Wook-Sung Kim

Polymer stabilized chiral nematic liquid crystals for fast switching and high contrast electro-optic devices

A fast switching electro-optic device, based upon the in-plane addressing of very short pitch polymer stabilized chiral nematic liquid crystals, is presented. Polymer stabilization of the standing helical arrangement is essential to prevent the appearance of defects above the in-plane electrodes. Response times as short as 50 μs are observed at room temperature along with contrast ratios greater than 3000:1 owing to the high optical extinction at visible wavelengths in the “Off” state. The combination of these fast response times with such high contrast ratios is of great importance for next generation electro-optical elements.

Spontaneous induction of the uniform lying helix alignment in bimesogenic liquid crystals for the flexoelectro-optic effect

Using in-plane electric fields, the electrical induction of the uniform lying helix (ULH) alignment in chiralnematic liquid crystals is reported. This process permits spontaneous induction of the ULH alignment to give an in-plane optic axis, without the need for complex processing. Flexoelectro-optic switching is subsequently obtained by holding the in-plane electrodes at a common voltage and addressing via a third, plane-parallel electrode on a second, or upper, substrate to give a field across the device in the viewing direction. For this device, in optimized bimesogenic materials, we demonstrate full intensity modulation and sub-millisecond response times at typical device temperatures.

25.4L: Late‐News Paper: A Novel Polarizer Glasses‐Type 3D Displays with an Active Retarder

In this paper, we suggested a novel method achieving high resolution and high brightness in the glasses-type 3D displays and fabricated a prototype of 15″ size in diagonal, which is composed of an active retarder synchronized with an image panel. The active retarder is configured to a TN mode to have a function of polarization switching for the input polarization states. We expect that the AR3D technology can give high resolution and high brightness for the 3D users with a convenience of simple polarizer glasses and an inexpensive cost compared with the shutter glasses type 3D display, where not only the image panel and but also the glasses should have an LCD panel.

Increasing the flexoelastic ratio of liquid crystals using highly fluorinated ester-linked bimesogens

We present experimental results on the bulk flexoelectric coefficients e and effective elastic coefficients K of non-symmetric bimesogenic liquid crystals when the number of terminal and lateral fluoro substituents is increased. These coefficients are of importance because the flexoelastic ratio e/K governs the magnitude of flexoelectro-optic switching in chiral nematic liquid crystals. The study is carried out for two different types of linkage in the flexible spacer chain that connects the separate mesogenic units: these are either an ether or an ester unit. It is found that increasing the number of fluorine atoms on the mesogenic units typically leads to a small increase in e and a decrease in K, resulting in an enhancement of e/K. The most dramatic increase in e/K, however, is observed when the linking group is changed from ether to ester units, which can largely be attributed to an increase in e. Increasing the number of fluorine atoms does, however, increase the viscoelastic ratio and therefore leads to a concomitant increase in the response time. This is observed for both types of linkage, although the ester-linked compounds exhibit smaller viscoelastic ratios compared with their ether-linked counterparts. Highly fluorinated ester-linked compounds are also found to exhibit lower transition temperatures and dielectric anisotropies. As a result, these compounds are promising materials for use in electro-optic devices.

Electrical addressing of polymer stabilized hyper-twisted chiral nematic liquid crystals with interdigitated electrodes: Experiment and model

Electro-optic switching in short-pitch polymer stabilized chiral nematic liquid crystals was studied and the relative contributions of flexoelectric and dielectric coupling were investigated: polymer stabilization was found to effectively suppress unwanted textural transitions of the chiral nematic liquid crystal and thereby enhance the electro-optical performance (high optical contrast for visible light, a near ideal optical hysteresis, fast electro-optic response). Test cells were studied that possessed interdigitated electrodes to electrically address the liquid crystal. Based on simulations, a well-fitted phenomenological description of the electro-optic response was derived considering both flexoelectro-optic and Kerr-effect based electro-optic response.

38.6L: Late‐News Paper: Advanced Coatable Polarizer Technology by Using Novel Liquid Crystalline Materials and Organic Dyes

We have demonstrated the feasibility of thin-film coatable type polarizer for high contrast. New liquid crystalline materials were developed and the manufacturing process was optimized to achieve high performance polarization characteristics. We made a 9.7 inch XGA prototype with our newly developed polarizer, and obtained good image quality and high electro-optical performance. More approaches to get higher polarization performance in terms of materials and manufacturing process were discussed.

P‐141: The Advanced Transflective IPS LCD by Photo Alignment Technology

We have developed 2.4″ QVGA transflective IPS LCDs with novel cell configuration. Transflective LCDs have intrinsically the difference of the optical phase retardation between the transmissive part and the reflective part. In order to compensate for this optical path length difference, we have newly designed the separate LC alignments for each transmissive and reflective parts with photo-alignment technique. The transmissive part has a homogenous liquid crystal alignment driven by an in plane electric switching field, which exhibits superb wide viewing angle characteristics. In the reflective part, the twisted liquid crystal alignment is adopted. Based on this new configuration, high reflectance and better contrast ratio can be provided without any compensation film or patterned retarder unlike conventional transflective LCDs.