A photographic technique for assessing the viewing‐angle performance of liquid‐crystal displays

Abstract— Liquid‐crystal displays (LCDs) have notable variation in luminance and perceived contrast as a function of the angle from which they are viewed. Though this is an important performance issue for LCDs, most evaluation techniques for assessing this variation have been limited to laboratory settings. This study demonstrates the use of a photographic technique for such an evaluation. The technique is based on an actively cooled charge‐coupled‐device (CCD) detector in combination with a macro lens covering a circular angular range (θ) of ±42.5°. The camera was used to evaluate the luminance and perceived contrast properties of an LCD. Uniform field images corresponding to 17 equally spaced gray‐scale values in the digital driving level (DDL) range of the display system were acquired. The 12‐bit gray‐scale digital images produced by the camera were converted to luminance units (cd/m²) via the measured luminance vs. DDL response function of the camera. The changes in perceived contrast as a function of viewing angle were derived from the Barten model of the gray‐scale response of the human‐visual system using the methods proposed by the AAPM TG18 Report. The results of this photographic technique were compared to measurements acquired from a similar display using a Fourier‐optics‐based luminance meter. The results of the two methods generally agreed to within 5%. The photographic methods used were found to be accurate and robust for in‐field assessment of the angular response of LCDs over the FOV of the camera.     

Progress in viewing‐angle properties of liquid‐crystal displays

Abstract— Viewing‐angle dependences of the contrast ratio and color shift of LCDs have been radically improved as evidenced by the increasing application of LCDs in high‐quality television. This paper describes the concept of optical compensation and the fundamental characteristics of the viewing‐angle property for various LC modes.     

A viewing‐angle‐controllable blue‐phase liquid‐crystal display

Abstract— A viewing‐angle‐controllable liquid‐crystal display (LCD) is proposed. When the device is only driven by an in‐plane electric field, it exhibits a wide‐viewing‐angle (WVA) mode. And it exhibits narrow‐viewing‐angle (NVA) mode when it is driven by a vertical electric field as well as an in‐plane electric field. In this manner, the viewing angle of the device can be controlled from 100° to 30°. The device exhibits a good viewing‐angle‐controlling characteristic and high transmittance.     

Active‐matrix and flexible liquid‐crystal displays with carbon‐nanotube pixel electrodes

Abstract— The necessary processes to use random carbon‐nanotube networks as transparent conductors in twisted‐nematic liquid‐crystal displays have been developed, replacing indium tin oxide. Because the nanotubes are deposited vacuum‐free from suspension, the potential advantages are lower costs for material, equipment, and production. Nanotube networks are also much better suited for flexible displays than the commonly used metal oxides. With the developed processes, the world's first full‐color active‐matrix LCDs as well as directly addressed flexible displays on plastic substrates with carbon‐nanotube pixel electrodes, have been realized.     

Technologies toward flexible liquid‐crystal displays

Abstract— Several leading technologies for flexible liquid‐crystal displays have been developed recently at ERSO. The roll‐to‐roll compatible techniques, polymer‐added liquid crystal, have been applied on a film‐like substrate. A flexible black‐and‐white cholesteric liquid‐crystal display was also implemented by photo‐induced phase separation. Color filters placed on a plastic substrate by a low‐temperature manufacturing process was successfully fabricated. A novel design of a wide‐viewing‐angle color plastic LCD was also proposed.     

Heterodyne method for determining the surface tilt angle of nematic liquid‐crystal displays

Abstract— The high‐sensitivity pretilt‐angle measurement of liquid‐crystal displays, based on the modified crystal‐rotation configuration and the use of a common‐path heterodyne interferometer, is proposed. In this technique, environmental disturbance and surface reflection are eliminated to a large extend, thus providing advantages for both constructing a simple‐optics measurement system and achieving fast measurement with high accuracy and sensitivity.     

Switchable transmissive and reflective liquid‐crystal display using a multi‐domain vertical alignment

Abstract— A wide‐view transflective liquid‐crystal display (LCD) capable of switching between transmissive and reflective modes in response to different ambient‐light conditions is proposed. This transflective LCD adopts a single‐cell‐gap multi‐domain vertical‐alignment (MVA) cell that exhibits high contrast ratio, wide‐viewing angle, and good light transmittance (T) and reflectance (R). Under proper cell optimization, a good match between the VT and VR curves can also be obtained for single‐gamma‐curve driving.     

Controling color of liquid‐crystal displays

Abstract— Two newly derived characterization models for a liquid‐crystal (LC) display have been tested for five LC‐based displays. Data measured from a series of test colors indicated that all LC‐based displays showed similar characteristics, including an S‐shaped tone curve and poor channel chromaticity constancy. Because they include a hyperbolic function in their definition, the models do not have analytical inverses, and so iterative mathematical techniques are applied. It was shown that a new characterization model based on a hyperbolic function fits the tone curve very accurately with only four coefficients per channel for any type of LCD. In addition, it was also shown that the first derivative of the function provides a means of accurate correction of the chromaticity variation.     

A continuous‐viewing‐angle‐controllable liquid‐crystal display using a blue‐phase liquid crystal

Abstract— A continuous‐viewing‐angle‐controllable liquid‐crystal display (LCD) using a blue‐phase liquid crystal is proposed. To realize both wide‐viewing‐angle (WVA) mode and narrow‐viewing‐angle (NVA) mode with a single liquid‐crystal panel, each pixel is divided into a main pixel and a subpixel. The main pixel is for displaying images in both modes. The subpixel is for displaying images in WVA mode and controlling the viewing angle in NVA mode. The device exhibits a good viewing‐angle‐controlling characteristic and high transmittance.     

Substrate‐free cholesteric liquid‐crystal displays

Abstract— This paper demonstrates the first substrate‐free cholesteric liquid‐crystal displays. The encapsulated cholesteric displays are ultra‐thin (with a total thickness around 20 μm) and ultra‐lightweight (0.002 g/cm²). The displays exhibit unprecedented conformability, flexibility, and drapability while maintaining electro‐optical performance and mechanical integrity. All functional display layers are sequentially coated on a preparation substrate and then lifted‐off from the preparation substrate to form a free‐standing display. The display fabrication process, electro‐optical performance, and display flexibility are discussed.     

High‐transmittance in‐plane‐switching liquid‐crystal displays using a positive‐dielectric‐anisotropy liquid crystal

Abstract— The in‐plane‐switching (IPS) mode exhibits an inherently wide viewing angle and has been widely used for liquid‐crystal‐display (LCD) TVs. However, its transmittance is limited to ～76% compared to that of a twisted‐nematic (TN) cell if a positive‐dielectric‐anisotropy LC is employed. A special electrode configuration that fuses the switching mechanism of the conventional IPS and the fringe‐field switching (FFS) to boost the transmittance to ～90% using a positive LC has been developed. The new mode exhibits an equally wide viewing angle as the IPS and FFS modes.     

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.     

Fast‐response liquid‐crystal displays using crossed fringe fields

Abstract— A fast‐response and wide‐view liquid‐crystal display (LCD) using the crossed fringe‐field‐switching (CFFS) mode is proposed, where the fringe‐field electrodes exist on both the top and bottom substrates. The bottom fringe field is used to turn on the LC directors and the top fringe field is used to assist in the LC decay process. The decay time is reduced by ～2× compared to that of the conventional FFS mode between the full bright and dark states, and more than a 2× improvement is obtained for other gray‐scale transitions. This CFFS mode also preserves the wide‐view characteristics as the conventional FFS mode. Its applications to LCD TVs and monitors for reducing image blur are addressed.     

Novel photo‐aligned LC‐polymer compensation film for wide‐view TN displays

Abstract— We demonstrate a novel TN‐display compensation film with excellent contrast and minimal color shift, meeting the requirements for avionics displays. The film configuration was identified via extensive computer modeling. The experimental implementation based on ROLIC's LPP/LCP (linearly photopolymerizable polymer/liquid‐crystal polymer) technology results in excellent agreement with theoretical predictions.     

Novel application of ink‐jet‐printing technology in multi‐domain alignment liquid‐crystal displays

Abstract— Based on the drop‐on‐demand characteristics of ink‐jet printing, the multi‐domain alignment liquid‐crystal display (LCD) could be achieved by using patterned polyimide materials. These polyimide ink locations with different alignment procedures could be defined in a single pixel, depending on the designer 's setting. In this paper, we combined the electro‐optical design, polyimide ink formulation, and ink‐jetting technology to demonstrate the application of multi‐domain alignment liquid‐crystal display manufactory. The first one was a multi‐domain vertical‐alignment LCD. After the horizontal alignment material pattern on the vertical alignment film, the viewing angle would reach 150° without compensation film. The second one was a single‐cell‐gap transflective LCD within integrating the horizontal alignment in the transmissive region and hybrid alignment in the reflective one in the same pixel. In addition, this transflective LCD was also demonstrated in the form of a 2.4‐in. 170‐ppi prototype.     

Evaluation of contrast metrics for liquid‐crystal displays under different viewing conditions

Abstract— A psychophysical experiment was carried out to assess the perceptual contrast on a large‐sized liquid‐crystal display (LCD) under nine phases of viewing conditions. Based on the results, six contrast models employing different color attributes or the index of just‐noticeable difference (JND) were developed. Their performances were also tested by the visual data of the nine phases, which indicated that the model C_Q employing CIECAM02 brightness gives the best performance in predicting visual data under different viewing conditions among those models. A preprocessing step was also proposed to utilize the contrast model C_Q conveniently in the practical contrast evaluation of LCDs.     

A single‐cell‐gap transflective blue‐phase liquid crystal display based on fringe in‐plane switching electrodes

A transflective blue‐phase liquid crystal display (TRBP‐LCD) based on fringe in‐plane switching (FIS) electrodes is proposed. The proposed structure generates combined fringe and in‐plane electric fields that cause more liquid crystal (LC) molecules to reorient almost in plane above and between the pixel electrodes. The fringe field is mainly generated in the transmissive (T) region, and the horizontal electric field is mainly generated in the reflective (R) region. By optimizing the width of the pixel electrodes and the gap between two adjacent pixel electrodes, the different electric field intensity in the T and R regions contribute to balance the optical phase retardation between the T and R regions. As a result, the proposed TRBP‐LCD exhibits a low operating voltage and high optical efficiency, while it preserves a relatively simple fabrication process.     

Ultra‐fast‐switching flexoelectric liquid‐crystal display with high contrast

Abstract— The flexoelectro‐optic effect provides a fast‐switching mechanism (0.01–0.1 msec), suitable for use in field‐sequential‐color full‐motion‐video displays. An in‐plane electric field is applied to a short‐pitch chiral nematic liquid crystal aligned in the uniform standing helix (or Grandjean) texture. The switching mechanism is experimentally demonstrated in a single‐pixel test cell, and the display performance is investigated as a function of device parameters. A contrast ratio of 2000:1 is predicted.     

A single‐cell‐gap transflective liquid‐crystal display with special electrodes

Abstract— A single‐cell‐gap transflective liquid‐crystal display with special electrodes was demonstrated. In the transmissive region, a strong longitudinal electric field was generated by decreasing the distance between the top and bottom transparent indium‐tin‐oxide electrodes; while in the reflective region, a weak longitudinal electric field is generated by increasing the distance between the top and bottom transparent indium‐tin‐oxide electrodes. And slit‐patterned electrodes were used to optimize the fringe field at the junction of the transmissive and reflective regions. As a result, both the transmissive and reflective display modes show well‐matched gray scales. The simulated single‐cell‐gap TR‐LCD has good performances.     

Towards nanoscale molecular switch-based liquid crystal displays

Cholesteric liquid crystals (Ch-LCs) have been extensively studied due to their unique self-organized helical molecular structures and selective Bragg reflection properties, which exhibit great potentials for color displays and other practical applications. When functional, nanoscale molecular switches are doped in liquid crystals (LCs), the phases of the LCs or the molecular structures of the Ch-LCs can be changed upon the influence of external stimuli, such as light and temperature. In this paper, the photoresponsive molecular switch-based LCs for display applications are reviewed. The progress and effort in developing molecular switches, the principles of light-tuning, photo-addressed color displays, information processing, bistable displays and flexible displays are presented.