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Your search keyword '"Yoon, Tae-Hoon"' showing total 1,009 results
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1,009 results on '"Yoon, Tae-Hoon"'

1. Studies on binary mixtures of nematic liquid crystals made of strongly polar molecules with identical cores and antagonistic orientation of permanent dipoles

Author

Sai, Dasari Venkata, Yoon, Tae Hoon, and Dhara, Surajit

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

We report experimental studies on optical (birefringence, $\Delta n$), dielectric $(\Delta \varepsilon)$ and bend-splay elastic anisotropies ($\Delta K=K_{33}-K_{11})$ of a few mixtures of two nematic liquid crystals, namely CCH-7 and CCN-47, made of highly polar molecules with identical cores and antagonistic orientation of permanent dipoles. In particular, the polar group (-CN) attached to the bicyclohexane core of CCH-7 is oriented along the longitudinal direction whereas, in CCN-47, it is oriented along the transverse direction. We show that apart from the significant contribution to the optical and dielectric anisotropies, the antagonistic orientation of strongly polar groups plays a crucial role in determining the bend-splay elastic anisotropy. The elastic properties are explained based on a model proposed by Priest, considering the effect of intermolecular association and the resulting length-to-width ratio of the molecules., Comment: 5 pages, 5 figures

Published
2020

20. Asymmetrically anchored liquid crystal cell for display and photonics applications.

Author

Han, Chan-Hee, Choi, Yeongyu, Oh, Seung-Won, and Yoon, Tae-Hoon

Subjects
LIQUID crystal displays, PHOTONICS, LIQUID crystals
Abstract

Asymmetrically anchored liquid crystal (LC) cells have different anchoring energies between the top and bottom substrates. A substrate with patterned electrodes has comparatively weak anchoring energy. Therefore, asymmetrically anchored LC cells exhibit more twisted deformation in the on-state than conventional in-plane switching or fringe-field switching cells. In this study, we introduced asymmetrically anchored LC cells for display and photonic applications. We first introduced asymmetrically anchored LC cells to achieve high transmittance for LC displays. The LC molecules can rotate between the two substrates more easily because one of the two substrates has weaker anchoring energy. This resulted in a significant increase in transmittance. Three-terminal electrodes can be used to provide a vertical trigger pulse to an LC cell, thereby overcoming the delayed turn-off switching of an asymmetrically anchored cell without reducing transmittance. Next, we introduced an adjustable polarisation rotator with an asymmetrically anchored LC cell. To offer optical waveguiding, the arrangement of LC molecules can be controlled into a twisted configuration. During the cover of the wavelength range of 400–800 μm, we confirmed that the proposed LC cell can rotate the polarisation axis of linearly polarised light by up to 90°. [ABSTRACT FROM AUTHOR]

Published
2023
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21. Formation of a fine polymer structure on a plastic substrate through phase separation of a liquid crystal mixture

Author

Choi Yeongyu, Yoon Tae-Hoon, Choi Tae-Hoon, Oh Seung-Won, Huh Jae-Won, and Do Su-Min

Subjects
010302 applied physics, chemistry.chemical_classification, Materials science, lcsh:Computer engineering. Computer hardware, fungi, food and beverages, Substrate (chemistry), lcsh:TK7885-7895, 02 engineering and technology, Polymer, 021001 nanoscience & nanotechnology, 01 natural sciences, polymer walls, chemistry, Chemical engineering, Liquid crystal, 0103 physical sciences, General Materials Science, liquid crystal, Electrical and Electronic Engineering, reactive mesogen, phase separation, 0210 nano-technology
Abstract

Reported herein is a method for the formation of a polymer structure on a plastic substrate through the phase separation of a liquid crystal mixture. Polymer walls can be formed on a specific location through phase separation induced by a spatial differences in elastic energy and electric field intensity. The fabricated polymer walls were observed through various methods. The measured aspect ratio of the fabricated polymer walls was about 12.9, with a 10.3 μm height and a 0.8 μm width.

Published
2021

43. Two-Dimensional Hybrid Photonic Crystal With Graded Low-Index Using a Nonuniform Voltage

Author

Ranjkesh, Amid, Rezaei, Behrooz, Giden, İbrahim Haiii, Yoon, Tae-Hoon, Zakerhamidi, Mohammad Sadegh, Ranjkesh, Amid, Rezaei, Behrooz, Giden, İbrahim Haiii, Yoon, Tae-Hoon, and Zakerhamidi, Mohammad Sadegh

Abstract

We proposed a new method for designing graded index lens using liquid crystal infiltration into annular photonic crystals. Applying an external nonuniform voltage in the transverse direction perpendicular to the direction of light propagation yields different orientation of liquid crystal molecules inside the photonic crystal unit cells. As a result, a gradient refractive index was modulated. We numerically investigate focusing properties of the designed graded index structure using plane-wave expansion and finite-difference time-domain methods. The gradient refractive index profile was adjusted by varying the nonuniform voltage excitations, which consequently altered the focal distance of the graded index structure. A wide tuning range of 1856 nm was achieved for focal distance by the proposed graded index structure. This feature can be implemented for planning a flat lens with tunable focal distance based on electro-optic effect. These achievements may have future applications in some optical devices such as near-field imaging and scanning.

Published
2021

45. Optical configurations for nematic liquid crystal device switchable between reflective and transmissive modes

Author

Kim, Ki-Han, Jin, Hye-Jung, Cheong, Byoung-Ho, Choi, Hwan-Young, Shin, Sung Tae, Kim, Jae Chang, and Yoon, Tae-Hoon

Subjects
Liquid crystal displays -- Optical properties, Liquid crystal displays -- Equipment and supplies, Polarizers (Light) -- Usage, Reflectance -- Research, LCD display, Astronomy, Physics
Abstract

We propose an optical configuration for a nematic liquid crystal (LC) device that is switchable between the reflective and the transmissive modes. By placing a reflective polarizer between the two LC layers, we obtain higher reflectance and reduce the parallax effect in the reflective mode. We can eliminate the parallax effect by using a wire-grid polarizer or other in-cell reflective polarizers. We expect that the proposed device can be used in various outdoor applications. [c] 2010 Optical Society of America OCIS codes: 230.0230, 230.3720.

Published
2010

48. Fringe field switching of a twisted nematic liquid crystal device for a single-cell-gap transflective display

Author

Lee, Gak Seok, Lee, Jeong Hyun, Song, Dong Han, Kim, Jae Chang, Yoon, Tae-Hoon, Park, Dae Lim, Hwang, Seong Soo, Kim, Dae Hyun, and Park, Sung II

Subjects
Liquid crystal displays -- Research, Diffraction patterns -- Research, LCD display, Astronomy, Physics
Abstract

We propose an optical configuration of a twisted nematic liquid crystal device driven by a fringe field for a single-cell-gap transflective display. The dark state of the reflective part is realized by a nematic liquid crystal layer with a twist angle of 63.6[degrees] and retardation of 194 rim, while a quarter-wave plate is inserted for the dark state of the transmissive part. Wavelength dispersion of the liquid crystal layer is suppressed by introducing a half-wave plate. Different directions of electric fields rotate liquid crystals to 15[degrees] for the bright state of the reflective part, but to -30[degrees] for that of the transmissive part. With the proposed configuration, we can realize a high-brightness single-gamma transflective display in a single-cell-gap structure without any in-cell retardation layers. OCIS codes: 230.0230, 230.3720.

Published
2008

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