Maurice Stanley

Computer-generated holography as a generic display technology

Computer-generated holography technique is a powerful technology suitable for a wide range of display types, including 2D, stereoscopic, autostereoscopic, volumetric, and true 3D imaging. Computer-generated holography is an emerging technology, made possible by increasingly powerful computers, that avoids the interferometric recording step in conventional hologram formation. Instead, a computer calculates a holographic fringe pattern that it then uses to set the optical properties of a spatial light modulator, such as a liquid crystal microdisplay. The SLM then diffracts the readout light wave, in a manner similar to a standard hologram, to yield the desired optical wavefront. Although CGH-based display systems can be built today, their high cost makes them impractical for many applications.

3D electronic holography display system using a 100-megapixel spatial light modulator

The display of 3D images containing all the depth cues required by the human vision system can be achieved using a reconfigurable Computer Generated Hologram (CGH) with high pixel count. Giga-pixel scale displays or spatial light modulators are required in order to form directly viewable 3-D images of 0.5m in size. A new Spatial Light Modulator (SLM) solution, Active Tiling (AT)1, has been developed by the authors to replay giga-pixel scale CGHs at video refresh rates. This has overcome a key bottleneck preventing commercial development of electro-holography to date. At the heart of an AT system is a set of replication optics which produces multiple images of an electrically addressed Spatial Light Modulator (SLM) on an optically addressed spatial light modulator (OASLM). Solutions employed within electronic holography will be discussed. A holographic 3D display system using a 4 channel Active Tiling modulator with a new replay optics system has demonstrated directly viewable 3-D images and animations from 100 Mega-pixel CGH data. This provided viewing of both horizontal parallax only (HPO) and full parallax 3-D images up to 140mm in size.

100-megapixel computer-generated holographic images from Active Tiling: a dynamic and scalable electro-optic modulator system

Giga-pixel scale displays or spatial light modulators are required in order to form directly viewable 3-D images of 0.5m in size using the principles of computer generated holography (CGH). This has been a key bottleneck preventing commercial development of electro-holography. Active Tiling is a modular spatial light modulator system developed by the authors to provide a route to replay images from giga-pixel scale CGHs. This paper will present the latest development of a multi-channel Active Tiling unit and results from this system for the first time. A holographic 3D display system using a 4 channel Active Tiling modulator with a new replay optics system has demonstrated directly viewable 3-D images and animations from 100 Mega-pixel CGH data. This provided viewing of both horizontal parallax only (HPO) and full parallax 3-D images up to 140mm in size. 25 Mega-pixels of CGH data is written by each channel onto a liquid crystal optically addressed spatial light modulator at high resolution. The modular design of Active Tiling permits CGH data to be written seamlessly across multiple channels which can be updated at rates up to 30 Hz. A Fourier Transform optical replay system was developed and integrated with the 4-channel Active Tiling system to form the CGH images.

Recent developments in computer-generated holography: toward a practical electroholography system for interactive 3D visualization

This paper will give an overview of some recent developments in electroholography for applications in interactive 3D visualisation. Arguably the ultimate technology for this task, it is the only approach having the potential to deliver full depth cue, 3D images, having resolutions beyond that which can be perceived by the human eye. Despite significant advances by many researchers, the high pixel counts required by the computer generated hologram (CGH) patterns in these systems remain daunting - in practice, systems able to calculate and display reconfigurable CGH having pixel counts of more than one billion may be required for 300 mm width, 3D images. Advances described include novel Fourier mode variants of diffraction specific algorithms and parallel binarisation techniques for design of the CGH patterns; computer architectures for effective implementation of these algorithms for interactive CGH calculation; the latest developments in the Active Tiling spatial light modulator technology and novel replay optics arrangements including folded mirror geometries, viewer tracking alternatives and new horizontal parallax configurations. Throughout, the emphasis is optimisation towards implementation as an interactive electroholography system having practical utility. Some recent results from demonstrations of aspects of the technology will be shown. These include monochrome and colour, static and dynamic, horizontal parallax only (HPO) and full parallax, 3D images, generated from true CGH systems with up to 24 billion pixels.

Computational challenges of emerging novel true 3D holographic displays

A hologram can produce all the 3D depth cues that the human visual system uses to interpret and perceive real 3D objects. As such it is arguably the ultimate display technology. Computer generated holography, in which a computer calculates a hologram that is then displayed using a highly complex modulator, combines the ultimate qualities of a traditional hologram with the dynamic capabilities of a computer display producing a true 3D real image floating in space. This technology is set to emerge over the next decade, potentially revolutionizing application areas such as virtual prototyping (CAD-CAM, CAID etc.), tactical information displays, data visualization and simulation. In this paper we focus on the computational challenges of this technology. We consider different classes of computational algorithms from true computer-generated holograms (CGH) to holographic stereograms. Each has different characteristics in terms of image qualities, computational resources required, total CGH information content, and system performance. Possible trade- offs will be discussed including reducing the parallax. The software and hardware architectures used to implement the CGH algorithms have many possible forms. Different schemes, from high performance computing architectures to graphics based cluster architectures will be discussed and compared. Assessment will be made of current and future trends looking forward to a practical dynamic CGH based 3D display.

Progress and prospects for practical electroholographic display systems

Continuing advances in both computing and modulator techniques and technologies increase the likelihood of electro-holography displays becoming practical in the next five years or so. These displays aim to allow high quality, interactive, 3D images to be generated from compte held dat. Until now, large pixel counts have precluded any systems of practical utility. This paper will describe recent progress towards meeting the challenges of implementing such displays. Despite more than exponential increases in computer performance, interactive hologram calculation remains an issue. A significant part of the cost of any electro-holography product will be associated with the computational requirements. These are strongly influenced by the choice of computer generated hologram (CGH) type, the algorithm used to calculate the CGH and the computer architecture chosen for implementation. The leading optics will be discussed and some experimental results presented indicating performance, cost and image quality tradeoffs. Eventual choice will depend on the specifications of the required system. Another traditional bottleneck has been the optical modulator employed. As one of the leading candidates for practical implementation, the current and projected performance of the DERA Active Tiling system will be explored, and the latest experimental results presented. These will include the first published, full parallax, true CGH, 3D image replays from an Active Tiling channel.

Optically addressed spatial light modulators for replaying computer generated holograms

Holographic techniques offer a route to the generation of 3D images having all the depth cues used by the human vision system. A new electro-optic modulator system has been developed by the authors to replay dynamic holographic images. This Active Tiling (AT) system offers a route to replay giga-pixel computer generated holographic (CGH) images with video refresh rates. A key component of the AT system is an Optically Addressed Spatial Light Modulator (OASLM), onto which segments of the large pixel count CGH are loaded or written sequentially before the whole CGH frame is read out simultaneously. The OASLM device structure used consists of an amorphous silicon photosensor layer combined with surface stabilised ferroelectric liquid crystal (SSFLC) light modulation layer. A number of experiments have been conducted to determine the performance and suitability of this device for replaying a CGH. These experiments include electro-optic switching to determine the operating window and diffraction efficiency (DE) measurements to determine spatial resolution performance. A detailed description of the experimental apparatus and method used for measuring DE is presented, and results show the OASLM to be capable of diffracting light from fringe patterns with spatial periods as low as 3 micrometers (333 lp/mm). Examples of CGH replay of 3D images from the OASLM when operating within the AT system are also presented.

Spatial sampling in pixelated-metal-mirror ferroelectric-liquid-crystal optically addressed spatial-light-modulator devices

We examine the spatial resolution of pixelated-metal-mirror (PMM) ferroelectric-liquid-crystal (FLC) optically addressed spatial light modulators (OASLMs). To characterize the resolution of OASLM devices, their diffraction efficiency is measured as a function of the spatial frequency of the write image. The results show that aliasing is produced by the PMM devices, which correspond qualitatively with the predictions of sampling theory.

Image replication with diffractive structures

Many techniques have been described in the literature for generating spot arrays from a single input beam. When such a device is used for image replication (IR), the finite field of view unavoidably introduces optical aberrations that reduce the fidelity of the replicated images. Fourier array generators offer a low-cost and flexible method of image replication with lower optical aberrations than other methods and aberrations that are sufficiently low for replication of extended images. Using multicriteria optimization, two-dimensional Fourier array generator-based optical systems can be designed with high diffraction efficiency and near-diffraction-limited imaging performance across an extended field of view.

Replication optics for a holographic 3D display system

The display of 3D images containing all the depth cues required by the human vision system can be achieved using a reconfigurable Computer Generated Hologram (CGH) with high pixel count. A technique which has been developed to produce CGHs with the required number of pixels, and at video refresh rates, is known as Active TilingTM (AT). At the heart of an AT system is a set of replication optics which produces multiple images of a Spatial Light Modulator (SLM) onto the CGH. The design of two alternative optical systems for geneating a 5x5 tiled array of de-magnified images of a single object is discussed. Results are presented from a 4-channel AT system which has recently been built and demonstrated.