Dual-domain mean-reverting diffusion model-enhanced temporal compressive coherent diffraction imaging.

Temporal compressive coherent diffraction imaging is a lensless imaging technique with the capability to capture fast-moving small objects. However, the accuracy of imaging reconstruction is often hindered by the loss of frequency domain information, a critical factor limiting the quality of the reconstructed images. To improve the quality of these reconstructed images, a method dual-domain mean-reverting diffusion model-enhanced temporal compressive coherent diffraction imaging (DMDTC) has been introduced. DMDTC leverages the mean-reverting diffusion model to acquire prior information in both frequency and spatial domain through sample learning. The frequency domain mean-reverting diffusion model is employed to recover missing information, while hybrid input-output algorithm is carried out to reconstruct the spatial domain image. The spatial domain mean-reverting diffusion model is utilized for denoising and image restoration. DMDTC has demonstrated a significant enhancement in the quality of the reconstructed images. The results indicate that the structural similarity and peak signal-to-noise ratio of images reconstructed by DMDTC surpass those obtained through conventional methods. DMDTC enables high temporal frame rates and high spatial resolution in coherent diffraction imaging.

Bibliometric study and review of Klotho research: global characteristics and trends from 2000 to 2023.

BACKGROUND: Although Klotho-related research has seen a significant upsurge, the field lacks comprehensive analytical representation and in-depth exploration of pertinent areas such as prevailing research trends and key focus areas. METHOD: This review presents a bibliometric analysis of literature data gathered from the Web of Science Core Collection databases from January 1, 2000, to April 30, 2023. Parameters such as co-authorship, co-citation, co-occurrence, and the emergence of publications, countries, categories, references, and keywords were scrutinized predominantly using Citespace software. RESULTS: Our investigation amassed a total of 3548 papers, with the United States leading in the quantity of publications (1175, accounting for 33.12%), followed by China (867, representing 24.44%), and Japan (439, accounting for 12.37%). While the United States is preeminent in the overall volume of publications, Scotland holds prominence in terms of centrality. Out of a total of 96 subject categories, urology and nephrology (573), and endocrinology and metabolism (542) were the two leading domains of Klotho-related publications. The 2011 paper titled "FGF23 induces left ventricular hypertrophy" by Faul C et al. holds the distinction of being the most frequently cited. The keywords "fibroblast growth factor 23," "phosphate homeostasis," and "functional variants" demonstrated the highest intensity, underscoring the potential of these research areas. CONCLUSION: As the volume of literature grows, the role of Klotho in disease management and its applicability as a marker in disease progression warrant vigilant tracking and study.

Holo-imprinting polarization optics with a reflective liquid crystal hologram template.

Liquid crystal polarization optics based on photoalignment technique has found pervasive applications in next-generation display platforms like virtual reality and augmented reality. Its large-scale fabrication, however, remains a big challenge due to the high demands in small feature size, fast processing speed, and defects-free alignment quality during the photoalignment process, especially for large-angle reflective devices. Here we propose a new concept of holo-imprinting based on non-contact replication of polarization pattern with a reflective liquid crystal hologram as a template. Our theoretical analysis and experimental results validate the possibility of generating a high-quality polarization pattern exploiting the self-interfering beams of reflective holograms. The method can be extended to numerous devices, from transmissive to reflective, from small angle to large angle, and from grating, lens, to freeform optics. Its widespread impact on the fabrication of liquid crystal polarization optics for advanced display and imaging systems is foreseeable.

Augmented reality and virtual reality displays: emerging technologies and future perspectives.

With rapid advances in high-speed communication and computation, augmented reality (AR) and virtual reality (VR) are emerging as next-generation display platforms for deeper human-digital interactions. Nonetheless, to simultaneously match the exceptional performance of human vision and keep the near-eye display module compact and lightweight imposes unprecedented challenges on optical engineering. Fortunately, recent progress in holographic optical elements (HOEs) and lithography-enabled devices provide innovative ways to tackle these obstacles in AR and VR that are otherwise difficult with traditional optics. In this review, we begin with introducing the basic structures of AR and VR headsets, and then describing the operation principles of various HOEs and lithography-enabled devices. Their properties are analyzed in detail, including strong selectivity on wavelength and incident angle, and multiplexing ability of volume HOEs, polarization dependency and active switching of liquid crystal HOEs, device fabrication, and properties of micro-LEDs (light-emitting diodes), and large design freedoms of metasurfaces. Afterwards, we discuss how these devices help enhance the AR and VR performance, with detailed description and analysis of some state-of-the-art architectures. Finally, we cast a perspective on potential developments and research directions of these photonic devices for future AR and VR displays.

Dual-depth augmented reality display with reflective polarization-dependent lenses.

Vergence-accommodation conflict (VAC) is a common annoying issue in near-eye displays using stereoscopy technology to provide the perception of three-dimensional (3D) depth. By generating multiple image planes, the depth cues can be corrected to accommodate a comfortable 3D viewing experience. In this study, we propose a multi-plane optical see-through augmented reality (AR) display with customized reflective polarization-dependent lenses (PDLs). Leveraging the different optical powers of two PDLs, a proof-of-concept dual-plane AR device is realized. The proposed design paves the way to a compact, lightweight, and fatigue-free AR display.

Aberration-free pupil steerable Maxwellian display for augmented reality with cholesteric liquid crystal holographic lenses.

Maxwellian displays offer unique features like always-in-focus quality, high efficiency, and large field-of-view, but its small eyebox remains a major challenge for augmented reality. To enlarge the eyebox, pupil steering is a promising approach. However, previous pupil steering methods generally rely on changing the incident light angle on the lens coupler, which results in serious aberrations. In this Letter, we demonstrate a pupil steerable see-through Maxwellian display incorporating novel cholesteric liquid crystal (CLC) holographic lenses. By actively modulating the polarization state of the incident light, we can schematically choose which holographic lens to function, which fundamentally eliminates the aberrations.

Patterning Liquid-Crystal Alignment for Ultrathin Flat Optics.

Liquid-crystal (LC)-based ultrathin flat optical elements (FOEs) exhibit several attractive properties, such as a high degree of optical tunability, strong polarization selectivity, nearly 100% diffraction efficiency, and a simple fabrication process. Investigating the alignment patterning of LC-FOEs to diversify their performance has attracted broad interest in the optics field. In this mini-review, we start from the photoalignment (PA) process and then dive into device structures and performances. By generating and recording the desired polarization fields on the PA layer, the LC molecules will follow the recorded patterns and establish the phase profiles for different functionalities, such as gratings and lenses. Because of the polarization dependency, LC-FOEs have found useful applications in near-eye displays. Understanding the interactions between the PA mechanism and LC molecules helps to optimize the device performance for novel optical systems.

Rigorous coupled-wave analysis of liquid crystal polarization gratings.

Several types of liquid crystal polarization gratings (LCPGs) can be achieved depending on their molecular configurations and diffraction properties. We perform detailed numerical studies of these LCPGs based on the rigorous coupled-wave analysis (RCWA) approach. The unique properties of Raman-Nath and Bragg gratings are investigated, and how the transition between them influences the diffraction behaviors is explained. Two types of LCPGs, corresponding to the planar and the slanted director configurations, are compared in detail. The influence of gradient-pitch on the performance of reflection grating is also explored. Potential applications of these LCPGs for near-eye displays are emphasized.

Foveated display system based on a doublet geometric phase lens.

We propose a new concept of a foveated display with a single display module. A multi-resolution and wide field of view (FOV) can be simultaneously achieved using only a single display, based on temporal polarization-multiplexing. The polarization-dependent lens set functions as an optical window or beam expander system depending on the polarization state, which can provide two operating modes: fovea mode for a high-resolution and peripheral mode for a wide viewing angle. By superimposing two-mode images, the proposed system supports a foveated and wide FOV image without an ultra-high-resolution display. We demonstrate the feasibility of the proposed configuration through the proof-of-concept system.

Augmented Reality and Virtual Reality Displays: Perspectives and Challenges.

As one of the most promising candidates for next-generation mobile platform, augmented reality (AR) and virtual reality (VR) have potential to revolutionize the ways we perceive and interact with various digital information. In the meantime, recent advances in display and optical technologies, together with the rapidly developing digital processers, offer new development directions to advancing the near-eye display systems further. In this perspective paper, we start by analyzing the optical requirements in near-eye displays poised by the human visual system and then compare it against the specifications of state-of-the-art devices, which reasonably shows the main challenges in near-eye displays at the present stage. Afterward, potential solutions to address these challenges in both AR and VR displays are presented case by case, including the most recent optical research and development, which are already or have the potential to be industrialized for extended reality displays.

Absorption-based polarization gratings.

We demonstrate an absorption-based polarization grating made of dichroic dye-doped polymerizable liquid crystal. These gratings manifest a polarization-sensitive diffraction efficiency over the absorption band of the employed dye material, based on our theoretical analysis and experimental evidence. The spectral range can be easily tailored by varying the dye material. Since these gratings generate first-order diffracted beams with orthogonal circular polarizations, they can be utilized as key components in polarimetry systems. Meanwhile, due to their absorptive nature, these polarization gratings can function as LED-compatible polarization masks for photopatterning while fabricating various liquid crystal devices.

Broadband wide-view Pancharatnam-Berry phase deflector.

We demonstrate a high-efficiency achromatic, wide-view Pancharatnam-Berry phase deflector (PBD) based on a three-layer multi-twist structure. A practical method to measure the thickness and twist angle of liquid crystal (LC) polymer films is developed based on Jones matrix of twist-nematic liquid crystals. With the help of this new measurement method, we fabricated a three-layer multi-twist PBD. The imaging performance and the angular response of the achromatic wide-view PBD are also characterized. Potential application of PBD for near-eye displays is foreseeable.

A versatile method for fabricating Pancharatnam-Berry micro-optical elements.

We report a simple method for fabricating Pancharatnam-Berry micro-optical elements based on relayed Mach-Zehnder interferometer. Two major advantages are fast processing speed and good quality phase profile. Both active and passive micro-lens arrays are fabricated and their imaging performances characterized. To demonstrate the versatility of the proposed method, we also fabricated asymmetric, axial-symmetric, and concentric types of micro-lens arrays.

Improving near-eye display resolution by polarization multiplexing.

We present here an optical approach to boost the apparent pixel density by utilizing the superimposition of two shifted-pixel grids generated by a Pancharatnam-Berry deflector (PBD). The content of the two shifted pixel grids are presented to the observer's eye simultaneously using a polarization-multiplexing method. Considering the compact and lightweight nature of PBD, this approach has potential applications in near-eye display systems. Moreover, the same concept can be extended to projection displays with proper modifications.

Device simulation of liquid crystal polarization gratings.

Liquid crystal polarization gratings manifest several unique features, such as high diffraction efficiency, polarization selectivity, and fast switching time. However, few works address the chiral-doped liquid crystal alignment issue in such gratings. Here, we develop an improved relaxation method to analyze the liquid crystal director distribution in chiral-doped polarization gratings. Our simulation result agrees well with experimental data on a polarization volume grating. The criteria for forming planar or slanted polarization grating are discussed.

Fabrication of Pancharatnam-Berry phase optical elements with highly stable polarization holography.

Polarization-dependent diffraction based on Pancharatnam-Berry phase optical elements (PBOEs) offers considerable benefits compared to conventional metasurfaces, such as negligible absorption, nearly 100% diffraction efficiency and an inexpensive fabrication process. Polarization holography is a simple way to fabricate PBOEs, which entails the interference of beams with different polarizations to generate a spatial-varying polarization field. Thus, the quality of recorded PBOEs manifests high sensitivity to the length change and phase shift between polarized beams, usually caused by environmental vibration and air flow. Here, new polarization holography based on modified Sagnac interferometry is developed for fabricating liquid crystal-based PB gratings and lenses, where the pitch of grating and optical power of lens could be easily tuned. This approach offers high tolerance to environmental disturbance during the exposure process. Detailed design parameters are analyzed, and the fabricated PBOEs with high optical quality are also demonstrated.

Polarization-multiplexed multiplane display.

We demonstrate a polarization-multiplexed multiplane display system for near-eye applications. A polarization-sensitive Pancharatnam-Berry phase lens is implemented to generate two focal depths simultaneously. A spatial polarization modulator is utilized to direct the two images to designated focal planes. Based on this design, a dual-focal-plane display system is constructed without space- or time-multiplexing operations, to suppress the vergence-accommodation conflict successfully.

Polarization-independent Pancharatnam-Berry phase lens system.

The conventional liquid crystal-based Pancharatnam-Berry (PB) phase lens exhibits distinct polarization selectivity, manifesting opposite optical power to circularly polarized light with opposite handedness. Here, a polarization-independent liquid crystal PB lens system is theoretically predicted and experimentally verified. Such a lens system consists of at least four PB lenses, with specific distances in between them. This enables the PB lens to be applied in polarization-independent optical systems.

Real-time micro-scale temperature imaging at low cost based on fluorescent intensity ratio.

Real-time temperature imaging with high spatial resolution has been a challenging task but also one with wide potential applications. To achieve this task, temperature sensor is critical. Fluorescent materials stand out to be promising candidates due to their quick response and strong temperature dependence. However, former reported temperature imaging techniques with fluorescent materials are mainly based on point by point scanning, which cannot fulfill the requirement of real-time monitoring. Based on fluorescent intensity ratio (FIR) of two emission bands of SrB4O7:Sm2+, whose spatial distributions were simultaneously recorded by two cameras with special filters separately, real-time temperature imaging with high spatial resolution has been realized with low cost. The temperature resolution can reach about 2 °C in the temperature range from 120 to 280 °C; the spatial resolution is about 2.4 µm and the imaging time is as fast as one second. Adopting this system, we observed the dynamic change of a micro-scale thermal distribution on a printed circuit board (PCB). Different applications and better performance could also be achieved on this system with appropriate fluorescent materials and high sensitive CCD detectors according to the experimental environment.