Reflective cholesteric liquid crystal displays (Ch-LCDs) are attracting more interest because power efficient displays are needed for the rapid growing mobile computation applications. Its capability of high-resolution full color with passive matrix drive method provides the market with a very powerful alternative display technology. In this paper, we will review the history of Ch-LCDs as well as the most recent developments.

Conventional reflective displays based on either color filter/polarizer or stacked color layers suffer from their marginal performance in terms of brightness, color, and cost. In this paper, we will present new full-color reflective display architecture: Electrically Tunable Color (ETC). In this display architecture, both color generation and its change are through the coupling of a cholesteric liquid crystal in its planar state and an in-plane electric field. Unlike the conventional cholesteric liquid crystal display, in which one liquid crystal layer only reflects one preset color, in ETC the in-plane field that is predominantly normal to the helix unwinds the helix to result a color shift from its initial color. We have fabricated such devices in our laboratory and demonstrated large color change covering all three primary colors with a single ETC pixel. Another advantage of ETC is its faster time response. Time response data will be presented and compared with model. Switching voltages depend much on cell parameters, in particular on the electrode configuration. Measured switch voltage vs. these parameters will be shown and challenging issue in voltage reduction will be discussed. Finally, we will propose full-color display architectures based on ETC and analyze their cost/performance.

We report the fabrication of a bistable, reflective cholesteric liquid crystal display (CLCD) with pixelated colors. The bistable color CLCD is prepared, instead of using stacked color panels, by the formation of polymer barrier walls at inter-pixel areas and color tuning with a tunable chiral material (TCM), whose chirality can be rendered and reduced by exposing to various amount of UV light at a selected wavelength. The polymer barrier walls are formed at the inter-pixel areas by a photopolymerization-induced phase separation via a photomask. Some of the blue color pixels are selectively changed to reflect the green or red color by exposing the panel to various amount of UV light with the assistance of a set of photomasks. The electro-optical study of a CLCD with pixilated colors reveal that the bistable switching behavior is retained with variation in switching voltages depending on the color of cholesteric pixels.

We have analyzed the nematic liquid crystal reorientation in IPS mode and we present the result of theoretical study of this problem. In calculations we used the non-uniform electric field profile for inter-digital electrode configuration.

Liquid crystal tunable filters are gaining wide acceptance in such diverse areas as optical fiber communications, astronomy, remote sensing, pollution monitoring, color generation for display and medical diagnostics. The large aperture and imaging capability of liquid crystal tunable filters represent a distinct advantage over conventional dispersive spectral analysis techniques. Furthermore, benefits of liquid crystal tunable filters over acousto-optic tunable filters include low power consumption, low addressing voltage, excellent image quality and large clear aperture. We discuss polarization interference filters based on liquid crystal tuning elements. While liquid crystal tunable filters based nematic liquid crystal, using Fabry-Perot and polarization interference effects are commercially developed, only recently has the emphasis been on liquid crystal tunable filters to include current novel developments in high-speed, analog ferroelectric-liquid crystals (FLCs). Compared to nematic liquid crystal, FLC-based tunable optical filters offer fast response time and increased field-of-view.

New generations of large area liquid crystal displays require very high optical performance to compete with CRT and other emerging technologies. This performance must include high contrast ratio, high stability of all grey levels, and excellent colour reproduction, and typically this is requested for up to 80# viewing angles in all directions. Some potential difficulties to achieving wide viewing performance in single domain LCD's are discussed, with explanation for the advantages to multi-domain LC display. Finally we shall describe some new optical film developments which can be used to achieve the targets for high performance at all viewing angles combining multi-domain LC display, together with optical films prepared from reactive mesogens.

A most important parameter for TV application of LCD is a fast switching time for displaying of moving image. To achieve the requirement of faster switching times, the novel LC single materials with large dielectric anisotropies (16~20), high clearing temperatures (195.5 ~ 237.4 degree(s)C), broad nematic ranges (up to 169.9 degree(s)C) and high birefringence (0.220 ~ 0.254) were developed. KUR-series LC mixtures blended these single materials have significantly higher clearing temperatures and dielectric anisotropy values compared with conventional LC mixture. Especially, clearing temperatures of them are 10~30 degree(s)C higher than their host mixture. These LC mixtures showing about 10ms of high-speed response time in TV/Monitor of TFT LCD, which are shorter enough to be addressed in one frame time of 60Hz (16.7ms). The threshold voltage V_th was low enough to operate at a driving voltage of 5V. The VHR values were found to high enough for TFT-LCD in wide temperature range. Our novel LC mixtures are suitable materials for inclusion in LC mixtures for TV application of TN-LCD.

New LCD cell structure includes plastic or glass substrates with ITO layers, Thin Crystal Film (TCF) polarizers coated on the ITO and a polyamide alignment layer on the top of the TCF. The TCF polarizer is molecularly oriented nano-film with the thickness in the range 60-600nm made by crystallization from lyotropic liquid crystals. First samples produced by Tecdis have demonstrated acceptable optical performance with superior viewing cone characteristics and thickness determined by the thickness of the plastic or glass walls plus 7 microns optical management path. Birefringence of the cell wall material is now not relevant to functionality of the display. It allows manufacturing plastic LCD's with robust environmental characteristics by using high temperature stable and birefringent inexpensive plastic.

The effect of the photoalignment on the electrooptic characteristics of polymer stabilized ferroelectric liquid crystal displays (FLCDs) exhibiting V-shaped switching and those of FLCDs exhibiting half-V switching are reported and discussed. Photoalignment technique and hybrid alignment, which is done by combining photoalignment and rubbing, are shown to be useful for fabricating zig-zag defect-free FLCDs and improving the electrooptic characteristics of FLCDs-SSFLCDs, V-F-LCDs, and H-V-FLCDs- especially in the reduction of operation voltage.

The glancing angle deposition (GLAD) technique may be used to fabricate thin films with a very porous chiral or helical microstructure, with geometry of the helices controlled and engineered to have specific porosity, helical pitch, and handedness. Such films with chiral morphology exhibit optical rotation and circular dichroism similar to certain classes of liquid crystals, with the pitch and handedness of the chiral film determining the resultant optical properties. When nematic liquid crystals (LCs) are introduced into the pores of chiral GLAD films, a composite material is formed that shows a significant enhancement of the chiral optic response, suggesting an alignment of LC molecules by the underlying inorganic chiral film 'backbone'. Results are presented from a study of the optical behaviour of chiral films fabricated from materials such as silicon dioxide, alumina, and magnesium fluoride, and from study of the effects of parameters such as helical pitch, film thickness, and film porosity on the optical properties. The enhancement of optical response created by impregnating these films with nematic LC is reported. The construction of electro-optic cells containing the composite GLAD/LC films is described, demonstrating reversible electro-optic switching of the LC component within the film.

Polymer-stabilized ferroelectric liquid crystal (PSFLCs) are made by photopolymerizing a small amount of reactive mesogenic monomer on a quasi-bookshelf texture of ferroelectric liquid crystals (FLCs). We observed the templated submicron-scaled polymer fibrils from the two- dimensionally ordered host. The polymer fibrils capture the orientation of the host with thin polymer fibrils interweaving the smectic layers that act as additional surfaces for controlling the reorientation of FLC molecules. T he SEM study shows the difference in morphology of the polymer fibrils depending on the polymerization conditions and FLC hosts. Improvements in electro-optical properties such as, the increase in spontaneous polarization, the fast switching at a lower applied field, and the voltage independent of switching time are achieved by PSFLCs using a mesogenic monomer and FLC with a smectic A phase. The polymer networks suppress the symmetric rotation of FLC under applied field and result in PSFLCs exhibiting the thresholdless switching behavior.

We developed a new technology for thin crystal film (TCF) manufacturing based on water-soluble salts of aromatic polycyclic compounds. TCF is produced by coating and subsequent drying of an aqueous solution on plastic or glass surface into molecularly oriented 100-1000 nm thick crystal nano-film. First industrial application of nano-films is TCF polarizer for liquid crystal displays (LCD). TCF polarizers are made from modified organic dyes with relatively narrow spectral absorption band. Mixing various dyes allows covering broad spectral region. Blending provides variety of combinations of background and character colors that are necessary for applications. TCF made from dichroic dyes are highly anisotropic, biaxial extraordinary polarizers. Birefringence of TCF made from some materials reaches 1.0. Several highly birefringent TCFs show specific retardation characteristics. For example, 300 nm thick TCF based on dichroic dye with narrow absorption band at 450 nm and transparent in the long-wave region, has maximum birefringence of 0.85 in the wavelength region of 500-800 nm. TCF are available for industrial application in LCD as external, internal polarizers and retarders.

Tunable semiconductor lasers are compact, versatile sources used extensively in dense-wavelength-division-multiplexing (DWDM) optical communication systems, precision metrology, environmental monitoring, and laser spectroscopy. We have developed a twisted nematic liquid crystal device, the liquid crystal pixel mirror (LCPM), successfully as electronically tunable spectral filters for wavelength selection in external cavity semiconductor lasers. In this talk, we report recent advances in this class of electronically tunable single- and multiple-wavelength semiconductor lasers at 650 and 830 nm. Preliminary results of operating the laser at 1.5 microns will also be shown. The laser output can be locked to the ITU grid at 100 GHz intervals. Output power of the laser is as high as several hundred milliwatts, with a tuning range of several tens of nanometers. The laser can be operated either in the continuous-wave (CW) or mode-locked configuration. The linewidth of the laser in the free-running CW mode is about 30 MHz. Fine-tuning of the cw output wavelength can be achieved by changing the driving voltage to the desired pixels of the LCPM. In the mode-locked configuration, the laser design allows intra-cavity dispersion compensation and pulse compression.

The contrast and color saturation of cathode ray tube (CRT) and plasma display images is negatively affected by the reflection of ambient light at the white phosphor dots. A variable photochromic transmission filter reversibly darkens upon exposure to sunlight, and could offer the optimal compromise between contrast and brightness of the image under a range of illumination conditions. The photochromic transmission filter that we present here consists of a soft polymer layer doped with a photochromic dye that has been sandwiched between the CRT screen and a front glass panel. The fabrication process of such a photochromic laminate involves the in-situ polymerization of a resin in the presence of the dye. For this purpose we have studied the radical polymerization of several (meth)acrylates in the presence of a photochromic dye, and evaluated the optical properties of the dye in the resulting polymer films. In this way a photochromic laminate has been developed that upon irradiation turns from a transparent state to an almost neutrally colored state and exhibits sufficiently fast coloration and decoloration kinetics. The photochromic laminate significantly improves the daylight contrast of the CRT under high illumination conditions (e.g. direct sunlight), while at the same time the brightness of the CRT is retained under low illumination conditions.

Since recent years some activity has developed and characterized the field of research on polymers dispersed liquid crystals (PDLC's). They are useful for a variety of electro-optical applications including windows, displays and other devices. We presented a color filter with PDLC optical activity. This PDLC device was doped with cholesteric liquid crystal. This substance rotates the plane of polarization of a beam of light traversing through them and they are said to be optically active. The mixtures make an uniform behavior pitch in each micro-droplet of the PDLC. The scattering do not destroyed the optical activity of the cholesteric liquid crystal. It is not necessary to observed colors by reflection; we can observe them by across linear polarizers. When the PDLC is on, the colors disappear and when the PDLC is off, colors return.

Reactive liquid crystal (LC) mesogen (trade mark C6M of Merck) is shown to possess efficient relief formation properties. Photosensitive formulation was made by mixing of the reactive LC mesogen C6M with 2% of photoinitiator (Irgacure 651). Photosensitive layer (thickness 70 micrometers ) was obtained by melting the formulation in the gap between two glass substrates. One of the substrates contained a photosensitive silver-halide layer, in which the amplitude mask was recorded with the resolution Fequals40 lines/mm. The amplitude function of the mask represented a phase function of the desired CO₂ laser focusing element, designed for wavelength 10.6 micrometers and 45 degrees incidence . Exposure of the reactive mesogen layer through the mask was carried out at elevated temperature of Tequals85 degrees C by UV source (wavelength 365 nm). Immediately after exposure a substrate with photomask was removed and the relief structure in the exposed layer was measured to be ca. hequals1 micrometers deep. After that a dark self-development was allowed resulting in the increase of relief depth h up to 15 micrometers within several hours. The desired hequals7.5 micrometers needed for the most efficient performance of CO₂ laser focusing element at 10.6 micrometers and 45 degrees incidence, was stabilized by interrupting self-development with uniform UV exposure of the recorded structure.

It is demonstrated experimentally that an efficient alignment of a reactive liquid crystal (LC) mesogen is achievable by employing a relief diffraction grating having a pitch smaller than the correlation length of the LC mesogen. Full alignment of the reactive LC mesogen using a 500 lines/mm diffraction grating is confirmed by polarization microscopy. A grating of 200 lines/mm exhibited partial alignment in the deepest regions of the groove. Alignment was not maintained in areas closer to the relief profile peaks of the periodic structure (which caused the spatial modulation of the alignment to occur). UV exposure of the aligned layer allowed to permanently fix the alignment due to polymerization of the unsaturated acrylate bonds. We estimate the correlation length of the reactive mesogen from this experiment to be 5 micrometers <(kappa) <2 micrometers .

Side chain effects on phase transition temperatures, birefringence and viscosity of four series of isothiocyanato tolane liquid crystals are investigated. In the alkyl and alkoxy isothiocyanato tolane families, short chain helps suppress smectic phase, enhance birefringence and reduce rotational viscosity. In the alkoxy difluoro and cyclohexane isothiocyanato tolane derivatives, the short chain homologues exhibit an enantiotropic nematic phase. These compounds are particularly attractive for forming eutectic mixtures.