Nematic Liquid Crystal Display Research Articles

Real‐Time Jones Matrix Synthesis by Compact Polarization Inline Holographic Microscopy

AbstractThe Jones matrix is a powerful quantitative tool for polarimetric imaging and characterization, where the matrix elements represent the intrinsic optical properties of the anisotropic objects on interaction with the polarized light. Most of the state‐of‐the‐art single‐shot Jones‐matrix imaging techniques rely on interferometric methods, which makes the design complex with the use of large number of polarization optics and produces space‐bandwidth limitations. The simultaneous extraction of Jones matrix elements with a compact system design is still a technical challenge in view of its potential applications in biomedical and real‐time characterization scenarios. In this paper, the imaging features of the in‐line holography are exploited to develop a compact polarization in‐line holography (PIH) system capable of single‐shot extraction of Jones‐matrix elements. The technique achieves simultaneous orthogonal polarization state generation and corresponding polarization multiplexed in‐line hologram detection by utilizing a compact polarization geometry. The imaging compatibility and measurement accuracy of the method is experimentally validated by the real‐time synthesis of Jones‐matrix elements corresponding to custom designed polarization sensitive samples and standard birefringent resolution target. Furthermore, to demonstrate the application of the system in dynamic imaging, the transient polarization changes of a custom‐designed parallel nematic liquid crystal display (LCD) are investigated.

P‐12.4: Low Voltage Switchable Bistable Twist Nematic Display

The most common electronic paper technology is E‐ink, which enables many novel applications such as e‐readers, watches and electronic shelf labels. However, due to the TFT backplane driving and complex production processes, the cost of this technology is high, which limits its popularity. Recently, a low‐cost π‐bistable twist nematic (π‐BTN) liquid crystal display with a high pretilt angle is proposed. It has the same structure and production method as an ordinary liquid crystal display. Passive driving enables the manufacture of high‐resolution bistable displays without the use of thin‐film transistors. Compared with the current bistable twist nematic display technology, the high pretilt angles structure helps to achieve a lowvoltage and fast‐respond bistable display. This wide viewing angle, high contrast and TFT‐free display is a promising candidate for flexible displays.

The Effect of Chemically Modified Multi-Walled Carbon Nanotubes on the Electro-Optical Properties of a Twisted Nematic Liquid Crystal Display Mode

In this study, we have chemically modified multi-walled carbon nanotubes (MWNTs) with different side chains for better dispersion in liquid crystal solutions, and fabricated twisted nematic liquid crystal cells doped with such MWNT derivatives. The introduction of MWNT derivatives affects the alignment of LC molecules with or without external electric fields. Electro-optical property tests showed that the contrast ratio changed slightly with the sharp decrease in drive voltage, improving the drive ability of the twisted nematic liquid crystal display (TN-LCD) mode.

A Resolution-Enhanced Digital Micromirror Device (DMD) Projection System

In this paper we present a resolution-enhanced system for digital micromirror device (DMD) projected images by utilizing time multiplexing and birefringence in order to achieve this with static components only. This provides a less expensive solution than reducing the size of the hardware pixels and can also be applied to higher resolution displays, as and when, these become available. Birefringent materials have different refractive indices for linearly polarized light with orthogonal polarization directions. A high-resolution projected image can be observed by overlapping two or three native resolution images at shifts of one half or one third of a DMD pixel diagonal respectively on successive frames. The optical components comprise a custom-made quartz plate as the birefringent component and an off-the-shelf twisted nematic liquid crystal display (TN-LCD) screen as a polarization rotator that is synchronized with the DMD frame rate. This paper covers the principle of operation and the system design. The functioning of the display is verified using enlarged images of the letter `R' and a checkerboard pattern that are formed from a small number of DMD pixels.

Interpretation of frequency modulation TN-LCD embedded with metal nanoparticles using equivalent circuit analysis

A twisted nematic (TN) liquid crystal display (LCD) with embedded Ag nanoparticles (NPs) covered with a diffusion cloud exhibits peculiar frequency dependent behavior. In particular, no TN response is observed below the dielectric relaxation frequency, fR, whereas above this frequency, revival of the TN response occurs. Such a device is called a frequency modulation (FM) TN-LCD, and its behavior is attributed to the reduction of the dielectric anisotropy Δɛ far below the relaxation frequency, fR. However, above this frequency, the revival of the torque driving the TN-LCD occurs, and the TN-LCD operation is revived with a fast response speed. The reduction of Δɛ may be due to the prevalence of the amplified dielectric constant caused by the inclusions covering the entire region. However, above fR, this amplification gradually vanishes, and the normal TN-operation is revived due to the revival of dielectric torque force. In this paper, an interpretation of the FM-LCD operation through dielectric spectroscopy and equivalent circuit analysis is presented. Interpretation of the dielectric constant amplification [whose factor, AC, is equal to 52 through a postulation of negative ɛ2 for the inclusions (NPs and diffusion cloud)] is also presented.

P‐136: A Low Voltage, Switchable, Bistable‐Twist‐Nematic Display

The most common electronic paper technology is E‐ink, which enables many novel applications such as e‐readers, watches and electronic shelf labels. However, due to the TFT backplane driving and complex production processes, the cost of this technology is high, which limits its popularity. Recently, a low‐cost π‐bistable twist nematic (π‐BTN) liquid crystal display with a high pretilt angle is proposed. It has the same structure and production method as an ordinary liquid crystal display. Passive driving enables the manufacture of high‐resolution bistable displays without the use of thin‐film transistors. Compared with the current bistable twist nematic display technology, the high pretilt angles structure helps to achieve a low‐voltage and fast‐respond bistable display. This wide viewing angle, high contrast and TFT‐free display is a promising candidate for flexible displays.

Influence of γ-Fe2O3 nanoparticles doping on the image sticking in VAN-LCD

Image sticking in liquid crystal display (LCD) is related to the residual direct current (DC) voltage (RDCV) on the cell and the dynamic response of the liquid crystal materials. According to the capacitance change of the liquid crystal cell under the DC bias, the saturated RDCV (SRDCV) can be obtained. The response time can be obtained by testing the optical dynamic response of the liquid crystal cell, thereby evaluating the image sticking problem. Based on this, the image sticking of vertical aligned nematic (VAN) LCD (VAN-LCD) with different cell thicknesses (3.8 μm and 11.5 μm) and different concentrations of γ-Fe2O3 nanoparticles (0.017 wt.%, 0.034 wt.%, 0.051 wt.%, 0.068 wt.%, 0.136 wt.%, 0.204 wt.%, and 0.272 wt.%) was evaluated, and the effect of nano-doping was analyzed. It is found that the SRDCV and response time decrease firstly and then increase with the increase of the doping concentration of γ-Fe2O3 nanoparticles in the VAN cell. When the doping concentration is 0.034 wt.%, the γ-Fe2O3 nanoparticles can adsorb most of the free impurity ions in liquid crystal materials, resulting in 70% reduction in the SRDCV, 8.11% decrease in the decay time, and 15.49% reduction in the rise time. The results show that the doping of γ-Fe2O3 nanoparticles can effectively improve the image sticking of VAN-LCD and provide useful guidance for improving the display quality.

Multi-layer protruded electrodes for reducing the operating voltage and gamma shift of fringe-field switching LCDs

ABSTRACTTo reduce the operating voltage and gamma shift of the nematic liquid crystal display (LCD), a single-domain-protruded fringe-field switching (PFFS) electrode structure is designed. In this work, a kind of nematic liquid crystal (NLC) is introduced firstly. Then, the operating voltage and gamma shift of the proposed PFFS LCD are investigated under various electrodes’ parameters. Besides, its light leakage and contrast ratio are also discussed. The results show that the operating voltage of the PFFS LCD is only 1.40 V, here the electrodes’ width is 2 μm and electrodes’ gap is 4 μm. The gamma shift of the PFFS LCD can be reduced to the indistinguishable level under various electrodes’ sizes, if the height of the insulation layer is proper. For contrast ratio, it is larger than 200:1 at full viewing-angle, and the zone of 500:1 covers 60° polar angle.

Time-dependent color simulation of active-matrix liquid crystal display adopting the field sequential driving method

A time-dependent display color simulation method is proposed. For the time-dependent simulation, we applied our behavioral model of liquid crystals (LC). The model provides the transient response characteristics of the LC. The color simulation of a twisted nematic active matrix liquid crystal display (AMLCD) adopting a field sequential (FS) driving method is possible when combining the transient LC responses with periodically operating red-greenblue (RGB) light emitting diodes (LEDs). By modifying the gate start pulse of the conventional AMLCD, we created a virtual AMLCD driven by the FS method. The color performance of the panel was measured at five vertical positions, and the results showed that the RGB LEDs should be driven by a 70% duty parameter and a 50% shifting parameter to minimize line-to-line color characteristic deviations in the AMLCD panel. By using the proposed simulation method, it is possible to find the optimal FS driving condition for any display with arbitrary response characteristics to exhibit the best color performance.

Global characterization of nematic liquid crystal display Sony LCX038ARA with applied electric field in the modulation amplitude-coupled regime

In this work, we showed experimental and theoretical results of the characterization of a spatial light modulator based in a nematic liquid crystal display Sony model LCX038ARA with electric field excitation. The parameters: effective molecular twist and equivalent retardation are determinated using the retarder-rotor technique in the amplitude-coupled regime.

Liquid crystal displays, LC-materials and LPP photo-alignment

ABSTRACTThe invention of the twisted nematic liquid crystal display (TN-LCD) by Schadt and Helfrich in 1970 started the development of field-effect LCDs.Today, LCDs are the dominant flat panel display technology. Milestones in the ongoing research and development are sub-millisecond responding nematic liquid crystal (LC) materials, integration of silicon-driving electronics into display substrates, complex optical thin-films enabling excellent image quality and, last but not least, high resolution, contact-free photo-alignment/pattering of monomeric liquid crystals in displays and surface-aligned liquid crystal polymer (LCP) optical films. Photo-alignment of liquid crystal molecules by the linear photo-polymerization (LPP) technology enables high resolution, fast responding multi-domain LCDs with broad fields of view and complex, ultra-thin liquid crystal polymer retarder films. LCD-applications range from reflective displays for digital watches with virtually zero power consumption to large-area flat television screens with photographic resolution as well as to optical security elements and integrated optics devices. The commercial impact of the global LCD technology is illustrated by its annual turnover above $140billion.The seminar gives a personal overview of the multidisciplinary efforts between applied physics, material sciences and engineering which have enabled nematic liquid crystals of becoming the dominant flat panel display technology since 1970.

Entanglement-free determination of pretilt angles of twisted nematic liquid-crystal cells by phase measurement

The pretilt angle of a twisted nematic (TN) liquid crystal display has a strong effect on viewing angles and response times of the display as well as shifting the light-leaking disclination lines into the black-matrix area within pixels of a thin-film-transistor driven TN panel for a high contrast ratio. In this Letter, we develop an optical method to determine the TN pretilt angle based on heterodyne measurements of the phase versus the incident angle of a thin TN cell subjected to out-of-plane rotations. We believe that our method of measuring phases has advantages of simpler setup and calculations, better stability, and less sensitive to ambient electromagnetic interference than the commonly used method of measuring intensities.

High-Performance and Low-Cost Aluminum Zinc Oxide and Gallium Zinc Oxide Electrodes for Liquid Crystal Displays

The majority of electro-optical devices use transparent conductive oxide (TCO) electrodes such as indium tin oxide (ITO) in their structure. In this study, we manufactured aluminum zinc oxide (AZO) and gallium zinc oxide (GZO) TCO films on glass substrates and demonstrate suitability of these materials for application as transparent electrodes of liquid crystal displays (LCD). We have established a deposition process for the fabrication of AZO and GZO coated glass substrates with average transmittance of 93% and 92% in the visible spectrum, and the sheet resistivity without annealing of ∼120 Ω/□. Using photolithographic patterning and wet etching of AZO and GZO films, we have successfully fabricated laboratory prototypes of twisted nematic, vertical alignment, in-plane switching, and fringe-field switching LCDs. The electro-optical performance of AZO and GZO prototypes is comparable to those of the ITO prototypes of identical design. The AZO and GZO have demonstrated great potential to compete with ITO as low-cost TCOs for display applications. Our findings validated by numerical analyses will be useful for the development of TCOs alternative for display and other optical or electro-optical applications.

Liquid Crystal Alignment on Solution Derived Zinc Oxide Films via Ion Beam Irradiation.

A 75-nm-thick ZnO film was deposited by a sol-gel method on indium-tin oxide (ITO)-coated glass. This film served as a liquid crystal (LC) alignment layer. We report the fabrication and characteristics of this film after ion-beam (IB) irradiation. Uniform LC alignment was achieved at an IB incident energy above 2400 eV. The IB-treated ZnO surface was analyzed by X-ray photoelectron spectroscopy (XPS), monitoring the intensity of the Zn 2p and O 1s peaks as a function of IB-irradiation energy density. The electro-optical (EO) characteristics of a twisted nematic-liquid crystal display (TN-LCD) were comparable to rubbed polyimide.

Circularly Polarized Luminescence and a Reflective Photoluminescent Chiral Nematic Liquid Crystal Display Based on an Aggregation‐Induced Emission Luminogen

Circularly Polarized Luminescence and a Reflective Photoluminescent Chiral Nematic Liquid Crystal Display Based on an Aggregation‐Induced Emission Luminogen

Super-fast switching of twisted nematic liquid crystals with a single-wall-carbon-nanotube-doped alignment layer

The application of a single-wall carbon-nanotube (SWCNT) and polyimide (PI) composite thin film on an indium tin-oxide (ITO) glass substrate, working as the command surface in a twisted nematic liquid crystal display (LCD), is described. SWCNTs were chopped and oxidized in a strong acid medium to make them more miscible in a polyimide solution. A film of this newly-developed PISWCNT composite was rubbed to determine the director direction for the LC molecules. The newlyfabricated command surface was examined using a laser beam profiler and atomic force microscopy. Sizes of shortened SWCNTs were characterized by using field-emission scanning electron microscopy (FE-SEM). Finally, small-sized test panels were fabricated from this composite-coated ITO glass, and their electro-optic performances were measured. Although the operating voltage to switch a cell was increased by around 41%, the switching speed was improved remarkably. The rise time of the test cells was found to be improved by around 10.12% and the decay time by around 29.77%. Thus, an overall improvement of around 16.12% in the total switching time was achieved. The change in the surface morphology of the newly-developed composite materials was found to be one of the factors responsible for the faster switching of the device. Detailed discussions are given in this report to explain the faster switching of the newly-developed twisted nematic liquid crystal display (TN-LCD). The device can be useful for practical applications.

P‐120: Nucleation‐control Bistable Twist Nematic Display

AbstractA fast π bistable twist nematic (π‐BTN) liquid crystal display controlled by nucleation process is developed. The nucleation induced by the patterned spacer inside the cell. The response time is fast and it depends on the density of patterned spacer.

High-transmittance liquid-crystal displays using graphene conducting layers

We report the use of graphene as a highly transparent conductive film in liquid-crystal displays (LCDs). Graphene films were synthesised via chemical vapour deposition, transferred onto glass substrates, and then used to fabricate typical twisted nematic LCD cells. LCD cells using graphene as transparent electrodes exhibited optical transmittances 7.7% higher than LCD cells fabricated using conventional conducting layers based on indium tin oxide (ITO) films. The device characteristics of LCD cells based on graphene electrodes, such as threshold voltage and voltage holding ratio, were comparable to those of conventional LCD cells based on ITO electrodes. These results indicate that graphene is a promising transparent conductive film compared to ITO, yielding LCDs with significantly improved optical transmittance.

Generation of three-dimensional optical structures by dynamic holograms displayed on a twisted nematic liquid crystal display

Reconstruction of computer generated holograms (CGHs) addressed on a spatial light modulator (SLM) is an effective way to dynamically generate designed light field distributions. Based on the classic Gerchberg–Saxton (GS) algorithm, we proposed a technique, which can greatly reduce the computation cost to about 60 % in calculating CGHs for three-dimensional (3D) structures but with little degradation of reconstructed light field compared with the classic GS algorithm. The CGHs calculated by our method were displayed on a twisted nematic liquid crystal display, working as a phase-only-modulation SLM, and 3D structures of optical fields, e.g., 3D array of optical traps and vortices, were reconstructed with high efficiency and high quality. Besides, the possibility for 3D holographic display or projection was also demonstrated with this algorithm by reconstruction several images simultaneously in distinct axial planes.

Color Shift Reduction of Liquid Crystal Displays by Controlling Light Distribution Using a Micro-Lens Array Film

A new optical film is proposed to reduce angular color shifts of liquid crystal displays (LCDs). The film is composed of microstructures to induce the angular light mixing by deflection and reflection at the microstructure surfaces. A simulation scheme was developed to predict color shifts based on geometrical optics, and applied to design and optimize the microstructures. Among various microstructures studied, parallel grooves with parabolic cross sections were found to be the most efficient in redistributing light. Experimental verification by the UV micro-imprinting method were conducted to show the new film design can reduce the angular shifts by 50% or more for 13 primary and secondary colors of a super-patterned vertical alignment (S-PVA) LCD, and greatly reduce the grey inversion of twisted nematic (TN) LCDs as well.