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

Add-on Occlusion: Turning Off-the-Shelf Optical See-through Head-mounted Displays Occlusion-capable

The occlusion-capable optical see-through head-mounted display (OC-OSTHMD) is actively developed in recent years since it allows mutual occlusion between virtual objects and the physical world to be correctly presented in augmented reality (AR). However, implementing occlusion with the special type of OSTHMDs prevents the appealing feature from the wide application. In this paper, a novel approach for realizing mutual occlusion for common OSTHMDs is proposed. A wearable device with per-pixel occlusion capability is designed. OSTHMD devices are upgraded to be occlusion-capable by attaching the device before optical combiners. A prototype with HoloLens 1 is built. The virtual display with mutual occlusion is demonstrated in real-time. A color correction algorithm is proposed to mitigate the color aberration caused by the occlusion device. Potential applications, including the texture replacement of real objects and the more realistic semi-transparent objects display, are demonstrated. The proposed system is expected to realize a universal implementation of mutual occlusion in AR.

Chromatic aberration correction in bi-focal augmented reality display by the multi-layer Pancharatnam-Berry phase lens

Chromatic aberration is a main obstacle for the commercial application of augmented reality displays. The current digital and optical compensation methods of reducing the chromatic aberration suffer from processing time, power consumption or complex design. Here, a simple strategy of chromatic aberration correction in bi-focal augmented reality near-eye display based on multi-layer Pancharatnam-Berry phase lens has been demonstrated and verified by experimental results. The multi-layer Pancharatnam-Berry phase lens, as a part of optical combiner, is fabricated by three liquid crystal polymer phase lenses with central wavelength in red, green, and blue, respectively. The multi-layer Pancharatnam-Berry phase lens can effectively reduce the chromatic aberration in both convex and concave mode of bi-focal augmented reality system, where the color breakup of virtual images captured in bi-focal augmented reality display is significantly alleviated. Comparing to the value of ΔK = 1.3 m^-1 in single green Pancharatnam-Berry phase lens, the multi-layer Pancharatnam-Berry phase lens system significantly reduce the ΔK to 0.45 m^-1 with reduction of 65.4%, which finally decreases the longitudinal chromatic aberration and improve the quality of images. The proposed broadband multi-layer Pancharatnam-Berry phase lens can benefit augmented reality displays and find widespread application in the near-eye 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.

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.