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The properties of AlxIn1-xSb light-emitting diodes (LEDs) and photodetectors have been investigated to establish their suitability for methane sensing. Using these components it is possible to achieve good signal-to-noise values at both the characteristic absorption wavelength and also at 4 ?m, an attractive wavelength for use as a reference channel. A limit of sensitivity of approximately 400 ppm, with an integration time of 10 s and a path length of 5 cm, was estimated for methane detection.

The addition of small amounts of nitrogen to III-V semiconductors leads to a large degree of band gap bowing, giving rise to band-gaps smaller than in the associated binary materials. The incorporation of active nitrogen has been previously demonstrated for InNxSb1-x (x≤0.7%) and GaNxSb1-x (x≤1.75%) material; however, the as-grown carrier concentrations precluded incorporation into a device structure. Here we report the reduction in the as-grown carrier concentration in InNSb by annealing, whilst retaining the active nitrogen content. FTIR absorption measurements show the first direct experimental evidence of narrowing of the InSb bandgap due to nitrogen incorporation. As an alternative route to defect reduction and device compatible material we report on the growth of Ga1-yInyNxSb 1-x with 0≤y≤30% and x=1.6±0.2% and demonstrate near lattice matching of the material to GaSb.

The resolution and switching characteristics of two Bistable Optically Addressed Spatial Light Modulators (OASLMs) one with and one without a pixelated metal mirror (PMM) are compared. The two devices use amorphous hydrogenated silicon (a-Si:H) Schottky diode structures as their photosensitive layer, Indium Tin Oxide (ITO) layers for electrodes, Nylon-6 alignment layer and a ferroelectric Liquid Crystal (LC) material (ZLI-5014-100) as their modulating layer. Both devices exhibit bistability when driven by alternating monopolar pulses. The pixelated metal mirror OASLM has both higher resolution and better optical efficiency than the non-mirrored device.

The growth, structural and optical characterisation of dilute nitride allows of InSb grown by plasma-assisted molecular beam epitaxy is presented. The lawyers were characterised by high-resolution X-ray diffraction indicating high crystalline quality and nitrogen incorporations up to 0.68%. Fourier-transform infrared absorption measurement reveal the position of the absorption edge to be a result of the competing effects of bandgap reduction (due to nitrogen incorporation and bandgap renormalisation) and Moss-Burstein band filling. The bandgap of InNSb as a function of nitrogen incorporation (using a 5-band k . p Hamiltonian and parameters from tight binding calculations) highlighting the applicability of the material in exploiting the atmospheric transmission window [S.D. Lord, NASA Technical Memorandum (1992) 103957] for long wavelength applications. (c) 2007 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim.

3D FDTD modelling is employed to design a surface pattern for mid-IR LEDs. Measured enhancement factors over an un-patterned device of 8% and 14% are found at 300 K and 25 K respectively. 3D FDTD modelling is employed to design a surface pattern for mid-IR LEDs. Measured enhancement factors over an un-patterned device of 8% and 14% are found at 300 K and 25 K respectively.

The aluminium-gallium-indium-antimonide (Al x Ga y In\({}_{1-x-y}\)Sb) material system offers great promise for efficient laser diode operation across the 3 to 5 μm wavelength range. It offers an excellent compromise between the requirements for good electronic and optical confinement and those for low series resistance. In addition, the use of an active region comprising compressively strained Type-I quantum wells (QWs) is predicted to lead to increased gain, which leads to lower threshold current densities and hence reduced non-radiative Auger recombination. In this paper a review of recent progress in the development of this material system is given, including the demonstration of multi-quantum well samples exhibiting photoluminescence up to room temperature, and laser diodes operating up to 219 K.

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.

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.

A new electro-optic modulator system has been developed by the authors to replay dynamic holographic images. This Active TilingTM system offers a route to replay giga- pixel computer generated hologram images with video refresh rates. High speed, medium complexity electrically addressed spatial light modulators are combined with a high resolution optically addressed spatial light modulator to provide ultra-high complexity, video frame rate holographic data suitable for coherent readout.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Monolayer and multilayer films of propanone adsorbed on an alloy metal single crystal have been studied using RAIRS. Analysis of the relative intensities of modes of different symmetry and comparison with the liquid spectrum leads to a determination of the orientation of the molecule. In the monolayer the molecular plane is close to parallel with the surface. On increasing coverage restructuring of the monolayer occurred due to interaction with the second adsorbed layer. Multilayer spectra show the propanone molecule to be orientated with the C=O axis parallel and the molecular plane perpendicular to the surface. IR spectra of considerably thicker films deposited on a KBr plate also show evidence for a strongly preferred molecular orientation with the molecular z axis parallel to the plate and the xy plane perpendicular to the plate.

Electroluminescence from GaInSb/AlGaInSb type I quantum well diode lasers, grown on GaAs, has been investigated as a function of strain in the quantum wells. Lasing was observed, in pulsed operation, up to temperatures of 161, 208, 219, and 202 K for structures containing 0.55%, 0.62%, 0.78%, and 1.1% strain, respectively, with lasing occurring at ∼3.3 μm at 200 K for the 1.1% structure.

Photoluminescence (PL) from GaInSb/AlInSb type I multi-quantum-wells, grown on GaAs, has been investigated as a function of strain in the quantum wells. Luminescence, between 3 and 4 mu m, was observed for all samples, with good agreement between the measured and calculated peak emission energies. Analysis of the temperature dependence of the luminescence suggests that population of excited quantum well hole subbands occurs at high temperature, leading to a reduction in the PL signal. Room temperature luminescence was obtained from a sample with similar to 0.8% strain in the quantum wells. Preliminary results from laser diodes fabricated from companion wafers indicate lasing up to 220 K

Emission characteristics, spectral properties, and quantum efficiencies of AlxIn1−xSb light-emitting diodes, with aluminum compositions between 0% and 8.75%, have been investigated as a function of temperature from 25 to 300 K, and a function of current from 1 to 100 mA. As both current and temperature are varied a change in the dominant recombination mechanism is observed as indicated by changes in the measured emission. An analysis of the light-current characteristics shows that Auger processes become important in all devices at temperatures above 100 K, implying an activation energy of approximately 7–13 meV depending on the aluminum composition.

At room temperature, we demonstrate an unambiguous detection of the ground- and excited-state transitions of mid-infrared GaInSb/AlGaInSb type I quantum well (QW) lasers grown on GaAs using a new technique based on Fourier transform infrared surface photovoltage spectroscopy. It is found that none of the currently established spectroscopic techniques is able to detect even the ground state transition of these mid-infrared QW lasers at room temperature. The spectroscopic results are in reasonable agreement with the laser emission spectra at low temperatures.

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.

Electroluminescence from GaInSb/AlGaInSb quantum well (QW) diode lasers, grown on GaAs, has been investigated as a function of strain in the QWs, with lasing occurring at ∼3.3µm at 200K with 1.1% strain in the QW.