Fabrication and characterization of new optical films based on UV curable cholesteric liquid crystal’s for LCD application

Abstract

The liquid crystal display is one of the most important optical display systems, which is primarily due to the superior properties of the LCD; flat panel, light weight, high definition, low driving voltages and relatively lower power consumption. The liquid crystal is the most essential component in the LCD system and has diverse application other than the LCD systems, like medical field as well as the electronic field. Cholesteric liquid crystal (CLC) polarizers have attracted much attention and been extensively studied for their unique properties in the liquid crystal displays. LCD devices incorporated with CLC have a very important feature to enhance the brightness of the devices through a light recycle. CLCs reflect circularly polarized incident light of the same chirality as the cholesteric helix. The reflected light can be recycled to enhance the brightness of the LCD devices. In this research, we plan to study on the optical parameters of the CLC polarizers for fundamental understanding. The optical constants for polymerized cholesteric liquid crystal (CLC) films were obtained by comparing theoretical transmittance and reflectance spectra with measured ones. The theoretical spectra were calculated using an exact solution for a cholesteric layer within the Berreman 4×4 matrix formalism. We applied the curve-fitting method to three CLC samples with different reflection bands and compared the fitted results with the measured refractive indices for a parallel-aligned LC sample. Secondary, focusing on the new structure of retarders, including the 45˚-aligned QWFs and twisted retarders (TRs), we investigated the possibility of using these retarders in the LCD. The possibility of applying twisted retarders to a cholesteric liquid crystal polarizer for the control of polarization states has been investigated. In particular, we focused on the application of twisted retarders to the conversion of circular polarization states into linear polarization state...