Crystals

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10 pages, 2971 KiB

Open AccessArticle

Ferroelectric Liquid Crystal Compound Lens Based on Pancharatnam–Berry Phase

by Ying Ma, Mingkui Yin, Yuhang Shan, Vladimir G. Chigrinov, Hoi-Sing Kwok and Jianlin Zhao

Crystals 2022, 12(2), 231; https://doi.org/10.3390/cryst12020231 - 8 Feb 2022

Viewed by 2307

Abstract

We report a ferroelectric liquid crystal (FLC) compound lens based on the Pancharatnam–Berry (PB) phase. The phase of the FLC compound lens is an integration of polarization grating and a PB lens. Thus, when light passes through an FLC compound lens, the output [...] Read more.

We report a ferroelectric liquid crystal (FLC) compound lens based on the Pancharatnam–Berry (PB) phase. The phase of the FLC compound lens is an integration of polarization grating and a PB lens. Thus, when light passes through an FLC compound lens, the output light’s polarization handedness will be changed accordingly. In this case, FLC compound lenses can function as concave/convex lenses with spatially separated output light and rapid transmittance tunability. The FLC compound lenses were fabricated using a single-step holographic exposure system, based on a spatial light modulator working as numerous phase retarders. Photosensitive azo-dye material was used as the aligning layer. The output light transmittance of the FLC compound lens can be operated at 150 μs. Our results achieve the potential applications on various displays and augmented reality. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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5 pages, 2424 KiB

Open AccessArticle

A Method to Improve the Lifetime of Microcapsule Electrophoretic Display Modules

by Xidu Wang, Guoyuan Li, Xi Zeng, Yu Chen and Dianlu Hu

Crystals 2021, 11(10), 1259; https://doi.org/10.3390/cryst11101259 - 18 Oct 2021

Cited by 1 | Viewed by 2165

Abstract

Microcapsule electrophoretic display (MED) is a kind of display with the properties of reflectivity and low power consumption. It is widely used in electronic book readers, but some new applications have appeared in the Internet of Things (IoT) products. Long working time is [...] Read more.

Microcapsule electrophoretic display (MED) is a kind of display with the properties of reflectivity and low power consumption. It is widely used in electronic book readers, but some new applications have appeared in the Internet of Things (IoT) products. Long working time is required in IoT products because it is not easy to replace or install such displays. The main failure phenomenon is the mura that will appear after about 1 to 2 years of use. The root cause of the failure is analyzed, and the lifetime prediction models for MED are introduced. The high temperature and high humidity (HTHH) test is used to evaluate the protective effect of the packaging structure. The HTHH test result is reported for the new MED structure; it shows that the MED with the new structure involves a longer working time. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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9 pages, 2360 KiB

Open AccessArticle

Broadband Tunable Terahertz Beam Deflector Based on Liquid Crystals and Graphene

by Yanchun Shen, Jinlan Wang, Qiaolian Wang, Ximing Qiao, Yuye Wang and Degang Xu

Crystals 2021, 11(9), 1141; https://doi.org/10.3390/cryst11091141 - 18 Sep 2021

Cited by 3 | Viewed by 2698

Abstract

Terahertz (THz) technology has unique applications in, for example, wireless communication, biochemical characterization, and security inspection. However, high-efficiency, low-cost, and actively tunable THz modulators are still scarce. We propose a broadband tunable THz beam deflector based on liquid crystals (LCs). By a periodic [...] Read more.

Terahertz (THz) technology has unique applications in, for example, wireless communication, biochemical characterization, and security inspection. However, high-efficiency, low-cost, and actively tunable THz modulators are still scarce. We propose a broadband tunable THz beam deflector based on liquid crystals (LCs). By a periodic gradual distribution of the orientation of the LC in one direction, a frequency-independent geometric phase modulation is obtained. The LC device with this specific orientation distribution was obtained through ultraviolet polarization exposure. We have verified the broadband beam deflection in both the simulation and experiment. The device can achieve a good spin-coupled beam deflection effect in the 0.8–1.2 Thz band, and the average polarization conversion efficiency exceeds 70%. Moreover, because the electro-optical responsivity of LCs is excellent, graphene transparent electrode layers introduced on the upper and lower substrates enable the deflection modulation to be switched and dynamic tuning to be achieved. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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10 pages, 3831 KiB

Open AccessEditor’s ChoiceArticle

Multi-View 2D/3D Switchable Display with Cylindrical Liquid Crystal Lens Array

by Fan Chu, Di Wang, Chao Liu, Lei Li and Qiong-Hua Wang

Crystals 2021, 11(6), 715; https://doi.org/10.3390/cryst11060715 - 21 Jun 2021

Cited by 23 | Viewed by 4035

Abstract

We propose a multi-view 2D/3D switchable display by using cylindrical liquid crystal (LC) lens array with a low operating voltage and fast response time. The cylindrical LC lens array is composed of three parts: the LC layer, a top-plane indium tin oxide (ITO) [...] Read more.

We propose a multi-view 2D/3D switchable display by using cylindrical liquid crystal (LC) lens array with a low operating voltage and fast response time. The cylindrical LC lens array is composed of three parts: the LC layer, a top-plane indium tin oxide (ITO) electrode, and bottom periodic strip ITO electrodes. In the voltage-off state, the cylindrical LC lens array is equivalent to a transparent glass substrate and the viewers can see a clear 2D image. In the 3D mode, the cylindrical LC lens array can be used as a cylindrical lens array under a suitable operating voltage. As a result, the 2D and 3D images can be switched according to the state of the cylindrical LC lens array. The experimental result shows that the 2D/3D switchable display with the cylindrical LC lens array has a wider viewing angle, has no moiré pattern, and is much thinner compared to the other 2D/3D switchable display devices. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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10 pages, 5710 KiB

Open AccessEditor’s ChoiceArticle

Template Effect of Multi-Phase Liquid Crystals

by Yao Gao, Tengfei Huang and Jiangang Lu

Crystals 2021, 11(6), 602; https://doi.org/10.3390/cryst11060602 - 27 May 2021

Cited by 4 | Viewed by 2702

Abstract

The template effects on stability of twist structure liquid crystals (LCs) were investigated. By refilling a cholesteric LC (CLC) of different pitch into a blue phase LC (BPLC) template or a sphere phase LC (SPLC) template, a multi-phase and multi-pitch twist structure LC, [...] Read more.

The template effects on stability of twist structure liquid crystals (LCs) were investigated. By refilling a cholesteric LC (CLC) of different pitch into a blue phase LC (BPLC) template or a sphere phase LC (SPLC) template, a multi-phase and multi-pitch twist structure LC, which includes the refilling CLC and intrinsic template BPLC or SPLC, can be fabricated. By refilling a CLC of different chiral pitch into a CLC template, a multi-pitch CLC that includes the refilling CLC and intrinsic CLC, can be fabricated. Twist structure LC devices with multi-phase and multi-pitch show great potential for applications in optical communication, displays, and LC lasing. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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7 pages, 1723 KiB

Open AccessArticle

Electrically Tunable Terahertz Focusing Modulator Enabled by Liquid Crystal Integrated Dielectric Metasurface

by Yanchun Shen, Zhixiong Shen, Yuye Wang, Degang Xu and Wei Hu

Crystals 2021, 11(5), 514; https://doi.org/10.3390/cryst11050514 - 6 May 2021

Cited by 9 | Viewed by 3000

Abstract

Active lenses with focal tunable properties are highly desired in the modern imaging systems from the visible to the microwaves. In this paper, we demonstrate a terahertz (THz) lens with electrically switchable focal length. It is composed of a large-birefringence liquid crystal (LC) [...] Read more.

Active lenses with focal tunable properties are highly desired in the modern imaging systems from the visible to the microwaves. In this paper, we demonstrate a terahertz (THz) lens with electrically switchable focal length. It is composed of a large-birefringence liquid crystal (LC) layer infiltrating a dielectric metasurface. When the birefringence of LC is tuned with an external bias, the phase shift of a single meta-unit will change. With parameter sweep using the finite-different time-domain (FDTD) simulation method, meta-units with varying geometries are optimized to achieve a focal length switchable metalens. The numerical results show that the focal length can be switched between 8.3 mm and 10.5 mm at bias OFF and ON states, respectively, which is consistent with the design. A feasible fabrication procedure of the lens is further discussed. Such a device can be designed beyond the THz band to the visible or the microwaves, and may be widely applied in integrated imaging systems. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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13 pages, 5531 KiB

Open AccessArticle

High-Efficiency Responsive Smart Windows Fabricated by Carbon Nanotubes Modified by Liquid Crystalline Polymers

by Yuan Deng, Shi-Qin Li, Qian Yang, Zhi-Wang Luo and He-Lou Xie

Crystals 2021, 11(4), 440; https://doi.org/10.3390/cryst11040440 - 18 Apr 2021

Cited by 10 | Viewed by 2944

Abstract

Smart windows can dynamically and adaptively adjust the light transmittance in non-energy or low-energy ways to maintain a comfortable ambient temperature, which are conducive to efficient use of energy. This work proposes a liquid crystal (LC) smart window with highly efficient near-infrared (NIR) [...] Read more.

Smart windows can dynamically and adaptively adjust the light transmittance in non-energy or low-energy ways to maintain a comfortable ambient temperature, which are conducive to efficient use of energy. This work proposes a liquid crystal (LC) smart window with highly efficient near-infrared (NIR) response using carbon nanotubes grafted by biphenyl LC polymer brush (CNT-PDB) as the orientation layer. The resultant CNT-PDB polymer brush can provide the vertical orientation of LC molecules to maintain the initial transparency. At the same time, the smart window shows a rapid response to NIR light, which can quickly adjust the light transmittance to prevent sunlight from entering the room. Different from common doping systems, this method avoids the problem of poor compatibility between the LC host and photothermal conversion materials, which is beneficial for improving the durability of the device. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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8 pages, 21375 KiB

Open AccessArticle

Light-Driven Pitch Tuning of Self-Assembled Hierarchical Gratings

by Yuan-Hang Wu, Sai-Bo Wu, Chao Liu, Qing-Gui Tan, Rui Yuan, Jing-Ge Wang, Ling-Ling Ma and Wei Hu

Crystals 2021, 11(4), 326; https://doi.org/10.3390/cryst11040326 - 25 Mar 2021

Cited by 3 | Viewed by 2625

Abstract

Gratings are of vital importance in modern optics. Self-assembled cholesteric liquid crystal (CLC) gratings have attracted intensive attention due to their easy fabrication and broad applications. However, simultaneously achieving arbitrary patterning and delicate tuning of CLC gratings remains elusive. Here, light-driven pitch tuning [...] Read more.

Gratings are of vital importance in modern optics. Self-assembled cholesteric liquid crystal (CLC) gratings have attracted intensive attention due to their easy fabrication and broad applications. However, simultaneously achieving arbitrary patterning and delicate tuning of CLC gratings remains elusive. Here, light-driven pitch tuning is accomplished in hierarchical gratings formed in a molecular switch doped CLC. We fabricate a checkerboard hierarchical CLC grating for a demonstration, whose pitch is optically tuned from 4.6 µm to 10.7 µm. Correspondingly, the first-order diffraction angle continuously changes from 9.4° to 4.8° and a significant polarization selectivity is also observed. In addition, hierarchical CLC gratings with triangular wave pattern, Archimedean spiral, and radial stripes are also demonstrated. This work creates new opportunities for soft-matter-based intelligent functional materials and advanced photonic devices. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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10 pages, 4873 KiB

Open AccessArticle

Fast Tunable Biological Fluorescence Detection Device with Integrable Liquid Crystal Filter

by Qing Yang, Tong Sun, Xinyu Wu, Guangchao Cui, Mengzheng Yang, Zhongyang Bai, Lin Wang, Helin Li, Wenjing Chen, Qunwen Leng, Robert Puers, Ceyssens Frederik, Michael Kraft, Qinglin Song, Huabin Fang, Dewen Tian, Dexin Wang, Huijie Zhao, Weisheng Zhao, Tianxiao Nie, Qi Guo and Lianggong Wen Show full author list Hide full author list

Crystals 2021, 11(3), 272; https://doi.org/10.3390/cryst11030272 - 10 Mar 2021

Cited by 2 | Viewed by 2492

Abstract

Detecting a variety of biological samples accurately and swiftly in an integrated way is of great practical significance. Currently, biofluorescent spectrum detection still largely relies on microscopic spectrometers. In this study, we propose an integrable method to detect biofluorescent spectrums with designed liquid [...] Read more.

Detecting a variety of biological samples accurately and swiftly in an integrated way is of great practical significance. Currently, biofluorescent spectrum detection still largely relies on microscopic spectrometers. In this study, we propose an integrable method to detect biofluorescent spectrums with designed liquid crystal tunable filter (LCTF), in order to identify typical biological samples such as cells and bacteria. Hela cells labeled with red and green fluorescent proteins and Pseudomonas with fluorescence wavelengths of 610 nm, 509 nm and 450 nm, respectively, are inspected. High-resolution (6 μm) biofluorescent results have been achieved, together with clear images of the Hela cell clusters and the Pseudomonas bacteria colonies. Biofluorescence signals can be detected at a high transmittance (above 80%), and the response time of the device can reach 20 ms or below. The proposed method has the potential to be integrated into a microfluidic system to detect and identify the biofluorescent signals as a high throughput, low-cost option, for both high resolution and large field observation applications. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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Review

Jump to: Research

19 pages, 3275 KiB

Open AccessReview

Mini-LED Backlight Technology Progress for Liquid Crystal Display

by Zhiwen Gao, Honglong Ning, Rihui Yao, Wei Xu, Wenxin Zou, Chenxiao Guo, Dongxiang Luo, Hengrong Xu and Junlin Xiao

Crystals 2022, 12(3), 313; https://doi.org/10.3390/cryst12030313 - 23 Feb 2022

Cited by 32 | Viewed by 10012

Abstract

As consumers pursue higher display quality, Mini-LED backlight technology has become the focus of research in the current display field. With its size advantage (100–200 μm), it can achieve one-thousand-level divisional dimming, and it can also be combined with quantum dot technology to [...] Read more.

As consumers pursue higher display quality, Mini-LED backlight technology has become the focus of research in the current display field. With its size advantage (100–200 μm), it can achieve one-thousand-level divisional dimming, and it can also be combined with quantum dot technology to greatly improve the contrast, color gamut, dark state and other element of the display performance of LCD displays. Mini-LED backlight technology is undoubtedly the most ideal solution to realize a highly dynamic range display of LCD displays, and has been widely commercialized in many fields such as TVs, tablet computers, notebook computers, and car monitors. This review mainly introduces the efforts made by researchers to eliminate the halo effect, thinning of the backlight module and reducing the backlight power consumption. The application of quantum dot technology in backlight is also presented. We predict that the number of Mini-LED backlight partitions is expected to reach a level of more than 3000 in the future, further utilizing the advantages of the small size in local dimming, but it will also inevitably be challenged by some issues such as power consumption and heat dissipation. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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21 pages, 3799 KiB

Open AccessReview

Survey of Mura Defect Detection in Liquid Crystal Displays Based on Machine Vision

by Wuyi Ming, Shengfei Zhang, Xuewen Liu, Kun Liu, Jie Yuan, Zhuobin Xie, Peiyan Sun and Xudong Guo

Crystals 2021, 11(12), 1444; https://doi.org/10.3390/cryst11121444 - 24 Nov 2021

Cited by 17 | Viewed by 8331

Abstract

Liquid crystal display (LCD) is a display device based on liquid crystal electro-optic effect, and LCDs have gradually appeared and have become an indispensable part of people’s lives. In the development of LCD technology, the detection of Mura defects is a key concern [...] Read more.

Liquid crystal display (LCD) is a display device based on liquid crystal electro-optic effect, and LCDs have gradually appeared and have become an indispensable part of people’s lives. In the development of LCD technology, the detection of Mura defects is a key concern in the manufacturing process. The Mura defect is a kind of display defect with low contrast and an irregular shape. This study first explains the mechanism of Mura defects in the LCD manufacturing process and classifies typical Mura defects. Then, three main purposes for the defect detection of LCDs are compared, and the advantages and disadvantages are conducted. Following that, this research examines reviews the linked literature on image preprocessing, feature extraction, dimension reduction, and classifiers of Mura defects. Finally, the future development trend and research direction of Mura defect detection based on machine vision can be drawn by this study. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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10 pages, 2592 KiB

Open AccessEditor’s ChoiceReview

Optically Rewritable Liquid Crystal Displays: Characteristics and Performance

by Vladimir G. Chigrinov, Aleksey A. Kudreyko and Fedor V. Podgornov

Crystals 2021, 11(9), 1053; https://doi.org/10.3390/cryst11091053 - 1 Sep 2021

Cited by 5 | Viewed by 2788

Abstract

Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing [...] Read more.

Recent achievements in the photoalignment technique for fabrication of optically rewritable electronic paper with high performance characteristics are surveyed with emphasis on temporal constraints on the exposure process. The possibility of creating electrode-free electronic paper has very important practical aspects. However, many existing studies do not include sufficient analysis on how to achieve acceptable reflective characteristics within short exposure time. In order to achieve this goal, we have applied the rotational diffusion model. We find that the parameters of the diffusion model can be adjusted to get acceptable light-reflecting characteristics within 10 s of exposure. In comparison with the long-time exposure, the reflectance coefficient reduces by 24%. The route to material improvements for optimized e-paper device is discussed. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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16 pages, 8742 KiB

Open AccessEditor’s ChoiceReview

A Review of Two-Dimensional Liquid Crystal Polarization Gratings

by Kai Zuo, Yue Shi and Dan Luo

Crystals 2021, 11(9), 1015; https://doi.org/10.3390/cryst11091015 - 25 Aug 2021

Cited by 10 | Viewed by 4531

Abstract

In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal [...] Read more.

In the past two decades, polarization gratings (PGs) have attracted intensive attention due to the high-efficient diffraction and polarization selectivity properties. On one hand, the one-dimensional (1D) PGs have been investigated widely and adapted to various applications. On the other hand, optical signal manipulation stimulates the development of multibeam optical devices. Therefore, the development of two-dimensional (2D) PGs is in demand. This review summarizes the research progress of 2D PGs. Different designs and fabrication methods are summarized, including assembling two 1D polarization patterns, a 2D holographic lithography by polarization interference and a micro-pixelated electric field stimulated 2D liquid crystal (LC) structure. Both experiments and analyses are included. The design strategy, diffraction property, merits and demerits are discussed and summarized for the different methods. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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17 pages, 30796 KiB

Open AccessReview

Fluorescent Azobenzene-Containing Compounds: From Structure to Mechanism

by Lulu Xue, Ying Pan, Shaohai Zhang, Yinjie Chen, Haifeng Yu, Yonggang Yang, Lixin Mo, Zhicheng Sun, Luhai Li and Huai Yang

Crystals 2021, 11(7), 840; https://doi.org/10.3390/cryst11070840 - 20 Jul 2021

Cited by 19 | Viewed by 8685

Abstract

The reversible photoisomerization of azobenzenes has been extensively studied to construct systems with optical responsiveness; however, this process limits the luminescence of these compounds. Recently, there have been many efforts to design and synthesize fluorescent azobenzene compounds, such as inhibition of electron transfer, [...] Read more.

The reversible photoisomerization of azobenzenes has been extensively studied to construct systems with optical responsiveness; however, this process limits the luminescence of these compounds. Recently, there have been many efforts to design and synthesize fluorescent azobenzene compounds, such as inhibition of electron transfer, inducing aggregation, and metal-enhancement, which make the materials ideal for application in fluorescence probes, light-emitting devices, molecular detection, etc. Herein, we review the recently reported progress in the development of various fluorescent azobenzenes and summarize the possible mechanism of their fluorescence emission. The potential applications of these materials are also discussed. Finally, in order to guide research in this field, the existing problems and future development prospects are discussed. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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22 pages, 3293 KiB

Open AccessReview

Recent Developments in Flexible Transparent Electrode

by Tingting Wang, Kuankuan Lu, Zhuohui Xu, Zimian Lin, Honglong Ning, Tian Qiu, Zhao Yang, Hua Zheng, Rihui Yao and Junbiao Peng

Crystals 2021, 11(5), 511; https://doi.org/10.3390/cryst11050511 - 5 May 2021

Cited by 54 | Viewed by 9123

Abstract

With the rapid development of flexible electronic devices (especially flexible LCD/OLED), flexible transparent electrodes (FTEs) with high light transmittance, high electrical conductivity, and excellent stretchability have attracted extensive attention from researchers and businesses. FTEs serve as an important part of display devices (touch [...] Read more.

With the rapid development of flexible electronic devices (especially flexible LCD/OLED), flexible transparent electrodes (FTEs) with high light transmittance, high electrical conductivity, and excellent stretchability have attracted extensive attention from researchers and businesses. FTEs serve as an important part of display devices (touch screen and display), energy storage devices (solar cells and super capacitors), and wearable medical devices (electronic skin). In this paper, we review the recent progress in the field of FTEs, with special emphasis on metal materials, carbon-based materials, conductive polymers (CPs), and composite materials, which are good alternatives to the traditional commercial transparent electrode (i.e., indium tin oxide, ITO). With respect to production methods, this article provides a detailed discussion on the performance differences and practical applications of different materials. Furthermore, major challenges and future developments of FTEs are also discussed. Full article

(This article belongs to the Special Issue Liquid Crystals in China)

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