Ferroelectric and antiferroelectric liquid crystals have shown great promise for use in large area flat panel displays because of their fast switching and bistable operation. However, the commercialization of FLCDs and AFLCDs using surface stabilized geometries has not materialized for a number of reasons, most notably shock instability, the need to control the cell spacing of the display to between 1 and 2 micrometer, and competition from actively addressed nematic displays. Surface stabilized displays are nevertheless finding niche markets in areas such as spatial light modulators, microdisplays, and projection systems. Even though this is the present situation, it is clear that FLCs and AFLCs will be used advantageously in the future in active matrix configurations to give LCDs that operate at video-frame rates. Furthermore, there are many emerging uses for such materials in the areas of photonics and sensors e.g., novel switching and wavelength filtering components based on liquid crystal phase modulators and filters. There is also interest in utilizing LC technology in fiber optic networks, telecommunication transmission systems, interconnecting networks in large computers, optical image processors, and optically accessible electronic memory structures. All of these applications require fast switching materials that are stable and non-absorbent to light of various wavelengths.

The recent move towards liquid crystal displays based on the electrically controlled birefringence (ECB) effect of the vertically aligned nematic (VAN) material has brought improvements in terms of contrast, viewing angle and switching times. However, different types of nematic liquid crystalline materials are required with a negative dielectric anisotropy, in addition to the usual requirements such as low viscosity, optimized mesomorphic behavior, and tailored elastic constants and birefringence. There are particular difficulties in generating the ideal combination of mesomorphic and physical properties in such materials. This paper outlines the various liquid crystal display device configurations in terms of the material requirements, and discusses in more detail the design, synthesis, mesomorphic and physical properties of suitable nematic materials of negative dielectric anisotropy.

The optically induced reorientation of nematic liquid crystal doped with azo-dye substituted polymer is investigated measuring photoinduced birefringence. These measurement reveal the value ((Delta) n approximately 0.1) of induced birefringence of liquid crystal with dye polymer which significantly exceeds the value of birefringence previously obtained in nematic mixture with the low molecular weight dye. More than one order of enhancement is connected with lower diffusivity of polymer. Applications for fiber all-optical switch and nonlinear filtering are suggested.

Antiferroelectric liquid crystal materials are very promising for high-resolution displays but so far suffer from two serious problems, both of which reduce the achievable contrast. These materials are first of all very hard to align to a high quality dark state. Most often this has been attributed to the fact that antiferroelectric materials lack a nematic phase. We believe, however, that there are other reasons behind the bad dark state as well, and that these reasons may be even more important. In addition antiferroelectric materials show a thresholdless linear electro-optic effect, conventionally called the 'pretransitional effect,' which gives a dynamic contribution to light leakage under addressing conditions. We have synthesized and now describe a new type of antiferroelectric material which gives an unprecedented black state due to a high static extinction as well as to the absence of a pretransitional effect. The performance of conventional antiferroelectric liquid crystal displays will be considerably enhanced with this kind of material. Among the numerous non- conventional electro-optic applications of the new material several polarizer-free display modes are described together with fast photonic modulation devices.

The use of liquid crystal devices for wavefront control has been suggested and implemented by several authors. Our group has been at the forefront of the development of this technology. In this paper we report some preliminary experimental results on the use of Nematic based liquid crystal devices. Several experimental efforts have been carried out in the past few months. One of the main aims was to characterize a new devices that uses dual frequency nematic material.

Photoluminescent liquid crystal displays use a phosphor screen to separate internal light traversing a liquid crystal display (LCD) from light seen by the viewer. The internal light is narrow bandwidth UV and can be spatially directed. The diffuse phosphor emissions transform the angular viewing characteristics of conventional LCDs to the almost perfectly wide, uniform characteristics of a cathode ray tube. This type of display has the potential to exceed the power efficiency of current LCDs and can boost electro-optic performance in such a way as to give, for instance, enhanced multiplexing in passive matrix displays. The continuous phosphor screen and separate light paths enable truly seamless tiling for the production of large-screen direct-view displays. Here we briefly review photoluminescent LCD operation and describe the main design criteria. Three product-focused architectures are discussed and the current state of the art described for each.

The ability of surface relief gratings to align liquid crystals has been known for many years. Renewed interest has recently been stimulated through the invention of novel devices in which the grating gives the additional benefit of bistability. This allows complex images to be retained without constant updating, and without the need for Thin Film Transistors at each pixel. Two types of bistable liquid crystal have been demonstrated: azimuthal bistability using bi-gratings, and zenithal bistability using gratings that give surface alignment to the liquid crystal director parallel to the local surface normal. The latter type is called ZBD and gives exceptional performance compared to all other bistable display technologies. This is because the nematic liquid crystal has different tilts in the direction of the applied field, allowing latching times of better than 40 microseconds (at 30 V) and switching thresholds below 10 V. The orientation of the liquid crystal is not required to change at the surface when switching between the two states and so there are no problems with image sticking. Also, the bistability is surface induced, which makes the states exceptionally tolerant to mechanical stress. An 83 by 90 pixel display is demonstrated, illustrating the potential of this exciting new technology.

Liquid crystals have been investigated for acoustic imaging purposes for more than 20 years, however, their practicality has become apparent only recently through a number of technological developments. This has led to the development of the world's first liquid crystal based acoustic imaging system, which is finding commercial applications. This paper will discuss some of the fundamental technical progress that was needed to make liquid crystal based acoustic imaging a reality. Numerous current and potential uses of the liquid crystal based acoustic imaging approach will be discussed, including nondestructive testing, underwater mine detection, medical imaging, etc.

The MicroDisplay Corporation's liquid crystal on silicon (LCOS) display devices are based on the union of several technologies with the extreme integration capability of conventionally fabricated CMOS substrates. The fast liquid crystal operation modes and new scalable high-performance pixel addressing architectures presented in this paper enable substantially improved color, contrast, and brightness while still satisfying the optical, packaging, and power requirements of portable applications. The entire suite of MicroDisplay's technologies was devised to create a line of mixed-signal application-specific integrated circuits (ASICs) in single-chip display systems. Mixed-signal circuits can integrate computing, memory, and communication circuitry on the same substrate as the display drivers and pixel array for a multifunctional complete system-on-a-chip. System-on-a-chip benefits also include reduced head supported weight requirements through the elimination of off-chip drive electronics.

The liquid crystal adaptive lens (LCAL) is an electro-optical device using a set of electrodes to grade the refractive index across its aperture. We report initial efforts at developing an LCAL using circular electrodes to provide a simpler architecture and faster response than previous devices based on linear electrodes. A Fresnel lens phase profile is applied to yield a lens with a useful F-number. Numerical simulation is developed to study the aberration of the LCAL and predict its performance with a circular electrode geometry. The LCAL is designed with a set of high density electrodes in the conductive ladder meshing configuration which results in a small number of externally controlled electrodes. A new feedback auto-focusing system based on LabVIEW software has been developed to optimize control output voltages using signals from a CID camera. The application of LCAL in microscope imaging systems for focus adjustment without lens motion is described. A prototype LCAL is being designed that has a 7.86 mm diameter aperture and a focal length adjustable from 0.38 m to infinity. It is fabricated on a glass substrate with two layers of transparent electrodes, insulating layers, and vias to connect the two conducting layers. The special fabrication challenges involved will be reviewed.

Novel electro-/photoactive multifunctional dyes were synthesized based on dithienothiophene, DTT ((pi) -center), linked by an electron D/D -- or D/A pair segment; D-(pi) -D (dye 1) or D-(pi) -A (dye 2), to develop efficient bipolar light-emitting (LE) materials capable of balanced electron/hole capture in a single-layer LE device. A strong bipolarity manifested by electrochemical amphotericity was observed notably with dye 1, which cannot be accounted for without the involvement of the (pi) -center, leading to the low HOMO/LUMO energy-gap and a small difference in the energy-gap between dye 1 and dye 2. Single-layer LE devices were fabricated by making a blend based on the dye (0.5 wt%), PVK (70%) as matrix and PBD (30%) as electron-transporting/hole blocking material, and by sandwiching between ITO and Al electrodes. PL intensity of the dyes by excitation at 440 - 450 nm ((lambda) _max) is much weaker compared to that at 340 nm (exciting mainly PVK), suggesting that the excitation of the dyes occur by energy-transfer from PVK. When compared PL intensities between the two dyes at a concentration less than 1%, dye 1 is slightly higher relative to dye 2. In contrast, the EL intensity shows an opposite trend in that dye 2 is much higher relative to dye 1 under the same condition. This implies that unlike the PL, the EL is not due to the transfer of the excited-energy from PVK but carrier trapping/exciton formation on the dye chromophore, and that dye 2 is strongly bipolar and thus more capable of balanced carrier capture.

Enhancement of Laterally Emitting Thin Film Electroluminescent (LETFEL) outcoupling efficiency has been achieved via the introduction of a novel outcoupling mechanism, the surface emitting edge emitter. This method incorporates PECVD SiO₂ microstructures underlying the device thin films at the device apertures which consequently bend the LETFEL structure at these locations. Additional etching of the bent thin films provides shaped edges at both sides of the aperture which outcouple the internally generated light as conventional edge emitters. Comparison of the conventional non etched and the surface emitting edge device light outputs demonstrates an improvement in the outcoupling efficiency by a factor of 4 at 620 Volts. Additionally, a Gaussian angular distribution with a FWHM approximately 40 degrees has been measured from each edge, being the Gaussian maximum coincident with the microstructure wall side angle. In this research 45 degree wall sided microstructures have been utilized however, perpendicular microstructures are proposed to further enhance the coupling efficiency for the two main LETFEL applications, Head Mounted Displays (HMDs) and Electrophotographic Printing (EP). The fabrication route which successfully defines the surface emitting edge mechanism is presented for the first time; this incorporates Ion Milling as the sputter etch technique to shape the device aperture.

In this paper we report recent results from an ongoing program designed to develop a fundamental understanding of the effects of materials, vacuum deposition parameters, and post fabrication processing on the performance of field-emitter arrays for displays. Molybdenum and silicon have been the materials of choice for first generation displays, and have produced acceptable results for the first trials. However, investigations of other emitter materials such as diamond- like-carbon (DLC) and zirconium carbide (ZrC) have produced intriguing improvements in emission performance. In addition in situ processes such as coating of molybdenum and silicon emitters with alternate materials and aggressive emitter- surface cleaning processes such as hydrogen-plasma cleaning and emission-stimulated desorption by high-current pulses, have also been shown to be beneficial. It has also been shown that when using the Spindt emitter fabrication process the emitter cone can be tailored to a preferred shape by appropriate materials selection and manipulation of the emitter deposition parameters. Finally, it is shown that the details of the emitter tip shape can have an impact on the performance of the emitter due to the dynamics of temperature and field-induced surface diffusion during cathode operation. Emitter tips of the same material, operated in the same environment and at the same emission levels can behave very differently depending on the details of the emitter-tip geometry.

We have developed a process for coating individual phosphor particles with different coating compositions. The phosphor is suspended in a solvent containing the appropriate coating material precursors (alkoxides, or metal salts). Coating deposition is via a sol-gel technique. The suspension is sprayed into a hot zone to dry. Coating thicknesses of 10 and 90 nm have been achieved in a single pass. Testing shows that the coated phosphor efficiency is not degraded, while the aging behavior is improved.

V-shaped switching in the smectic-C* like phase of a three- component mixture has been studied from the viewpoint of surface behavior. Two alignment layers, polyvinylalcohol (PVA) and polyimide (PI), were used to study the effect of alignment layer. Electro-optic, switching current and dielectric measurements were conducted using cells with various cell thicknesses. The PI cells exhibit V-shaped switching, though the PVA cells show bistable switching, clearly indicating the importance of alignment layer to realize V-shaped switching. The specialty of the three-component mixture was confirmed in the cell thickness dependence of the dielectric strength (Delta) (epsilon) and the relaxation time (tau) _r. Namely, (Delta) (epsilon) and (tau) _r show linear dependences on the cell thickness and does not saturate even in 50 micrometer cells, which are quite different from those in conventional ferroelectric liquid crystals. Attenuated total internal reflection ellipsometry was made to evaluate the molecular orientation and switching behavior near the surfaces. It was found that the orientation and the switching characteristics are almost the same as in the bulk, i.e., (1) molecules are aligned along the layer normal at 0 V, which is deviated from the rubbing direction by about 10 degrees, and (2) switching occurs collectively without threshold.

Remarkable enhancement of second-harmonic (SH) generation in a ferroelectric liquid crystal was theoretically studied. The enhancement occurs when SH wavelength coincides with the wavelength at odd-number-th dips of subsidiary oscillation in one edge of the selective reflection band. To interpret this behavior, the electric field of inhomogeneous and homogeneous SH light in a cell was simulated for a right-handed (R) ferroelectric liquid crystal. It was found that R-circularly polarized light forms a standing wave inside the cell at the odd-number-th dips, when two counter-propagating beams with the same polarization (e.g., R-R) are incident. On the other hand, inhomogeneous and homogeneous waves are out of phase to each other at the bounding surface at the even-number-th dips, so that no enhancement occurs. As for an incidence of R- and L-polarized light, enhanced SH light is generated only toward the R-incidence side. The SH light is L-polarized in this case, while R-polarized SHG is observed from both sides for the incidence of counterwaves with the same polarization.