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We investigate the processes involved in writing real-time holographic gratings in a photorefractive polymer (PRP) that incorporates an azo-dye. In such systems there may be gratings due to mechanisms associated with trans–cis isomerization (angular hole burning (AHB) and/or angular redistribution), which appear in addition to those arising from the photorefractive (PR) effect. The work presented here helps to understand the interactions which may occur between these different gratings. The formation of local gratings due to mechanisms associated with photoisomerization is studied, in a new PRP based on the photoconductor poly(N-vinylcarbazole):2, 4, 7-trinitro-9-fluorenone, plasticized with N-ethylcarbazole. The polymer includes the azo-dye 4-nitro-4'-pentyloxy-azobenzene and we observe both PR and photoisomerization gratings. The gratings are shown to be both polarization-sensitive and reversible. The presence of the photoisomerization gratings (which diffract almost as strongly as the PR gratings) significantly affects the field-dependent diffractive behaviour of the composite. A measurement of the lifetime of the cis state is made (τcis = 38 s) using photoinduced dichroism. This is close to the decay time constant of the local gratings (τdecay = 42 s), and it is suggested that the local grating mechanism is AHB of the azo-dye. This is the first time (to the knowledge of the authors) that a local grating due to AHB has been demonstrated in a PRP.

Passive mm-wave imaging has great potential for all-weather flying aids and security applications. To achieve useful real time images of an ambient temperature scene, >100 detectors are required, and uptake of the technology has been limited by the high cost of detectors. We propose a novel, cost effective solution using integrated arrays of antenna-coupled HTS Josephson junction video detectors. Arrays of 16 antenna coupled YBa 2 Cu 3 O 7 interface engineered junctions have been fabricated with a design centre frequency of ∼100GHz, optically immersed behind a single lens. Detector characteristics have been compared to stochastic RCSJ model simulations, with the antenna represented by an equivalent circuit. A real time demonstration imager has been built, and the first images obtained.

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.

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.

Reconfigurable computer generated holography - sometimes known as electroholography - is the only technique capable of using computer held data to generate interactive, high quality, 3D images containing all the depth cues used by the human visual system. Practical applications of electroholography require computer generated hologram (CGH) patterns of between 10/sup 9/ to 10/sup 10/ pixels to be calculated and displayed at interactive rates. These pixel counts are necessary in order to generate images which are both big enough (upwards of 300 mm width) and possess a large enough field of view (FOV) to permit simultaneous, multiuser viewing. Advances in several key areas may now make such high performance electroholographic systems practical in the near future. We describe CGH design algorithms, computer architectures and CGH display engines, including the Active Tiling/spl trade/ 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.

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.

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.

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.

Taking the QR factorisation of the covariance matrix M — XHX raised to increasing integer powers is shown to beequivalent to the process of Orthogonal Iteration and to converge upon a diagonal matrix with the eigenvalues of M raised tothe corresponding power as its diagonal entries. This is a consequence of M being Hermitian (a special case of a "normal"matrix). In addition, whereas the eigenvalues of a matrix are not in general rank-revealing, the eigenvalues of M are as theyare the squares of the singular values of X . In this way the Row-Zeroing approach to rank-revealing QR factorisation is nolonger defeated by the rank-deficient matrix due to Kahan. A connection is also noted with Chan's RRQR algorithm and aphysical interpretation is developed for the function of Chan's permutation mathx.In practice, just a few steps of Orthogonal Iteration coupled with Row-Zeroing appears to be a very effective means ofestimating the rank and signal subspace. The analytical error bounds upon the subspace estimate are much improved and asa consequence the diagonal value spectrum is sharpened, making thresholding easier and the R matrix much more naturallyrank revealing. Hence it is sufficient to perform Row-Zeroing merely upon M or M2 . As a result, insight is also providedinto the LMI method favoured by Nickel.Keywords: QR, rank-estimation, rank-revealing, sub-space, projection, least-squares, beamforming

A recursive algorithm is described which performs approximate numerical rank estimation and subspace-projection of the least squares weight vector. Although it appears to work well in practice, being based upon a one-sided rank-revealing QR factorization, it lacks a formal guarantee to reveal the rank and it is more approximate than URV or Chan's rank-revealing QR factorization. However, it may be implemented very simply, requires little additional computation and, being based upon QR, it is able to exploit the established and numerically sound architecture of the Gentleman-Kung QRD-based RLS algorithm. It is implemented by redefining the cells in the array and performing additional updates so that the R matrix which is stored at any time approximates that which would be obtained for the QR factorization of the projected data matrix. Thus, the projected least-squares residual is output directly from the array and the projected weight vector is readily extracted if required.

Conventional least squares minimization beamforming algorithms suffer from `weight jitter' when small data sequences are used. One method for overcoming this problem requires that the SVD of the data matrix is calculated and the `signal' and `noise' subspaces identified. A more stable beampattern can then be formed by projecting the least squares weight vector onto the appropriate subspace. The SVD is computationally expensive to perform and difficult to implement in a parallel architecture. Several approximate `rank revealing' algorithms have been presented of late (e.g. URV, RRQR) which have a much reduced computational load. However, being `two-sided' decompositions, they all suffer from implementation difficulties. In this paper we present an algorithm, based on QR decomposition, that can approximately reveal the rank and signal subspace of a matrix and simultaneously perform a subspace projection. The algorithm has the potential for very simple parallel implementation.