Controlled Liquid Crystal Research Articles

A liquid-crystal microlens with dual-layers arrayed pattern electrode for the effective modulation of incident light beams

In this paper, an electrically controlled liquid crystal (LC) microlens array based on dual-layer arrayed planar pattern electrode is reported for effective light wave modulation. By adjusting the voltages applied to two planar arrayed electrodes within one substrate of the LC microlens, an adjustable focused circular ring or point-shaped light spot can be formed. Dual-layers arrayed pattern electrode with a minimum interval spacing of approximately ~10μm and a maximum of 130μm are achieved on one substrate by using standard microelectronic lithography, etching, coating film, and other processes. Experimental results are presented and discussed to illustrate outstanding performance of electrically focusing and modulation capability of the proposed LC device. This approach will serve as inspiration for the continued development and design of LC optical elements, enabling applications such as light field imaging, wavefront detection/correction, and the advancement of imaging augmented systems.

Broadband Vortex Beam Modulating System Based on Electrically Controlled Liquid Crystal Devices

Vortex beams with helical phase wavefronts have recently emerged as a research hotspot because of their widespread applications such as ultra-high dimensional information encoding, quantum entanglement, and data transmission due to their unique properties. Research, as of yet, on the easy preparation of vector vortex beams is hindered by technical bottlenecks such as large mechanical modulation errors and limited bandwidths of meta-structured devices in spite of the massive experimental and theoretical breakthroughs in the generation of vortex beams that have been made. To make up for the deficiency in this area, we propose here a broadband vortex beam modulating system based on electrically controlled liquid crystal (LC) devices. An electrically controlled LC q-plate and an LC broadband polarization grating (PG) are integrated in the system as the crux devices. The system enables pure vortex-phase modulation within a wide spectral range in the visible spectrum and electrical control on the output beam intensity of the vortex and Gaussian components. Experiments at different voltages of 533 nm and 632.8 nm were conducted for validation. This system overcomes the complexity and stringent optical path requirements of traditional methods for generating vortex beams, offering an efficient, convenient, and rapidly tunable approach for generating vortex beams that is easily and highly integrable.

Inexpensive bioprinting on a microscope using liquid crystal displays and visible light

Patterned photocrosslinking has several uses in the biofabrication of microstructurally complex tissue constructs, through both photolithography of scaffolds and photoconjugation of cell adhesive and instructive moieties. Often the polymers used are modified by methacrylation while photoactivation requires ultraviolet light. In contrast, this study aimed to design, build and evaluate a low-cost platform to place photocrosslink patterns into unmodified collagen and gelatin hydrogels using visible light and ruthenium-mediated tyrosine crosslinking in a way compatible with cell culture and inverted microscopes commonly used in biological laboratories. A photoprinting module was constructed above an inverted microscope sample stage to be confocal with the imaging system. The module consists of a blue light emitting diode array, light pipe, diffuser, microelectronically controlled liquid crystal display as photomask, and focusing objective. Resulting Ruthenium-mediated photocrosslink patterns were visible in unmodified collagen and gelatin hydrogels due to altered local polymer network density and optical contrast. Green fluorescent protein was conjugated in patterns to both gelatin and collagen gels, dependent on light exposure, intensity, and polymer network density. Pattern resolution varied from 2.0 ± 0.5 μm to 102 ± 33 μm (mean ± standard deviation) dependent on the focusing objective magnification and the pattern used (display pixel versus diode element). Further, photocrosslink patterns placed in collagen hydrogels and incubated without rinsing in serum-containing media swelled over 20–48 h, breaking the collagen network and forming ∼50 μm diameter holes. Fibroblasts cultured in photopatterned collagen hydrogels aligned and moved on and around crosslinked regions, consistent with durotaxis and contact guidance. The platform for photocrosslinking described in this study will impact several research fields, notably bioprinting of microstructurally and mechanically complex tissue constructs.

Rewritable Electrically Controllable Liquid Crystal Actuators

AbstractConductive structures determine the functions and actuation modes of electrically responsive soft actuators. The rewritability of conductive structures is highly desirable but has not been realized in electro‐driven actuators. Typically, once conductive pathways are established, they can hardly be modified; thus, the function of the actuator is permanently fixed. In this study, poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is developed as a rewritable conductive coating for actuators composed of liquid crystalline elastomers (LCEs). This enables reconfigurable, adaptive, and precisely controllable electro‐driven motions and the repeated use of the same actuator for various purposes without disposal. Moreover, different PEDOT:PSS layers can be coated onto different regions, thus enabling the assembly of different actuation behaviors in a monolithic actuator under a single input voltage. Unlike all previously reported soft actuators that respond to electricity and light, opposite shape changes in an actuator with a series circuit can be performed under these two stimuli. Furthermore, when combining LCEs with dynamic covalent bonds, the PEDOT:PSS‐coated LCE (PEDOT:PSS‐LCE) actuator can be reprogrammed based on two different mechanisms: rewriting the conductive PEDOT:PSS patterns and re‐aligning the LCEs. This versatile method can be adapted to other types of actuators.

Жидкокристаллический управляемый оптический фильтр, комбинируемый с устройствами видеонаблюдения

Operating in a wide temperature interval controlled liquid crystal optical filter for the visible and near infrared spectral ranges, combining with video surveillance devices, is described. The configurations of the filter using liquid crystal cells with a twist, homeotropic and planar orientations are considered. It is shown that the change in the transmission depending on the attached control voltage, typical for a neutral filter, is shown by the twist cell. The effect of the filter on the angular resolution of the video camera is evaluated.

Real-time noise-free inline self-interference incoherent digital holography with temporal geometric phase multiplexing

In this paper, we propose a real-time incoherent digital holographic (IDH) recording system free from bias and twin-image noises. A motionless three-step polarization-encoded phase-shifter operating at 99 Hz is realized with two electrically controllable birefringence-mode liquid crystal cells operating in tandem with a geometric phase lens and polarizers. Based on the proposed optical configuration, a coaxial straight-line self-interference IDH recording system is devised. Notably, the elimination of bias and twin-image noise from three phase-shifted images is demonstrated as a proof of concept. Moreover, complex-valued holographic video acquisitions with a resolution greater than 20 megapixels are demonstrated, with an effective acquisition frequency of 33 Hz.

Electrically controlled liquid crystal nonlinear optical devices prepared by multi-layer composite structures

In this study, a multi-layer composite structure is used to prepare nonlinear optical devices from multi-walled carbon nanotubes (MWCNTs)/liquid crystal (LC) composite systems. Their third-order optical nonlinearity is investigated. The MWCNTs were coated and modified to improve their dispersion in the solvent. The coated and modified MWCNTs were characterized by IR absorption spectroscopy and transmission electron microscopy (TEM). The nonlinear optical (NLO) properties of the devices prepared by the multi-layer composite structures with varying design parameters were studied. The conventional devices were also prepared by mixed doping method for comparison with the proposed devices. Both devices underwent Z-scan testing. The third-order nonlinear polarizability of the conventional hybrid-doped devices was calculated with a value of 5.39 × 10-10 esu. The third-order nonlinear polarizability of the proposed devices prepared by the multi-layer composite structures has a value of 2.97 × 10-9 esu, which is about five times the corresponding value for the hybrid-doped devices. So, the devices prepared by the multi-layer composite structures have better NLO properties. Moreover, the third-order nonlinear polarizability of the proposed devices was further increased up to 3.88 × 10-9 esu, which is an increase of almost 31% after applying voltage to these devices prepared by the multi-layer composite structures. The limiting threshold of S-CTAB/MWCNTs@BHR33400 is 0.245 J/cm2 after voltage application. Applying voltage plays a role in promoting the NLO properties of the devices. Using the multi-layer composite structure to prepare the liquid crystal nonlinear optical devices can significantly improve the NLO properties of the devices. Such prepared devices can be electrically tuned, providing new avenues for preparing nonlinear optical devices.

Electrically controllable liquid crystal paraxial Fresnel zone plate based on concentric zones patterned electrode

A twist nematic liquid crystal Fresnel zone plate (LCFZP) with controllable diffraction efficiency based on concentric zones patterned electrode is demonstrated. The alternating “transparent” and “opaque” state occurs when the LCFZP placed between two crossed polarizers. When the electric field was applied to the odd (even) zones, the odd (even) zones were dark, and the even (odd) zones were bright. The diffraction efficiency was varied with changing the voltage or by rotating the incident polarization direction. The maximum diffraction efficiency can reach 37.8% which is close to the theoretical limit of 40.5%, and the response time is reasonably fast. The proposed LCFZP with the advantages of easy fabrication, compact structures, low power consumption, and good stability, which has potential applications in many modern optical devices.

Controlled Liquid Crystal Optical Filter Combined with Video Surveillance Devices

Controlled Liquid Crystal Optical Filter Combined with Video Surveillance Devices

Fast response electrically controlled liquid crystal lens array for high resolution 2D/3D switchable display.

A fast response electrically controlled liquid crystal (LC) lens array is revealed. In order to realize the fast response, a double LC layer structure is adopted. The fabricated LC lens array has a small pitch of 310µm and LC layer with a thickness of 50μm. Experimental results show that the focal length of the LC lens array can be continuously adjusted by low driving voltage (∼6.5Vrms), and the shortest focal length is 0.5mm. The switching between 2D display and 3D display is realized by controlling the voltage off and on state of the LC lens array. Experimental result shows that the 2D/3D switchable display has a fast response time of 16ms. The short pitch LC lens array is expected to be used in high-resolution 2D/3D switchable display.

Research Progress of p-Type Oxide Thin-Film Transistors.

The development of transparent electronics has advanced metal–oxide–semiconductor Thin-Film transistor (TFT) technology. In the field of flat-panel displays, as basic units, TFTs play an important role in achieving high speed, brightness, and screen contrast ratio to display information by controlling liquid crystal pixel dots. Oxide TFTs have gradually replaced silicon-based TFTs owing to their field-effect mobility, stability, and responsiveness. In the market, n-type oxide TFTs have been widely used, and their preparation methods have been gradually refined; however, p-Type oxide TFTs with the same properties are difficult to obtain. Fabricating p-Type oxide TFTs with the same performance as n-type oxide TFTs can ensure more energy-efficient complementary electronics and better transparent display applications. This paper summarizes the basic understanding of the structure and performance of the p-Type oxide TFTs, expounding the research progress and challenges of oxide transistors. The microstructures of the three types of p-Type oxides and significant efforts to improve the performance of oxide TFTs are highlighted. Finally, the latest progress and prospects of oxide TFTs based on p-Type oxide semiconductors and other p-Type semiconductor electronic devices are discussed.

Liquid-crystal q-plates with a phase core to generation vortex beams with controllable number of singularities

Based on the method of azo dye photoalignment, electrically controlled liquid crystal (LC) q-plates for the generation of a given number of polarization and phase optical singularities have been designed. The results of experimental studies of polarization and phase characteristics of the generated singular beams are in good agreement with the proposed theoretical model. The proposed devices can be adapted for a variety of problems of modern photonics, including implementation of structured illumination microscopy, information coding, optical security technology, microrheology etc.

Investigation of electro-optical properties in bistable liquid crystal films doped with CsxWO3 nanorods

ABSTRACT It is of great practical significance to develop efficient and reversible bistable liquid crystal films. This work provides a multiple phase-shift controllable liquid crystal film containing tungsten bronze (CsxWO3) nanorods (NRs) and cholesteric liquid crystal, which can reversibly control the phase-shift via electric field, temperature or near infrared light. The CsxWO3 NRs were coated by polyvinylpyrrolidone (PVP) layer, and the CsxWO3/PVP NRs could form a compatible NIR-absorbing film, which could generate heat to switch LC film from planar texture to focal conic texture. The bistable liquid crystal film could save almost 53% time at thermal elimination compared to LC mixture without NIR absorbent when the content of CsxWO3/PVP NRs reaches 0.8%. The functional bistable liquid crystal films reported in this paper expand the application field of bistable liquid crystal display.

Intermittent Visual Occlusions Increase Balance Training Effectiveness.

Improving dynamic balance can prevent falls in humans with neurological and mechanical deficits. Dynamic balance requires the neural integration of multisensory information to constantly assess the state of body mechanics. Prior research found that intermittent visual rotations improved balance training during walking on a narrow beam, but limitations from the immersive virtual reality headset hindered balance training effectiveness overall. We theorized that intermittent visual occlusions with electrically controlled liquid crystal glasses would overcome the previous limitations of the immersive virtual reality headset and provide a means to enhance dynamic balance training efficacy. Forty healthy young individuals walked on a treadmill-mounted balance beam for 30 min (20 subjects with intermittent visual occlusions and 20 subjects with unperturbed vision). Balance performance, in number of step-offs of the beam, improved by 78% for the visual occlusions group on the same day of the training, a near fourfold improvement compared to the 21% improvement for the unperturbed vision group (t(38) = –5.2, p < 0.001). The difference between groups was also apparent 2 weeks later testing for retention (60% improvement for the visual occlusions group, 5% for the unperturbed vision group; t(38) = –4.2, p < 0.001). Intermittent visual occlusions are likely a simple method for enhancing balance training in dynamic motor tasks.

SEM observation of light control liquid crystal composite films

SEM observation of light control liquid crystal composite films

Facile indium recovery from waste liquid crystal displays: Chloride-facilitated indium electroreduction and stepwise Cu/MoO2 and indium electrodeposition

With a huge amount of waste liquid crystal displays (LCDs) generated annually, their proper recycling raises continuous concern to realize pollution control (heavy metal and liquid crystal) and resource recovery (indium). However, due to their multi-metal feature, traditional hydrometallurgy lacks of sufficient selectivity, which makes the recycling route lengthy, costly, and generate more waste. Electrodeposition acts as a promising technique for selective metal extraction from multi-metal system due to its high selectivity and electron as clean reagent. To fully develop its application in metal recovery, stepwise Cu/MoO2 and In electrodeposition from In-Cu-Mo-Fe waste LCD leachate is explored in depth. Electrochemical behavior analysis shows Cu and MoO2 can be first electrodeposited for their higher electroreduction potential. Cl- plays a key role in accelerating indium electroreduction kinetics, which largely shortens the extraction time without the sacrifice of current efficiency. This accelerating effect is attributed to the increased concentration of electroactive species or collision frequency. Under optimized condition, 99.41% of indium (> 99% purity) can be electrodeposited within 13 h with high current efficiency. This study provides a cleaner approach for waste LCDs recycling and gives implications for the potential application of electrochemical technique in e-waste recycling.

Controllable liquid crystal diffractive sail and its potential applications

This paper introduces a new type of diffractive solar sail composed of liquid crystal optical phased arrays, which control the thrust through electric modulation. The main feature of the proposed liquid crystal diffractive sail is its capability of generating a continuously variable and actively controllable tangential radiation pressure at the sun-facing attitude. The principles governing the generation of radiation pressure by electric modulation of the liquid crystal optical phased array under a broad spectrum of solar radiation are derived by considering a periodical voltage distribution analogous to a reflection step-shaped binary phase grating. Then the reliability of the theoretical model of radiation pressure is verified through comparison with finite-difference time-domain (FDTD) simulation results. A sun-facing liquid crystal diffractive sail may be utilized to replace the reflective sail in space missions by taking the advantage that no active attitude control of the sail surface towards sunlight is required. We also study the attitude control strategy of the proposed diffractive sail along its normal axis, allowing for the direction of tangential radiation pressure to be varied without changing its sun-facing attitude.

Thermal properties of polymer networks used in light control liquid crystal sheets for cars

Thermal properties of polymer networks used in light control liquid crystal sheets for cars

Viewing angle controllable liquid crystal display technology with micro structure

Viewing angle controllable liquid crystal display technology with micro structure

Electronically controlled liquid crystal terahertz polarization manipulation under static magnetic field pre-anchoring

In this work, a new strategy was proposed for active control of mm-thick liquid crystals (LC) cell to realize the polarization manipulation in terahertz (THz) regime, which through the electric field control and static magnetic field pre-anchoring. The LC cell was fabricated by a nematic 5CB LC and two silica substrates that were coated with the graphite layer as the transparent electrode. Under the pre-anchoring of the static magnetic field, the optical axis of LC can be precisely controlled by the variable electric field. By using a THz-TDS with a wire grid polarizer, the output THz polarization from the LC cell can be deduced from the amplitude and phase shift of ±45° components. Here, we systematically analyzed three different outfield configurations. Only if the ±45° components that output from the polarizer have phase shifts, can the polarization state conversion be realized. The results show that the linear to circular or the cross-polarization conversion were realized under the specific electric field. This work provides a new approach for the thick-LC layer anchoring and orientation control, and also the tunable polarization manipulation of THz LC devices.