最新刊期
期 1 ， 2023
- 摘要：In recent years， optical vortex arrays have attracted increasing attention for their potential applications in numerous areas， such as optical communications， multiple-particle manipulation and parallel laser fabrication. However， the generation of switchable longitudinal vortex arrays remains a great challenge. In this paper， a liquid crystal （LC） spiral Dammann zone plate is designed via the Dammann encoding method and fabricated via the LC photoalignment technology. The experimental results show that this device can create a 1×5 longitudinal vortex array with high efficiency， and with space-variant topological charges. Through tuning the applied voltage， the device can be switched between ON and OFF state dynamically. Besides， the topological charges of the generated longitudinal vortex array can undergo a reversal or additive transformation by horizontally/vertically flipping the device or altering the mode of incident light. The LC spiral Dammann zone plate is distinguished by low cost， high efficiency and electro-optical tunability， thus facilitating the applications of LC elements in the field of multi-dimensional beam shaping.关键词：liquid crystal;photoalignment technology;Optical vortex array;Dammann grating
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发布时间：2023-03-15 - 摘要：A liquid crystal （LC） lens array based on polymer protrusion is proposed. The indium tin oxide （ITO） electrodes are coated on periodic polymer protrusion， a dielectric layer is used for flattening phase profile， and the vertical electric field across the LC layer varies linearly over the lens aperture， which is obtained in the voltage-on state. As a result， a centrosymmetric gradient refractive index profile within the LC layer is generated， which causes the focusing behavior. As a result of the optimization， a thin cell gap which greatly reduces the switching time of the LC lens array can be achieved in our design. The main advantages of the proposed LC lens array are in the comparatively low operating voltage， the flat substrate surface， the simple electrodes， and the uniform LC cell gap. The simulation results show that the focal length of the LC lens array can be tuned continuously from infinity to 1.28 mm by changing the applied voltage.关键词：liquid crystal lens;polymer protrusion;dielectric layer;short focal length
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发布时间：2023-03-15 - 摘要：Blue phase liquid crystals have received widespread attention due to their excellent electro-optical properties for applications in information display and optoelectronic devices. Nowadays， the ultra-rapid development of information technology is posing even higher demands on the speeds of information delivery， processing and storage. To further improve the response time of blue phase liquid crystal in electro-optical performance， we utilize a dual-frequency nematic liquid crystal as the host， doped with reactive monomer， chiral dopant， photo-initiator to prepare polymer-stabilized dual-frequency blue phase liquid crystals （PS-DF-BPLCs）. By adjusting the durations of the two voltage pulses， fast electro-optical response of PS-DF-BPLCs is achieved. Both the switching-on and switching-off processes of the PS-DF-BPLC are less than 500 ns.关键词：polymer stabilized;blue phase liquid crystal;electro-optical switching;dual-frequency liquid crystal
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发布时间：2023-03-15 - 摘要：Hybrid-order Poincaré Sphere is always used to describe arbitrary vector vortex beams and it makes the physical process of their polarization and phase evolution more intuitive. The vector vortex beam can be generated by using spatial light modulator， laser resonator and the combination of metasurface and spiral phase plate. However， the vector vortex beams generated by these methods are usually limited to specific polarization states， and have disadvantages such as low damage threshold， low conversion efficiency， and large structure size. Moreover， these methods can only generate the vector vortex beam on a specific hyrid-order Poincaré sphere. In this paper， we present a method to generate arbitrary vector vortex beam on two hyrid-order Poincaré spheres of different orders using two electronically controlled adjustable liquid crystal q-plates and a wave plate. The results were verified by theory and experiment. The generated vector vortex beam is also verified， which is largely consistent with the predictions. This method has the advantages of good electrical controllability， good integration and high conversion efficiency. This scheme can provide basic optical system support for the application of structured beams.关键词：Mixed-order Poincaré sphere;Vector vortex beam;Liquid crystal photopatterned technology
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发布时间：2023-03-15
Liquid Crystal Optics
- 摘要：Due to the existence of color filter， the traditional displays have large power consumption but relatively low efficiency. In this article， we propose a method to utilize the polarization of an ultraviolet light， which is modulated by liquid crystal， to influence the light intensity distribution of a designed nanostructure in order to tune the stimulated fluorescent light of the quantum dots deposited in the corner of the metallic nanostructure. The concept is fundamentally based on the polarization-influenced local surface plasmon resonance and the proposed device comprises of the metallic nanostructure， quantum dots and liquid-crystal-based light polarization modulator. We simulate the electric field distribution for a single pixel case， and calculate the light intensity distributions for several metallic nanostructures under different polarization states of light. Thus， we theoretically verify the light intensity enhancement via local surface plasmon resonance arising from the specific metallic nanostructure. Through the technologies of E-beam etching and semiconductor deposition， the quantum dots with different sizes for corresponding colors can be implanted in specific “hot” areas， i.e.， the corner of the metallic nanostructure， whose stimulated emitting fluorescent light intensity can be controlled via light polarization modulation through liquid crystal module. Thus， we propose a novel display mode， which possesses relatively high efficiency and large color gamut. Although it currently encounters some unexpected issues such as relatively low contrast ratio and low resolution， our proposed device does provide a potential way for the information display in people’s daily life. We believe that with the development of the technology and the optimization of the device， the proposed device is promising in the field of display or beyond.关键词：Plasma resonance;fluorescent quantum dot;liquid crystal;polarization states of light;light intensity enhancement
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发布时间：2023-03-15 - 摘要：The optically driving liquid crystal display （ODLCD） realizes display function by controlling the alignment directions of liquid crystal （LC） molecules under exposure light， which has applications in electric-optic （E-O） devices. However， it is still limited to the laboratory for its long rewriting time and response time of the ODLCD. In this work， the composite film with Nickel oxide （NiO） and azo dye （SD1） was fabricated， and the rewriting time and the response time of ODLCD depending on SD1 with NiO doping were studied. Meanwhile， the SD1-NiO distribution and morphology were discussed by scanning electron microscopy （SEM）， transmission electron microscopy （TEM）， and atomic force microscopy （AFM） images， respectively. The results show that the nanoparticle size of NiO increases with the concentration of NiO-SD1. Among the different ratios （1∶0 to 1∶0.1） of SD1-NiO concentration， the ratio of 1∶0.08 is optimal and a minimum rewriting time of 6.8 s has been reached. Besides， for the conventional electricity driven LCD application， the response time of ODLCD can be decreased to a maximum value of 5 ms at the optimal ratio （1∶0.02） between SD1 and NiO.关键词：optically driving liquid crystal display;photo-alignment;Nickel oxide;rewriting time;response time
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发布时间：2023-03-15
LCD Technology
- 摘要：Liquid crystalline networks have attracted more and more interest in recent years because of the potential application in artificial muscles， soft robotics， microfluidics， 4D printing， etc. Since their chemical structures contain the cross-linked networks and mesogens endowing them with good processability， stability and mechanical performance of polymers along with the adjustable orientation of liquid crystal molecules， the liquid crystalline networks usually have the advantages such as editable appearance， tunable function， and responsiveness to diverse stimuli. Thus， shape and color information can be accurately written into the material， which will reappear under specific external stimulus （e.g.， light， heat， electric field， and solvent）， thus can realize the storage， encryption and reading of information. This review briefly discusses the information storage mechanism based on liquid crystalline networks with manipulatable color （e.g.， structural color and fluorescence） and shape memory. Their applications in camouflage， multi-level information storage and information transmission are also summarized.关键词：Liquid crystalline network;shape memory;programmable color;information storage
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发布时间：2023-03-15 - 摘要：Liquid crystal polymers （LCPs） are functional polymers that have both the orientational order of liquid crystal and mechanical properties of polymers. The introduction of structural units with photochemical isomerization or photothermal response into liquid crystal polymers can make them undergo phase transition under light or thermal stimulation， inducing macroscopic deformation. After LCPs are oriented by one-step or two-step alignment methods， the alignment of the LCPs can be programmed. Shape changing of LCPs has potential applications in the fields of biomimetic soft robots， microfluidics， soft actuators， structural color and anti-counterfeiting. This review introduces the major orientation techniques for liquid crystal polymers and developed shape-change-based functions， and finally， an outlook of LCPs in future technological applications is proposed.关键词：Liquid crystal polymers;actuators;microfluidics;smart materials
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发布时间：2023-03-15
Intelligent Liquid Crystal Materials
- 摘要：Ferroelectricity is a spontaneous polarization state possessed by dielectrics， which generally occurs in crystalline （solid） material systems with low symmetry. Fluid or highly fluid soft matter systems usually exhibit high symmetry， which is contrary to the requirement of ferroelectricity. The introduction of strong polarity or ferroelectricity is a strategy that has attracted much attention in the fields of new liquid crystal materials and flexible optoelectronic devices. Compared with the traditional liquid crystals and soft matter systems， the ferroelectric nematic liquid crystals possess several revolutionary properties， including ultra-high dielectric permittivity， strong nonlinear optical response， low-voltage driving and high fluidity. It provides numerous possibilities for the development of novel advanced flexible optical and electronic devices. This review looks back the history of the foundation and development of the ferroelectric nematic liquid crystals， then， explains the relationship between the ferroelectric nematic liquid crystals and the molecular structure， physical topology， and characteristic properties. Finally， this review summarizes and makes a short perspective on the future applications by employing the ferroelectric nematic liquid crystals. The ferroelectric nematic liquid crystals have great potential in new memory devices， flexible high-end optoelectronic devices， nonlinear optics， and other fields.关键词：Ferroelectricity;liquid crystal;nonlinear optics;Ferroelectric nematic;polarity
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发布时间：2023-03-15 - 摘要：From the ocean to the sky， from physical to biological systems， solitons are ubiquitous and have been observed in different kinds of nonlinear systems. Liquid crystals， well known for their applications in electro-optics and displays， have been broadly used as a perfect platform for studying solitons. Solitons in liquid crystals have received increasing attention recently due to their great potentials in fundamental physical science and various applications. This review discusses the most recent advances in the experimental researches of directrons in achiral and chiral nematics， respectively. The novel dissipative soliton has received increasing attention recently due to its various fascinating nonlinear dynamic behaviors and its potential applications in optics and microfluidics.关键词：nematic liquid crystals;cholesteric liquid crystals;solitons;directrons
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发布时间：2023-03-15
Liquid Crystal Frontier
- 摘要：In the three-dimensional （3D） shape measurement based on structural light fringe projection， various factors due to such as environmental environment can produce point cloud noise. In the existing point cloud denoising method， the point cloud denoising needs to be carried out by analyzing the geometric relationship between 3D space and point cloud， and is faced with a series of problems such as complex calculation and low efficiency. In order to improve point cloud accuracy and denosing speed， a point cloud denoising method is proposed based on image segmentation. Firstly， a 2D point cloud map image is established according to the 3D point cloud reconstructed by structured light fringe projection. Secondly， segmentation of 2D point cloud map image is performed by using threshold segmentation method and region growing method. Then， the segmented noise area is recorded and removed. Finally， the new 2D point cloud mapping image is re-reconstructed in 3D space to obtain a point cloud with noise removed. Experimental results show that point cloud accuracy can reach 99.974% after the proposed method， and denoising time is 0.954 s，which can effectively remove point cloud noise and avoid complex calculations in 3D space.关键词：structured light projection;image segmentation;point cloud denoising;three-dimensional measurement
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发布时间：2023-03-15 - 摘要：Aiming at the problems of missing and false detection in existing smoke and fire detection algorithms， a new lightweight algorithm based on Effective Global Context Network （EGC-Net） is proposed. It takes the lightweight object detection network YOLOX as the basic network， and embeds an improved EGC-Net between the backbone feature extraction network and feature pyramid network of YOLOX. EGC-Net is composed of a three-stage structure of context modeling， feature transformation and feature fusion， which is used to obtain the global context information of image， model the long-range dependency of smoke or fire objects and its background， and learn more discriminative visual features by combining the channel attention mechanism for smoke and fire detection. Experimental results indicate that the image-level recall rate of the proposed smoke and fire detection algorithm EGC-YOLOX is 95.56%， and the image-level false alarm rate is 4.75%， both of which are superior to the compared typical lightweight algorithms， and the speed also meets the requirements of real-time detection. The proposed algorithm can be promoted and applied to the field of security and fire protection for real-time fire monitoring and early warning management.关键词：smoke and fire detection;EGC-Net;YOLOX;global context;attention mechanism
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发布时间：2023-03-15 - 摘要：For the problem of omission and misdetection of small-scale aircraft targets in aerial images， an improving SSD object detection model is proposed based on SSD （Single Shot MultiBox Detector） model. Firstly， in view of the lack of semantic and detailed information in the shallow feature map in the SSD model， a feature fusion mechanism is designed to enrich the semantic and detailed information of the shallow feature layer by adding the supplementary feature layer obtained from the recursive reverse path. Then， to address the problem of the SSD model to focus on the channels and spatial information， a hybrid attention module combining channels and space is introduced to improve the overall attention ability of the model. Finally， the proportion of prior boxes is adjusted for the problem of mismatch to small-scale targets in the SSD model. The self-made aerial images data set is used for verification. The results show that the improved algorithm accuracy is 95.7%， which is 7.5% higher than original SSD algorithm， and the detection speed is 30.8 FPS.关键词：object detection;feature fusion;attentional mechanism;aerial images
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发布时间：2023-03-15
Image Processing
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