The projection display industry represents a multibillion- dollar market that includes four distinct technologies. High-volume consumer products and high-value business products drive the market, with different technologies being used in different application markets. The consumer market is dominated by rear CRT technology, especially in the projection television segment. But rear LCD (liquid crystal display) and rear reflective (DLP, or Digital Light ProcessingTM) televisions are slowly emerging as future competitors to rear CRT projectors. Front CRT projectors are still popular in the high-end home theater market. Front LCD technology and front DLP technology dominate the business market. Traditional light valve technology was the only solution for applications requiring high light outputs, but new three-chip DLP projectors meet the higher light output requirements at a lower price. In the last few years the strongest growth has been in the business market for multimedia presentation applications. This growth was due to the continued increase in display pixel formats, the continued reduction in projector weight, and the improved price/performance ratio. The projection display market will grow at a significant rate during the next five years, driven by the growth in ultraportable (< 10 pound) projectors and the shift in the consumer market to digital and HDTV products.
Although analog CRTs continue to enable most of the world's electronic projection displays such as US consumer rear projection televisions, discrete pixel (digital) active matrix LCD and DLP reflective mirror array projectors have rapidly created large nonconsumer markets--primarily for business. Recent advances in image quality, compactness and cost effectiveness of digital projectors have the potential to revolutionize major consumer and entertainment markets as well. Digital penetration of the mainstream consumer projection TV market will begin in the hear 2000. By 2005 digital projection HDTVs could take the major share of the consumer HDTV projection market. Digital projection is expected to dominate both the consumer HDTV and the cinema market by 2010, resulting in potential shipments for all projection markets exceeding 10 M units per year. Digital projection is improving at a rate 10X faster than analog CRT projectors and 5X faster than PDP flat panels. Continued rapid improvement of digital projection is expected due to its relative immaturity and due to the wide diversity of technological improvements being pursued. Key technology enablers are the imaging panels, light sources and micro-optics. Market shares of single panel projectors, MEMs panels, LCOS panels and low T p-Si TFT LCD panel variants are expected to increase.
This paper presents the concept and study of an innovative device dedicated to compact illumination devices. Partially reflecting micro-prisms are sealed inside a plastic plate. Light injected by an edge of the panel is propagating under total internal reflection condition. Partial light extraction is performed by the micro-prism surfaces. Fan-out application is also described in the field of optical network.
Flying-spot displays scan an image across the display screen using a high-energy beam. Each pixel can be a narrow, submicrosecond pulse. When such displays are measured with conventional light-measuring devices (LMDs), such as luminance or illuminance meters, there is concern that the LMD may not accurately measure the display light output because of the unique characteristics of the source. The LMD may be unable to properly integrate the narrow pulses, or the high-energy signal may saturate the detector. As in all areas of metrology, it is essential to verify that the instruments used are providing the desired information. A diagnostic has been developed that allows for an evaluation of LMDs for use in measuring flying-spot and similar displays. This method tests for both integration and saturation errors using a bipartite comparator and a neutral density filter. Errors resulting from the saturation of the LMD by the flying-spot display are demonstrated. The construction and procedure of the diagnostic is described. Limitations of the technique as well as sources of error are presented.
A thin film color selective beam splitter is designed and the method of fabrication is described through a single deposition process of a coating system onto the two lateral faces of a triangular prism with base angles of 60 deg. and 45 deg. respectively. Properly prepared contact prisms are then cemented onto the two coated surfaces to make all the incoming and outgoing light beams normal to the prism block. The tri-chromatic prism provides the primary colors R, G, B according to the sequence that the red color is first reflected when the modulated white beam is incident at 30 deg. onto the dichroic filter deposited on the lateral face with the base of 60 deg., and then the rest part of the spectrum is incident at the other dichroic filter of the system at 45 deg. to get the blue and green beams separated. Color performances of the system from the thin film filters constructed with TiO2 and Al2O3 as the high and low index layers respectively are analyzed. The advantages to use the tri-color prism block in a projection device with reflective liquid crystal light valves are discussed.
Projectors that use LCOS lightvalves face special contrast requirements. Most configurations for reflective light valves employ tilted beam-dividing coatings that see both bright and dark polarization states. The optics must then be designed to eliminate polarization mixing at these coatings, which ordinarily arises when the S and P planes for different rays are non-parallel. We show how phase- controlled coatings can exploit the double-pass symmetry of the Plumbicon tri-prism geometry to correct this effect, reducing cross-polarized reflectivity to approximately 1E-3 when the light valve is mirror-like in black-state. Though contrast in different rays varies as a function of both ray skew component and coating angle of incidence, we show that for NA <EQ 0.2 the computation involved in calculating beam contrast is essentially equivalent to tracing a single ray. Light valves that use a normally-black TN mode exhibit a non-mirror-like phase dispersion in their black-state, complicating contrast control in the optics. Scatter depolarization at the edges of pixel electrodes is enhanced in these light valves, because the inherent twist causes the backplane polarization to be rotated out of alignment with pixel edges. We show that all of these contrast degradation mechanisms can be addressed by incorporating into the light valve a compensating layer having opposite birefringence to the black-state TN active layer. Moreover, when the compensating layer and driven layer are blue-shifted to a shorter LC thickness than would ordinarily be appropriate for the wavelength band of interest, a highly achromatic response is obtained at all gray levels.
Many micro-display devices have been proposed and used for projection display. The author will review about the characteristics of these devices and will discuss about optics to achieve their performance with full function. This paper shows typical approach of projection optics and describe about the advantage of the commercialization.
Liquid crystal on silicon (LCOS) is becoming an established technology for personal viewers and projection applications. However no unique technology is used at present. One has different silicon backplane architectures as well as liquid crystal technologies. Analog addressed DRAM backplanes are often preferred in projection applications, however these architectures often require higher voltage addressing schemes than the standard used 5 V CMOS. Using oblique evaporation of SiO2, a reflective vertically aligned nematic liquid crystal technology was developed enabling the manufacturing of microdisplays for projection applications in a standard 5 V CMOS backplane technology. The developed technology showed acceptable optical performance and might be an interesting alternative to the present used microdisplay technologies.
Future display configurations will encompass multiple displays (as well as multiple display technologies within a single display), configured in a manner that allows the displays to be perceived as a single integrated image. Visual display technology is progressing rapidly beyond the traditional capabilities of the early industry display workhorse `the cathode ray tube'. Configuring multiple displays (to perform as a video wall, a high-resolution display monitor or a tiled display) will enhance display performance as well as requiring display designer to perform trade-off to compensate for a specific display technology's limitation. This paper will document and discuss the many of the technology issues that may be optimized for multiple digital display configurations.
The range of the reproducible color, i.e., color gamut, of the conventional display devices such as CRTs (cathode ray tubes) and LCDs (liquid crystal displays) is sometimes insufficient for reproducing the natural color of an object through color imaging systems. In this paper, six-primary color display is presented to reproduce the expanded color gamut, by using two conventional RGB projectors and six interference filters. The design method of the filters is also introduced to maximize the volume of the color gamut in CIE-LUV uniform color space. Using the experimental system, the gamut of the six-primary projection display is evaluated comparing with that of conventional CRTs and projectors.
JENOPTIK Laser, Optik, Systeme GmbH has developed for the first industrial all-solid-state Red-Green-Blue laser system for large image projection systems. Compact in design (0.75 m3, 180 kg, 3 kW power consumption), the system consists of a modelocked oscillator amplifier subsystem with 7 ps pulse duration and 85 MHz pulse repetition frequency, an optical parametric oscillator, and several non-linear stages to generate radiation at 628 nm, 532 nm and 446 nm with an average output power above 18 W. Each of the three colors is modulated with the video signal in a contrast ratio of 1000:1 and coupled into a common low order multi mode fiber. The system architecture relies on efficiently manufacturable components. With the help of FEM analysis, new engineering design principles and subsequent climatic and mechanical tests, a length stability below 50 micrometers and an angle stability below 10 (mu) rad have been achieved. The design includes efficient laser diodes with integrated thermo- electric cooler and a lifetime above 10000 hours. The stability of the output power is better than +/- 2% in a temperature range from 5 degree(s)C to 40 degree(s)C. The system operates reliably for more than 10000 hours under field conditions. The design is based (among others) on work by Laser-Display-Technologie KG and the University of Kaiserslautern.
A compact and efficient laser source is required as an enabling technology for laser projection displays. We discuss a scalable green-pumped, non-critically phase- matched LBO optical parametric oscillator (OPO) which simultaneously generates red and blue wavelengths that are ideal for display applications. Pumping the OPO with 9.7 W of 523 nm green light from a frequency-doubled, diode-pumped Nd:YLF oscillator/amplifier laser system has resulted in a measured 4.0 W of 896 nm signal power and an estimated idler power of 2.8 W. The signal was extra-cavity frequency doubled to produce 1.10 W of blue light at 448 nm. Intra- cavity frequency doubling of the idler produced 1.95 W of red light at 628 nm.
We report on concepts and the performance of diode pumped solid state laser systems which generate simultaneously red (R), green (G) and blue (B) laser light with output powers of up to 7.1 W at 629 nm, 6.9 W at 532 nm and 5.0 W at 446 nm. The superposition of this RGB radiation provides white light with a power of 19 W. In respect to the diode pump power of 110 W the RGB output corresponds to an optical efficiency of 17%.
Laser light sources present many advantages for projection displays over the currently employed incoherent light sources. Perhaps the most significant attribute is the laser's high degree of polarization, which greatly improves the efficiency of liquid crystal light valve (LCLV) projectors. The maximum achievable efficiency of an LCLV projector is severely limited with the use of an unpolarized light source such as an arc lamp. The polarized emission from a laser can be coupled to the screen much more efficiently, offering the possibility of smaller projectors with higher luminous efficacies. Additionally, the RGB primaries of laser light fall along the spectrum locus of the chromaticity diagram allowing for a much expanded color gamut over dichroically-separated lamp spectra. This provides the possibility of offering unprecedented color reproduction for the emerging digital cinema industry. The combined properties of polarization, monochromaticity, and low divergence result in a significant increase in image contrast when coupled to LCLV image engines. Substituting lasers for lamp light sources have shown to increase sequential contrast by as much as five-fold. This simple substitution has also resulted in broad improvements to the projector's entire MTF, thereby increasing the apparent resolution of the image. These are all striking arguments as to the potential of lasers in the emerging e-cinema market and the impetuous behind our current development effort presented here.
We demonstrate bright pictures in the pixel format of HDTV and XGA with a current power consumption lower than 2.5 kW and a RGB laser output power of 15 W with the wavelengths 446 nm, 532 nm and 629 nm. The laser projection system consists of a scanning unit with a rotating polygon scanner (rotational frequency up to 2 kHz) to write the lines and a galvanometer scanner for the vertical deflection of the lines. The system allows the separation of the RGB-laser with the video modulation part from the free moving scanning unit with an optical fiber. The optical fiber provides the video modulated RGB-laser power in a collinear beam to the scanner. We explain detailed the requirements for RGB--laser beams. The main demands for high resolution and sharp scanned pictures are near diffraction limited laser beams, but at least with an optical beam product of < 0.75 mm mrad. Furthermore we give an outlook for an increase of pixel resolution.
In projectors employing reflective liquid crystal light valves, polarizing beam splitters (PBS) have to be used. However, ordinary wide bandwidth PBSs have relatively small acceptance angles. This reduces the optical efficiency of the projectors. In this paper we present new designs for the PBS which has the advantage of large acceptance angles without compromising the operating bandwidth.
Ultra-portable projector size and weight have decreased more than 50% in the last three years. DLP projectors are the smallest currently available, but three-path polysilicon LCD projectors are also rapidly improving and LCOS technology is emerging. Future miniaturization will come from shrinking of the display devices, lamp arc size improvements, increasing of optical engine efficacy, integration of electronics, improved thermal management techniques and high power density power supplies. Electronics integration and to some extent power supply shrinking should provide relatively easy near-term improvements. Optics, display device and lamp improvements appear feasible, but will be more challenging. Projector thermal management is not yet optimized, but improvement is another key challenge since power density is already high. Within the next five years, sub-2 lb. projectors with volumes less than notebook PCs should be possible.
A compact 60-inch LCD rear projection television optimized with depth less than 60 cm has been developed by using three 1.3' poly-Si TFT-LCDs of 1024 X 768 pixels resolution. Three primary colors of the projection system are separated and synthesized by dichroic mirrors and X-prism respectively. Polarization converter is used to increase the optical throughput and an aspherical hybrid projection lens with f equals 19.97 mm and f/# equals 2.4 is designed to effectively shorten the projection distance. A Fresnel lens and a fine lenticular lens screen can create a morie' pattern free picture. Under a 120 W UHP lamp, the brightness of the rear projection TV can achieve 460 nits luminance.
A 0.9' high resolution reflective microdisplay using ferroelectric liquid crystal on Si backplane has been developed. This device has 2.3 million pixels (UXGA/HDTV) with 16:10 aspect ratio. The highest resolution of 10 micrometers pixel pitch with 86% fill factor was achieved by the newly- designed pixel driver circuit. This circuit consisted of 5 transistors and 3 capacitors fabricated with only NMOS using conventional 0.35 micrometers CMOS process and the architecture with two memories per each pixel realized to write the next data into the pixel memory while the image was displayed. This enabled all the pixel data to be rewritten simultaneously with high refresh rate of 6.5 kHz, giving higher efficiency of light utilization than conventional scanning technique which rewrite the data at a line. The high refresh rate made color break-up invisible even in moving picture. In this system a new modulation technique using LED light source to generate grayscale was devised. The combined technique of pulse width modulation and light source modulation gave full color image using sequential color with high grayscale. This microdisplay is promising for projection displays and virtual image displays.
This talk summarizes research being conducted on a `laser television' capable of successfully entering the consumer market. Using lasers for the RGB light source has the advantage of producing superior color (large color triangle, narrow spectral bandwidth) and high image resolution (large modulation bandwidth, small `pixel area'.) Unique challenges of this technology and progress to date in dealing with them are presented.
The vertical aligned nematic cell is favored in reflective projector systems because of its inherent high contrast ratio, which is essentially independent of cell gap variation and wavelength. Off-axis projectors are of commercial interest due to lower manufacturing cost. A computational study of projector contrast ratio as a function of projection f/number and offset angle is presented. The off-axis system maintains a contrast ratio greater than 100 up to offset angles of 15-degrees. Modest compensation with a negative uniaxial retarder allows the off-axis projector to reach contrast ratios comparable with on-axis systems.
Recent developments in arc modeling have stressed increasingly detailed representations of arc structure, but there is little or no published data on how well these arc models predict measured efficiency in a light collection system. We develop a highly simplified arc model consisting of two main components and a few minor components. We then compare the predictions of this arc model with actual measured collection efficiencies for an Ushio 350W short-arc metal halide lamp. The predictions of the simplified model are shown in this instance to be as good or better than much more complex models. The simpler approach may be more cost- effective in volume, and may have advantages for describing lamp variability.
A 3-inch phosphor screen using YAG single crystal as the substrate has been developed for compact projection displays. In order to obtain higher brightness, high resolution and high resistivity against high-density electron bombardment, the phosphor screen properties are improved from the bulk property of the phosphor as well as the screen process. An improved phosphor which has an optimum phosphor composition of (formula available in paper) has been developed.
It is found that the deterioration of the projection phosphor screen is accelerated by phosphor screen heating. Therefore, a critical step in the development of projection tubes of greater luminosity is the improvement of the phosphor deposition method that relies in a higher thermal conductivity of the phosphor layer. We have developed a novel phosphor deposition technique for YAG projection display application.
During the past decade the performance and price of projection systems based on microdisplays have demonstrated dramatic improvements. Ultraportable front projection systems can deliver nearly 1000 lumens of light at XGA definition and street prices of such systems are rapidly falling to $2,000. The market leading low priced presentation projectors use two alternative microdisplay technologies: transmissive liquid crystal with a high temperature poly-silicon on quartz backplane (HT p-Si) or the reflective digital micromirror device (DMD1' , made with CMOS. These incumbent microdisplay technologies are now being challenged by several new approaches, including reflective liquid crystal on a silicon backplane (LCOS) and transmissive liquid crystal with a low temperature poly silicon on glass backplane (LT p-Si). In addition to new microdisplay technologies, developers have been demonstrating new single imager projector architectures that have the promise of leading to even lower systems costs. While the color field sequential DMD system and the larger 3 to 6 inch spatial color transmissive liquid crystal with an amorphous silicon on glass backplane (a-Si) are the only commercial single imager designs, single microdisplay projectors have been demonstrated using color field sequential LCOS1, spatial holographic microlens LCOS2, and a spatial system than employs color scrolling and a LCOS imager3. While the presentations market continues to offer a major growth opportunity for the projector developers, the potential use of microdisplay technology in the television market offers, at minimum, an incremental market opportunity, and at maximum, a huge potential additional market. But for the home market to amount to much, the microdisplay based televisions will have to offer much better value to consumers than the current rear projection CRT TVs. Otherwise, rear projection televisions will remain a North American niche market with demand of 1 million units per year and modest growth. Unless the new microdisplay televisions offer better value, their makers will be fighting for a share of a modest market against deeply entrenched competitors What does better value mean? Published market research as well at several studies completed by McLaughlin Consulting Group4 (MCG) indicate a hierarchy of consumer preferences for NTSC televisions. Not surprisingly, for the American market two characteristics lead all consumer preference lists: price and size. As shown in Table 1 ,secondary preferences include brightness, contrast, image quality, tuning options, cabinet depth, weight, and sound system. Well down the list are features such as power and safety.
Pixelated spatial light modulators (SLMs) are commonly used in projection displays. The total number of columns and rows in the device define its `native' resolution. This native resolution may not match the resolution of the signal that is to be displayed. It is common to use electronic methods to re-scale the signal to match the resolution of the panel. This resizing introduces artifacts that may be unacceptable in some applications. A new technique is described using optical methods to obtain an artifact free representation of the signal. This method works particularly well with high- resolution 1.8' diagonal devices where the signals to be displayed have equal or lesser resolution than the SLM. The system requires a zoom illumination system and a zoom projection lens. Information is sent to a sub-area of the panel that matches the native resolution of the signal. The zoom illumination system concentrates the total light flux onto this sub-area. A zoom projection lens adjusts the size of the final image to be constant.