High-capacity MIMO visible light communication integrated into mini-LED LCDs.

Visible light communication (VLC) can be integrated into a liquid crystal display (LCD) by modulating its backlight while normally showing pictures. Received by ordinary cameras, such integrated display and communication (IDAC) systems are promising for the Internet of Things and Metaverse. However, in the premise of unaffected display function, the capacity of current IDAC systems is limited, with data rates of very few kbps. This work proposes a new architecture: multiple-input, multiple-output (MIMO) VLC integrated into a mini-LED LCD, whose many backlight segments act as multiple transmitters. A camera utilizes the rolling shutter effect with independent pixel columns to form multiple outputs. The communication capacity is thus significantly multiplied by the backlight column number. In addition, local dimming, which is favorable for an LCD's contrast and power consumption, is exploited to achieve efficient signal modulation. We built a mini-LED LCD prototype with 8-by-20 backlight segments for experimental verification. The backlight segments multiplex a video-rate signal for local dimming and a high-frequency (∼34 kHz) signal modulated through multi-pulse position modulation (MPPM) for VLC. By taking photographs with a camera 1.1 m away from the screen, a record-high rate of 201.6 kbps (approximately ten times faster than current IDAC systems) was experimentally achieved with a bit error rate satisfying the forward error correction. Improved image contrast due to local dimming was also observed.

Enhancing the spatial resolution of light-field displays without losing angular resolution by a computational subpixel realignment.

Low spatial resolution is an urgent problem in integral imaging light-field displays (LFDs). This study proposes a computational method to enhance the spatial resolution without losing angular resolution. How rays reconstruct voxels through lenslets is changed so that every ray through a lenslet merely provides a subpixel. The three subpixels of a pixel no longer form one voxel but three independent voxels. We further demonstrate imperfect integration of subpixels, called the sampling error, can be eliminated on specific image depths, including the central depth plane. By realigning subpixels in the above manner under no sampling error, the sampling rate of voxels is three times the conventional pixel-based LFDs. Moreover, the ray number of every voxel is preserved for an unaffected angular resolution. With unavoidable component alignment errors, resolution gains of 2.52 and 2.0 are verified in simulation and experiment by computationally updating the elemental image array. The proposed computational method further reveals that LFDs intrinsically have a higher space-bandwidth product than presumed.

Multi-grayscale driving system for passive-matrix alternating current electroluminescence display.

Alternating current electroluminescence (ACEL) has great potential in flexible displays, especially in textile displays. However, since ACEL needs high-frequency, high-voltage AC signal to drive, there remains no driving scheme for pixelated ACEL display to achieve multiple gray scales. In this work, a driving scheme based on full-bridge inverters is proposed for passive-matrix ACEL (PMACEL) display, which achieves multiple gray scales by changing the duty cycle of the square wave. A single-pixel ACEL displaying 16 gray levels (4 bits) and a 5 × 8 fabric PMACEL displaying eight gray levels are demonstrated, enabling flexible ACEL devices to exhibit more vivid tones on a fabric substrate.

Cation-Modified Poly(vinyl alcohol) Film to Optimize the Bistability of Transparent Electrophoretic Display Based on Charge Adsorption Behavior in Nonpolar Solvent.

Electrophoretic displays (EPDs) utilize the electrophoretic particles in electronic ink (e-ink) to display different color states with bistability. Bistability of EPDs is achieved by placing colloidal particles in a highly viscous solvent to keep the distribution of colloidal particles stable without sustaining the external field, so it only consumes power when updating the image. The feature of low power consumption makes it suitable for applications such as advertising boards, price tags, etc. Apart from these applications, recent research on lateral-driving EPDs extends its applications to smart windows, privacy control, and so on. However, achieving bistability by simply increasing the viscosity of solvent is inefficient in the case of lateral driving operation. Therefore, it is deserving to have intensive study on the mechanism of bistability from other aspects. Herein, we propose a mechanism to investigate the charge adsorption behavior on the electrode to affect the bistability of particles, which is based on the "Stern layer adsorption/desorption" model. Based on the above mechanism, we further fabricated a hexadecyl trimethylammonium bromide (CTAB)/poly(vinyl alcohol) (PVA) composite film on the electrode to improve the bistability of lateral-driving EPD by reducing the diffusion current caused by unabsorbed charges. This developed lateral-driving EPD can significantly improve the bistability, which is enhanced from 40 s to 7 min, an increase by a factor of approximately 10. This work gives a way to consider the bistability of colloidal particles in nonpolar solvent.

CO2-Promoted and Copper-Catalyzed Dehydroxylative Coupling of Benzylic Alcohols by the NaBH4/I2 System.

An efficient and CO2-promoted dehydroxylative coupling of benzylic alcohols catalyzed by ligand-free cuprous chloride has been achieved. The discovered catalytic reductive coupling reaction is a newly C-C bond-forming transformation of alcohols. Mechanistic insight is gained through control reactions.

High Sensitivity, Wide Linear-Range Strain Sensor Based on MXene/AgNW Composite Film with Hierarchical Microcrack.

Stretchable strain sensors suffer the trade-off between sensitivity and linear sensing range. Developing sensors with both high sensitivity and wide linear range remains a formidable challenge. Different from conventional methods that rely on the structure design of sensing nanomaterial or substrate, here a heterogeneous-surface strategy for silver nanowires (AgNWs) and MXene is proposed to construct a hierarchical microcrack (HMC) strain sensor. The heterogeneous surface with distinct differences in cracks and adhesion strengths divides the sensor into two regions. One region contributes to high sensitivity through penetrating microcracks of the AgNW/MXene composite film during stretching. The other region maintains conductive percolation pathways to provide a wide linear sensing range through network microcracks. As a result, the HMC sensor exhibits ultrahigh sensitivity (gauge factor ≈ 244), broad linear range (ɛ = 60%, R2 ≈ 99.25%), and fast response time (<30 ms). These merits are confirmed in the detection of large and subtle human motions and digital joint movement for Morse coding. The manipulation of cracks on the heterogeneous surface provides a new paradigm for designing high-performance stretchable strain sensors.

Fast shadow casting algorithm in analytical polygon-based computer-generated holography.

Shadow casting is essential in computer graphics, which can significantly enhance the reality of rendered images. However, shadow casting is rarely studied in polygon-based computer-generated holography (CGH) because state-of-art triangle-based occlusion handling methods are too complicated for shadow casting and unfeasible for complex mutual occlusion handling. We proposed a novel drawing method based on the analytical polygon-based CGH framework and achieved Z-buffer-based occlusion handling instead of the traditional Painter's algorithm. We also achieved shadow casting for parallel and point light sources. Our framework can be generalized to N-edge polygon (N-gon) rendering and accelerated using CUDA hardware, by which the rendering speed can be significantly enhanced.

Deep learning-based real-time driving for 3-field sequential color displays with low color breakup and high fidelity.

Field sequential color liquid crystal displays (FSC-LCDs) are promising for applications needing high brightness and high resolution because removing color filters brings three times the light efficiency and spatial resolution. In particular, the emerging mini-LED backlight introduces compact volume and high contrast. However, the color breakup severely deteriorates FSC-LCDs. Concerning color breakup, various 4-field driving algorithms have been proposed at the cost of an additional field. In contrast, although 3-field driving is more desired due to fewer fields used, few 3-field methods that can balance image fidelity and color breakup for diverse image content have been proposed. To develop the desired 3-field algorithm, we first derive the backlight signal of one multi-color field using multi-objective optimization (MOO), which achieves a Pareto optimality between color breakup and distortion. Next, considering the slow MOO, the MOO-generated backlight data forms a training set to train a lightweight backlight generation neural network (LBGNN), which can produce a Pareto optimal backlight in real-time (2.3 ms on GeForce RTX 3060). As a result, objective evaluation demonstrates a reduction of 21% in color breakup compared with currently the best algorithm in color breakup suppression. Meantime, the proposed algorithm controls the distortion within the just noticeable difference (JND), successfully addressing the conventional dilemma between color breakup and distortion for 3-field driving. Finally, experiments with subjective evaluation further validate the proposed method by matching the objective evaluation.

Real-time computer-generated integral imaging light field displays: revisiting the point retracing rendering method from a signal processing perspective.

Integral imaging light field displays (InIm-LFDs) can provide realistic 3D images by showing an elemental image array (EIA) under a lens array. However, it is always challenging to computationally generate an EIA in real-time with entry-level computing hardware because the current practice that projects many viewpoints to the EIA induces heavy computations. This study discards the viewpoint-based strategy, revisits the early point retracing rendering method, and proposes that InIm-LFDs and regular 2D displays share two similar signal processing phases: sampling and reconstructing. An InIm-LFD is demonstrated to create a finite number of static voxels for signal sampling. Each voxel is invariantly formed by homogeneous pixels for signal reconstructing. We obtain the static voxel-pixel mapping through arbitrarily accurate raytracing in advance and store it as a lookup table (LUT). Our EIA rendering method first resamples input 3D data with the pre-defined voxels and then assigns every voxel's value to its homogeneous pixels through the LUT. As a result, the proposed method reduces the computational complexity by several orders of magnitude. The experimental rendering speed is as fast as 7 to 10 ms for a full-HD EIA frame on an entry-level laptop. Finally, considering a voxel may not be perfectly integrated by its homogeneous pixels, called the sampling error, the proposed and conventional viewpoint-based methods are analyzed in the Fourier domain. We prove that even with severe sampling errors, the two methods negligibly differ in the output signal's frequency spectrum. We expect the proposed method to break the long-standing tradeoff between rendering speed, accuracy, and system complexity for computer-generated integral imaging.

Compact dual-focal augmented reality head-up display using a single picture generation unit with polarization multiplexing.

The augmented reality head-up display (AR-HUD) attracts increasing attention. It features multiple focal planes to display basic and AR information, as well as a wider field of view (FOV). Using two picture generation units (PGUs) to create dual-focal AR-HUDs leads to expanded size, increased cost, and reduced reliability. Thus, we previously proposed an improved solution by dividing one PGU into two partitions that were separately imaged into two virtual images with an optical relay system. However, the resolution of the PGU was halved for either virtual image. Regarding the drawbacks, this paper proposes a dual-focal AR-HUD using one PGU and one freeform mirror. Either virtual image utilizes the full resolution of the PGU through polarization-multiplexing. By performing optical design optimization, high image quality, except for the distortion, is achieved in an eyebox of 130 by 60 mm for far (10 m, 13° by 4°) and near (2.5 m, 10° by 1°) images. Next, we propose a distortion correction method by directly inputting the distorted but clear images acquired in the design stage into the real HUD with an inversed optical path. The proposed optical architecture enables a compact system volume of 9.5 L, close to traditional single-focal HUDs. Finally, we build an AR-HUD prototype, where a polarizing reflective film and a twisted nematic liquid crystal cell achieve polarization-multiplexing. The expected image quality of the two virtual images is experimentally verified.

Light field displays with computational vision correction for astigmatism and high-order aberrations with real-time implementation.

Vision-correcting near-eye displays are necessary concerning the large population with refractive errors. However, varifocal optics cannot effectively address astigmatism (AST) and high-order aberration (HOAs); freeform optics has little prescription flexibility. Thus, a computational solution is desired to correct AST and HOA with high prescription flexibility and no increase in volume and hardware complexity. In addition, the computational complexity should support real-time rendering. We propose that the light field display can achieve such computational vision correction by manipulating sampling rays so that rays forming a voxel are re-focused on the retina. The ray manipulation merely requires updating the elemental image array (EIA), being a fully computational solution. The correction is first calculated based on an eye's wavefront map and then refined by a simulator performing iterative optimization with a schematic eye model. Using examples of HOA and AST, we demonstrate that corrected EIAs make sampling rays distributed within ±1 arcmin on the retina. Correspondingly, the synthesized image is recovered to nearly as clear as normal vision. We also propose a new voxel-based EIA generation method considering the computational complexity. All voxel positions and the mapping between voxels and their homogeneous pixels are acquired in advance and stored as a lookup table, bringing about an ultra-fast rendering speed of 10 ms per frame with no cost in computing hardware and rendering accuracy. Finally, experimental verification is carried out by introducing the HOA and AST with customized lenses in front of a camera. As a result, significantly recovered images are reported.

High contrast ratio electrophoretic displays based on high structural stability and high transmittance microcup.

In the age of Internet of Things, electrophoretic electronic paper (E-paper) holds a unique position in the display area due to its energy-saving, environmental friendliness, excellent readability in strong ambient light, and eye protection. Compared with E-papers of microcapsules, microcups have several advantages including higher mechanical strength, lower production costs, and better feasibility to show multiple colors with high contrast, thereby making it a significant research interest. However, there is currently no systematic study on the structural mechanics and display performances of microcups. Herein, we simulate the structural stability of microcups with various shapes and sizes during nanoimprint process, and also calculated the aperture ratio of these microcups. We fabricated devices with different geometrical morphologies to verify the microcups for achieving a balance between high contrast, high transmittance and high structural stability. This study provides a new method for designing and manufacturing the E-papers of microcups in using nanoimprint roll-to-roll (R2R) production.

Active matrix driven electrophoretic display with in-plane switching layout and driving waveform for reflective and transparent modes.

In-plane switching electrophoretic display (IPS-EPD) is an emerging field of display technology which achieves particles moving horizontally through a lateral electric field. Compared to vertically driven electrophoretic display (V-EPD), IPS-EPD exhibits the feasibility of transparent display function. However, most of the previous research was hindered by long response time, low optical transmittance, or complex structures. In this paper, we have proposed a newly developed electrode layout and driving waveform for IPS-EPD, achieving a device with fast response time of 0.32 s, high transmittance of 58.07%, good transmittance-contrast ratio of 11.25, and simple structure, which show a significant improvement over other related research. Additionally, we elucidated the physical mechanism for the device through developing a particles motion simulation. Finally, we presented a prototype of an IPS-EPD with TFT panel, which exhibits excellent performance in various application scenarios, making it a possible application prospect in mobile phone cases, glasses, windows, and so on.

Two-field sequential color liquid crystal displays with deep learning-enabled real-time driving.

Two-field driving is the ultimate goal of field sequential color liquid crystal displays (FSC-LCDs) because it requires the lowest refresh rate and transmission bandwidth in addition to the intrinsic advantages of FSC-LCDs, e.g., tripled light efficiency and spatial resolution. However, fewer fields create a more significant challenge in controlling color breakup and distortion, as well as higher computational complexity in calculating LC signals. Regarding the difficulties, we propose a two-field FSC driving method that synchronously generates backlight and LC signals through two lightweight neural networks. The runtimes of the two networks are as fast as 1.23 and 1.79 ms per frame on a GeForce RTX 3090Ti graphic card, fully supporting real-time driving. Next, an over-partitioning approach is proposed to overcome the cross talk between backlight segments while processing high-resolution images. Besides the real-time feature, a reduction of 14.88% in color breakup concerning current methods and low distortion are verified. We also provide our open-source code.

Deep learning-enabled image content-adaptive field sequential color LCDs with mini-LED backlight.

The mini-LED as the backlight of field sequential color LCD (FSC-LCD) enables high contrast, thin volume, and theoretically tripled light efficiency and resolution. However, color breakup (CBU) induced by a relative speed between an observer and the display severely limits the application of FSC-LCDs. Several driving algorithms have been proposed for CBU suppression, but their performance depends on image content. Moreover, their performance plateaus with increasing image segment number, preventing taking advantage of the massive segments introduced by mini-LEDs. Therefore, this study proposes an image content-adaptive driving algorithm for mini-LED FSC-LCDs. Deep learning-based image classification accurately determines the best FSC algorithm with the lowest CBU. In addition, the algorithm is heterogeneous that the image classification is independently performed in each segment, guaranteeing minimized CBU in all segments. We perform objective and subjective validation. Compared with the currently best algorithm, the proposed algorithm improves the performance in suppressing CBU by more than 20% using two evaluation metrics, supported by experiment-based subjective evaluation. Mini-LED FSC-LCDs driven by the proposed algorithm with outstanding CBU suppression can be ideal for display systems requiring high brightness and high resolution, such as head-up displays, virtual reality, and augmented reality displays.

Ion-Conductive Hydrogel-Based Stretchable, Self-Healing, and Transparent NO2 Sensor with High Sensitivity and Selectivity at Room Temperature.

Here stretchable, self-healable, and transparent gas sensors based on salt-infiltrated hydrogels for high-performance NO2 sensing in both anaerobic environment and air at room temperature, are reported. The salt-infiltrated hydrogel displays high sensitivity to NO2 (119.9%/ppm), short response and recovery time (29.8 and 41.0 s, respectively), good linearity, low theoretical limit of detection (LOD) of 86 ppt, high selectivity, stability, and conductivity. A new gas sensing mechanism based on redox reactions occurring at the electrode-hydrogel interface is proposed to understand the sensing behaviors. The gas sensing performance of hydrogel is greatly improved by incorporating calcium chloride (CaCl2 ) in the hydrogel via a facile salt-infiltration strategy, leading to a higher sensitivity (2.32 times) and much lower LOD (0.06 times). Notably, both the gas sensing ability, conductivity, and mechanical deformability of hydrogels are readily self-healable after cutting off and reconnection. Such large deformations as 100% strain do not deprive the gas sensing capability, but rather shorten the response and recovery time significantly. The CaCl2 -infiltrated hydrogel shows excellent selectivity of NO2 , with good immunity to the interference gases. These results indicate that the salt-infiltrated hydrogel has great potential for wearable electronics equipped with gas sensing capability in both anaerobic and aerobic environments.

Interaction between sampled rays' defocusing and number on accommodative response in integral imaging near-eye light field displays.

In an integral imaging near-eye light field display using a microlens array, a point on a reconstructed depth plane (RDP) is reconstructed by sampled rays. Previous studies respectively suggested the accommodative response may shift from the RDP under two circumstances: (i) the RDP is away from the central depth plane (CDP) to introduce defocusing in sampled rays; (ii) the sampled ray number is too low. However, sampled rays' defocusing and number may interact, and the interaction's influence on the accommodative response has been little revealed. Therefore, this study adopts a proven imaging model providing retinal images to analyze the accommodative response. As a result, when the RDP and the CDP coincide, the accommodative response matches the RDP. When the RDP deviates from the CDP, defocusing is introduced in sampled rays, causing the accommodative response to shift from the RDP towards the CDP. For example, in a system with a CDP of 4 diopters (D) and 45 sampled rays, when the RDP is at 3, 2, 1, and 0 D, the accommodative response shifts to 3.25, 2.75, 2, and 1.75 D, respectively. With fewer rays, the accommodative response tends to further shift to the CDP. Eventually, with fewer than five rays, the eye accommodates to the CDP and loses the 3D display capacity. Moreover, under different RDPs, the ray number influences differently, and vice versa. An x-y polynomial equation containing three interactive terms is finally provided to reveal the interaction between RDP position and ray number. In comparison, in a pinhole-based system with no CDP, the accommodative response always matches the RDP when the sampled ray number is greater than five.

Low Driving Voltage Electroluminescence Device for Integrated Visual Strain Sensing.

As a pivotal component in human-machine interactions, display devices have undergone rapid development in modern life. Displays such as alternative current electroluminescence|alternative current electroluminescent (ACEL) devices with high flexibility and long operational lifetimes are essential for wearable electronics. However, ACEL devices are constrained by their inherent high driving voltage and complex fabrication processes. Our work presents an easy blade-coating method for fabricating flexible ACEL display devices based on an all-solution process. By dispersing BaTiO3 and ZnS/Cu powder into waterborne polyurethane, we successfully combined dielectric and fluorescence functionalities within a single layer, significantly reducing the device's driving voltage. Additionally, the ionic conducting hydrogel was chosen as a transparent electrode to achieve good electrical contact and strong interfacial adhesion through in situ polymerization. Owing to the unique method, our ACEL device exhibits high flexibility, low driving voltage (20-100 V), high brightness (300+ cd/m2 at 60 V), and environmental friendliness. Furthermore, by repurposing the hydrogel electrode, we integrated strain visualization capabilities within a single device, highlighting its potential for applications such as wearable healthcare monitoring.

Flexible, Transparent and Conductive Metal Mesh Films with Ultra-High FoM for Stretchable Heating and Electromagnetic Interference Shielding.

Despite the growing demand for transparent conductive films in smart and wearable electronics for electromagnetic interference (EMI) shielding, achieving a flexible EMI shielding film, while maintaining a high transmittance remains a significant challenge. Herein, a flexible, transparent, and conductive copper (Cu) metal mesh film for EMI shielding is fabricated by self-forming crackle template method and electroplating technique. The Cu mesh film shows an ultra-low sheet resistance (0.18 Ω â–¡-1), high transmittance (85.8%@550 nm), and ultra-high figure of merit (> 13,000). It also has satisfactory stretchability and mechanical stability, with a resistance increases of only 1.3% after 1,000 bending cycles. As a stretchable heater (ε > 30%), the saturation temperature of the film can reach over 110 °C within 60 s at 1.00 V applied voltage. Moreover, the metal mesh film exhibits outstanding average EMI shielding effectiveness of 40.4 dB in the X-band at the thickness of 2.5 µm. As a demonstration, it is used as a transparent window for shielding the wireless communication electromagnetic waves. Therefore, the flexible and transparent conductive Cu mesh film proposed in this work provides a promising candidate for the next-generation EMI shielding applications.

Self-Assembled Monolayer and Nanoparticles Coenhanced Fragmented Silver Nanowire Network Memristor.

Silver nanowire (AgNW) networks with self-assembled structures and synaptic connectivity have been recently reported for constructing neuromorphic memristors. However, resistive switching at the cross-point junctions of the network is unstable due to locally enhanced Joule heating and the Gibbs-Thomson effect, which poses an obstacle to the integration of threshold switching and memory function in the same AgNW memristor. Here, fragmented AgNW networks combined with Ag nanoparticles (AgNPs) and mercapto self-assembled monolayers (SAMs) are devised to construct memristors with stable threshold switching and memory behavior. In the above design, the planar gaps between NW segments are for resistive switching, the AgNPs act as metal islands in the gaps to reduce threshold voltage (Vth) and holding voltage (Vhold), and the SAMs suppress surface atom diffusion to avoid Oswald ripening of the AgNPs, which improves switching stability. The fragmented NW-NP/SAM memristors not only circumvent the side effects of conventional NW-stacked junctions to provide durable threshold switching at >Vth but also exhibit synaptic characteristics such as long-term potentiation at ultralow voltage (≪Vth). The combination of NW segments, nanoparticles, and SAMs blazes a new trail for integrating artificial neurons and synapses in AgNW network memristors.