The projection display industry is diverse, embracing a variety of technologies and applications. In recent years, there has been a high level of interest in projection displays, particularly those using LCD panels or light valves because of the difficulty in making large screen, direct view displays. Many developers feel that projection displays will be the wave of the future for large screen HDTV (high-definition television), penetrating the huge existing market for direct view CRT-based televisions. Projection displays can have the images projected onto a screen either from the rear or the front; the main characteristic is their ability to be viewed by more than one person. In addition to large screen home television receivers, there are numerous other uses for projection displays including conference room presentations, video conferences, closed circuit programming, computer-aided design, and military command/control. For any given application, the user can usually choose from several alternative technologies. These include CRT front or rear projectors, LCD front or rear projectors, LCD overhead projector plate monitors, various liquid or solid-state light valve projectors, or laser-addressed systems. The overall worldwide market for projection information displays of all types and for all applications, including home television, will top $DOL4.6 billion in 1995 and $DOL6.45 billion in 2001.

This paper will review the currently available light sources, and also introduces a new, patented compound orthogonal parabolic reflector to be integrated with the light source, which focuses a relatively large light source into a very small point. The reflector creates a nearly ideal intense point source for all next generation image display systems. The proposed system is not limited by the radiation source whether it is a short arc lamp or a long tungsten filament lamp. Our technologies take the finite size of radiation sources into account to address the common problem for all reflector lamp systems, i.e., intensity and uniformity (dark hole). Successful examples will be shown on how to make the efficient intense light source match the requirements of LCD and DMD display systems. A method for reducing U.V. and I.R. radiation will also be demonstrated.

Recently, progress has been made in the development of projectors used for large screen displays. Projection systems employing high luminous efficiency Metal Halide Lamps as a light source demonstrate unique and desirable features. For example, compared to conventional lamps, a Metal Halide Lamp has longer life, higher luminous efficiency, the shortest arc length possible, and higher color-rendering characteristics, resulting in an overall superior performance. Several lamps, including Metal Halide, Xenon, and Halogen lamps, are used in HDTV (High Definition Television). Recently, Metal Halide Lamps have become accepted as the light source of choice. The reason for this is the high brightness, color balance, and long life of the Metal Halide Lamp. The fundamental operating principal for Metal Halide Lamps is almost the same as that of Mercury lamps. A Metal Halide Lamp has very different characteristics in that, the spectrum of illumination can be varied by varying the mixture of Metal Halide generated in the lamp. For these lamps, we have improved the electrode, the chemical composition of the Metal Halide, and the glass envelope. We have achieved a longer average life (greater than 2500 hours) for a compact, single-bulb, projection-type lamp.

Apparatus consists of a short-arc metal halide lamp and a dichroic mirror in parabolic-like shape has been widely employed in portable projection TV (PTV) as the light source to illuminate liquid crystal display (LCD) panels. Advantages include high luminous efficacy, near-daylight color temperature, and superior color rendering index. At MRL or ITRI we have successfully developed such light sources of 150 W input power, using Dy-Nd-Cs iodides in appropriate amount. Nominal efficiency exceeds 73 lm/w with color temperature of 6500 K. Higher efficiency better than 80 lm/w was possible at the cost of color temperature. Continuous lifetime test has been conducted for 3000 hours, compared to effective `ON' history in ON/OFF start-ups longer than 2300 hours. Luminous decay in the ON/OFF test was observed lower than 35%. A 70% reduction of the initial value is estimated around 2000 hours, better than most of the commercial counterparts. Quality of image in display is improved by matching illumination spectrum to the characteristics of flat panel devices. Monochromes after being projected are compared using (u,v) coordinates against NTSC data. Computer simulation was integrated to resolve the brightness distribution on a 3.6-inch (diagonal) LCD panel, with which lamp fixture was precisely determined. Know-hows leading to more favorable PTV systems lie in the combination of lamp spectra and color filters that comprises of the core interests in lamp assessment.

Projection lenses are often designed without due consideration to the illumination system. Likewise, most illumination systems are designed to produce a specified intensity and distribution at the LCD surface, without full consideration of the projection optics, and their potential impact to the uniformity at the projection screen. In addition, the effect of the illumination system on the actual MTF of a projection lens can be dramatic (both favorably and unfavorably) compared to the standard MTF calculation which assumes uniformly filling the entrance pupil of the lens. These and other matching issues are discussed, along with ways to analyze and design a well matched system.

Illumination is one of the key factors of LCD projection TV. It is important to design a light source that provides uniform illuminance and high intensity light beams parallel to optical axis direction. There are various kinds of light sources that correspond to different light radiation distributions. It is necessary to use a back reflector in the light source system, to confine the light radiation into a solid angle and to conserve the highest illuminance efficiency. In this paper, we compare four different kinds of reflector curves that are simple Cartesian surface, compound Cartesian surface, multiple facet surface, and complex surface. The light source used in this work is a metal halide lamp. The lengths of lamp arc as well as the lamp tube shape are playing an important role in the design of the reflector curve for final illuminance performance. Our results provide a selection rule of reflector configurations toward a desired illumination distribution.

Diffractive optics technology offers optical system designers new degrees of freedom that can be used to optimize the performance of optical systems. For example, the zone spacing of a diffractive lens can be chosen to impart focusing power as well as aspheric correction to the emerging wavefront. The surface (or blaze) profile within a given zone determines the diffraction efficiency of the element, or in other words, determines how the incident energy is distributed among the various diffraction orders. In this review, we present the fundamental properties of diffractive lens systems that can be useful for display applications. We also review briefly the application of multi-order diffractive lenses and subwavelength structured surfaces.

A couple of polarizers attached to LCD is one of the basic factors which determines the display quality and the reliability. In the application to LCD projection system, polarizers are requested to have increasingly high contrast consistent with adequate endurance under intense emission of light. A new dyed polarizer has been developed for this application. A neutral gray dichroic dye system has been composed by mixing two newly synthesized dichroic dyes with other several dyes. Using this system, dichroic dye polarizer provides superior polarizing ability of maximum CR equals 1,500 consistent with superior endurance of 1,000 hours under the surface illuminance between 1,500,000 and 2,200,000 lux at the temperature between 90 degree(s)C and 115 degree(s)C.

Projection system utilized liquid crystal display (LCD) module has become a modern trend of large screen viewing system. The display is normally ranged from 40 to 100 inches in diagonal. This is a great advantage over conventional CRT display that is very difficult to have size more than 40 inches. The LCD projection system consists of different optical components in order to have high intensity of illumination as well as good image quality. The arrangement of main optical components is typically following; light source, cold mirror, condenser, UV- IR filter, polarizer, then objective lens. In the work, we have studied the influence of UV-IR filter spectrum toward the picture quality. Three kinds of UV-IR filters with different spectrums were used. The selection rules of UV-IR filter are based on emitting spectrum of metal halide lamp, and the transmitting spectrum of LCD module. The optical performances of different spectrum in UV-IR filters were analyzed with NTSC standard in CIE (U,V) chart. Our result indicated that the chromaticity and illumination efficiency were varied by spectrum profile of UV-IR filter.

The digital micromirror device is the product of a technological development program that began at Texas Instruments over 15 years ago. It is a microelectromechanical system device that includes an array of mirrors fabricated above CMOS static random-access memory elements. Rapid switching of the diagonally hinged mirrors allows incident light to be modulated to form the highest quality video images for projection displays systems. Recent developments, discussed here, improve the optical and electronic performance as well as reduce the required number of active elements.

Active Matrix Liquid Crystal Displays used for projection applications are commonly manufactured in Thin Film Transistor (TFT) technology using amorphous or poly silicon. Displays available on the market exhibit an aperture ratio of about 30%. The rather low aperture ratio is due to the presence of column and row electrodes, a storage capacitor and a black mask. This black mask also has to hide light leakage due to disclination lines caused by lateral electrical fields. In this paper it will be shown that the TFD-R technology offers several advantages over the TFT technology with respect to the aperture ratio and the elimination of disclination lines resulting from lateral fields. On the basis of the TFD-R technology LCDs have been developed exhibiting a high aperture ratio. The high luminance capability of TFD-R LCD based projectors was demonstrated by comparing a projector provided with 2.8' TFT LCDs and the same projector provided with 2.8' TFD-R LCDs.

Producing a projection system with a single full-color LCD, which requires only one optical train instead of three, greatly reduces system cost, weight, and size but further reduces image brightness while increasing pixel visibility due to the additional appearance of individual red, green, and blue sub-pixels. At Projectavision, we have devised various optical techniques to reduce these drawbacks. This paper reports on several of these techniques and presents a computer analysis to quantify the effectiveness and limitations of some of this optical technology. The paper reports on `Depixelization' utilizing micro-lens arrays, as well as prism wedges and spatial filtering. Quantification analysis demonstrates a 90% reduction in pixel visibility due to depixelization as well as 60% reduction in the brightness difference between dead pixels and neighboring functioning pixels. This results in a greater tolerance for such dead pixels, while retaining resolution with very minimal loss of MTF. This paper also reports on some of the optical designs we devised for `brightness enhancement' to reduce light loss in the projection systems. Additionally, the paper reports on both front- and rear-screen projection prototypes and 3D video projection.

A new liquid crystal projector for a work station with high resolution, high level brightness and multisynchronous functions has been developed. It produces a high quality image showing 1280 X 1024 color pixels through a-Si TFT liquid crystal light valves and a high luminous flux at 400 lm through the use of a novel polarization converter. The projection mechanism can be employed not only in front and rear projector, with a screen projection size of up to 200', but also in a novel console type projector with a 70' screen. These projectors can be used for multi media displays, for example, as an electrical overhead projector or a tele-conference system, connected to a work station or a personal computer in the office.

A great deal of effort has been directed to the production of large area, high pixel density, high brightness displays systems. Hughes Aircraft (Carlsbad), who continues the work under the Hughes/JVC joint venture, has been and continues to be a leader in this field. This class of display uses projection of images from a reflective mode liquid crystal under the control of a photoactivated panel. Alternate means for reaching the same goal are being explored in a number of laboratories. Many designs use a matrix of transistors or scanned row and column electrodes coupled to a liquid crystal modulator. They are used either in a transmissive, or under development, reflective mode. The leader in this field is Sharp Corporation. LighTouch Systems is taking the approach of using the photoactivated reflective mode approach, similar to Hughes. However, the internal structure developed by LighTouch Systems recognizes the need for a more efficient structure in coupling the source image to the liquid crystal modulator. In particular, an internal structure that is in essence a phototransistor, rather than a photodiode, will support sensitivities, resolutions, and speeds that are a marked improvement over existing designs. These advances are critical for low cost, simple and effective large screen projection systems.

A brief introduction to Philips' color sequential projection display is given. Picture quality in a conventional three light valve display is only slightly degraded by the electrical anisotropy of the liquid crystal (LC) material as only the changing parts of the image are affected. This is not true for a color sequential display where the static parts are also affected since the LC material is in a continuous state of change. We show how a feedforward correction scheme works, why it converges and how the convergence is linked to the LC's physical properties.

We discuss and summarize several approaches to remove the pixel structure of a liquid crystal projection display that are based on the concept of multichannel low pass filtering for partially coherent light. We further demonstrate a simple technique using a diffuser to remove the pixel structure.

Holographic surface relief screens for use in either front or rear projection TV systems offer significant advantages due to light weight, easily sculpted viewing area, high contrast and gain. Produced by the holographic construction of randomized refractive structures, there is no possibility of moire effects and due to the micron size features are perfectly adapted for very high resolution. When operated in white light there is no color fringing. Reflective and transmission screens have been produced with application specific viewing angles ranging from `privacy' screens with 20 degree(s) circular to 100 degree(s) X 30 degree(s) elliptical. Reflection screens have been produced up to 12 ft X 9 ft by tiling smaller holograms with near invisible seams. Work is underway to produce single component rear projection screens with full `Fresnel' correction and contrast control.

Pure dye layers, dyes embedded into polymer matrix and pure photopolymer films (e.g. PVC- polyvinyl 4-methoxy-cinnamate) form the so called Photoanisotropic Films (PAFs), which undergo molecular and structural transformations under the action of the external polarized UV-illumination. The spectral sensitivity, spatial resolution, thermostability and reversibility of such processes strongly depend on the chemical nature of PAFs. Various applications of PAFs in LCD technology are envisaged such as: (1) the alignment of LC molecules without rubbing operation thus avoiding electrostatic charges and impurities; (2) possibility to make delicate structure of the preferred azimuth of LC director on the substrate to improve LCD viewing angles; (3) forming of phase retardation plates with local orientations of optical axes and optical path length varying from pixel to pixel; (4) implementation of B/W and color supertwist high information content displays based on birefringent colors; and (5) modification of the configuration of subtractive color supertwist cells for projection displays. The paper presents a brief introduction of physical phenomena in PAFs and its application in LCDs.

The optical efficiency of a liquid-crystal light-valve projector is determined by the optical design, the method of modulation and the efficiency of the light source. A projector has been built with efficient optics. This projector has been tested with polarized and unpolarized light using rotation of polarization as a modulation technique and also with unpolarized light by using a diffraction grating formed in the liquid crystal. The diffraction technique uses a Schlieren optical system. The light sources tested have been xenon arcs, metal halide arcs and efficient solid-state lasers. The optical system reduces laser speckle significantly when laser sources are used. All combinations exceeded 3 lumens per watt when compared on a white light basis. Experimental results of the combinations will be given. Heating of the panel by absorption of visible light limits the minimum panel size that can be used for a given light output. Typical values will be presented for the choice of panel size for a given light output.

Lead Lanthanum Zirconate Titanate (PLZT--a transparent, ferroelectric ceramic) exhibits a large quadratic electro-optic effect, allows full modulation at relatively low voltages and is commercially available in wafer form up to 150 mm diameter. PLZT modulators can handle large amount of light power. They can be configured for either reflective or transmissive operation and the pixel switching speed is in the order of 500 ns. High contrast ratio (4000:1) and throughput (90%) can be accommodated. A new technique referred to as direct bonding that involves the bonding of a thin Si film containing circuits onto PLZT substrates allows a monolithic-like integration without affecting the performance of modulators or electronic circuits. Lenslet arrays and Wollaston prisms can be added to the input of the modulator array to improve the light throughput for unpolarized light. An electro-optic light deflector stage added to the output will improve the space-bandwidth product by trading off the speed of the PLZT modulator. The availability of an excellent modulator and the possibility for monolithic integration with Si circuits makes Si/PLZT technology attractive for high performance display applications.

The ability to translate digital images into photo-recordable images is one characteristic of a light valve. It is now becoming evident that resolutions will be achieved in this process which will match the resolution capabilities of the normal eye. Thus the spatial light modulator can play a key role as a transducer between digital memories and the user who wishes this information to be presented in a graphical, real world format. The advantages of a light valve which does not have a particular pixel structure, i.e. photoactivated light valve, are many. Newer input scanning techniques are moving to the point where small compact structures are becoming feasible. The challenges between a raster scanned structure and an x-y matrix scanned structure represent two extremes. The raster scan addressing requires an increasingly high bandwidth video amplifier. The x-y matrix address requires an outstanding number of perfect address lines and drive transistors. It is likely that a linear array of LED's scanned in one dimension, will be the preferred configuration for very high quality output. Photoconductors, especially composite phototransistor configurations, allow the expansion of the response of a given device well into the best output wavelengths of LED's. This class of device, parallel drive in one dimension and scanned in the orthogonal dimension begins to display the real capability of the optical computing nature of these light valves.

The advantages of applying flat panel Liquid CRystal Displays (LCD) for Projection Displays will be extensively discussed. The selection and fabrication of flat panel LCD in order to meet the specific requirements of projection displays through various technologies will be suggested and explored in detail. The compact, flexible size and easy portability of flat panel LCDs are well known. For practical reasons, it is desirable to take advantages some of these useful properties in Projection Displays. With the recent popularity of large format display sizes, high information content and practicality all increases the demand of projection enlargement for high level performance and comfortable viewing. As a result, Projection Displays are becoming the chosen technological option for effective presentation of visual information. In general, the Liquid Crystal Light Valves (LCLV) used in Projection Displays are simply transmissive flat panel liquid crystal displays. For example at the low end, the monochromatic LCD projection panels are simply transmissive LCDs to be used in combination with laptops or PCs and light sources such as overhead projectors. These projection panels are getting popular for their portability, readability and low cost. However, due to the passive nature of the LCD used in these projector panels, the response time, contrast ratio and color gamut are relatively limited. Whether the newly developed Active Addressing technology will be able to improve the response time, contrast ratio and color gamut of these passive matrix LCDs remain to be proven. In the middle range of projection displays, Liquid Crystal Light Valves using color Active Matrix LCDs are rapidly replacing the dominant CRT based projectors. LCLVs have a number of advantages including portability, easy set-up and data readability. There are several new developments using single crystal, polysilicon as active matrix for LCDs with improved performance. Since single crystal active matrix came from silicon wafer processing, they are limited to small sizes as in Integrated Circuits. Polysilicon needs relative high temperature for active matrix processing. The usual non-alkali LCD glass substrates can not withstand such high temperature. As a result, polysilicon is also limited to small sizes. However, they can be used in Projection Displays with enlargement for comfort viewing. It is our hope some of these flat panel LCD technologies will be developed into the high end Projection Displays such as HIgh Definition Television, Multimedia or Interactive Video Communication, Entertainment and Presentation Systems of the future.

The system based on combination `CRT--Optically Addressed Liquid Crystal Spatial Light Modulator (LC SLM)' is constructed for application as projection display and device for laser beam controlling device in adaptive optics and optical image processing.

An automatic and computerized system, using stepping motor controlling and photometric sensing techniques, is specifically designed to measure photometric and chromatic characteristics of projection TV. The head of luxmeter in this system is set on a translation stage whose position is constrained along two orthogonal linear rails. The x-y translation stage is controlled by two stepping motors with a personal computer. It can take two dimensional scan at any position on projection screen. Byu scanning the screen, the measurements of total lumen, uniformity, efficiency, color coordinate, color temperature, color uniformity, and contrast for projection TV can be wholly done spontaneously. The controlling and analyzing software of these measurements were also well developed and described. In this paper, the experimental set up and results were shown. The methods and standards of these measurements were also discussed.

The first industrial, mass-production prototypes of several designs of Quantoscopes (Electron Beam Pumped Semiconductor Laser based Cathode Ray Tubes) and a pioneer prototype of a full-color, high-brightness and high-resolution television projector, based on Quantoscope technology, was developed and demonstrated in operation by the Scientific Research Institute `Platan'. As the Quantoscope's brightness increases, its resolution also increases within a certain range. The Quantoscope's emission combines the advantages of high color intensity characteristics of laser sources with minimized optical radiation hazards due to its low coherence.

Very effective conversion of an unpolarized light into polarized one is demonstrated. The prototype of high intensity polarized light source for projection systems is investigated. This prototype is based on layers of cholesteric liquid crystal mixtures with optimal properties.

A Modeling Universal System of LC-electrooptics (MOUSE-LCD) is proposed. The system enables to optimize the output optical characteristics of LCDs, such as B/W and color contrast, viewing angles, response times, multiplexing capability etc. for various LC physical parameters, display configuration and driving modes.

(pi) -regime of nematic liquid crystal based on shutters is investigated. Optimized liquid crystal mixtures with improved factor of merit for fast and high contrast ratio stereo projection displays are developed. (pi) -cell has the initial nontwist orientation of liquid crystal, retardation is switched between (pi) and zero, response time equals 1 - 3 ms, contrast ratio is more than 20:1 and controlling voltage is 20 V.

By using aspherical lens design is one of the keys to reduce the size and weight for a compact lens applied in Projection TV. The other approach is to use plastic lenses instead of glass lenses to reduce weight and cost. In this work, we describe the optical design of projection zoom objective by using aspherical surface and plastic-glass hybrid lens sets. Our aspherical design can significantly reduce dimensional scale 30% off comparing with spherical design. We also calculate the compensation of focus shift owing to the changes of temperature and humidity for plastic lenses. Results of this work and other questions raised by this attempt will be discussed in this paper.

Active-matrix addressing of a polymer dispersed liquid crystal can be achieved by a silicon- chip in the form of a reflective readout spatial light modulator (silicon backplane device). The optimum area of the chip is explored in terms of electric field fringing limitations on resolution, and optical readout efficiency.

The computer modelling of projection TV screen with additive and subtractive multicolor formation was made. The neutral polarizers with phase compensator films were shown to be suitable for LC subtractive color systems instead of color polarizers. The advantages of such construction of subtractive color systems include the application of three identical STN cells. This approach considerably simplifies the technology and results in a lower price of the color projection systems. The additive LC screen can be also produced on the basis of neutral polarizers and phase retardation plates instead of the conventionally used microfilters. The phase retardation plates can be generated, using photoanisotropic polymer films. According to calculations, the proposed construction of an additive LC screen enable to increase the brightness several times as much as compared with usual configurations.

Portable laser light show system LS-3500-10M is connected to the parallel port of IBM PC/AT compatible computer. Computer performs output of digital control data describing images. Specially designed control device is used to convert digital data coming from parallel port to the analog signal driving scanner. Capabilities of even cost nothing 286 computer are quite enough for laser graphics control. Technology of scanning used in laser graphics system LS-3500-10M essentially differs from widely spread systems based on galvanometers with mobile core or with mobile magnet. Such devices are based on the same principle of work as electrically driven servo-mechanism. As scanner we use elastic system with hydraulic dampen oscillations and opened loop. For most of applications of laser graphics such system provides satisfactory precision and speed of scanning. LS-3500-10M software gives user ability to create on PC and play his own laser graphics demonstrations. It is possible to render recognizable text and pictures using different styles, 3D and abstract animation. All types of demonstrations can be mixed in slide-show. Time synchronization is supported. Software has the following features: (1) Different types of text output. Built-in text editor for typing and editing of textural information. Different fonts can be used to display text. User can create his own fonts using specially developed font editor. (2) Editor of 3D animation with library of predefined shapes. (3) Abstract animation provided by software routines. (4) Support of different graphics files formats (PCX or DXF). Original algorithm of raster image tracing was implemented. (5) Built-in slide-show editor.

A full color TV projector based on three laser cathode-ray tubes (L-CRT) is described. A water-cooled laser screen (LS) is the radiation element of the L-CRT. We have produced three main colors (blue, green and red) by using the LS made of three II-VI compounds: ZnSe ((lambda) equals 475 nm), CdS ((lambda) equals 530 nm) and ZnCdSe (630 nm). The total light flow reaches 1500 Lm, and the number of elements per line is not less than 1000. The LS efficiency may be about 10 Lm/W. In our experiments we have tested new electron optics: - (30 - 37) kV are applied to the cathode unit of the electron gun; the anode of the e-gun and the e-beam intensity modulator are under low potential; the LS has a potential + (30 - 37) kV. The accelerating voltage is divided into two parts, and this enables us to diminish the size and weight of the projector.

There is hopefully expected a projection display using spatial light modulators (SLMs) converting a faint input-image into a brilliant output-image. A conventional liquid crystal SLM loses more than 50% of a reading light in polarizer. To solve this problem, we developed a new SLM consisting of polymer-dispersed liquid crystal (PDLC) and Bi₁₂SiO₂₀ photoconductive layers. This SLM needs no polarizer, because it lets a reading light pass or scatter depending on whether a writing light is incident upon the photoconductive layer. We calculated the dependence of the resolution of the device on the several parameters including thickness, dielectric constants and conductivities of the dielectric mirror and PDLC layer by using a new electrical image method. A high-definition SLM with limiting resolution (36 - 50 lp/mm) was fabricated by stacking the optimized mirror and PDLC layer. In cooperating the device into a Schlieren optical system consisting of an LC panel as an input image source and a 1 kW Xenon lamp as a projection light source, we performed high-contrast green image projection with a total luminous flux of 1500 lumen.