A plastic holographic waveguide combiner for light‐weight and highly‐transparent augmented reality glasses

There is a high demand for light‐weight, stylishly designed augmented reality (AR) glasses with natural see‐through capabilities for the wide‐spread distribution of novel wearable device to general consumers. We have successfully developed a unique production process of a holographic waveguide combiner that enables us to laminate holographic optical elements (HOEs) onto a plastic substrate with optical grade quality. The plastic substrate waveguide combiner has a number of advantages over conventional glass substrate combiners; the plastic substrate makes AR glasses lighter in weight and unbreakable. With the lamination process of HOEs, we can apply them to a various designs to satisfy general customers' wide range of preferences for the style. We also potentially made it possible for the holographic waveguide combiner to be produced in larger volumes at lower costs by using our novel roll‐to‐roll hologram recording and laminating process. In this paper, we present our approach of the plastic substrate HOE production process for AR glasses.     

Color holographic system without undesirable light based on area sampling of digital lens

In this paper, we demonstrate a color holographic system without undesirable light based on area sampling of a digital lens. This system, which improves the quality of the reconstructed color image, is fundamentally realized by using three spatial light modulators and a rectangle aperture. By altering the sampling area of the digital lens on the spatial light modulator panels, we can control the offset position of the reconstructed image. Thus, the zero‐order diffraction light as the undesirable light and the reconstructed images are separated, and the chromatic aberration can be corrected. In addition, a rectangle aperture is used to eliminate the zero‐order diffraction light. The final reconstructed image with improved quality can be observed, which verifies the effectiveness of our proposed system.     

Compact and lightweight optical see-through holographic near-eye display based on holographic lens

Optical see-through holographic near-eye display (NED) is one of the most promising augmented reality (AR) technologies for commercialization in the future. However, the conventional optical elements used in holographic NED make the optical display huge and heavy. In this paper, an optical see-through holographic NED with a compact and lightweight structure is proposed, in which the traditional optical elements are replaced by reflection-type holographic lenses (HLs). The HLs are thin and lightweight compared with the conventional optical lenses. We fabricate the HLs according to the reflection volume holographic grating theory. The HLs have high transmittance at Bragg-mismatched beam and high diffraction efficiency at Bragg-matched beam. In addition, we analyze the reason for the distortion of the holographic image caused by the HL and perform the distortion pre-compensation. In the experiment, an HL-based optical see-through holographic NED is developed, which is compact and lightweight. It can present clear holographic images at different focus depths without the vergence-accommodation conflict.     

Laser‐addressed full‐color photo‐quality rewritable sheets based on thermochromic systems with leuco dyes

We have developed a laser‐addressed full‐color photographic quality rewritable sheet. The sheet was composed of a vertically stacked Cyan/Magenta/Yellow‐thermochromic system with a mixture of leuco dyes, developers and photothermal conversion agents in a polymer matrix. The sheet was simply manufactured by roll‐to‐roll (R2R) processes. Writing and erasing were performed by scan of near‐infrared laser light. It achieved full‐color photographic quality images with a wide color gamut with 70% coverage of the Specifications for Web Offset Publications (SWOP) standards and a high resolution of 426 ppi. Clear rewritability has also been confirmed. Non‐contact laser writing has other advantages in that it can create an image under a protection film, and it has form factor flexibility. We have developed a reliability model for high‐temperature storage and a light fastness test. This model showed a good agreement with experimental data, and the lifetime of an image was estimated to be over 8 years under ambient conditions. This technology will create applications for on‐demand rewritable image design while saving power and reducing the use of paper, which will eventually contribute to a sustainable society.     

Numerical investigation of zoomable holographic projection without a zoom lens

Holographic projection is for laser displays and has the merits of being aberration free, producing high‐contrast images, having the ability of color reconstruction with one spatial light modulator, and so on. In this paper, we propose a zoomable holographic projection without using a zoom lens and verify the proposed method by using numerical simulation. Although such a system can be readily realized to use the features of holography, which is capable of recording a large image exceeding the hologram size, the required calculation is very time consuming. For acceleration, we used shifted Fresnel diffraction for setting different sampling rates on a hologram and projected image. The proposed method can project any zoom‐in and zoom‐out image between zeroth‐order and first‐order lights, and the processing time and required memory for the zoom are constant.     

A framework for holographic scene representation and image synthesis

We present a framework for the holographic representation and display of graphics objects. As opposed to traditional graphics representations, our approach reconstructs the light wave reflected or emitted by the original object directly from the underlying digital hologram. Our novel holographic graphics pipeline consists of several stages including the digital recording of a full-parallax hologram, the reconstruction and propagation of its wavefront, and rendering of the final image onto conventional, framebuffer-based displays. The required view-dependent depth image is computed from the phase information inherently represented in the complex-valued wavefront. Our model also comprises a correct physical modeling of the camera taking into account optical elements, such as lens and aperture. It thus allows for a variety of effects including depth of field, diffraction, interference, and features built-in anti-aliasing. A central feature of our framework is its seamless integration into conventional rendering and display technology which enables us to elegantly combine traditional 3D object or scene representations with holograms. The presented work includes the theoretical foundations and allows for high quality rendering of objects consisting of large numbers of elementary waves while keeping the hologram at a reasonable size     

Eye‐safety analysis of phase‐only holographic projection systems

Abstract— Recently, laser‐safety analyses have been presented for scanned‐beam and LCOS imaging projectors. A third class of projection technology, based on the properties of phase‐only diffraction, is differentiated from scanned‐beam and LCOS counterparts in its ability to provide a significantly higher effective luminous flux for video style images. In this paper, this desirable property is recognized by the definition of the “video lumen” and a detailed design fora hypothetical holographic projector and corresponding laser safety analysis is presented. As in the case of conventional amplitude‐modulating LCOS projectors, a holographic projector is capable of delivering several hundred white lumens in Class 2; an appropriately specified holographic projector can also provide several tens of video lumens while maintaining a Class 1 classification.     

Direct imaging exposure equipment with high overlay accuracy for flexible substrate in roll‐to‐roll method

In order to fabricate thin‐film transistors on a flexible substrate, it is required to overlay patterns with high alignment accuracy. A polymer film can be deformed greatly and easily through thin‐film transistor fabrication processes because the glass transition point of a polymer film is below the maximum temperature of the processes. Furthermore, low stiffness of a polymer film can cause deformation when the polymer film is loaded on a working holder. These matters make it difficult to make patterns directly on a polymer film with high alignment accuracy. We proposed three concepts that solve three technical issues in order to directly make patterns with high overlay accuracy on a flexible film without a support substrate. We developed roll‐to‐roll exposure equipment with high overlay accuracy for a flexible substrate. Using this equipment, we succeeded to directly make patterns on a PET film, achieving a resolution of less than 6‐μm line and space pattern and an overlay accuracy of less than ±5 μm.     

Switchable helical holographic structures

Abstract— A 3‐D array of helical structures fabricated using holographic polymer‐dispersed liquid crystals (H‐PDLC) is presented. Multiple coherent beams are interfered to create a constructive helical pattern which is permanently captured using the standard H‐PDLC method. Films with such array of helical structures have both diffractive and circular polarization sensitive reflective properties. Iso‐intensity patterns, design parameters, fabrication process, optical/electro‐optical performance of these periodic helical structures are discussed along with their potential application for advanced electro‐optical devices.     

Color holographic magnification system based on spatial light modulators

In this paper, we propose a color holographic magnification system based on spatial light modulators. Three spatial light modulators are used to set up the system in our experiment by using space‐division method. With the similarity principle of Fourier transform, the size of the reconstructed images can be magnified. By setting the green reconstructed image as standard and readjusting the sizes of the red and blue reconstructed images, the color images can be magnified to four times without chromatic aberration, which is verified by the experiment.     

Dual-view holographic AR display based on Bragg mismatched reconstruction of the holographic optical element

A method for dual-view holographic display based on Bragg mismatched reconstruction of holographic optical element (HOE) is proposed. Under the Bragg mismatched condition, the reconstructed images are guided into two separated viewing zones to realize dual-view holographic display. Meanwhile, the viewing angle of each perspective is increased to 11.2°, which is almost 2.5 times as large as the traditional holographic display system. The design process of HOE is simple only by interference of plane reference wave and converging spherical signal wave, which has high practicability. Furthermore, the HOE can mix the virtual 3D image with real-world scenes, which could implement augmented reality (AR) display. Experiments validate that the proposed system can achieve dual-view holographic AR three-dimensional (3D) display with accommodation effect.     

A method of holographic magnification based on Fresnel diffraction

In this paper, we propose a method of holographic magnification based on Fresnel diffraction. Similarity principle of Fourier transform is used in convolution algorithm in order to adjust the size of the reconstructed image. With the splicing technology based on a spatial light modulator, the reconstructed images can be magnified. By combining the similarity principle of Fourier transform with the splicing technology, the reconstructed images can be further magnified to eight times, which is verified by the experiments.     

新型全息光栅指纹传感器的研究

基于大量实验和全息光栅技术,提出一种新型的指纹传感器。该传感器主要由单色光源、全息光栅、透镜和CCD组成,其中,关键的器件——全息光栅应用激光全息技术制作而成。该传感器很好地解决了传统光学全反射指纹传感器和全息棱镜指纹传感器所存在的问题,能获得高清晰、无畸变、无失真的指纹像,可以很清楚地观察到指纹脊上腺孔,并给出了一个具体的实例。     

Method to suppress speckle noise using time multiplexing in phase‐only holographic display

In holographic display, the reconstructed image suffers from speckle noise severely. In this paper, we propose a method to suppress speckle noise using time multiplexing in phase‐only holographic display. Adjacent pixels of the recorded object are separated into object point groups firstly. Particularly, the pixel interval of each object point group is larger compared with the conventional pixel separation method. And then, sub‐computer–generated holograms (sub‐CGHs) are calculated by the modified Gerchberg–Saxton (GS) algorithm with different initial random phases. Finally, the final integrated image is reconstructed with low speckle noise using time multiplexing technique. Both numerical and optical experimental results are presented to demonstrate the effectiveness and feasibility with our proposed method.     

A high‐efficiency holographic waveguide display system with a prism in‐coupler

Holographic waveguide display system with high efficiency is presented by embedding an in‐coupling prism and an out‐coupling reflective volume holographic element, which enables a small‐type configuration. The improved coupling scheme can achieve 25% efficiency and the chromatic is corrected properly.     

New multiplexing method of holographic data storage system

Data storage related with writing and retrieving requires high storage capacity, fast transfer rate and less access time. Today any data storage system cannot satisfy all of these conditions, however holographic data storage system can perform faster data transfer rate because it is a page oriented memory system using volume hologram in writing and retrieving data. System can be constructed without mechanically actuating part therefore fast data transfer rate and high storage capacity about 1Tb/cm3 can be realized. In this research, to record and retrieve binary data by a new hologram multiplexing in our holographic data storage system, we propose a new multiplexing method that is cyclone multiplexing method. Also, three algorithms were integrated in our holographic data storage system.     

Holographic waveguide display with large field of view based on volume holographic grating

The field of view (FOV) of waveguide display systems based on volume holographic grating (VHG) is primarily constrained by the diffraction response bandwidth, which is currently insufficient to meet the need for AR immersive displays. Through the composite diffraction response bandwidths, red-responsive and green-responsive double-layer VHG structures are proposed to expand the FOV under varied image sources. The influence of several input spectral bandwidths on FOV improvement is also considered, and OLED micro-display and LCOS micro-display are selected as image sources. As a consequence, the horizontal FOV of the red-responsive double-layer VHG waveguide based on the LCOS micro-display is 19.5°, and that of the green-responsive double-layer VHG waveguide based on the OLED micro-display is 33.4°. Through the simulation and experiment, we effectively illustrate the effect of the double-layer VHG and the input spectral bandwidth on the FOV.     

Viewing‐angle enhancement in holographic reflective displays by nanoscale holographic patterning

Abstract— This work presents a method to increase the viewing angle of holographic polymer‐dispersed liquid‐crystal (H‐PDLC) reflective displays. One of the drawbacks to H‐PDLC technology is the existence of a narrow viewing angle. We present a way to alleviate this problem by structuring the phase front of the recording beams to increase the viewing cone of the display. Analysis of the diffractive properties of these holograms shows that the macroscopic and the nanoscale morphologies both play a role in the optical properties of the films.     

Visual perception of noise in a simulated holographic display—A user study

This work explores ways to bypass the fundamental image quality limitations of displays using Computer Generated Holograms (CGHs) and, specifically, the high-frequency noise associated with phase-only holograms. Although there is a wealth of literature on building experimental holographic systems, there are no user studies to assess the performance of a holographic system projecting a dynamic two-dimensional image. In this study, 18 participants blindly compared three groups of images displayed on a conventional monitor. The first group contained the original image, the second the simulated holographic reconstruction of the original image, and the third group had the foveated reconstruction of the original image, based on the pupil position. Holograms in the second group were computed using the Fienup algorithm and the third group using the Fienup with Perceptual Don’t Care Areas (FiPDoC) algorithm, a novel algorithm that uses eye tracking to optimize image quality in CGHs. The aim of the study was to find out if the holographic display, assuming an ideal hardware, can be as good as a conventional display and whether eye tracking can help this goal. Most participants distinguished between the original image and the un-foveated simulated reconstruction. However, the participants could not differentiate between the original image and the foveated reconstruction. Thus, foveation may be essential in designing and building the first commercial holographic displays.     

Flexible,stretchable, transparent and electrically conductive polymer films via a hybrid electrospinning and solution casting process: In-plane anisotropic conductivity for electro-optical applications

A new method is developed for the preparation of a transparent electrically conductive hybrid polymer films which maintain their electrical conductivity when subjected to deformation in two and three dimensions including bending, stretching and twisting. These films are made by a hybrid roll to roll (R2R) process where electrically conductive nanofibers are partially embedded in solution cast dielectric polymer films such as poly(methyl methacrylate) (PMMA), polyimide (PI) or polyurethanes (PU). Nanofibers partially embedded in films can be laser ablated to obtain in-plane anisotropic electrical conductivity created in the form of parallel conductive lines separated by non-conductive spaces on the film surface. The patterned films can be used for high resolution pixel addressable liquid crystal displays. There are several situations, such as wearable sensors, curved displays and advanced flexible OLED lightings, where elastic extensibility and/or permanent deformability are desired without significant loss of electrical conductivity. To satisfy this demand, the multifunctional films can be made elastic, thermally deformable with the judicious choice of materials comprising the nanofibers and the matrix they are embedded in. The multifunctional transparent conductive films are easily manufactured through a low-cost continuous hybrid roll to roll process. Furthermore, they can be used in future displays, solar cells, wearable electronics and skin attached sensors requiring flexibility as well as stretchability and more desirably subsequent recovery after cessation of stress and strains without any loss of electrical conductivity.