Reflective Display Research Articles

Morphology of Holographically-Formed Polymer Dispersed Liquid Crystals (H-PDLC)

Photopolymerization induced phase-separation of liquid crystal/polymer mixtures in holographic gratings show promise as switchable Bragg reflectors for optical communication and reflective display applications. The electro-optic properties of such Holographic Polymer Dispersed Liquid Crystals (H-PDLCs) are strongly dependent on polymer morphology and the degree of separation of the LC/polymer mixture. We report scanning electron microscopy, optical polarizing, and electro-optic studies on H-PDLC materials.

Introduction to Special Issue on Reflective Displays (Volume II)

Journal of the Society for Information DisplayVolume 8, Issue 1 p. 1-1 Introduction Andras I. Lakatos, Andras I. Lakatos EditorSearch for more papers by this author Andras I. Lakatos, Andras I. Lakatos EditorSearch for more papers by this author First published: 18 June 2012 https://doi.org/10.1889/1.1828693Citations: 11AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume8, Issue1March 2000Pages 1-1 RelatedInformation

P‐55: Reflective LCD with High Brightness and Wide Viewing Angle by Using Optically Compensated Twist‐LC Cell (OCT)

AbstractWe studied the design rules of the reflective type liquid crystal display (LCD) and the retardation films in order to prevent the color shift and the change of the reflectance. By analyzing the polarized state of light after passing through the LCD, and excellent reflective LCD, which shows almost constant reflectance in wide viewing angle without color shift by using the twist liquid crystal cell.

47.3: Performance Enhancement of Reflective CMOS TN Displays in Projection Applications Using Compensating Films

AbstractReflective twisted nematic μLCDs used in projection applications show a significant reduction in contrast as the F‐number of the system is reduced. A method is provided to optimize contrast of a reflective twisted nematic display. In a reflective off‐axis projection system where the polarizers and analyzers are separated, contrast of>500:1 are plausible.

44.2: Novel Fabrication of Inorganic Color Filter Using Transmittance of Thin‐Film Layers

AbstractA novel inorganic color filter (ICF) for the reflective liquid crystal display (LCD) has been proposed and fabricated for red color filter. The optical interference film of only 3‐layer consists of thin films of Iridium Tin Oxide (ITO), silicon nitride (SiNx) as transmittance layer and hydrogenated amorphous silicon (a‐Si:H) as an absorption layer. There was no color shift as defined value less than 3.0 of ΔE*ab for the ICF in the viewing angle up to 30 degrees.

Optical Modeling of Small Pixels in Reflective Mixed‐Mode Twisted Nematic Cells

AbstractWe present optical modeling of small pixels in reflective liquid crystal display (LCD). The optical analysis is divided into two parts. In the first part, the two‐dimensional (2D) director configuration of the LCD in rectangular mesh was calculated by simultaneously solving the 2D Poisson and continuum theory equations. In the second part, the generalized Jones matrix was used to simulate for the optical reflectance through the LCD with the 2D director configuration obtained from the first part. This optical modeling was applied to analyze the optical reflectance of small pixels in reflective mixed‐mode twisted nematic and birefergence (MTB) cells on silicon substrate. Both the simulated and experimental data of the MTB cells under frame and column inversions of polarity are presented.

320‐dpi 4‐inch Reflective Stacked Crossed Guest‐Host Display

AbstractWe describe a 320‐dpi, 4‐inch diagonal a‐Si:H TFT‐driven monochrome reflective display panel, in which two guest‐host nematic liquid crystal layers separated by a thin polymer film are orthogonally aligned to realize high reflectivity and high contrast ratio simultaneously. The TFT manufacturer used a four mask process with a high aperture ratio. The structure and characteristics of the panel are presented.

45.1 Optical Properties of the Gray Scale States of Cholesteric Reflective Displays

AbstractWe studied the bistable cholesteric reflective display in gray scale states. The display exhibits wide viewing angles with no gray scale inversions. By modeling the reflection spectra, we characterized the helical axis orientations, the pitch variations and the effective volume fractions of the gray scale states.

Introduction to Special Issue on Reflective Displays (Volume I)

Introduction to Special Issue on Reflective Displays (Volume I)

Optimization of polymer‐stabilized bistable black‐white cholesteric reflective display

Abstract— Cholesteric liquid crystals at zero field exhibit two optically contrasting stable states: planar texture and focal‐conic texture. When a cholesteric liquid crystal is in the planar texture, the helical axis is perpendicular to the cell surface; the material Bragg‐reflects colored light. When the liquid crystal is in the focal‐conic texture, the helical axis is more or less parallel to the cell surface; the material is forward‐scattering and has a black appearance if the back plate of the cell is painted black. We develop a cholesteric liquid‐crystal/polymer composite in which a small amount of polymer is dispersed in the liquid crystal. The dispersed polymer changes the planar texture to a poly‐domain structure, which has a white appearance but has little effect on the optical properties of the focal‐conic texture. The result is a bistable black‐white reflective display which is a good candidate for electronic‐paper applications.

Full‐color reflective display device using holographically fabricated polymer‐dispersed liquid crystal (HPDLC)

Abstract— A method of controlling the color of a holographic polymer‐dispersed liquid‐crystal (HPDLC) reflective display device has been achieved. By merely controlling the optical setup during fabrication, without changing the materials or laser light source, three primary‐color devices were fabricated. Since the color of the device can be controlled continuously, a large color‐reproducible area on the chromaticity diagram can be obtained. The resulting device was adequately transparent at other wavelengths to enable multiple devices to be stacked to obtain a mixture of colors. There was no significant change in color when applying an electric field. The three devices had similar reflectances and electro‐optical characteristics. Therefore, this device has good potential for full‐color display applications.

Alignment-Controlled Holographic Polymer Dispersed Liquid Crystal for Reflective Display Devices

A new type of holographic polymer dispersed liquid crystal (HPDLC) device in which liquid-crystal (LC) alignment is controlled by polymerized layers has been developed. In the alignment-controlled HPDLC device, the polymerized regions (polymer layers) are formed periodically in homogeneously aligned LC. When an electric field is applied vertically between the substrates, the LC molecules in the residual regions (LC layers) rotate towards the electric field. This causes a difference in refractive index between the polymer layers and LC layers, so selective reflection occurs in accordance with Bragg's law. The selectively reflected light shows strong polarization dependence. Only light polarized parallel to the alignment direction of LC molecules is reflected.

Advances in Holographic Polymer Dispersed Liquid Crystal Technology

ABSTRACTWe discuss recent advances in reflective holographically-formed polymer dispersed liquid crystal materials in the context of their suitability for reflective display applications. A dual-domain phenomenon resulting in a broadened reflection peak is presented. A simple phenomenological model is developed to explain this unusual effect The effect of monomer functionality on the reflectance characteristics of these materials is also discussed. Monomers of effective functionality ∼4.5 yield the brightest holograms, however, the data suggests that these systems are currently far from optimal.

Reflective color display using cholesteric liquid crystals

Abstract— A stacked‐type reflective color display using cholesteric liquid crystals has been developed. The display has high luminance and 512‐color capability. This device also has display‐image memory features without a field owing to its intermediate multi‐stability. We will discuss a new fast‐addressing scheme and device construction to obtain intermediate stability and excellent color‐display characteristics.

Multiple Light Scattering Model Applied to Reflective Display Materials

An estimate for the minimum film thickness required to give the scattering state of a reflective display material, such as a polymer dispersed liquid crystal (PDLC) or polymer stabilized cholesteric texture (PSCT), a desired diffuse luminous reflectance is presented. It is concluded that single scattering models are not suited for this task. To account for the multiple scattering of light, a previously developed model based on Mie scattering and two-flux radiative transfer theory is implemented. This simple model relates the size, composition, and the volume fraction of the scattering entities to the diffuse reflectance of the material. It is shown that the diffuse reflectance predictions from this model are in good agreement with measurements from other turbid systems. Using assumptions intended to produce an underestimate, it is concluded that the most birefringent liquid crystal materials currently available would require a film thickness between 11.5 µm and 17 µm to give an ideal black substrate a diffuse luminous reflectance of 60%.

A memory-type holographic polymer dispersed liquid crystal (HPDLC) reflective display device

A memory-type colour reflective display device is proposed. Introducing smectic liquid crystal to holographic polymer dispersed liquid crystal (HPDLC) successfully produced a memory function while keeping the advantages of HPDLC. This device is electrically writable and thermally erasable. It was able to maintain the memory state for more than 4 months. The mechanism of the memory function was analysed by comparing three HPDLC devices which were made with three different cyano-biphenyl compounds. The compounds had similar molecular structures but different phase transition temperatures. Small passive matrix devices for three primary colour devices were successfully demonstrated and colour mixing was confirmed to occur on stacking.

12.4L: Late‐News Paper: Polymer LEDs for Edge‐Lighting Reflective LCDs

AbstractWe present a study on the use of Polymer Light Emitting Diode (PLED) materials as possible integrated edge lighting components for reflective liquid crystal displays. The use of PLEDs for illumination of reflective displays does not compromise the positive attributes of portable reflective display technology; such as lightweight, thin and compact construction, and low‐power consumption. We have optimized the peak reflectance of a cholesteric reflecting cell with the emission spectrum of an PLED, and compared the important optical parameters to other illumination sources.

A high resolution, full colour, head mounted ferroelectric liquid crystal-over-silicon display

The development of a compact, head mounted display based on ferroelectric liquid crystal-over-submicron CMOS technology is described. The reflective display has an array of 1024 × 768 DRAM pixels with aperture ratios of ∼55% (being upgraded to 75%) and covers an area of 12·3mm × 9·2mm providing a resolution of >2000 lines per inch. Colour images are created using time sequential illumination of binary images displayed on the array of DRAM pixels with light from red (660nm), green (525nm) and blue (470nm) pulsed LEDs. The images are projected into the eye over a field of view of 40° diagonal with less than 4% geometrial distortion. Pictures are presented of XGA images with three red, three green, and two blue bit-frames at a frame rate of 1·2KHz (upgrade 2·5KHz) giving 256 colour hues with full 1024 × 768 pixel resolution in each colour (upgrade 216 hues).

Reflective Bistable Twisted Nematic Liquid Crystal Display

A reflective bistable twisted nematic (BTN) liquid crystal display has been developed. It combines the advantages of a truly reflective display without the rear polarizer, and the bistable nature of the zero voltage state. It was found experimentally that switching between the two bistable twist states could be achieved by adjusting the magnitude of the selection voltage pulse, just like the case in transmittive BTNs. In demonstrating the reflective BTN, we also show for the first time bistability between the -36° and 324° twist states.

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.