Byeong-Hun Yu

Light shutter using dichroic-dye-doped long-pitch cholesteric liquid crystals

We propose a light shutter device using dichroic-dye-doped liquid crystals (LCs) whose Bragg reflection wavelength is set to be infrared by controlling the pitch of cholesteric liquid crystals (ChLCs). A dye-doped long-pitch ChLC cell is switchable between the dark planar state and the transparent homeotropic state. It has the advantages of high transmittance, low operation voltage, and an easy fabrication process relative to previous LC light shutter devices. The proposed light shutter device is expected to achieve high visibility for transparent organic light-emitting diode displays and emerging smart windows, which can be used in airplanes, cars, and other similar applications.

Simultaneous control of haze and transmittance using a dye-doped cholesteric liquid crystal cell

We propose a light shutter device using dye-doped cholesteric liquid crystals for a high-visibility see-through display. In the focal-conic state, the proposed device can perfectly block the background image through simultaneous use of light scattering and absorption effects in a single-layered structure. By switching the proposed device placed at the backside of a see-through display, we can choose transparent or high-visibility display modes in a see-through display.

Double-layered light shutter using long-pitch cholesteric liquid crystal cells

We propose a double-layered light shutter device using two cholesteric liquid crystal (ChLC) cells. The proposed light shutter consists of a light-scattering layer using long-pitch cholesteric LCs and a light-absorption layer using dye-doped ChLCs. The light shutter has four switchable states: light scattering, light absorption, absorption and scattering, and transparent. The light shutter in the absorption and scattering state can block the background image and provide a black color. By switching of the proposed light shutter positioned at the rear side of a transparent display, we can operate a transparent display in various modes, not just showing the images produced by a transparent display along with the background.

Dual mode switching of cholesteric liquid crystal device with three-terminal electrode structure

We propose a cholesteric liquid crystal device with a three-terminal electrode structure that can be operated in both the dynamic and the bistable modes. Fast switching (less than 5 ms) between the planar and the in-plane-field-induced states can be realized by applying an in-plane electric field, and conventional bistable switching between the planar and focal conic states can be realized by applying a vertical electric field.

Dark-state Color Shift and Gray Scale Inversion in an In-plane Switching Liquid Crystal Display Device

Off-axis color shift in the dark state and gray scale inversion in an in-plane switching (IPS) liquid crystal display (LCD) device were investigated. Analyses were performed using the Poincare sphere representation. The results show that color shift in the dark state and gray scale inversion in an IPS LCD can be reduced by using a biaxial film. We confirmed the extent of these improvements by measuring the optical performance of a fabricated IPS LCD.

Formation of Polymer Networks for Fast In-Plane Switching of Liquid Crystals at Low Temperatures

We formed a polymer structure to enable fast in-plane switching of liquid crystals at low temperatures. The problem of the inevitable slow response at low temperatures was reduced by the formation of in-cell polymer networks in in-plane switching (IPS) cells. The electro-optic characteristics of polymer-networked IPS cells were measured at temperatures ranging from -10 to 20 °C. The turn-on and turn-off times of an IPS cell were reduced by 44.5 and 47.2% at -10 °C by the formation of polymer networks. We believe that the proposed technology can be applied to emerging display devices such as mobile phones and automotive displays that may be used at low temperatures.

Bistable Light Shutter Using Dye-doped Cholesteric Liquid Crystals Driven with Crossed Patterned Electrodes

To reduce power consumption by light shutters, bistable light shutters using cholesteric liquid crystal have been proposed. However, these bistable light shutters, which utilize the scattering of the incident light, are switchable only between transparent and translucent states. In this work, we successfully demonstrate a bistable light shutter that is switchable between transparent and opaque states because it utilizes not only scattering, but also the absorption of the incident light. We hide the objects behind a display panel and provide black color by switching the light shutter that is positioned at the backside of a see-through display. We realized a good opaque state by optimization of the electrode structure.

Light shutter using dye-doped cholesteric liquid crystals with polymer network structure

ABSTRACT Proposed herein is a light shutter using dye-doped cholesteric liquid crystals with a polymer network structure for a high-visibility see-through display. The proposed light shutter shows an initially focal-conic state by forming the polymer network structure at the focal-conic state. The proposed light shutter can be easily switched between the focal-conic and homeotropic states without a complicated drive scheme.

Technologies for display application of liquid crystal light shutters

ABSTRACT By switching a light shutter placed at the backside of a see-through display, we can select the transparent or high-visibility mode of the display panel. In this paper, we introduce technologies for liquid crystal (LC) light shutters that can scatter and absorb the incident light simultaneously, which is preferable for display applications. A light shutter for display applications can be realized in the normally-opaque mode by using a double-layered structure using cholesteric LCs or a single-layered structure using dye-doped cholesteric LCs. Whereas, it can be realized in the normally-transparent mode by using dye-doped polymer-networked LC cells using negative or positive LCs. Operation of each of the technologies is reviewed and the performance of these technologies is compared in this paper.

Bistable switching between homeotropic and focal-conic states in an ion-doped chiral nematic liquid crystal cell

Operation of a light shutter usually requires that an electric addressing field is applied continuously to switch between a transparent and an extinct or opaque scattering state. To achieve low-power operation, a bistable light shutter, which consumes power only when switching between the two stable states, is preferred. Here, switching between the two stable states is induced with a short pulse rather than by applying a continuous field. In this work, we report bistable switching of an ion-doped chiral nematic liquid crystal between the transparent homeotropic and the scattering focal-conic states. Owing to ionic dopants, the use of complicated patterned electrodes or dual-frequency liquid crystals was not required for switching of the device. The light shutter exhibited an opaque state, which has higher scattering than previously reported bistable light shutters. Furthermore, doping of the reported device with a dichroic-dye enabled simultaneous control of light scattering and absorption. A new candidate for both smart window and see-through display applications is presented.