hv photonics

Article Aerial Projection 3D Display Based on

Wu-Xiang Zhao 1, Han-Le Zhang 2,*, Qing-Lin Ji 1, Huan Deng 1 and Da-Hai Li 1

1 College of Electronics and Information Engineering, Sichuan University, Chengdu 610065, China; [email protected] (W.-X.Z.); [email protected] (Q.-L.J.); [email protected] (H.D.); [email protected] (D.-H.L.) 2 School of Instrumentation Science and Optoelectronics Engineering, Beihang University, Beijing 100191, China * Correspondence: [email protected]

Abstract: We proposed an aerial projection 3D display based on integral imaging. It is composed of a projector, a -array holographic optical element (HOE), and two parabolic . The lens-array HOE is a diffraction grating and is made by the volume technique. The lens-array HOE can be produced on a thin glass plate, and it has the optical properties of a lens array when the Bragg condition is satisfied. When the display beams of the element image array (EIA) are projected on the lens-array HOE, 3D images can be reconstructed. The two parabolic mirrors can project 3D images into the air. The Bragg-unmatched light simply passes through the lens-array HOE. Therefore, the aerial projection 3D images appear to be imaged in the air without any medium. In the experiment, a BenQ projector was used for the projection of 3D images, with a resolution of 1600 × 1200. The diameter and the height of each parabolic are 150 mm and 25 mm, respectively. The inner diameter of the parabolic mirror is 40 mm. The 3D images were projected in the air, and the experimental results prove the correctness of our display system.

Keywords: 3D display; integral imaging; lens-array holographic optical element; parabolic mirror

 

Citation: Zhao, W.-X.; Zhang, H.-L.; 1. Introduction Ji, Q.-L.; Deng, H.; Li, D.-H. Aerial Aerial projection or floating 3D display has been widely investigated. There are many Projection 3D Display Based on types of floating 3D displays. For example, the light-field display can present floating Integral Imaging. Photonics 2021, 8, glass-free 3D images in the air, but more projectors are needed [1–3], or scanning [4–6], 381. https://doi.org/10.3390/ rotating [7–11], and processing are required. Therefore, the system of the light-field display photonics8090381 is quite complex and expensive. Volumetric displays can also float 3D images in the air, and they consist of bubbles [12,13], photoactivatable dye [14], nonlinear optical crystals [15], Received: 3 August 2021 quantum dots [16], fog [17,18], and water drops [19]. However, a special medium or multi- Accepted: 3 September 2021 Published: 9 September 2021 beam simultaneous projection is needed, so the volumetric display is impractical because of the difficulty of fabrication and construction. The can also

Publisher’s Note: MDPI stays neutral project 3D images in the air [20–26], but there are still some bottleneck problems, especially with regard to jurisdictional claims in the large computational amount and quantity of data. published maps and institutional affil- Integral imaging can also project 3D images floating in the air [27–30], which is an ideal iations. way to display 3D images. It can be formed via arbitrary viewpoint without supplementary glasses or tracking devices [31,32]. In addition, it can provide observer accommodation cues and smooth motion parallax [33–36]. The floating 3D display system-based integral imaging can be divided into two categories: one is swept type, and the other is static type. The swept-type floating 3D display system-based integral imaging generally consists of Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. a high-speed rotating motor [10,29,30]. The system is bulky and noninteractive. To solve This article is an open access article these issues, there are many studies on the static-type floating 3D display system-based distributed under the terms and integral imaging, because the system is free of spinning devices [27,28,32–35]. Therefore, conditions of the Creative Commons the static-type floating 3D display-based integral imaging has the advantages of simple Attribution (CC BY) license (https:// structure and easy implementation. creativecommons.org/licenses/by/ In this paper, we propose a simple-structured aerial projection 3D display based on 4.0/). integral imaging, which is composed of a projector, a lens-array HOE, and two parabolic

Photonics 2021, 8, 381. https://doi.org/10.3390/photonics8090381 https://www.mdpi.com/journal/photonics Photonics 2021, 8, x FOR PEER REVIEW 2 of 11

Photonics 2021, 8, 381 In this paper, we propose a simple-structured aerial projection 3D display based on2 of 11 integral imaging, which is composed of a projector, a lens-array HOE, and two parabolic mirrors. It can present a floating 3D display with only one projector and no spinning de- vices. The observers can touch the 3D images directly; the principles and the characteris- mirrors. It can present a floating 3D display with only one projector and no spinning devices. tics of the proposed aerial projection 3D display were analyzed through display experi- The observers can touch the 3D images directly; the principles and the characteristics of ments. the proposed aerial projection 3D display were analyzed through display experiments.

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