Suraj P. Gorkhali

Stable polarization gratings recorded in azo-dye-doped liquid crystals

We report on the design, fabrication, electro-optical performance, and stability of switchable polarization gratings formed in azo-dye-doped nematic liquid crystals. Stable gratings are demonstrated even after applying saturating electric fields (8V∕μm) and after heating to extreme temperatures (T=190°C). A simple phenomenological model is presented to show that the Freedericksz threshold voltage depends on surface and volume contributions. The observed thresholdless behavior indicates that the grating stability is consistent with a surface-stabilizing effect.

Reliability of transparent conducting substrates for rollable displays: A cyclic loading investigation

Failure mechanisms for flexible conducting substrates are investigated herein in the context of rollable/flexible display applications. Cyclic loading experiments (substrates subjected to multiple cycles of tensile strain) were carried out on both ITO-coated PET and PEDOT:PSS-coated PET substrates. The resistance was measured after each bending cycle. The resistance increased with the number of cycles and was not reversible. Even when the tensile strain on the ITO/PET was below the virgin cracking threshold (∼2%) previously reported [Appl Phys Lett76, 1425 (2000)], slight increases in resistance were measurable after just a few cycles.

Electrically switchable mesoscale Penrose quasicrystal structure

We present the design, fabrication, and electro-optical properties of a switchable Penrose quasicrystal configuration in holographic polymer dispersed liquid crystal (H-PDLC) materials using a 5-beam hololithography exposure technique. The Penrose quasicrystal structure is confirmed through diffraction patterns and scanning electron microscopy (SEM); both show the expected tenfold symmetry. We also present electro-optic switching parameters of this quasicrystal structure and determine its index modulation to be 3×10−3 using coupled wave theory.

Conformable displays based on polymer-dispersed liquid-crystal materials on flexible substrates

We have developed a process that enables one to conform polymer-dispersed liquid-crystal (PDLC) displays into a particular shape indefinitely. Planar PDLC displays are first fabricated between indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrates. This fully functional display can then be conformed to a particular shape by heating above the glass-transition temperature of PET and then allowing it to cool down to room temperature. The display retains its shape and is fully functional after processing. We have created spiral-and wave-like samples and have demonstrated their operation after the conformal process. The stress is relieved in the substrate by conforming. Temperature effects on polymer substrates were investigated for two types of polymer films (PET/ITO substrates and a conducting polymer PEDOT:PSS/PET substrate) to analyze the effects of temperature on the resistance and mechanics of the films under an applied uniaxial strain. We have found a decrease in contrast of the PDLC after conforming, but surprisingly, a reduced threshold voltage and reduced hysterisis occurs.

Two-dimensional vectorial photonic crystals formed in azo-dye-doped liquid crystals

A 2D, square lattice, vectorial photonic crystal is formed by vectorial holography using an azo-dye-doped liquid-crystal material. Four coherent beams are interfered to generate a highly stable, switchable polarization holography structure. The formation of the vectorial lattice by the liquid-crystal molecular orientation is confirmed by diffraction pattern and polarization microscopy analysis. Simulations of the alignment and diffraction pattern are in good agreement with the experimental results. Polarization sensitive diffraction behavior is also consistent with the Kakichashvili model.

47.3: Reliability of Transparent Conducting Substrates for Rollable Displays: A Cyclic Loading Investigation

Failure mechanisms for flexible conducting substrates are investigated in the context of rollable/flexible display applications. Cyclic loading experiments (substrates subjected to multiple cycles of tensile strain) were carried out on both ITO coated PET and PEDOT:PSS coated PET substrates. The resistance was measured after each bending cycle. The resistance increased with number of cycles and was not reversible. Even if the tensile strain on the ITO/PET was below the virgin cracking threshold (∼2%) previously reported [APL 76, 1425 (2000)], slight increases in resistance were measurable after just a few cycles.

L‐1: Late‐News Paper: Conformable‐Polymer Dispersed Liquid Crystals (C‐PDLC) Displays With Indefinitely Captured Form

We have developed a conformable-polymer dispersed liquid crystal (C-PDLC) by processing a PDLC material between conducting indium-tin-oxide (ITO) coated polyethylene terephthalate (PET) substrates above the glass transition temperature of the PET. After first fabricating a PDLC between ITO/PET substrates at room temperature, the display is then molded to conform to a particular template, heated above the glass transition temperature, and then allowed to cool back to room temperature where it is then released from its template. Using this process the PDLC display remains indefinitely conformed while retaining its optical functionality. We present a comprehensive study on the optical performance of these conformable displays, the processing steps necessary for fabrication, and the issues associated with the conducting substrate technology processed above the glass transition temperature.

Electrically Switchable Two-Dimensional Penrose Quasi-Crystal

ABSTRACT We present the fabrication of a quasi-crystal liquid crystal polymer morphology using holographic polymer dispersed liquid crystal (H-PDLCs). By interfering five coherent, laser beams on a liquid crystal polymer mixture, a quasi-crystal morphology can be created on the mesoscale. We present scanning electron microscope (SEM) images mapped onto the calculated irradiance profiles confirming the quasi-crystal structure. Diffraction and electro-optic data are presented in the context of potential photonic applications.

Optical Diffraction Properties of Polymer Dispersed Liquid Crystals Switched by Interdigitated Electrodes

ABSTRACT We investigated optical properties of a polymer dispersed liquid crystal (PDLC) film in-plane switched by a periodic pattern of interdigitated electrodes. Such a system acts as a thin optical phase grating which diffraction efficiency strongly depends on polarization state of the incident light. The intensity and dynamic response of various diffraction orders were analyzed as a function of the applied voltage amplitude. Our results demonstrate that by using a PDLC very effective phase gratings with response times below 10 ms can be achieved at the expense of slightly higher driving fields than needed for the similar bulk nematic liquid crystal gratings.

P-206: Circular Polarization Separation Elements for Display Applications

We report on a circular polarization discrimination element for potential use in display applications. A highly stable and efficient polarization grating based on an azo-dye doped liquid crystal (azoLC) is fabricated using a polarization holographic method. In this paper we present the design, fabrication, electro-optical characterization, efficiency and stability of these polarization gratings and their potential use in projection displays.