Response Time Of Liquid Crystal Research Articles

Correlations between liquid crystal director reorientation and optical response time of a homeotropic cell

Correlations between the director reorientation time and its consequent optical response time (both decay and rise) of a homeotropic liquid crystal (LC) cell under crossed polarizers are derived theoretically based on small angle approximation. Results indicate that the optical response time is linearly proportional to the LC director reorientation time and is weakly dependent on the initial bias voltage. To validate the derived correlations, transient phase and transmittance responses at various bias voltages are analyzed numerically by solving the Erickson–Leslie equation. Pretilt angle is found to make an important contribution to the optical response time. Gray scale switching of the homeotropic cell is also investigated.

LP‐13: Late‐News Poster: A Study of Motion Adaptive CODEC Feedforward Driving without SDRAM

AbstractAuthors have been engaged in the development of a feed forward driving technique, as part of the overdrive technique to improve the response time of liquid crystal displays. They have developed, in particular, a compression feed forward driving system in which an image compression technique was applied, focusing on a method of reducing the frame memory necessary for the signal processing of overdrives. Further, they are now studying motion adaptive CODEC feed forward driving that reduces the amount of overdrive errors by adding a motion‐adaptive process to the image decoding section in cFFD. This paper discusses macFFD that does not use SDRAM as the overdrive for entry model LCD TVs. Setting the image compression ratio to 1/10 or so will enable the fabrication of frame memory for overdrive for SDTV using SRAM.

43.3: Summary of Moving Picture Response Time (MPRT) and Futures

AbstractMoving Picture Response Time (MPRT) measurement method has discussed with several companies since 2001. The basic MPRT is designed to represent and quantify the visual perception of moving images across an AM‐LCD screen for PC monitor and TV applications. MPRT measurement method takes into account three basic LCD panel characteristics: the capacitive‐hold‐type brightness variations, brightness level dependent transition times and a liquid crystal response time including gray scales transition. This measurement system incorporates the synchronously moving some combined gray scale test patterns and the evaluation of the pattern edge brightness changes. MPRT keyword is for only liquid crystal display. But this measurement method can be used to specify new index parameter that is motion blur characteristics on each display devices (PDP, CRT and etc).

Reducing the memory of compression Feedforward driving for a new LCD controller

Abstract— The authors have studied a method of reducing the frame memory for signal processing used to improve the response time of liquid crystals. Compared with cases in which quantization is used, the compression Feedforward driving method, which reduces frame memory by applying an image‐compression technique, can effectively reduce the frame‐memory size. The study revealed that errors decrease by 6–10 dB or so if the image data was reduced to 1/3 by means of image compression. Based on the results of the study, the authors have developed a second‐generation LCD controller. With just one SDRAM unit, this LCD controller can produce almost ideal processing effects.

Curing temperature effects on liquid crystal gels

The curing temperature is found to greatly affect the operating voltage, contrast ratio, hysteresis, and response time of the reversed-mode liquid crystal (LC) gels. For the gels using E48 LC host, the optimal curing temperature is around 40–50 °C. An LC gel with contrast ratio exceeds 2000:1 (at ∼2° collection angle), operating voltage lower than 7 Vrms, and response time of about 20 ms is demonstrated. Potential applications of such LC gels for optical switches, displays, and switchable polarizers are emphasized.

31.2: Proposal of the Perceptive Parameter Motion Picture Response Time (MPRT)

AbstractThe proposed Motion Picture Response Time (MPRT) measurement is designed to represent and quantify the visual perception of moving images across an AM‐LCD screen. MPRT measurement method takes into account three basic LCD panel characteristics: the capacitive‐hold‐type brightness variations, brightness level dependent transition times and a liquid crystal response time. Further, MPRT figure is affected by a back light control method and video signal processing algorithms. The proposed measurement method incorporates the synchronously moving test pattern and the evaluation of the pattern edge brightness changes.

Improvement of the Response Time of Super Thin Film Transistor Liquid Crystal Displays by Using a Backlight System

To enable application to full moving images, the response time of liquid crystal displays (LCDs) must be improved. In this paper, we will discuss our results of improving the response time using the blink backlight system. When the display image changes from black to white, the lamp turns on after the rise of the LCD response. On the other hand, when the display image changes from white to black, the lamp turns off before the LCD response falls. The total response time of the super thin film transistor (TFT)-LCD was improved from 25 ms to 8 ms, which corresponded to the lamp response time. Moreover, the response time was dependent on the fluorescence wavelength of the lamp material. The blue fluorescent lamp (CFL) material has the fastest response time, 2 ms. If the response time of green and red fluorescent materials can be improved similarly to the blue one, it will be possible to obtain a moving picture quality comparable to that of a cathode-ray tube.

Optimized active-matrix drives for liquid crystal displays

A combination of computer simulation and experimental methods is used to provide a reliable and systematic means of optimizing the response time of active-matrix liquid crystal displays. Optical transients are measured and simulated (within a continuum elastic framework including hydrodynamic backflow) and are thereby related to director reorientation processes under various driving conditions. We find that an unconventional “overdrive” method, in which the device is briefly biased to a voltage exceeding the target voltage, leads to dramatic improvements in device response time which approach a factor of 6 in some cases. The computational model is capable of accurately predicting the optimum overdrive voltage. The physical origins of these findings and the importance of hydrodynamic backflow are discussed.

Spontaneous polarization and response time of polymer dispersed ferroelectric liquid crystal (PDFLC)

Results reported on the spontaneous polarization, switching time and rotational viscosity measurement of a FLC compound in neat phase and that in polymer matrix in the present paper. Polymer-dispersed ferroelectric liquid crystal film was formed by photopolymerization due to polymerization induced phase separation. A detailed study has been made on the spontaneous polarization, switching time at different temperatures and measuring field. It has been observed that the magnitude of spontaneous polarization of the PDFLC mixture is not in accordance with their mixing ratio. The switching time in PDFLC mixture is less than that in neat FLC mixture.

Dynamic holographic telecommunications components based on spatial light modulation with pixelated χ(2) polymers in a Fabry-Pe´rot cavity

The provision of a range of wavelength division multiplexing (WDM) network component functionalities by ferroelectric liquid crystal (FLC) spatial light modulators (SLMs) has already been demonstrated in both transmissive and reflective arrangements. The FLC-SLM reconfiguration rate is limited to ~100 kHz by the liquid crystal response time. x(2) nonlinear optical polymers (NLOPs) might form the material basis of a future generation of faster and less costly SLMs for WDM applications, with response time limited only by electronic RC product. We present a theoretical analysis and the experimental characterization of single-pixel SLMs based on an ~2-?m film of commercially available x(2) NLOP in an asymmetric Fabry-Perot (AFP) cavity. Rigorous modeling enables optimization of the generic pixel design and specific pixel parameters, with the design guidelines and constraints dictated by the context of wideband WDM operation ~1.55 ?m. Polymer films are poled at a low field of ~35 V/?m and a 10-V modulating signal is applied. A modulation depth of 1.4% is provided by an AFP device of optimal pixel structure. Further characterization reveals a 3-dB width of transmitted intensity modulation ~10.8 nm near 1.55 ?m. The modeled behavior is extrapolated to yield two significant performance indicators. One indicator is that the holographic diffraction efficiency n of a full-scale pixelated AFP NLOP-SLM will be principally phase-modulation-dependent if the polymer Pockels coefficient r13 is of the order of 5 pm/V. For the preferred reflective geometry, the diffraction efficiency has a maximum value of ~13.5% cf. ~40% for a binary phase FLC-SLM. The second indicator is that for experimental devices, the 3-dB bandwidth of n~1.55 ?m will be only ~5 nm, but a~190 nm-thin cavity-optimized structure will have y3dB of ~30 nm.

Addressing requirements for chiral smectic liquid crystal active backplane spatial light modulators

Abstract An account is given of the charge effects associated with chiral smectic liquid crystal switching. It is noted that below a certain Ps ‘fast’ scan switching, i.e. switching where the addressing time is less than the liquid crystal response time, is possible for binary switching. However at higher values of Ps the liquid crystal must be addressed at approximately its optical response time. For analogue switching the ‘fast’ scan option is not generally useful. Addressing schemes designed to maintain overall charge balance for binary switching are described. In most cases these schemes require an inverse frame or a blanking pulse to achieve this. For some applications the loss of validity of the image thus produced renders these schemes unsuitable and schemes to overcome this are presented. They rely on bistable switched states. A brief account is given of possible schemes for analogue switching.

Optical resonant system for measurement of liquid crystal display response times

A novel method is reported by which the alignment response time of liquid crystals contained in a display may be measured by a relatively simple and inexpensive system. The method has the advantage that the output is in the frequency domain and is strongly intensity independent. The dependence of the resonance frequency of the system with temperature is measured, and it is envisaged that the system can be further miniaturized to serve as a compact optical temperature sensor.

Infrared Properties Of Nematic Liquid Crystals: An Overview

Infrared properties and electro-optic effects of nematic liquid crystals are reviewed. Physical origins and characterization techniques of infrared birefringence and rotatory power are described. Advantages and disadvantages of three device configurations--parallel, twisted, and perpendicular alignments--are analyzed. Among them, parallel alignment shows the best potential for long-wavelength applications. Several methods for improving the response times of nematic liquid crystals with emphasis in the infrared region are briefly discussed.

Phase retardation dependent optical response time of parallel-aligned liquid crystals

Correlation between the director reorientation and its consequent optical response time of the parallel-aligned nematic liquid crystals was investigated. This optical decay time is found to depend on the phase retardation introduced by the liquid-crystal layer. To verify theory, dependence of optical decay time on three parameters—liquid-crystal thickness, wavelength, and birefringence (through temperature effect)—was demonstated. Taking the phase retardation dependence into consideration, the optical decay time measurement technique is a simple, convenient, and accurate method for characterizing the ratio of rotational viscosity and splay elastic constant of liquid crystals.

Determination of the rotational viscosity from the director pattern relaxation in twisted nematic cells

The rotational viscosity γ1 is an essential physical quantity directly related to the response times of liquid crystals. We have developed a new method to determine γ1 which utilizes the capacitive detection of the director pattern relaxation in a twisted nematic cell upon switching off the applied voltage of the twisted nematic liquid-crystal display. Measurements have been performed on two liquid-crystal mixtures. The agreement between the results obtained with the new method and those obtained from a magnetic field-induced nematic deformation method is quite satisfactory.

Pulse stretching of Q-switched laser emission by intracavity nonlinear ellipse rotation

Stretching of Q-switched laser pulses has been investigated using an intracavity nonlinear loss element based on the ellipse rotation effect in liquid crystals EBBA and MBBA. The roles of Q-switching speed, liquid crystal response time, and ellipse rotation coefficient were studied. Experimental results with a ruby laser and theoretical calculations based on modified Statz-deMars rate equations are presented.