting as its electrode and high-reflection mirror. Particularly, compared to the common filters, it has a multi-directional layer of ployimide (PI) film which can make the LC distributed along two mutually perpendicular directions so that the incident infrared light in different polarization orientations are able to be modulated. The experiment results indicate that the filter's polarization insensitivity is substantially improved, thus it can work well in various polarized infrared radiations, and obviously will have a broader prospect of application.