The projection display industry has gown rapidly over the past few year. This growth has been mainly sparked by the impact of compact units that use either liquid crystal displays or the digital light processing system developed by Texas Instruments. These units have created a large market in the multi-media business presentation segment. With the continued development of improved multi-media software, new light modulation systems, and the expanded use of 'electronic presentations', the market for projector swill continue to grow at a significant rate during the next five years. The overall worldwide unit consumption of projection information displays of al types and for all applications, including home television, topped 1.8 million units in 1998; this represented a market of 7.2 million dollars. The market is forecast to grow to 4 million units valued at 11.7 billion dollars in 2004. THe various application segments of the market and the relative sizes of the segment by the major technologies are presented in this paper.
Projection system based on microdisplays have the advantage of lower cost and weight due to the reduction in size of the image generating devices and associated optics. Reflective devices are favored because the pixel aperture remains high for small pixels. However, at high resolution the performance is compromised by the reduction in size of the pixel. Increased diffraction loss with reduction in pixel size reduces the optical throughput of the projector. Electric field fringing is enhanced for smaller pixels in liquid crystal devices, sacrificing throughput in general. Computed diffraction losses are presented for a range of pixel geometry and projection f/numbers. An approximation for fringe field modulation is used to estimate throughput losses associated with field fringing.
Compact LCD projectors require compact, low power metal halide lamps to achieve maximum screen brightness. We have previously described such lighting systems, taking into account ballast stability, source etendue, and collection optics. Metal halide sources have a significant advantage over high pressure xenon, high pressure mercury, and halogen sources in that the spectral power distribution of the source can be optimized for the projection system. This is in addition to the inherently greater luminous efficacy of metal halide source. We present the result of recent studies on chemical dose composition in 50 Watt, 1.2 mm arc gap, long life metal halide lamps. Through designed experiments on chemical species, dose weight, and molar composition we were able to increase the luminous output by as much as 50 percent in some cases. The optimized metal halide lamp has 50 percent more red radiation than a 50 Watt, 1.3 mm gap high pressure mercury lamp and also produces a preferred color temperature. Knowledge of the significant factors that effect color allows us to design virtually any color gamut. It was possible to match the filter characteristics of a number of projection systems.
Gradient dichroic mirrors consisting 25 alternating layers of TiO2 and SiO2 were prepared by reactive electron beam deposition at a glass-substrate temperature of 300 degrees C in a home made planetary planar coating system without mask. Samples with the various tilt angles from the rotating axis were hanged on the edge of four specially designed hollow planets. The thickness variation for a single layer SiO2 over a planet of 16 cm diameter at the height of 60 cm was less than 3 percent. This coating system was very suitable for the coating of gradient dichroic mirrors with large area showing the consistent color performance with various incident angles across the mirror surface.
A novel high performance thin film polarizing beam-splitter (PBS) is described. This PBS is non-absorbing and has a broad band, a wide angular field and high extinction ratios for both reflected and transmitted beam. Several high efficiency projection displays based on this novel PBS will be presented.
In this paper the design aspect and fabrication issues of a GXGA reflective silicon light valve are discussed. Special attention is paid to the layout and architecture of the silicon backplane using submicron CMOS processing with a medium voltage extension. A careful layout yields a silicon backplane with an analog DRAM architecture with a pixel pitch of 15 micrometers , addressed by analog integrate drivers using a 16-fold parallelism. The investigated reflective TN and vertical aligned NLC technologies showed both an acceptable performance for application in high-end reflective light valves, although the vertical aligned NLC showed a slightly better contrast ratio and black state.
The objective of this paper is to detail the grating light valve technology and demonstrate its flexibility in attaining high performance in a variety of optical systems and applications, concentrating particularly on its application toward projection display systems. The GLV technology represent a unique approach to light modulation and offers remarkable performance in terms of contrast, efficiency, switching speed, and cost. The electro- mechanical response of the GLV device can be tuned through various design and operational modes to deliver desired performance for a given application. The design and fabrication of a linear array module of 1,088 GLV pixels is described. This module enables a scanned linear GLV architecture for HDTV projection products. The flexibility of the GLV technology and the scanned linear GLV architecture can support line sequential and frame sequential color, as well as 3-valve color systems. System level optical design either include embedded scanners to emulate 2D film source planes or external scanner elements for greater system simplicity. Results with actual projection display system yield unparalleled on-screen performance, having uniformity greater than 99 percent corner-to-corner, high contrast, 10-bits of grayscale per color, and no visible pixel boundaries.
A novel projection optical system has been developed for application with reflective CMOS LCD technology. The optical design for an off-axis system will be described and the performance of this system compared with traditional transmissive LCD. The advantages and disadvantages of this type of architecture are discussed.
Reflective x-Si backplanes allow projection displays to evolve toward higher pixel count and greater miniaturization, extending the range of competitive application. As light valve area A is reduced, projector output into solid angle S equalsV (pi) NA2 can in many cases be considered to decrease roughly as approximately (A*S)0.5, with the 0.5 exponent representing typical microdisplay operating in a regime that is neither purely brightness-limited nor purely power-limited. Polarization modulation entails a modified scaling approximately (A*S/2)0.5; color sequential operation, approximately (1/3)*(A*S)0.5; spatially divided single-light-valve RGB projection, approximately (A*S/3)0.5. Projection lenses for three-light-valve system must provide an increased working distance to accommodate a color recombiner. Zoom lens are often required in front projectors, and rear projection usually entails a short lens-to-screen distance. It has become cost-effective to use plastic aspherical elements to meet these requirements. Periodic strip-PBS arrays have been widely adopted for polarization recycling, but aperiodic homogenizers are sometimes used to correct the uneven magnification and symmetry limitations of conic reflectors. Bright-state and dark-state beams must occupy distinct etendues in the half space above a reflective light valve, creating a vulnerability to crosstalk. Crosstalk from a polarizing beamsplitter gives rise to a residual background intensity approximately 0.3*NA2, unless a quarterwave corrector is used. Crosstalk can also arise from stress birefringence in prism substrates. Stray light makes an indirect contribution to background, but can sometimes be corrected by filtering.
Software packages capable of simulating complex optical systems have the power to shorten the design process for non-imaging illumination, projection display, and other imaging illumination systems, Breault Research Organization's Advanced Systems Analysis Program (ASAP) and Robert McNeel and Associates' Rhinoceros computer aided design software, together, allow complicated optical systems to be simulated and analyzed. Through the use of Rhinoceros, an optical system can be accurately modeled in a 3D design environment. ASAP is then used to assign optical properties to the Rhinoceros CAD model. After the optical system has been characterized, it can be analyzed and optimized, by way of features specific to the ASAP optical analysis engine. Using this simulation technique, an HID arc source manufactured by Ushio America, Inc. is accurately represented. 2D CCD images are gathered for the source's emitting-volume across its spectral bandwidth. The images are processed within ASAP, via the inverse Abel command, to produce a 3D emitting-volume. This emitting-volume is combined with an accurate model of the source geometry and its optical properties, to finalize a functioning virtual source model. The characterized source is then joined with a simulated optical system for detailed performance analysis: namely, a projection display system.
The optical sub-systems for reflective mode silicon based CMOS-LCD projection display are discussed in this paper. Various methods to improve the optical efficiency of the projection system are proposed. First, new optical modes for the reflective light valve are discussed. The emphasis is on improving the reflectance. Second, a new high throughput projection system employing a 2-step process is proposed. It employs a conventional LCLV projection system capable of very high luminous output. FInally, the color separation and recombination schemes for a full color projector are discussed. A new trichroic prism assembly design is described which has the advantages of low s and p polarization splitting in the reflectance spectrum. Hence it can be used for both color separation and recombination. Thus a compact optical system for reflective projectors is possible with good light efficiency.
Digital Light Processing (DLP) projection displays based on the Digital Micromirror Device (DMD) were introduced to the market in 1996. Less than 3 years later, DLP-based projectors are found in such diverse applications as mobile, conference room, video wall, home theater, and large-venue. They provide high-quality, seamless, all-digital images that have exceptional stability as well as freedom from both flicker and image lag. Marked improvements have been made in the image quality of DLP-based projection display, including brightness, resolution, contrast ratio, and border image. DLP-based mobile projectors that weighted about 27 pounds in 1996 now weight only about 7 pounds. This weight reduction has been responsible for the definition of an entirely new projector class, the ultraportable. New applications are being developed for this important new projection display technology; these include digital photofinishing for high process speed minilab and maxilab applications and DLP Cinema for the digital delivery of films to audiences around the world. This paper describes the status of DLP-based projection display technology, including its manufacturing, performance improvements, and new applications, with emphasis on DLP Cinema.
Modern video projectors are becoming more compact and capable. Various display technologies are very competitive and are delivering higher performance and more compact projectors to market at an ever quickening pace. However the end users are often left with the daunting task of integrating the 'off the self projectors' into a previously existing system. As the projectors become more digitally enhanced, there will be a series of designs, and the digital projector technology matures. The design solutions will be restricted by the state of the art at the time of manufacturing. In order to allow the most growth and performance for a given price, many design decisions will be made and revisited over a period of years or decades. A modular open digital system design concept is indeed a major challenge of the future high definition digital displays for al applications.
The polymer-dispersed liquid crystal (PDLC) films of the optically addressed light valves in the high-definition television (HDTV) projection display described here can modulate unpolarized light with high spatial resolution as well as with a high optical efficiency based on the light scattering effect. A PDLC film suitable for use in HDTV projection display was developed by evaluating the microscopic spatial light modulation and polymer-network morphological properties of test films prepared using various curing conditions for photopolymerization-induced phase separation. Films produced under optimum curing conditions have a fine polymer-network structure appropriate for films used in the light valves of a HDTV projection display. Our prototype full-color HDTV projection display using three PDLC light valves provides a resolution of 850 TV lines, a brightness greater than 1800 ANSI lumens, and a maximum contrast ratio of 100:1.
Diffraction modulator exploiting transverse electro-optic effect in ferroelectric liquid crystals is proposed for display applications. Experiments performed with short pitch ferroelectric liquid crystal aligned homeotropically showed that an achromatic contrast ratio better than 100:1 available with oblique readout. The sources of the contrast deterioration and a tolerance of the proposed scheme to them are analyzed. For the selected directions of readout the light output obtains low sensitivity to the polarization of readout light.
We have constructed a high resolution projection display with a single reflective LCD panel. Reflective technology based on standard silicon CMOS processing has emerged as a favorable direction for projection displays. Advantages include low investment and fabrication costs, high resolution capability, and high aperture ratio. As a move towards lower cost and high performance, we have applied reflective technology to a single panel projection display. The pixel array is SXGA and is fabricated in a process with both 5 Volt logic and 15 Volt structures. A thin 1 micron liquid crystal cell is formed over the array. A fast on time of 0.2 ms is attained with a nematic LC effect. System architecture is based upon a scrolling color illumination system wherein three color bands are present on the panel at all times. This arrangement avoids the 2/3 light loss in spectral efficiency present in a more conventional color wheel system. The system demonstrates that color sequential projection displays are feasible with LCD devices. And this direction holds great promise in a wide variety of applications including consumer HDTV displays.
A stereoscopic display using a curved directional reflection (CDR) screen is a promising approach towards realizing an immersive 3D display system that does not require users to wear special glasses. A CDR screen consists of a corner reflective mirror array and lenticular sheets and can provide an ultra-high gain of more than 25. Consequently, 3D images are visible even in a bright room.
Stretchable Membrane Mirrors (SMMs) have been developed at the University of Strathclyde as a cheap, lightweight and variable focal length alternative to conventional fixed- curvature glass based optics. A SMM uses a thin sheet of aluminized polyester film which is stretched over a specially shaped frame, forming an airtight cavity behind the membrane. Removal of air from that cavity causes the resulting air pressure difference to force the membrane back into a concave shape. Controlling the pressure difference acting over the membrane now controls the curvature or f/No. of the mirror. Mirrors from 0.15-m to 1.2-m in diameter have been constructed at the University of Strathclyde. The use of lenses and mirrors to project real images in space is perhaps one of the simplest forms of 3D display. When using conventional optics however, there are severe financial restrictions on what size of image forming element may be used, hence the appeal of a SMM. The mirrors have been used both as image forming elements and directional screens in volumetric, stereoscopic and large format simulator displays. It was found that the use of these specular reflecting surfaces greatly enhances the perceived image quality of the resulting magnified display.
Major technology and market trends that could generate a 20 billion dollar electronic projector market by 2010 are reviewed in the perspective of recent product introductions. A log linear analysis shows that the light outputs of benchmark transportable data video projectors have increased at a rate of almost 90 percent per year since 1993. The list prices of these same projectors have decreased at a rate of over 40 percent per year. The tradeoffs of light output vs. resolution and weight are illustrated. Recent trends in projector efficacy vs. year are discussed. Lumen output per dollar of list price is shown to be a useful market metric. Continued technical advances and innovations including higher throughput light valve technologies with integrated drivers, brighter light source, field sequential color, integrated- and micro-optical components, and aerospace materials are likely to sustain these trends. The new technologies will enable projection displays for entertainment and computer applications with unprecedented levels of performance, compactness, and cost-effectiveness.
The thin-film micromirror array (TMA) is a new reflective type spatial light modulator fabricated with the optical microelectromechanical system (MEMS) technology. Micromachined thin-film piezoelectric actuators are used to control the tilt angle of each micromirror, which simply defines the gray scale of the matching screen pixel when it reflects the light for the lamp. The hidden actuator design with the two-sacrificial layer process provides the highest fill factor and flat enough micromirrors resulting the system optical efficiency of 22 percent, which is the highest efficiency among all the reflective and transmissive light modulators in the world at the present time. A working projector prototype of 5,400 true ANSI lumen is realized with three TMA modules and a 1 kW Xenon lamp. TMA projector prototype is brighter than any competing technology projectors in the world at the same lamp power, at least three times or more. The simplicity of the underlying principle and the highest optical efficiency of TMA enables high-brightness and cost competitive projection displays which has been impossible in the past. At the same cost, more brightness can be provided for the high-end large venue projectors. At the same brightness, lower cost products can be provided as desktop projectors for no-more-darkroom digital presentation and affordably priced HDTVs.
Projection lamps and light sources are on the critical path to the widespread application of projection systems. Not only are the projection lamps the weak link in determining system lifetime, but the purchase price of the lamp and power supply could limit the growth of projection technology in system that sell for less than 3,000 dollars.