Chris C. Bowley

Variable-wavelength switchable Bragg gratings formed in polymer-dispersed liquid crystals

We report a holographic polymer-dispersed liquid crystal cell whose reflection peak can be tuned as a function of applied voltage. Electro-optic results are presented which are in excellent agreement with our model based on coupled wave theory.

Enhanced dynamic response of the in-plane switching liquid crystal display mode through polymer stabilization

A significant improvement in the dynamic response time of the in-plane switching nematic liquid crystal mode, useful in flat-panel display applications, is achieved through polymer stabilization. This improvement is achieved by introducing a low-density, stabilizing polymer network that causes the nematic director to favor the zero-field orientation at the expense of transmission and slightly higher drive voltages. We present a simple model that treats the polymer network as an effective field in the general framework of elastic continuum theory.

Multiple gratings simultaneously formed in holographic polymer-dispersed liquid-crystal displays

We report single-layer holographic polymer-dispersed liquid-crystal materials with multiple reflection and/or diffraction gratings. Three switchable gratings are observed in a single film formed in a three-beam interference pattern. Two reflection gratings and one transmission grating are formed, corresponding to each of the three possible two-beam interference fringes. We present scanning electron microscopy and electro-optic results which are in good agreement with our model based on matrix methods and coupled-wave theory.

Morphology of Holographically-Formed Polymer Dispersed Liquid Crystals (H-PDLC)

Abstract Photopolymerization induced phase-separation of liquid crystal/polymer mixtures in holographic gratings show promise as switchable Bragg reflectors for optical communication and reflective display applications. The electro-optic properties of such Holographic Polymer Dispersed Liquid Crystals (H-PDLCs) are strongly dependent on polymer morphology and the degree of separation of the LC/polymer mixture. We report scanning electron microscopy, optical polarizing, and electro-optic studies on H-PDLC materials.

P-60: Spatially Pixelated Reflective Arrays from Holographic-Polymer Dispersed Liquid Crystals

In this paper, we report on multiplexing techniques to create multicolor reflective displays formed in holographic polymer dispersed liquid crystals using a single holographic exposure through spatial color synthesis techniques. We present the electro-optical performance parameters of these color-reflecting arrays, and describe our fabrication process.

Reflection from dual-domains in a holographically-formed polymer-dispersed liquid crystal material

A holographically-formed polymer-dispersed liquid crystal is reported with two distinctive reflective states brought about by a single laser exposure of a liquid crystal-rich emulsion. The two reflective states are the result of two structurally different domains that are formed during the holographic cure. A simple phenomenological model is presented that describes the dual-domain effect.

Improving the voltage response of holographically-formed polymer dispersed liquid crystals (H-PDLCs)

Abstract We report a significant improvement in the switching voltage of holographic PDLCs. This is achieved by doping the prepolymer with small amounts of organic surfactants. The effect of these dopants on other important H-PDLC performance parameters is also investigated. Possible explanations for the reduction in switching voltage are discussed in relation to simple phenomenological switching models.

Two Wave Mixing in Holographic Polymer Dispersed Liquid Crystal (H-PDLC) Formation

Abstract The intensity of transmitted laser beams is monitored during the holographic formation of polymer dispersed liquid crystal gratings. Significant attenuation of the total transmitted intensity is experienced after brief illumination. In most cases the attenuation increases for several seconds before reaching a steady-state value. Analysis of the individual beam intensities reveals energy exchange between the beams in a nonlinear two-wave mixing process. This information is analyzed to help gain insight into the complex dynamics of H-PDLC formation.

HPDLC color reflective displays

We have carried out experiments and simulations to optimize the materials and processes for fabricating holographically formed polymer dispersed liquid crystal (HPDLC) devices. Bright reflective HPDLC displays with peak reflection above 60% have been achieved with fast, sub-millisecond (tau) ON + (tau) OFF switching speed. The switching voltage has been reduced by more than a factor of 2 by selecting appropriate liquid crystal and polymer materials and by the addition of surfactants. The viewing angle of HPDLCs has been extended by a novel fabrication technique. We have fabricated color HPDLC demonstration displays by stacking red, green, and blue HPDLC layers and have achieved the widest color gamut that has ever been reported for a reflective display. The methods for making these novel color reflective displays and the measured are presented.

P-58: Diffuse H-PDLC Reflective Displays: An Enhanced Viewing-Angle Approach

We demonstrate a Holographic-Polymer Dispersed Liquid Crystal (H-PDLC) with an enhanced viewing-angle, formed by writing a diffuse hologram structure directly into our H-PDLC material. We model the diffuse H-PDLC reflectance by summing over the contributions of discrete grating domains of differing orientations. We use a normal distribution function to weight each orientation to describe the grating densities. SEM studies were performed to determine the morphologies and orientations of multiple gratings within the sample.