Reflective Cholesteric Display Research Articles

Characteristics of dual mode reflective cholesteric display

AbstractIn this article, we report our study of a dual mode reflective cholesteric display, which works in the traditional bistable mode as well as in the new and fast monostable mode. Because both modes are compatible, they can be used according to the need for video or static images. The bistable mode operates between the reflecting planar state and non‐reflecting focal conic state, both of which are stable at zero voltage. The bistable mode is suitable for displaying static images. In the monostable mode, it is operated on wrinkled cholesteric layers. It is fast and has low driving voltage, and can exhibit gray levels of reflectance determined by the applied voltage. The monostable mode is suitable to display video rate dynamic images.

40.3: Distinguished Student Paper: Dual Mode Reflective Cholesteric Display

AbstractWe developed a dual mode reflective cholesteric display which works in the traditional bistable mode as well as in a monostable mode. In the bistable mode, it is operated between the reflecting planar state and non‐reflecting focal conic state, both of which are stable at zero voltage. The bistable mode is suitable to display static images. In the monostable mode, it is operated on all the intermediate states between the planar and focal conic states. It is fast and has low driving voltage, and can exhibit gray levels of reflectance determined by the applied voltage. The monostable mode is suitable to display video rate dynamic images.

P-234L: Late-News Poster: Polymer Stabilized Black and White Reflective Cholesteric Displays

Polymer stabilized black and white reflective cholesteric displays have been developed. This type of displays employ a small amount of helical polymer network to stabilize the bistability and enable a distribution of helical pitches that reflect different wavelengths of white light, which are suitable for electronic signs and papers. The features affecting performance of the displays such as type and concentration of polymer network and alignment are investigated against brightness, color and electro-optical properties. A prototype display displaying both black and white images at zero voltage is presented.

22.4: Novel Drive Techniques and Temperature Compensation Mechanisms in Reflective Cholesteric Displays

AbstractThe driving techniques used for bistable reflective cholesteric displays are typically a function of application, temperature, and other material constraints. As such, new and unique driving techniques are employed continuously in order to optimize the updating methods of cholesteric displays. This paper focuses on several such techniques and related issues with these methods.

54.1: Ultra Low Power Black and White Cholesteric Display with COG and Solar Array

AbstractThe first chip‐on‐glass polymer modified black and white reflective cholesteric display is reported. The COG module contains an integrated solar array panel for energy harvesting providing an ultra low power concept for electronic books. The module is addressed with an enhanced dynamic drive scheme to enable higher voltage operation and improved image uniformity.

Bragg Reflective Polymer Stabilized Cholesteric Liquid Crystal Display

In the paper, we investigated the Bragg reflective cholesteric display based on polymer stabilization. We studied the bistability in the polymer stabilized cholesteric texture (PSCT) films and baused on which we achieved wider viewing angle though imperfect planar texture.

P‐70: Optimization of Dye Concentration in Reflective Cholesteric Displays

AbstractThe detailed study of the relationship between dye concentration and optical characteristics of reflective cholesteric LCDs is presented. It is found that color purity, chromaticity, lightness, and contrast ratio are dependent on the dye concentration. This provides a method to achieve the optimal optical characteristics of Ch‐LCDs by simply adjusting the dye concentration.

P‐82: Cumulative Drive Schemes for Bistable Reflective Cholesteric LCDs

AbstractWe have designed drive schemes which can update gradually the content of a bistable reflective cholesteric display. These scheme make use of the “kicking” effect as in addressing STN displays. The cholesteric material is kicked from the planar texture to the focal conic texture step‐by‐step or vice versa. We have also developed a new cholesteric display cell structure which has a 2 ms homeotropic‐planar transition time. Using the new cell structure and the new drive scheme, we have achieved an addressing speed of 0.5 ms/line; the cholesteric display can be operated at a quasi‐video rate.

Tunable chiral materials for multicolour reflective cholesteric displays

A polymerizable tunable chiral material (TCM) has been prepared for the fabrication of multicolour reflective cholesteric displays. This photosensitive chiral material, whose chirality is adjustable upon UV irradiation, enables us to adjust the pitch of a cholesteric material and thus to produce the three reflected colours (red, green and blue) for a multicolour reflective cholesteric display. Furthermore, the possibility of linking this compound to a polymer network helped to solve the problem of colour diffusion. Reflection spectra of the corresponding cells show broad reflection peaks, because of scattering from the large amount of polymerizable compound. We also report the difference of response under UV irradiation between this polymerizable tunable chiral material and a non-polymerizable material.

Photo-Asymmetric Synthesis of Helicenes in Liquid Crystals

Photo-asymmetric synthesis of pentahelicenes have been carried out in liquid crystals. The objective of this investigation is to study the feasibility of using polyhelicenes as tunable chiral materials in the color pixelation of reflective cholesteric displays (RCDs). Since the pitch of a cholesteric liquid crystal phase can be changed by the addition of a small amount of chiral compounds, in-situ photo-asymmetric synthesis in display cells provides a valuable method in the modification of liquid crystal properties. We describe herein attempts to use linearly//circularly polarized light to modify the pitch and hence, the color of a RCD.

Bistable reflective cholesteric liquid crystal display

A new type bistable reflective cholesteric liquid crystal display is reported. The texture and the relaxation process are very different from other types of the reflective cholesteric displays reported previously. The contrast ratio of the display is about 2.5 times higher than regular cholesteric displays. The response time of the display is 10 ms, which is much faster than the 230 ms response of regular cholesteric displays made with the same liquid crystal materials. A model to explain the unique textures of the display is presented.