Showing papers by "Seung Hee Lee published in 2010"
TL;DR: In this article, a new cell structure with a protrusion shape of electrode and a driving scheme using two transistors to reduce operating voltage and enhance light efficiency was proposed for liquid crystal displays based on the Kerr effect.
Abstract: Liquid crystal displays based on the Kerr effect are emerging because of their attractive features, such as symmetric viewing angle, no need for alignment layer, and sub-millisecond response time. However, high operating voltage and low optical efficiency remain as challenges to be overcome. Here, we propose a new cell structure with a protrusion shape of electrode and a driving scheme using two transistors to reduce operating voltage and enhance light efficiency. Confirming simulation results are obtained.
67 citations
TL;DR: In this article, the authors proposed a liquid crystal display (LCD) whose viewing angle can be switched from wide view to narrow view using only one panel, where each pixel is divided into two parts: a major pixel and a sub-pixel.
Abstract: An optically isotropic liquid crystal (LC) such as a blue phase LC or an optically isotropic nano-structured LC exhibits a very wide viewing angle because the induced birefringence is along the in-plane electric field. Utilizing such a material, we propose a liquid crystal display (LCD) whose viewing angle can be switched from wide view to narrow view using only one panel. In the device, each pixel is divided into two parts: a major pixel and a sub-pixel. The main pixels display the images while the sub-pixels control the viewing angle. In the main pixels, birefringence is induced by horizontal electric fields through inter-digital electrodes leading to a wide viewing angle, while in the sub-pixels, birefringence is induced by the vertical electric field so that phase retardation occurs only at oblique angles. As a result, the dark state (or contrast ratio) of the entire pixel can be controlled by the voltage of the sub-pixels. Such a switchable viewing angle LCD is attractive for protecting personal privacy.
52 citations
TL;DR: In this article, the electro-optic response of a carbon nanotube (CNT) cluster has been investigated, where the cluster absorbs incident light before stretching and transmits incident light with its electric vector propagating parallel and perpendicular to the long axis of the stretched cluster, respectively.
Abstract: The electro-optic response of a carbon nanotube (CNT) cluster has been investigated. The cluster absorbs incident light before stretching. In the presence of an electric field, the cluster starts stretching along the field direction and contracts back to its original stage when the applied voltage is removed. The stretched cluster absorbs and transmits incident light with its electric vector propagating parallel and perpendicular to the long axis of the stretched cluster, respectively. Utilizing this selective light absorption property of a CNT cluster, a tunable polarizer or non-emissive light modulator can be realized.
24 citations
TL;DR: New viewing angle controllable homogeneously aligned liquid crystal display in which the pixel is composed of red, green, blue, and white pixels, which overcomes the long standing problem of transmittance sacrifice in the conventional devices.
Abstract: All conventional viewing angle switchable liquid crystal displays with pixel division have drawback in light efficiency because the sub-pixel that controls viewing angle does not transmit the incident light at normal direction. In this paper, we propose new viewing angle controllable homogeneously aligned liquid crystal display in which the pixel is composed of red, green, blue, and white pixels. The colored pixels are driven by fringe-field switching and the white pixel is driven by complex field. In wide-viewing angle mode, the liquid crystal (LC) directors in all pixels rotate in plane, contributing to high transmittance. In narrow-viewing angle mode, the LC directors in color pixels rotate in plane for light transmission while the LC directors in white pixel can rotate or tilt upward by simultaneous fringe and vertical electric field. The high tilted LC directors generate light leakage in oblique directions which can be utilized for viewing angle control and also transmission at normal direction for image expression. The proposed device overcomes the long standing problem of transmittance sacrifice in the conventional devices.
22 citations
TL;DR: In this paper, the authors explored the dependence of the light efficiency of the device on the magnitude of the dielectric anisotropy of the liquid crystal (LC) for both types of the LCs as functions of other cell parameters such as the rubbing angle and the cell gap.
Abstract: The light efficiency of the homogeneously aligned liquid crystal (LC) mode driven by fringe electric fields depends on the magnitude of the dielectric anisotropy when using a LC with positive dielectric anisotropy. However, this dependency is not observed when using a LC with negative dielectric anisotropy. This difference is mainly associated with the molecular reorientation especially in the tilt angle of the LC between the edges and the centers of the pixel electrodes in the voltage-on state. This paper explores the dependence of the light efficiency of the device on the magnitude of the dielectric anisotropy of the LC for both types of the LCs as functions of other cell parameters such as the rubbing angle and the cell gap.
21 citations
TL;DR: In this article, the optical retardation of a polymer-stabilized blue phase (BP) with in-plane electric field has been measured in a micrometer scale by combining an electrically controllable birefringence liquid crystal (ECB) cell and image processing software.
15 citations
TL;DR: In this article, a viewing angle switchable liquid crystal display associated with fringe-field switching mode is proposed, where one pixel is composed of a main pixel and a sub-pixel, in which both pixels are formed to generate a fringe electric field.
Abstract: A viewing angle switchable liquid crystal display associated with fringe-field switching mode is proposed. In the device, one pixel is composed of a main pixel and a sub-pixel, in which both pixels are formed to generate a fringe electric field. However, the field directions are different from each other so that in the main pixel, the fringe field rotates the liquid crystal for displaying the main image, whereas it controls only the tilt angle of the liquid crystal without rotating in the sub-pixel region. In this way, phase retardation to cause leakage of light at the off-normal axis can be generated in the sub-pixel, and by utilizing the light, the main displayed image in the normal direction can be blocked in the oblique viewing direction.
12 citations
TL;DR: An optical configuration for a transflective mode with a circular polarizer for the vertical alignment liquid crystal cell, which can show the wideband property of high contrast in oblique incidence, is proposed.
Abstract: We propose an optical configuration for a transflective mode with a circular polarizer for the vertical alignment liquid crystal cell, which can show the wideband property of high contrast in oblique incidence. The proposed configuration consists of a biaxial film and two uniaxial films for satisfying both the transmissive and the reflective modes. Optimization of the optical configuration of the circular polarizer has been performed on the Poincare sphere in the entire visible wavelength range using the Stokes vector and the Mueller matrix method. We also verify the excellent optical characteristics of the proposed configuration by comparing the viewing angle and contrast ratio in the oblique direction with a conventional optical configuration in calculation.
9 citations
TL;DR: In this paper, a chemically linked rod-disk (cyanobiphenyl-triphenyl) liquid crystalline (LC) molecule (RD12), where 12 is a number of carbon atoms in each alkyl chain linkage between the rod and the disk mesogens, was investigated under vertically applied alternative current (AC) electric fields.
Abstract: Molecular orientation of a chemically linked rod-disk (cyanobiphenyl-triphenyl) liquid crystalline (LC) molecule (RD12, where 12 is a number of carbon atoms in each alkyl chain linkage between the rod and the disk mesogens) in an antiparallel rubbed LC cell was investigated under vertically applied alternative current (AC) electric fields. Upon varying vertical AC electric fields from the initial state (0 V) to a fixed voltage ranging between 2.5 and 5.0 V, it was found that RD12 responded to the electric field with two-steps. The rod mesogen having a higher dipole interaction first aligned parallel to the electric field, while the disk mesogen behaved like an anchor of RD12. After the frustration and stabilization of rod mesogens, the in-plane axis of disk mesogen also aligned parallel to the electric field. Based on our experimental results, it was concluded that the peculiar molecular frustrations of RD12 under the vertical AC electric field occurred in a consequence of the competition among rods attac...
8 citations
TL;DR: In this article, the setting voltage, transition time, and response time of the device as a function of the surface pretilt angle were studied, and the results indicate that with decreasing surface preilt angle in the OCS cell, both phase transition time and setting voltage decrease and response times become faster.
7 citations
TL;DR: Based on the polymer morphology and electro-optic characteristics, the authors conjecture that the stabilization temperature affects the nanoscopic structure of LC phase prior to and consequently after the polymer stabilization, and conjecture that optical birefringence is induced by the Kerr effect from initially optically isotropic LC states, phase structures, morphology of the stabilizing polymer networks, and electrooptic properties such as contrast ratio, hysteresis and threshold voltage of the cells.
TL;DR: Without using any compensation film or in-cell retarder, the single cell-gap and single-gamma transflective LCD with high performance is realized.
Abstract: Conventional transflective liquid crystal displays (LCDs) with single cell-gap requires optical compensation films or patterned retarders to balance the optical path-length difference between transmissive and reflective regions. In this paper, novel single cell-gap transflective LCDs driven by fringe electric field without using the compensation film or in-cell retarder have been proposed. The liquid crystal director is aligned parallel to analyzer but makes an angle of 45° with respect to analyzer in reflective region. In addition, the surface pretilt angle in the reflective region is controlled by vertical field and polymerization of an UV curable reactive mesogen at the same time and thus, the effective cell retardation in the reflective region becomes smaller than that in transmissive region. Consequently, without using any compensation film or in-cell retarder, the single cell-gap and single-gamma transflective LCD with high performance is realized.
TL;DR: In this paper, the voltage-dependent characteristics between two devices have been analyzed, and the authors studied the problem of lower threshold voltage and operating voltage for blue phase liquid crystal (BP LC) driven by fringe electric field.
Abstract: Lowering threshold voltage and operating voltage is a critical issue for blue phase liquid crystal (BP LC) because the Kerr constant of liquid crystal mixture is not so high. In order to switch BP LC from optically isotropic to anisotropic state, in-plane electric field should be generated by interdigitated electrodes in general, however, the operating voltage is high and transmittance is relatively low. In this paper, the BP LC driven by fringe electric field is studied as one of the solutions for those problems. Detailed analysis of voltage-dependent characteristics between two devices has been performed.
01 May 2010
TL;DR: In this article, a new alignment layer free vertical alignment (VA) liquid crystal device is proposed, where the nanoparticles, reactive mesogen, and liquid crystal mixture are mixed together and filled into the cell with fishbone electrode structure.
Abstract: New alignment layer free vertical alignment (VA) liquid crystal device is proposed. In the device, the nanoparticles, reactive mesogen, and LC mixture are mixed together and filled into the cell with fishbone electrode structure. Through diffusion process, the particles moved to both surfaces of substrates, generating vertical alignment and then UV is exposed while applying proper voltage to the cell. Then, LC director is stabilized to form multi-domain by polymerization of reactive mesogen. Consequently, the device shows, wide-viewing-angle and fast response time although conventional polymer layer is not used.
TL;DR: In this paper, a turn-around effect in colour tracking of the fringe-field switching mode is associated with the generation of a tilt angle of the liquid crystal molecules with increasing voltage in the electrode position.
Abstract: Colour tracking behaviour is observed in most liquid crystal displays. In in-plane switching and vertical alignment devices, the colour chromaticity in the normal direction changes linearly from bluish- to yellowish-white as the grey level is increased from the dark to white state. Interestingly, abnormal behaviour in colour tracking is observed in fringe-field switching devices using a liquid crystal with positive dielectric anisotropy, such that the colour chromaticity changes from bluish to yellowish up to a certain grey level, then turns around and becomes bluish-white as the grey level is further increased to the fully white state. According to our theoretical and experimental results, this ‘turn around’ effect in the colour tracking of the fringe-field switching mode is associated with the generation of a tilt angle of the liquid crystal molecules with increasing voltage in the electrode position where the light modulation is associated with the polarisation rotation.
TL;DR: In this article, a carbon nanotubes (CNTs) doped homogeneously aligned nematic liquid crystal cells driven by fringe-field switching and their electro-optic characteristics were investigated.
Abstract: We have fabricated carbon nanotubes (CNTs) doped homogeneously aligned nematic liquid crystal cells driven by fringe-field switching and their electro-optic characteristics were investigated. The CNTs doped liquid crystal cell shows lower transmittance, higher driving voltage but faster response time than those in the pure liquid crystal cell. In addition, CNTs-doped liquid crystal cells as a function of the CNT length were investigated. This paper gives an explanation on difference in electro-optic characteristics of pure and CNT-doped LC in the FFS mode.
TL;DR: Li et al. as mentioned in this paper have published a paper called ''2010 KIEEME. http://www.transeem.org 134 † Author to whom all correspondence should be addressed: E-mail: lsh1@chonbuk.ac.kr
Abstract: Copyright 2010 KIEEME. All rights reserved. http://www.transeem.org 134 † Author to whom all correspondence should be addressed: E-mail: lsh1@chonbuk.ac.kr
01 May 2010
TL;DR: In this paper, the authors proposed viewing angle switchable liquid crystal displays (LCDs) with optically isotropic liquid crystal mixture such as polymer-stabilized blue phase (PSBP) LC and nano-structured LC.
Abstract: We propose viewing angle switchable liquid crystal displays (LCDs) with optically isotropic liquid crystal mixture such as polymer-stabilized blue phase (PSBP) LC and nano-structured LC. The devices are featured by two concepts: (1) using one panel, a pixel is divided into two parts; main pixel being in charge of displaying main images and sub pixel for controlling viewing angle, (2) using two panels; one panel is nematic LC panel which displays main images and the other is PSBP LC panel which controls viewing angle. In both devices, main information is interrupted at off-normal direction by light leakage and luminance control, respectively. By controlling the applied voltages in sub pixel and PSBP LC panel, wide viewing angle can be switched to narrow viewing angle.
11 Feb 2010
TL;DR: Based on experimental observation of electric field-dependent shape of the CNT cluster, it elongates along the field direction and its original morphology of the cluster is restored after the removal of the field as discussed by the authors.
Abstract: Carbon nanotubes (CNTs) can exist as clusters whenever doping amount in nematic liquid crystal (LC) mixture exceeds
critical point. Based on experimental observation of electric field-dependent shape of the CNT cluster, it elongates along
the field direction and its original morphology of the cluster is restored after the removal of the field. The elongation was
fully reversible only below a certain breakdown field. Both clusters and elongated CNTs were observed under nonpolarized
and polarized light. The cluster absorbs incident light completely while the elongated one absorbs light
propagating along the long axis only. Utilizing the field-controlled cluster, light modulation for display application is
possible.
01 May 2010
TL;DR: In this paper, the authors focus on optimization of electrode shape in polymerstabilized blue phase or nanostructured liquid crystal composites to lower operating voltage and improve light efficiency.
Abstract: This paper focuses on optimization of electrode shape in polymerstabilized blue phase or nanostructured liquid crystal composites to lower operating voltage and improve light efficiency. The electrode with taper angle of reverse elliptic shape decreases operating voltage by 18.9% and improves transmittance by 29.8% compared to that in conventional electrode structure. Additionally, the performance of the device such as contrast ratio and viewing angle characteristic is improved.
TL;DR: In this paper, a single cell-gap and single gamma transflective liquid crystal displays (LCDs) associated with fringe-field switching (FFS) device is proposed, where the twist angle of LC director is dependent on electrode position in on state.
01 May 2010
TL;DR: In this paper, a single-gap transflective liquid crystal display (LCD) driven by fringe electric field is proposed, where the initial LC orientation is parallel to top polarizer in transmissive (T) region and is 45° with respect to top polarity in reflective (R) region.
Abstract: Single-gap transflective liquid crystal display (LCD) driven by fringe electric field is proposed. The initial LC orientation is parallel to top polarizer in transmissive (T) region and is 45° with respect to top polarizer in reflective (R) region. The surface pre-tilt angle of the R-region is controlled by vertical field and polymerization of an UV curable reactive mesogen and thus, the effective cell retardation in the R- region becomes smaller than that in T- region. Consequently, a single gap transflective LCD driven by fringe electric field without compensation film or in-cell retarder is realized.