A dye-doped LC/polymer light shutter with a polymer structure that is formed using the thermally-induced phase separation (TIPS) method is demonstrated. The TIPS method relies on the difference in solubility between thermoplastic polymer and solvent, and thus there is no degradation of the dye during the fabrication process. The light shutter can be fabricated quickly because the optical properties are not affected by the cooling time. The fabricated TIPS cell shows a superior black color with excellent optical properties, such as a low haze value of 0.5% in the transparent state, and a high haze value of 99.1% in the opaque state. This result can be applied for the high image quality of see-through displays using organic light-emitting diodes.
See-through displays have got high attention as one of the next generation display devices. Especially, see-through
displays that use organic light-emitting diodes (OLEDs) and liquid crystal displays (LCDs) have been actively studied.
However, a see-through display using OLEDs cannot provide black color because of their see-through area. Although a
see-through display using LCDs can provide black color with crossed polarizers, it cannot block the background. This
inevitable problem can be solved by placing a light shutter at the back of a see-through display. To maintain the
transparent or opaque state, an electric field must be applied to a light shutter. To achieve low power consumption, a
bistable light shutter using polymer-stabilized cholesteric liquid crystals (CLC) has been proposed. It is switchable
between the translucent and transparent states only. Therefore, it cannot provide black color. Moreover, it cannot block
the background perfectly because of poor performance in the translucent state. In this work we will introduce a bistable
light shutter using dye-doped CLCs. To improve the electro-optic characteristics in the opaque state, we employed a
crossed electrode structure instead of a parallel one. We will demonstrate that the light shutter can exhibit stable bistable
operation between the transparent homeotropic and opaque focal-conic states thanks to polymer stabilization.
Recently, see-through displays have been attracted much attention as next-generation displays. There are two basic
technologies by which we can realize a see-through display: organic light-emitting diodes (OLEDs) and liquid crystal
(LC) displays. The pixel structure of a see-through display includes a transparent window area through which the
background image can be seen. Therefore, background images are always seen along with the displayed image. In
addition, a see-through display using OLEDs cannot provide the black color. As a result, a see-thorough display exhibits
poor visibility. This inevitable problem can be solved by placing a light shutter at the back of a see-through display.
Light shutter technology can be divided into two types; light absorption and light scattering. Light shutter based on light
absorption can be used to control the transmittance, but it cannot block the object behind the display panel completely.
Light shutters based on light scattering can be used to control the haze, but it cannot provide black color. To realize a
high-visibility see-through display, we need a light shutter by which we can control haze and transmittance
simultaneously. In this talk we would like to introduce technologies for LC light shutters by which we can block the
background image and provide black color by utilizing light scattering and absorption effects simultaneously.
Recently, a transparent display has got much attention as one of the next generation display devices. Especially, active studies on a transparent display using organic light-emitting diodes (OLEDs) are in progress. However, since it is not possible to obtain black color using a transparent OLED, it suffers from poor visibility. This inevitable problem can be solved by using a light shutter. Light shutter technology can be divided into two types; light absorption and scattering. However, a light shutter based on light absorption cannot block the background image perfectly and a light shutter based on light scattering cannot provide black color. In this work we demonstrate a light shutter using two liquid crystal (LC) layers, a light absorption layer and a light scattering layer. To realize a light absorption layer and a light scattering layer, we use the planar state of a dye-doped chiral nematic LC (CNLC) cell and the focal-conic state of a long-pitch CNLC cell, respectively. The proposed light shutter device can block the background image perfectly and show black color. We expect that the proposed light shutter can increase the visibility of a transparent display.
Cholesteric liquid crystals (CLCs) have been used for a reflective display because of their reflective nature in the planar state. In a reflective display, the planar and the focal-conic states are used for the bright state and the dark state, respectively. In this paper we introduce a long-pitch CLC device, in which a selective wavelength of the reflected light is shifted to infrared (IR) wavelengths by controlling the pitch. The planar state of a long-pitch CLC device is transparent over the entire visible wavelengths in the field-off state. Omni-directional achromatic reflection through light scattering in the focal-conic state can be achieved without a polarizer. Compared to conventional CLC cells that reflect the visible light in the planar state, a long-pitch CLC device has a longer pitch, of which the operating voltage for switching between the two state is much lower so that achromatic reflective displays and light shutters with low power consumption can be realized using long-pitch CLC devices. By coupling with a reflector, the light efficiency of a longpitch CLC cell in the focal-conic state can be enhanced, by which higher brightness can be obtained for application to reflective displays. A dye-doped long-pitch CLC device can be placed behind a transparent organic light-emitting diode display for use as a light shutter to block the ambient light.
Recently, active studies on a transparent organic light-emitting diode (OLED) are in progress as a next generation display. However, since it is not possible to obtain a dark state using a transparent OLED, it exhibits poor visibility. This inevitable problem can be solved by placing a light shutter behind a transparent OLED display. In this paper, we propose a light shutter using dye-doped liquid crystals (LCs) whose Bragg reflection wavelength is chosen to be infrared by controlling the pitch of cholesteric liquid crystals (ChLCs). The proposed light shutter is switchable between the dark planar state and the transparent homeotropic state. The proposed light shutter has the advantages of the high transmittance, low operation voltage, and easy fabrication process compared with previous light shutter devices using liquid crystals. It is expected that the proposed light shutter can be applied to realize high visibility transparent OLEDs and emerging smart windows.
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