Integral imaging system using an electroluminescent film backlight for three-dimensional-two-dimensional convertibility and a curved structure

Large-Area and Rapid Fabrication of a Microlens Array on a Flexible Substrate for an Integral Imaging 3D Display

A curved integral imaging three-dimensional (3D) display attracts a lot of interest due to its enhanced 3D sense of immersion and wider viewing angle. In this paper, a microlens array (MLA) based on a flexible poly(ethylene terephthalate) (PET) substrate was achieved by a straightforward, rapid, and low-cost technique. The reactive ion etching (RIE) process treated PET/CYTOP covered with a flexible mask to generate a hydrophilic-hydrophobic patterned surface. The well-designed arrays of confined adhesive droplets with a controlled geometry on a hydrophilic-hydrophobic patterned surface were formed using the blade-coating method. A flexible MLA with a diameter of 820 μm, a size of 5.3 cm × 5.1 cm, and a radius of curvature of 25 cm was fabricated and combined with a curved two-dimensional (2D) monitor to realize a lateral viewing range of 6.4 cm at a viewing distance of 25 cm, which is 4 times larger than with flat integral imaging 3D display system. The flexible MLA has the advantages of a controllable lens profile and large pitch, and it can be manufactured on a large scale. In addition, it provides a large viewing angle for the reconstructed 3D image.

Resolution-preserving passive 2D/3D convertible display based on holographic optical elements

We propose and demonstrate a resolution-preserving passive 2D/3D convertible display by two individual wavelengths. It uses a holographic optical element to generate two images and passively separate the exit pupils for these two wavelengths, which forms two viewpoints for each of the observer's eyes. Due to Bragg-mismatched reconstruction of two similar but distinct wavelengths, the images are separated in space. They can be fused into one through the convergence function of human eyes. By switching the input image source, the conversion between 2D and 3D mode can be realized. This method is resolution-preserving and 2D/3D convertible with no extra active components. For experimental verification, a proof-of-concept projection-type prototype is assessed.

2D/3D mixed frontal projection system based on integral imaging

Two-dimensional (2D)/three-dimensional (3D) convertible or mixed display is one of the most important factors for the fast penetration of 3D display into the display market. In this paper, we propose a 2D/3D mixed frontal projection system that mainly contains a liquid crystal micro-lens array (LCMLA) and a quarter-wave retarding film with pinholes (QWRF-P). The LCMLA exhibits the focusing effect or no optical effect depending on the polarization direction of the incident lights. The forward incident lights pass through the LCMLA without any bending. After passing through the QWRF-P twice, half of the backward lights change the polarization direction with 90°, and the other half remains. Using our designed system, different display modes, including 2D display, 3D display, and 2D/3D mixed display, can be realized. The unique feature of the proposed 2D/3D mixed frontal projection system is that it can switch the display modes by simply changing the image sources without the need of any active optical devices. Moreover, the proposed system is compact, simple and space-efficient, which is suitable for the application in glassless 3D cinema and home 3D theatre.

Recent progress in see-through three-dimensional displays using holographic optical elements [Invited]

The principles and characteristics of see-through 3D displays are presented. We especially focus on the integral-imaging display system using a holographic optical element (IDHOE), which is able to display 3D images and satisfy the see-through property at the same time. The technique has the advantage of the high transparency and capability of displaying autostereoscopic 3D images. We have analyzed optical properties of IDHOE for both recording and displaying stages. Furthermore, various studies of new applications and system improvements for IDHOE are introduced. Thanks to the characteristics of holographic volume grating, it is possible to implement a full-color lens-array holographic optical element and conjugated reconstruction as well as 2D/3D convertible IDHOE. Studies on the improvements of viewing characteristics including a viewing angle, fill factor, and resolution are also presented. Lastly, essential issues and their possible solutions are discussed as future work.

Three-dimensional/two-dimensional convertible projection screen using see-through integral imaging based on holographic optical element

We propose a 3D/2D convertible screen using a holographic optical element and angular multiplexing method of volume hologram. The proposed screen, named a multiplexed holographic optical element screen (MHOES), is composed of passive optical components, and displaying modes between 3D and 2D modes are converted according to projection directions. In a recording process, the angular multiplexing method by using two reference waves with different incidence angles enables the functions of 3D and 2D screens to be recorded in a single holographic material. Also, in order to avoid the bulky experimental setup due to adopting different projectors for the 3D and 2D modes, the projection part is realized based on a prism. The designed projection part enables the single projector to present 3D on 2D mode, where the 3D and 2D contents are simultaneously displayed in one scene, without active components. The optical characteristics of MHOES are experimentally analyzed, and displaying experiments with a full-color MHOES are presented in order to verify the 3D/2D convertibility and see-through properties.

Bi-sided integral imaging with 2D/3D convertibility using scattering polarizer

We propose a two-dimensional (2D) and three-dimensional (3D) convertible bi-sided integral imaging. The proposed system uses the polarization state of projected light for switching its operation mode between 2D and 3D modes. By using an optical module composed of two scattering polarizers and one linear polarizer, the proposed integral imaging system simultaneously provides 3D images with 2D background images for observers who are located in the front and the rear sides of the system. The occlusion effect between 2D images and 3D images is realized by using a compensation mask for 2D images and the elemental images. The principle of proposed system is experimentally verified.

Integral imaging using a color filter pinhole array on a display panel

We propose methods of enhancing pinhole-type integral imaging ray density, resolution, and expressible depth range using a color filter pinhole array on a liquid crystal display panel with a projection scheme. A color filter structure on a liquid crystal display panel acts as pinhole array in integral imaging with separation of color channels. In conventional pinhole-type integral imaging, the resolution, viewing angle, and ray density are limited by the pinhole interval, the width and thickness of the pinhole structure, and the gap between the display panel and the pinhole array. To overcome the limitation of the pinhole interval, we use a color filter pinhole array on a display panel and a projection-type integral imaging scheme. The use of a color filter pinhole array and the projection scheme can enlarge the region of one elemental image and improve the resolution and ray density remarkably. This paper presents the experimental results of the proposed method and a comparison with conventional methods.

Three-dimensional display technologies of recent interest: principles, status, and issues [Invited]

Recent trends in three-dimensional (3D) display technologies are very interesting in that both old-fashioned and up-to-date technologies are being actively investigated together. The release of the first commercially successful 3D display product raised new research topics in stereoscopic display. Autostereoscopic display renders a ray field of a 3D image, whereas holography replicates a wave field of it. Many investigations have been conducted on the next candidates for commercial products to resolve existing limitations. Up-to-date see-through 3D display is a concept close to the ultimate goal of presenting seamless virtual images. Although it is still far from practical use, many efforts have been made to resolve issues such as occlusion problems.

Tunable viewing scope of three-dimensional integral imaging

This article defines the tunable viewing scope (TVS) of three-dimensional integral imaging (3DII) considering the human eye's performance, which could provide a fine viewing effect without flipping or information missing. TVS required by different applications is achieved through an innovative method, attaching the reserved blank to the elemental images. The viewing comfort improvement resulting from TVS is verified by practical experiments, which indicates that it would be promising for future applications of 3DII.

Frequency domain depth filtering of integral imaging

A novel technique for depth filtering of integral imaging is proposed. Integral imaging captures spatio-angular distribution of the light rays which delivers three-dimensional information of the object scene. The proposed method performs filtering operation in the frequency domain of the captured spatio-angular light ray distribution, achieving depth selective reconstruction. Grating projection further enhances the depth discrimination performance. The principle is verified experimentally.

3D/2D convertible projection-type integral imaging using concave half mirror array

We propose a new method for implementing 3D/2D convertible feature in the projection-type integral imaging by using concave half mirror array. The concave half mirror array has the partially reflective characteristic to the incident light. And the reflected term is modulated by the concave mirror array structure, while the transmitted term is unaffected. With such unique characteristic, 3D/2D conversion or even the simultaneous display of 3D and 2D images is also possible. The prototype was fabricated by the aluminum coating and the polydimethylsiloxane molding process. We could experimentally verify the 3D/2D conversion and the display of 3D image on 2D background with the fabricated prototype.

Recent progress in three-dimensional information processing based on integral imaging

Recently developed integral imaging techniques are reviewed. Integral imaging captures and reproduces the light rays from the object space, enabling the acquisition and the display of the three-dimensional information of the object in an efficient way. Continuous effort on integral imaging has been improving the performance of the capture and display process in various aspects, including distortion, resolution, viewing angle, and depth range. Digital data processing of the captured light rays can now visualize the three-dimensional structure of the object with a high degree of freedom and enhanced quality. This recent progress is of high interest for both industrial applications and academic research.