54.5: Holographic Screens for 3 Dimensional Image Projection

color transmission type holographic screen having a size of 40cm X 60cm are developed recently at Korea Institute of Science and Technology. This screen can be operated in reflection mode by adding a mirror at its back. This operation extends viewing angle of the screen to be more than 30degree. This wide viewing angle permits the screen to be operated in viewer tracking regime. By mosaicking the screens, a 120cm X 80cm screen is made. The mosaicked screen shows a good image performance. Introduction screen has been developed to use as an image projection screen for forming viewing zones for the projected images(1). It is a kind of holographic optical element(HOE)s which has the properties of a spherical mirror or a lens + a diffuser. Since HOE is basically a spectral selective component, full color images can not be projected on the holographic screen(2), unless a specific optical recording set-up is used or a special development process is developed. One good example of the screen is the image combiner in Head Up Display for airplanes(3). It is tuned to have the maximum diffraction efficiency for the spectral range corresponding to that of the image display device used for the Display, i.e., CRT. This means that the screen has an uniform period fringe structure. To make the screen has a wide spectral response comparable to visible spectral range, it is necessary to make the screen have a variable period fringe structure. Based on this concept, Korea Institute of Science and Technology(KIST) developed a full color transmission type holographic screen with use of a long slit type diffuser as an object(4). The screen creates a full color viewing zone for images projected from a projector by making the reconstructed diffuser image for each spectral com ponent of the images overlap partially in space. The viewers can perceive the full color images displayed on the screen through the viewing zone. The advantages of the holographic screen compared with popularly used optical plates to form viewing zones, such as Lenticular, Parallax Barrier and Integral Photography plates and Fresnel lens(5) are such that resolution and depth of the viewing zone of the screen are higher and more, respectively. However, making larger size screen with full color capability is difficult due to problems related with optimizing the recording set-up to minimize aberrations and exposition time, and changing viewing zones following to the viewer's movement. It found that the problems could be solved by mosaicking smaller size screens and by operating the screen in a reflection mode. This reflection mode operation allows the angular selectivity of the screen to be two times of that of transmission mode. In this paper, some features of the full color transmission type holographic screens developed at KIST are described.