Multi-depth hologram generation using stochastic gradient descent algorithm with complex loss function.

The stochastic gradient descent (SGD) method is useful in the phase-only hologram optimization process and can achieve a high-quality holographic display. However, for the current SGD solution in multi-depth hologram generation, the optimization time increases dramatically as the number of depth layers of object increases, leading to the SGD method nearly impractical in hologram generation of the complicated three-dimensional object. In this paper, the proposed method uses a complex loss function instead of an amplitude-only loss function in the SGD optimization process. This substitution ensures that the total loss function can be obtained through only one calculation, and the optimization time can be reduced hugely. Moreover, since both the amplitude and phase parts of the object are optimized, the proposed method can obtain a relatively accurate complex amplitude distribution. The defocus blur effect is therefore matched with the result from the complex amplitude reconstruction. Numerical simulations and optical experiments have validated the effectiveness of the proposed method.

Occlusion-capable see-through display without the screen-door effect using a photochromic mask.

Conventional occlusion-capable see-through display systems have many practical limitations such as the form factor, narrow field of view, screen-door effect, and diffraction of a real scene. In this Letter, we propose an occlusion-capable see-through display using lens arrays and a photochromic plate. By imaging the occlusion mask on the photochromic plate with near-UV light, the visible light transmittance of the plate changes. Since no black matrix lies on the photochromic plate, our system provides a clear real scene view without the grid structure of the pixels and can prevent diffraction defects of the real scene. We also alleviate the drawback of a narrow field of view using the lens arrays for a reduced form factor.

Retinal projection type lightguide-based near-eye display with switchable viewpoints.

We present a retinal-projection-based near-eye display with switchable multiple viewpoints by polarization-multiplexing. Active switching of viewpoints is provided by the polarization grating, multiplexed holographic optical elements and polarization-dependent eyepiece lens that can generate one of the dual-divided focus groups according to the pupil position. The lightguide-combined optical devices have a potential to enable a wide field of view (FOV) and short eye relief with compact form factor. Our proposed system can support a pupil movement with an extended eyebox and mitigate image problem caused by duplicated viewpoints. We discuss the optical design for guiding system and demonstrate that proof-of-concept system provides all-in-focus images with 37 degrees FOV and 16 mm eyebox in horizontal direction.

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

A waveguide-based near-eye display (WNED) with an extended viewing angle using a polarization-dependent steering combiner (PDSC) is proposed. The novel eyepiece-combiner is composed of polarization gratings and polarization optics attached to the outcoupler part of the waveguide, which can control the output beam path depending on the polarization state. The viewing angle limited by the grating properties can be extended up to twice. Also, an ultrathinness of about 1.4 mm is suitable for the WNED. The demonstrated prototype system achieves a horizontal field of view of 33.2°, which is 2 times wider than the conventional structure (without the PDSC). The proposed configuration can resolve the viewing angle issue for the WNED.

Waveguide holography for 3D augmented reality glasses.

Near-eye displays are fundamental technology in the next generation computing platforms for augmented reality and virtual reality. However, there are remaining challenges to deliver immersive and comfortable visual experiences to users, such as compact form factor, solving vergence-accommodation conflict, and achieving a high resolution with a large eyebox. Here we show a compact holographic near-eye display concept that combines the advantages of waveguide displays and holographic displays to overcome the challenges towards true 3D holographic augmented reality glasses. By modeling the coherent light interactions and propagation via the waveguide combiner, we demonstrate controlling the output wavefront using a spatial light modulator located at the input coupler side. The proposed method enables 3D holographic displays via exit-pupil expanding waveguide combiners, providing a large software-steerable eyebox. It also offers additional advantages such as resolution enhancement capability by suppressing phase discontinuities caused by pupil replication process. We build prototypes to verify the concept with experimental results and conclude the paper with discussion.

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.