Browsing by Author "Yao, IA"

Now showing 1 - 5 of 5

Direction-tunable cholesteric phase gratings
(2004-08-01)
Yao, IA
;
Liaw, CH
;
Chen, SH
;
Wu, JJ
;
光電工程學系
In suitable conditions, the homeotropic aligned cholesteric liquid crystal (ChLC) cell can be in fingerprint texture when abruptly switching off the applied electric field. The stripe orientation depends not only on the thickness-to-pitch (d/P-0) ratio, but also on the applied driving voltage. In this paper, the ChLC phase grating with the field-controllable grating orientation is realized and the operational mechanism of this device is presented. (C) 2004 American Institute of Physics.
Observation of electric-field-driven modulated textures in cholesteric liquid crystal cells
(2004-09-01)
Yao, IA
;
Wu, JJ
;
Chen, SH
;
光電工程學系
;
Department of Photonics
We observed the modulated textures in a planar-aligned cholesteric liquid crystal cell by applying an electric field parallel to its helical axis. In this system, the twist favored by the chirality competes with the applied electric field. This competition causes the system to develop a series of ordered textures, in the sequence of striped texture-hexagonal texture-striped texture, with the increase of electric field. Of these textures, the hexagonal texture was experimentally observed for the first time.
Relaxation of a field-unwound cholesteric liquid crystal
(2004-11-01)
Yao, IA
;
Lai, YC
;
Chen, SH
;
Wu, JJ
;
光電工程研究所
We have numerically investigated the homogeneous-planar and homeotropic-planar transitions, respectively, in a planar-aligned cholesteric liquid crystal by using our multidimensional software based on the finite element method. When the unwinding field is turned off abruptly, the relaxation process of a field-unwound cholesteric liquid crystal is accompanied by an elastic-induced Helfrich deformation without introduction of defects, which will continuously convert into a stable planar texture with natural pitch and domain wall.
Study of the transient phenomenon during homeotropic to planar transition in cholesteric liquid crystal cells
(2004-04-01)
Yao, IA
;
Wu, JJ
;
Chen, SH
;
光電工程學系
;
Department of Photonics
The transient behavior of homeotropic-planar relaxation in surface stabilized cholesteric liquid crystals bounded by parallel substrates has been investigated both experimentally and numerically. By monitoring the evolution of transient transmittance, we observe that the homeotropic-planar relaxation after the electric field is switched off occurs via a transient planar state. The effect of bias waveform on the relaxation process is also studied. On the basis of this knowledge, we design a driving waveform to reduce the relaxation time.
Three-dimensional simulation of the homeotropic to planar transition in cholesteric liquid crystals using the finite elements method
(2004-02-01)
Yao, IA
;
Wu, JJ
;
Chen, SH
;
光電工程學系
;
Department of Photonics
We investigated numerically the evolution of the director field in the homeotropic-planar transition of cholesteric liquid crystals bounded by parallel substrates. The simulation reproduces the observed relaxation from the homeotropic state to the long pitch transient planar state. The simulation agrees with the suggestion that the transient planar-planar transition occurs via a three-dimensional Helfrich-type deformation without the introduction of defect cores. On the basis of this understanding, we suggest improvements for increasing the speed of these transitions.