Yoonseuk Choi

Physical mechanism for flat-to-lenticular lens conversion in homogeneous liquid crystal cell with periodically undulated electrode

A convertible lenticular liquid crystal (LC) lens architecture is demonstrated using an index-matched planarization layer on a periodically undulated electrode for the homogeneous alignment of an LC. It is found that the in-plane component of the electric field by the undulated electrode plays a primary role in the flat-to-lens effect while the out-of-plane component contributes to the anchoring enhancement of the LC molecules in the surface layer. Our LC device having an index-matched planarization layer on the undulated electrode is capable of achieving the electrical tunability from the flat surface to the lenticular lens suitable for 2D/3D convertible displays.

Nanoparticle scattering layer for improving light extraction efficiency of organic light emitting diodes

Nanoparticle scattering layer based on polymer-metal oxide composite is successfully introduced to enhance the light extraction efficiency of organic light emitting diodes (OLEDs). We find that the density and the distribution of nanoparticles is the key factor to maximize the light extraction efficiency of pristine OLEDs by out-coupling the unusable light with the scattering film. In our experiment, 71 wt% of Al(2)O(3) mixed with polymer matrix shows the increase of light extraction efficiency of 40%. This method is expected to play a critical role to create the low-power OLED application such as OLED lightings with simple fabrication process and low cost.

Determination of surface nematic liquid crystal anchoring strength using nano-scale surface grooves.

Based on several nano-scale groove models, we propose a new technique to simultaneously determine the azimuthal and polar surface anchoring strengths of nematic liquid crystal (LC). The optical analysis of LCs on a grooved surface made by nanoimprinting lithography was performed on special alignment material, using a typical rubbing process. In our approach, using a polarizing microscope, we can determine the LC alignment exactly as it is in a parallel state, rather than a twisted state. This simple proposed method gives an accurate value of the surface LC anchoring of various surfaces, as well as simultaneously measuring the azimuthal and polar anchoring energy.

Fast HEVC Intra Mode Decision Based on Bayesian Classification Framework with Relative SATD

HEVC (high efficiency video coding) achieves much higher coding efficiency compared with previous video coding standards at cost of significant computational complexity. This paper proposes a fast intra mode decision scheme, where a Bayesian classification framework using relative sum of absolute Hadamard transformed difference (SATD) is introduced and combined with conventional fast encoding methods. Experimental results show that this scheme reduces encoding run time by about 30% with a negligible coding loss of 0.9% BD-rate for the all intra coding scenario.

Topographic Confinement of a Ferroelectric Liquid Crystal for Highly Efficient Tunable Electrooptic Effect with Reduced Threshold

We report a highly efficient linear electrooptic (EO) effect of a tight-pitch ferroelectric liquid crystal (FLC) in a microchannel architecture where the FLC molecules are vertically aligned on the surrounding surfaces. Due to the topographic confinement in a large surface-to-volume configuration, the competing anchoring forces exerted by the lateral walls and the substrates impose directly the restrictions on the deformations of the smectic layers and the molecular director. The observed EO effect should be directly applicable for diverse optical devices requiring fast response, high optical modulation, and high subthreshold slope at a reduced operation voltage.

Zenithal alignment of liquid crystal on homeotropic polyimide film irradiated by ion beam

We investigate the pretilt characteristics of a nematic liquid crystal [LC] in terms of ion beam exposure conditions on the homeotropic polyimide alignment layer. The pretilt angle of LCs in the case of high-energy ion beam treatment was decreased considerably almost the same to that of the homogenous alignment layer though we used homeotropic polyimide film at first. Increasing irradiating energy, we could control the pretilt from 90° to 1° with several steps. We believe that this is because the side chain with hydrophobicity in the used polyimide is broken by ion beam exposure. To confirm it, contact angle measurement was carried out. With this result, we can easily control the LC pretilt in the pixel with appropriate exposure conditions which is critical to achieve excellent electrooptic characteristics and good image quality.

Development of functional nano-particle layer for highly efficient OLED

Organic light emitting diodes (OLEDs) are now widely commercialized in market due to many advantages such as possibility of making thin or flexible devices. Nevertheless there are still several things to obtain the high quality flexible OLEDs, one of the most important issues is the light extraction of the device. It is known that OLEDs have the typical light loss such as the waveguide loss, plasmon absorption loss and internal total reflection. In this paper, we demonstrate the one-step processed light scattering films with aluminum oxide nano-particles and polystyrene matrix composite to achieve highly efficient OLEDs. Optical characteristics and surface roughness of light scattering film was optimized by changing the mixing concentration of Al2O3 nano-particles and investigated with the atomic force microscopy and hazemeter, respectively.