Self-assembled plasmonics for angle-independent structural color displays with actively addressed black states.

Nanostructured plasmonic materials can lead to the extremely compact pixels and color filters needed for next-generation displays by interacting with light at fundamentally small length scales. However, previous demonstrations suffer from severe angle sensitivity, lack of saturated color, and absence of black/gray states and/or are impractical to integrate with actively addressed electronics. Here, we report a vivid self-assembled nanostructured system which overcomes these challenges via the multidimensional hybridization of plasmonic resonances. By exploiting the thin-film growth mechanisms of aluminum during ultrahigh vacuum physical vapor deposition, dense arrays of particles are created in near-field proximity to a mirror. The sub-10-nm gaps between adjacent particles and mirror lead to strong multidimensional coupling of localized plasmonic modes, resulting in a singular resonance with negligible angular dispersion and ∼98% absorption of incident light at a desired wavelength. The process is compatible with arbitrarily structured substrates and can produce wafer-scale, diffusive, angle-independent, and flexible plasmonic materials. We then demonstrate the unique capabilities of the strongly coupled plasmonic system via integration with an actively addressed reflective liquid crystal display with control over black states. The hybrid display is readily programmed to display images and video.

In vivo study of a reserved atrial septal puncture area patent foramen ovale occluder.

PURPOSE: After patent foramen ovale interventional closure, puncture of the interatrial septum through the occluder is difficult but sometimes needed for further interventional treatment. This paper presents findings from an in vivo experimental study of a reserved atrial septal puncture area patent foramen ovale occluder. MATERIALS AND METHODS: A patent foramen ovale model was established in canines using trans-septal puncture of the fossa ovale and high-pressure balloon dilation. Then, patent foramen ovale closure was performed with a reserved atrial septal puncture area and all canines were raised for 3 months. Then, the occluder was crossed and left atrial angiography was performed on the septal area with the occluder. Finally, DSA angiography, echocardiography, and histology were used to evaluate the performance and feasibility of the reserved atrial septal puncture area. RESULTS: A patent foramen ovale model was successfully established in 10 canines using the atrial septal puncture method. The average diameter of the patent foramen ovale was 3.77 ±0.19 mm, and the patent foramen ovale was successfully closed in all canines using a reserved atrial septal puncture area. As assessed using transoesophageal echocardiography, the new occluder exhibited an ideal position and was occluded entirely without a residual shunt intraoperatively and postoperatively. A 100% success rate of atrial septum puncture was achieved across the new occluder. The occluders were completely endothelialised 3 months post-implantation. CONCLUSIONS: The reserved atrial septal puncture area was effective in patent foramen ovale closure and exhibited positive sealing performance and biological compatibility. Trans-septal puncture was feasible and effective after reserved atrial septal puncture area patent foramen ovale closure.

Planar Alvarez tunable lens based on polymetric liquid crystal Pancharatnam-Berry optical elements.

Virtual reality (VR) and augmented reality (AR) have widespread applications. The vergence-accommodation conflict (VAC), which causes 3D visual fatigue, has become an urgent challenge for VR and AR displays. Alvarez lenses, with precise and continuously tunable focal length based on the lateral shift of its two sub-elements, are a promising candidate as the key electro-optical component in vari-focal AR display systems to solve the VAC problem. In this paper, we propose and fabricate a compact Alvarez lens based on planar polymetric liquid crystal Pancharatnam-Berry optical elements. It can provide continuous diopter change from -1.4 D to 1.4 D at the wavelength of 532 nm with the lateral shift ranging from -5 mm to 5 mm. We also demonstrate an AR display system using this proposed Alvarez lens, where virtual images are augmented on the real world at different depths.

Peculiar polarization response in chiral liquid crystal stacks for multispectral camouflage.

Chiral liquid crystals are self-organized Bragg reflectors which respond to circularly polarized light. Manipulation of the chiral structure has aroused great research interest. The x-y plane two-dimensional patterning of chiral liquid crystals leads to reflective planar optics, and the z-axis modulation results in a variety of photonic bandgap controls. Here, the optical properties of even-number left- and right-handed chiral liquid crystal stacks are investigated, with emphasis on the linear polarization response. Under certain conditions, a linearly polarized incidence can result in a linearly polarized reflected light. More intriguingly, the linear polarization has different forms of response to thick and thin chiral liquid crystal sublayers and responds to the rotation of liquid crystal alignment. Based on the peculiar polarization response, a new type of wavelength-response camouflage and anti-counterfeiting is conceptually proposed, which can hide two different images simultaneously within a small spectral range. Our work paves the way for three-dimensional manipulation of chiral liquid crystals and enlightens novel applications.

Doubling the FOV of AR displays with a liquid crystal polarization-dependent combiner.

We propose a glasses-like augmented reality (AR) display with an extended field-of-view (FOV) using a liquid crystal polarization-dependent combiner (PDC). Such a PDC consists of two polarization volume lenses (PVLs) that are based on patterned liquid crystals to selectively control the beam path according to the right-handed or left-handed circularly polarized light. By encoding the left and right half of the FOV into two orthogonal polarization states, the overall horizontal FOV can be doubled while maintaining an ultrathin and flat form factor. Based on this multiplexing concept, the FOV can be further extended by integrating more PVLs with different diffraction angles. The proposed configuration with polarization-time multiplexing provides a promising solution for overcoming the limited FOV issue in AR displays.

Tailoring the light distribution of micro-LED displays with a compact compound parabolic concentrator and an engineered diffusor.

We propose a novel optical design to tailor the angular distribution of a micro-LED (µLED) display system and use vehicle display as an example to illustrate the design principles. The display system consists of a µLED array with a tailored LED structure, a small formfactor compound parabolic concentrator (CPC) system, and a functional engineered diffusor. It provides high efficiency, high peak brightness, and small formfactor. In the design process, a mix-level optical simulation model, including the angular distribution of polarized emission dipole (dipole emission characteristics), Fabry-Perot cavity effect (wave optics), and light propagation process (ray optics), is established to analyze the angular distribution of µLEDs. Such an optical design process from dipole emission to display radiation pattern can be extended to other µLED display systems for different applications.

Large-angle two-dimensional grating with hybrid mechanisms.

We demonstrate a large-diffraction-angle two-dimensional (2D) grating based on cholesteric liquid crystal (CLC). One dimension is a polarization volume grating (PVG) working in the Bragg regime, which is produced by a patterned photoalignment layer. The other dimension is a CLC grating working in the Raman-Nath regime, which is introduced by CLC self-assembly under a weak anchoring energy condition. The condition for the coexistence of the CLC Raman-Nath grating (RNG) and PVG is analyzed, and the efficiency and grating period of the CLC RNG are also characterized. Potential application of this 2D grating for enlarging the eyebox of augmented reality displays is discussed.

Standing wave polarization holography for realizing liquid crystal Pancharatnum-Berry phase lenses.

A standing wave polarization holography setup is proposed to generate the desired polarization field for fabricating both on-axis and off-axis liquid crystal Pancharatnum-Berry phase lenses. Compared to other interference exposure setups, standing wave interferometry can double the polarization field amplitude because it does not require a beam splitter. Moreover, the optical axis angle of the lenses can be easily adjusted without realigning the optical setup. Based on the design, we first theoretically derive the polarization field distribution. In the experiment, we build the recording optical system and fabricate a series of on-axis and off-axis lenses. Further optical characterization proves the high diffraction efficiency of the fabricated lenses.

Passive polymer-dispersed liquid crystal enabled multi-focal plane displays.

A multi-focal plane see-through near-eye display using a transparent projection display is demonstrated. The key component of the transparent projection display is a passive polymer-dispersed liquid crystal (PDLC), which is highly transparent for a large range of incident angles in air but strongly scattering at large oblique angles in high refractive index medium (e.g. glass). The use of a passive device can avoid temporal multiplexing. Such a display is highly transparent in air and can easily deliver full-color images. The proposed method is an important step toward transparent display-enabled multi-focal plane displays.

Halo effect in high-dynamic-range mini-LED backlit LCDs.

We develop an optical model including the glare effect in the human vision system to analyze the halo effect of high-dynamic-range (HDR) mini-LED backlit liquid crystal displays (LCDs). In our model, an objective function is first introduced to evaluate the severity of the halo effect with different image contents. This function is further combined with PSNR to establish a new evaluation metric to analyze the image quality affected by the halo effect. A subjective visual experiment is also conducted to verify the above-mentioned evaluation metrics. In addition, we analyze the influence of ambient environment (viewing angle and ambient light illuminance) on the halo effect. After considering the requirements on local dimming zones, dynamic contrast ratio, gamma shift, and color shift for practical applications, we find that fringe-field-switching mode is a strong contender for the mini-LED backlit LCD system.

High dynamic range head-up displays.

We demonstrate a full-color high dynamic range head-up display (HUD) based on a polarization selective optical combiner, which is a three-layer cholesteric liquid crystal (CLC) film. Such a CLC film has three reflection bands corresponding to the three primary colors. A key component in our HUD system is a polarization modulation layer (PML) consisting of a twisted-nematic LC polarization rotator sandwiched by two quarter-wave plates. This spatially switchable PML generates opposite polarization states for the displayed image and its background area. Thus, this optical combiner reflects the displayed image to the observer and transmits the background noise, making the black state darker. Furthermore, by matching the reflection spectra of the optical combiner with the colors of the display panel, the bright state gets brighter. Therefore, both bright state and dark state are improved simultaneously. Our experimental results show that the dark state of the new HUD is lowered by 3x and bright state is boosted by 2.5x. By applying antireflection coating to the optical components and optimizing the degree of polarization, our simulation results indicate that the dynamic range can be improved by ∼50x (17 dB). Potential applications of the proposed HUDs for improving the driver's safety are foreseeable.

Swelling-Deswelling Microencapsulation-Enabled Ultrastable Perovskite-Polymer Composites for Photonic Applications.

Metal halide perovskite nanocrystals are emerging as novel optoelectronic materials. Owing to their excellent optical and electronic properties such as tunable band gap, narrow-band emission and high charge mobility, they are quite promising in various fields including liquid-crystal display backlighting, solid-state lighting and other energy conversion applications. However, the intrinsic low formation energy makes them vulnerable to external stimulus, e. g. water, oxygen, heat, etc. Among many methods, swelling-deswelling microencapsulation emerges as one of the most promising strategies to improve their stability. Herein, recent developments and future research directions in swelling-deswelling microencapsulation-enabled ultrastable perovskite-polymer composites are summarized. We believe this strategy has great potential to deliver successful perovskite-based commercial products for many photonics applications.

Stretchable, flexible, rollable, and adherable polarization volume grating film.

Volume Bragg gratings (VBGs) have many applications, including filters, wavelength multiplexing devices, and see-through displays. As a kind of VBGs, polarization volume gratings (PVGs) based on liquid crystal polymer have the advantages of nearly 100% efficiency, large deflection angle, and high polarization selectivity. However, previous reports regarding PVGs did not address high efficiency, tunable periodicity, and flexibility. Here, we report a stretchable, flexible, and rollable PVG film with high diffraction efficiency. The control of PVG by mechanical stretching is investigated, while the Bragg reflection band shift is evaluated quantitatively. Moreover, we quantified the deflection angle change's behavior, which has promising potential for laser beam steering applications. The mechanical robustness under stretch-release cycles is also scrutinized.

Novel liquid crystal photonic devices enabled by two-photon polymerization [Invited].

In addition to displays, liquid crystals (LCs) have also found widespread applications in photonic devices, such as adaptive lens, adaptive optics, and sensors, because of their responses to electric field, temperature, and light. As the fabrication technique advances, more sophisticated devices can be designed and created. In this review, we report recent advances of two-photon polymerization-based direct-laser writing enabled LC devices. Firstly, we describe the basic working principle of two-photon polymerization. With this powerful fabrication technique, we can generate anchoring energy by surface morphology to align LC directors on different form factors. To prove this concept, we demonstrate LC alignment on planar, curvilinear surfaces as well as in three-dimensional volumes. Based on the results, we further propose a novel, ultra-broadband, twisted-nematic diffractive waveplate that can potentially be fulfilled by this technique. Next, we briefly discuss the current status of direct-laser writing on LC reactive mesogens and its potential applications. Finally, we present two design challenges: fabrication yield and polymer relaxation/deformation, remaining to be overcome.

Adaptive liquid crystal microlens array enabled by two-photon polymerization.

A tunable-focus liquid crystal microlens array is demonstrated and characterized. Using two-photon polymerization based direct-laser writing, a polymerized microlens array is fabricated on one substrate. Such a microlens array creates inhomogeneous electric field distribution and homogeneous-like liquid-crystal alignment, simultaneously. The phase profile and thus the focal length can be tuned dynamically by the applied voltage. We also further investigate the focusing property and the imaging capability of the fabricated sample. Using the adaptive microlens array as an example, we demonstrate that directly forming a curvilinear surface with liquid-crystal alignment is feasible. In addition to adaptive lens, this direct-laser writing method is also a powerful tool for making other tunable photonic devices.

Tuning the correlated color temperature of white light-emitting diodes resembling Planckian locus.

We report a new electrically tunable color filter to actively adjust the correlated color temperature of white light-emitting diodes. With four passive cholesteric films and an active polarization rotator, both circular polarizations of the incident light are utilized to generate complementary blue and yellow colors. The blue/yellow ratio can be tuned by the applied voltage of the polarization rotator. In experiment, the tunable color filter offers a reasonably wide tuning range (1900 K and 2400 K), which resembles the Planckian locus. This design is promising for next generation smart lighting.

Switchable Pancharatnam-Berry microlens array with nano-imprinted liquid crystal alignment.

We report a rapid nano-imprinting technique to pattern the liquid crystal alignment of a Pancharatnam-Berry phase microlens array. Through implementing a single-side aligned cell, we demonstrate a switchable microlens array with fast response time and low operation voltage. Further investigation of focusing property as well as imaging capability ensure the good quality of the microlens array. Besides planar structures, this method is also promising for patterning liquid crystal alignment on curvilinear surfaces.

Mid-wave infrared beam steering based on high-efficiency liquid crystal diffractive waveplates.

We demonstrated two liquid crystal diffractive waveplates: one optimized for near-infrared (1.06 µm), and another for mid-wave infrared (MWIR, 3~5 µm). By employing a low loss liquid crystal mixture UCF-M3, whose absorption loss is below 2% in the 4~5 µm spectral region, the grating achieves over 98% diffraction efficiency in a broad MWIR range. To switch the grating, both active and passive driving methods can be considered. In our experiment, we used a polymer-stabilized twisted nematic cell as the polarization rotator for passive driving. The obtained rise time is 0.2 ms and decay time is 10 ms.

A novel photoelectrochemical aptasensor based on 3D flower-like g-C3N4/BiOI p-n heterojunction for the sensitive detection of kanamycin.

BACKGROUND: Kanamycin (KAN) residues in animal-derived foods continuously enter the human body, which will pose serious threats to human health such as hearing loss, nephrotoxicity and other complications. Therefore, to sensitively detect KAN residues by a reliable technology is extremely urgent in food quality and safety. Compared with traditional methods being limited by cost and complexity, photoelectrochemical (PEC) biosensors benefit from some merits such as rapid response, excellent sensitivity and good stability. In this study, the construction of a highly efficient PEC platform to realize KAN residues detection is discussed. RESULTS: Herein, a novel p-n heterojunction consisting of flower-like BiOI microspheres and graphite carbon nitride (g-C3N4) nanoflakes was developed to establish a PEC aptasensor for KAN detection at 0 V. The prepared g-C3N4/BiOI heterostructure showed not only significantly enhanced PEC activity due to the larger specific surface area but also greatly increased charge separation efficiency owing to the strong internal electric field. Meanwhile, using g-C3N4/BiOI as a highly efficient photoactive material for binding amine-functionalized aptamers to capture KAN, the photocurrent signals showed a 'turn off' mode to achieve the sensitive detection of KAN. The proposed PEC aptasensor exhibited linear response for KAN from 5 × 10-9 to 3 × 10-7 mol L-1 with a low detection limit of 1.31 × 10-9 mol L-1, and satisfactory recoveries (97.44-107.38 %) were obtained in real food samples analysis. SIGNIFICANCE: This work presented a novel p-n heterojunction-based PEC aptasensor with strong selectivity and stability, rendering it allowed to detect KAN in animal-derived foods including milk, honey and pork. Additionally, the detection range satisfied the MRLs for KAN specified by the national standards, demonstrating the potential application for food analysis. The study provides a new insight into the development of efficient and practical biosensors for antibiotic residues detection.

Apple peel polyphenol alleviates antibiotic-induced intestinal dysbiosis by modulating tight junction proteins, the TLR4/NF-κB pathway and intestinal flora.

The intestine and its flora have established a strong link with each other and co-evolved to become a micro-ecological system that plays an important role in human health. Plant polyphenols have attracted a great deal of attention as potential interventions to regulate the intestinal microecology. In this study, we investigated the effects of apple peel polyphenol (APP) on the intestinal ecology by establishing an intestinal ecological dysregulation model using lincomycin hydrochloride-induced Balb/c mice. The results showed that APP enhanced the mechanical barrier function of mice by upregulating the expression of the tight junction proteins at the transcriptional and translational levels. In terms of the immune barrier, APP downregulated the protein and mRNA expression of TLR4 and NF-κB. As for the biological barrier, APP promoted the growth of beneficial bacteria as well as increasing the diversity of intestinal flora. In addition, APP treatment significantly increased the contents of short-chain fatty acids in mice. In conclusion, APP can alleviate intestinal inflammation and epithelial damage as well as inducing potentially beneficial changes in the intestinal microbiota, which helps to reveal the potential mechanisms of host-microbial interactions and polyphenol regulation of intestinal ecology.