Design, implementation and characterization of a quantum-dot-based volumetric display

Ultrafast Response Organic Photoswitch Materials and Their Application in Volumetric 3D Display

Volumetric three-dimensional (3D) display technology based on static screens is a crucial branch of 3D displays. The essential component in volumetric 3D displays is selectively excitable display media that can generate voxels at any position. Here, we synthesized a series of organic photoswitch materials to meet the specific requirements of 3D display mediums. In these photoswitch solutions, voxels are activated ultrafast within tens of picoseconds at the intersection of two control lasers and faded rapidly within tens of milliseconds when switching light is turned off. An experimental volumetric 3D display system utilizing an organic photoswitch solution as a screen is demonstrated. The system not only achieves a dynamic 3D display but also enables 360° viewing. The volumetric 3D display system can display true 3D images without auxiliary glasses and is expected to be applicable in fields as diverse as virtual reality, medical imaging, architectural design, and military visualization.

Projection of multiple directional images on a volume structure with refractive surfaces

We present a new refraction-based approach to embed multiple images into a single volume structure rendered on a glass solid (3D crystal). Each of the images can only be revealed when looked at from the certain viewpoint. While configurations of viewing directions in conventional methods are limited, our method can compensate for refractive effects at glass surfaces regardless of the viewing directions and enable the viewing directions to be set more flexibly, even allowing for 180 ^∘ opposite projection by leveraging refraction. These unique features are verified with prototyping of 3D crystals projecting multiple grey-scale images and numerical assessments. In addition, we present a color dynamic representation of our method with computer graphics to demonstrate the potential use of our method as a novel information service system.

Improvement of an algorithm for displaying multiple images in one space

Volumetric displays are attracting attention in fields such as media art and digital signage. In previous research, we developed a method to display multiple images in the same space using a volumetric display. However, because of the nature of the algorithm, the images could not be displayed when they contained a pure black image (in which all the pixel values are "0"). In the current study, we present a revised algorithm that can display such images. Therefore, a wider range of images can be displayed in the same space. Image quality evaluation using structural similarity shows that the proposed algorithm yields images that are superior or equivalent to those of the previous algorithm.

Binocular holographic three-dimensional display using a single spatial light modulator and a grating

In this paper, a binocular holographic three-dimensional (3D) display system combining a single spatial light modulator (SLM) and a grating is proposed and implemented. A synthetic phase-only hologram of the left and right 3D perspective images of an object is calculated by the layer-based Fresnel diffraction method according to the depth information, and uploaded onto the SLM for holographic 3D reconstruction with correct depth cues. The grating is designed and fabricated to guide the reconstructed left and right 3D perspective images to the corresponding eyes. Optical experiments demonstrate that the proposed system can successfully present binocular holographic 3D images with both the accommodation effect and binocular parallax, which enables observation free of the accommodation-vergence conflict and visual fatigue problem.

Three-dimensionally structured voxels for volumetric display

A three-dimensional (3D) volumetric display has been the goal of the display research field for many years. However, volumetric displays capable of rendering multicolor and updatable graphics that users can view with the naked eye are still a challenge. Here, we show a new volumetric display using three-dimensionally structured fluorescent voxels. The fluorescent voxels were generated by two-photon excitation with a femtosecond laser. To realize colorization, volumetric graphics were spatially rendered on a fluorescent screen in which structured voxels having different luminescent colors were arranged in each layer. The color of the fluorescent voxels was changed by a holographic color switching method using computer-generated holograms displayed on a liquid-crystal spatial light modulator. Because this display employed RGB fluorescent voxels that are accessed optically, it has a number of advantages, such as being observable with the naked eye, and being capable of multicolor rendering and refreshable graphics. This technology will open up a wide range of applications in 3D displays, augmented reality, and computer graphics.

Interactive Holographic Display Based on Finger Gestures

In this paper, we demonstrate an interactive, finger-sensitive system which enables an observer to intuitively handle electro-holographic images in real time. In this system, a motion sensor detects finger gestures (swiping and pinching) and translates them into the rotation and enlargement/reduction of the holographic image, respectively. By parallelising the hologram calculation using a graphics processing unit, we realised the interactive handling of the holographic image in real time. In a demonstration of the system, we used a Leap Motion sensor and a phase modulation-type spatial light modulator with 1,920 × 1,080 pixels and a pixel pitch of 8.0 µm × 8.0 µm. The constructed interactive finger-sensitive system was able to rotate a holographic image composed of 4,096 point light sources using a swiping gesture and enlarge or reduce it using a pinching gesture in real time. The average calculation speed was 27.6 ms per hologram. Finally, we extended the constructed system to a full-colour reconstruction system that generates a more realistic three-dimensional image. The extended system successfully allowed the handling of a full-colour holographic image composed of 1,709 point light sources with a calculation speed of 22.6 ms per hologram.

Efficient method for fabricating a directional volumetric display using strings displaying multiple images

In this study, we describe the fabrication of a high-resolution directional volumetric display that can display multiple images in different directions. The display designs can be used to show animations using strings; however, improving the resolution of such displays is difficult. Previously, the arrangement of strings has only been determined experimentally, making fabrication of volumetric displays a challenge. The goal of the present study is to improve resolution using simulations and to determine the arrangement of strings under three constraints. This simplified the fabrication of a directional volumetric display with 345 strings, which can display two different 20×20  pixel images in two different directions. A large high-resolution directional volumetric display can be fabricated using the proposed method. The string-type display has high artistic potential and is expected to find applications in the amusement and entertainment fields.

Hybrid remote quantum dot/powder phosphor designs for display backlights

Quantum dots are ideally suited for color conversion in light emitting diodes owing to their spectral tunability, high conversion efficiency and narrow emission bands. These properties are particularly important for display backlights; the highly saturated colors generated by quantum dots justify their higher production cost. Here, we demonstrate the benefits of a hybrid remote phosphor approach that combines a green-emitting europium-doped phosphor with red-emitting CdSe/CdS core/shell quantum dots. Different stacking geometries, including mixed and separate layers of both materials, are studied at the macroscopic and microscopic levels to identify the configuration that achieves maximum device efficiency while minimizing material usage. The influence of reabsorption, optical outcoupling and refractive index-matching between the layers is evaluated in detail with respect to device efficiency and cost. From the findings of this study, general guidelines are derived to optimize both the cost and efficiency of CdSe/CdS and other (potentially cadmium-free) quantum dot systems. When reabsorption of the green and/or red emission is significant compared to the absorption strength for the blue emission of the pumping light emitting diode, the hybrid remote phosphor approach becomes beneficial.

Inkjet printing-based volumetric display projecting multiple full-colour 2D patterns

In this study, a method to construct a full-colour volumetric display is presented using a commercially available inkjet printer. Photoreactive luminescence materials are minutely and automatically printed as the volume elements, and volumetric displays are constructed with high resolution using easy-to-fabricate means that exploit inkjet printing technologies. The results experimentally demonstrate the first prototype of an inkjet printing-based volumetric display composed of multiple layers of transparent films that yield a full-colour three-dimensional (3D) image. Moreover, we propose a design algorithm with 3D structures that provide multiple different 2D full-colour patterns when viewed from different directions and experimentally demonstrate prototypes. It is considered that these types of 3D volumetric structures and their fabrication methods based on widely deployed existing printing technologies can be utilised as novel information display devices and systems, including digital signage, media art, entertainment and security.

Optical Addressing of Multi-Colour Photochromic Material Mixture for Volumetric Display

This is the first study to demonstrate that colour transformations in the volume of a photochromic material (PM) are induced at the intersections of two control light channels, one controlling PM colouration and the other controlling decolouration. Thus, PM colouration is induced by position selectivity, and therefore, a dynamic volumetric display may be realised using these two control lights. Moreover, a mixture of multiple PM types with different absorption properties exhibits different colours depending on the control light spectrum. Particularly, the spectrum management of the control light allows colour-selective colouration besides position selectivity. Therefore, a PM-based, full-colour volumetric display is realised. We experimentally construct a mixture of two PM types and validate the operating principles of such a volumetric display system. Our system is constructed simply by mixing multiple PM types; therefore, the display hardware structure is extremely simple, and the minimum size of a volume element can be as small as the size of a molecule. Volumetric displays can provide natural three-dimensional (3D) perception; therefore, the potential uses of our system include high-definition 3D visualisation for medical applications, architectural design, human–computer interactions, advertising, and entertainment.

Study of Perovskite QD Down-Converted LEDs and Six-Color White LEDs for Future Displays with Excellent Color Performance

A narrow-emitting red, green, and blue (RGB) perovskite quantum dot (PeQD)-based tricolored display system can widen the color gamut over the National Television System Committee (NTSC) to 120%, but this value is misleading with regard to the color perception of cyan and yellow reproduced in the narrow RGB spectra. We propose that a PeQD-based six-color display system can reproduce true-to-life spectral distributions with high fidelity, widen the color gamut, and close the cyan and yellow gap in the RGB tricolored display by adding cyan (Cy), yellowish green (Yg), and orange colors (Or). In this study, we demonstrated pure-colored CsPbX3 (X = Cl, Br, I, or their halide mixtures; Cl/Br and Br/I) PeQD-based monochromatic down-converted light-emitting diodes (DC-LED) for the first time, and we incorporated PeQDs with UV-curable binders and long-wavelength-pass-dichroic filters (LPDFs). CsPbX3 PeQD-based pure Cy-, G-, Yg-, Or-, R-emitting monochromatic DC-LED provide luminous efficacy (LE) values of 81, 184, 79, 80, and 35 lm/W, respectively, at 20 mA. We also confirmed the suitability and the possibility of access to future color-by-blue backlights for field-sequential-color liquid crystal displays, using six-color multipackage white LEDs, as well as future six-colored light-emitting devices with high vision and color performance. The fabricated six-color multipackage white LEDs exhibited an appropriate LE (62 lm/W at total 120 mA), excellent color qualities (color rendering index (CRI) = 96, special CRI for red (R9) = 97) at a correlated color temperature (CCT) of 6500 K, and a wide color gamut covering the NTSC up to 145% in the 1931 Commission International de l'Eclairage (CIE) color coordinates space.

Image quality improvement for a 3D structure exhibiting multiple 2D patterns and its implementation

A three-dimensional (3D) structure designed by our proposed algorithm can simultaneously exhibit multiple two-dimensional patterns. The 3D structure provides multiple patterns having directional characteristics by distributing the effects of the artefacts. In this study, we proposed an iterative algorithm to improve the image quality of the exhibited patterns and have verified the effectiveness of the proposed algorithm using numerical simulations. Moreover, we fabricated different 3D glass structures (an octagonal prism, a cube and a sphere) using the proposed algorithm. All 3D structures exhibit four patterns, and different patterns can be observed depending on the viewing direction.

Aerial projection of three-dimensional motion pictures by electro-holography and parabolic mirrors

We demonstrate an aerial projection system for reconstructing 3D motion pictures based on holography. The system consists of an optical source, a spatial light modulator corresponding to a display and two parabolic mirrors. The spatial light modulator displays holograms calculated by computer and can reconstruct holographic motion pictures near the surface of the modulator. The two parabolic mirrors can project floating 3D images of the motion pictures formed by the spatial light modulator without mechanical scanning or rotating. In this demonstration, we used a phase-modulation-type spatial light modulator. The number of pixels and the pixel pitch of the modulator were 1,080 × 1,920 and 8.0 μm × 8.0 μm, respectively. The diameter, the height and the focal length of each parabolic mirror were 288 mm, 55 mm and 100 mm, respectively. We succeeded in aerially projecting 3D motion pictures of size ~2.5 mm³ by this system constructed by the modulator and mirrors. In addition, by applying a fast computational algorithm for holograms, we achieved hologram calculations at ~12 ms per hologram with 4 CPU cores.

Implementation of active-type Lamina 3D display system

Lamina 3D display is a new type of multi-layer 3D display, which utilizes the polarization state as a new dimension of depth information. Lamina 3D display system has advanced properties - to reduce the data amount representing 3D image, to be easily made using the conventional projectors, and to have a potential being applied to the many applications. However, the system might have some limitations in depth range and viewing angle due to the properties of the expressive volume components. In this paper, we propose the volume using the layers of switchable diffusers to implement the active-type Lamina 3D display system. Because the diffusing rate of the layers has no relation with the polarization state, the polarizer wheel is applied to the proposed system in purpose of making the sectioned image synchronized with the diffusing layer at the designated location. The imaging volume of the proposed system consists of five layers of polymer dispersed liquid crystal and the total size of the implemented volume is 24x18x12 mm³(3). The proposed system can achieve the improvements of viewing qualities such as enhanced depth expression and widened viewing angle.