Holographic Display Research Articles

Magneto-optical spatial light modulator driven by current-induced domain wall motion for holographic display applications.

We have developed a magneto-optical spatial light modulator (MO-SLM) with a 10 k × 5 k pixel layout and with a pixel pitch horizontally of 1 µm and vertically of 4 µm. An MO-SLM device pixel has a magnetic nanowire made of Gd-Fe magneto-optical material whose magnetization was reversed by current-induced magnetic domain wall motion. We successfully demonstrated the reconstruction of holographic images, showing large viewing zone angles as wide as 30 degrees and visualizing different depths of the objects. These characteristics are unique to holographic images, providing physiological depth cues which may play a vital role in three-dimensional (3D) perception.

Perceived ease of use on visual learning application for mathematics using holography display for the topic on shape and space

Background: A person's life is built on a solid foundation of mathematics. Common causes of learning difficulties in mathematics include abstract ideas, a lack of imagination, and a lack of comprehension of the concepts being studied. Because 3D shapes are abstract concepts, the aim of this study is to better understand how to recognize them in primary school students. Methods: The development of the Mathematics E-Learning Visual application MEL-VIS(MEL-VIS) application involves the design of the Visual Learning Application Iteration-Evolution Development Model, MEL-VIS (PIEMEL-VIS), the MEL-VIS ID Model, and the MEL-VIS Application Module. The development methodology and ID model are built based on the application of various components such as learning theory, a visualization approach, a play-while-learning approach based on scaffolding techniques, as well as interaction and interface based on various touch technologies using tablet computers. The study's contributions are: (i) an iterative-evolutionary development model of the Visual Learning Application, MEL-VIS (PIEMEL-VIS); (ii) a MEL-VIS ID model; (iii) a MEL-VIS application prototype; and (iv) a usability testing instrument for the ease of use of the MEL-VIS application. Results: The usability testing of the MEL-VIS application was carried out through a case study involving 80 students at a primary school in Putrajaya. A task-based, semi-experimental approach was used to assess the ease-of-use construct. Research instruments such as questionnaires and observation checklists are used in this test. The results of the study found that MEL-VIS has a positive impact on students after using the application. Conclusions: Based on the test conducted, primary school students have given positive feedback to the prototype of the E-Visual MEL-VIS application. Thus, it can be concluded that the prototype of the E-Visual MEL-VIS application as a whole is effective, easy to learn and easy to use for student use for primary school mathematics subjects.

Eyebox expansion with accurate hologram generation for wide-angle holographic near-eye display.

Small eyebox in wide-angle holographic near-eye display is a severe limitation for 3D visual immersion of the device. In this paper, an opto-numerical solution for extending the eyebox size in these types of devices is presented. The hardware part of our solution expands the eyebox by inserting a grating of frequency fg within a non-pupil forming display configuration. The grating multiplies eyebox, increasing the possible eye motion. The numerical part of our solution is an algorithm that enables proper coding of wide-angle holographic information for projecting correct object reconstruction at arbitrary eye position within the extended eyebox. The algorithm is developed through the employment of the phase-space representation, which facilitates the analysis of the holographic information and the impact of the diffraction grating in the wide-angle display system. It is shown that accurate encoding of the wavefront information components for the eyebox replicas is possible. In this way, the problem of missing or incorrect views in wide angle near-eye display with multiplied eyeboxes is efficiently solved. Moreover, this study investigates the space-frequency relation between the object and the eyebox and how the hologram information is shared between eyebox replicas. The functionality of our solution is tested experimentally in an augmented reality holographic near-eye display that has maximum field of view of 25.89°. Obtained optical reconstructions demonstrate that correct object view is obtained for arbitrary eye position within extended eyebox.

19‐4: Improving Defocus Blur in Holographic Displays

In this paper we present a novel multiplane computer generated hologram calculation approach that enables artifact free and realistic‐looking defocus blur for optical reconstructions in a holographic display. We introduce a new targeting method and a loss function that evaluates the focused and defocused parts of the reconstructed images. We demonstrate that our method is applicable to various standard hologram generation routines such for both iterative and non‐iterative CGH calculation methods. We also demonstrate our new gradient descent‐based optimization with double phase constraint combined with our targeting scheme and loss function provides the best image quality. We validate our findings for both the numerical reconstructions and optical captures that are acquired from our holographic display prototype.

19‐3: Slim Backlights for Holographic 3D Displays by Advanced Coatings Capabilities

Advanced high precision AR coating stacks are key enabler for backlight units for slim holographic 3D displays. This is achieved by an optical functionalization of these units to ensure the optimized incoupling of coherent “RGB” light under an extremely shallow angle of 87°. In order to provide for a homogenous illumination, the elaborate coating stacks had to be applied with optical precision over an area of 300x200 mm² for a display size of 260x160 mm². This was achieved by advanced inline magnetron sputtering, which enables this technology for even larger display sizes. Results of the optical performance, the technology and hardware will be presented.

Depth-Enhanced Holographic Super Multi-View Maxwellian Display Based on Variable Filter Aperture.

The super multi-view (SMV) near-eye display (NED) effectively provides depth cues for three-dimensional (3D) displays by projecting multiple viewpoint images or parallax images onto the retina simultaneously. Previous SMV NED suffers from a limited depth of field (DOF) due to the fixed image plane. Aperture filtering is widely used to enhance the DOF; however, an invariably sized aperture may have opposite effects on objects with different reconstruction depths. In this paper, a holographic SMV display based on the variable filter aperture is proposed to enhance the DOF. In parallax image acquisition, multiple groups of parallax images, each group recording a part of the 3D scene on a fixed depth range, are captured first. In the hologram calculation, each group of wavefronts at the image recording plane (IRP) is calculated by multiplying the parallax images with the corresponding spherical wave phase. Then, they are propagated to the pupil plane and multiplied by the corresponding aperture filter function. The size of the filter aperture is variable which is determined by the depth of the object. Finally, the complex amplitudes at the pupil plane are back-propagated to the holographic plane and added together to form the DOF-enhanced hologram. Simulation and experimental results verify the proposed method could improve the DOF of holographic SMV display, which will contribute to the application of 3D NED.

Intelligent recognition method of laser image based on big data analysis technology

In order to improve the recognition effect of laser images, this study designed an intelligent recognition method of laser images based on big data analysis technology. On the basis of setting up the laser holographic scanning device and parameters, the laser image is obtained by using the calibration method of vision system. In order to avoid the limitation of coordinate system in the process of laser image recognition, a rational function model with general attributes is constructed. Then, convolutional neural network is used to output the feature data of laser images, and Spark parallel support vector machine algorithm is used to complete the classification of laser images. Finally, the SVM classification model based on the big data analysis technology is constructed. The texture feature data can be input to quickly output the classification results of laser images, and then the intelligent classification and recognition of laser images can be realized according to the probability distribution. Experimental results show that this method can accurately identify the tiny features in laser images, and the recognition results have high peak signal-to-noise ratio and high recognition accuracy.

Fast optimization of computer-generated holograms using conjugate gradient

Holographic display, as an ideal three-dimensional (3D) display method, can provide a realistic stereo-perception sense, and is expected to be used in the next generation of augmented reality (AR) prototypes without complex optical devices. While holographic 3D displays have been proposed in the past decades, high-quality holographic reconstructed images have always relied on well-designed generation algorithms, and it is still a challenge to obtain an accurate phase profile fast. In this work, we utilize a first-order optimization algorithm to optimize the phase profile using the conjugate gradient direction instead of the steepest gradient direction to update the phase parameters. We validate this proposed method by comparing the current widely used stochastic gradient method and the wirtinger holography method. The simulation and experimental results illustrate the superiority of the proposed method, which can achieve faster optimization with the same quality metrics.

Programable structural color generation by phase-change-medium-enabled pixelated hyperbolic metamaterial

Phase-change-medium-enabled hyperbolic metamaterial structures were investigated for generating a wide range of colors by applying external electrical pulses to the embedded graphene-based micro-heater system. The stochastic particle swarm optimization method was implemented to accelerate the design process, followed by the transfer-matrix method to observe the effects of incidence polarization and angle. The results revealed a wide range of colors attainable via the constitutive properties of the designed pixels, which remains insensitive to the incidence polarization, and under a wide range of incidence angle. The investigated programable structure can find potential use in reflective displays and holographic devices for security systems.

Exciting-frequency-adaptive amplitude/phase hybrid holographic inscription in plasmonic polymers.

Plasmonic holography is generally regarded as an effective technology for 3D display that meets the requirements of the human visual system. However, low readout stability and large cross talk in the frequency field during a plasmonic photo-dissolution reaction set a huge obstacle for application of color holography. Herein, we propose a new, to the best of our knowledge, route toward producing exciting frequency sensitive holographic-inscription based on plasmonic nano-Ag adaptive growth. Donor-molecule-doped plasmonic polymers on polyethylene terephthalate substrates exhibit wide spectral response range, accurate optical frequency sensing, and bending durability. The resonant plasmonic particles act as optical antennas and transfer energy to surrounding organic matrices for nanocluster production and non-resonant particle growth. The surface relief hologram is also highly dependent on the excitation frequency, so we successfully obtain a controllable cross-periodic structure with amplitude/phase mixed information, as well as color holographic display. This work provides a bright way to high-density storage, information steganography, and virtual/augmented reality.

Preview the Products on Display at Display Week 2023

Preview the Products on Display at Display Week 2023

Nanofabrication of Bulk Diffraction Nanogratings via Direct Ultrashort-Pulse Laser Micro-Inscription in Elastomers and Heat-Shrinkable Polymers.

Optical-range bulk diffraction nanogratings were fabricated via challenging direct inscription by ultrashort (femtosecond, fs) laser pulses inside heat-shrinkable polymers (thermoplastics) and VHB 4905 elastomer. The inscribed bulk material modifications do not emerge on the polymer surface, being visualized inside the materials by 3D-scanning confocal photoluminescence/Raman microspectroscopy and by the multi-micron penetrating 30-keV electron beam in scanning electron microscopy. The laser-inscribed bulk gratings have multi-micron periods in the pre-stretched material after the second laser inscription step, with their periods continuously reduced down to 350 nm on the third fabrication step, using thermal shrinkage for thermoplastics and elastic properties for elastomers. This three-step process allows facile laser micro-inscription of diffraction patterns and their following controlled scaling down as a whole pattern to pre-determined dimensions. In elastomers, utilizing the initial stress anisotropy, the post-radiation elastic shrinkage along the given axes could be precisely controlled until the 28-nJ threshold fs-laser pulse energy, where elastomer deformation ability is dramatically reduced, producing wrinkled patterns. In thermoplastics, the fs-laser inscription does not affect their heat-shrinkage deformation up to the carbonization threshold. The measured diffraction efficiency of the inscribed gratings increases during the elastic shrinkage for the elastomers and slightly decreases for the thermoplastics. High 10% diffraction efficiency was demonstrated for the VHB 4905 elastomer at the 350 nm grating period. No significant molecular-level structural modifications were observed by Raman micro-spectroscopy in the inscribed bulk gratings in the polymers. This novel few-step method paves the way for facile and robust ultrashort-pulse laser inscription of bulk functional optical elements in polymeric materials for diffraction, holographic and virtual reality devices.

Bibliometric analysis of holographic data storage literature

Objectives. Snapshots of data can be stored in a holographic medium at varying depths. Data can be written via a spiral data channel in spinning holographic media in the form of circular disks like CDs or DVDs. This data is then read by shining a reference beam through the refraction following writing. However, holographic storage is distinct from CD/DVD media in the sense that information is encoded in all three dimensions. Two-dimensional data is written using a single laser beam that spirals around the material. Prototype holographic storage solutions use minuscule cones formed by individual snapshots or pages to store one million pixels. As compared with magnetic disks and tapes, which have a finite lifespan of 50 years at most, the longevity and dependability of optical media storage is advantageous for long-term archiving. Holographic technology allows for the portability of data-intensive media such as broadcast or high-definition video. However, the shelf life of holographic media remains low due to its sensitivity to light. The primary goals of most storage devices are more storage space and faster data transport. Holographic storage devices have the potential to outperform traditional optical storage devices both in terms of capacity and performance. The present paper aims to evaluate the current international research trends in Holographic Data Storage (HDS) and produce a graphical mapping of co-authorship and countries.Methods. The major outputs of the dataset were authors, document type, publication, institution, nation, and citations. After exporting 1052 data sources, HistCite software was used to analyze the citations; visualization mapping was carried out using VOSviewer software and R programming language for the analysis of the authorcountry-title association on Holographic Storage Devices.Results. The most prominent authors, papers, journals, organizations, and nations in the field of HDS were identified in HistCite. Then, four clusters were investigated using VOSviewer based on author keywords, citation collaboration networks among different organizations, countries, and the HDS co-authorship network.Conclusions. During the study period from 2000–2020 (21 years), 4636 authors contributed to 1052 publications. The highest number of publications was in 2009, with a linear adjustment of R2 = 0.0136. The most prolific author, Lee J., published 3.14% of the articles on this subject. In terms of country distribution, Japan took first-place ranking, claiming 16.54% of the total number of articles. The “holographic” keyword was used in 62.55% of the articles.

57.2: Error Analysis in LCoS Phase Uniformity Measurement with Classical Polarimetric Method for Holographic Display Applications

The classical polarimetric method has been widely used in Liquid Crystal on Silicon (LCoS) phase depth measurement with a simple optical setup. However, the current method does not provide sufficient accuracy to measure the phase uniformity due to interference caused by LCoS cover glass reflections. This paper is aimed at mathematically analyzing the errors caused by non‐ideal glass reflections, and proposing procedures to reduce or eliminate such errors. The measurement is discussed in three conditions, including an ideal condition with no reflections off the LCoS cover glass, a second condition with only forward reflection off the cover glass and a third condition with only backward reflection off the cover glass. It is discovered that the backward reflection has the largest contribution to the overall measurement error, and is the main obstacle to high‐quality measurements. Several procedures including optical alignment, gap thickness measurement and phase estimation based on gap thickness are proposed, making the uniformity measurement more qualitative and consistent.

A Full-Color Holographic System Based on Taylor Rayleigh–Sommerfeld Diffraction Point Cloud Grid Algorithm

Real objects-based full-color holographic display systems usually collect data with a depth camera and then modulate the input light source to reconstruct the color three-dimensional scene of the real object. However, at present, the main problems of the real-time high quality full-color 3D display are slow speed, low reconstruction quality, and high consumption of hardware resources caused by excessive computing. Based on the hybrid Taylor Rayleigh–Sommerfeld diffraction algorithm and previous studies on full-color holographic systems, our paper proposes Taylor Rayleigh–Sommerfeld diffraction point cloud grid algorithm (TR-PCG), which is to perform Taylor expansion on the radial value of Rayleigh–Sommerfeld diffraction in the hologram generation stage and modify the data type to effectively accelerate the calculation speed and ensure the reconstruction quality. Compared with the wave-front recording plane, traditional point cloud gridding (PCG), C-PCG, and Rayleigh–Sommerfeld PCG without Taylor expansion, the computational complexity is significantly reduced. We demonstrate the feasibility of the proposed method through experiments.

Analog-to-digital conversion of information archived in display holograms: I. discussion.

This discussion paper highlights the potential of display holograms in the storage of information about objects' shape. The images recorded and reconstructed from holograms have high visual appeal, and the holographic carrier has far higher information capacity than other storage media. One hindrance to the application of display holograms is the inadequate development of techniques for digitizing information from them, which is compounded by insufficient analysis and discussion of existing approaches. In this review, we provide a historical retrospective of the use of display holography to save comprehensive information on object morphology. We also discuss existing and emerging technologies for converting information into a digital format, addressing one of the most serious challenges to the widespread use of display holography. Potential applications of these technologies are also analyzed.

Analog-to-digital conversion of information archived in display holograms: II. photogrammetric digitization.

We demonstrate the opportunities of photogrammetry in digitizing information about objects by acquiring a set of photographic images captured from three-dimensional scenes, which are reconstructed from volume reflection holograms. The corresponding requirements are determined for both recording the display hologram and digitizing the information reconstructed from it by photogrammetry. They include the choice of the radiation source used to reconstruct the object wave from the hologram; requirements for object positioning when recording a display hologram relative to the recording medium; and requirements for the glare minimization procedure during the construction of a photogrammetric three-dimensional model.

End-to-end real-time holographic display based on real-time capture of real scenes.

Holographic display is considered as a promising three-dimensional (3D) display technology and has been widely studied. However, to date, the real-time holographic display for real scenes is still far from being incorporated in our life. The speed and quality of information extraction and holographic computing need to be further improved. In this paper, we propose an end-to-end real-time holographic display based on real-time capture of real scenes, where the parallax images are collected from the scene and a convolutional neural network (CNN) builds the mapping from the parallax images to the hologram. Parallax images are acquired in real time by a binocular camera, and contain depth information and amplitude information needed for 3D hologram calculation. The CNN, which can transform parallax images into 3D holograms, is trained by datasets consisting of parallax images and high-quality 3D holograms. The static colorful reconstruction and speckle-free real-time holographic display based on real-time capture of real scenes have been verified by the optical experiments. With simple system composition and affordable hardware requirements, the proposed technique will break the dilemma of the existing real-scene holographic display, and open up a new direction for the application of real-scene holographic 3D display such as holographic live video and solving vergence-accommodation conflict (VAC) problems for head-mounted display devices.

Novel approach based on stochastic gradient descent for controlling the reconstructed phase randomness of computer-generated holograms

Depth of field, as one of the essential adjustment cues, affects the user experience and restricts the application of holographic displays. However, it is often underappreciated in modern holographic displays. In this study, we propose a novel computer-generated hologram (CGH) method that uses a pre-calculation procedure and a standard deviation-based loss function to generate realistic depth-of-field effects. The depth-of-field size is adjusted by controlling the randomness of the reconstructed phase. The ability of the proposed algorithm to control the reconstructed phase randomness was confirmed. Finally, a holographic display prototype was built to demonstrate the proposed method experimentally. The experimental results were consistent with the simulation results. Our findings may open up a new perspective on the application of existing stochastic gradient descent (SGD) algorithms to traditional methods for image quality optimization by adding random phases.

Spherical crown holographic display with planar SLM

Spherical holography can expand the viewing angle, while the unavailability of spherical spatial light modulators (SLM) and the huge sampling number are challenges for spherical holography. In this paper, we propose a spherical crown holographic display method based on planar SLM. First by analyzing the diffraction formula of concentric spheres, the relationship between it and the plane diffraction is found. Then it is proposed that a spherical hologram loaded on a commercial planar SLM can reproduce the target object correctly with a reasonable number of sampling points. The method can be combined with spatiotemporal multiplexing and curved multiplexing to further expand the viewing angle and information capacity, respectively. It provides a new perspective for spherical holography, and has broad prospects in the field of 3D holographic display.