Joong Ha Lee

Monoview/dual-view switchable liquid crystal display.

We present an optical device capable of displaying in two distinct viewing modes, i.e., monoview and dual-view modes. The monoview mode has a joint viewing cone and allows only the same image or video content to be displayed. The dual-view mode splits one viewing cone into two so that two different pieces of information can be displayed simultaneously in the left and the right viewing directions from the screen. Each viewing mode can be mutually switched through the modulation of the birefringence of liquid crystals. This proposed device has technical advantages of easy operation, low cost, and versatility of applications.

Fast polarization switching panel with high brightness and contrast ratio for three-dimensional display

We propose a polarization switching device using optically compensated pi cell for polarization-glass-type three-dimensional display. This device shows good optical properties such as high transmittance and low cross-talk ratio because of its fast dynamic response characteristics. To improve the brightness and contrast ratio on the right- and left-hand sides, we attach optical retardation films on each side of the polarization glasses instead of attaching the films on the polarization switching panel. From the calculation and experiment, we obtain high contrast ratios, over 200:1, on both sides and a high brightness using only one film on each side.

High-temperature ferromagnetism in amorphous semiconductor Ge3Mn thin films

The Ge1−xMnx thin films were fabricated at x=0.25, of which the composition is close to Ge3Mn. They showed ferromagnetism up to above 350K, even though their structure is amorphous. Ge3Mn amorphous samples grown at 200°C have n-type characteristics, while those grown at 500°C have p-type characteristics. The former has a different state from the latter, energetically. It is suggested that the different short range orders of Ge3Mn5 and/or Ge8Mn11 have already formed in the amorphous phase according to the growth temperature. The authors have also discussed the relationship between ferromagnetism and cluster formations after annealing at 800°C.

Bistable switching of twist direction in a twisted-nematic liquid crystal cell

We propose a bistable liquid crystal mode based on switching of the twist direction in a conventional π/2-twisted nematic cell. Switching between the −π/2 and +π/2 twist states can be performed by applying vertical and/or in-plane electric fields. The proposed bistable mode has an infinite memory time because the two stable twist states have the same elastic free energy.

Stereoscopic three-dimensional display based on polarization-switching device with low cross talk and high contrast ratio

We present a polarization-switching device with dual-frequency liquid crystal material for a stereoscopic three-dimensional (3D) display. This device shows good properties, such as low 3D cross talk and high brightness, due to a fast dynamic response time. Without optical compensation, however, this device has an asymmetric contrast ratio on the left- and right-hand sides of 3D glasses, because the viewing principles on both sides are different from each other. To solve this problem, we design an optical structure with two half-wave plate films using the Jones matrix method. As the results of simulation and experiment show, excellent dark states and high brightness are realized over the entire range of visible wavelengths on both sides.

Dual mode operation of bistable chiral splay nematic liquid crystal cell using horizontal switching for dynamic operation

We propose a dual mode liquid crystal display (LCD), which can realize dynamic and memory operating LCD modes in a display panel. Horizontal switching and bistable chiral splay nematic LCD modes are used for the dynamic and memory operations, respectively. As the horizontal switching is applied to the dynamic operation, it is possible to use the same LC texture of splay for realizing dark states of both the dynamic and memory operations. Because, for each operation, pixel division is not required in the proposed dual mode LCD, there is no decrease in aperture ratio and resolution. In order to obtain superior display performance for both operations, a wideband half-wave configuration is employed to the proposed dual mode LCD. Due to the wideband configuration, very low light leakages at the dark state and good dispersion characteristics for the entire visible range are obtained. As a result, the proposed dual mode LCD shows a high contrast ratio of over 100:1 for both the dynamic and memory operations.

Reflective Dual Mode Liquid Crystal Display with Dynamic Mode Utilizing the Transition Behavior between the Two Stable States of Its Memory Mode

In this study, we have proposed a dual-mode liquid crystal display (D-LCD) that can display both the memory and dynamic modes in one cell. The two stable states of the memory mode use splay and -π-twist states. The operation of the dynamic mode is realized by the transition behavior between the two stable states of its memory mode. For a green display, we have also proposed a reflective D-LCD with an optically compensated structure. We found that both the memory and dynamic modes have contrast ratios (CRs) of 30:1 by a good wavelength dispersion of dark state.

Long memory retention time and high contrast ratio in a tristate liquid crystal display device.

We propose a method to obtain long memory retention time and high contrast ratio in a tristate liquid crystal display device. The proposed device has three unique liquid crystal (LC) states that are known as splay, π twist, and bend, with different operating schemes for the two modes of operation, which are the memory (M) mode or dynamic (D) mode. A form of selective vertical or horizontal switching changes the optically compensated π twist LC as a common black state in both the M and D modes into a bend LC state for the D mode or into the splay LC state for the M mode, respectively.

Reflective dual-mode liquid crystal display switchable between dynamic and memory modes

This study proposes a reflective dual-mode liquid crystal display (RD-LCD) that can be operated in memory mode or dynamic mode according to the image contents. The proposed RD-LCD needs three states to represent dark and bright states, while a general reflective liquid crystal display has two states. Nevertheless, a compensation structure that can obtain high contrast ratios in both dynamic and memory modes has been optimized. The proposed RD-LCD can be operated without internal backlighting, thus making it a candidate for real green display.

Transflective Configuration of Dual Mode Liquid Crystal Display for High Contrast Ratio

We propose a transflective dual mode liquid crystal display, which is composed of a transmissive part for dynamic mode and a reflective part for a memory mode in a pixel. The proposed configuration has single cell gap and single rubbing direction in both parts. In order to make the reflectance minimized and maximized for dark and bright states of memory part, the parameters of LC layer and retardation film are optimized by using the Jones matrix method. Moreover, the operating voltage of dynamic part is found to depend on the retardation values of compensation films. With this configuration, the dynamic and memory modes show high contrast ratio of 1100:1 and 20:1, respectively, by calculation, while 220:1 and 10:1, respectively, by experiment.