See-through optical combiner for augmented reality head-mounted display: index-matched anisotropic crystal lens

See-through display based on commercial photopolymer: Optimization and shrinkage effects

Nowadays augmented reality, 3D Image, mixed reality and see-through applications are very attractive technologies due to their great potential. Holographic optical elements can provide interesting solutions for injection and extraction of the image in the waveguides that are part of the see-through devices. We have developed a coupled waveguide system based on slanted transmission gratings recorded in manufactured photopolymers. In this work we optimize our schedule to a commercial photopolymer for this high demanded application. We demonstrate that high diffraction efficiencies can be obtained if we optimize the recording geometry, recording intensity and recording time for this material. In addition, we study the effects of shrinkage in our holographic system. In general shrinkage is an important drawback for holographic applications, nevertheless we demonstrate how shrinkage can help these systems open new possibilities. Lastly, we show how to significantly improve the quality of the guided image.

Design, analysis and optimization of a waveguide-type near-eye display using a pin-mirror array and a concaved reflector

Waveguides have become one of the most promising optical combiners for see-through near-eye displays due to the thickness, weight, and transmittance. In this study, we propose a waveguide-type near-eye display using a pin-mirror array and a concaved reflector with a compact outlook, optimized image uniformity and stray light. Issues have been discussed in detail, which include field of view (FOV), eye-box, resolution, depth of field (DOF), display uniformity and stray light artifacts. It can be shown that the DOF can be extended (when compared with traditional waveguide-type near-eye displays) to alleviate the vergence-accommodation conflict (VAC) problem, and the uniformity & stray light can be improved with an optimal structure. Moreover, reflective surfaces have been introduced as the input and output coupling with a compact outlook, an easy-processing structure and the achromatic performance. A prototype based on the proposed method have been successfully developed, and virtual images with an extended DOF can be shown along with the real-world.

LensIet VR: Thin, Flat and Wide-FOV Virtual Reality Display Using Fresnel Lens and LensIet Array

We propose a new thin and flat virtual reality (VR) display design using a Fresnel lenslet array, a Fresnel lens, and a polarization-based optical folding technique. The proposed optical system has a wide field of view (FOV) of 102°x102°, a wide eye-box of 8.8 mm, and an ergonomic eye-relief of 20 mm. Simultaneously, only 3.3 mm of physical distance is required between the display panel and the lens, so that the integrated VR display can have a compact form factor like sunglasses. Moreover, since all lenslet of the lenslet array is designed to operate under on-axis condition with low aberration, the discontinuous pupil swim distortion between the lenslets is hardly observed. In addition, all on-axis lenslets can be designed identically, reducing production cost, and even off-the-shelf Fresnel optics can be used. In this paper, we introduce how we design system parameters and analyze system performance. Finally, we demonstrate two prototypes and experimentally verify that the proposed VR display system has the expected performance while having a glasses-like form factor.

Theoretical model of a subwavelength grating polarization beam splitter

This study presents a theoretical model of a subwavelength grating polarization beam splitter (SWGPBS) using a combination of the theory of thin-film interference and the effective medium theory for guided-mode resonance. The structural parameters of SWGPBSs at oblique incidence calculated by our theoretical models and electromagnetic wave simulation were in good agreement within the range of the predicted approximation error. Feasibility of the oblique incidence SWGPBSs was verified, and the physical limitations of the SWGPBSs were clarified. Because the design procedure of SWGPBSs was simplified with our theoretical analysis, the range of their applications can be expanded to other fields.

Aberration-corrected full-color holographic augmented reality near-eye display using a Pancharatnam-Berry phase lens

We present a full-color holographic augmented reality near-eye display using a Pancharatnam-Berry phase lens (PBP lens) and its aberration correction method. Monochromatic and chromatic aberrations of the PBP lens are corrected by utilizing complex wavefront modulation of the holographic display. A hologram calculation method incorporating the phase profile of the PBP lens is proposed to correct the monochromatic aberration. Moreover, the chromatic aberration is corrected by warping the image using the mapping function obtained from ray tracing. The proposed system is demonstrated with the benchtop prototype, and the experimental results show that the proposed system offers 50° field of view full-color holographic images without optical aberrations.

Development of an ultra-compact optical combiner for augmented reality using geometric phase lenses

We present an ultra-compact optical combiner using a waveguide and geometric phase lenses (GPL) for augmented reality displays. By sandwiching the output coupler of a planar waveguide between two flat, thin GPLs, we create two optical sub-systems with different optical powers for displaying the virtual objects and transmitting the ambient light rays, respectively. We implemented our method in a scanning-based Maxwellian display and demonstrated the augmentation of an all-in-focus Maxwellian-view image with real-world objects within a 15° field of view. Our device is light (50 g) and thin (4 mm), making it well suited for wearable applications.

An online SSVEP-BCI system in an optical see-through augmented reality environment

OBJECTIVE

This study aimed to design and evaluate a high-speed online steady-state visually evoked potential (SSVEP)-based brain-computer interface (BCI) in an optical see-through (OST) augmented reality (AR) environment.

APPROACH

An eight-class BCI was designed in an OST-AR headset which is wearable and allows users to see the user interface of the BCI and the device to be controlled in the same view field via the OST head-mounted display. The accuracies, information transfer rates (ITRs), and SSVEP signal characteristics of the AR-BCI were evaluated and compared with a computer screen-based BCI implemented with a laptop in offline and online cue-guided tasks. Then, the performance of the AR-BCI was evaluated in an online robotic arm control task.

MAIN RESULTS

The offline results obtained during the cue-guided task performed with the AR-BCI showed maximum averaged ITRs of 65.50  ±  9.86 bits min^-1 according to the extended canonical correlation analysis-based target identification method. The online cue-guided task achieved averaged ITRs of 65.03  ±  11.40 bits min^-1. The online robotic arm control task achieved averaged ITRs of 45.57  ±  7.40 bits min^-1. Compared with the screen-based BCI, some limitations of the AR environment impaired BCI performance and the quality of SSVEP signals.

SIGNIFICANCE

The results showed the potential for providing a high-performance brain-control interaction method by combining AR and BCI. This study could provide methodological guidelines for developing more wearable BCIs in OST-AR environments and will also encourage more interesting applications involving BCIs and AR techniques.

Tomographic near-eye displays

The ultimate 3D displays should provide both psychological and physiological cues for depth recognition. However, it has been challenging to satisfy the essential features without making sacrifices in the resolution, frame rate, and eye box. Here, we present a tomographic near-eye display that supports a wide depth of field, quasi-continuous accommodation, omni-directional motion parallax, preserved resolution, full frame, and moderate field of view within a sufficient eye box. The tomographic display consists of focus-tunable optics, a display panel, and a fast spatially adjustable backlight. The synchronization of the focus-tunable optics and the backlight enables the display panel to express the depth information. We implement a benchtop prototype near-eye display, which is the most promising application of tomographic displays. We conclude with a detailed analysis and thorough discussion of the display's optimal volumetric reconstruction. of tomographic displays.

Augmented reality near-eye display using Pancharatnam-Berry phase lenses

An augmented reality (AR) near-eye display using Pancharatnam-Berry (PB) phase lenses is proposed. PB phase lenses provide different optical effects depending on the polarization state of the incident light. By exploiting this characteristic, it is possible to manufacture an AR combiner with a small form factor and a large numerical aperture value. The AR combiner adopted in the proposed system operates as a convex lens for right-handed circularly polarized light and operates as transparent glass for left-handed circularly polarized light. By merging this combiner with a transparent screen, such as diffuser-holographic optical elements (DHOEs), it is possible to make an AR near-eye display with a small form factor and a wide field of view. In addition, the proposed AR system compensates the chromatic aberration that occurs in PB phase lens by adopting three-layered DHOEs. The operating principle of the proposed system is covered, and its feasibility is verified with experiments and analysis.

Dual-focal waveguide see-through near-eye display with polarization-dependent lenses

A waveguide near-eye display (NED) with a dual-focal plane using a polarization-dependent lens device is proposed. The novel optical device is composed of a geometric phase holographic lens, a wave plate, and a circular polarizer, which is operating as a concave lens or a see-through optical window, depending on the polarization state of the input beam. Such property and ultra-thinness of about 1.5 mm can be applied to a combiner-eyepiece lens for augmented reality. This optical device attached to the waveguide provides two depth planes with polarization multiplexing. We have demonstrated that our proof-of-concept system has image planes at infinity and 20 diopters. The devised system can be expected to offer a better immersive experience, compared to a NED system with a single-focal plane.

Holographic Three-Dimensional Virtual Reality and Augmented Reality Display Based on 4K-Spatial Light Modulators

In this paper, we propose a holographic three-dimensional (3D) head-mounted display based on 4K-spatial light modulators (SLMs). This work is to overcome the limitation of stereoscopic 3D virtual reality and augmented reality head-mounted display. We build and compare two systems using 2K and 4K SLMs with pixel pitches 8.1 μm and 3.74 μm, respectively. One is a monocular system for each eye, and the other is a binocular system using two tiled SLMs for two eyes. The viewing angle of the holographic head-mounted 3D display is enlarged from 3.8 ∘ to 16.4 ∘ by SLM tiling, which demonstrates potential applications of true 3D displays in virtual reality and augmented reality.

Holographic waveguides in photopolymers

The possibilities that offer the holographic optical elements for photovoltaic and "see through display" applications open new windows for holographic recording materials. In this sense, some specific characteristics are required for each particular application. Waveguides are one of the key elements for these applications. Photopolymers are one of the most competitive candidates for waveguide fabrication. In this work, we evaluate the performance of one example from each of three families of photopolymer material in fabrication of a 633nm waveguide. Firstly, polyvinyl alcohol acrylamide, PVA/AA, the second one, a nanoparticle-thiol-ene, NPC, and on the last place a penta/hexa-acrylate based polymer with dispersed nematic liquid crystal molecules, PDLC. We study the critical role of the material and in particular, spatial resolution for this application.

Metasurface eyepiece for augmented reality

Recently, metasurfaces composed of artificially fabricated subwavelength structures have shown remarkable potential for the manipulation of light with unprecedented functionality. Here, we first demonstrate a metasurface application to realize a compact near-eye display system for augmented reality with a wide field of view. A key component is a see-through metalens with an anisotropic response, a high numerical aperture with a large aperture, and broadband characteristics. By virtue of these high-performance features, the metalens can overcome the existing bottleneck imposed by the narrow field of view and bulkiness of current systems, which hinders their usability and further development. Experimental demonstrations with a nanoimprinted large-area see-through metalens are reported, showing full-color imaging with a wide field of view and feasibility of mass production. This work on novel metasurface applications shows great potential for the development of optical display systems for future consumer electronics and computer vision applications.

Hybrid multi-layer displays providing accommodation cues

Hybrid multi-layer displays are proposed as the system combines additive light field (LF) displays and multiplicative LF displays. The system is implemented by integrating the multiplicative LF displays with a half mirror to expand the overall depth of field. The hybrid displays are advantageous in that the form factor is competitive with existing additive LF displays with 2 layers implemented by a half mirror and two panels, only half of brightness loss is experienced compared to multiplicative LF displays with 2 layers, and no time-division is required to provide images for multi-layer displays. The images for presentation planes are processed by light field factorization and optimized with the presented algorithm. Retinal images are reconstructed based on various accommodation states and display types to check the accommodation response and utilized to compare the proposed displays with existing displays. With ray tracing method, retinal images generated by the proposed displays can be obtained. To verify the feasibility of the system, a prototype of hybrid multi-layer displays was implemented and display photographs were captured with different accommodation states of camera. With the simulation results and experimental results, this system was confirmed to support accommodation cues in a range of 1.8 diopters.