A preview of some of the most interesting papers appearing in the August 2008 issue of the Journal of the SID.
To obtain access to these articles on-line, please go to www.sid.org
Edited by Aris Silzars
Konstantin A. Grebenyuk
Vladimir V. Petrov
Saratov State University
Abstract — A stereoscopic display configuration for presenting stereoscopic images without keystone and depth-plane-curvature distortions is proposed. The main idea of the proposed configuration is to perform optical compensation for these distortions by presenting left and right perspective images at two intersecting screens. The possibility of such distortion elimination was proven by two independent ways: analytically and graphically.
In a converged configuration, the camera sensors are not parallel to the plane of convergence, which yields incorrect values for the horizontal and vertical parallaxes of the stereopair. Incorrect values of the horizontal parallax result in incorrect locations of the observed 3-D image points, so that the 3-D image of the scene looks curved. This is called depth-plane curvature. Incorrect values of the vertical parallax (i.e., non-zero vertical parallax) make it difficult for the fusion of the left and right perspective images into a single stereoscopic image.
FIGURE 3 — Detecting depth-plane curvature in a stereoscopic image on the test grid.
Martin J. J. Jak
Eefje J. Hornix
Luciano de Sio
Dick K. G. de Boer
Hugo J. Cornelissen (SID Member)
Philips Research Laboratories
Abstract — A large part of the light generated in a backlight is usually absorbed in the color filters of the liquid-crystal display. A new backlight system that uses a grating to split thewhite light into different colors and a lens array to focus this light onto the pixels is presented. The absorbing filters can be eliminated and efficiency is improved. The system is characterized, as well as its different components.
One can eliminate the color filter by spatially separating the colors. This can be achieved with diffractive components that can separate white light into its spectral components. The basic principle of such a backlight is shown in Fig. 1. As in a normal side-lit backlight, white light is coupled into a light guide. A grating is used to diffract the extracted light into different directions, corresponding to the different colors. In our case, the diffraction grating itself is used to extract the light from the light guide. Since, in practice, the grating is separated from the liquid-crystal layer by a glass plate of approximately 1 mm thick, a lens array is used to focus the light onto the pixels.
FIGURE 1 — Schematic representation of a color display without color filters. The grating on top of a light guide extracts light from the light guide and separates the light into the red, green, and blue components. A lens array focuses the colors onto the appropriate pixels.
Toni Järvenpää (SID Member)
Marja Salmimaa (SID Member)
Nokia Research Center
Abstract — Display-measurement methods different from conventional 2-D display measurements are needed for verifying the optical characteristics of autostereoscopic (3-D) displays and for comparing different 3-D display technologies. Industry is lacking standardized measurement methods, and the reported results can not always be compared. The selected set of characteristics discussed in this paper and partly defining the quality of the 3-D experience are crosstalk, viewing freedom, and optimum viewing distance. Also, more conventional display characteristics such as luminance are discussed, since the definitions for these characteristics in 3-D mode usually differ from those used for the 2-D displays. How these chosen 3-D display characteristics can be objectively measured from transmissive two-view and multi-view 3-D displays have been investigated. The scope of this article is to generally define those basic characteristics as well as the different measurement methods. Most of the 3-D characteristics can be derived from the luminance and colors versus the viewing angle. Either a conoscopic or a goniometric measurement system can be used, as long as the angular and stray-light properties are suitable and known. The characteristics and methods are currently discussed in the display-quality standardization forums.
Viewing freedom is the movement within which the user can comfortably move in front of the 3-D display, and it is a very important yet complicated three-dimensional characteristic, similar to that of virtual displays. With two-view 3-D displays, at least crosstalk, luminance difference, and color shift all confine the movement and at least a five-point measurement (center and corners) of all these parameters must be made. Figure 9 illustrates the cross-section of the repeating "viewing cones" in the horizontal plane and the exemplary viewing freedom (VF) for each eye based on only center measurement.
FIGURE 9 — Viewing freedom for a two-view display and the minimum crosstalk angles θ1 and θ2.
A. V. Emelyanenko
E. P. Pozhidaev (SID Member)
V. E. Molkin
N. M. Shtykov
Moscow State University
Abstract — A mixture with intermediate biaxial (ferrielectric) smectic phases existing in a broad temperature range has been developed. At any temperature within this range, as well as in the antiferroelectric phase range, several birefringence color states can be switched stepwise by application of an electric field, and therefore a LC cell placed between crossed polarizers can display several colors without the use of color filters. A very small time switching between color states (about 10 μsec) can be a basis for this new mode in display technology because several full-color optical states can be realized in the same material (or in the mixture of materials). These possibilities were investigated both theoretically and experimentally.
The light transmission spectra of the developed mixture (layer thickness is 4.75 μm) placed between two crossed polarizers at T = 25°C are presented in Fig. 16. The color switches from blue to green and then to red by application of different voltage.
FIGURE 16 — Light transmission spectra for newly developed mixture.
Putilin N. Andrew
Lebedev Institute of theRussian Academy of Science
Abstract — Focusing cones (FOCON) have been designed for fiber-optic communication systems as coupling devices. The main aim of these couplers is to match the spatial distribution of the light source or photodetector with the aperture configuration of light-guiding modes of the optical fibers. In this paper, the application of a 2-D array of FOCONs for collimating large-sized optical beams in display devices is proposed. The design of a light-efficient illumination unit for LCDs that can operate in the reflection mode as a backlight has been demonstrated. The approach proposed is based on the spatial separation of the light propagation in a FOCON array for reflected beams and light that comes from the backlightunit. The application of a FOCON array in backlight units and antiglare coatings has been demonstrated.
This paper is devoted to the application of a FOCON in optical processing and, in particular, in display design. A 2-D array of FOCONs for collimating large-sized optical beams in display devices has been applied. Figure 1 shows the basic element of such an array, the aperture of TIR operation that depends upon the index of refraction of the FOCON material, and the shape of the TIR surface. The FOCON is formed by a TIR surface and one or two output-input surfaces (Si and So). The TIR surface is designed to transform the input light distribution into an output light distribution, and perfect light concentration can be achieved for a parabolic shape.
FIGURE 1 — Basic FOCON array element and the principle of its operation.
Toshiyuki Akiyama (SID Member)
Tsutae Shinoda (SID Fellow)
Advanced PDP Development Center Corp.
Abstract — Under high-Xe-content conditions, the luminous characteristics were evaluated for the sustaining electrode width and the sustaining pulse cycle. It was recognized that the proper designs for them in a high-Xe-content gas mixture make it possible to obtain high luminous efficacy. In this research, it was found that narrower electrodes can gain higher luminous efficacy in high-Xe-content conditions. The dependency of the luminous characteristics on the electrode width was analyzed and the differences of discharge phenomena from low-Xe-content conditions, which explain the dependency on the electrode width, were recognized. In an 8-in. test panel, 5.2 lm/W of the maximum white efficacy was obtained. Thefound phenomenon that narrower electrodes are more advantageous for the luminous efficacy is favorable in high-definition PDPs.
Figures 12(a) and 12(b) show a visible-light image and a NIR-radiation image of a single discharge for a pulse cycle of 10 μsec, a pulse voltage of 280 V, an electrode width of 50 μm, and a Ne + Xe 20% gas mixture. The visible-light image shows a relatively wide extension. The distribution of visible luminescence exceeds the area of the electrodes. On the other hand, NIR radiation is limited on the area of the electrodes. The area of the NIR radiation corresponds to the area radiating VUV radiation. These indicate that VUV radiation from a relatively small area lead to a relatively wide area of visible luminescence.
FIGURE 12 — The visible light image and NIR radiation image of a single discharge for a pulse cycle of 10 μsec, a pulse voltage of 280 V, an electrode width of 50 μm, and a gas mixture of Ne + Xe 20%. The light was integrated over the entire 5 μsec of the sustain pulse. (a) Visible-light image. (b) NIR-radiation image.
Tapani Levola (SID Member)
Abstract — Near-to-eye displays (NEDs) provide a unique way to perceive a larger image than the device itself. The user acceptance of commercially available NEDs has not been high partly because of reported physiological symptoms. Devices also tend to be thick and heavy, and therefore uncomfortable to wear. To overcome these shortcomings and to make a very usable device, a new approach was needed. By using very thin plastic light guides with diffractive structures on the surfaces, many of the known obstacles can be notably reduced. These exit pupil expanders (EPEs) enable a light and thin design for see-through NEDs. The so-called chevron EPE was designed to further improve the design and usability aspects of NEDs. The diffractive EPE has typically one incoupling grating area that delivers light into the light guide symmetrically towards the left and right eyes. By using slanted or overhanging gratings, the incoupling is very asymmetric. If the incoupling area is divided into two parts, each having opposite slanting angles, the EPE plate can be cut in half, and the left and right parts can be separated. The plates can be further tilted to a chevron shape following more closely the human face and mimicking the conventional eyeglass design. The reflection of the light from the tilted plate is directed out from the image-forming optics, and therefore the contrast is improved.
The volume production of slanted gratings on a plastic substrate enables many new features in the VRD that is based on a diffractive EPE. By splitting the incoupling grating in two oppositely slanted grating areas a chevron configuration of the EPE can be formed. This configuration mimics the conventional eye-glass design.
FIGURE 10 — Experimental stack of two chevron EPEs for the left and right eye. Each EPE plate has six different grating areas. The chevron angle is 10°.
Marcel P. C. M. Krijn
Siebe T. de Zwart
Dick K. G. de Boer
Oscar H. Willemsen
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.
FIGURE 7 — Exploded view of LC-based locally switchable lenticular.
FIGURE 8 — Prototype (42 in.) of a locally switchable 2-D/3-D display. Shown is a 3-D window on a 2-D background.
Jyrki Kimmel (SID Member)
Tapani Levola (SID Member)
Abstract — The display backlight unit (BLU) is the most power-consuming sub-unit in mobile liquid-crystal displays. The state-of-the-art BLUs utilize scattering, refractive, and reflective microstructures to generate a uniform distribution of white light through the display. More effective means of transmitting light through the display color filters could be obtained by using diffraction, but previously proposed diffractive backlights do not fully utilize all the possibilities to design gratings effectively for optimal color separation and outcoupling. A new pixelated diffractive backlight grating array as an approach for overcoming these obstacles in BLU design is presented. A model array was fabricated to couple out red, green, and blue primary colors from the respective subpixel locations. The results show that it is possible to manufacture such an array and that the light couples out as intended, giving a starting point to design mobile-display modules with low light-transmission losses.
Figure 1 shows the new BLU concept in broad detail. Light from red, green, and blue LEDs is launched into the BLU from different corners of the BLU. The light is then spread out into uniform beams propagating in the backlight, by fan-out gratings. A pixel array of gratings is then used for outcoupling the light toward the LCD pixel array. With polarizing gratings, there would be no need for a polarizer between the BLU and the LCD. Also, by designing the BLU grating array to pass light through the active aperture area only, it is possible to prevent unwanted light from hitting the areas outside the active aperture of the LCD pixel.
FIGURE 1 — Pixelated backlight concept, not to scale.
S. Kobayashi (SID Fellow)
K. Takatoh (SID Member)
Tokyo University of Science, Yamaguchi
Abstract — The electro-optical characteristics of TN-LCD and ECB-LCD cells, both of which were embedded with MgO and SiO2nanoparticles at a low concentration of about or below 1 wt.%, were investigated. The threshold voltage and operating voltage of these LCD cells were found to decrease by 5–16%, depending on the materials and the concentration of nanoparticles. Measurements of the physical properties of nanoparticle-embedded NLCs, such as the order parameter, clearing point, birefringence, dielectric anisotropy, elastic constants, and rotational viscosity on the nanoparticle-doped NLC sample cells, were performed. Through these measurements, it is shown that the decrease in the threshold voltage and the operating voltage may be attributed to the decrease in the order parameter by 10–30% due to the existence of these nanoparticles.
FIGURE 1 — V–T curves of TN-LCD doped with and without SiO2 nanoparticles in NLC-1.
TABLE 1 — Measured values of the dielectric anisotropy, elastic constants, and viscosity on ECB cells with NLC-1 and NLC-2 embedded with and without SiO2 nanoparticles.
Masaya Adachi (SID Member)
Abstract — The blue-light-emission properties of organic light-emitting-diode (OLED) displays must be enhanced to meet the requirements for color purity and luminous efficiency because few blue-light-emitting materials meet these requirements. This is particularly true for polymeric and phosphorescent light-emitting materials. To attain the required purity and efficiency, a polarized-light-recycling structure for blue light that is called a blue enhanced circular polarizer (BECP) has been developed. The principle of the structure and the fabricated prototype device is described and it is shown that the structure increases blue-light intensity and color purity, improves efficiency, provides a wide color gamut, and limits ambient-light reflection.
As shown in Fig. 2, the BECP for the proposed blue-light recycling structure consists of a polarizer, a retardation film (quarter-wave plate), and a cholesteric liquid-crystal polymer layer (CLC) with a selective reflection property in the wavelength corresponding to pure blue. Thepolarizer and retardation film constitute the so-called circular polarizer. The CLC has specific optical characteristics based on a helical molecular alignment.
FIGURE 2 — Schematic cross section of BECP for a full-color OLED display in the case of light emission. The BECP consists of a polarizer, a retardation film (quarter-wave plate), and a cholesteric liquid-crystal polymer layer (CLC) with a selective reflection property for the wavelength range corresponding to pure blue. The BECP is arranged on all the pixels (which includes red and green ones).
Hyung Ki Hong
Abstract — Image deformation caused by an outside force is observed to remain for hours at high gray levels for liquid-crystal displays (LCDs) in the multi-domain (MD) vertical-alignment (VA) mode. This so-called moving-image-sticking phenomenon demonstrated a non-symmetric luminance profile for the left and right viewing direction for MDVA-mode LCDs which have original symmetric viewing-angle characteristics. The generation of a stable reverse-tilt domain by an outside force was assumed to be the cause of this phenomenon, and the stability of a reverse-tilt domain under an electric fringe field was calculated by changing the electric-fringe-field distribution which determines the LC tilt direction. The domain of a given tilt direction is calculated to change to another tilt direction induced by a fringe field at a low gray condition, but to remain unchanged at a high gray condition. This agrees with the observed trends of duration time of the moving-image-sticking phenomenon.
In this paper, the term "moving image sticking" is used to describe the phenomenon where a trace of the previous image displayed at the moment that an outside force is applied remains even after the image data is changed. An example is shown in the photograph shown in Fig. 1, where the trace of a soccer ball image is observed at the upper left region behind the soccer ball shortly after the LC panel is pressed by hand. Duration times of the moving image sticking are found to be different for the displayed moving images and LC modes.
FIGURE 1 — Photograph of the moving-image-sticking phenomenon. Position of the moving image sticking is noted by the white arrows.
Hyun-Sang Park (SID Member)
Tae-Jun Ha (SID Student Member)
Yongtaek Hong (SID Member)
Seoul National University
Abstract — A new digital ambient-light sensor system has been designed and fabricated on a glass substrate using a conventional low-temperature polycrystalline-silicon (LTPS) technology. In the proposed system, analog-to-digital conversion (ADC) is performed in the time domain instead of the voltage domain and is combined with a light-detection process. The proposed system employs self-reset architecture and requires only one comparator for n-bit digital output. Because the complex analog circuitry is eliminated from the system, it can be readily integrated on the glass substrate.
The block diagram of the proposed system is shown in Fig. 1. It consists of a light sensor, a converter, an n-bit binary counter, and an n-bit output register. Several features were incorporated in our design such as a light sensor, comparator, and self-reset conversion process. In the proposed system, only one was required, simplifying the conversion process.
FIGURE 1 — The block diagram of the proposed ambient-light sensor system.