Jyrki Kimmel

Display technologies for portable communication devices

Telecommunications networks are rapidly advancing toward adequate capacity to support multimedia content transmission between mobile terminals. This development opens opportunities for terminal manufacturers to realize functions on the devices that previously have been considered impractical. It is necessary for the terminals, however to exploit advances in new display technologies, such as reflective-color liquid-crystal displays, bistable displays, organic emissive displays, and microdisplays, to make use of the new functionality. The state of the art of mobile phone and personal digital assistant displays as well as some of the emerging technologies are reviewed based on their applicability in new uses in mobile terminals.

A novel diffractive backlight concept for mobile displays

efficiency demands on mobile communication device displays have become severe with the emergence of full video capable phones and mobile telephony services such as the third- generation networks (3G). One way of reducing the power dissipation of a mobile liquid-crystal display (LCD) is to efficiently distribute and outcouple the light available in the backlight unit (BLU) to direct the light in a spectrum-specific fashion through the respective color pixels. This paper describes a diffractive optics approach to realize a novel backlight unit. A model grating structure was fabricated and the outcoupled distribution of light was studied. The results verify that the new BLU concept based on an array of spectrum-specific gratings is possible.

Diffractive backlight grating array for mobile displays

— The display backlight unit (BLU) is the most power-consuming subunit 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. This paper presents a new pixelated diffractive backlight grating array as an approach for overcoming these obstacles in BLU design. 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.

Review Paper: Diffractive backlight technologies for mobile applications

— 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.

Displays enabling mobile multimedia

With the rapid advances in telecommunications networks, mobile multimedia delivery to handsets is now a reality. While a truly immersive multimedia experience is still far ahead in the mobile world, significant advances have been made in the constituent audio-visual technologies to make this become possible. One of the critical components in multimedia delivery is the mobile handset display. While such alternatives as headset-style near-to-eye displays, autostereoscopic displays, mini-projectors, and roll-out flexible displays can deliver either a larger virtual screen size than the pocketable dimensions of the mobile device can offer, or an added degree of immersion by adding the illusion of the third dimension in the viewing experience, there are still challenges in the full deployment of such displays in real-life mobile communication terminals. Meanwhile, direct-view display technologies have developed steadily, and can provide a development platform for an even better viewing experience for multimedia in the near future. The paper presents an overview of the mobile display technology space with an emphasis on the advances and potential in developing direct-view displays further to meet the goal of enabling multimedia in the mobile domain.

Visual Performance With Small Concave and Convex Displays.

Objective: In this study, we aim to investigate how users’ visual performance with a small flexible display changes based on the direction (i.e., convex, concave) and the magnitude (i.e., low, high) of the display curvature. Background: Despite the wide interest in flexible display materials and deformable displays, the potential effects of nonplanar display surfaces on human perception and performance have received little attention. This study is the first to demonstrate how curving affects visual performance with an actual flexible display (4.5-in. active-matrix organic light-emitting diode). Method: In a series of three experiments, we compared the performance with a planar display to the performance with concave and convex display surfaces with low and high curvature magnitudes. Two visual search tasks were employed that required the subject to detect target letters based on their contrast (Experiments 1 and 2) and identity (Experiment 3). Performance was measured as the sensitivity of target detection (d′) and threshold time of the search, respectively. Results: There were similar sensitivities for targets across the curvature variants, but the high-magnitude curvatures resulted in prolonged search times, especially for the convex form. In both of the tasks, performance was dependent on the display location, which was defined as the target’s distance from the display center. Conclusion: High curvature magnitudes should be avoided, even in small displays, because large local changes in visual stimuli decrease processing speed outside the central display. Application: The findings have implications for the development of technologies, applications, and user interfaces for flexible displays and the design of visual display devices.

55.3: Diffractive Backlight Light Guide Plates in Mobile Electrowetting Display Applications

Power efficiency demands on mobile displays are increasing rapidly, as new multimedia services and applications are being adopted by users. Diffractive backlights and electrowetting displays have been proposed as some of the solutions to solve the poor efficiency of current mobile display systems. In this study, an electrowetting display was coupled with a pixelated, diffractive becklight light guide plate. This is to our knowledge the first time when a pixelated, diffractive backlight has been demonstrated in conjunction with an actual display. The results of the study show that the backlight and display panel need to be optimized as a system in order to obtain an applicable module for mobile use.

Mobile display backlight light guide plates based on slanted grating arrays

Modern mobile communication devices have user interfaces that are dominated by high-quality displays. Increased multimedia use imposes high demands on the design of display modules, as the content available for mobile use becomes visually richer. Especially the power dissipation of the display can limit the amount of time available for multimedia consumption and interaction. In the mobile liquid-crystal display (LCD), the energy efficiency is determined by the backlight design. State-of-the-art backlights direct white light through a display subpixel array, with high uniformity and up to 90% efficiency in white light output. Therefore, it is difficult to obtain system-level energy savings by improving the backlight design alone. Diffractive backlights have recently been proposed to reduce the power dissipation of the display module, and slanted grating arrays are among the enabling optical features that allow for reduction in power dissipation beyond what is available in the state of the art. By the use of diffractive grating arrays, the required primary color (red, green, or blue) is directed through the LCD subpixel array with geometrical registration, instead of flooding the whole LCD with white light and filtering the primary colors through the subpixel color filter array. We present a study on grating structures based on slanted grating arrays fabricated in high refractive index materials. The grating design principles and grating outcoupling results are provided, and an outline of a new embedded system design is given. Emphasis is on grating array design aspects for future energy-efficient display system design. The results show that savings in power consumption can be expected with advanced display system design based on embedded slanted grating array backlight light guide plates.

P-108: Backlights in Mobile Display Power Management

Power efficiency of a mobile multimedia display relies on power management methods that affect the on-state of the display. Other means of power management in mobile devices are dependent on managing the transitions between the off-state, power-saving mode, and on-state effectively. These methods do not readily apply to modern consumption of mobile multimedia, as the display is in the on-state continuously. A conceptual display system power management model was developed. The model was used to estimate the efficacy of a new diffractive optical mobile display backlight concept, and the effect of the display backlight design especially was found to result in considerable power savings in modern mobile multimedia displays.

P‐38: Flexible Displays: Cognitive Performance Studies

In this research project, we studied peoples ability to read and understand information using, to our knowledge, for the first time a real flexible display. The test consisted of three different bending angles and font sizes with two different lighting conditions. According to the subjective test results, both bending angles and font sizes had a significant influence on the final performance.