3D/2D convertible projection screen with bidirectionality based on integral imaging

Abstract

This dissertation investigates new projection screens composed of passive optical components, which display both three-dimensional (3D) and two-dimensional (2D) images bidirectionally. Two types of passive screens are proposed: one is a polarization selective screen (PSS) where the display modes are converted by the polarization states of projectors, and the other one is a multiplexed holographic optical element (MHOE) where the display modes are converted by the projection directions. For implementing the 3D mode of the PSS and MHOE, an integral imaging method is adopted, because it provides quasi-continuous view images with horizontal and vertical parallaxes. Before describing the bidirectional imaging properties, principles of mode changes in the PSS and MHOE are presented in the view of unidirectional observations. The PSS consists of a concave mirror-array, scattering polarizer, and absorbing polarizer. The optical properties of PSS are analyzed according to the polarization states of incident light, and the displaying experiments for the 3D/2D convertible functionality according to the polarization states are presented. Meanwhile, the MHOE supports different modes according to the projection directions. The angular multiplexing of volume hologram is adopted for recording the functions of 3D screen and 2D screen on a single holographic material. The angular selectivity of MHOE is experimentally examined, and the displaying experiments for the 3D/2D convertible functionality are presented by using a full-color MHOE. The unidirectional PSS is extended into a bidirectional projection-type autostereoscopic display so that the aforementioned 3D/2D convertible functionality can be provided for observers in the front and rear sides. For realizing occlusion effects between 3D images and 2D images, image compensation methods are proposed, which are applied on the elemental images and 2D images. Also, in order to enhance the fill factor of 3D images displayed by the projection-type integral imaging in the PSS, the use of diffuser holographic optical elements is proposed. The analysis on the fill factor problem is conducted, and the experimental results with the fill-factor-improved 3D images are presented. In order to apply the 3D/2D convertibility of MHOE to the bidirectional projection-type displays, the use of two reconstruction conditions (i.e., the forward and the phase-conjugated reconstructions) on the MHOE is proposed. The optical properties of diffracted wavefront by two reconstruction conditions are analyzed using wave vector space diagrams and the experiments. Also, it is verified that the elemental images projected in the phase-conjugated reconstruction condition have to contain pseudoscopic information in order to present orthoscopic 3D images. Projection parts for the bidirectional imaging of MHOE are realized using prisms, so that a single projector for each side can provide 3D images and 2D images simultaneously. The displaying experiments verify that the full-color MHOE can provide the 3D and 2D images bidirectionally.