Search

An improved dynamic driving scheme is proposed to eliminate data-pattern-dependent defects in cholesteric LCD images by inserting a framing voltage pulse between each successive selected pixel voltage pulse, such that the effective selection time is independent of the preceding and following non-selected pixel voltages.

The impact of Fresnel's reflection from a clear optical film, a polarizer, and a reflective polarizer on light recycling in a variety of LCD backlight configurations is investigated. It is found that Fresnel's reflection plays an important role in on-axis and off-axis gain, and this reflection results in higher gain at an angle near Brewster's angle in a horizontal plane in the presence of a polarizer with its pass axis in the horizontal plane.

We use the Jones matrix method to develop a numerical method which can be used to calculate the reflection of cholesteric liquid crystals. We derive the formula for the propagation of normally incident light in a cholesteric liquid crystal with multiple reflections taken into account. Using the derived formula, we numerically calculate the reflection spectra of the cholesteric liquid crystal under various conditions, and compare them with the results obtained using the Berreman 4 × 4 method.

We studied the orientation of nematic liquid crystals when they were being filled into cells by capillary action. We found that, in the flow front, the liquid crystal was always aligned along the flow direction. Far behind the flow front, the orientation of the liquid crystal depended on the anchoring direction of the alignment layers and the direction and speed of the flow. In cells with the anchoring direction parallel to the flow direction, the liquid crystal always oriented along the flow direction. In cells with the anchoring direction perpendicular to the flow direction, at low flow speed gradients, the liquid crystal orientated uniformly along the anchoring direction; at high flow speed gradients, the liquid crystal in bulk was tilted to the flow direction. The experimentally observed critical flow speed gradient was in agreement with the theoretical prediction.

To understand the mechanism behind the pitch change during the transient planar to the planar state transition of a cholesteric liquid crystal (while it is relaxing from the homeotropic state to the planar state), we studied a more controlled situation of pitch change in a thermochromic liquid crystal. We studied the pitch change in the liquid crystal, as a function of temperature, under various surface alignment conditions such as homogeneous and homeotropic surface alignments. In a cell with homogeneous surface treatment, the liquid crystal showed a discontinuous pitch change, while the pitch change was rather continuous in a cell with homeotropic treatment. The numerical simulations also showed an existence of continuous pitch change in a homeotropic cell, but not in a homogeneous one. This led to a prediction that when a cholesteric material is switched from the homeotropic state to the planar state, the transition may be much faster for the homeotropically treated cell as compared to the homogeneously treated cell. We performed experiments to verify this prediction with a chiral nematic mixture. Indeed, the homeotropic to planar state transition time of a homeotropic cell was 5 msec, much faster compared to about 200 msec for corresponding transition in a homogeneous cell.

By the decoration-iteration transformation, we find a general relation between interaction parameters of a general spin-1 model on any lattice with unique coordination number and on its decorated lattice. We obtain three exact phase transition points of the general spin-1 model on two-dimensional decorated lattices in terms of the exact results of the model on corresponding two-dimensional regular lattices, including the triangle, square, kagome and honeycomb lattices. We find the critical temperatures have no exact relation with the average coordination number and the type of coordination number for both the Ising model and the general spin-1 model.

We study Ising model on Sierpinski carpets by using mean field theory. We find a phase transition at which is dependent on the geometrical factors. The critical exponents are calculated and found to be the same as the values for translationally invariant lattices.

We have found that ionic effects play an important role in driving cholesteric liquid crystal displays. The ions change the effective electric field inside the liquid crystal and help to create nucleation seeds for transitions. These effects reduce the driving voltages by about 10%, make the response of the liquid crystal faster, and result in a higher contrast ratio.

We describe a novel two-slope turning film (TSTF) that improves light utilization efficiency. As a result, the TSTF both improves on-axis luminance and widens viewing angle. The TSTF lowers power consumption for notebook and mobile displays.

Crossed A-plates are known to exhibit properties similar to a negative C-plate. Extending this concept, we examined compensation schemes for Twisted Nematic (TN), Optically Compensated Birefringence (OCB), and Vertically Aligned (VA) modes. By adjusting the tilt angle profile and the phase retardation, considerable improvements in contrast ratio over a wide viewing angle have been achieved for these modes.

Improved wide viewing-angle polarizers are proposed that employ symmetrically identical compensator designs having relaxed manufacturing tolerances relative to their orientation to the transmission axis of the polarizer. These designs can be realized in numerous ways and can comprise two A-plates, one A-plate and one C-plate, or one biaxial plate.

— A digital cinema projector that utilizes three JVC QXGALCDs, and provides 12,000 lumens, 2000:1 contrast, and 3-Mpixel resolution was developed. This system, which was described in a prior paper (see Ref. 10), has a novel optical configuration based on the use of intermediate imaging optics and wire-grid polarizers and is described in greater detail in this paper. The polarization optics, including the polarization compensators, contribute to a system that provides high contrast at a low f/#, with a wide color gamut and minimal color shading at high power.

Flexible displays having a polymer dispersed cholesteric layer, a dark layer and a thin electrical conductor have been found to respond to a combination of high-intensity xenon flash energy and electrical field. A variety of writing schemes have been discovered. Simple super-twisted-nematic displays can be used as an imaging mask. The technology further permits dry fingerprint imaging through contact printing.

We have investigated a new design for a turning film used in combination with wedge-shaped light guide plates. The selected design has a top periodic lenticular structure that is in registration with the bottom periodic prisms. Relative registration shift in the prisms and the top lenticular structure was found to be beneficial. Use of such turning film drastically enhances the on-axis brightness.

Design rules for wire grid polarizers, used as polarizing beamsplitters and reflective polarizers for polarization recycling, are found to be different. Wire grid polarizers with low fill factors of ∼0.18–0.25 are found to be more efficient in polarization recycling than regular polarizers with fill factors of ∼0.4–0.6.

A bistable flexible electronic display has been developed based on photographic technology, processes, and materials. Using photographic film coating techniques, an aqueous cholesteric liquid crystal dispersion, a dielectric layer, and a dark layer were deposited onto patterned transparent conductors on a polymeric web. Second conductors were printed over the active display layers to complete display manufacture in a roll-to-roll process. Simple seven-segment displays and matrix displays have been generated using these techniques. The displays can use contact electronics to eliminate drive cost from the displays. Several prototype applications were demonstrated. Displays produced with these processes were low-cost, thin, flexible, passively driven, and retained an image without an applied electric field.

High pretilt angle can help stabilizing the desired bend configuration of π-cells but also changes the electro-optical behaviors. We report here a study on how the pretilt angle affects the electro-optical properties of π-cells, including the critical voltages needed to stabilize the bend configuration, the minimum voltages needed to turn the π-cells fully on, the cell gap required to produce the desired π phase retardation, the transmittance-voltage curves, the response time, and the viewing angle characteristics. The results provide a guidance to construct π-cells with various pretilt angles.

We numerically study the dynamic process of transitions among textures in bistable cholesteric reflective displays, and analyze the effects of the parameters: surface anchoring, applied field, cell thickness, pitch and elastic constants. Our result shows that fast homeotropic-planar transition, essential in order to use cholesteric liquid crystals in video rate operations, can be achieved using cells with homeotropic anchoring.