Seong-Min Ji

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.

Fabrication of flexible light shutter using liquid crystals with polymer structure

ABSTRACT We fabricated a light shutter using plastic substrates for high visibility of a flexible see-through display. To achieve a flexible light shutter using liquid crystals (LC), it is essential to maintain the cell gap when the light shutter is bent. We studied methods to fabricate flexible LC light shutters using plastic substrates. We demonstrated light shutters that are initially transparent and flexible with or without polymer walls. We have elucidated that polymer walls and networks provide mechanical stability against the bending of an LC light shutter without any degradation in the electro-optic characteristics. We predict that a flexible light shutter provides not only high visibility but also mechanical stability to a flexible see-through display by positioning it at the back of a flexible see-through display panel. Graphical Abstract

Transmittance control of a liquid crystal device using a dye mixture

Transmittance-control devices, such as a suspended particle device, electrochromic device, and dye-doped liquid crystal (LC) device, have been studied for a smart window, eyewear, and automotive applications. These devices require a high transmittance difference between the transparent and opaque states. Among the dye-doped LC devices, a dye-doped chiral-nematic LC (CNLC) cell has been widely used for transmittance-control devices. However, the colors of cells are different between the homogeneously aligned and CNLC cell. In this study, we demonstrated a systematic approach to find optimum dye concentrations for black color in a dye-doped CNLC cell. We took its transmission spectrum into account in the numerical calculation to realize the black color in a dye-doped CNLC cell. Through the iterative method, we could optimize the concentration of each single dye for realizing the black color. We confirmed that a dye-doped CNLC cell designed by considering transmission spectrum of it could provide the black color in the CIE 1931 color space.

Control of the haze value by the electro-hydrodynamic effect in a liquid crystal cell

Liquid crystal (LC) devices have been used for smart window and see-through display applications. Especially, LC devices which can be used to control the haze value have been studied for smart window applications. LC devices with the polymer structure, such as polymer-dispersed and polymer-stabilized LC cells, can be used to control the haze value. However, for wider applications, it is urgent to overcome disadvantages, such as the high operating voltage, low transmittance in the transparent state, and narrow viewing angle because of the index mismatch between the LC and polymer structure. In this paper, we introduce LC devices based on the electro-hydrodynamic effect. They can provide a high haze in the translucent state because of the turbulence caused by the electro-hydrodynamic effect. They can provide a high transmittance in the transparent state and wide viewing angle because it does not contain any polymer structure. We believe that LC devices based on the electro-hydrodynamic effect can be an excellent candidate for smart window applications.

Control of haze value by dynamic scattering in a liquid crystal mixture without ion dopants

We report a method to control the haze value by dynamic scattering in a liquid crystal mixture without ion dopants. The liquid crystal (LC) mixture consists of chiral smectic C (SmC*) and nematic (N) LC molecules. In the absence of an electric field, LC molecules in the SmC* phase are oriented by the neighboring vertically-aligned N-LC molecules so that the LC cell is transparent. When a vertical electric field is applied to the LC cell, N-LC molecules with negative dielectric anisotropy tilt down in a random direction parallel to the two substrates, whereas SmC*-LC molecules are rotated with the polarity reversal of the applied field. During the switching process, we observed dynamic scattering because the random orientation of N-LCs is maintained via the rotation of SmC*-LCs, resulting in a high-haze translucent state without the use of ionic dopants. The LC mixture exhibited a very high haze of 96.1% in the translucent state while maintaining the haze-free (<1%) transparent state owing to the use of an LC layer without a polymer structure.We report a method to control the haze value by dynamic scattering in a liquid crystal mixture without ion dopants. The liquid crystal (LC) mixture consists of chiral smectic C (SmC*) and nematic (N) LC molecules. In the absence of an electric field, LC molecules in the SmC* phase are oriented by the neighboring vertically-aligned N-LC molecules so that the LC cell is transparent. When a vertical electric field is applied to the LC cell, N-LC molecules with negative dielectric anisotropy tilt down in a random direction parallel to the two substrates, whereas SmC*-LC molecules are rotated with the polarity reversal of the applied field. During the switching process, we observed dynamic scattering because the random orientation of N-LCs is maintained via the rotation of SmC*-LCs, resulting in a high-haze translucent state without the use of ionic dopants. The LC mixture exhibited a very high haze of 96.1% in the translucent state while maintaining the haze-free (<1%) transparent state owing to the use of an...