Optical properties of solvent‐cast polarizer films for liquid‐crystal displays: A viscoelastic modeling framework

Abstract— Many of the films used in polarizer assemblies in LCDs (e.g., triacetyl cellulose or TAC) are produced by a solvent‐casting process, which is known to impart optical anisotropy to the film expressed as finite out‐of‐plane birefringence. This feature of the film could have a significant impact on the optical performance of the display and it needs to be accounted for in any compensation scheme for the LC cell. This paper reviews the origin of this optical anisotropy, and it presents a viscoelastic model that links this property to the solvent‐casting process and to some key material parameters. The model results are compared with experimental data generated for polystyrene films cast from toluene, and generally good agreement is demonstrated.     

Deformed nanostructure of photo‐induced biaxial cholesteric films and their application in VA‐mode LCDs

Abstract— Novel biaxial retardation films made from photo‐induced deformed cholesteric liquid‐crystal (LC) nanostructures using reactive mesogen mixtures (RMMs) for a viewing‐angle compensation of vertically aligned liquid‐crystal displays (VA‐LCDs) was developed. The deformed cholesteric LC nanostructure has been observed by X‐ray‐diffraction (XRD) measurement. The birefringence of the film was described well by our optical model based on a form birefringence theory. The VA‐LCDs with photo‐induced biaxial cholesteric films have excellent viewing‐angle properties.     

Viewing‐angle compensation of TN‐ and ECB‐LCD modes by using a rod‐like liquid‐crystalline polymer film

Abstract— A liquid‐crystal line retardation‐film technology by using a rod‐like liquid‐crystalline polymer (LCP) for various LCD modes have been developed. In particular, considerable improvements in viewing‐angle performance have been achieved for the twisted‐nematic (TN) and the transmissive/transflective electrically controlled birefringence (ECB) modes by using hybrid aligned nematic film (NH Film).     

LCD applications of thin‐crystal‐film polarizers

Abstract— We have developed a new technique for the production of thin crystal film (TCF) by deposition, molecular alignment, and the drying of water‐based lyotropic‐liquid‐crystal (LLC) materials. TCF exhibits high optical anisotropy and birefringence. This paper presents liquid‐crystal‐display (LCD) applications and opportunities for TCF plastic sheet polarizers, retarders, and color‐correction films as well as LCD designs with TCF internal polarizers.     

Efficiency analysis for multi‐view spatially multiplexed autostereoscopic 2‐D/3‐D displays

Abstract— The wide‐viewing freedom often requested by users of autostereoscopic displays can be delivered by spatial multiplexing of multiple views in which a sequence of images is directed into respective directions by a suitable autostereoscopic optical system. This gives rise to two important design considerations — the optical efficiency and the resolution efficiency of the device. Optical efficiency is particularly important in portable devices such as cell phones. A comparison is given between lens and barrier systems for various spatial multiplexing arrangements. Parallax‐barrier displays suffer from reduced optical efficiency as the number of views presented increases whereas throughput efficiency is independent of the number of views for lens displays. An autostereoscopic optical system is presented for the emerging class of highly efficient polarizer‐free displays. Resolution efficiency can be evaluated by investigating quantitative and subjective comparisons of resolution losses and pixel appearance in each 3‐D image. Specifically, 2.2‐in.‐diagonal 2‐D/3‐D panel performance has been assessed using Nyquist boundaries, human‐visual contrast‐sensitivity models, and autostereoscopic‐display optical output simulations. Four‐view vertical Polarization‐Activated Microlens technology with either QVGA mosaic or VGA striped pixel arrangements is a strong candidate for an optimum compromise between display brightness, viewing angle, and 3‐D pixel appearance.     

Demonstration of a technological prototype of an active‐matrix BiNem liquid‐crystal display

Abstract— The first implementation of active‐matrix addressing on a BiNem bistable nematic liquid‐crystal display has been demonstrated. Compared to previous passive‐matrix addressing, major improvements have been made for the bistable mode: a smoother image refreshment, shorter refreshing frame time compatible with that of high‐resolution e‐book displays, the use of a touch screen for interactive functions such as hand‐writing, a virtual keyboard, improved functionality for scrolling menus, partial refreshment, etc. On the same display but in the monostable mode, by using electrically controlled birefringence (ECB), the potential of displaying moving pictures at a rate of 25 images/sec, at an extended room temperature, has been demonstrated. In the ECB monostable mode, static images can be displayed down to ?20°C. A new transflective single‐polarizer optical mode has been developed to optimize the indoor and outdoor readability of the display. By lowering the surface reflection and enhancing the panel transmission, a contrast ratio of 94:1 and a transmittance of 17% have been achieved.     

Environmental and optical testing of Thin Crystal Film™ polarizers

Abstract— We have developed an advanced polarizing nanomaterial that provides new technical and economical advantages over traditional iodine film polarizers for LCD designers and manufacturers. Thin Crystal Film (TCF)? polarizer material is based on modified organic dichroic dyes and can be simply coated as a thin molecular oriented film (less than 1 μm) directly onto a plastic or glass substrate. This crystalline material exhibits enhanced viewing‐angle characteristics, high thermal stability, and lightfastness. Replacement of conventional polarizers by the new TCF polarizer allows decreasing thickness of LCD designs by 20–75%, improving LCD durability and reliability, all while significantly reducing cost. This paper presents TCF polarizer products for LCD applications. We report the results of TCF optical and environmental testing. Ultraviolet‐light photostability of TCF is also studied.     

Low‐leakage off‐angle in E‐polarizers

Abstract— New thin‐film polarizers have been developed for use in optical applications. The polarization technology is based upon liquid‐crystalline material built from dichroic dyes that can be deposited on virtually any substrate. Theoretical calculations and experimental results on viewing‐angle characterization of conventional O‐type polarizers and new E‐type polarizers are presented. At large viewing angles, the E‐type polarizers demonstrate lower light leakage, higher contrast ratio, and higher efficiency. Spectral performance depends on the composition of the dye mixture that is used to produce the polarizer coating. The new polarizers exhibit enhanced viewing angle and more design flexibility, providing new opportunities for the liquid‐crystal‐display industry.     

Current status and future prospect of in‐cell‐polarizer technology

Abstract— A thin‐crystalline‐film (TCF) polarizer has been developed which can be used internally in liquid‐crystal‐display cells. Based on this material, a manufacturing process has been developed for the fabrication of monochrome LCDs with internal polarizers. A new TCF polarizer material and coating equipment, developed to realize a high‐performance color TFT‐LCD, are discussed.     

Single‐layered retardation films with negative wavelength dispersion birefringence made from liquid‐crystalline monomers

Organic light‐emitting diode displays have a cathode composed of a layer of highly reflective metal. Reflection of external light from this layer can be suppressed with a broadband quarter‐wave plate. Although various types of quarter‐wave plate retardation films have been prepared by copolymerizing, mixing, or laminating multiple polymers, ideal wavelength dispersion has not been achieved with thin retardation films because of their relatively low birefringence and the complexity of the procedure required manufacturing them. In this study, we developed (i) new liquid‐crystalline monomers with negative wavelength dispersion birefringence that we used to obtain thin, single‐layered retardation films suitable for coating and (ii) retardation films with different molecular alignments. We found that the monomers showed high solubility and high regularity of molecular alignment, with less damage to the substrate and alignment films. We also investigated the wavelength dispersion and thermal stability of the films. We succeeded in developing retardation films that had a homeotropic alignment or a hybrid alignment with negative wavelength dispersion. These alignments can be used to obtain antireflection films with an improved viewing angle for organic light‐emitting diode displays or next‐generation thin displays.     

Analysis of angular dependence of 3‐D technology using polarized eyeglasses

Abstract— The cause of the angular dependence of 3‐D technology that requires the use of eyeglasses with linear or circular polarization is analyzed. For 3‐D technology that requires the use of eyeglasses, anisotropic media such as a polarizer or retardation film determines the polarization state. Therefore, the angular behavior of 3‐D display performance is also affected by the characteristics of the anisotropic media that have intrinsic angular dependence. Various conditions of the optic axes of the imaging display and eyeglasses are investigated to understand their effect on 3‐D display performance. The result shows that some conditions of the optic axes can cause non‐negligible degradation of 3‐D display performance.     

Tailored liquid‐crystal switching on ferroelectric polymer films

Abstract— The development of voltage‐controlled visible‐wavelength progression in displays and optical data storage devices using ferroelectric polymers and liquid crystals is described. Ferroelectric polymers are materials that have a ready distribution of dipoles which can be oriented by manipulating material composition and external fields. Utilizing the charge polarization distribution, their performance as an alignment layer for inducing liquid‐crystal alignment is presented. The switching response of the devices was tailored by changing the material composition through copolymers and nanoclay doping.     

Application of re‐crystallized metal‐induced unilaterally crystallized polycrystalline‐silicon thin‐film‐transistor technology to reflective liquid‐crystaldisplay

Single‐polarizer reflective twisted‐nematic (RTN) liquid‐crystal modes offer larger viewing angles, higher contrast ratios and lower power dissipation compared to regular double‐polarizer transmissive‐ reflective liquid‐crystal implementations. The application of re‐crystallized metal‐induced unilaterally crystallized polycrystalline‐silicon thin‐film‐transistor (TFT) technology to realize active matrices and peripheral circuit components for hand‐held direct‐view RTN‐mode video displays is reported.     

Optimization of bi‐layered nano‐wire grids as high‐efficiency polarizers for power recycling in liquid‐crystal displays

Abstract— Bi‐layered Al nano‐wire grids (N WGs) are proposed as high‐efficiency polarizers for power recycling in liquid‐crystal displays (LCDs). In comparison with single‐layered NWGs, the bi‐layered scheme is more cost‐effective with both less and more controllable fabrication steps. Two types of 150‐nm‐period NWGs with different cross sections were characterized and theoretically analyzed. A TM transmittance of over 66% and a contrast ratio as high as 8000 in the visible range were calculated. Furthermore, 5–8% increase in TM transmittance and an almost 20% enhancement in contrast ratio are achievable. The NWG sheet with a large contrast ratio as well as a high optical throughput acts as a reflective polarizer in the power‐recycling system of LCD backlight units. A total transmittance of above 70% in the visible region is predicted for the power‐recycling process, which is at least 9% higher in total light efficiency than the claimed result of commercial dual brightness‐enhancement film (DBEF).     

Analytic Spectral Integration of Birefringence‐Induced Iridescence

Optical phenomena that are only observable in optically anisotropic materials are generally ignored in the computer graphics. However, such optical effects are not restricted to exotic materials and can also be observed with common translucent objects when optical anisotropy is induced, e.g. via mechanical stress. Furthermore accurate prediction and reproduction of those optical effects has important practical applications. We provide a short but complete analysis of the relevant electromagnetic theory of light propagation in optically anisotropic media and derive the full set of formulations required to render birefringent materials. We then present a novel method for spectral integration of refraction and reflection in an anisotropic slab. Our approach allows fast and robust rendering of birefringence‐induced iridescence in a physically faithful manner and is applicable to both real‐time and offline rendering.     

Optical rewritable liquid‐crystal‐alignment technology

Abstract— A new optical rewritable (ORW) liquid‐crystal‐alignment technology has been developed to create a display and to demonstrate its maturity and potential. ORW displays have no electrodes and use polarizers as substrates. The display requires no photolithography on plastic. Its simple construction secures durability and low cost for mass production. The on‐screen information is optically changed in a writing unit that consists of an LCD mask and an exposure source that is based on LEDs, low power, and low cost in comparison with Hg lamps or lasers. A high contrast image can be easily written, viewed, and rewritten through a polarizer, while the multi‐stable gray‐level image requires zero power to maintain the image. Reconfigurable LC alignment using ORW technology best suits plastic‐card displays as well as for LC photonics and various one‐mask processes of patterned LC‐alignment applications.     

An optical design for reflective color STN‐LCDs

In reflective color STN‐LCDs, it is necessary to achieve achromatic representation in single‐polarizer STN‐LCD modes. We propose an optimization method for the optical components of single‐polarizer STN‐LCD modes in order to achieve achromatic representation. By applying this method, it is shown that a contrast ratio of more than 20 can be achieved in the normally black (NB) mode. Furthermore, we prove that the normally white (NW) mode can be realized as well as an NB mode which is usually used in current reflective color STN‐LCDs. Comparing the viewing‐angle characteristics of the NW and NB modes, it was found that those of the NW mode are better than those of the NB mode. Particularly, high reflectance can be realized even at larger viewing angles in the NW mode.     

Antiferroelectric LCD with one polarizer in a reflective configuration

A reflective antiferroelectric liquid‐crystal (AFLC) display with one polarizer is proposed. An optical retardation film was introduced into the reflective configuration to obtain enhanced electro‐optic (EO) characteristics. Numerical simulations were carried out to optimize the cell parameters so that the EO switching between the black and white states could be easily achieved. The reflective AFLC display with optimized cell parameters was found to exhibit high contrast, excellent brightness, and fast response.     

Translucent LCDs

Abstract— Current LCD designs have about 5–7% transmittance in the white state without the use of DBEF^3M (double brightness enhancing film) and up to 10–14% with DBEF film. We presented a design which can further increase the brightness by up to 60%. The basics for this design are new Optiva materials which have a high birefringence about 0.3–0.4 and low absorption losses in the visible spectrum. This material can be used to produce multilayer interference reflective polarizer and polarization interference color filters. Initial prototypes of these interference elements will be discussed in the paper.     

Fast‐response nematic liquid‐crystal mixtures

Abstract— High birefringence and relatively low‐viscosity isothiocyanate‐based liquid‐crystal compounds and mixtures were developed. A high figure‐of‐merit (FoM), which implies a fast response time of the described liquid crystals was observed. Using the new UCF mixture in a 2‐μm cell, a submillisecond response time was obtained. The UV stability dilemma is discussed as a common concern for high‐birefringence LC materials.