비틀린 위상지연 필름의 콜레스테릭 액정 편광판 응용에 관한 연구

Abstract

In this thesis, we have performed theoretical investigations using Jones matrix formulation on structural parameters of twisted retarder (TR) with which circular polarization states can be converted into linear polarization states. Especially, it was theoretically predicted that x-axis and y-axis polarization states can be obtained with a right-handed TR film and a left-handed TR film, respectively, when the incident light into the TR films has the left-handed circular polarization (LCP) state. The x-axis indicates the alignment direction of the directors for nematic liquid crystals (LCs) just on the substrate film of TR and the y-axis the perpendicular direction to the x-axis. Also, we have fabricated TR films using LCs supplied by Merck, Ltd., RMM522 (nematic LC) and RMM498 (nematic LC blended with right-handed chiral component). Twist rate and total retardation value could be controlled by adjusting the relative content of RMM498 in the mixture with RMM522 and the thickness of TR film, respectively. Precise control of the thickness of TR films, however, has been found very difficult with the current fabrication process employing bar-coating method. Now, process improvement is actively in progress. Mueller matrices for a cholesteric liquid crystal (CLC) film (CLC900, Samsung Fine Chem., Ltd.), a TR film and a laminated sample of the two films were measured, and optical characteristics and output polarization states of the samples were discussed. For the case of the CLC film, degree of polarization of the output light for an unpolarized input was 0.82, which implies that about 18% of the output light is still unpolarized even after transmitting the CLC film, and most of the output light is in the LCP state. One can expect that extraction efficiency of useful linear polarization state would be only 91% using the CLC film reported in this study compared with that using an ideal left-handed circular polarizer. The structural parameters of the retardation film fabricated in this study with the mixture of RMM522 and RMM498 didn’t match with any theoretically predicted parameters with which circular polarization states can be converted into linear polarization states. We have found that, however, the retardation film could be theoretically modeled nicely as a twisted retardation film and from the experimental point of view the retardation film acted as a twisted retardation film quite very well.