Yong-kyu Jang

Analysis of the Multireflection Effects in Compensated Liquid Crystal Devices

The effect of multiple internal reflections on the extinction ratio of perfectly compensated liquid crystal devices is studied. We find the previously unexplained wavelength dependence of light leakage in an ideally compensated device is caused by the interference of the internally reflected ordinary and extraordinary waves. While these effects have not been previously made clear, they can place a limit on the performance of liquid crystal devices used as displays, optical switches, and optical attenuators.

Optimization of the White State Director Configuration for Perfectly Compensated Pi-cell Devices

We have studied the off-axis light transmission properties of the bright state in Pi-cell (π-cell) devices as a function of the white state director configuration that is determined by the applied white state voltage and the pretilt angle of the device. Results show that below certain values of the voltage or pretilt angle, the off-axis light transmission properties are insensitive to these parameters and can be described by a previously considered simple model. However, above a critical pretilt angle or white state voltage, the light transmittance is a much stronger function of the incident angle of light. To understand the facts, we develop a model that explains this result and provides a description of the basic issues affecting the optics of these types of devices.

Analysis of optical bounce associated with two-step molecular reorientation in the fringe-field switching mode

The dynamic electro-optic response of liquid crystals (LCs) having positive dielectric anisotropy has been investigated in the fringe-field switching device. Simulation and experimental results show a huge optical bounce near the centre of the pixel electrodes of the device during decaying time of the LC director from an operating voltage. The causality of the said behaviour has been detected as two-step molecular relaxation, first tilt down and then rotating of the LC, which is associated with splay/bend and then twist relaxation, respectively. Reduction of dielectric anisotropy of the used LC material in the device has been suggested as a remedy of reducing optical bounce. The reduction of rotational viscosity also produces optical bounce of lesser duration; however, the intensity of the bounce remains invariant.

48.3: Distinguished Paper: A Novel Hole Induced Vertical Alignment LC Mode with Superior Transmittance

A novel pixel design for vertical alignment LCD with superior transmittance is developed in this work. The new liquid crystal mode, named as Hole Induced Vertical Alignment mode (Hi-VA), uses a via hole of an organic layer on TFT substrate to achieve multi domain alignment. Compare to conventional design, the Hi-VA mode has up to the transmittance of 135% with the contrast ratio of 2000:1. Moreover, the new structure is free from the ITO patterning or protrusion on color filter side, which makes the fabrication process simple and low cost.

Universal off-axis light transmission properties of the bright state in perfectly compensated liquid crystal devices

We studied the off-axis light transmission characteristics of the bright state of common liquid crystal device modes. The dark state of these device modes is optically compensated to have minimum light transmittance at all angles. Our research shows there is an unexpected universal shape of the off-axis light transmission value in its bright state, regardless of what liquid crystal mode is used. To understand this surprising fact, we consider simple dark and bright state models in terms of phase retardation and transmittance.

A new vertical-alignment LC mode with high-transmittance and fast-response-time features

— A novel pixel design for vertical-alignment LCDs with superior transmittance has been developed. The new liquid-crystal mode, refered to as the hole-induced vertical-alignment mode (Hi-VA), uses a via hole of an organic layer on a TFT substrate to achieve multi-domain alignment. Compared to the conventional design, the Hi-VA mode has a transmittance of up to 135% with a contrast ratio of 2000:1. Moreover, the new structure is free from ITO patterning or protrusion on the color-filter side, which makes the fabrication process simple and low cost.

52.2: S‐mPVA LCD Technologies for Superior Off‐Axis Image Quality

Off-axis image quality of a mobile PVA (mPVA) LCD has been improved by active level-shifting technology and optimization of pixel and polarizer structures. The measured gray distortion index is reduced to 0.25, compared to 0.51 for a conventional mPVA LCD, resulting in decreased color shift at off-axis viewing positions.

Comparison and Analysis of Off-Axis Color Shift Properties of Compensated Liquid Crystal Devices

We investigated the off-axis luminance and color properties of the bright states of common liquid crystal device modes when the dark states are optically compensated. The investigation was carried out as a function of the on-axis luminance of the devices, and analyzed in terms of a simple universal model of the bright state. We show good agreement of the simple model with the calculations of actual vertical alignment and electrically controlled birefringence devices, and explain deviations from this model for twisted nematic and Pi-cell devices. The results of the study add insight into the nature of the color shift problems in common liquid crystal devices.

P‐22: A Single Cell‐Gap Transflective LCD with Active Level‐Shifting Technology

A novel single cell-gap transflective liquid crystal display (LCD) with active level—shifting technology has been developed. Pixel structure design enables different voltages to be independently applied to transmissive and reflective sub-pixels. The prototype 2.2-inch vertical alignment (VA) mode transflective LCD achieves a 17% increase in aperture ratio compared to the conventional dual cell-gap approach. The reflective mode has 15:1 contrast ratio and 3.6% reflectance, and the transmissive mode accomplishes much higher contrast ratio of 500:1, compared to 200:1 for the dual cell-gap transflective LCD.

Conditions and Limitations of Perfect Phase Compensation in Liquid Crystal Devices

We investigated the optical phase compensation of uniaxial layers and found a thickness ratio that gives the perfect phase compensation. However, the ratio is a function of the incident light angle and director configuration. Therefore, it is impossible to compensate the phase of a generally configured uniaxial layer perfectly for all viewing directions. We also found that the efficiency of the phase compensation is a strong function of the residual birefringence and the director tilt angle of a liquid crystal layer. We confirmed these facts for both the uniformly and non-uniformly aligned liquid crystal layers.