Browsing by Author "Liang, BJ"

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A method to determine the higher order polar anchoring coefficients for the non-twisted liquid crystal cells
(2005-08-01)
Hsu, JS
;
Hsieh, MC
;
Yang, CL
;
Liang, BJ
;
Chen, SH
We propose a method to determine the higher order polar anchoring coefficients for the non-twisted liquid crystal cells. The surface anchoring energy density was determined by measuring the phase retardations as a function of applied voltage. We extended the Rapini-Papoular model and obtained the coefficients of the first and the second terms by analyzing the measured phase retardations with the simulated curves for the homogeneous and homeotropic cells. A discussion of the experimental results is given.
A simple method for determining the pretilt angle of a vertically aligned reflective LCD
(2005-05-01)
Hsu, JS
;
Liang, BJ
;
Chen, SH
;
光電工程學系
;
Department of Photonics
A field-induced birefringence method is demonstrated for determining the pretilt angle of a vertically aligned reflective liquid crystal display. We derive theoretically that the field-induced optical phase retardation is linearly proportional to the square of the applied voltage in the low-voltage regime. The pretilt angle can be deduced from the slope of this linear relation. The optical phase retardation is measured by a simple optical system and the pretilt angle can be determined easily. The experimental results agree well with that obtained theoretically. We also describe the applicable range of the applied voltage and the advantage of our method.
Bistable chiral tilted-homeotropic nematic liquid crystal cells
(2004-12-06)
Hsu, JS
;
Liang, BJ
;
Chen, SH
;
光電工程學系
;
Department of Photonics
A bistable chiral tilted-homeotropic nematic cell which uses dual-frequency liquid crystal is demonstrated. This cell can be switched between the tilted homeotropic state and the twisted state. The switching mechanisms are achieved by the backflow effect together with the anisotropic properties of the dual-frequency liquid crystal material. The experimental results of this bistable cell are described explicitly. (C) 2004 American Institute of Physics.
Electro-optical properties of conic cylindrical-cavities liquid crystal displays
(2002-05-01)
Liang, BJ
;
Chen, SH
;
Wu, CR
;
光電工程學系
;
Department of Photonics
Experimental results have shown that the conic cavities in conic closed-cavity liquid crystal displays (conic CCLCDs) can give a wide viewing angle and grey levels without grey-scale inversion. The purpose of this paper is to extend investigations of conic CCLCDs. In experiments, we describe in detail the fabrication process, microscopic observations and optical measurements for conic CCLCDs. The simulation of director distribution will be based on the tensor form formulation of the free energy density. The differential equations satisfied by the steady-state director distribution are derived from this form of free energy and are solved in conjunction with Poisson's equation. The simulation of the optical propagation and the calculation of the optical transmittance will be based on the extended Jones matrix method. We show by simulation that a normal umbilical structure is the final stable state and that indeed conic CCLCDs can have a wide viewing angle and grey scale without grey-scale inversion. The theoretical results are compared with the experimental results. Transmittance, contrast ratio and viewing angle with various parameters of the LC are measured. Improved iso-contrast contours of the conic CCLCD with a c-plate compensator are also shown. Finally, we have also compared the electro-optical performance and the off axis colour-shift of the CCLCD, the 4-domain VAN device and the 4-domain twist-VAN device.
Liquid crystal display with wide viewing angle
(1998-03-16)
Liang, BJ
;
Chen, SH
;
Wang, YF
;
光電工程學系
;
Department of Photonics
A conic-cylindrical-cavities liquid crystal (conic CCLC) cell is developed for wide-viewing-angle displays. This conic-CCLC cell has been successfully manufactured and inquired. This display has a superwide viewing angle of over +/- 70 degrees in both the horizontal and vertical directions under the condition of no gray-scale inversion. The enhancement of viewing angle is believed to result from the director symmetric alignment in the conic-CCLC. (C) 1995 American Institute of Physics.
The transient behavior of the bistable nematic liquid crystal cells
(2005-08-01)
Hsu, JS
;
Liang, BJ
;
Chen, SH
;
光電工程學系
;
Department of Photonics
The transient behaviors switched from homogeneous state in the bistable nematic liquid crystal (BiNem) cell have been studied by simulation. We find two different dynamic relaxation processes of the directors when we apply pulses of the same voltage with 1 and 2 ms durations to the cell. The directors which respond to the 2 ms pulse go directly to the so called twisted state and the relaxation time is short. Those which respond to the 1 ms pulse go through an over twisted process before toward the twisted state and the relaxation time is longer. When the pulse duration is too short, the cell is unable to be switched to the twisted state. The explanation is given via the dynamic behavior of the director near the weak anchoring boundary of the cell.