Driving passive‐matrix LCDs with low hardware complexity and reduced supply voltage

In passive‐matrix liquid‐crystal displays (LCDs), multiplexing is achieved by using the intrinsic non‐linear characteristics of the liquid‐crystal material. If the electro‐optic characteristic is steeper than necessary for the matrix display, the selection ratio need not be maximized. Instead, the selection ratio can be reduced to match the electro‐optic characteristics of the display. This leads to a reduction in the supply voltage of the drive electronics. We have considered the possibility of using addressing techniques with low hardware complexity along with displays having steep electro‐optic characteristics. Supply voltages for these techniques are compared with that of multi‐line addressing (MLA). The supply voltages of the Hybrid Addressing Technique (HAT), Improved Hybrid Addressing Technique‐S3 (IHAT‐S3), and Improved Hybrid Addressing Technique‐S4 (IHAT‐S4) are lower than that of MLA for the lower range of N. These hybrid addressing techniques with lower hardware complexity are a better choice for driving passive‐matrix LCDs, especially in portable equipment.     

Pixel‐isolated liquid‐crystal mode by using a patterned anisotropic phase separation for flexible LCDs

Abstract— A pixel‐isolated liquid‐crystal (PILC) mode for enhancing the mechanical stability of flexible‐display applications is proposed. Because liquid‐crystal (LC) molecules in this mode are isolated in each pixel by patterned or phase‐separated microstructures, and the two substrates are tightly attached to each other by a solidified polymer layer, the LC alignment is stable against external pressure, and the cell gap of our structure is uniformly preserved against bending deformation of the plastic substrates. The mechanical stability of the PILC structure having plastic substrates was tested for its electro‐optic properties.     

MEMS variable‐capacitor phase shifters part I: Loaded‐line phase shifter

This article describes the design and characterization of a continuously variable loaded‐line phase shifter using micro‐electro‐mechanical system (MEMS) variable capacitors as phase shifting components. The design and characterization of micro‐electro‐mechanical system (MEMS) variable capacitors for operation at 26.5 GHz is described. A lumped‐element model is obtained from measurements and physical consideration. Experimental results show a capacitance‐tuning ratio of 3.7:1. The capacitor's characterization results are used for designing the phase shifter. A phase shift of 40.5° at 26.5 GHz for a loaded‐line type has been measured. There is good agreement between simulated and measured results. A companion article (Part II) describes the application of these variable capacitors to the design of reflection‐type phase shifters. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 321–337, 2003.     

Molecular design for stabilizing a blue phase III and electro‐optical switching in the blue phase

Abstract— The molecular design of a liquid crystal to stabilize a blue phase III (BPIII) is reviewed, and the electro‐optical switching with a response time on the order of 10^?2 sec for BPIII exhibited by a novel chiral liquid crystal is reported. Binaphthyl derivatives and T‐shaped compounds are presented, and the structure‐property correlations of the chiral compounds are discussed. Two origins of the twisting power of the compounds, i.e., their inherent molecular chirality and the chirality‐induced twist conformation, play an important role in the appearance of the BPIII. Furthermore, BPIII was also induced in some binary mixtures of a host nematic liquid‐crystal possessing molecular biaxiality and a conventional chiral compound. The electro‐optical switching in the BPIII is attributed to an electric‐field‐induced phase transition between the BPIII and nematic (N) phases. BPIII is on the microscopically twisted nematic order, but is macroscopically isotropic. Therefore, the present technology can offer a pronounced black state in the BPIII without surface treatment and a homogeneous bright state in the induced N phase.     

Antiferroelectric LCD with one polarizer in a reflective configuration

A reflective antiferroelectric liquid‐crystal (AFLC) display with one polarizer is proposed. An optical retardation film was introduced into the reflective configuration to obtain enhanced electro‐optic (EO) characteristics. Numerical simulations were carried out to optimize the cell parameters so that the EO switching between the black and white states could be easily achieved. The reflective AFLC display with optimized cell parameters was found to exhibit high contrast, excellent brightness, and fast response.     

Low‐temperature‐applicable polymer‐stabilized blue‐phase liquid crystal and its Kerr effect

Abstract— A type of polymer‐stabilized blue‐phase liquid crystal, which can be used in a low‐temperature environment, is proposed. The blue‐phase range after polymerization was widened to more than 73°C, and the blue‐phase texture is very stable even at a temperature as low as ?35°C. The electro‐optical performances dependence on polymer concentration was investigated. The results indicate that the saturation voltage increases and the hysteresis enhances as the polymer concentration increases. The rise and decay times could reach as low as 391 and 789 μsec, respectively. Such material also shows good electro‐optical behavior at a temperature of ?35°C. In addition, the Kerr constant was tested under a uniformly distributed electric field to be 2.195 nm/V² at room temperature and 2.077 nm/V² at ?35°C. The Kerr constant tested under white‐light illumination was 1.975 nm/V², which shows a small dispersion.     

Fabrication of a highly bendable LCD with an elastomer substrate by using a replica‐molding method

Abstract— A highly bendable liquid‐crystal display was fabricated by using a multi‐functional elastomer substrate of self‐aligning LC molecules without any surface treatment. One of the two substrates is a plastic substrate while the other is a multi‐functional elastomer substrate produced by a replica‐molding technique. The multi‐functional elastomer substrate has pixel‐encapsulating walls that serve as spacers and provide mechanical stability and reproducibility against bending deformations. The highly bendable LCD demonstrates great flexibility, durability, and excellent electro‐optic performances in a highly bent state.     

Fast phase modulation using dual‐frequency nematic liquid crystals

Abstract— Experimental study and numerical simulations of optical phase modulators based on nematic liquid crystals characterized by frequency sign inversion of the dielectric anisotropy has been performed. The received results point out an extreme role of back‐flow effects and electro‐hydrodynamic instability, which make restrictions for creating high‐speed phase modulators with large switchable values of phase retardation. It is shown by numerical simulations that the hydrodynamic destabilization can be suppressed by decreasing the ratio of Leslie coefficients |α²/α^4,5|.     

Progress toward a liquid crystal contact lens display

A contact lens embeddable display using electro‐optic modulation was designed and fabricated. Using a guest–host liquid crystal configuration, a spherically deformed liquid crystal cell was fabricated comprising poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT : PSS) as a conductive layer and obliquely evaporated SiO₂ as an alignment layer. An additional SiO₂ buffer layer was evaporated on top of the PEDOT : PSS to overcome compatibility problems with the patterning of the photolithographically defined spacers. Although the contrast is modest, a patterned modulation could clearly be observed, indicating that our approach and fabrication process could eventually lead to a fully pixelated contact lens display.     

A dual‐cell‐gap transflective liquid‐crystal display with identical response time in transmissive and reflective regions

Abstract— A dual‐cell‐gap transflective liquid‐crystal display (TR‐LCD) with identical response time in both the transmissive and reflective regions is demonstrated. In the transmissive region, strong anchoring energy is used to decrease the response time, while in the reflective region, weak anchoring energy is used to increase the response time. And overdrive voltage technology is adopted to make the response time identical in both the transmissive and reflective regions. The device structure and operating principle of the TR‐LCD was analyzed, the anchoring energy in the transmissive and reflective regions was designed, and the response time and electro‐optic characteristics of the TR‐LCD was calculated. The simulated dual‐cell‐gap TR‐LCD demonstrated good performances.     

Plasma‐beam alignment of passive liquid crystals (Invited Paper)

Abstract— A plasma‐beam process, developed for the alignment of liquid crystals (LC) in electro‐optic applications, has been successfully applied to align “non‐standard” LC, such as crystalline materials with LC phases at elevated temperatures and reactive mesogenes. In addition to the high alignment quality of the materials, there is no need for an intermediate layer between the substrate and the LC layer. Furthermore, the construction of our source simplifies the alignment procedure of large‐area rigid substrates and the roll‐to‐roll processing of flexible films. This method opens new horizons for optical retarders and polarizers, as well as anisotropic semiconducting films for organic electronics.     

Electro‐optic effects of the optically isotropic state induced by the incorporative effects of a polymer network and the chirality of liquid crystal

Abstract— The electro‐optical properties of optically isotropic liquid‐crystalline composites prepared by in‐situ photo‐polymerization of cross‐linking monomers in the isotropic phase of chiral liquid crystals were investigated. The magnitude of the electric birefringence of the composites decreased as the chirality of the liquid crystal increased. The clear Kerr effect was observed for the composites with high chirality. A large Kerr constant, being relatively insensitive to temperature, was obtained for the composites even in a temperature range below the isotropic‐chiral‐nematic phase‐transition temperature. The response time of the Kerr effect at room temperature was on the order of tens to hundreds of microseconds.     

Substrate‐free cholesteric liquid‐crystal displays

Abstract— This paper demonstrates the first substrate‐free cholesteric liquid‐crystal displays. The encapsulated cholesteric displays are ultra‐thin (with a total thickness around 20 μm) and ultra‐lightweight (0.002 g/cm²). The displays exhibit unprecedented conformability, flexibility, and drapability while maintaining electro‐optical performance and mechanical integrity. All functional display layers are sequentially coated on a preparation substrate and then lifted‐off from the preparation substrate to form a free‐standing display. The display fabrication process, electro‐optical performance, and display flexibility are discussed.     

Practical implementation of a depth‐feeling‐enhanced two‐plane electro‐floating display system using three‐dimensional integral images

Abstract— Although there are numerous types of floating‐image display systems which can project three‐dimensional (3‐D) images into real space through a convex lens or a concave mirror, most of them provide only one image plane in space to the observer; therefore, they lack an in‐depth feeling. In order to enhance a real 3‐D feeling of floating images, a multi‐plane floating display is required. In this paper, a novel two‐plane electro‐floating display system using 3‐D integral images is proposed. One plane for the object image is provided by an electro‐floating display system, and the other plane for the background image is provided with the 3‐D integral imaging system. Consequently, the proposed two‐plane electro‐floating display system, having a 3‐D background, can provide floated images in front of background integral images resulting in a different perspective to the observer. To show the usefulness of the proposed system, experiments were carried out and their results are presented. In addition, the prototype was practically implemented and successfully tested.     

Fast full‐color reflective display via photoluminescent enhancement

Reflective displays are advantageous in applications requiring low power or daylight readability. However, there are no low‐cost reflective technologies capable of displaying bright colors. By employing photoluminescence to more efficiently use ambient light, we created a prototype display that provides bright, full color in a simple, low‐cost architecture. This prototype includes a novel electrokinetic shutter, a layer that incorporates patterned luminescent red, green, and blue sub‐pixel elements, and a novel optical out‐coupling scheme. The luminescent elements convert otherwise‐wasted portions of the incident spectrum to light in the desired color band, resulting in improved color saturation and lightness. This prototype provides a color gamut that is superior to competing reflective display technologies that utilize color filters in single‐layer side‐by‐side sub‐pixel architectures. The current prototype is capable of switching in <0.5 s; future displays based on an alternative electro‐optic shutter technology should achieve video rate operation. A transflective version of this technology has also been prototyped. The transflective version utilizes its backlight with a power efficiency that is at least three times that of a conventional liquid crystal display. These photoluminescence‐based technologies enable a host of applications ranging from low‐power mobile products and retail pricing signage to daylight readable signage for outdoor advertising segments.     

Properties of azo‐dye alignment layer on plastic substrates

Abstract— The alignment properties of the azo‐dye photo‐alignment material SD‐1/SDA‐2 on plastic substrates are investigated. Important liquid‐crystal cell parameters, such as azimuthal and polar anchoring energy, pretilt angle, voltage holding ratio, and the corresponding electro‐optical properties are presented. Excellent alignment with high anchoring energy can be achieved with a polarized UV dose less than 1.0 J/cm². A reflective six‐digit flexible passive‐matrix‐driven TN‐LCD for smart‐card applications showing excellent electro‐optical properties is demonstrated.     

Adaptive Control of the Electro‐Hydraulic Servo‐System with External Disturbances

The paper deals with the structure of the adaptive control electro‐hydraulic servo‐system (EHSS) with external load disturbances, practical verification of the identification, and control algorithms. The electro‐hydraulic servo system composed of a servo‐cylinder controlled with a servo‐valve is discussed. It is a strongly nonlinear object with parameters changing over time. Adaptive adjuster parameters were determined by means of current identification resulting in the parametric model. Identification was conducted on the basis of measurement of the controlling size and regulated size objects. The identified model of the object was applied to carry out the on‐line synthesis of the proportional–integral–derivative (PID) controller. The selected problems connected with obtaining the algorithm of adaptive control are presented. The computer program for implementing the algorithm with numerical simulation and identification of the control physical model object were calculated. The aim of the research was to examine the effectiveness of the adaptive control method in an electro‐hydraulic servo system, both theoretically and experimentally.     

Maximizing electro‐optic performances in the fringe‐field switching liquid crystal mode with negative dielectric anisotropic liquid crystal

The fringe‐field switching (FFS) mode that uses liquid crystals (LCs) with negative dielectric anisotropy is used in high‐resolution FFS liquid crystal display owing to its higher transmittance over positive LC, although its response time becomes slow and operating voltage (V_op) becomes high. In the device, reduction of the cell gap is required to achieve fast response time, which results in increase in V_op in general. In this paper, we propose the FFS mode with electrode width 1 µm and distance between the electrodes 1.5 µm. In such an electrode structure, V_op decreases with decreasing cell gap to 2 µm so that a proper V_op, high LC's light efficiency of 90%, a high color temperature, and a fast response time less than 10 ms, can be achieved, which maximizes electro‐optic performance of the FFS mode.     

Switchable helical holographic structures

Abstract— A 3‐D array of helical structures fabricated using holographic polymer‐dispersed liquid crystals (H‐PDLC) is presented. Multiple coherent beams are interfered to create a constructive helical pattern which is permanently captured using the standard H‐PDLC method. Films with such array of helical structures have both diffractive and circular polarization sensitive reflective properties. Iso‐intensity patterns, design parameters, fabrication process, optical/electro‐optical performance of these periodic helical structures are discussed along with their potential application for advanced electro‐optical devices.     

Inverse display characterization: A two‐step parametric model for digital displays

Abstract— A simple additivity model is often used as a basic model for digital‐display characterization. However, such a simple model cannot satisfy the needs of demanding color‐management applications all the time. On the other hand, systematic sampling of the color space and 3‐D interpolation is an expensive method in terms of measurement and computation time when precision is needed. This paper presents an enhanced method to characterize the XYZ‐to‐RGB transform of a digital display. This parametric method exploits the independence between the luminance variation of the electro‐optic response and the colorimetric responses for certain display types. The model is generally applicable to digital displays, including 3‐DMD projectors, single DMDs, CRTs, LCDs, etc., if the independence condition is satisfied. While the problem to solve is a 3‐D‐to‐3‐D transformation (from XYZ to RGB), the proposed parametric model is the composition of a 2‐D transform followed by a 1‐D transform. The 2‐D transform manages the chromatic aspects and, in succession, the 1‐D transform manages the luminance variations. This parametric digital model is applicable in the field of color management, with the objective of characterizing digital displays and applying a reference look such as a film look.