J. A. M. M. van Haaren

8.1: Novel High Performance Transflective LCD with a Patterned Retarder

For a better optimization of the transflective AM-LCD, a new technology with extra free parameters is inevitable. Our novel transflective AM-LCD with in-cell patterned retarder enables us to optimize further, resulting in a good brightness, contrast ratio, viewing angle and low chromaticity for reflection and transmission at the same time.

The possibilities of ferroelectric liquid crystals for video displays

— Different approaches were used to examine the possibility of using surface-stabilized ferroelectric liquid-crystals (SSFLCs) in video displays. The advantages of such displays lie in the viewing-angle independence and the high switching speed. The large number of gray levels needed for video can, in principle, be obtained by digital or analog techniques. From simulation experiments on a high-resolution CRT, it is estimated that for video, for the case of equidistant luminance levels, 128 levels for each primary colour are needed. Discrete gradation by means of bi-level subpixels (spatial dither) is simulated for projection and direct-view displays. Efficient subpixelation (minimum number of extra connections) results in perceptual artefacts when the three primary colours (RGB) are projected onto each other, as in a projection system. In the case of a direct-view display with mosaic colour filter, the layout of this mosaic turns out to be more important than subpixelation. Analog gradation methods are based on in-pixel domain switching effect. They require accurate control of the multidomain structures. Active-matrix addressing for the SSFLC strongly enhances the reproducibility of the multidomain gray levels via the charge-control process. This is demonstrated on test displays. Passive-matrix addressing takes advantage of the bistability and switching speed of the SSFLC effect. One approach to control the multidomain gray levels in passive-matrix addressing is the “texture method,” which is based on a distribution of the threshold voltage for switching within each pixel. The mechanism, the addressing scheme, the obtainable contrast in the different textures, the applicability of various FLC mixtures, and the resulting temperature sensitivity are discussed. The performance of test displays, operating at video rate, is evaluated. Several issues, such as temperature sensitivity, texture stability, and hysteresis in the transmission-voltage curve have to be further improved.

Temporal behaviour of the electroclinic effect in chiral smectic A

Abstract We have measured the temporal behaviour of the electroclinic effect in chiral SmA by monitoring the optical response to a square voltage pulse as function of the pulse height for various small cell gaps. We corrected for the distortion of the pulse shape as arriving at the liquid crystal layer due to the RC-time of the cell. (Here R is the resistance of the ITO contact leads, and C is the cell capacitance.) The Garoff and Meyer dynamical formula (Phys. Rev. Lett. 38, 848 (1977)) with the aforementioned correction was shown to correctly describe the temporal behaviour of the induced tilt angle. However, the electroclinic response time τ depended on the applied electric field E and the cell gaps d. The static, equilibrium value of the induced tilt angle did not depend on d and remained linear in E down to values of 0.1 V/μm, which agrees with results of a continuum theory calculation. We believe that the d and E-dependence of τ is caused by the aligning interaction of the boundaries, which gains im...

51.4: Fast Addressing of Cholesteric Texture Liquid Crystal Displays

Long addressing times form a problem for the application of CTLC displays in, for example, an electronic book, and inhibit displaying moving images. We investigated methods to improve the addressing time by addressing several rows at a time. This multiple-row addressing method was combined with single-phase addressing and three-phase addressing. In the case of single-phase addressing, this led to image artefacts. With three-phase addressing, however, the display performance was good and high frame rates were demonstrated. This addressing scheme allows for fast updating of very high resolution CTLC displays.

Elastic parameters of smectic C∗ liquid crystals

Numerical simulations of the electro-optic properties of smectic C∗ liquid crystal layers can be helpful in the research into and development of displays. A major problem is that the number of elastic parameters that is open to experimental determination is less than the number of parameters that occurs in the elasticity theory for the smectic C∗ phase. Two elastic parameters contained in a simplified expression for the deformation energy are experimentally determined for the smectic C∗ material ZLI 3654 (Merck, Germany). The accuracy of the measured results is discussed.

Pretilt angle measurements on smectic A cells with chevron and tilted bookshelf layer structures

Abstract We have measured the pretilt angle induced by rubbed polymer films in a smectic A and in a nematic liquid crystalline medium using an optical phase retardation method. The pretilt angle was found to depend on the liquid crystalline phase (smectic A versus nematic) and on the smectic layer structure (chevron versus tilted-bookshelf). The occurrence of the different smectic layer structures was verified by X-ray diffraction measurements. The effect of the applied rubbing energy on the pretilt angle obtained is measured.

Pushing the limits of optical storage

Philips Research has been working on improvements of optical disc storage technology for three decades. In this period, optical discs have become the technology of choice for storing and sharing of data on removable media. In 30 years we have made an improvement of about 2 orders of magnitude in both data rate and storage density. The new Blu-ray Disc (BD) optical storage system offers 25 GB on a single layer, with 36 Mbps base data rate. Philips has made an optical pick-up unit with a single lens and a single detector that can be used for BD as well as for DVD and CD. We doubled the BD-storage capacity and increased the data rate by another order of magnitude in our two-dimensional optical storage format TwoDOS. Furthermore, we are exploring near-field optical storage for capacities beyond Blu-ray Disc. By using a solid immersion lens in a conventional actuator, we have realized an experimental laboratory system with remarkable robustness. We have found that near-field optical storage may be used on discs that have a cover layer to protect the data from scratches.

Switching on stray electric fields in ferroelectric liquid crystal cells

Abstract In liquid crystal dot-matrix displays light may leak through the display area between the pixels. To obtain sufficient contrast this non-pixel area has to be made non-transmissive. For ferroelectric liquid crystal (FLC) displays this may be done by switching the material in the gaps between the picture elements to a non-transmissive state by the stray electric fields that occur during application of voltages to the pixel electrodes. This is experimentally studied for test cells with an electrically modified smectic layer structure. The gap region considered is an asymmetric environment of the FLC material, as the transparent conductive coating has been removed on one substrate, whereas on the other substrate a conductor covers the glass. The FLC molecules in the non-pixel area prefer to direct their dipoles towards the covered substrate. To switch the FLC material with the stray electric fields, it is a prerequisite to outweigh this preference. We made spatially resolved observations for various ...

Electrohydrodynamic instabilities in chiral smectic C cells

Abstract Experimental results are presented on the optical response of chiral smectic C cells of various thicknesses (between 2 and 9 μm) on AC voltages. For part of the voltage and frequency range the electric field induces patterns of disclination lines. The threshold voltages for these electrohydrodynamic instabilities turn out to be independent of the cell thickness for 4, 6, and 9 μm cell gaps. In the 2 μm cells, structural changes of the chiral smectic C texture are found at voltages below the threshold for the instabilities. The applicability of the Carr-Helfrich model for electrohydrodynamic instabilities in nematics to these chiral smectic C layers is discussed.