Étendue‐density homogenization lens optimized for high‐pressure mercury lamps

Abstract— In order to increase the screen brightness of Digital Micromirror Device? projectors (DMD?), we have developed a new aspherical lens. Homogenizing the étendue‐density distribution made by a high‐pressure mercury lamp, this lens improves the light convergence at its focal point where the rod integrator's entrance is placed. Our simulation showed that the percentage of increase in brightness is up to 18.4%.     

Development of a dual‐lamp projector with higher brightness

Stationary projectors mainly used in system applications have recently gained a wider application range, including general presentations in halls and large conference rooms and being used, for example, in digital signage and for monitoring purposes. Consequently, they are required to meet new market demands for durability, reliability, and flexibility in installation in addition to their conventional basic performance such as especially high brightness. To achieve especially high brightness, a new optical system with two lamps is proposed; the profile of the cover glass that prevents the glass from scattering is made aspherical, the profile of the beam‐combining mirror is improved with its position optimized, and the size of the incident plane of the integrator rod is made larger (1.1 times). These measures resulted in an optical system of an even higher efficiency with 7000 lm, which is the highest in its class (according to a June 2010 investigation). Also, the arrangement of two parallel lamps completely eliminated the effect of heat passing from one lamp to the other, which helped secure durability, reliability, and flexibility in installation. Furthermore, the combined use of the unique non‐telecentric optical system, adopted from the conventional single‐lamp model, helps maintain the class‐highest contrast ratio.^1,2     

High‐efficiency light‐collection optics for lamp‐based projection TV

Abstract— A new light‐collection optics has been developed that enhances the luminance of projection TV which use lamps as the light source. The conventional optical system consists of an elliptical reflector and a flat‐surface front glass, but these systems cannot sufficiently collect the beams coming from the light source, and they cause loss in the coupling with the light pipe. To solve this problem, we devised a new optical system through a structure of an aspherical reflector and an aspherical front glass. This new optical system concentrates the beams coming from the light source to a smaller point which improves the coupling efficiency. Thus, we have successfully increased the luminance of the projection TV by approximately 10%. This paper reports the design principles of the new optical system and the results of a prototype experiment.     

Higher‐output more‐compact UHP lamp systems

Abstract— Projection systems have reached convincing performance with several thousand screen lumens created by systems of only a few liters in volume. With more than 10 lm/W they are the most efficient display systems realized today. The tremendous progress achieved up to now relies on the outstanding properties of the UHP lamp. The combination of high brightness with lifetimes extending up to more than 10,000 hours is ideal for projection applications. This paper will summarize some recent technological achievements: the volume of the lamp and driver system has been reduced by a factor of 10, exploiting a reduced ignition voltage as well as new optical concepts for the reflector. The optical performance of short‐arc projection lamps can be improved dramatically: a dichroic coating on one half of the UHP burner is applied to focus all light into one hemisphere. This allows for extremely compact reflector systems and an improvement by 20–30% in light collection.     

Color‐tuning projection system for adaptive combination of high brightness and wide color gamut

Abstract— The demand for projectors with high brightness and wide color gamut has been increasing; however, UHP lamp projectors cannot deliver those two qualities efficiently and simultaneously because of its color‐separation system. The newly developed projection system — “Color‐Tuning Projection System” — realizes the adaptive combination of high brightness and wide color gamut with one projector. This projector features a fourth liquid‐crystal panel — “Color Tuner” — with a 3LCD optical engine, which controls yellow light separately from the RGB light of a UHP lamp. This color‐tuner‐based optical engine — “Color‐Tuning Optical Engine” — and a new color‐conversion signal‐processing algorithm — “Adaptive Color Conversion Algorithm” — controls the yellow‐light volume and corrects color‐shifted pixels according to the brightness and chromaticity analysis of the input image, key technologies of the Color‐Tuning Projection System. This additional panel system enables the projector to ach ieve up to 115% higher brightness and 120% wider color gamut according to the input image. This paper presents an innovative design concept, a novel technology regarding brightness and a color‐gamut conversion projection system, and the characteristics of the prototype.     

Development and application of less‐mercury flat fluorescent lamps for backlights and general lighting

Abstract— A novel flat discharge fluorescent lamp used as the light source of backlight modules for LCDs and general lighting systems has been researched and developed. This new type of lamp is a less‐mercury flat fluorescent lamp with two‐dimensional emission and superior to conventional one‐dimensional cold‐cathode fluorescent lamps in terms of optics, energy‐savings, production efficiency, reliability, and chromatic performances. Physical characterization of the optics, temperature, mechanical design, thermal shocking, reliability, and corresponding environments have verified that flat fluorescent lamps will be the next‐generation light sources for backlight modules and general lighting systems.     

Design of a dual‐f‐number illumination system and its application to DMD™ projection displays

Abstract— A dual‐f/# optical system is evaluated and considered for illumination. Étendue theory has been employed to increase the optical throughput and collection efficiency. A classical Cooke triplet with a dual f/# is included for illustration. As a demonstration of the potential application to projection displays, an elliptically shaped illumination‐pupil system is proposed to increase the optical collection efficiency in the DMD? (Digital Micromirror Device?)‐based projection system. With a dual‐f/# configuration, this design can eliminate the f/2.4 constraint that was caused by the light‐steering action of the narrow ±12° tilt angles on the DMD?. The percentage of increase in the optical collection efficiency is 6.2% in the dual f/2.0 × f/2.4 optical projection system by using ray‐tracing simulation. This method enables a lower than f/2.4 optical design with a high brightness and an adequate contrast ratio in the DMD?‐based projectors.     

Invited Paper: UHP‐lamp systems for projection applications

Abstract— Projection systems have found widespread use in conference rooms and other professional applications during the last decade and are now entering the home‐TV market with considerable pace. Projectors as small as about one liter are nowadays able to deliver a screen flux of several thousand lumens and are, with a system efficacy of more than 10 lm/W, the most‐efficient display system realized today. Because such highly efficient projectors employ microdisplays as light valves, short‐arc lamps are a key component in realizing these properties. The introduction of the UHP‐lamp system by Philips in 1995 can be identified as one of the key enablers for the commercial success of projection systems. The ultra‐high‐performance (UHP) lamp concept features outstanding arc luminance, a well‐suited spectrum, long life, and excellent flux maintenance. For the first time, it combines a very‐high‐pressure mercury‐discharge lamp having an extremely short and stable arc length with a regenerative chemical cycle that keeps the discharge walls free from blackening, leading to lifetimes of over 10,000 hours. In this review, the most important aspects of the UHP concept that enabled its success in the projection market are described, followed by a discussion of some recent additions to the UHP‐product portfolio.     

Sphere‐supported thin‐film electroluminescence: A new platform technology for displays and lighting

Abstract— Currently, powder electroluminescence is used for low‐brightness flexible lamps offering durable plastic‐based lighting solutions principally for low‐ambient light conditions where lighting or backlighting is required. Sphere‐supported thin‐film electroluminescence (SSTFEL) promises dramatic new capability in both flexible lamps and displays owing to its high brightness and long‐life capability. SSTFEL is based on robust thin‐film phosphors deposited on spherical ceramic dielectric particles which are embedded in a thin plastic sheet. A printing approach permits versatile, low‐cost manufacturing of patterned SSTFEL devices and eliminates the need for high‐temperature substrates.     

A 100,000‐cd/m2 capacity‐coupled electrodeless discharge backlight with high efficacy for LC TVs

A capacity‐coupled electrodeless Hg discharge lamp has been developed for LC TV backlightings. By applying sinusoidal voltages which are 180° out of phase with a pair of external electrodes, a luminous uniformity of over 84% is attained in two types of lamps whose lengths are 190 and 390 mm. Luminance, efficacy, and input power to the lamp are 114,000 cd/m², 35 lm/W, and 21.5 W when the 390‐mm lamp is driven at 5 MHz. With a frequency below 1.1 MHz, eight 390‐mm lamps, connected in parallel to one another without external ballast impedance, can be driven by using a single inverter.     

High‐efficiency optical system for ultra‐short‐throw‐distance projector based on multi‐laser light source

Abstract— A novel laser‐light‐source projector having the three outstanding features of high brightness, ultra‐short throw distance, and high color reproduction has been developed.These features have recently come to be required in the high‐end projector market. The technologies for the laser‐light‐source projectors fully utilize the advantages of lasers, such as high luminance, small étendue, and high color purity. By integrating a triple‐rod illumination system with a multi‐laser light source and an ultra‐wide‐angle projection system, the developed high‐efficiency optical system has achieved a brightness of 7000 lm and a throw ratio of 0.28 with an image size of 100–150 in. Another new technology, laser color processing (LCP), has offered vivid color reproduction which has a color gamut that is up to 180% wider than the BT.709 standard without appearing unnaturally colored. Furthermore, a speckle suppression effect produced by the multi‐laser light source has been demonstrated. In this paper, an overview of these newly developed technologies that are used in the novel laser‐light‐source projector is presented, and solutions to the issues of speckle noise and safety are presented.     

Time‐multiplexed tiled projection system with improved pixel and spatial resolution

We propose two methods to increase the pixel and spatial resolution of Digital Micromirror Devices (DMD)‐based projectors by utilizing the large bandwidth provided by their high pattern rates. By varying the intensity of the illumination for each binary pattern displayed on the DMD, the time required to display an 8‐bit grayscale image can be reduced by up to factor 32 compared to using constant illumination and binary pulse‐width modulation (BPWM). The high image rate projection is then spatially separated by either using a galvanometer scanner or sequentially illuminating the DMD from different directions, thus creating multiple independently addressable projections which are then tiled to form a larger, higher resolution image.     

Parametric study using distributed computing and genetic algorithm in TFT‐LCD projector

We present an analysis of the parameters affecting light engines in liquid crystal display (LCD) projectors, using actual LCD projectors as examples. The significant parameters affecting light engines in LCD projectors are evaluated using the light uniformity as the determining standard. Optimization is performed on those parameters that affect the uniformity as well as the rendering effects of the projectors, by employing our own distributed genetic algorithm. The rotation angle of the collimator and its position are shown to improve the uniformity of the LCD projection, but we find that their effect on improving the brightness is not significant. Increased length of a projectors' light tube promotes better integration results. In our study, we effectively improved the performance index of an LCD projector, increasing projection uniformity by 4% (to 91.5%) and the brightness by 12% (to 7.9 lm).     

Compact and efficient green lasers for mobile projector applications

Abstract— Efficient and very‐compact projectors embedded into mobile consumer‐electronic devices, such as handsets, media players, gaming consoles, and GPS units, will enable new consumer use and industry business models. A keystone component for such projectors is a green laser that is commensurately efficient and compact. A synthetic green‐laser architecture is described that can achieve efficiencies of 15%. The architecture consists of an infrared distributed Bragg reflector laser coupled into a second‐harmonic‐generation device for conversion to green.     

2‐D/3‐D displays based on switchable lenticulars

Abstract— An attractive concept for 3‐D displays is the one based on LCDs equipped with lenticular lenses. This enables autostereoscopic multiview 3‐D displays without a loss in brightness. A general issue in multiview 3‐D displays is their relatively low spatial resolution because the pixels are divided among the different views. To overcome this problem, we have developed switchable displays, using liquid‐crystal (LC) filled switchable lenticulars. In this way, it is possible to have a high‐brightness 3‐D display capable of fully exploiting the native 2‐D resolution of the underlying LCD. The feasibility of LC‐filled switchable lenticulars was shown in several applications. For applications in which it is advantageous to be able to display 3‐D and 2‐D content simultaneously, a 42‐in. locally switchable prototype having a matrix electrode structure was developed. These displays were realized using cylindrically shaped lenticular lenses in contact with LC. An alternative for these are lenticulars based on gradient‐index (GRIN) LC lenses. Preliminary results for such switchable GRIN lenses are presented as well.     

Sparse high‐degree polynomials for wide‐angle lenses

Rendering with accurate camera models greatly increases realism and improves the match of synthetic imagery to real‐life footage. Photographic lenses can be simulated by ray tracing, but the performance depends on the complexity of the lens system, and some operations required for modern algorithms, such as deterministic connections, can be difficult to achieve. We generalise the approach of polynomial optics, i.e. expressing the light field transformation from the sensor to the outer pupil using a polynomial, to work with extreme wide angle (fisheye) lenses and aspherical elements. We also show how sparse polynomials can be constructed from the large space of high‐degree terms (we tested up to degree 15). We achieve this using a variant of orthogonal matching pursuit instead of a Taylor series when computing the polynomials. We show two applications: photorealistic rendering using Monte Carlo methods, where we introduce a new aperture sampling technique that is suitable for light tracing, and an interactive preview method suitable for rendering with deep images.     

DLP Cinema™ projection: A hybrid frame‐rate technique for flicker‐free performance

Abstract— Film is recorded at 24 Hz, which is sufficient to achieve the effect of motion but is well within the flicker sensitivity of the human‐visual system (HVS) and thus would result in severe flicker. To avoid this, film projectors project at twice this rate, using a 48‐Hz screen refresh rate. While this greatly mitigates flicker, projected film images still exhibit considerable flicker in bright scenes. DLP Cinema? projection technology allows us to display images at any frame rate, and in practice we have been able to match the 48‐Hz refresh rate of film projectors. This paper describes a technique by which we take advantage of the fact that the HVS temporal sensitivity curve shows more sensitivity with bright content but much less sensitivity as content dims. This is done using the control versatility of the Digital Micromirror Device? (DMD?), which allows independent control of every bit. The result is an overall image signal that is beyond the HVS temporal sensitivity curve, resulting in the complete removal of any visible flicker. This technique gives DLP Cinema? projection its characteristic “solid” and “stable” appearance that standard film projection does not provide.     

Advances in contrast enhancement for DLP projection displays

Abstract— Increased contrast ratios are essential to the continued success of DLP? products in the marketplace, from rear‐projection televisions and home‐theatre systems to large venue displays and DLP Cinema?. The contrast of DLP projection systems has increased steadily over the past 5 years due to improvements in illumination and projection optics, as well as changes to the DMD itself. The authors will present an overview of the contrast performance of DLP projectors over time as well as describe illumination and projection techniques that optimize the performance of the DMD.     

Refractive‐reflective optical system for realizing an ultra‐thin rear projector

Abstract— This paper presents a new optical system used in an ultra‐thin rear projector with a 1500‐mm diagonal size and 260‐mm depth. A refractive‐reflective optical system was developed to achieve a large projection angle of 136° with a small optical distortion of 0.1%. The optics consists of a convex aspherical mirror and a refractive lens. In addition, a new Fresnel screen composed of hybrid blades of refractive‐TIR (total internal reflection) elements was developed to attain good uniformity of brightness and color within the image area.     

Modified functional light‐guide plate for backlighting transmissive LCDs

Abstract— An improved wedge‐type light‐guide plate (LGP) for reducing the light losses and increasing the brightness has been developed. It incorporates a modified design of a molded micro‐line prism array at the rear of the LGP, a molded microdeflector (MD) at the front side of the LGP, and is surrounded by reflectors. The modified LGP employs a single prism sheet. As a result, the brightness is enhanced by 1.56 times compared to that of a conventional LGP and the light rays reaching the back of the LCD is confined to +/?10° on the vertical axis and +/?19° on the horizontal axis.