Michael J. Escuti

Tunable face-centered-cubic photonic crystal formed in holographic polymer dispersed liquid crystals

We report on the fabrication and electro-optic measurements of face-centered-cubic (fcc) lattices in holographic polymer dispersed liquid-crystal materials. Four linearly polarized coherent plane waves were interfered to generate a fcc optical lattice that was subsequently and indefinitely recorded as an arrayed pattern of nanometer-sized liquid-crystal droplets (approximately 50 nm) at lattice nodes within a polymer matrix. Observed transmission spectra and Kossel diffraction curves are consistent with fcc crystal structure. A completely reversible 2% wavelength shift of the (+/- 111) stop band was observed on application of an electric field.

Two-dimensional tunable photonic crystal formed in a liquid-crystal/polymer composite: Threshold behavior and morphology

A two-dimensional (2D) transverse square lattice is formed using holographic methods in a liquid-crystal/polymer composite through a photoinduced diffusion process. The polymer morphology is investigated using scanning electron microscopy. The kinetics of formation is described within the framework of a 2D diffusion model, and a simple phenomenological description captures the nature of the Freedericksz transition, allowing the estimation of the surface anchoring strength W≈3×10−4 J/m2.

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.

Expanded viewing-angle reflection from diffuse holographic-polymer dispersed liquid crystal films

A switchable diffuse reflective film with high color purity is demonstrated using holographic-polymer dispersed liquid crystals (HPDLC). By recording a diffuse hologram directly into the LC/polymer film, the diffuse mode HPDLC exhibit viewing angles an order of magnitude larger than the conventional mode. A simple phenomenological model based on coupled-wave theory is developed to describe our observations.

Model of the Fast-Switching, Polymer-Stabilized IPS Configuration

A significant improvement in the dynamic response times of IPS mode LCDs is achieved through polymer-stabilization. The improvement is a result of the introduction of a low-density, stabilizing polymer network that causes the LC director to favor the zero-field orientation. We report on the effect of the polymer concentration and network orientation on the electro-optic performance of our novel polymer-stabilized IPS mode cells. Furthermore, we present a detailed model derived using elastic continuum theory to explain our observations.

Optical-strain characteristics of anisotropic polymer films fabricated from a liquid crystal diacrylate

The optomechanical characteristics of oriented polymer films made from a photopolymerizable liquid crystal diacrylate (BASF LC242) were examined, with general implications for oriented films of similar materials being used and considered for display-component applications. The birefringence of these uniaxial films before and after polymerization was determined by measuring the retardation between crossed polarizers, (resulting in Δn=0.142±0.002 at 633 nm for the cured polymer films). Optical-strain characteristics were also determined by measuring the transmittance of the films between crossed polarizers at two wavelengths (612 and 633 nm) during the application of a monotonically increasing tensile strain. Under the conservative assumption that Poisson’s ratio is constant for the relatively small strains in our experiment, we develop a strained-waveplate model to detect changes in birefringence directly from the modulation in transmittance with increasing strain. We show that strain applied along the axi...

Mesoscale Three Dimensional Lattices Formed in Polymer Dispersed Liquid Crystals: A Diamond-Like Face Centered Cubic

Mesoscale three-dimensional lattices are formed in polymer-dispersed liquid crystals using one-step holographic fabrication. Nematic liquid crystal domains are patterned within a rigid polymer binder through an irradiance-driven diffusion and phase-separation process, forming a low index-contrast photonic crystals whose dielectric profile mimics the irradiance profile applied during formation. Electric fields are used to align the liquid crystal domains, allowing electrical control of the coherent scattering from these lattices. Here we present a diamond-like face centered-cubic-lattice(fcc), highlighting the several advantages over the simple fcc counterpart, including easier processing, operation in the near infrared, and deeper stopbands.

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.

An efficient illumination system for liquid crystal displays incorporating an anisotropic hologram

An anisotropic hologram is combined with an edge-lit planar waveguide to produce an improved liquid crystal display (LCD) backlight. A holographic-polymer dispersed liquid crystal material is exposed to a slanted one-dimensional interference pattern to produce an anisotropic Bragg transmission grating with strong diffraction for P-polarized light and very low diffraction for S-polarized light. While the hologram is recorded at a UV wavelength (351 nm), light at visible wavelengths propagating from the waveguide edge is redirected toward the normal direction. The emission is collimated, polarized, and unidirectional, effectively integrating several functions that are typically embodied in separate optical films in a conventional LCD.

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.