Liquid Crystal Technology Research Articles

Dual-sided transparent display enabled by polymer stabilized liquid crystals for augmented reality.

In the past decade, display technology has been reimagined to meet the needs of the virtual world. By mapping information onto a scene through a transparent display, users can simultaneously visualize both the real world and layers of virtual elements. However, advances in augmented reality technology have primarily focused on wearable gear or personal devices. Here we present a single display capable of delivering visual information to observers positioned on either side of the transparent device. This dual-sided display system employs a polymer stabilized liquid crystal waveguide technology to achieve a transparency window of 65% while offering active-matrix control. An early-stage prototype exhibits full-color information via time-sequential processing of a red-green-blue light-emitting diode strip. The dual-sided display provides a perspective on transparent mediums as display devices for human-centric and service-related experiences that can support both enhanced bi-directional user interactions and new media platforms.

Low-voltage and high-contrast polymer dispersed liquid crystals enabled by ferroelectric fluoro-copolymer doped polyimide film

Smart windows incorporating polymer dispersed liquid crystal (PDLC) technology provide user-friendly operation and play a significant role in intelligent buildings and building energy conservation. Long standing issues of the PDLCs such as high driving voltage, low contrast ratio, and narrow viewing angle hinder their applications. Here PDLCs are sandwiched between the hybrid substrates composed of the ferroelectric polyvinylidene fluoride trifluoroethylene (P(VDF-TrFE)) copolymer and the homogeneous polyimide. The high dielectric constant and ion-trapping ability of ferroelectric copolymers increase the effective voltage drop in the PDLCs. Concurrently, the local electric field created by large dipole moment of ferroelectric copolymers triggers the alignment of liquid crystals (LCs) along the applied field. These synergistic effects contribute to a substantial decrease in the driving voltage of PDLCs. In the opaque state, the random dipole moments in ferroelectric copolymers disrupt the LC orientations near hybrid substrates, thereby increasing the light scattering and reducing the transmission of PDLCs. Consequently, the proposed PDLCs exhibit a contrast ratio ∼2× higher compared to the conventional PDLCs at normal incident. Moreover, the proposed PDLCs demonstrate a wider viewing angle in the transparent state compared to conventional PDLCs. This development promises energy-efficient, eco-friendly, and cost-effective smart windows.

Polarization Independent Dynamic Beam Steering based on Liquid Crystal Integrated Metasurface

Digital Micromirror Devices, extensively employed in projection displays offer rapid, polarization-independent beam steering. However, they are constrained by microelectromechanical system limitations, resulting in reduced resolution, limited beam steering angle and poor stability, which hinder further performance optimization. Liquid Crystal on Silicon technology, employing liquid crystal (LC) and silicon chip technology, with properties of high resolution, high contrast and good stability. Nevertheless, its polarization-dependent issues lead to complex system and low efficiency in device applications. This paper introduces a hybrid integration of metallic metasurface with nematic LC, facilitating a polarization-independent beam steering device capable of large-angle deflections. Employing principles of geometrical phase and plasmonic resonances, the metallic metasurface, coupled with an electronically controlled LC, allows for dynamic adjustment, achieving a maximum deflection of ± 27.1°. Additionally, the integration of an LC-infused dielectric grating for dynamic phase modulation and the metasurface for polarization conversion ensures uniform modulation effects across all polarizations within the device. We verify the device’s large-angle beam deflection capability and polarization insensitivity effect in simulations and propose an optimization scheme to cope with the low efficiency of individual diffraction stages.

Fast-response and high figure of merit phase shifter based on polymer- stabilised liquid crystals

ABSTRACT This article presents a novel fast-response and high figure of merit (FoM) phase shifter based on polymer-stabilised liquid crystal (LC) for Ka-band. The developed LC phase shifter (LCPS), utilising a coplanar differential line loading 19 parallel-plate variable capacitors with 4.6 μm LC-cell, adopts polymer-stabilised LC technology in which the parallelly orientated polymer networks facilitate the LC molecules’ return to their initial state upon removal of the bias voltage, thus accelerating response time. The proposed LCPS has been fabricated to evaluate its superior capabilities. The experimental results closely match the simulation results, confirming its good congruity. This design has measured S 11 < −10 dB in 29–31 GHz. LCs with different HCM002 concentrations are injected to LCPS, and the experimental outcomes showed that LCs with 9 wt% HCM002 concentration significantly improve the response time of LCPS to 2.8 ms with a high FoM of 91.2°/dB at 30 GHz.

Dynamic geometric phase holography based on in-plane switching liquid crystal

ABSTRACT Liquid crystal geometric phase modulation technology is expected to achieve thin, small and achromatic spatial light modulation, which in turn has the potential to achieve holographic displays with large field angles and high clarity. This article presents a continuous dynamic geometric phase liquid crystal spatial light modulation method based on in-plane switching (IPS) mode. The relationship between geometric phase modulation and driving voltage is calibrated by using interferometry. Two hundred fifty-six phase orders within the phase modulation range of 0~π/2 is achieved. Subsequently, a phase hologram with a modulation range of 0~π/2 was designed by combining the GS (Gerchberg-Saxton) algorithm and single Fourier transform, demonstrating the holographic display capability. This article provides a low-cost approach for dynamic geometric phase holographic display.

A reconfigurable narrow-band bandpass filter using electrically-coupled open-loop resonators based on liquid crystals

Abstract This paper introduces an electrically reconfigurable narrowband bandpass filter that exploits liquid-crystal technology. The filter uses two electrically-coupled open-loop resonators to produce two transmission zeros, resulting in a more compact structure than a single open-loop resonator. The spacing between resonators contributes to easy manipulation of the fractional bandwidth (FBW) and return loss. Theoretical calculations of the electrical length using multilayer microstrip line equations are presented. Experimental results demonstrate that the center frequency can be tuned from 9.70 GHz to 10.86 GHz with a maximum bias voltage of 30 V, achieving a tuning range of 11.34%. With applied bias, the maximum FBW reaches 8.10% and the maximum return loss attains 15.97 dB in each biased state.

Design of a Ka‐band low‐cost microstrip line phase shifter and a sum‐difference beam antenna based on liquid crystal technology

AbstractThis letter presents a Ka‐band low‐cost microstrip line phase shifter based on liquid crystal (LC) technology. Furthermore, a sum‐difference beamforming antenna array based on the LC phase shifter is designed. The phase shifter is composed of two coaxial connectors, a metal base, an intermediate dielectric layer, a gradient metal sheet and a top glass layer. The simulated results show that a nearly 360° phase shift coverage can be achieved with the effective permittivity of LC varying from 2.5 to 3.5. The sum‐difference beam antenna array is composed of a circulator, a sum‐difference network, a one‐to‐eight power‐division network, eight liquid crystal phase shifters, and a serious fed antenna array. The simulation results show that the antenna array can achieve sum‐difference beam scanning range of ±30°. A prototype of LC phase shifter is fabricated and tested. The results show that the designed LC phase shifter can achieve a 360° phase coverage by applying a direct current (DC) voltage ranging from 0 to 12 V. Compared to traditional phase shifters, the proposed design offers a simple structure at a lower cost. When applied in the design of a sum‐difference beam antenna array, it can reduce the producing cost and enable integrated design.

Liquid crystal immunosensors for the selective detection of Escherichia coli with a fast analysis tool

The consumption of contaminated food may cause serious illnesses, and traditional methods to detect Escherichia coli are still associated with long waiting times and high costs given the necessity to transport samples to specialized laboratories. There is a need to develop new technologies that allow cheap, fast, and direct monitoring at the site of interest. Thus, in this work, we developed optical immunosensors for the selective detection of E. coli, based on liquid crystal technology, whose molecules can align in different manners depending on the boundary conditions (such as substrates) as well as the environment that they experience. Each glass substrate was functionalized with anti-E. coli antibody using cysteamine as an intermediate, and a vertical alignment was imposed on the liquid crystal molecules by using DMOAP during functionalization. The presence of bacteria disrupts the alignment of the liquid crystal molecules, changing the intensity of light emerging between cross polarizers, measured using a polarized optical microscope and a monochromator. It was possible to detect E. coli in suspensions in the concentration range from 2.8 cells/mL to 2.8×109 cells/mL. Selectivity was also evaluated, and the sensors were used to analyze contaminated water samples. A prototype was developed to allow faster, in-situ, and easier analysis avoiding bulky instruments.

Liquid Crystal Technologies for Augmented and Mixed Reality Displays

AbstractWhile LC display technologies have deep roots in augmented, virtual, and mixed realities, LC optics is emerging as a pivotal area within AR/VR/MR optics and the display community.

Alignment assessment of anisotropic liquid crystals through an automated image processing algorithm

Liquid crystals (LCs) are recognised as an emerging type of responsive and functional materials that exhibit diverse technological applications. The spatial arrangement or alignment of LC molecules creates an optical anisotropy, which influences the propagation of light. This study presents an automated image processing algorithm designed to quantitatively assess LC alignment. The algorithm calculates the image structure tensor and computes a score ranging from 0 to 1 to represent the uniformity of LC alignment. The tool was verified on both artificially generated images of lines with pre-defined orientations and then tested on microscope images of LCs. For the latter, test samples of deformed helix ferroelectric LCs were constructed using three different alignment methods. Analysis of microscopic images of samples prepared utilising photoalignment, polymer rubbing, and oblique evaporation alignment techniques, determined average alignment scores (mean ± standard error of the mean) of 0.44 ± 0.03, 0.26 ± 0.1, and 0.17 ± 0.04, respectively, in comparison to commercially sourced control samples with a score of 0.64 ± 0.03 (n=5 each). This study paves the way for automated objective assessment of LC alignment, a critical aspect to ensure the optimal performance, reliability, and efficiency of various devices and sensors relying on LC technology.

Printed Liquid Crystal Optical Vortex Beam Generators

AbstractThis study presents an innovative application of inkjet printing technology in the construction of a switchable optical vortex beam generator. The fabrication process involves drop‐on‐demand printing of liquid crystal (LC) droplets that can generate an optical vortex beam in the far‐field with the application of a voltage. Notably, this vortex beam can be activated and deactivated by manipulating the amplitude of the electric field. Both simulations and experiments are used to determine the optical characteristics of the printed LC devices and the resulting far‐field patterns for different polarizations of light. The study showcases the versatility of the generator in that it can produce both vortex and vector beams, the choice of which is simply determined by the polarization of the input light. This highlight the potential of this printed LC technology for integration into a multitude of optical systems.

P‐224: Late‐News Poster: Development of 660Hz LCD with Low Resistance Gate LTPS Backplane

16‐inch FHD+ (Full High Definition Plus, 1920*1200) LCD featuring LTPS TFTs with a new low‐resistance alloy gate metal and fast response AFFS (Advanced Fringe Field Switching) liquid crystal technology has been developed, which achieves a ClearMR value of 9000 at 480Hz frame rate and fulfills the requirement for product reliability test. These technologies, including the new gate metal TFTs and employing Fast‐Response time liquid crystal, have also been implemented in a 17.3‐inch FHD (Full High Definition, 1920*1080) gaming laptop LCD. This larger panel operates at an even higher frame rate of 660Hz and higher ClearMR values with GtG (Gray to Gray) liquid crystal response time within 1ms. These advancements mark significant progress in the field of high‐performance gaming displays.

49‐3: Invited Paper: High‐Resolution Color‐Reflective Bistable Cholesteric Liquid Crystal Technology for Signage Applications

An optimized color‐reflective LCD with high optical performances and cost‐effective structure has been proposed by association with cholesteric liquid crystal technology. By way of a color dithering algorithm, the cholesteric liquid crystal display (Ch‐LCD) can visualize a 24‐bit RGB color pixel and display over 16 million colors. Moreover, the waveform module (WF) is applied to emulate the display timing controller, which is a lowcost and more accessible way to drive the Ch‐LCD. In this paper, we demonstrated a 13.3‐inch passive matrix (PM) driven Ch‐LCD with a high resolution of 202 PPI, high reflectance of 30%, and high color gamut of 20%, which is suitable for electronic signage applications.

Liquid Crystal Materials for Electronically Reconfigurable Antennas: Overview Toward 5G Applications

This paper discusses the use of Liquid Crystal (LC) technology for Electronically Reconfigurable Antennas (ERAs) that are essential for future-based 5G communication systems and satellite platforms. This comprehensive study covers the development of liquid crystal performance metrics and the deployment of LC technology for RF front-end antenna systems, ranging from GHz to THz frequency bands. Here, low profile LC varactor with phase shifter-based antenna systems is investigated for beam steering, enabling to scan a wide range with minimum scan time of operation. The LC phase shifter-based antenna has shown an insertion loss of ≪3[Formula: see text]dB for 5G frequency bands and a high figure-of-merit over a bandwidth of 2.5[Formula: see text]GHz with minimum time response of 30[Formula: see text]ms. These LC-based ERAs can feature wide beam scanning angles with high power-handling capability, better efficiency, high linearity with low power consumption for satellite ground terminals and 5G communication systems.

Exploring the interplay of liquid crystal orientation and spherical elastic shell deformation in spatial confinement.

The application of liquid crystal technology typically relies on the precise control of molecular orientation at a surface or interface. This control can be achieved through a combination of morphological and chemical methods. Consequently, variations in constrained boundary flexibility can result in a diverse range of phase behaviors. In this study, we delve into the self-assembly of liquid crystals within elastic spatial confinement by using the Gay-Berne model with the aid of molecular dynamics simulations. Our findings reveal that a spherical elastic shell promotes a more regular and orderly alignment of liquid crystals compared to a hard shell. Moreover, during the cooling process, the hard-shell confined system undergoes an isotropic-smectic phase transition. In contrast, the phase behavior within the spherical elastic shell closely mirrors the isotropic-nematic-smectic phase transition observed in bulk systems. This indicates that the orientational arrangement of liquid crystals and the deformations induced by a flexible interface engage in a competitive interplay during the self-assembly process. Importantly, we found that phase behavior could be manipulated by altering the flexibility of the confined boundaries. This insight offers a fresh perspective for the design of innovative materials, particularly in the realm of liquid crystal/polymer composites.

Recent progress in liquid crystal devices and materials of TFT-LCDs

Thin-film-transistor-liquid crystal displays (TFT-LCDs) still dominate most of the display markets due to a big leap in image quality while keeping low cost and superior reliability, and its evolution is continuing to compete with emerging emissive displays. In this paper, recent progress in liquid crystal technologies mainly focusing on fringe-field switching (FFS) and polymer-stabilized vertical alignment (PS-VA) modes and materials for improving electro-optic performances is reviewed.

Zwitterion-doped liquid crystal speckle reducers for immersive displays and vectorial imaging

Lasers possess many attractive features (e.g., high brightness, narrow linewidth, well-defined polarization) that make them the ideal illumination source for many different scientific and technological endeavors relating to imaging and the display of high-resolution information. However, their high-level of coherence can result in the formation of noise, referred to as speckle, that can corrupt and degrade images. Here, we demonstrate a new electro-optic technology for combatting laser speckle using a chiral nematic liquid crystal (LC) dispersed with zwitterionic dopants. Results are presented that demonstrate when driven at the optimum electric field conditions, the speckle noise can be reduced by >90% resulting in speckle contrast (C) values of C = 0.07, which is approaching that required to be imperceptible to the human eye. This LC technology is then showcased in an array of different display and imaging applications, including a demonstration of speckle reduction in modern vectorial laser-based imaging.

Synthesis and characterization of functional thermoresponsive photoactive copolymers and study of their thermal and photoluminescence properties

ABSTRACT Poly(N-isopropyl acrylamide-co-disperse yellow 7 methacrylate) (PNIPAM) copolymers were synthesized by radical polymerization of N-isopropyl acrylamide with disperse yellow 7 methacrylate using 2,2/-Azo-bis-isobutyronitrile (AIBN) as an initiator. N-isopropyl acrylamide is a thermoresponsive monomer, and disperse yellow 7 methacrylate is a photoactive monomer. The synthesized photoactive and thermoresponsive copolymers were characterized by FTIR, NMR, and UV-Vis spectrophotometer with a temperature variation. A proton NMR signal at 8.16 ppm is observed for aromatic protons surrounded by an azo (-N=N-) group. The peak that appeared at 4.0 ppm is due to the CH-CONH group. The amide group proton of CONH appeared at 8.16 ppm. The molecular weights of homopolymers (like PNIPAM and PDY7MA) and their copolymers (PNIPDY) were observed to be 104 and 103 Da, respectively. The optical band gaps for synthesized copolymers, PNIPDY-1B, PNIPDY-2B, and PNIPDY-3B, are 2.98 eV, 2.95 eV, and 2.91 eV, respectively. The multiple emission spectra were observed at 407 nm, 428 nm, and 460 nm for the excitation energy of 365 nm due to the n-π* and π-π* transitions of the azobenzene chromophore. Thermal properties were also studied using TGA analysis. Stimuli-responsive polymers are widely used in optoelectronics and photonics, such as optical switching, optical information storage devices, liquid crystal display technology, and diffractive optical elements.

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Experimental study on the solidification and melting performances of magnetic NEPCMs composited with optimized filling metal foam in a uniform magnetic field

The present study experimentally investigates the magnetic nano-enhanced phase change material (NEPCM) filled with different strategies of metal foam in a uniform magnetic field for the solidification and melting processes. The thermochromic liquid crystals (TLC) technology is used to evaluate, compare and analyze the effects of magnetic field, partial filling (H = 0 h, 1/4h, 2/4h, 3/4h, 4/4h) and gradient porosity (positive and negative). The evolution of phase change interface, the temperature distributions and differences, solidification/melting rate, energy released/stored, and Nusselt number are comprehensively analyzed. The results show that the magnetic field inhibits convection but accelerates local heat transfer by the Kelvin force. As the porous filling height increases, the solidification rate and energy released increase firstly and then decrease. Comparing to pure PCM, the H = 3/4h case has the excellent solidification performance for 2.08 times increase and energy released for 40.22% improvement. The melting rate is advanced with the growth of filling height, but the energy storage capacity gradually decreases. In terms of heat transfer performance, the positive gradient porosity case owns best temperature uniformity and fastest phase change rate. Compared with pure PCM, its solidification rate and energy released are increased by 4.30 times and 36.7%, and melting time is reduced by 64.29%, but the energy stored is lost by 16.44%. As for the energy storage, the negative gradient porosity case can release and store more energy at the same time as maintaining high heat transfer performance.