Robert B. Akins

Electrically tunable color for full-color reflective displays

Conventional reflective displays based on either color filter/polarizer or stacked color layers suffer from their marginal performance in terms of brightness, color, and cost. In this paper, we will present new full-color reflective display architecture: Electrically Tunable Color (ETC). In this display architecture, both color generation and its change are through the coupling of a cholesteric liquid crystal in its planar state and an in-plane electric field. Unlike the conventional cholesteric liquid crystal display, in which one liquid crystal layer only reflects one preset color, in ETC the in-plane field that is predominantly normal to the helix unwinds the helix to result a color shift from its initial color. We have fabricated such devices in our laboratory and demonstrated large color change covering all three primary colors with a single ETC pixel. Another advantage of ETC is its faster time response. Time response data will be presented and compared with model. Switching voltages depend much on cell parameters, in particular on the electrode configuration. Measured switch voltage vs. these parameters will be shown and challenging issue in voltage reduction will be discussed. Finally, we will propose full-color display architectures based on ETC and analyze their cost/performance.

Design of Hologram for Brightness Enhancement in Color LCDs

Transmission holographic film for brightness enhancement in full color reflective LCDs is proposed. The hologram is attached to the front of the LCD. The goal is paper-like brightness within the viewing zone under typical ambient lighting conditions. Optimum viewing and illumination angles have been identified. Modeling and measurements on holograms show that a viewing zone of 20° × 40° will provide a 12× film gain which is adequate to maintain a wide color gamut and brightness.