Wearable near-eye displays for virtual and augmented reality (VR/AR) have seen enormous growth in recent years. While researchers are exploiting a plethora of techniques to create life-like three-dimensional (3D) objects, there is a lack of awareness of the role of human perception in guiding the hardware development. An ultimate VR/AR headset must integrate the display, sensors, and processors in a compact enclosure that people can comfortably wear for a long time while allowing a superior immersion experience and user-friendly human–computer interaction. Compared with other 3D displays, the holographic display has unique advantages in providing natural depth cues and correcting eye aberrations. Therefore, it holds great promise to be the enabling technology for next-generation VR/AR devices. In this review, we survey the recent progress in holographic near-eye displays from the human-centric perspective.

Toward the next-generation VR/AR optics: a review of holographic near-eye displays from a human-centric perspective.

Holographic three-dimensional display is an important display technique because it can provide all depth information of a real or virtual scene without any special eyewear. In recent years, with the development of computer and optoelectronic technology, computer-generated holograms have attracted extensive attention and developed as the most promising method to realize holographic display. However, some bottlenecks still restrict the development of computer-generated holograms, such as heavy computation burden, low image quality, and the complicated system of color holographic display. To overcome these problems, numerous algorithms have been investigated with the aim of color dynamic holographic three-dimensional display. In this review, we will explain the essence of various computer-generated hologram algorithms and provide some insights for future research. 

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Review of computer-generated hologram algorithms for color dynamic holographic three-dimensional display

Computer-generated holography can obtain the wavefront required for constructing arbitrary intensity distributions in space. Currently, speckle noises in holography remain an issue for most computational methods. In addition, there lacks a multiplexing technology by which images from a single hologram and light source can be switched by a lens. In this work, we first come up with a new algorithm to generate holograms to project smoother images by wavevector filtering. Thereupon, we propose a unique multiplexing scheme enabled by a Fourier lens, as the incident light can be decomposed either by a superposition of spherical waves or plane waves. Different images are obtained experimentally in the spatial and wavevector domains, switchable by a lens. The embedded wavevector filtering algorithm provides a new prospective for speckle suppression without the need for postprocessing. The multiplexing technology can double the capacity of current holographic systems and exhibits potential for various interesting display applications.

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Domain multiplexed computer-generated holography by embedded wavevector filtering algorithm

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A novel encryption method for 3D biomedical objects is introduced.It is based on the use of cellular automata, boolean functions and discretized chaotic maps.The protocol involves two phases that produce confusion and diffusion.The encryption method directly acts on the 3D structure of the object defined by voxels. A novel encryption protocol for 3D biomedical objects is introduced in this work. This method consists of two phases which are iteratively applied: the confusion phase and the diffusion phase. In the confusion phase the position of the voxels are permuted by means of a discretized chaotic map, whereas in the diffusion phase the value of each voxel is changed. The diffusion phase is divided into two sub phases: in the first one a memory reversible 3D cellular automata is applied using the 3D object as the initial conditions, and in the second sub phase, a discrete dynamical system with delay defined by a non-linear boolean function is applied to the output of the evolution of the cellular automaton. The protocol is shown to be secure against the most important cryptanalytic attacks.The impact and novelty of this method lies on directly ciphering the 3D objects and considering these objects as the aggregation of voxels. Moreover, this allows to design a new and efficient encryption algorithm which is the generalization of those methods to encrypt digital images that are based on the iteration of a confusion and a diffusion phase.The use of cellular automata and boolean transition rules in the diffusion phase opens new possibilities for the use of expert and intelligence systems in cryptography since cellular automata can be used and inference machines.

3D medical data security protection

We propose a full color computer generated holographic near-eye display (NED) based on white light illumination. The method inspired from color rainbow holography is used for calculation of 2D and 3D color holograms. The parameters of the color hologram calculation are designed based on the parameters of the spatial light modulator (SLM) with 4K resolution. A slit type spatial filter is designed in frequency domain to extract red, green and blue frequency components for full color display. A NED system including a white light source, an achromatic collimating lens, a 4K SLM, a 4f optical filtering system, and an achromatic lens as eyepiece is designed and developed. The main contribution of this paper is the first time to apply the rainbow holography concept to the dynamic full color NED with a compact display system. The optical experiments prove the feasibility of the proposed method.

Full-color computer-generated holographic near-eye display based on white light illumination.

We propose an optical method to eliminate pseudoscopic issue in the integral imaging three-dimensional (3D) display by using a transmissive mirror device (TMD) and a light filter. Object light rays passing through the TMD can form an undistorted and depth inverted real image. Therefore, the TMD can eliminate the pseudoscopic issue existing in the traditional integral imaging. However, two ghost images appeared in integral imaging using the TMD. After studying the causes of the ghost images, a light filter is designed and fabricated to eliminate the ghost images. Integral imaging using TMD is developed, and it presents a high quality 3D image without a pseudoscopic issue.

Method to eliminate pseudoscopic issue in an integral imaging 3D display by using a transmissive mirror device and light filter

A fast computer-generated holographic method with multiple projection images for a near-eye VR (Virtual Reality) and AR (Augmented Reality) 3D display is proposed. A 3D object located near the holographic plane is projected onto a projection plane to obtain a plurality of projected images with different angles. The hologram is calculated by superposition of projected images convolution with corresponding point spread functions (PSF). Holographic 3D display systems with LED as illumination, 4f optical filtering system and lens as eyepiece for near-eye VR display and holographic optical element (HOE) as combiner for near-eye AR display are designed and developed. The results show that the proposed calculation method is about 38 times faster than the conventional point cloud method and the display system is compact and flexible enough to produce speckle noise-free high-quality VR and AR 3D images with efficient focus and defocus capabilities.

https://www.mdpi.com/2076-3417/9/19/4164/pdf

Xin Yang

Papers

Full-color computer-generated holographic near-eye display based on white light illumination.

Method to eliminate pseudoscopic issue in an integral imaging 3D display by using a transmissive mirror device and light filter

A Fast Computer-Generated Holographic Method for VR and AR Near-Eye 3D Display

On the difference between single- and double-sided bandpass filtering of spatial frequencies

Computer generated full-parallax synthetic hologram based on frequency mosaic