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Holography is a diffraction-based coherent imaging technique in which a complex threedimensional object can be reproduced from a flat, two-dimensional screen with a complex transparency representing amplitude and phase values. It is commonly agreed that real-time holography is the ne plus ultra art and science of visualizing fast temporally changing 3-D scenes. The integration of the real-time or electro-holographic principle into display technology is one of the most promising but also challenging developments for the future consumer display and TV market. Only holography allows the reconstruction of naturallooking 3-D scenes, and therefore provides observers with a completely comfortable viewing experience. But to date several challenges have prevented the technology from becoming commercialized. But those obstacles are now starting to be overcome. Recently, we have developed a novel approach to real-time display holography by combining an overlapping sub-hologram technique with a tracked viewing-window technology (Schwerdtner, Leister & Haussler, 2007; Schwerdtner, Haussler & Leister, 2007). For the first time, this enables solutions for large screen interactive holographic displays (Stolle & Haussler, 2008; Reichelt et al., 2008). This chapter presents these novel solutions for large real-time holographic 3-D displays in the context of previous and current approaches to electro-holography. The holographic display developed by us combines a tailored holographic recording scheme with active tracking of the observer. This unique approach dramatically reduces the demand for the space-bandwidth product of the hologram and thus allows the use of state-of-the-art spatial light modulators and enables real-time calculation. The fundamentals and challenges of the holographic display technology are described, its implementation in prototypes is demonstrated, and the bright prospects for the 3-D display market are discussed.

Among 3D displays solely electro-holographic displays are in principle capable of completely matching natural viewing. Our new approach to electro-holography facilitates large object reconstructions with moderate resolution of the spatial light modulator. We verified our approach with a standard 20 inch LCD as spatial light modulator.

Large real-time holographic displays with full color are feasible with SeeReal's new approach to holography and today's technology. The display provides the information about the 3D scene in a viewing window at each observer eye. A tracking system always locates the viewing windows at the observer eyes. This combination of diffractive and refractive optics leads to a significant reduction of required display resolution and computation effort and enables holographic displays for wide-spread consumer applications. We tested our approach with two 20 inch prototypes that use two alternatives to achieve full color. One prototype uses color filters and interlaced holograms to generate the colors simultaneously. The other prototype generates the colors sequentially. In this paper we review our technology briefly, explain the two alternatives to full color and discuss the next steps toward a consumer product.

Novel solutions for large real-time holographic 3D displays are presented. The holographic display combines a tailored holographic recording scheme with active tracking of the observer. This approach dramatically reduces the demand for the space-bandwidth product of the hologram and thus allows the use of state-of-the-art spatial light modulators and enables real-time calculation. The fundamentals and challenges of the holographic display technology are described, its implementation in prototypes is demonstrated, and the bright prospects for the 3D display market are discussed.

Auto-stereoscopic 3D displays capable of high quality, full-resolution images for multiple users can only be created with time-sequential systems incorporating eye tracking and a dedicated optical design. The availability of high speed displays with 120Hz and faster eliminated one of the major hurdles for commercial solutions. Results of alternative display solutions from SeeReal show the impact of optical design on system performance and product features. Depending on the manufacturer's capabilities, system complexity can be shifted from optics to SLM with an impact on viewing angle, number of users and energy efficiency, but also on manufacturing processes. A proprietary solution for eye tracking from SeeReal demonstrates that the required key features can be achieved and implemented in commercial systems in a reasonably short time.

3D displays comprise stereoscopic displays and holographic displays. Eye convergence and accommodation are important depth cues for human vision. Stereoscopic displays provide only convergence information whereas holographic displays also provide accommodation information. Due to the inherently better 3D quality we consider holographic displays as the preferred alternative to stereoscopic displays. Our new approach to holographic displays omits unnecessary wavefront information and significantly reduces the requirements on the resolution of the spatial light modulator and the computation effort compared to conventional holographic displays. We verified our concept with holographic display prototypes and measurements. SeeReal's approach makes holographic displays feasible as a consumer product for mass-market applications.

Dependence on sub-micron pixel pitch and super-computing have prohibited practical solutions for large size holographic displays until recently. SeeReal Technologies has developed a new approach to holographic displays significantly reducing these requirements. This concept is applicable to large "direct view" holographic displays as well as to projection designs. Principles, advantages and selected solutions for holographic projection systems will be explained. Based on results from practical prototypes, advantageous new features, as large size full-color real-time holographic 3D scenes generated at high frame rates on micro displays with state of the art resolution will be presented.

Holography is generally accepted as the ultimate approach to display three-dimensional scenes or objects. Principally, the reconstruction of an object from a perfect hologram would appear indistinguishable from viewing the corresponding real-world object. Up to now two main obstacles have prevented large-screen Computer-Generated Holograms (CGH) from achieving a satisfactory laboratory prototype not to mention a marketable one. The reason is a small cell pitch CGH resulting in a huge number of hologram cells and a very high computational load for encoding the CGH. These seemingly inevitable technological hurdles for a long time have not been cleared limiting the use of holography to special applications, such as optical filtering, interference, beam forming, digital holography for capturing the 3-D shape of objects, and others. SeeReal Technologies has developed a new approach for real-time capable CGH using the socalled Tracked Viewing Windows technology to overcome these problems. The paper will show that today's state of the art reconfigurable Spatial Light Modulators (SLM), especially today's feasible LCD panels are suited for reconstructing large 3-D scenes which can be observed from large viewing angles. For this to achieve the original holographic concept of containing information from the entire scene in each part of the CGH has been abandoned. This substantially reduces the hologram resolution and thus the computational load by several orders of magnitude making thus real-time computation possible. A monochrome real-time prototype measuring 20 inches has been built and demonstrated at last year's SID conference and exhibition 2007 and at several other events.

This paper illustrates one of the various capabilities of static diractive optical elements (DOE) benecial to realtime holographic displays. Custom kinoform-type DOE can be used as elements for illumination of the spatial light modulator, i.e. the display where the video hologram is encoded. For an RGB application of diractive optical elements, particular issues concerning the inherent wavelength-dependence have to be addressed. Multiorder DOE oer a way to compensate for chromatic as well as monochromatic aberrations. We will discuss concepts and performance of multi-order DOE, show their application in holographic displays, describe issues of fabrication and replication, and give experimental results of the multi-order DOE performance.

Our primary goal is to reconstruct the wavefront in a virtual observer window at the eye position. This approach facilitates large object reconstructions with moderate resolution of the spatial light modulator and was verified.

Display technology has made big advances in last years. Displays are flat, offer high resolution, are bright, fast and almost free of flicker. Apart from new technologies that make displays still more affordable the major direction of development turns to applications, especially TV. In this consolidation process new features are sought. Still lacking is the 3D display capability most obvious compared to viewing real-world scenes. In the last decades a lot of new 3D technologies have been proposed, developed and only few have reached the commercial market. A breakthrough into the mass market has been prevented for technical as well as commercial reasons. Most natural viewing is provided by holography. Unfortunately, even the technical challenges are so demanding that the 3D research community turned to the stereoscopic technology known for more than a century. Many technologies have been proposed and the shutter technique has already matured to a commercial product. But the mass market requires 3D viewing without using additional viewing aids. Currently, these Autostereoscopic 3D Displays still cannot meet the quality standard and comfort of today's 2D displays. In our opinion 3D displays should first of all match all of today's 2D demands and additionally be capable of 3D displaying.

For tracking based autostereoscopic displays an eye position detection system is needed. We built a real-time image processing unit that not only achieves a high level of detection reliability but also is cost effective and can be integrated in a display housing. The device is able to autonomously find the eyes of the user and track them without the need of any markers or special lighting. The system consists of a stereo camera and proprietary DSP-based hardware and software. We describe determination of parameters of the optical system and correction of image distortion as well as algorithmic details. Performance results and future developments are discussed.

A tracking based autostereoscopic 3D Display (D4D) has been developed at Dresden University of Technology. It employs a Flat Panel Display (FPD) and is designed for single users. Both stereoscopic half images are displayed simultaneously in alternating FPD columns. The separation of both half images to the viewer's eyes is accomplished using a prism mask in front of the FPD. The tracking is performed in two ways. Firstly, the separation mask is shifted mechanically against the stereoscopic image according to the viewer's position. Secondly, the stereoscopic image is shifted electronically. The D4D is extremely flat. Regular flat panel displays or even notebooks can be made autostereoscopic using the D4D technology Add-Ons. The development of the D4D has been funded by the Saxonian State Ministry of Economy and Labor.

The SeeReal electro-holographic display approach — using an observer window — has for the first time made possible large volume holographic reconstruction with real-time calculation. The observer tracking solution as implemented in the first SeeReal prototype is compared to new concepts providing for a larger tracking angle.