Chiral Surface-Driven Optical Image Selection by Polarization in Liquid Crystal Devices

Abstract

Recently, many approaches have been developed to construct different images depending on the polarization state of light. Constructing different images depending on the polarization state of light has various applications such as optical image storage systems, stereoscopic three-dimensional (3D) displays, and anti-counterfeiting. In previous studies, optical image selection through linear polarization state of light has extensively studied due to the simple polarization state generation through polarizers and through intuitive structures of the image generating systems. However, image selection through linear polarization has a severe disadvantage that the alignment of the polarizer and the polarization state of the image should be aligned perfectly. For example, 3D displays using linear polarization cannot show the 3D images when the viewer does not see the display in a straight way. To be specific, if the viewer sees the display in a lying position, the 3D images are not constructed due to the misalignment of the polarizers on the viewers eyes and the polarization state from the 3D display. To overcome such drawbacks, image selection through circularly polarized light has been demonstrated since circular polarization does not depend on the alignment direction. To retrieve circular polarization, chiral structures or phase retarders have been used. However, previous studies were limited in their polarization switching capability, which could enhance the quality and the applicable range of these systems. Also, simple fabrication of such circular polarization generating structures are required for practical applications. This thesis demonstrates chiral surface-driven images in liquid crystal devices with polarization switching capability that can be selected according to the polarization state of the viewing polarizer. The patterned surface chiral layer reflects a circularly polarized light with a certain color. The homogeneous LC layer placed on the patterned surface chiral layer acts as a tunable wave retarder that modifies the polarization state of the reflected light from the surface chiral layer. Depending on the applied voltage across the LC layer, either right-handed or left-handed circular polarized images are produced so that selective reading of recorded images can be achieved with a polarization detector. Our polarization switchable image selection allows simple fabrication, higher quality, and diverse usage for visual applications including displays and image storage systems.