Liquid Crystal Cell Research Articles

Continuously focus tunable 2D/3D switchable cylindrical liquid crystal microlens arrays for autostereoscopic displays.

Cylindrical microlens arrays are important optical elements for autostereoscopic display. Conventional fixed focal length cylindrical microlens arrays do not allow switching between 2D mode and 3D mode when constructing a 3D viewing zone. In contrast, cylindrical liquid crystal microlens arrays with zoom characteristics allow switching between 2D and 3D states, as well as adjusting the width of the sub-viewing zone. Therefore, based on the quantitative analysis of the geometrical structure of the viewing zone in different states, this paper proposes a continuous zoom type cylindrical liquid crystal microlens array structure, which is a liquid crystal cell composed of an array of plano-concave glass substrates and planar glass substrates. Theory and experiments show that it is close to a favorable parabolic phase profile at different driving voltages, and at the same time, it can realize a zoom range of 1.6mm-36 mm at a smaller driving voltage. The wide zoom range and excellent zoom effect make this structure particularly suitable for autostereoscopic display, and this characteristic can achieve the effect of switching between 2D and 3D by adjusting the shape of the central viewing zone.

Electrically Switchable Multi-Stable Topological States Enabled by Surface-Induced Frustration in Nematic Liquid Crystal Cells.

In liquid crystal (LC) cells, the surface patterning directs the self-assembly of the uniaxial building blocks in the bulk, enabling the design of stimuli-response optical devices with various functionalities. The combination of different anchoring patterns at both substrates can lead to surface induced frustration, preventing a purely planar and defect-free configuration. In cells with crossed assembly of rotating anchoring patterns, elastic deformations allow to obtain a defect-free bulk configuration, but an electrical stimulus can induce disclination lines. The disclination network is preserved without applied voltage. Depending on the electric field treatment and geometrical parameters, different multi-stable states with and without disclinations are obtained. This is demonstrated with the help of dual-frequency LCs, for which the frequency dependent dielectric properties allow repeatable switching between multi-stable states. Topological protection and the associated energy barrier between different states explains the observed metastability. The obtained configurations are retrieved with Q-tensor simulations and the validity is confirmed by matching optical simulations with experimentally obtained microscopy images. The realized multi-stable topological states interact differently with light, resulting in distinct optical properties. Optimization allows to switch between a highly transparent state and an opaque state, opening up opportunities for smart windows with low energy consumption.

Fabry–Perot enhancement of liquid crystals birefringence effects in terahertz range

Abstract THz technology is a rapidly advancing field in both fundamental and applied research, integrating novel approaches from optical and microwave ranges. Despite the wide applications of liquid crystals (LCs) in the visible range, their efficiency in the THz range is limited due to the low optical path length of existing anisotropic LC materials. In this work, we propose and explore the advantages of incorporating a LC core layer into the Fabry-Perot resonator as a simple strategy to enhance the observed birefringence effects. This enhancement is achieved through multiple wave passes through the LC layer, effectively increasing the effective optical path length.
In particular, we demonstrate a more than tenfold improvement in the efficiency of wave transformation within a plane-parallel LC layer.
Our findings are well correlated with the THz response of an LC cell composed of two parallel thick quartz substrates infiltrated with commercially available E48 liquid crystal, as observed in our experiments. The low switching voltage for cells with pyrocarbon-based electrodes is also demonstrated.

Light control using a double-stacked liquid crystal cell with enhanced viewing angle–blocking performance

In the future, there will be technological challenges between providing entertainment to passengers and eliminating driver distractions to ensure safety. Viewing angle control technologies for automotive display panels depending on each mode are required to integrate and provide both entertainment and advanced driver assistance system functions because watching videos while driving is regulated in most countries. In automotive display panels, unique electro-optical characteristics are required to control blocking or transmission only from the driver's direction while always being well observed from the passenger's direction. In this study, we developed a viewing angle control technology using double-stacked twisted nematic liquid crystal (TN-LC) films with excellent light-blocking performance only in the driver's direction over wide polar angle ranges in the privacy mode. By configuring the two TN-LC films in ordinary-ray mode and the other in the extraordinary-ray mode, the light could be completely blocked in the privacy mode, whereas it remained well transmitted in the normal mode in a specific left direction. Moreover, using double-stacked TN-LC films, light leakage at high polar angles in the privacy mode can be completely eliminated even without an optical compensation film, which is typically used to eliminate light leakage at high polar angles. Electro-optical films based on polarization optics are potential candidates for accelerating the growth of infotainment in self-driving cars.

Review of Angular-Selective Windows with Guest–Host Liquid Crystals for Static Window Applications

This review focuses on the development and advancements in angular-selective smart windows, with particular emphasis on static windows utilizing guest–host liquid crystal (GHLC) systems. Angular-selective windows are designed to adjust their transmittance based on the angle of incident light, offering enhanced energy efficiency and visual comfort in both architectural and automotive applications. By leveraging the anisotropic absorption properties of dichroic dyes, GHLC-based windows can selectively block oblique sunlight while preserving clear visibility from normal viewing angles. Various liquid crystal (LC) alignment configurations, including vertically aligned, homogeneously aligned, hybrid aligned, uniformly lying helix, and twisted aligned LC cells, have been investigated to optimize light control for different installation angles, such as for automotive windshields and building windows. These advancements have demonstrated significant improvements in energy conservation and occupant comfort by reducing cooling demands and regulating sunlight penetration. This review summarizes key findings from recent studies, addresses the limitations of current technologies, and outlines potential future directions for further advancements in smart window technology.

Controlling the dielectric constant values of nematic liquid crystals using ferroelectric and multiferroic nanoparticles

Notably, the simultaneous manifestation of ferromagnetic and ferroelectric properties at ambient temperature has spurred significant interest in incorporating multiferroic bismuth ferrite nanoparticles (BiFeO3) into liquid crystal matrices. In this study, the parallel and perpendicular dielectric components (ε∥ and ε⊥) and dielectric anisotropy (△ε=ε∥−ε⊥) of two different nanoparticles, barium titanate (BaTiO3) and BiFeO3, doped into E7, were measured at various temperatures and frequencies. Nematic mixture E7, a widely utilized nematic liquid crystal in research and display technologies, is a eutectic mixture composed of four cyanobiphenyl derivatives i.e. 5CB, 7CB, 8OCB, and 5CT. The findings indicate a substantial reduction in dielectric anisotropy upon introducing nanoparticles into the nematic liquid crystal environment. This research highlights the significant influence of barium titanate nanoparticles, which are smaller (approximately 12 nm), on the dielectric constant. This effect was analyzed based on varying concentrations and compared to a nanoparticle with ferroic properties. Moreover, the dielectric constant can be modulated through an alternative approach. Specifically, applying an electric field during the filling process of liquid crystal cells leads to changes in the dielectric constant. These changes, observed for both nanoparticles, were particularly evident at a precise concentration of 0.1 wt%, resulting in a decreased dielectric constant.

Viewing angle controller using two parallel alignment liquid crystal cells for automotive systems.

We proposed a viewing angle controller (VAC) for car co-driver displays (CDDs). This VAC, integrated with the co-driver display, provides necessary information to the co-driver while minimizing driver distraction. It comprises two parallel alignment liquid crystal cells and two negative C films. It maintains a wide viewing angle without an applied voltage, and it can achieve an anti-peeping angle of 35° (simulation) and 30° (experiment) under an appropriate voltage, effectively blocking the driver's direct-view light intensity from CDD and reflect-view light intensity from the side window, which can reduce the driver's attention. This VAC maintains excellent light transmittance at a normal direction and symmetrical brightness in both privacy and share modes, making it suitable for various in-vehicle displays. Those results indicate that this VAC can be broadly applied in automotive displays to enhance driving safety and improve co-driver entertainment.

Topological charge of a Gaussian beam with an off-axis optical vortex

We show that when an optical vortex with a topological charge n shifts from the optical axis of a Gaussian beam, the orbital angular momentum decreases, whereas the topological charge remains unchanged. We experimentally confirmed this phenomenon with the aid of a q-plate array generated in a liquid crystal cell filled with a frustrated chiral nematic. We also theoretically proved that the topological charge of an optical vortex is conserved when the optical vortex is displaced from the axis.

Advancing Automotive Displays: Liquid Crystal Cells for Precision Viewing Angle Adjustment

Advancing Automotive Displays: Liquid Crystal Cells for Precision Viewing Angle Adjustment

Ultra-wideband and high-efficiency polarization rotator based on liquid crystals

We propose a novel design of an asymmetrically anchored negative liquid crystal (LC) cell capable of linearly rotating the polarization axis of broadband light, with the rotation angle controlled by voltage. Unlike conventional LC cells that require polarization filters or retarders, our LC cell can directly modulate the polarization state of light without any additional components. The LC cell exhibits high polarization rotation efficiency over a wide wavelength range (200 nm to 2000nm), superior to the existing polarization modulators. We validate our design through theoretical calculations and numerical simulations, proving that a degree of linear polarization of over 0.95 can be achieved in the UV, visible, and NIR regions. Our design can be applied in optical communications, biological imaging, and spectroscopic technologies.

Bifocal lenses with adjustable intensities enabled by bilayer liquid crystal structures.

In this paper, we propose bifocal lenses based on bilayer structures composed of a liquid crystal (LC) cell and LC polymer, and the relative intensity of two foci can be adjusted arbitrarily through applying an external voltage. Two LC layers have different light modulation functions: when circularly polarized light passes through the first layer, part of the outgoing light is converted with PB phase modulation and another part is not converted; followed by the second layer, PB modulation of these two parts would be simultaneously realized but with opposite signs; thus the transmitted left- and right-handed circularly polarized (LCP and RCP) light can be independently controlled. As proof-of-concept examples, longitudinal and transverse bifocal lenses are designed to split an incident LCP light into two convergent beams with orthogonal helicity, and the position of the two foci can be flexibly arranged. Benefitting from the electrically controlled polarization conversion efficiency (PCE) of the LC cell, the relative intensity of the two foci can be adjusted arbitrarily. Experimental results agree well with theoretical calculations. Besides, a broadband polarization and an edge imaging system based on the proposed bifocal LC lenses have also been demonstrated. This paper presents a simple method to design a functional multilayer LC device and the proposed bifocal lenses may have potentials in the optical interconnection, biological imaging, and optical computing.

Off-axis viewing angle control technology applied to displays

ABSTRACT With the development of display technology and the expansion of application fields, such as vehicle/airborne displays, medical imaging displays, industrial control displays, etc., spatial constraints of these displays often result in viewers observing them at specific off-axis viewing angles. Therefore, the frequently using demands of off-axis viewing angles lead to increasing requirements for the viewing angle performance of displays. A method to enhance the off-axis viewing angle effect is proposed in this paper by attaching a designed liquid crystal cell on the surface of the display to control the emission direction. When an appropriate driving voltage is applied to the liquid crystal cell, the liquid crystal molecules align in a specific periodic arrangement, creating an optical effect similar to micro/nano structured light control devices. Different driving voltages induce distinct modulations of light within the liquid crystal layer. When no driving voltage is applied, the frontal viewing angle effect of the display is optimal, suitable for vertical viewing by a single individual, as an on-axis viewing mode. When a driving voltage is applied, certain off-axis viewing angle properties such as brightness is increased and colour shift is reduced, making it suitable as an off-axis viewing mode. In practical use, individuals can freely switch between these two display modes based on their actual needs.

Frequency and voltage-modulation multistable wave plate based on liquid crystals doped with silica nanoparticles

In this study, we demonstrate an all-range multistable liquid crystal (LC) wave plate. Its multistability arises from the formation of silica nanoparticle networks within the LC cell on the substrates, which stabilize LC molecules and induce varying phase retardation. Modulating the phase retardation of the LC wave plate can be achieved through the application of a DC pulse or by adjusting the frequency of the pulse. This multistable characteristic not only conserves energy but also enhances its versatility across diverse domains.

Electrically tunable planar liquid-crystal singlets for simultaneous spectrometry and imaging

Conventional hyperspectral cameras cascade lenses and spectrometers to acquire the spectral datacube, which forms the fundamental framework for hyperspectral imaging. However, this cascading framework involves tradeoffs among spectral and imaging performances when the system is driven toward miniaturization. Here, we propose a spectral singlet lens that unifies optical imaging and computational spectrometry functions, enabling the creation of minimalist, miniaturized and high-performance hyperspectral cameras. As a paradigm, we capitalize on planar liquid crystal optics to implement the proposed framework, with each liquid-crystal unit cell acting as both phase modulator and electrically tunable spectral filter. Experiments with various targets show that the resulting millimeter-scale hyperspectral camera exhibits both high spectral fidelity ( > 95%) and high spatial resolutions ( ~1.7 times the diffraction limit). The proposed “two-in-one” framework can resolve the conflicts between spectral and imaging resolutions, which paves a practical pathway for advancing hyperspectral imaging systems toward miniaturization and portable applications.

Pretilt angle modulation of liquid crystals based on single crystal rubrene with incorporation of homeotropic polyimides.

The alignment control of liquid crystals (LCs) is critical for various practical applications. The pretilt angle modulation of LCs typically requires a mechanical rubbing on substrates to orient the LCs. This study presents a contact-free approach to achieve pretilt angle modulation of LCs. Initially, a single crystal rubrene (SCR) film is deposited on the substrate. Subsequently, a mixture of nematic LCs and homeotropic polyimides (HPIs) is introduced between two SCR substrates via capillary action. During capillary filling, the synergy of capillary flow and the interaction between LCs and SCR ensures specific LC orientation. Subsequently, HPI dopants migrate toward and organize on the SCR through vertical phase separation, enhancing surface hydrophobicity and thereby increasing the pretilt angle of LCs. The pretilt angle of LCs can be continuously adjusted over a wide range from 2° to 90° by varying the HPI concentration. The contact-free process preserves against electrostatic charges, dust contamination, and surface damage typical of rubbed LC cells. This believed to be novel technique shows promise for developing no-bias-bend and bistable bend-splay LC displays.

Rotational dynamics of a disk in a thin film of weakly nematic fluid subject to linear friction

Dynamics at low Reynolds numbers experiences recent revival in the fields of biophysics and active matter. While in bulk isotropic fluids it is exhaustively studied, this is less so in anisotropic fluids and in confined situations. Here, we combine the latter two by studying the rotation of a disk-like inclusion in a uniaxially anisotropic, globally oriented, incompressible two-dimensional fluid film. In terms of a perturbative expansion in parameters that quantify anisotropies in viscosity and in additional linear friction with a supporting substrate or other type of confinement, we derive analytical expressions for the resulting hydrodynamic flow and pressure fields as well as for the resistance and mobility coefficients of the rotating disk. It turns out that, in contrast to translational motion, the solutions remain well-behaved also in the absence of the additional linear friction. Comparison with results from finite-element simulations shows very good agreement with those from our analytical calculations. Besides applications to describe technological systems, for instance, in the area of microfluidics and thin cells of aligned nematic liquid crystals, our solutions are important for quantitative theoretical approaches to fluid membranes and thin films in general featuring a preferred direction.

The effects of side-chain flexibility on the photosensitivity of polyimide alignment film

ABSTRACT To examine the impact of side-chain flexibility on the photosensitivity of polyimide liquid crystal (LC) alignment films, two polyimides (OD-HAB-CA and OD-HAB6-CA) were synthesised. OD-HAB6-CA contains flexible hexamethylene side chains. This study demonstrates that the OD-HAB-CA alignment film can induce LC molecular alignment after 80 min of non-polarised ultraviolet light (NPUVL) irradiation. In contrast, the OD-HAB6-CA alignment film can achieve the same result after only 35 min of irradiation. This suggests that the flexibility of the side-chain can significantly improve the photosensitivity of the alignment film and shorten the required irradiation time. In addition, OD-HAB-CA and OD-HAB6-CA exhibit good thermal stability and light transmittance properties. The resulting LC cell have pretilt angles of 0.2° and 0.5°, respectively, which are suitable for in-plane switching mode LCDs.

Optical measurements of the twist constant and angle in nematic liquid crystal cells

We present a reliable optical method for measuring the twist elastic constant K2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext {K}_2$$\\end{document} and for assessing the total twist angle in a standard nematic twist cell. The method relies on the use of a non-standard configuration of crossed polarisers and a twist cell, which allows us to measure accurately the twist-cell parameters by reducing the degeneracy between them. Grid patching and an efficient beam propagation method are utilised in the numerical models used for fitting the experimental data. The modelling shows that the polarisation dynamics in a twist cell is non-trivial and much more complex than in a planar cell. The twist elastic constant of three commonly used liquid crystals (5CB, 6CHBT and E7) was successfully extracted from cross-polarised intensity measurements.

ATO and Cs0·33WO3 loaded bilayer nanofiber membrane doped polymer dispersed liquid crystals for infrared shielding

Liquid crystals possess a wide range of applications in modulating infrared (IR) light and have drawn great interest especially in near-infrared shielding and passive radiative cooling. Here, a composite structure containing polymer dispersed liquid crystals (PDLC) with antimony doped tin oxide and cesium tungsten oxide loaded bilayer nanofiber membranes with IR shielding properties is proposed. The composite film and the blank liquid crystal cell are irradiated simultaneously under IR light, and the temperature detector shows that the average temperature drop of the PDLC composite film in the scattered state and the fully transparent state over the blank sample are 6.8 °C and 4.1 °C, respectively. More importantly, the dynamic IR shielding properties of the composite films are demonstrated by patterning the nanofiber films. In addition, this organic/inorganic hybrid PDLC system not only modulates IR light, but also exhibits excellent electro-optical properties, aging resistance, flexural stability (1000 cycles), and tensile resistance. The composite film combines ease of preparation with compatibility for industrial-scale roll-to-roll or continuous manufacturing processes, highlighting the great potential of PDLC for applications in tunable optical heat transport materials.

Nano/microgroove zirconium‐doped lanthanum oxide film with self‐aligned molecules for liquid crystal device application

Herein, we propose a brush‐coated zirconium‐doped lanthanum oxide (ZrLaO) film as a liquid crystal (LC) alignment layer. The film‐curing temperature was adjusted to 70, 150, and 230°C. Polarized optical microscopy and pre‐tilt angle analysis confirmed that there was uniform and homogeneous LC alignment on the 230°C cured ZrLaO film. Atomic force microscopy revealed that the surface had a nano/microgroove structure, which was caused by the shear stress generated by the brush‐coating process. This structure induced the uniform LC alignment. X‐ray photoelectron spectroscopy verified that the ZrLaO film was well‐formed on a glass substrate. The ZrLaO film displayed hydrophilic characteristics, and its surface energy increased as the film‐curing temperature increased. The ZrLaO alignment layer displayed suitable optical transmittance for LC device applications. The ZrLaO layer‐based twisted‐nematic LC cell exhibited more stable switching properties and better threshold voltage characteristics than conventional polyimide layers. Therefore, we expect that this brush‐coated ZrLaO layer will be a suitable LC alignment layer for LC device applications.