Hybrid Alignment Research Articles

Film compensation of twisted nematic liquid crystal display using a rod-like reactive mesogen

A hybrid aligned nematic liquid crystal compensation film using UV curable rod-like mesogen has been made to compensate the residual birefringence of a twisted nematic (TN) device at oblique viewing directions in the dark state. Effective retardation value of the fabricated film was characterized by experiment and calculation using simulation. The results showed that the film has a hybrid alignment with a tilt angle variation from 3° to 19°. The optical compensation effects are evaluated in terms of light leakage in the dark state and contrast ratio (CR). The measured results showed that the light leakage is greatly suppressed with the compensation film and the viewing angle characteristics of TN device are greatly improved, most particularly in the up direction.

Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogens with a Nematic-Nematic Transition and a Negative Elastic Constant

Hydrocarbon linked mesogenic dimers are found to exhibit an additional nematic phase below the conventional uniaxial nematic phase as confirmed by x-ray diffraction. The phase produces unusual periodic stripe domains in planar cells. The stripes are found to be parallel to the rubbing direction (in rubbed cells) with a well-defined period equal to double the cell gap. The stripes appear without external electromagnetic field, temperature or thickness gradients, rubbing or hybrid alignment treatments. Simple modeling proposes a negative sign for at least one of the two elastic constants: splay and twist, as a necessary condition for the observed pattern.

Switching and defect dynamics in multistable liquid crystal devices

We investigate the switching dynamics of multistable nematic liquid crystal devices. In particular, we identify a remarkably simple two-dimensional device which exploits hybrid alignment at the surfaces to yield a bistable response. We also consider a three-dimensional tristable nematic device with patterned anchoring, recently implemented in practice, and discuss how the director and disclination patterns change during switching.

Polarization‐independent and electrically tunable liquid‐crystal Fresnel lenses based on photoalignment in dye‐doped liquid crystals

Abstract— This work demonstrates polarization‐independent and electrically tunable liquid‐crystal (LC) Fresnel lenses based on photoalignment in dye‐doped liquid crystals (DDLCs). The LC alignments in the adjacent odd and even zones of the LC Fresnel lens are orthogonally hybrid alignments. Those are generated by surface treatment of homeotropic and homogeneous alignment layers, and the dye‐adsorption layer onto the UV‐cured surface‐relief Fresnel zone plate. The maximum focusing efficiency (∼34.14%) of the fabricated LC Fresnel lens by applying a suitable AC voltage is close to the maximal theoretical focusing efficiency of a binary phase LC Fresnel lens (∼40.5%). Additionally, the focusing efficiency is polarization‐independent and electrically tunable.

RAPID AND ACCURATE INS ALIGNMENT FOR LAND APPLICATIONS

INS has been widely used in applications such as aerospace guidance and land vehicle navigation. Position, velocity and attitude are navigation parameters which need to be determined on a moving platform by processing the measurements of inertial sensors including specific forces and angular rates. Generally speaking, the initial attitude angles between the body and navigation frames play an important role, because they could affect the accuracy of the navigation solutions. Therefore, those angles have to be estimated accurately prior to switching the INS into navigation mode using a technique known as INS alignment. In the fine alignment, an optimal estimator such as the Kalman filter is used to perform the alignment process. Due to measurement errors, the Kalman filter takes about 10 to 15 minutes to converge. Those errors increase the alignment time and deteriorate the overall accuracy of the initial attitude angles estimated. In this article, a hybrid alignment scheme which integrates an ANFIS with the Kalman filter is proposed to obtain a better accuracy of the initial attitude angles with the emphasis on the heading angle. This method reduces the time required to achieve reasonable results for fine alignment. A tactical grade inertial measurement unit is used to verify the performance of the proposed scheme in this study. The preliminary results presented in this article indicate that a faster alignment procedure with higher accuracy can be achieved through the use of proposed scheme.

Thermally Driven Giant Bending of Liquid Crystal Elastomer Films with Hybrid Alignment

We have investigated the thermally induced bending deformation of nematic elastomers with hybrid alignment (HNEs) where the director continuously rotates by 90° (from planar alignment to vertical alignment) between the top and bottom surfaces. The flat specimen of nematic gel in the preparation state exhibits a considerable bending when allowed to deswell to the dry state. The curvature of the dried elastomer film markedly depends on temperature. The curvature in the nematic state increases with heating, and the film apparently becomes flat at a certain temperature. Further heating induces the bending in the opposite direction. In the high-temperature isotropic state, the curvature is independent of temperature. This bending deformation is thermally reversible. We successfully interpret the temperature dependence of curvature for the HNEs assuming a linear variation of strain in the thickness direction on the basis of the thermally uniaxial deformation of the nematic elastomers with globally planar or ver...

Binary liquid crystal alignments based on photoalignment in azo dye-doped liquid crystals and their application

This work demonstrates the feasibility of binary liquid crystal (LC) alignments, in which two forms of LC alignment are in a single pixel or a specific area using a surface-treated alignment layer and a photoalignment film of the adsorption of azo dyes onto the polymer surface in azo dye-doped liquid crystals. Binary LC alignments that involve two of common LC alignments, which are homogeneous, homeotropic, hybrid, and twisted nematic alignments, are initially demonstrated. Then, a binary LC alignment that comprises hybrid and homeotropic alignments is adopted to fabricate a viewing-angle-dependent liquid crystal display, which displays two images by changing viewing angles.

Chapter 4 - Adaptive Lens

Publisher Summary Adaptive or varifocal lenses with variable focusing powers have attracted much attention because of their wide applications in vision care, consumer electronics such as digital cameras, aberration correction, optical interconnects, and three-dimensional biomedical imaging. The focal power of an optical system is usually changed by nonlinear movement of lenses with spherical or cylindrical powers along the optical axis and such a system consists of several lens components. A lot of efforts have been devoted to the research in adaptive lens. Recent advances in this field have been reviewed in this chapter. For liquid crystal lens, refractive and diffractive LC lenses based on discrete electrodes, hole-patterned electrodes, modal control electrode, hybrid alignment, and polymer/LC materials have been discussed in detail. For liquid lenses, lenses based on mechanic pressure, electrowetting effect, dielectric effect, and hydrogel and thermal effect have been reviewed. Examples of applications in vision care, aberration compensation, zoom lens, and optical tweezers have been discussed.

Single-cell-gap transflective liquid-crystal display based on photo- and nanoparticle-induced alignment effects

This work presents a transflective liquid-crystal (LC) display with a single cell gap in a dual-alignment configuration. This dual structure was fabricated via single-step laser-light exposure through a photomask. The vertical alignment induced by nanoparticles of polyhedral oligomeric silsesquioxanes can be changed into a homogeneous alignment via absorption of photoexcited azo dye. The LC molecules at the transmissive and reflective pixels are homogeneous and hybrid alignment, respectively, at which optimal phase retardations of half and quarter wavelengths are achieved.

Single‐layered microscale linear‐gradient PDLC material for electro‐optics

AbstractWe report on single‐layered optical material of linear‐gradient microscale polymer‐dispersed liquid crystal (PDLC). E7/NOA65 composite films formed by pulsed UV laser photopolymerization‐induced phase separation exhibit two morphology types, namely a bipolar and a hybrid alignment of liquid crystal droplets. The specific structural properties of the produced PDLC layers, such as the droplet shape uniformity and alignment, as well as the droplet size control through the film thickness, facilitate the efficient control on the electro‐optical (EO) response, thus being of practical interest for EO device applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

66.4: Surface Polarity Controlled Horizontal Chevron Defect Free Surface Stabilized Ferroelectric Liquid Crystal Devices

AbstractThe asymmetrical surface polarity controlled hybrid alignment technique was proposed to suppress the alignment defects of half V‐shaped switching FLC materials. When the material was cooled from N* to SmC*, two kinds of layer arrangements were formed with opposite spontaneous polarization directions (Ps). Alignment layers with opposite surface polarity direction were utilized in asymmetrical hybrid cells and produced uni‐surface‐polarity direction. FLC Ps was only controlled by this surface polarity; therefore, double domains were suppressed into mono‐domain. A 2.4” prototype TFT‐LCD was presented with defect‐free alignment texture. This alignment technique provided promising FLC material with well alignment and fast switching for TFT‐LCD application.

High-Precision Measurement of Polar Anchoring Strength and Elastic Constant Ratio using Hybrid Alignment Nematic Cell

The surface polar anchoring strength is the most crucial element which controls the alignment distribution of a liquid crystal (LC) cell. We devised a new measurement method for the surface polar anchoring strength and the elastic constant using a hybrid aligned nematic LC (HAN) cell. We obtained these parameters from the measurement of the angle dependence of the phase difference and the amplitude ratio in the direction perpendicular to the alignment plane of a HAN cell and confirmed that these parameters can be measured with a high degree of accuracy.

39.3: Wide‐View Transflective LCD Using Fringe‐Field Switching Mode

AbstractA high optical efficiency and wide‐view transflective LCD for mobile displays based on fringing field switching is proposed. The transmissive part uses homogenous alignment while the reflective part uses hybrid alignment with different optic axis orientation. In addition, the transmissive and reflective parts exhibit a similar gamma curve.

Novel application of ink‐jet‐printing technology in multi‐domain alignment liquid‐crystal displays

Abstract— Based on the drop‐on‐demand characteristics of ink‐jet printing, the multi‐domain alignment liquid‐crystal display (LCD) could be achieved by using patterned polyimide materials. These polyimide ink locations with different alignment procedures could be defined in a single pixel, depending on the designer 's setting. In this paper, we combined the electro‐optical design, polyimide ink formulation, and ink‐jetting technology to demonstrate the application of multi‐domain alignment liquid‐crystal display manufactory. The first one was a multi‐domain vertical‐alignment LCD. After the horizontal alignment material pattern on the vertical alignment film, the viewing angle would reach 150° without compensation film. The second one was a single‐cell‐gap transflective LCD within integrating the horizontal alignment in the transmissive region and hybrid alignment in the reflective one in the same pixel. In addition, this transflective LCD was also demonstrated in the form of a 2.4‐in. 170‐ppi prototype.

Photoinduced Deformation Behavior of Crosslinked Azobenzene Liquid-Crystalline Polymer Films with Unimorph and Bimorph Structure

The use of a crosslinked azobenzene liquid-crystalline polymer (CALP) system for micro-integrated actuators becomes especially attractive. CALPs can deform along the alignment direction of mesogens upon irradiation of UV/visible light owing to photochemical phase transition. In this study, to improve the bending speed, CALP films with a homogenous alignment on one surface and a homeotropic alignment on the opposite surface (hybrid alignment) were prepared and their bending behavior was investigated. The films showed photoinduced bending whose direction was determined by the surface alignment treatment, and the bending speed was greatly enhanced upon irradiation from both surfaces of the film at the same time.

P‐112: Low Driving Voltage with Clean Aligned Ferroelectric Liquid Crystal Devices

AbstractLow driving voltage FLC material, R3206 with Vsat. at 3.5V (AZ Electronic Materials), and its mixtures were under evaluation for potential TFT display application. Poor alignment issue was overcome by the diluted pitch mixtures and asymmetric hybrid alignment cells. In the series of diluted pitch mixtures, the contrast and alignment are better than pure compound in pre‐made cells (1.8±0.1μm, from EHC). In particular, the 70% R3206 mixture showed the best result with low driving voltage below 5V and fast response time (T on +T off) under 1.1 ms. The hybrid alignment cell was successfully suppressed horizontal chevron defects and achieved the best contrast ratio of 750. These results provide promising FLC materials with low driving voltage, well aligned, and fast switching for TFT‐LCD application.

Design and Fabrication of High-Performance Liquid Crystal Gratings

We present basic principles of designing and fabricating high-performance liquid crystal (LC) gratings with binary alignment structures which produce a variety of the diffraction properties. The periodic binary structure in the LC layer was fabricated through a selective irradiation of the UV light using the single-masking process. An alternating homeotropic and hybrid alignment configuration produces the input polarization-dependent diffraction suitable for the polarization-separating devices while an oppositely twisted binary alignment configuration gives the input polarization-insensitive diffraction. It is found that a dye-doped bidirectional alignment configuration can be used for obtaining optically controllable polarization properties.

A tunable liquid-crystal microlens with hybrid alignment

A tunable liquid-crystal microlens with hybrid alignment was fabricated using micro-imprinting technology. The imprinted hybrid alignment, which was surrounded by homogeneous (homeotropic) alignment, resulted in spatial refractive-index distribution of liquid-crystal molecules in the microlens. With different hybrid-alignment configurations, the microlens functioned either as a convex or concave lens. The focal length of the microlens was electrically controlled at applied voltages of less than 4 V. The focal length was adjusted from 7.8 to 8.6 mm and from −10 to −35 mm for a convex and a concave lens, respectively. The rising response time was 0.5 s, and the falling response time was 5 s.

Polarization-insensitive liquid crystal Fresnel lens of dynamic focusing in an orthogonal binary configuration

We report on a polarization-insensitive liquid crystal (LC) Fresnel lens with the centrosymmetry of dynamic focusing in an orthogonally alternating hybrid configuration. The polarization-insensitive Fresnel lens having such successive orthogonal hybrid alignment in two adjacent zones was fabricated using a single-masking process through two-step exposure of a linearly polarized ultraviolet light. It was found that the dynamic focusing property of the LC Fresnel lens is electrically controllable and entirely centrosymmetrical irrespective of the polarization state of an incident light.

The Wide View (WV) Film for Enhancing the Field of View of LCDs

This paper reviews the technologies of the wide view (WV) film. The WV film is an optical compensation film, which remarkably enhances the field of view of twisted nematic (TN) thin-film transistor liquid crystal displays (TFT-LCDs). We have recently developed a new WV film for the OCB mode, which promises a fast optical response speed and wide viewing angle LCD-TV. The WV film is made of a hybrid alignment polymerized discotic material (PDM) layer coated on a (tri-acetyl cellulose (TAC) substrate. The PDM layer alignment technology and the TAC retardation control technology give us the flexibility to develop a compensation film for any LCD mode and allow a cost effective roll-to-roll polarizer lamination process.