Two-dimensional and three-dimensional transparent screens based on lens-array holographic optical elements

Locally controllable 2D/3D mixed display and image generation method

In this paper, a locally controllable two-dimensional (2D)/ three-dimensional (3D) mixed display system and corresponding image generation method are proposed. The proposed system is mainly composed of a collimating backlight module (CBM) and a light control module (LCM). The CBM provides collimating polarized light. The LCM modulates a part of the collimating polarized light to form point light sources for 3D display and the other part to form scattered light sources for 2D display. The 2D and 3D display states can be locally controlled by using a pixelated mask loaded on a polarization switching layer. In addition, a corresponding image generation method is proposed. According to observer's demand, the parallax image is divided into target image area and residual image area by using deep learning matting algorithm, and a 2D/3D mixed light field image with full parallax 3D target image and high-resolution 2D residual image is generated. We developed a prototype based on the proposed locally controllable 2D/3D mixed display structure and generated two sets of 2D/3D mixed light field image with different target objects and residual objects from the same parallax images. The experimental results demonstrated the effectiveness of our proposed system and the corresponding image generation method. High-resolution 2D image and full parallax 3D image were displayed and locally switched in the experimental system.

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.

Electrochemical Strategy for High-Resolution Nanostructures in Laser-Heat-Mode Resist Toward Next Generation Diffractive Optical Elements

For achieving high-resolution nanostructures for next-generation diffractive optical elements (DOEs) using an environmentally friendly process, an electrochemical development strategy is proposed and developed using AgInSbTe-based laser heat-mode resist (AIST-LHR). Based on the electrical resistivity difference of amorphous and crystalline phases for this resist, an etching selectivity ratio of ≈30:1 (i.e., the etch ratio between the amorphous and crystalline ones) is achieved through the oxidation of Fe³⁺ ions with the assisted pitting activation etching using Cl^- ions in an acid medium. Nanostructures with a minimum feature size down to 41 nm are successfully generated, including grating patterns, meta-surface optical structures, gears, and English characters. Using a post-plasma etching process, the nanostructures are successfully transferred from the AIST-HLR onto silica substrate, and X-ray grating patterns with a line space of 80 nm are created as a demonstration for its potential applications in DOEs.

Three-dimensional see-through augmented-reality display system using a holographic micromirror array

It is difficult to find the micromirror array with desired specifications for augmented-reality displays, and the custom fabricating methods are complicated and unstable. We propose a novel, to our knowledge, three-dimensional see-through augmented-reality display system using the holographic micromirror array. Unlike the conventional holographic waveguide-type augmented-reality displays, the proposed system utilizes the holographic micromirror array as an in-coupler, without any additional elements. The holographic micromirror array is fabricated through the simple, effective, and stable method of applying the total internal reflection-based hologram recording using a dual-prism. The optical mirror and microlens array are set as references, and the specifications can be customized. It reconstructs a three-dimensional image from a displayed elemental image set without using any additional device, and the user can observe a three-dimensional virtual image while viewing the real-world objects. Thus, the principal advantages of the existing holographic waveguide-type augmented-reality system are retained. An optical experiment confirmed that the proposed system displays three-dimensional images exploiting the augmented-reality system simply and effectively.

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.

2D/3D mixed display based on integral imaging and a switchable diffuser element

In this paper, we present a 2D/3D mixed system with high image quality based on integral imaging and a switchable diffuser element. The proposed system comprises a liquid crystal display screen, lens array, switchable diffuser element and projector. The switchable diffuser element can be controlled to present 2D/3D mixed images or 2D and 3D images independently, and can reduce the Moire fringe and black grid. In addition to the improved display quality, the proposed system has advantages of a simple structure and is low cost, which contribute to the portability and practicability.

High-resolution augmented reality 3D display with use of a lenticular lens array holographic optical element

An augmented reality (AR) three-dimensional (3D) display based on one-dimensional integral imaging (1DII), by using a lenticular lens array holographic optical element (LLA-HOE), is proposed. The 3D image of the 1DII has higher vertical resolution compared with the image of conventional integral imaging whose resolution is sharply reduced for providing quasi-continuous viewpoints in both the horizontal and vertical directions. The proposed 3D display consists of a projector and an LLA-HOE and is compact. As an image combiner, the LLA-HOE can diffract Bragg-matched light rays that have the same wavelength and incident angle as the original reference wave; it can also function as a lenticular lens array to reconstruct a 3D image but transmit other light rays emitted from the surroundings. In the experiment, an LLA-HOE of 80  mm×80  mm size is recorded, and a combination of a high-resolution 3D virtual image and a real 3D object is presented by the proposed AR 3D display.

Integral imaging-based 2D/3D convertible display system by using holographic optical element and polymer dispersed liquid crystal

An integral imaging-based 2D/3D convertible display system is proposed by using a lens-array holographic optical element (LAHOE), a polymer dispersed liquid crystal (PDLC) film, and a projector. The LAHOE is closely attached to the PDLC film to constitute a projection screen. The LAHOE is used to realize integral imaging 3D display. When the PDLC film with an applied voltage is in the transparent state, the projector projects a Bragg matched 3D image, and the display system works in 3D mode. When the PDLC film without an applied voltage is in the scattering state, the projector projects a 2D image, and the display system works in 2D mode. A prototype of the integral imaging-based 2D/3D convertible display is developed, and it provides 2D/3D convertible images properly.

Digitally designed holographic optical element for light field displays

Concave micro-mirror arrays fabricated as holographic optical elements are used in projector-based light field displays due to their see-through characteristics. The optical axes of each micro-mirror in the array are usually made parallel to each other, which simplifies the fabrication, integral image rendering, and calibration process. However, this demands that the beam from the projector be collimated and made parallel to the optical axis of each elemental micro-mirror. This requires additional collimation optics, which puts serious limitations on the size of the display. In this Letter, we propose a solution to the above issue by introducing a new method to fabricate holographic concave micro-mirror array sheets and explain how they work in detail. 3D light field reconstructions of the size 20  cm×10  cm and 6 cm in depth are achieved using a conventional projector without any collimation optics.

Rapid calibration of a projection-type holographic light-field display using hierarchically upconverted binary sinusoidal patterns

A projection-type holographic light-field (LF) display is a full-parallax, full-color, and glass-free three-dimensional (3D) display with a holographic optical element and a projector. The display has unique characteristics, including transparency; however, a rapid calibration method has not yet been established. In this paper, we propose a rapid calibration method for a holographic LF display without sacrificing its accuracy. The proposed method performs calibration via the projection of binary sinusoidal patterns whose frequencies are iteratively and hierarchically upconverted. Compared to the conventional method, in the proposed method, the required number of projections is reduced from linear to logarithmic with the projector's resolution. We confirm the successful reconstruction of the 3D image using the proposed method.

Design, fabrication and characterization of transparent retro-reflective screen

A transparent retro-reflective screen, which can be used as head-up-display (HUD) or a see-through screen for head mounted projection displays (HMPD) is proposed. The high optical gain of screen enables the use of low power projectors to produce very bright content. The screen assembly is based on retro-reflective microspheres, patterned on an optically clear substrate using steel stencil as a shadow mask. The incident light is retro-reflected as a narrow angular cone to create an eyebox for the viewer. The optical gain and transparency of screen is varied by changing the fill factor of the mask. The optical design and fabrication of the screen is presented. The retro-reflective and transmission characteristics of screen are evaluated. The impact of fill factor on screen luminance and transparency is studied. The screen provides high luminance (up to 280cd/m² with 50% transparency) from about 40cm to >3m when used with a low power (15 lumen) mobile projector. Unlike regular diffusers, luminance remains nearly constant with projection distance. Furthermore, the screen offers prominent see-through capability with small degradation in modulation transfer function for transmitted light. For a particular camera and imaging configuration, MTF10 (10% cutoff) for 50% transparent screen is reduced from 37 cyc/deg to 30 cyc/deg when screen is inserted at an intermediate distance.

Volume holographic printing using unconventional angular multiplexing for three-dimensional display

We propose and demonstrate a volume holographic printing method for dynamic three-dimensional (3D) display with an expanded space-bandwidth product (SBP) using unconventional angular multiplexing techniques. By wavefront encoding of the 3D scene, with the help of computer-generated holography, the object beam is loaded onto a 2D phase spatial light modulator (SLM) with a limited SBP. The printing method then writes a single hologram through the interference of the object beam with a reference beam as a holographic element (hogel) in the volume holographic polymer. In addition, multiple 3D scenes can be recorded and dynamically reconstructed by angular multiplexing in the same hogel location. The SBP can be increased by two orders of magnitude compared to the conventional holographic printing method, showing the potential to realize a dynamic and high-resolution 3D display.

See-through multi-projection three-dimensional display using transparent anisotropic diffuser

We propose a see-through multi-projection three-dimensional (3D) display using a transparent anisotropic diffuser. By immersing a metal-coated anisotropic diffuser into index matching oil which has the same refractive index of anisotropic diffuser, a transparent anisotropic diffuser is implemented. The reflectance of the transparent anisotropic diffuser is analyzed with the transfer matrix. Two multi-projection methods are proposed based on reflection type integral imaging and multi-view method. Especially, the reflection type multi-view-based system is realized with a curved anisotropic diffuser. High resolution see-through 3D display can be realized with the proposed methods. They can be used in various applications with the two multi-projection methods. In order to show the augmented reality features, real objects and virtual 3D images are presented at the same time in the experimental setup.

Holographic display for see-through augmented reality using mirror-lens holographic optical element

A holographic display system for realizing a three-dimensional optical see-through augmented reality (AR) is proposed. A multi-functional holographic optical element (HOE), which simultaneously performs the optical functions of a mirror and a lens, is adopted in the system. In the proposed method, a mirror that is used to guide the light source into a reflection type spatial light modulator (SLM) and a lens that functions as Fourier transforming optics are recorded on a single holographic recording material by utilizing an angular multiplexing technique of volume hologram. The HOE is transparent and performs the optical functions just for Bragg matched condition. Therefore, the real-world scenes that are usually distorted by a Fourier lens or an SLM in the conventional holographic display can be observed without visual disturbance by using the proposed mirror-lens HOE (MLHOE). Furthermore, to achieve an optimized optical recording condition of the MLHOE, the optical characteristics of the holographic material are measured. The proposed holographic AR display system is verified experimentally.

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.

Viewing angle enhancement of an integral imaging display using Bragg mismatched reconstruction of holographic optical elements

Holographic-optical-element (HOE)-based integral imaging display can be applied to augmented reality. However, a narrow viewing angle is a bottleneck for commercialization. Here, we propose a method to enhance the viewing angle of the integral imaging display using Bragg mismatched reconstruction of HOEs. The viewing angle of the integral imaging display can be enlarged with two probe waves, which form two different viewing zones. The effect of Bragg mismatched reconstruction is analyzed with simulation and experiment. In order to show feasibility of the proposed method, a display experiment is demonstrated.

A transparent projection screen based on plasmonic Ag nanocubes

A transparent and colourless projection screen is fabricated by depositing a silver nanocube sub-monolayer on a titania thin film. Backward scattering of the silver nanocubes is enhanced by titania in the blue and red regions, to which human eyes are less sensitive. As a result, this screen, which is cost-effective even for large areas, allows projection of full colour images.

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.

Flat-panel see-through three-dimensional display based on integral imaging

This study proposes a technique to construct a flat-panel see-through three-dimensional (3D) display based on integral imaging. This display consists of multiple lens arrays, a transparent flat-panel display, and a light-blocking wall (LBW). Rays behind the display are reconstructed in front of it by combination of the lens arrays and the LBW to provide the see-through function. The combination of one of the lens arrays and the transparent flat-panel display produces full-parallax 3D images, which are superimposed on background images. The experimental system is constructed to verify the proposed technique. The see-through and superposition capabilities of the experimental system are demonstrated.

Reflection-type integral imaging system using a diffuser holographic optical element

A reflection-type integral imaging (InIm) system using a diffuser holographic optical element (DHOE) is proposed for improving the fill factor of displayed three-dimensional images. The DHOE performs an optical function similar to that for a conventional diffuser only for Bragg matched light, while Bragg mismatched light passes through the DHOE. Elemental images projected under Bragg matching condition are scattered by the DHOE. Meanwhile, light reflected by a concave mirror-array becomes Bragg mismatched light, and is integrated into three-dimensional images without the fill factor problem. The optical characteristics of the DHOE are examined by measuring diffraction efficiencies, and the feasibility of the fill-factor-improved InIm is verified by a concave mirror-array and DHOE.

See-through integral imaging display using a resolution and fill factor-enhanced lens-array holographic optical element

We report on the development of a high-resolution see-through integral imaging system with a resolution and fill factor-enhanced lens-array holographic optical element (HOE). We propose a procedure for fabricating of a lens pitch controllable lens-array HOE. By controlling the recording plane and performing repetitive recordings process, the lens pitch of the lens-array HOE could be substantially reduced, with a high fill factor and the same numerical aperture compared to the reference lens-array. We demonstrated the feasibility by fabricating a lens-array HOE with a 500 micrometer pitch. Since the pixel pitch of the projected image can be easily controlled in projection type integral imaging, the small lens pitch enhances the quality of the displayed 3D image very effectively. The enhancement of visibility of the 3D images is verified in experimental results.