Extended-viewing-angle waveguide near-eye display with a polarization-dependent steering combiner

Gradient polarization volume grating with wide angular bandwidth for augmented reality

Angular bandwidth, which is critical to field-of-view, plays important role in diffractive optical waveguide augmented reality display. However, design and fabrication of large angular bandwidth is still a challenge. Herein, we demonstrate a liquid crystal reflective gradient polarization volume grating with three-dimensional gradient periodic structure for waveguide near-eye display. Two-beam polarization interference with special designed periodic gradient photomask are applied to chiral-dopant reactive mesogens doped with ultraviolet dye for generating gradient three-dimensional configuration of liquid crystals, resulting in gradient polarization volume grating with extended angle bandwidth of 61° while keeping 80% diffraction efficiency, with peak efficiency near 100%. The proposed gradient polarization volume grating provides an effective method to broaden the angular bandwidth in waveguide for wide field-of-view augmented reality display.

Complex amplitude modulated holographic display system based on polarization grating

We propose a holographic display system for complex amplitude modulation (CAM) using a phase-only spatial light modulator (SLM) and two polarization gratings (PG). The two sub-holograms of the complex-amplitude computed generated hologram (CGH) are loaded in different regions of SLM. Two diffractive components couple in space after longitudinal migration from the double PGs, and finally interfered through the line polarizer. The influence of the system error on the reconstructed image quality is analyzed, which provides a theoretical assessment for adding pre-compensation to CGH to compensate the system error. Moreover, on the base of the proposed system, a large depth of field and enlarged display area display is realized and the real-time display can be achieved because of the analytical complex-amplitude computed generated hologram. The optical experimental results show that the proposed system has high energy efficiency, and can provide high-quality holographic display with a large depth of field and enlarged display area.

Binary geometric-phase holograms

Diffractive optics elements have exhibited many novel characteristics through various methods of employing Pancharatnam-Berry, or geometric, phase. One geometric-phase hologram (GPH) subset, consisting of a π-difference binary sampling, shows polarization-independent properties that are not present in the continuous GPH and the dynamic-phase binary analog. Here, we investigate the binary geometric-phase holograms (bin-GPHs) realized with anisotropic liquid crystal (LC) polymers. First, the optical properties of the ideal binary polarization grating are derived and simulated showing 81% cumulative first-order efficiency, polarization-independent diffraction when applying a π-switching scheme, innate odd (m = 2k + 1) diffractive orders, and variable polarization output. After, experimental results of two key bin-GPH elements, the binary polarization grating (Λ = 30μm) and binary geometric-phase lens (f/100), with π-offset regions and a 0.5μm transition pixel are presented. We found that the fabricated non-ideal bin-GPHs exhibit near-maximum theoretical polarization-insensitive diffraction efficiency and tunable polarization outputs. The simple, and scalable, fabrication of the anisotropic bin-GPH provides the potential for implementation within the next-generation near-eye displays for polarization-invariant beam-steering and waveguides.

In-Depth Review of Augmented Reality: Tracking Technologies, Development Tools, AR Displays, Collaborative AR, and Security Concerns

Augmented reality (AR) has gained enormous popularity and acceptance in the past few years. AR is indeed a combination of different immersive experiences and solutions that serve as integrated components to assemble and accelerate the augmented reality phenomena as a workable and marvelous adaptive solution for many realms. These solutions of AR include tracking as a means for keeping track of the point of reference to make virtual objects visible in a real scene. Similarly, display technologies combine the virtual and real world with the user's eye. Authoring tools provide platforms to develop AR applications by providing access to low-level libraries. The libraries can thereafter interact with the hardware of tracking sensors, cameras, and other technologies. In addition to this, advances in distributed computing and collaborative augmented reality also need stable solutions. The various participants can collaborate in an AR setting. The authors of this research have explored many solutions in this regard and present a comprehensive review to aid in doing research and improving different business transformations. However, during the course of this study, we identified that there is a lack of security solutions in various areas of collaborative AR (CAR), specifically in the area of distributed trust management in CAR. This research study also proposed a trusted CAR architecture with a use-case of tourism that can be used as a model for researchers with an interest in making secure AR-based remote communication sessions.

Tunable focal waveguide-based see-through display with negative liquid crystal lens

A see-through display based on a planar holographic waveguide with a tunable focal plane is presented. A negative liquid crystal lens is attached on the outcoupling location of the waveguide to manipulate the image distance. The continuous tunable range for the focal length is from negative infinity to -65 cm. The demonstrated prototype system provides 10.5° field-of-view (FOV) for the images not locating at infinity. The FOV for the images not locating at infinity is limited by the diameter of the liquid crystal lens. The lens function of the liquid crystal lens is polarization dependent. By controlling the polarization states of the real scene and the input information image, the liquid crystal lens keeps the see-through function for a real scene and simultaneously plays the role of a negative lens for the input information image. Compared to the see-through display system with a single focal plane, the presented system offers a more comfortable augmented reality (AR) experience.

Near-eye display with a triple-channel waveguide for metaverse

We present a near-eye display featuring a triple-channel waveguide with chiral liquid crystal gratings. Our triple-channel waveguide is capable of dividing one field of view into three through both the polarization orthogonality and angular separation. To illustrate its principle, a k-space diagram, which takes into account the aspect ratio of field of view, is depicted. Our results demonstrate that its diagonal field of view reaches 90°, eye relief is 10 mm, exit pupil is 4.9 × 4.9 mm², transmittance is 4.9%, and uniformity is 89%.

Advanced liquid crystal devices for augmented reality and virtual reality displays: principles and applications

Liquid crystal displays (LCDs) and photonic devices play a pivotal role to augmented reality (AR) and virtual reality (VR). The recently emerging high-dynamic-range (HDR) mini-LED backlit LCDs significantly boost the image quality and brightness and reduce the power consumption for VR displays. Such a light engine is particularly attractive for compensating the optical loss of pancake structure to achieve compact and lightweight VR headsets. On the other hand, high-resolution-density, and high-brightness liquid-crystal-on-silicon (LCoS) is a promising image source for the see-through AR displays, especially under high ambient lighting conditions. Meanwhile, the high-speed LCoS spatial light modulators open a new door for holographic displays and focal surface displays. Finally, the ultrathin planar diffractive LC optical elements, such as geometric phase LC grating and lens, have found useful applications in AR and VR for enhancing resolution, widening field-of-view, suppressing chromatic aberrations, creating multiplanes to overcome the vergence-accommodation conflict, and dynamic pupil steering to achieve gaze-matched Maxwellian displays, just to name a few. The operation principles, potential applications, and future challenges of these advanced LC devices will be discussed.

Waveguide-type Maxwellian near-eye display using a pin-mirror holographic optical element array

We propose a novel, to the best of our knowledge, waveguide-type optical see-through Maxwellian near-eye display for augmented reality. A pin-mirror holographic optical element (HOE) array enables the Maxwellian view and eye-box replication. Virtual images with deep depth of field are presented by each pin-mirror HOE, alleviating the discrepancy between vergence and accommodation distance. The compact form factor is achieved by the thin waveguide and HOE couplers.

Wide-Field-of-View Near-Eye Display with Dual-Channel Waveguide

We propose a wide-field-of-view near-eye display featuring a dual-channel waveguide with cholesteric liquid crystal gratings. Our dual-channel waveguide is capable of splitting the field of view through the orthogonal polarization division multiplexing. To explain its mechanism, a diagram of k-domain, which factors into both the waveguide size and the number of pupils, is depicted. Our results demonstrate that the diagonal field of view reaches up to 80°, eye relief is 10 mm, exit pupil is 4 × 3 mm2, and uniformity is 79%.

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.

Recent Advances in Photoalignment Liquid Crystal Polarization Gratings and Their Applications

Liquid crystal (LC) circular polarization gratings (PGs), also known as Pancharatnam–Berry (PB) phase deflectors, are diffractive waveplates with linearly changed optical anisotropy axes. Due to the high diffraction efficiency, polarization selectivity character, and simple fabrication process, photoalignment LC PGs have been widely studied and developed especially in polarization management and beam split. In this review paper, we analyze the physical principles, show the exposure methods and fabrication process, and present relevant promising applications in photonics and imaging optics.

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.

Extending eyebox with tunable viewpoints for see-through near-eye display

The Maxwellian display presents always-focused images to the viewer, alleviating the vergence-accommodation conflict (VAC) in near-eye displays (NEDs). However, the limited eyebox of the typical Maxwellian display prevents it from wider applications. We propose a Maxwellian see-through NED based on a multiplexed holographic optical element (HOE) and polarization gratings (PGs) to extend the eyebox by viewpoint multiplication. The multiplexed HOE functions as multiple convex lenses to form multiple viewpoints, which are copied to different locations by PGs. To mitigate the imaging problem that multiple viewpoints or no viewpoints enter the eye pupil, the viewpoints can be tuned by mechanically moving a PG. We implement our method in a proof-of-concept system. The optical experiments confirm that the proposed display system provides always in-focus images within a 12 mm eyebox in the horizontal direction with a 32.7° diagonal field of view (FOV) and a 16.5 mm eye relief (ERF), and its viewpoints are tunable to match the actual eye pupil size. Compared with other techniques to extend the eyebox of Maxwellian displays, the proposed method shows competitive performances of a large eyebox, adaptability to the eye pupil size, and focus cues within a large depth range.

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.

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.