TN LC Research Articles

Electrically tunable metasurface in TN LC configuration with enhanced quality factor and metaatom-induced alignment.

Dynamic metasurface with subwavelength dimensions has emerged as a key optical technology in recent years. Although various active tuning mechanisms are being proposed, liquid crystal-based dynamic metasurface remains attractive due to its large index variation, electrical tunability, reliability, and mass fabricability. In this work, we report a dynamic metasurface for amplitude modulation in reflection, with twisted nematic liquid crystal configuration to reduce broadband reflection in the off state. The metasurface consists of coupled subwavelength grating fingers, which provide alignment for the liquid crystal without the need for an additional alignment material or process. The alignment of liquid crystal materials was examined between crossed polarizers, and the twist of nematic liquid crystal was confirmed. The coupled grating fingers exhibit a resonance quality factor of 27 at telecommunication wavelength and an amplitude modulation depth of 8 times of the minimum at 1630 nm. This work highlights the potential of liquid crystal-based tunable metasurface, combining polarization control via liquid crystal and spectrum control via metasurface. Furthermore, it also shows a way in which the interaction between liquid crystal and metasurface is used for an alignment layer-free cell assembly process.

10‐4: Stereoscopic / Light Field Hybrid Head‐mounted Display by Using Time‐multiplexing Method

Stereoscopic / Light Field Hybrid Head‐mounted Display was proposed to avoid accommodation — convergence conflict and improve the resolution of light field image. This new system generate images in LF and stereoscopic mode, further producing hybrid images by the visual persistence of human eyes. To build a mechanism for the time‐multiplexing of the polarized light, we designed and fabricated a micro‐lens array with the liquid crystal material. Specifically, with the function of TN cell and LC MLA, Hybrid HMD could time‐multiplex two images in flicker‐free frame rate. In our results, the resolution of hybrid image can be significantly enhanced from 5.5 ppd to 10 ppd in horizontal direction and 6.2 ppd to 15.9 ppd in vertical direction.

Large-aperture transparent beam steering screen based on LCMPA.

A large aperture transmissive step-steering screen composed of a liquid crystal microprism array (LCMPA) deflector and a 90° twisted nematic liquid crystal (TN LC) polarization modulator is developed. The designed 3 in. (7.62 cm) device provides a steering angle of 0.95° that differs from the projected value by only 1.26% and the angular difference caused by dispersion is less than 5%. Using two-layer cascaded screens a three-direction beam steering system for stereoscopic displays is achieved with a steering step of 0.95°, undesired residual polarization contrast less than 2%, and high optical uniformity.

Applying a Self-Made Automobile Heterodyne Interferometer to Measure the Parameters of Twisted Nematic Liquid Crystal

A self-made automobile heterodyne interferometer with a closed control loop is presented. In addition, we will apply the self-made automobile heterodyne interferometer to measure the parameters of optically compensated twisted nematic liquid crystal (TN LC). It is worthy to be mentioned that the self-made automobile heterodyne interferometer has a compact size because all the optical components are installed in the mechanism of the system. Besides, the self-made automobile heterodyne interferometer has some much more merits, for example, automobile control, a simple setup, in real-time test, reliability, and so forth. Besides, it is very stable because of its common optical path insensitive to environmental disturbances. And its feasibility is demonstrated.

33.1: Implementation of Mobile Hi‐Resolution TFT‐LCD with Color‐Sequential Driving Schema

AbstractChunghwa Picture Tubes LTD. has successfully developed the 2.8‐inch TN‐type mobile hi‐resolution TFT‐LCD module using color‐sequential driving method in 5‐mask a‐Si Processes. DT‐LPAD structure is designed specially for the mobile hi‐resolution TFT‐LCD, which can make the data addressing period and BRD addressing period overlapped in color‐sequential driving period. Due to the overlapped driving, we can attain the scanning‐BL driving method and four fields driving methods to improve the efficiency of transmission and to reduce color‐breakup phenomenon. Hence, the driving frequency and power consumption are reduced directly and the display shows better quality. The main features of our mobile hi‐resolution display module include 480 × 640 resolution, TN Type Liquid Crystal (Response Time is less than 5ms by high speed TN LC and low cell gap), wider color gamut and high color expression characteristic (NTSC 96%), and the BL power consumption is similar to commercial 2.8‐inch TFT‐LCD.

P‐95: Implementation of TN‐Type Color‐Sequential TFT‐LCD with Low Power Array Design (LPAD) Structure and Black Data Rehashed Driving (BRD) Schema

AbstractChunghwa Picture Tubes LTD. has successfully developed the 4 inches TN‐type Color‐Sequential TFT‐LCD module with LPAD (Low Power Array Design) structure and novel driving method named Black Data Rehashed Driving (BRD) schema. LPAD structure is designed specially for Color‐Sequential TFT‐LCD, where a pixel consists of only one dot and each pixel are rearranged according to the output polarity of source drivers to obey the dot inversion policy. Hence, the power consumption is reduced directly.We also invent the novel driving method BRD to drive the TN‐type Color‐Sequential display by black field insertion without extra cost. The main features of our TN‐type Color‐Sequential display module include 480 × 272 resolution, TN Type Liquid Crystal (Response Time is less than 8ms by high speed TN LC and low cell gap), wider color gamut and high color expression characteristic (NTSC 96%), and the power consumption of panel is similar to commercial 4 inches TFT‐LCD.

P-153: Flexible Photoaligned Optically Rewritable LC display

Flexible optically rewritable reflective TN LC display based on photoalignment technology has been demonstrated. The rewritable display does not require any electronic scheme, power supply, or conductive layers, when operating. Such a display can erase and write images for many times because of LC alignment reorientation onto one photoalignment layer under exposure of a polarized UV light. The image can be saved with a very high contrast for a long time.

Eigenmodes of a reflective twisted-nematic liquid-crystal cell

The eigenmodes of a reflective twisted-nematic liquid-crystal (TN LC) cell are analyzed based on the Jones matrix method. Two models are developed to describe the LC system in the low- and high-voltage regimes. The simulated transmission spectra of LC Fabry–Perot etalons are used to investigate the eigenmodes. In a general reflective TN LC cell, the eigenmodes are two orthogonal linear polarization states. Under some specific conditions, these two linear polarization states will approach the bisector or orthogonal to the bisector of the TN LC cell. This bisector effect is useful for reducing the operating voltage and enhancing the contrast ratio of LC display devices and for eliminating the mode coupling of the tunable Fabry–Perot etalons.

53.2: A Goniometric Reflective Display Measurement System and its Application to the Measurement of Pretilt for 45TN Mode LCoS Displays

AbstractWe have designed and built a goniometric display measurement system, which allows a direct measurement of the viewing angle performance of reflective displays. We have used this system to measure contrast over viewing angle. Additionally, we have developed a simple and quick method for measuring the pretilt of LCoS displays using a 45 TN LC mode, and have also applied Isocon to the measurement of polarization over viewing angle and applied voltage.

P‐24: Incorporation of Optiva Polarizers in LCD Production Line

AbstractA new concept of a production line for fabrication of LC displays with Optiva polarizers is discussed. Depending on LCD design the polarizer may be formed at diverse stages of the LCD process. A common approach and basic features of incorporation of new polarizer in LCD mass production are considered. Prototype equipment was fabricated and sample TN LC displays were produced to demonstrate the viability of this new technology.

Cell Gap Measurement Method for Single-Polarizer Reflective Liquid Crystal Cells

A novel method to measure the cell gap of a single-polarizer reflective twisted nematic liquid crystal (TN LC) cell by using a spectrometer is proposed. By rotating a LC cell, we can measure the cell gap of a LC cell as well as the wavelength dependence of retardation Δnd.

P‐25: An Accurate Spectral Method for Measuring Twist Angle of Twisted Cells with Rubbed and Grooved Surfaces

AbstractAccurate optical method for measuring twist angle in TN LC cells is presented. Deviation of the measured values for different orientations of the cell and polarizes have been analyzed. The method allows to determine twist angle with high accuracy for cells with rubbed surfaces as well as for cells where at least one surface is corrugated.

17.4: Novel Liquid‐Crystal Materials with High Birefringence and Low Rotational‐Viscosity for the Field‐Sequential Color TN‐LCDs

AbstractLiquid crystal (LC) materials with features of coexistence of high birefringence and low rotational‐viscosity were developed, by introducing novel class of tolane substances. Those LC mixtures exhibit voltage‐holding‐ratio high enough for active matrix addressing, and their excellent physical properties improve the TN‐mode display performances significantly. The extremely fast switching characteristics enable TN LC panels to be applicable to field sequential color displays.

The contrast ratio in twisted nematic with black dichroic dye LCD

The paper presents results of studies on TN LC mixture containing black dichroic dye. The general information concerning a principle of action of TN display with a dye is given. Contrast ratio of a display for different dye concentration and angle characteristic of contrast at room temperature is presented.

Optimization of light‐valve mirrors

Abstract— A mirror structure for reflective Si‐based light valves was fabricated using chemical‐mechanical polishing and a thin 150‐nm Al(Cu)/Ti mirror to minimize hillock formation. The use of chemical‐mechanical polishing planarization resulted in only a 1% loss in reflectivity from topography under the mirrors. The reflectivity for pixel sizes from 7.5 to 40 μm and 0.7‐ or 0.5‐μ.m gaps were measured, and the performance of TN LC pixels with different sizes and inversion methods are reported.

40.4: Optimization of Light‐Valve Mirrors

AbstractA mirror structure for reflective Si based light valves was fabricated using chemical mechanical polishing and a thin 150 nm Al(Cu)/Ti mirror to minimize hillock formation. The use of chemical‐mechanical polishing planarization resulted in only a 1% loss in reflectivity from topography under the mirrors. The reflectivity for pixel sizes from 7.5–40 μm and 0.7 or 0.5 μm gaps were measured and the performance of TN LC pixels with different sizes and inversion methods are reported.

A Novel π/2 and 5π/2 Twist Bistable TN Cell

AbstractWe have developed a novel π/2 and 5π/2 twist bistable TN LC cell. The optical properties of such bistable TN LCD was optimized by a parameter space approach. The switching behaviour was investigated using several switching waveforms. Greyscaling was found to be possible in this bistable TN LCD.

Comparison of Temporal Changes of Molecular Alignments in a Twisted Nematic with a Supertwisted Nematic Liquid Crystal

The lagging effect of LC molecular alignments was studied through conoscopic figures in both a twisted nematic liquid crystal (TN LC) and a supertwisted nematic (STN) LC. The time required for the effect to show in STN LC was shorter than the time in TN LC. The time difference depended on film structure and the applied voltage, but it did not depend on the duration after the voltage was applied. It was qualitatively expressed by an equation of alternating current circuit considering the inductance which represents the inertial force. It became clear that the energy required for a tilt angle of 90 degrees could be reduced by using a double-block-pulse method instead of the method of a continuously applied electric field.

Effect of the Pretilt Angle and Temperature on the Multiplexing Limits of Dual Frequency Addressed TN–LC Cell

We present below the results of (our studies on) dual frequency addressed twisted nematic liquid crystal (TN–LC) cells using recently developed Hoffmann La-Roche LC mixtures 3090 and 2851 which exhibit large positive and large negative dielectric anisotropy at low and high frequencies respectively. It is found that the surface alignment i.e., the tilt bias angle of LC molecules at the bounding surfaces and the temperature of the cell modify the electro-optic transmission characteristics significantly which in turn affect the multi-plexing limits. It is also shown that the cross over frequency `fc' can be easily determined from the threshold voltage variation studies with frequency.