Browsing by Author "Wu, ST"

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Applications of multidirectional asymmetrical microlens-array light-control films on reflective liquid-crystal displays for image quality enhancement
(2004-06-20)
Huang, YP
;
Shieh, HPD
;
Wu, ST
;
光電工程學系
;
Department of Photonics
The multidirectional asymmetrical microlens-array light-control film (MAMA-LCF) is developed for enhancing the image brightness and contrast ratio of various reflective liquid-crystal displays. By use of index-matching material, the interface reflection is greatly reduced. Through optimized designs, the surface-scattering effect is also suppressed; thus the contrast ratio is much enhanced. From experimental results, the MAMA-LCF leads to a similar to1.5x gain in brightness over the MgO standard white and a 15:1 contrast ratio for the reflective color super-twist nematic liquid-crystal display, 2.8x MgO and a 23:1 contrast ratio for the polymer-dispersed liquid-crystal, and 2.8x MgO and a 13:1 contrast ratio for the cholesteric liquid-crystal display. Potential applications of this low-cost plastic thin film for reflective liquid-crystal displays are foreseeable. (C) 2004 Optical Society of America.
Diffraction effect on high-resolution liquid-crystal-on-silicon devices
(2005-05-01)
Chiang, KHF
;
Chen, SH
;
Wu, ST
;
光電工程學系
;
Department of Photonics
We extend the beam propagation method to calculate light propagation in reflective liquid crystal displays. The effect of diffraction on the optical performance of high-resolution liquid-crystal-on-silicon devices is investigated. The light efficiencies are simulated with respect to the pixel pitch for the vertically aligned and finger-on-plane modes. Computer simulation results indicate that the effect of diffraction on these devices is significant.
Dipping and photo-induced liquid crystal alignments using silane surfactants
(2000-02-01)
Liao, YJ
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Hsu, CS
;
Wu, ST
;
應用化學系
;
Department of Applied Chemistry
Dipping and photo-induced liquid crystal (LC) alignments were demonstrated using new silanes as surface coupling agents. In the dipping method, both homogeneous and homeotropic alignments can be achieved depending on the alkyl chain length of the silane employed. The 110 degrees C post curing temperature makes the dipping method especially attractive for low temperature processing of active matrix displays. In the UV-induced LC alignment, homogeneous cells are obtained and the LC directors are perpendicular to the impinging UV polarization. The pretilt angle of both methods is found to be similar to 0.5 degrees.
Fringing field effect of the liquid-crystal-on-silicon devices
(2002-07-01)
Chiang, KHF
;
Wu, ST
;
Chen, SH
;
光電工程學系
;
Department of Photonics
The fringing field has an important effect on the contrast ratio of liquid-crystal-on-silicon (LCOS) display devices. Computer simulation results of five commonly employed LC operating modes are compared: mixed-mode twisted nematic (MTN) cell, 45degrees twisted nematic cell, vertical alignment (VA) cell, film-compensated homogeneous cell, and fringe-field switching cell. The slope of the pixel electrodes is found to make an important contribution to the brightness and contrast ratio of each mode. Simulation results indicate that the VA mode has the best contrast ratio when all the pixels are on and off. However, the MTN cell shows the smallest fringing field effect when alternating pixels are switched on and off.
High birefringence and wide nematic range bis-tolane liquid crystals
(1999-01-18)
Wu, ST
;
Hsu, CS
;
Shyu, KF
;
應用化學系
;
Department of Applied Chemistry
Several dialkyl and fluoro bis-tolane liquid crystals were synthesized and their physical properties evaluated. These highly conjugated liquid crystals exhibit a wide nematic range, small heat fusion enthalpy, high birefringence, and relatively low viscosity. Their excellent compatibility with commercial cyano mixtures makes these liquid crystals attractive for many electro-optic applications. (C) 1999 American Institute of Physics. [S0003-6951(99)02103-8].
High birefringent bistolane liquid crystals for LCD application
(1999)
Hsu, CS
;
Shyu, KF
;
Chuang, YY
;
Wu, ST
;
應用化學系
Several series of bistolane liquid crystals were synthesized and characterized. The structure-properties relationship of the obtained compounds is discussed. These highly conjugated liquid crystals exhibit not only high birefringence but also low melting temperature. Their potential applications for Rat panel display employing light scattering on Bragg reflection are emphasized.
High birefringent liquid crystals
(1995)
Wu, ST
;
Margerum, JD
;
Ho, MS
;
Fung, BM
;
Hsu, CS
Several liquid crystal dyes and fluorinated compounds with high birefringence are synthesized and their properties evaluated. These polar compounds are useful dopants for enhancing the dielectric anisotropy of the dialkyl diphenyl-diacetylene host.
High-definition vertically aligned liquid crystal microdisplays using a circularly polarized light
(2005-07-18)
Fan-Chiang, KH
;
Chen, SH
;
Wu, ST
;
光電工程學系
;
Department of Photonics
A high-definition vertically aligned liquid crystal (LC) microdisplay exhibits a excellent contrast ratio, but its fringing field effect splits the bright state unevenly and leads to a very slow response time. By utilizing a circularly polarized light instead of conventional linearly polarized light, we have overcome the long-standing problems of poor sharpness, low brightness, and slow response time. Confirming computer simulations agree with the experimental results well. This approach can be applied to both reflective and transmissive LC microdisplays. (c) 2005 American Institute of Physics.
Liquid crystal alignment with a photo-crosslinkable and solvent-soluble polyimide film
(2000-05-15)
Lee, WC
;
Hsu, CS
;
Wu, ST
;
應用化學系
;
Department of Applied Chemistry
A new photo-crosslinkable and solvent-soluble polyimide containing cinnamate side chains (PICA) was developed for aligning nematic liquid crystals (LCs). Good LC alignment was achieved by exposing a long-wave linearly polarized ultraviolet (LPUV) light to the PICA film. The LC alignment direction is found perpendicular to the polarization axis of the incident LPUV light. The uniform alignment of LC molecules induced by PICA Films remains intact after being heated at 85 degreesC for 450 hours. A small pretilt angle on the PICA film was generated by the double exposure method.
Micro optical components for enhancing the image quality of transflective LCDs
(2003)
Shieh, HPD
;
Huang, YP
;
Su, MJ
;
Wu, ST
;
光電工程學系
Obliquely tilted discotic phase compensation films
(2000-08-15)
Wu, LH
;
Luo, SJ
;
Hsu, CS
;
Wu, ST
;
應用化學系
A three-step method was developed to fabricate the obliquely tilted discotic negative birefringence phase compensation films. Model fitting reveals that the tilt angle of the discotic directors is about 46 degrees from surface normal. The total phase retardation value of the film can be controlled by the discotic layer thickness. These asymmetric phase retardation films are useful for widening the viewing angle of a liquid crystal display device.
Photo-alignment of liquid crystals using a crosslinked discotic film
(2001-02-01)
Wu, LH
;
Lee, WC
;
Hsu, CS
;
Wu, ST
;
應用化學系
A new photo-alignment layer using a crosslinked discotic compound was demonstrated. This discotic compound exhibits excellent solubility in common organic solvents, the possibility of low temperature processing and good thermal stability. A linearly polarized long wavelength ultraviolet (LPUV) light (lambda = 350 nm) was used to initiate the crosslinking process and induce liquid crystal alignment on the discotic film surface. The induced LC directors were found parallel to the electric field direction of the LPUV light. A 1.2 degrees pre-tilt angle was achieved using a single exposure at a 30 degrees oblique angle.
Photo-induced liquid crystal alignment with discotic films
(2000-10-01)
Wu, LH
;
Lee, WC
;
Hsu, CS
;
Wu, ST
;
應用化學系
Photo-induced liquid crystal alignment using cross-linked discotic compounds was demonstrated. These discotic compounds exhibit good solubility in common organic solvents, 60 degreesC processing temperature and excellent thermal stability. A linearly polarized long wave ultraviolet light (lambda = 350 nm) was used to initiate the cross-linking process which, in turn, induces liquid crystal alignment on the discotic film surface. The polarity of discotic compounds plays an important role in affecting the pretilt angle of the liquid crystal alignment. A pretilt angle of 1 +/- 0.4 degrees was obtained using single exposure at oblique angle. Potential application of this new photo-alignment film for low temperature poly-silicon thin-film-transistor liquid crystal display is foreseeable.
Physical properties of polar bis-tolane liquid crystals
(2000-01-15)
Wu, ST
;
Hsu, CS
;
Chuang, YY
;
Cheng, HB
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應用化學系
Several cyano and fluoro bis-tolane liquid crystals were synthesized and their physical properties evaluated. Some of these highly conjugated liquid crystals possess birefringence larger than 0.5 in the visible region. Adding 10% of a binary bis-tolane mixture to a cholesteric display enhances the brightness by more than 20%.
Room temperature bis-tolane liquid crystals
(1999-03-15)
Wu, ST
;
Hsu, CS
;
Chuang, YY
;
應用化學系
;
Department of Applied Chemistry
Several room temperature bis-tolane liquid crystals were synthesized and their physical properties evaluated at elevated temperatures. These highly conjugated liquid crystals exhibit not: only high birefringence (Delta n > 0.4) but also low melting temperature. Their applications for flat panel displays employing light scattering or Bragg reflection and for infrared spatial light modulators are emphasized.
Room temperature difluoro-tolane and diphenyl-diacetylene liquid crystals with negative dielectric anisotropy
(1997)
Wu, ST
;
Hsu, CS
;
Chen, JM
;
應用化學系
;
Department of Applied Chemistry
Several laterally difluorinated tolane and diphenyl-diacetylene liquid crystals were synthesized and their physical properties evaluated. These compounds exhibit low melting temperature, small heat fusion enthalpy and large negative dielectric anisotropy. Their potential applications are in the high contrast displays using a homeotropic cell and for infrared spatial light modulators.
Sensitivity of the photo-crosslinkable polyimide for liquid crystal alignment
(2001-10-01)
Lee, WC
;
Hsu, CS
;
Wu, ST
;
應用化學系
;
Department of Applied Chemistry
Two methods were developed for enhancing the photosensitivity of the cinnamates-contained polyimide (PICA), One is to increase the content of cinnamate side chain in PICA main chain and another is to blend some photosensitizer into PICA films. Our experimental results show that increasing the rate of photo-dimerization decreases the alignment ability of the PICA films. Using the molecular simulation method, we successfully describe the photoalignment mechanism of the PICA films. It is also found that photo-induced LC alignment ability of the PICA film could be enhanced through choosing a proper coating solvent.
Single cell-gap transflective color TFT-LCD by using image-enhanced reflector
(2003)
Shieh, HPD
;
Huang, YP
;
Su, MJ
;
Wu, ST
;
光電工程學系
By building an image-enhanced reflector above the transmissive region of liquid crystal cell, the transmissive light can follow the similar path with ambient light that both reflective and transmissive portions can achieve high optical efficiency, same response time and color saturation. Furthermore, only single retardation film is required in this transflective color TFT-LCD, and ambient light and backlight utilization ratio can be increase to 68% and 24% respectively. With image-enhanced reflector built in, a high image performance display under both bright and dark ambience can be accomplished.
Super high birefringence isothiocyanato biphenyl-bistolane liquid crystals
(2004-11-01)
Gauza, S
;
Wen, CH
;
Wu, ST
;
Janarthanan, N
;
Hsu, CS
We have designed, synthesized, and evaluated the physical properties of some high birefringence (An) isothiocyanato biphenyl-bistolane liquid crystals. These compounds exhibit Deltan = 0.7-0.8 at room temperature and wavelength lambda = 633 nm. Laterally substituted short alkyl chains and fluorine atom eliminate smectic phase and lower the melting temperature. The moderate melting temperature and very high clearing temperature make those compounds attractive for eutectic mixture formulation. A eutectic mixture based on those compounds was formulated and its physical properties evaluated. The simulated absorption spectra agree reasonably well with the measured results.
Synthesis of alkyl-branched main chain copolyimides and their effect on the pretilt angles of liquid crystal alignment
(2002-07-01)
Lee, WC
;
Chen, JT
;
Hsu, CS
;
Wu, ST
;
應用化學系
Three series of copolyimides containing long alkyl branches were synthesized using the two-step method via poly(amic acid) precursors and chemical imidization. Most of the copolyimides prepared are soluble in polar organic solvents. Good liquid crystal alignment was achieved by buffing the copolyimide films spin-coated onto indium tin oxide glass substrates. The measured liquid crystal pretilt angles range from 0.16degrees to 15.54degrees. The Titan simulation program was used to calculate the dipole of each dianhydride structure and correlate with the observed pretilt angles. Main chain copolyimides with a long alkyl side chain, small dipole, and linear, symmetric and rigid core structures are favourable for generating large pretilt angles.