Browsing by Author "Wang, Sheng-Ya"

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A Simple Method to Measure Pretilt Angles of Inverse Twisted Nematic Liquid Crystal Cells
(2014-12-01)
Wang, Sheng-Ya
;
Lin, Chia-Yi
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Yang, Kei-Hsiung
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交大名義發表
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National Chiao Tung University
We have developed a simple optical method based on measurements of phase retardation[1] versus out-of-plane cell rotation angle and data analyzed by extended Jones matrix method to obtain pretilt angles of inverse twisted nematic (ITN) and tilted homeotropic liquid crystal (LC) cells. In our Jones-matrix calculations, we have assumed a constant pretilt angle as the LC-director tilt angles throughout the ITN cell as well as the tilted homeotropic cell. We have compared the measured pretilt angles of the ITN cell with those of an accompanying tilted homeotropic (ATH) cell. The results showed increasing discrepancies between them with increasing rubbing depth for LC alignments. However, these discrepancies could be explained by assuming that the surface-LC tilt angle of the ITN cell was equal to the measured pretilt angle of the ATH cell to generate a convex-type LC-director-deformation profile within the ITN cell based on Oseen-Frank elastic continuum theory with infinite anchoring energies. The average of the LC-director tilt angles over this profile was equivalent to the measured pretilt angle of the ITN cell.
Investigation of Curtain Mura in TFT-TN panels after COG ACF process
(2012-10-01)
Wang, Sheng-Ya
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Liao, Wei-Hsiang
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Yang, Kei-Hsiung
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光電系統研究所
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影像與生醫光電研究所
We have utilized a transmission ratio (TR) between curtain-shaped (Curtain) Mura and non-Mura zones as a key parameter to characterize the optical appearance of Curtain Mura occurred on a 13.3-in TFT-TN panel (Mura sample) after bonding process to place silicon-based driver-IC chips on one of the panel substrates using anisotropic conductive film as a binder (COG ACF process). Our measured TRs of the Mura sample at zero applied voltage were in good agreement with calculated TRs using optical parameters of the Mura sample derived from the measured Stokes parameters of the liquid crystal (LC) medium in that sample. We conclude that the occurrence of Curtain Mura is dominant by the stress-induced change in the twist angle, less sensitive and insensitive to the corresponding induced changes in the cell gap and pretilt angle of the in-panel-LC medium, respectively. By simulation, we also point out a way to reduce the occurrence of Curtain Mura by designing the cell gap for a 90 degrees-twsit TN panel to satisfy the condition of Gooch-Terry first minimum. (C) 2012 Elsevier B.V. All rights reserved.
Simple and direct measurements of pretilt angles in hybrid-aligned nematic liquid-crystal cells
(2013-07-20)
Wang, Sheng-Ya
;
Wu, Huang-Ming
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Yang, Kei-Hsiung
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光電系統研究所
;
影像與生醫光電研究所
We have developed a general approach to perform direct measurements of the pretilt angles from 0 degrees to 75 degrees in hybrid-aligned nematic (HAN) liquid-crystal cells whose cell gaps can also be accurately determined with the help of known pretilt angles. In this paper, we have used a Zeeman laser system to measure the angular-dependence phase retardation of the HAN cells and MATLAB mathematical software to carry out theoretical calculations and fit the measured data to derive the pretilt angles. In general, pretilt angles adjacent to opposite substrates of a HAN cell are different. Our measured pretilt angles of the HAN cell were in good agreement with the measured pretilt angles of two accompanying homogenous cells whose alignment methods were the same as applied to opposite substrates of the HAN cell, respectively. The advantage of direct measurement is easily applicable to measure the pretilt angles of aged HAN cells. (C) 2013 Optical Society of America
Simple method to obtain accurate pretilt angles for thin twisted nematic liquid-crystal cells
(2013-01-10)
Wang, Sheng-Ya
;
Yang, Kei-Hsiung
;
光電系統研究所
;
影像與生醫光電研究所
;
Institute of Photonic System
Modern thin-film-transistor-driven twisted nematic (TN) products on the market require thin cell gaps below the value to satisfy the condition of the Gooch-Tarry first minimum in transmission for fast response times and wide viewing angles. For the first time to our knowledge, we have developed a simple experimental method based on a new configuration of out-of-plane cell rotation and analyzed our data by extended Jones matrix method to obtain accurate pretilt angles for such thin TN cells where the well-accepted configuration of the out-of-plane cell rotation method analyzed by Birecki and Kahn [ The Physics and Chemistry of Liquid Crystal Devices (1980), p. 115] was insufficient to address. (C) 2013 Optical Society of America