Kyu Young Hwang

Applications of multidirectional reflective light-control films on reflective polymer-dispersed liquid crystal displays for enhancement in image quality at lower viewing angles

In this paper, multidirectional light-control reflective (LCR) films are developed in order to create an active reflective structure that will enhance the image brightness and contrast ratio of reflective dye-doped polymer-dispersed liquid crystal (D-PDLC) displays at lower viewing angles. Advantages of LCR films are that their production is low cost and they require a simple photolithographic fabrication method. The optimum design prism-type light-control reflective film succeeded in minimising the surface scattering effect; thus, the contrast ratio is much enhanced. The symmetric and asymmetric LCR films produced multidirectional scattering that enhances the reflectance at lower viewing angles, which has importance in future display applications. In particular, the prism LCR film has been found to be more influential on the reflectance of D-PDLC films due to multidirectional scattering of light by non-symmetric arrays. The improvement in contrast ratio has been confirmed by the enhancement of optical properties for reflective D-PDLC displays at lower viewing angles below 30°.

40.4: The Research of Various Mode Color PDLC Structures for Flexible Reflective Display

Various type color PDLC structures have been characterized on a glass and a plastic substrate for reflective mode color display. The standard PDLC and the black diachronic dye mixed PDLC structure with color filter (RGB) show a good black state with high color purity and 256 gray levels, even though both structures have a dark color images. Color dichroic dye (RGB/CMY) mixed PDLC cells promise a good white reflectance. The problem of using color dye system is the enhancement of a poor black state. Using new CMY color based filter with black dye PDLC shutter structure can improve a white state with a proper color vision.

Bright color optical switching device by polymer network liquid crystal with a specular reflector.

The color optical switching device by polymer network liquid crystal (PNLC) with color filter on a specular reflector shows excellent performance; white reflectance of 22%, color gamut of 32%, and contrast ratio up to 50:1 in reflective mode measurement. The view-angle dependence of the reflectance can be adjusted by changing the PNLC thickness. The color chromaticity shown by the device is close to the limit value of color filters, and its value nearly remains with respect to the operating voltage. These optical properties of the device can be explained from the prediction based on multiple interactions between the light and the droplets of liquid crystal. The high reflectance, vivid color image, and moderate responds time allow the PNLC device to drive good color moving image. It can widely extend the applications of the reflective device.

Color Polymer-Stabilized Liquid Crystal for the Optical Shutter with Fast Response Time

A color-reflective optical shutter structure has been studied using polymer-stabilized liquid crystal (PSLC) devices with a specular reflector. The combined effect of an LC, a polymer, a color dye, and a specular reflector results in a high performance of a reflective-mode optical shutter as well as of a simple structure with a fast response time capable of smooth moving images. The reflectance is up to 40%, one of highest for reflective devices, whose response times are fast enough to provide video speed response (<16.6 ms). This effective and simple shutter concept can be applied in reflective-mode flexible displays and optical equipment with high performance.