Photo‐aligned photonic ferroelectric liquid crystal fibers

Preliminary studies of photonic crystal fibers (PCFs) partially infiltrated with photo‐aligned ferroelectric liquid crystals (FLCs) under the influence of external electric field are reported. The proper alignment of the FLC molecules is achieved by generating a photo‐aligning layer on the inner side of the PCF microcavities. The sulfonic azo dye, which is used as an alignment layer, offers a variable anchoring energy depending on the irradiation energy, and thus, a good control on the FLC alignment inside microchannels is possible. Moreover, a state of polarization of the light being guided inside the PCF infiltrated selectively with FLC changes under the influence of external electric field.     

Defect‐free half‐V‐mode ferroelectric liquid‐crystal device

Abstract— The horizontal chevron defect found in a half‐V‐mode ferroelectric‐liquid‐crystal (HV‐FLC) device can be suppressed by lowering the FLC's total free energy. The energy levels between spontaneous polarization (PS) up and down domains were degenerated by asymmetrical‐alignment treatments. The difference in the polar surface coefficient (γ²) was the key to suppressing the alignment defect. Alignment layers with opposite surface polarities and different anchoring energies were applied to control the sign and value of γ². The asymmetric cells of PIrub ‐ PIplasma (rubbed polyimide and plasma‐treated polyimide surfaces), PVArub ‐ PIplasma (rubbed polyvinyl alcohol and plasma‐treated polyimide surfaces), and PVArub ‐ PIplasma (both rubbed PI and PVA) alignment conditions presented defect‐free alignment textures under a slow‐cooling process. Among these different alignment treatments, the PVArub ‐ PIrub treated cell demonstrated the best alignment result, benefited by the largest difference in polar surface coefficient.     

Photoalignment and photo‐patterning of planar and homeotropic liquid‐crystal‐display configurations

Abstract— Optical alignment and micro‐patterning of the alignment of liquid‐crystal displays (LCDs) by linear photopolymerization (LPP) technology renders high‐quality multi‐domain twisted‐nematic (TN) and supertwisted‐nematic (STN) displays with broad fields of view over wide temperature ranges feasible. The prerequisites are the generation of photo‐induced high‐resolution azimuthal alignment patterns with defined bias‐tilt angles 0° ≤ θ ≤ 90°. For the first time, LPP‐aligned single‐ and dual‐domain vertically aligned nematic LCDs (VAN‐LCDs) are presented. Dual‐domain VAN‐LCDs are shown to exhibit broad fields of view which are further broadened by combining the displays with LPP‐aligned optical compensators made of liquid‐crystal polymers.     

A flexible ferroelectric liquid‐crystal display with improved mechanical stability for smart‐card applications

A bistable ferroelectric liquid‐crystal display (FLCD) for application in a smart card has been developed together with Infineon Technologies Business Unit Security and Chip Card ICs. The manufacturing process of the display will be explained. To further improve the functionality and reliability of the display, its layout has been modified. Barrier layers to reduce water permeation have been introduced. Defects in the FLC have been observed around the spacers. A change in the process order can help to avoid them. To reduce the sensitivity of the smectic layers of the FLC to shear forces, a special display layout with enlarged spacers has been developed together with an appropriate vacuum‐free filling process.     

Defect‐free deformed‐helix ferroelectric liquid‐crystal mode in a vertically aligned configuration (Invited Paper)

Abstract— A novel deformed‐helix ferroelectric liquid‐crystal (DHFLC) mode in a vertically aligned (VA) configuration is described. In this configuration, several unique features of display performance such as uniform alignment, fast response, and analog gray‐scale capability are obtained. Particularly, this VA‐DHFLC mode allows for the defect‐free uniform alignment of both the FLC molecules and the smectic layers over a large area without employing additional processes such as rubbing or electric‐field treatment that are generally required for planar FLC modes. Based on the VA‐DHFLC mode, a transflective display having a single‐gap geometry with in‐plane electrodes on two substrates in the transmissive regions and on one substrate in the reflective regions is described.     

Field‐induced photo‐reactive alignment technology for the vertical‐alignment liquid‐crystal mode

Abstract— An advanced vertical‐alignment liquid‐crystal (VA‐LC) technology based on field‐induced photo‐reactive alignment (FPA) as an advanced alignment mode for VA is proposed. FPA realizes uniform alignment and a faster rising response time, especially at high voltage. This technology can generate a pre‐tilt angle only by using photo‐reactive alignment material so that the tact time is shorter and the long‐term reliability is higher than that of conventional photo‐reactive processes, which require additional photo‐reactive monomers. The advanced hybrid FPA was developed by adopting both the tilted alignment with a pre‐tilt angle and conventional vertical alignment. By using an advanced hybrid structure, the response time and contrast ratio can be further improved.     

A single‐cell‐gap transflective liquid‐crystal display using different pretilt angles in transmissive and reflective regions

Abstract— A single‐cel l‐gap transflective liquid‐crystal display with two types of liquid‐crystal alignment based on an in‐plane‐switching structure is proposed. The transmissive region is almost homeotropically aligned with the rubbed surfaces at parallel directions while the reflective region has a homeotropic liquid‐crystal alignment. For every driving voltage for a positive‐dielectric‐anisotropy nematic liquid crystal, the effective cell‐retardation value in the transmissive region becomes larger than that in the reflective region because of optical compensation film which is generated by low‐pretilt‐angle liquid crystal in the transmissive region. Under the optimization of the liquid‐crystal cell and alignment used in the transmissive and reflective areas, the transmissive and reflective parts have similar gamma curves. An identical response time in both the transmissive and reflective regions and a desirable viewing angle for personal portable displays can also be obtained.     

Transflective ferroelectric liquid‐crystal display with a single‐cell gap

Abstract— A ferroelectric liquid‐crystal (FLC) display was optimized as a transflective liquid‐crystal display (LCD). In this configuration, the single‐cell‐gap approach was considered. The optimized configuration exhibits a high contrast ratio, wide viewing angles, and achromatic (black/white) switching in both the transmissive and reflective modes. Because no double‐cell‐gap structure, no subpixel separation, and no patterning polarizers and retarders are included in the configuration, the configuration is easy to fabricate and also possess a perfect dark state. This configuration is also suitable for bistable applications.     

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.     

Speckle‐noise suppression due to a single ferroelectric liquid‐crystal cell

Abstract— A novel principle and simple technique of suppressing the speckle noise in images displayed by a laser projection system is proposed. Wave coherence in a laser beam and speckles are destroyed in real time when the beam passes through a single FLC cell where spatially inhomogeneous phase light modulation takes place due to special FLC material and an electrical pulse regime.     

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.     

Ferroelectric nanoparticle/liquid‐crystal colloids for display applications

Abstract— A non‐synthetic approach to modify liquid crystals (LCs) by dispersing low concentrations of ferroelectric nanoparticles is reported. These dilute colloids are stable and appear similar to a pure LC. However, by changing the concentration and the type of ferroelectric particles, the physical properties of the LC materials can be tailored, including the nematic isotropic transition temperature (T_NI), the dielectric constants, the birefringence (Δn), elastic constants, and the threshold voltage. Specifically, doping low concentrations of BaTiO₃ nanoparticles (～1%) into a LC MLC‐6609 increases T_NI up to ～40°C. This giant shift of T_NI has never been previously reported and indicates strong interactions between the LC and ferroelectric nanoparticles on a molecular level. The doped LC also demonstrates significant enhancement in birefringence (by 10–30%), dielectric anisotropy (by ～50%), and the elastic constant K₃₃ (by ～20%). Ferroparticles act as molecular additives and modify the intrinsic properties of LC materials without time consuming and expensive chemical synthesis. The new LC materials are very attractive and suitable for use in displays, switchable lenses, beam steering, as well as other light‐controlling devices.     

Photostable liquid‐crystal guest‐host nano‐materials for display applications

Abstract— We theoretically modeled the optical plasmon absorption of anisotropic metallic nanoparticles in a liquid‐crystal host medium. Metallic nanorods and spheroids act as pleochroic dopants with virtually unlimited photostability. Calculations predict that full‐color displays based on nanorod orientation driven by the transition from homogeneous to homeotropic LC alignment are feasible. These displays are expected to have large viewing angles without the need for polarizers or LC anchoring surfaces.     

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.     

Transflective blue‐phase liquid‐crystal display with corrugated electrode structure

Abstract— A transflective polymer‐stabilized blue‐phase liquid‐crystal display (BP‐LCD) with a corrugated electrode structure is proposed. To balance the optical phase retardation between the transmissive (T) and reflective (R) regions, two device structures are proposed. The first device structure has the same inclination angles but different cell gaps in the T and R regions. And the second device structure has the same cell gap but different inclination angles in the T and R regions. Both of the device structures can obtain well‐matched VT and VR curves. This display exhibits low operating voltage, high optical efficiency, and a wide viewing angle.     

Flexible ferroelectric liquid‐crystal devices containing fine polymer fibers

A new flexible ferroelectric liquid‐crystal‐display device with gray‐scale capability has been created by using submicrometer‐diameter polymer fibers. The polymer fibers, which are formed by photopolymerization of aligned monomer molecules in liquid crystal, align the ferroelectric liquid crystal and mechanically support two flexible thin plastic substrates. The composite film made of liquid crystal and polymer with a thickness of 2 μm was formed between the plastic substrates by using a fabrication method consisting of coating, lamination, and ultraviolet irradiation processes without the conventional gap‐forming and injection processes. The fabricated flexible device revealed gray‐scale capability due to the change in spatial distribution of micrometer‐sized binary‐switching liquid‐crystal domains. From the polarizing microscope observation, it was found that the switching domains are generated and expanded from the areas with poor polymer density. The experimental results indicated that the polymer fibers spatially modulate the threshold voltage for molecular switching. Our device exhibits great potential for flexible large‐sized light‐weight motion‐image displays.     

A 5‐in. flexible ferroelectric liquid‐crystal display driven by organic thin‐film transistors

Abstract— An organic thin‐film‐transistor (OTFT) driven color flexible ferroelectric‐liquid‐crystal (FLC) display with 160 × 120 pixels and a resolution of 50 ppi has been developed. The flexible FLC was fabricated on a pentacene‐OTFT array using printing and lamination techniques. To drive the display at a fast driving speed, an OTFT was developed with a short channel length having a large current output. The fabricated OTFT array with a channel length of 5 μm exhibits a carrier mobility of 0.3 cm²/V‐sec and an ON/OFF ratio of over 10⁷ at a low drain voltage of ?6 V. A field‐sequential‐color system with a flexible backlight unit was also developed and used to drive the display. Color moving images were successively shown on the 5‐in. display using an active‐matrix driving technique of the OTFT.     

A self‐aligned multi‐domain liquid‐crystal display on polymer gratings in a vertically aligned configuration

Abstract— We report on a new method of fabricating a vertically aligned multi‐domain liquid‐crystal display (LCD) using surface‐relief gratings. A linear array of surface‐relief gratings was produced by using a photosensitive polymer material coated on glass substrates by the illumination of the UV light through a photomask. The LCD cell was assembled with two substrates with polymer gratings in such way that the grating vectors were orthogonal to each other. In this LCD configuration, the nematic molecules were reoriented by distortions of an external electric field at the grating surfaces to make four different domains. The LC cell with self‐aligned four domains shows excellent extinction in the off‐state and wide‐viewing characteristics in the on‐state.     

A single‐substrate multicolor cholesteric liquid‐crystal display prepared through ink‐jet printing

Abstract— Ink‐jet printing was used to prepare a single‐substrate multicolor cholesteric liquid‐crystal (Ch‐LC) display incorporating three Ch‐LCs exhibiting different reflective wavelengths. A room‐temperature low‐vacuum chemical‐vapor‐deposition process was developed for coating a thin polymer film onto the Ch‐LC so that the top electrode could be coated onto the Ch‐LC layer. Herein, the successful operation of such a 10.4‐in. QVGA Ch‐LC display at 40 V will be described.     

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.