Optical characterization and ergonomical factors of near‐to‐eye displays

Abstract— Near‐to‐eye displays (NEDs) have unique optical properties requiring different characterization techniques compared to direct‐view display measurements. Here, a new version of a NED measurement system is introduced, and optical measurements of five commercially available consumer NED products are discussed. Luminance, focal distance, qualified viewing space, angular properties, and interocular differences are among the values. In addition, these results are compared to extensive subjective studies. The main intention is not to benchmark between the different products, but to show that display measurements are important for NEDs. According to the results, the determination of NED's characteristics helps to predict the subjective experiences, but the nature of the relation between subjective and objective findings is rather complex and depends on several NED‐, user‐, and task‐related features. Measured characteristics indicate that with a conventional biocular NED system approach of using two microdisplays and their enlarging optics, it is a design and a manufacturing challenge to build an ergonomically satisfactory NED device that fits everyone.     

A broadband wide‐incident‐angle reflective polarization converter

Abstract— A high‐performance reflective polarization converter which could be used in a backlight recycling system for liquid‐crystal‐display (LCD) devices is proposed. The device consists of a twisted‐nematic (TN) liquid‐crystal film, a uniaxial A‐plate, and a reflector. The configuration parameters, such as thickness and orientation of the films, are optimized using a genetic algorithm. As a result, the design can convert light from TM to TE polarization (or TE to TM) at a maximum 99.7%, minimum 91.3%, and average 96.7% conversion efficiency for the entire visible spectrum and incident angle from 0 to 60°. Such a broadband reflective polarization converter is particularly useful for enhancing the light efficiency and reducing the power consumption of LCDs.     

Resolution enhancement of integral‐imaging three‐dimensional display using directional elemental image projection

Abstract— A new approach to resolution enhancement of an integral‐imaging (II) three‐dimensional display using multi‐directional elemental images is proposed. The proposed method uses a special lens made up of nine pieces of a single Fresnel lens which are collected from different parts of the same lens. This composite lens is placed in front of the lens array such that it generates nine sets of directional elemental images to the lens array. These elemental images are overlapped on the lens array and produce nine point light sources per each elemental lens at different positions in the focal plane of the lens array. Nine sets of elemental images are projected by a high‐speed digital micromirror device and are tilted by a two‐dimensional scanning mirror system, maintaining the time‐multiplexing sequence for nine pieces of the composite lens. In this method, the concentration of the point light sources in the focal plane of the lens array is nine‐times higher, i.e., the distance between two adjacent point light sources is three times smaller than that for a conventional II display; hence, the resolution of three‐dimensional image is enhanced.     

Development of a color‐tunable polychromatic organic‐light‐emitting‐diode device for roll‐to‐roll manufacturing

A flexible vertically stacked flexible polychromatic color‐tunable OLED has been developed by means of low resistive intermediate electrode technology. The polychromatic OLED has a capability to show 16 million colors with 105% National Television Committee Standard (NTSC) color reproduction. The device can produce arbitrary shape with arbitrary colors, suitable for artistic expressions, just as many as those used in information displays. Independently controlled red, green, and blue light‐emitting layers are stacked vertically. With conventional indium tin oxide technology, because of the temperature restriction, it was quite difficult to achieve low resistance on plastic substrate. The reported numbers were all more than 80 Ω/□. According to the surface mobility control using Fick's law analysis, low sheet resistance 7.34 Ω/□ on plastic film was developed. At first, flexible 7.17 cm² transparent OLED was fabricated for the performance confirmation of transparent electrode. And then polychromatic color‐tunable OLED with the same size were successfully fabricated on plastic. With optical length optimization for each color stack of polychromatic OLED, more than 100% color reproduction in National Television Committee Standard was achieved by stack design. The polychromatic device can be used for colored illumination, as well as for organic‐light‐emitting display pixels for three times emission than conventional pixel design. The device is fabricated on plastic substrate so that the polychromatic organic‐light‐emitting‐diode device is manufacturable with roll‐to‐roll production line.     

Improvement of off‐axis color shift on hybrid viewing‐angle device using dual γ‐voltage method

We have mass production on one kind of liquid crystal display (LCD) device with hybrid viewing‐angle (HVA), which can be switched between the wide viewing‐angle (WVA) and narrow viewing‐angle (NVA) by one button. This device adopts the single cell design that with lower cost, and utilizes the optical properties of electrically tilted LC to achieve the function of NVA display. An issue has received less attention in the past and been indeed found in the production process. It is that the off‐axis color shift will appear in NVA mode. We put forward one method to improve this issue here, which is combined with the concepts of Gray Frame Insertion (GFI) and Impulse‐type driving. By switching the voltage between two different γ values, the color shift will be perfected on the produce.     

Nano‐emissive display technology for large‐area HDTV

Abstract— Using nano‐emissive display (NED) technology, Motorola labs has successfully developed 5‐in. full‐color display prototypes. Carbon‐nanotube‐based field‐emission displays with a pixel size of 0.726 mm for a 42‐in. HDTV exhibit video image quality comparable to CRT displays and demonstrate a luminance of 350 cd/m². These novel low‐drive‐voltage NEDs take advantage of selective growth of CNTs to obtain the desired electron‐emission performance while maintaining inexpensive manufacturing due to a simple self‐focusing and self‐regulating planar structure. Improved video image quality and color purity are achieved with very low power consumption and without the need for an expensive focusing grid.     

High‐quality direct‐view display combining multiple integral 3D images

This paper proposes a method for combining multiple integral three‐dimensional (3D) images using direct‐view displays to obtain high‐quality results. A multi‐image combining optical system (MICOS) is used to enlarge and combine multiple integral 3D images without gaps. An optical design with a simple lens configuration that does not require a diffuser plate prevents the deterioration in resolution resulting from lens arrangement errors and the diffuser plate. An experiment was performed to compare a previously developed method with the proposed method, and the latter showed a significant improvement in image quality. A method for expanding the effective viewing angle of the proposed optical design was also developed, and its effectiveness was confirmed experimentally. A prototype device of the proposed optical design was constructed using a high‐density organic light‐emitting diode (OLED) panel with 8K resolution and 1058 ppi pixel density to achieve 311 (H) × 175 (V) elemental images, a viewing angle of 20.6° in both the horizontal and vertical directions, and a display size of 9.1 in. In addition, the proposed optical design enabled making device considerably thinner, ie, with a thickness of only 47 mm.     

SOM‐based projection module for mobile displays

Abstract— The development of a compact, efficient VGA projection module to be embedded in mobile devices is reported. The design incorporates laser/laser diode (LD) light sources, Schlieren optics, and a one‐dimensional diffractive spatial optical modulator (SOM). During development, the optical parameters were determined and the relationships between the parameters to optimize the optical specifications were derived. The resulting optimized specifications enable us to manufacture two types of optical modu les as compact as 13 cc and with as little as 10% speckle contrast ratio.     

A novel electron‐transport material for organic light‐emitting devices

Abstract— A nanocrystalline electron‐transport material [ET68] was introduced into organic light‐emitting devices (OLEDs). By integrating a p‐doped transport system and phosphorescent emitters, a very bright and stable device could be obtained. Furthermore, 40% saving in power consumption can be achieved when the efficient pixels with ET68 were applied to AMOLEDs.     

Local dimming light‐guiding plate type backlight system using alignment‐controlled polymer‐dispersed liquid crystals

A new technology which enables a local brightness control according to the displayed images has been expected in the thin and lightweight backlight systems to improve a contrast ratio and power consumption of the liquid crystal displays (LCDs). In this paper, we have proposed a novel local‐dimming backlight system using alignment‐controlled polymer‐dispersed liquid crystals as a light‐guiding plate and investigated the forming conditions of polymer‐dispersed liquid crystals to achieve both a high‐luminance ratio and a fast response speed. As a result, we found that a luminance ratio and response speed of the backlight system can be improved by using bifunctional LC monomer materials and forming fine and rigid polymer network in the LCs, and achieved high luminance ratio of 16:1 and fast response time less than 0.5 ms. In addition, we fabricated the twisted nematic‐mode LCD using the local dimming light‐guiding plate‐type backlight based on this design, and successfully realized eight times higher contrast ratio than that of the traditional twisted nematic‐mode LCD.     

Analysis and reduction of dark zone in ultra‐thin wedge‐plate displays

Abstract— A wedge plate can be used as the screen of a display, and the thickness of the display can be incredibly thin. In this paper, a basic formula for ray tracing in such a wedge plate is deduced. The fundamental limitation on the display quality of a wedge plate is explored, and the formation of a dark zone on the display screen is analyzed and verified numerically. Experimental exploration and confirmation of one 14‐in. acrylic wedge plate with a white‐light‐emitting diode is also provided. Two approaches to eliminate the dark zone are proposed, and the corresponding numerical demonstration of a 52‐in. wedge‐plate display is also shown.     

Surface‐light‐emitting transistors based on vertical‐type metal‐base organic transistors

Abstract— Light‐emitting transistors having a metal‐base organic transistor (MBOT) structure demonstrate both the function of an organic thin‐film transistor (OTFT) and organic light‐emitting diode (OLED). The MBOT is a vertical‐type organic transistor having a simple structure composed of organic/metal/organic layers demonstrating high‐current and low‐voltage operation. The light‐emitting MBOT was fabricated simply by inserting additional layers of hole‐transporting and emissive materials used in the OLED into the col lector layer. The device showed perfect surface emission similar to an OLED. A luminance modulation of 370 cd/m² was observed at a collector voltage of 20 V and a base voltage of 3 V. This device can be applied to an OLED display device to increase the numerical aperture or reduce the required current of the TFT backplane.     

Review Paper: Diffractive backlight technologies for mobile applications

Abstract— Liquid‐crystal‐display backlight units have developed in their conventional configuration into very efficient and uniform components that allow the display to present a high‐quality image to the user. Developing the backlight unit itself further faces a challenge of diminishing returns to the investment in innovation. A system‐level redesign is required for the entire display module, and diffractive alternatives to the backlight design can allow a more‐energy‐efficient design for the display. This review concentrates on small‐to‐medium displays because diffractive backlight studies have also centered in this class of displays. The state of the art of backlight design is summarized and the motivation for energy‐efficient system design is outlined. The theoretical basis of diffractive backlights is given, and key research studies in the area of diffractive backlights are reviewed. Finally, a discussion on the performance and future outlook of diffractive backlights completes the paper.     

Tilted bi‐sense circularly‐polarized antenna and its application for radio frequency identification system

A tilted bi‐sense circularly polarized (CP) antenna and its application for UHF radio frequency identification (RFID) system is proposed. A planar concial monopole working as the electric dipole is designed at first. When a shorting pin is added, a loop radiator would be generated, and thus a pair of orthogonally oriented complementary dipoles is realized. In this way, both right‐handed circularly polarized (RHCP) and left‐handed circularly polarized waves (LHCP) are generated simultaneously in tilted directions within one hemisphere. Then, closed‐form formulas are derived to reveal the tunability mechanism of bi‐sense property and provide a design guideline for system application. It is demonstrated that flare angle of conical monopole has a linear relationship and sine function to CP beam direction and 3‐dB axial ratio (AR) beamwidth, respectively. Finally, antenna prototypes are fabricated and tested for validation. It is also demonstrated that at the tilted direction of θ = ± 45°, a 3‐dB AR bandwidth of 4.9%, and gain up to 5 dB are realized. Comparing with conventional microstrip patch antenna, an enhanced reading range over 5 m can be obtained in the tilted range from 40° to 75° and ? 75° to ?40° in UHF RFID sytem application.     

Defect‐free half‐V‐mode ferroelectric liquid‐crystal device

Abstract— The horizontal chevron defect found in a half‐V‐mode ferroelectric‐liquid‐crystal (HV‐FLC) device can be suppressed by lowering the FLC's total free energy. The energy levels between spontaneous polarization (PS) up and down domains were degenerated by asymmetrical‐alignment treatments. The difference in the polar surface coefficient (γ²) was the key to suppressing the alignment defect. Alignment layers with opposite surface polarities and different anchoring energies were applied to control the sign and value of γ². The asymmetric cells of PIrub ‐ PIplasma (rubbed polyimide and plasma‐treated polyimide surfaces), PVArub ‐ PIplasma (rubbed polyvinyl alcohol and plasma‐treated polyimide surfaces), and PVArub ‐ PIplasma (both rubbed PI and PVA) alignment conditions presented defect‐free alignment textures under a slow‐cooling process. Among these different alignment treatments, the PVArub ‐ PIrub treated cell demonstrated the best alignment result, benefited by the largest difference in polar surface coefficient.     

Active‐matrix technology for high‐efficiency OLED displays

Organic light‐emitting device (OLED) technology has recently been shown to demonstrate excellent performance and cost characteristics for use in numerous flat‐panel‐display (FPD) applications. Universal Display Corp. (UDC), together with its academic partners at Princeton University and the University of Southern California, are developing high‐efficiency electrophosphorescent OLEDs, based on triplet emission. These material systems show good lifetimes, and are well suited for the commercialization of low‐power‐consumption full‐color active‐matrix OLED displays. Their very high conversion efficiencies may even allow them to be driven by amorphous‐silicon backplanes, and in this paper we consider design guidelines for an amorphous‐silicon pixel to minimize display non‐uniformities due to threshold voltage variations.     

Design of a prism light‐guide plate for an LCD backlight module

Abstract— This paper describes the development of a design method for a prism pattern for an LCD light‐guide plate to improve the uniformity of its exiting light. First, the prism surface of the light‐guide plate is divided into several equal regions. With the aid of ASAP simulation, this method uses the mean light flux of all regions as a reference value to adjust the distribution density of the prism pattern for each region. Curve fitting is then performed to provide a smoothly changing distribution density for further improvement of the exiting light uniformity. ASAP results demonstrate that the illuminance uniformity for a 2.5‐in. light‐guide plate is substantially improved from 45% to 90.9% by using this design method.     

Optical characteristics of tandem and microcavity tandem organic light‐emitting devices

Abstract— In pursuit of the further enhancement of the luminance and efficiency of organic light‐emitting devices (OLEDs), it is worthy of exploring what benefits could be obtained by combining two luminance‐enhancement techniques, i.e., microcavity and tandem OLEDs. Furthermore, a deeper understanding of the optics in tandem OLEDs will be useful for the design and optimization of tandem OLEDs. In this paper, the optical characteristics of noncavity and microcavity tandem OLEDs are theoretically and experimentally investigated. By the use of rigorous electromagnetic modeling of OLEDs, the radiation characteristics of tandem OLEDs as a function of device structures are analyzed and correspondingly, the guidelines for optimizing the performance of tandem devices are suggested. By making use of the analytical results, it is shown that with well‐designed microcavity conditions and device structures, a five‐fold enhancement in luminance in the normal direction can be achieved with cavity‐tandem devices having only two emitting units. A very high efficiency of 200 cd/A for a rather broad brightness range of 100–4000 nits is demonstrated with a phosphorescent cavity two‐unit device.     

Energy‐recycling high‐contrast organic light‐emitting devices

Abstract— It is reported that by integrating OLEDs with solar cells, ambient‐light reflection as low as 1.4% (even superior to that achieved with polarizers) can be achieved without compromising the EL efficiency for high‐contrast display applications. Furthermore, in such a configuration, the photon energies of both the incident ambient light and the portion of OLED emission not getting outside of the device can be recycled into useful electrical power via the photovoltaic action, instead of being wasted as in other reported contrast‐enhancement techniques. These features, we believe, shall make this present technique attractive for high‐contrast display applications and portable/mobile electronics that are highly power‐aware.     

EPE‐Mobile—A framework for early performance estimation of mobile applications

Considering the constrained resources of mobile devices, a thorough performance evaluation of a mobile application is crucial. However, performance evaluation in the mobile domain is still a manual and time‐consuming task. The diversity of mobile devices only increases the complexity of this task. We propose EPE‐Mobile, a framework to automate early performance estimation in mobile applications. It is composed of a configurable library of basic operations and an engine that automatically creates a synthetic program based on the specification of a new app. The synthetic program that EPE‐Mobile generates provides feedback for mobile developers at the first design stages and before the actual implementation of a new application. The fast evaluation can also guide developers in optimizing their applications or in choosing devices with the best trade‐off between cost and performance to run a given application. Finally, developers can reuse the data collection infrastructure of the framework to collect performance data during all development stages. We validate the proposed framework using 4 applications from the Android Play Store. Based on their specifications, 4 synthetic programs were generated and executed on different devices. We compared the results to those obtained from the execution of the actual applications in the same devices. Experimental results show that it is possible to create synthetic applications with similar behavior to that of real applications and, thus, classify devices based on the actual application needs. The framework uses aspect‐oriented programming to collect the metrics of interest. This approach provides increased modularity and separation of concerns, thus facilitating the improvement of the framework itself, by adding other metrics or basic operations.