Towards tuneable thin film filters with the use of liquid crystals

For many years, liquid crystals have been used in display devices. In the present study, the usability of liquid crystal thin films for tunable optical filters has been investigated. In contrast to display devices, where the effect of polarization is utilized, the change of the refractive index by an applied electrical field was used to modify the spectral properties. A single-cavity Fabry-Perot filter is presented, which is based on a liquid crystal film located between two ITO-substrates each coated with dielectric mirrors stacks. A fast switching in the msec range could be demonstrated with the thickness of the liquid crystallayer being less than 1 mm. Tunable color filters for the colors red, green and blue are presented. A tuning range of some 10 nm has been obtained.