Switchable holographic gratings formed in polymer-dispersed liquid-crystal cells by use of a He-Ne laser

High-Contrast and Scattering-Type Transflective Liquid Crystal Displays Based on Polymer-Network Liquid Crystals

The methods to enhance contrast ratios (CRs) in scattering-type transflective liquid crystal displays (ST-TRLCDs) based on polymer-network liquid crystal (PNLC) cells are investigated. Two configurations of ST-TRLCDs are studied and are compared with the common ST-TRLCDs. According to the comparisons, CRs are effectively enhanced by assembling a linear polarizer at the suitable position to achieve better dark states in the transmissive and reflective modes of the reported ST-TRLCDs with the optimized configuration, and its main trade-off is the loss of brightness in the reflective modes. The PNLC cell, which works as an electrically switchable polarizer herein, can be a PN-90° twisted nematic LC (PN-90° TNLC) cell or a homogeneous PNLC (H-PNLC) cell. The optoelectric properties of PN-90° TNLC and those of H-PNLC cells are compared in detail, and the results determine that the ST-TRLCD with the optimized configuration using an H-PNLC cell can achieve the highest CR. Moreover, no quarter-wave plate is used in the ST-TRLCD with the optimized configuration, so a parallax problem caused by QWPs can be solved. Other methods for enhancing the CRs of the ST-TRLCDs are also discussed.

Optically rewritable dynamic phase grating based on blue-phase-templated azobenzene liquid crystal

We propose an optically rewritable dynamic phase grating based on polymer-templated azo liquid crystal in a blue-phase structure. The grating consists of alternating blue-phase and light-induced isotropic-phase regions, patterned by ultraviolet illumination. In the field-off state, the grating is hidden (showing no diffraction), due to index matching between the two phases. An index change is induced in the blue-phase regions when an external voltage is applied, while the refractive index of the isotropic-phase regions remains the same. The resulting periodic index modulation causes the grating to diffract light. The diffraction efficiency is independent of incident polarization, and the electro-optic response is in the sub-millisecond scale. Enabled by the reversible photoisomerism of the azobenzene, we demonstrate optical-patterning, -erasure, and re-patterning of a single liquid-crystal cell into different grating geometries.

Harnessing diffraction grating in an in-plane switching cell submitted to zigzag lattice

Programmable diffraction gratings are relevant in optical data processing. One of the adequate device candidates is the in-plane switching liquid crystal cell. This technology, developed initially for liquid crystal screens, has also been studied with two inter-digital electrodes as a diffraction grating. Recently, the apparition of programmable zigzag wall lattices in an in-plane switching configuration has been reported. Here, we report a theoretical and experimental study of programmable diffraction grating in an in-plane switching cell.

Tri-color composite volume H-PDLC grating and its application to 3D color autostereoscopic display

A tri-color composite volume holographic polymer dispersed liquid crystal (H-PDLC) grating and its application to 3-dimensional (3D) color autostereoscopic display are reported in this paper. The composite volume H-PDLC grating consists of three different period volume H-PDLC sub-gratings. The longer period diffracts red light, the medium period diffracts the green light, and the shorter period diffracts the blue light. To record three different period gratings simultaneously, two photoinitiators are employed. The first initiator consists of methylene blue and p-toluenesulfonic acid and the second initiator is composed of Rose Bengal and N-phenyglycine. In this case, the holographic recording medium is sensitive to entire visible wavelengths, including red, green, and blue so that the tri-color composite grating can be written simultaneously by harnessing three different color laser beams. In the experiment, the red beam comes from a He-Ne laser with an output wavelength of 632.8 nm, the green beam comes from a Verdi solid state laser with an output wavelength of 532 nm, and the blue beam comes from a He-Cd laser with an output wavelength of 441.6 nm. The experimental results show that diffraction efficiencies corresponding to red, green, and blue colors are 57%, 75% and 33%, respectively. Although this diffraction efficiency is not perfect, it is high enough to demonstrate the effect of 3D color autostereoscopic display.

Holographic polymer dispersed liquid crystal enhanced by introducing urethane trimethacrylate

This work characterizes holographic polymer dispersed liquid crystals (HPDLC) composite material based on a new monomer, urethane trimethacrylate, by fabricating switchable diffraction grating. The highest diffraction efficiency achieved was 90.3%. Details of the fabrication and preliminary results of electro-optical switching of the HPDLC diffraction gratings are presented and discussed based on the functionality of the monomer. These experimental results are explained by means of morphological scanning electron microscopy analyses.

Effects of monomer functionality on switchable holographic gratings formed in polymer-dispersed liquid-crystal cells

We investigate the effects of monomer functionality on the formation and switching characteristics of holographic transmission gratings in polymer-dispersed liquid-crystal cells fabricated by using the 633 nm wavelength of an He-Ne laser. We present results for the microstructure, diffraction efficiency eta, and switching characteristics of gratings formed with acrylate monomers of functionalities ranging from 2 to 4. The microstructure and diffraction efficiency are sensitive to functionality; both improve with increasing functionality. For functionalities of 2.5 or more, eta approaches 34% and can be switched off with electric fields of about 20 MV m(-1).