Design of ghost-free floating 3D display with narrow thickness using offset lens and dihedral corner reflector arrays

Omnidirectional mid-air image system using micro-mirror array plates

We proposed and implemented an omnidirectional mid-air image optical system that suppresses stray light and transmitted light. When micro-mirror array plates (MMAP) are integrated with view control films and rotated these optical elements at high speed, stray and transmitted light are effectively suppressed. This enables the visibility of omnidirectional mid-air image. We evaluated the effects of the view control film and high-speed rotation on the luminance and resolution of mid-air images, respectively. Our system facilitates the simultaneous viewing of mid-air images by multiple users, expanding the accessibility of mid-air image content to a large audience.

Resolution improvement in aerial imaging by a retroreflector using micro aperture arrays

For a floating display system using a prism- or bead-type retroreflector, non-retroreflected light is the key cause of the deterioration in image resolution. In the present study, a micro aperture array was used to enhance the image resolution of aerial imaging displays based on prism and bead retroreflectors. The effects of different micro aperture parameters on the divergence angle of the retroreflector were experimentally studied, and the modulation of the point spread function of different retroreflectors was also explored in detail. The experimental results showed that by properly arranging the micro aperture array, the divergence angle of the retroreflective light could be effectively reduced. Moreover, the full width at half maximum of the point spread function of the retroreflector was effectively narrowed. Finally, after the modulation of the micro aperture array, the imaging resolution was increased by 115%-150% compared to the original resolution. The proposed micro array is low cost, easy to process, and flexible and can be applied to a retroreflector-based aerial imaging system to provide high image quality.

Shadowless Projection Mapping using Retrotransmissive Optics

This paper presents a shadowless projection mapping system for interactive applications in which a target surface is frequently occluded from a projector with a user's body. We propose a delay-free optical solution for this critical problem. Specifically, as the primary technical contribution, we apply a large format retrotransmissive plate to project images onto the target surface from wide viewing angles. We also tackle technical issues unique to the proposed shadowless principle. First, the retrotransmissive optics inevitably suffer from stray light, which leads to significant contrast degradation of the projected result. We propose to block the stray light by covering the retrotransmissive plate with a spatial mask. Because the mask reduces not only the stray light but the achievable luminance of the projected result, we develop a computational algorithm that determines the shape of the mask to balance the image quality. Second, we propose a touch sensing technique by leveraging the optically bidirectional property of the retrotransmissive plate to support interaction between the user and the projected contents on the target object. We implement a proof-of-concept prototype and validate the above-mentioned techniques through experiments.

Depth of field and resolution-enhanced integral imaging display system

Depth of field (DOF) and resolution are mutually restricted in integral imaging (II) display. To overcome the trade-offs, we propose an II display system that simultaneously enhances the DOF and resolution. The system consists of a transmissive mirror device (TMD), a semi-transparent mirror (STM), and two II display units. Each II display unit consists of a 4K display screen and a micro-lens array (MLA). Benefiting from the parallel placement of the TMD and the STM, two central depth planes are reconstructed, which effectively enhances the DOF. Meanwhile, the resolution in the overlapping DOF region is increased to two times due to the interpolation of the light field information from two II display units. The impact of the distance between the two II display units and the TMD on the 3D image quality is analyzed. In geometric optics, a distance between the II two display units and the TMD is optimized to eliminate ghost images. In wave optics, a distance is optimized to eliminate 3D pixel gaps by exploiting the diffraction effect of the TMD. Both the geometric and wave optics are considered simultaneously to obtain a high-quality 3D image without ghost images and 3D pixel gaps. A DOF and resolution-enhanced II display system is developed, and the experimental results verify its feasibility.

Improvement of a floating 3D light field display based on a telecentric retroreflector and an optimized 3D image source

For a floating three-dimensional (3D) display system using a prism type retroreflector, non-retroreflected light and a blurred 3D image source are two key causes of the deterioration in image quality. In the present study, ray tracing is used to analyze the light distribution of a retroreflector at different incident angles. Based on this analysis, a telecentric retroreflector (TCRR) is proposed to suppress non-retroreflected light without sacrificing the viewing angle. A contrast transfer function (CTF) is used to evaluate the optical performance of the TCRR. To improve the 3D image source, the relationship between the root mean square (RMS) of the voxels and the 3D image quality is discussed, and an aspheric lens array is designed to reduce aberrations. Computational simulation results reveal that the structural similarity (SSIM) of the 3D image source increased to 0.9415. An experimental prototype system combining the TCRR and optimized 3D image source is then built. Experimental analysis demonstrates that the proposed method suppresses non-retroreflected light and improves the 3D image source. In particular, a clear floating 3D image with a floating distance of 70 mm and a viewing angle of 50° can be achieved.

See-through aerial display using a dihedral corner reflector array and hologram mirrors

In this study, we reveal a novel aerial display system, to the best of our knowledge, that combines volume hologram mirrors with a dihedral corner reflector array (DCRA). The suggested aerial display has a see-through capability, which allows for a new design of aerial displays by combining with other types of displays. Furthermore, the virtual image, which frequently disrupts the observation of aerial images, can be suppressed by the Bragg condition of the volume hologram. The color dispersion in the holograms is efficiently compensated by employing features of the DCRA. The findings of preliminary experiments are demonstrated using a DCRA device and full-color hologram mirrors.

Aerial floating 3D display device with lenticular-type naked-eye 3D display and a crossed-mirror array

The depth feeling of a naked-eye 3D display is determined by the combination of the display and the lenticular lens, and because the parallax of the displayed image cannot be made stronger, providing a more stereoscopic effect is difficult. In this study, we propose a system that provides a clearer stereoscopic effect by enabling the naked-eye 3D display to be observed as an aerial stereoscopic image without the framework of the display. By comparing it with the conventional aerial display method, we demonstrate that it is possible to maintain the same level of resolution as the method without a crossed-mirror array and that natural stereoscopic view is possible.

Compact in-line floating display system using a dihedral corner reflector array

We propose a compact type floating display system using a dihedral corner reflector array. Conventional floating displays using the dihedral corner reflector array usually have a folded configuration which makes the system bulky. The proposed technique achieves the compact in-line configuration using a pair of decentered lenses. The decentered lenses make the effective incident angle to the dihedral corner reflector array be tilted while maintaining the display panel and the dihedral corner reflector array in parallel. The ghost images are also refracted largely by the decentered lenses, being separated from the desired floating images. The proposed technique is verified by optical experiments.