Large screen information displays are defined as dynamic electronic displays that can be viewed by more than one person and are at least 2-feet wide. These large area displays for public viewing provide convenience, entertainment, security, and efficiency to the viewers. There are numerous uses for large screen information displays including those in advertising, transportation, traffic control, conference room presentations, computer aided design, banking, and military command/control. A noticeable characteristic of the large screen display market is the interchangeability of display types. For any given application, the user can usually choose from at least three alternative technologies, and sometimes from many more. Some display types have features that make them suitable for specific applications due to temperature, brightness, power consumption, or other such characteristic. The overall worldwide unit consumption of large screen information displays of all types and for all applications (excluding consumer TV) will increase from 401,109 units in 1995 to 655,797 units in 2002. On a unit consumption basis, applications in business and education represent the largest share of unit consumption over this time period; in 1995, this application represented 69.7% of the total. The market (value of shipments) will grow from $DOL3.1 billion in 1995 to $DOL3.9 billion in 2002. The market will be dominated by front LCD projectors and LCD overhead projector plates.

New developments in visual communication technologies, and the increasingly digital nature of the industry infrastructure as a whole, are converging to enable new visual environments with an enhanced visual component in interaction, entertainment, and education. New applications and markets can be created, but this depends on the ability of the visual communications industry to provide market solutions that are cost effective and user friendly. Industry-wide cooperation in the development of integrated, open architecture applications enables the realization of such market solutions. This paper describes the work being done by Texas Instruments, in the development of its Digital Light Processing^TM technology, to support the development of new visual communications technologies and applications.

The emerging market of combining computer and consumer electronics technologies has resulted in the progress of projection display design. TFT LCD, which has been primarily driven by notebook PC applications, has become a critical component in achieving low cost high performance projection display. Requirements of TFT LCD needed to design LC projector are discussed. Taking advantage of the strength of information industry in Taiwan, a national TFT LCD program aiming to establish LCD industry in Taiwan is supported by the Ministry of Economic Affairs (MOEA). Four companies, including one CRT maker, one computer maker, and two material manufacturers, join the program as early technology licensees. Both (alpha) -Si and poly-Si technologies are used to develop TFT LCD panels. Under a separate MOEA R&D program, ITRI engineers are developing LC projection displays for NTSC, VGA, and HDTV applications. This program is participated by five consumer electronics makers in Taiwan. First product supporting NTSC and VGA applications has been developed and under sampling by these companies. High definition projector development is now under way.

Light-valve projectors are becoming increasingly popular for large screen displays. This is particularly true for high definition displays over 50' diagonal. In these applications light output of 1000 to 10,000 lumens is desirable. For consumer applications this is needed to overcome ambient light levels and for commercial applications it is needed for the longer screen sizes. Optical efficiency, contrast ratio and cost are the major problems for satisfying the requirements of these applications. These parameters are interrelated. Increased optical efficiency reduces the cost of the light source and its power. In many systems high contrast and light modulator heat dissipation require larger modulator areas which increases the cost of the light modulator and its associated optics. Several light modulator options will be discussed with these trade-offs in mind. These include active matrix LCD's, passive matrix LCD's, optically addressed LCD's, digital micromirror device projectors and light-valve projectors using liquid-crystal phase diffraction gratings. Many of these compromises can be alleviated if solid-state laser light sources can be used. Experiments on projectors using these light sources in all three primary colors will also be discussed. Since efficient solid-state laser sources are quite a recent experimental development, their current price is prohibitive. However, they should not be ruled out as an option if they can be manufactured in large quantities at a reasonable cost. Their use could greatly reduce the cost of the other components in the projector.

Liquid-crystal projection displays (LCPD) have been in production for many years, and have demonstrated performance equal to HDTV requirements. Projection CRT displays are cheaper to manufacture, making it difficult for LCPDs to compete in the consumer market. This could change with recent developments in metal halide arc lamps which will lead to smaller and cheaper LCPDs. The arc dimensions determine the light source etendue, which is a basic parameter in projector design. The influence of source etendue on the optical efficiency of various LCPDs is assessed with the goal of reducing the diameter of the spatial light modulator (SLM) while maintaining high-efficiency. The SLM diameter is a measure of the manufacturing cost.

This paper describes a diascopic projection system that efficiently combines and integrates the output from multiple light sources. The images of these light sources are superposed at a common focus in the projection lens, resulting in a projected screen brightness considerably greater than that produced by a single lamp of equivalent wattage. The illumination system consists of a series of collimating and converging plastic Fresnel lenses, and a linear beam- integrating micro-prismatic element. Glass anamorphic condenser optics are also used. The optics can be cascaded, and the design requirements of a four-lamp system is described. The experimental results from a laboratory developed overhead projection system using dual tungsten-halogen lamps is discussed.

Modern projection light sources must be capable ofhandling obstacles such as heat and light concentration. This paper shall review the patented Cheng Orthogonal Parabolic Reflector (OPR®) and how it resolves these problems. High intensity discharge (HID) lamps may be optimized using the new compound OPR® designed together all light from their most intensely radiating areas to a 3mm point. Performance ofthis system is up to 100% better than existing systems for projection. This technology may be applied to a diverse combination oflamps and projection applications for increased performance and reduced cost.

When considering several projection system designs, one of the important characteristics is the total luminous flux the system will deliver to the projection screen. This is the main factor controlling perceived brightness to the viewer for a given screen size and gain. This luminous flux depends on a number of factors, such as lamp lumen output, reflector collection efficiency, projector architecture, light valve aperture ratio and the transmission/reflection efficiency of each optical component in the system. Many of these factors are amenable to accurate estimation prior to construction of a prototype projector. However, quantitative estimates of lamp/reflector light collection efficiency are difficult to make accurately. This paper will give an analytical approach based on etendue (optical extent) that can accurately predict lamp/reflector collection efficiency prior to the construction of a prototype projector. Collection efficiencies and projector lumen throughputs for several lamp/reflector/projector combinations will be estimated with this technique.

Recently, progress has been made in the development of projectors used for large screen displays. Projection systems employing Metal Halide lamps as a light source, demonstrate unique and desirable features such as longer life and high luminous efficiency. These features are especially important for data projectors. Compared to conventional lamps, Metal Halide lamps have shorter arc lengths and higher color-rendering characteristics, resulting in overall superior performance. For the Hamamatsu 575 W Metal Halide lamp, we have modified the electrodes and chemical composition of the Metal Halide, as well as the glass envelope, all of which result in improved performance. We have extended the average life to 3000 hours or longer, for a compact, single-bulb, projection-type, 575 W lamp.

Prior constraints of typical Cathode Ray Tube (CRT) have been overcome by a novel design of miniature CRT's as an image source for addressing liquid crystal light valves. A new 1.5' CRT has been developed using a fine grain phosphor screen, unique electron gun and new focusing magnets for projector application. It is very compact, low in power consumption, cost effective and exhibits a high resolution of 1,200 TV lines.

Field-sequential color displays and digital color cameras require tunable filters with high- throughput, saturated colors, and rapid switching between bands. ColorLink has developed a new digital tunable filter technology that provides > 37% average transmission of unpolarized light in each primary band, saturated colors, sub-millisecond transition times between colors, and view-angles exceeding +/- 30 degree(s). Performance improvements are derived from proprietary color polarizer and achromatic liquid crystal switch technologies.

LC-arrangement with 3(pi) /2 twist angle as fast LC-shutter having a high contrast ratio, large square, fast relaxation time and low controlling voltage compatible with output voltages of personal computer COM-ports is investigated.

Diffractive optics represents a new and fundamental optical manufacturing technology that has tremendous potential in both the government and commercial sectors. Diffractive optics technology provides system designers with new and exciting degrees of freedom for the design and optimization of precision optical systems. Using diffractive optics one can: provide color correction for projection systems using a single, economical refractive material; create aspheric wavefronts without using aspheric surfaces; eliminate the need for exotic (and expensive) flint-type materials; produce high-performance, high-numerical-aperture, lightweight optical elements; produce high performance microlens arrays; construct custom diffusers for beam homogenization and beam shaping; convert Gaussian beams to a square- aperture, flat-top beam profile, create novel polarization components and narrowband filters; athermalize optical systems; and reduce the weight, complexity and cost of optical systems--all of which are important for projection display systems. In this paper, we describe several features of diffractive optical elements that are useful for projection display applications.

A definition doubler is an optical device, which can increase both the resolution and the fill of discrete fixed pixel displays, such as flat panel LCDs. These devices can operate in either 1 or 2 axis. They can be either passive or active in operation. The construction and operation of definition doublers are described.

Groups of video projectors can be arrayed into electronic displays that offer larger, brighter, and higher resolution images. This paper provides a broad overview of the design considerations and opportunities inherent in arraying projectors in a group. A projector array provides: increased image size, increased image brightness, increased image resolution, reduced projection distances, and increased depth of focus. Although video walls are the most common example of electronic image arrays, the limiting factor of traditional video walls is the visual segmentation. Minimizing the segregation between arrayed images is highly desirable with the goal being to make the segregation indistinguishable. Overlapping and seamlessly blending multiple video projectors into a single composite image goes a long way toward eliminating the segregation of projector elements and opens the way to many new practical applications. This is particular significant in displaying computer graphics. Computers have the ability to generate multi-channel composite images at resolutions that far exceed traditional electronic media and even the maximum resolution of any single monitor or projector. These images can then only be displayed using an arrayed system. The challenge is to make the entire projection array behave as a single imaging device. This can seem to be a daunting task with large arrays, but one whose solutions are already closer. Consider that a typical CRT projector is, in fact, an array of three projectors (R, G, & B) engineered into a single plastic housing and arrayed in a superimposed and converged geometry. Similarly, an array can be managed with integrating electronics to create a `virtual' packaging around multiple projectors, arrayed in adjacent and registered geometries, with the entire package behaving as a single cohesive imaging device.

We describe a new approach for the fabrication of highly integrated low-cost displays based on liquid crystal on silicon technology. The method employs a liquid crystal modulator structure built directly on top of a VLSI die and is suitable to both head-mounted and projection displays.

A technique to remove the pixel structure by randomly scrambling the relative phase among the multiple spatial spectra is described. Due to the pixel structure of the liquid crystal display panel, multiple spectra are generated at the Fourier spectrum plane (usually at the back focal plane of the imaging lens). A transparent phase mask is placed at the Fourier spectrum plane such that each spectral order is modulated by one of the subareas of the phase mask. The thickness of these phase mask subareas are randomly assigned and the phase delay resulted from each pair of subareas is longer than the coherent length of the light source, which is about one micron for white light. Such a phase scrambling eliminates the coherence between different spectral orders, therefore, the reconstructed images from the multiple spectra will superimpose incoherently and the pixel structure will not be observed in the projection image.

The effective applications of universal modeling systems MOUSE-LCD for the development of new LCDs with high contrast and wide viewing angles are presented. The software enables to combine LCDs both with uni and biaxial phase retardation plates as well as to use double cell configuration for the purpose of optimization. Any type of the director distribution inside LC cell with arbitrary (nonsymmetric) tilts and twist angles can be taken into account. The wideness of viewing angles can be estimated using equi-contrast ratio and equi transmission curves for various angles of light incidence. Special examples demonstrate the effectiveness of application of MOUSE-LCD for the purpose of the design of new color displays with high brightness and wide viewing angles.

A few optical schemes are considered and discussed for display devices, based on liquid crystal image converters. These schemes promise enhancement in light output and diminishing in system sizes in comparison to well-known ones realized yet.

We have developed an LCD projector based on a new concept utilizing human vision characteristics. It is known that human vision has high spatial resolution for monochrome images and low spatial resolution for color images. The new projector generates a wide-band frequency luminance signal, and low-frequency color signals from input signals. The present system uses an LCD panel of high definition for high resolution luminance image and three panels of low definition for low resolution color image. Use of low definition LCD panels, which are available at low cost, permits reduction in the cost of the system. In the developed projector, all the LCD panels have 640 X 480 pixels, but the number of pixels is electrically limited to 320 X 480 for the color panel. Light from a lamp is split by a polarizing beam splitter into two linearly polarized beams, one of which irradiates the luminance panel and the other of which irradiates the color panels, and thus both the polarized beams are utilized unlike conventional projectors where only one polarized component is utilized and the other component is lost away as heat. The projected NTSC (National Television System Committee) images were substantially of the same quality as the images which are obtained using three panels of 640 X 480 pixels. The projected VGA images had a picture quality sufficient for presentations at conferences.

The Digital Micromirror Device (DMD^TM) developed by Texas Instruments is a highly useful Micro-Opto-Electro-Mechanical Structures (MOEMS) device that enables high quality projection display. Acting as a semiconductor light switch, the DMD can modulate incident light to produce truly digital projection display systems. Illumination and projection optics are described for three fundamental display system architectures based on the DMD light modulator. These systems include one, two, and three DMD configurations all producing full color image projection. The single device configuration implemented with a rotating color filter system represents the least system hardware while providing the capability of full color and a high brightness monochromatic mode. A two device configuration using a rotating color filter combined with a secondary color splitting filter is of particular interest when using a light source that is spectrally imbalanced. The two device configuration is also capable of a high brightness monochromatic mode of operation. The three device configuration is the most efficient with respect to light throughput considerations providing the highest brightness full color projection with the DMD light modulators. Comparisons of system performance characteristics are described indicating the features of each configuration.

A new high-brightness compact projector is presented, which uses three 9.4' AMLCD monochrome panels at 640 X 480 pixels. The projector produces a minimum brightness of 900lm (ANSI), with a minimum contrast ratio of 50:1 (ANSI) or 100:1 (full field) using a 575 W, 7 mm arc, metal halide lamp. The corner brightness is typically 60% of the center brightness due primarily to a novel integration method utilizing a rectangular integrator. Choosing large panels for the projector offered several advantages namely, high clear aperture ratio (66%), relaxed arc size requirements and lower energy density on the polarizers. The large LCD panels also introduced significant optical challenges and made a collimated light path impractical. A crossed dichroic `over-under' design was used to produce a compact system. Lower crossed dichroics split the light into red, green and blue primaries, and fold mirrors direct this light from the lower level to the upper level to pass through the panels. The three primary channels are recombined into a single path via a set of large crossed dichroic mirrors. Due to the non-collimated nature of the light path, it was necessary to employ non- linear gradient dichroic mirrors to ensure color uniformity.

We report progress to develop a miniature reflective display with a silicon backplane that can be used to project full color video images. This display has sufficient speed for sequential color at full video rates. It can tolerate the high light flux levels required for projecting bright images. The display has more than 640 X 480 pixels on a 20 micron pitch. Each pixel is an 18 micron square mirror. The mirror surface can be either overcoated aluminum or a high efficiency dielectric mirror.

We report prototype active-matrix liquid crystal spatial light modulators using ordinary silicon integrated-circuit backplanes and incorporating a fast-switching ferroelectric liquid crystal light modulating layer at the backplane's surface. Backplanes reported here utilize a fully- planarized three-metal CMOS process for improved optical throughput, contrast, and light tolerance. We report a 256 X 256 device with 15 micrometers SRAM pixels having 87% fill- factor, optical throughput of 36 - 45%, contrast ratio of 80:1, and electrical rise/fall times of 85 microsecond(s) . We also report DRAM arrays with pixel pitches of 7.5 micrometers and 5.7 micrometers , with fill factors of 75% and 69%, respectively.

A new liquid crystal display (LCD) mode based on diffraction effects, which result from the application of lateral electric fields on the liquid crystal (LC) layer, is proposed in order to realize bright and high-contrast images in projection displays. The LC cell structure and its electro-optical characteristics are presented and its performance is compared to several other conventional liquid crystal display modes. In the new LCD, the upper and lower substrates support striped transparent electrodes which have a width and a pitch of 7 micrometers and 22 micrometers , respectively, for a typical case. The upper and lower electrodes are positioned parallel to each other and shifted by a half pitch, i.e. the upper electrodes are aligned with the spacings separating the lower electrodes. We refer to this design as the staggered inter-digital electrode configuration. Both substrates are coated with a polyimide layer rubbed in the direction perpendicular to the striped electrodes resulting in an anti-parallel LC alignment. In a typical cell, a nematic LC material with a positive dielectric anisotropy and a thickness of 5 micrometers are used. Lateral electric fields are generated between the upper and lower substrates and we therefore call this LC mode the Lateral Electric Field Diffraction (LEFD) mode. The transmission-voltage (T-V) curves of the LEFD liquid crystal cell were measured by using a polarized and unpolarized He-Ne laser beam ((lambda) equals 632.8 nm). The plane of incidence of the laser was set to be parallel or perpendicular to the longitudinal axis of the striped electrode and the transmitted light (zeroth order diffraction light) was measured by a photometer. The T-V curves did not show any dependence on the polarization of the incident light and no hysteresis was observed. The transmission was found to be about 80% when no voltage was applied. The threshold voltage was found to be about 1.8 volts and the voltage at which the minimum transmission occurred was 4.5 volts. The contrast ratio was calculated to be about 200:1. In the LEFD LCD, the effective indices of refraction in the directions both perpendicular and parallel to the striped electrodes are modified by the lateral electric field. Diffraction effects occur for all polarizations and it is therefore possible to obtain a high contrast ratio for unpolarized light. This means that the LEFD LCD does not require any polarizer. By combining this LEFD design with a schlieren optical system, it would be possible to create bright and high contrast images in projection displays. We think that the use of LEFD LCD is one of the most promising solutions to realize a very high performance in projection display systems.

A new approach for volumetric 3D display is introduced, which features new optical- mechanical mechanisms enabling creation of volumetric 3D images by successive projection of whole frames of 2D images. This new method projects a series of frames of profiling images, through an optical-mechanical image delivery system, onto a translucent screen which moves periodically and sweeps a space. As viewed from outside the space, the series of profiling images distributed in the space form a volumetric image because of the after-image effect of human eyes. Many viewers can walk around the space and see the image from omni-directions simultaneously without wearing any kind of glasses. Feasibility of this concept is demonstrated on two test displays, using rotating reflectors and moving lens as the image delivery mechanisms respectively. A LED projector and a slide projector with a high speed LCD shutter were used as the image source. Volumetric images of simple geometry and patterns are successfully generated and displayed on the test displays. Major technical issues involved in commercialization of volumetric displays based on this approach is discussed. Potential applications in medical displays, radar/sonar displays, computer aided design, and electronic games are expected.

In this paper, an innovative approach of a true 3D image presentation in a space filling, volumetric laser display will be described. The introduced prototype system is based on a moving target screen that sweeps the display volume. Net result is the optical equivalent of a 3D array of image points illuminated to form a model of the object which occupies a physical space. Wireframe graphics are presented within the display volume which a group of people can walk around and examine simultaneously from nearly any orientation and without any visual aids. Further to the detailed vector scanning mode, a raster scanned system and a combination of both techniques are under development. The volumetric 3D laser display technology for true reproduction of spatial images can tremendously improve the viewers ability to interpret data and to reliably determine distance, shape and orientation. Possible applications for this development range from air traffic control, where moving blips of light represent individual aircrafts in a true to scale projected airspace of an airport, to various medical applications (e.g. electrocardiography, computer-tomography), to entertainment and education visualization as well as imaging in the field of engineering and Computer Aided Design.

A 3D volumetric display system utilizing a rotating helical surface is described. The rotating helix system permits images to be displayed in a 3D format that can be observed without the use of special glasses. Its rotating helical screen sweeps out a cylindrical envelope, providing a volumetric display medium through which scanned laser pulses are projected. The light scatters from the surface of the helix so that each voxel appears to emanate from specific points in space. Each point has x-y-coordinates determined by the laser scanner and a z- coordinate determined by the intersection of the laser beam and the helix surface. Display images are created by synchronizing the interaction of the laser pulses and the moving screen to address a full 3D volume that gives the viewer true depth cues (binocular parallax, accommodation, convergence) without the need for any special viewing aids. We describe recent work on the development of mechanical, optical, electronic, and software engineering for a display system based on a 36-inch diameter helix using high speed, multichannel, random access laser scanners. Color images are created using red, green and blue laser sources. The system is capable of displaying 800,000 voxels per second, per color. A portable, 12-inch diameter, translucent helix system is also presented.

Single-LCD projection is the simplest and most compact architecture for LCD projection. It is simply made of a lamp, a LCD with color filters and a projection lens. However it suffers from poor luminous efficiency due to color filter losses, since each filter transmits only about one third of the flux emitted by the lamp. We report a new bright single-LCD architecture based on innovative use of an holographic microlens matrix, which provides the spatio- chromatic illumination of the LCD. This specific component illuminates each LCD pixel with the primary color corresponding to the color video signal driving the pixel. Correct RGB spatial repartition is obtained by taking advantage of the holographic lens spectral dispersion. When illuminated by white light, the focus is spectrally spread out. This effect has been utilized to illuminate three adjacent LCD pixels within red, green and blue light, the LCD being located at the focal plane. The use of holographic microlens arrays allow the suppression of color filters and a compensation of LCD aperture ratio. Thus, this new compact single-LCD projection architecture ensures a flux gain factor above three compared to classical ones, as well as saturated primary colors compatible with high quality LCD video image projection.

The successful demonstration of a novel 3D volumetric display based on the intersection of two low power diode laser beams in an atomic vapor is presented. A 780 nm laser and a 630 nm laser are directed via mirrors and x-y scanners towards an enclosure containing rubidium vapor, where they intersect at 90 degrees. Rubidium atoms within the small intersection volume undergo 5s_1/2 to 5p_3/2 excitation from the 780 nm laser, and then 5p_3/2 to 6d_5/2 excitation from the 630 nm laser, resulting in red omnidirectional fluorescence from the intersection point. Tuning of the lasers to the exact excitation wavelengths resulted in an extended red spot with maximum brightness. By tuning the lasers slightly off the transition wavelengths, a very localized red spot with slightly less brightness was produced. A series of intersection points were scanned in a time less than the eye's 15 Hz refresh rate to create true 3D volumetric images such as a floating cube and rotating globe, which were viewable from many angles. The maximum speed of the mechanical scanners limited the complexity of the 3D images. By incorporating higher power lasers and faster acousto-optical scanners, this technique could allow the 3D viewing of real time air traffic control, medical images, or theater battlefield management.

The educational, business and military community has indicated a need for information dealing with the performance of projection equipment. Systems which present pictorial and alphanumeric video information to groups are well known. Many technologies are available, each with characteristic performance for brightness, resolution and color rendition. The end- user is primarily interested in the perceptual quality rather than what technology is used. The current standard (NAPM IT7.228 - 1996) addresses this need by providing a specification to describe parameters and performance characteristics that allow one to compare fixed resolution systems in a meaningful way. Results should be available with a minimum number of measurements and expressed in common terms. This standard deals only with test methods and specifying terms for basic characteristics of front and rear projectors that use fixed resolution spatial light modulators (pixel based), such as LCD (liquid crystal devices) or digital mirror devices. This standard also could be applied to fixed resolution systems such as overhead projectors with LCD based data displays.