Holographic Printing Research Articles

Recent Works on Direct-Write Digital Holography

Abstract Direct-write digital holographic (DWDH) printing is a highly flexible technique for the generation of photoresist masters, which are required to produce the metallic shims used for the mass production of holograms in the security and packaging industries. Here we describe a new type of holographic feature, which can be combined with any other feature printable using DWDH: full-parallax, full-colour transmission masters containing limited animation. We will also describe a technique to print the fringe pattern of each hogel without using a reference beam. By programming the required fringe calculation algorithm on a graphics card using CUDA, we obtain acceptable calculation times. The advantage of using such direct fringe writing is that once again DWDH allows extra features to be written onto a master and combined with other features to produce a stronger security solution. Finally, we present results concerning the use of hogel image dithering to improve the grey-scale performance of DWDH printers.

Laser direct writing of efficient 3D TiO2 nano-photocatalysts

The increasing demand for functional nanodevices in sustainable energy applications necessitates the development of innovative approaches. In this study, we present the fabrication and characterization of three-dimensional (3D) structures coated with titanium dioxide (TiO2) nanorods (NRs). These novel devices are created through the integration of four distinct techniques, multi-photon lithography, post-thermal treatment, pulsed laser deposition, and an aqueous chemical growth, enabling their unique properties and functionalities in photocatalysis. The photocatalytic performance of the 3D devices is evaluated through the degradation of organic pollutants, such as methylene blue and stearic acid, showcasing their efficiency in reducing pollutant concentrations. The devices demonstrate a remarkable decomposition coefficient (k=0.059min−1), highlighting their enhanced photocatalytic efficiency. Additionally, we propose a rapid fabrication technique using 3D holographic printing to create large-area TiO2-coated micro-structured photocatalytic devices at the mesoscale regime. This approach increases the active surface area, further enhancing the devices’ photocatalytic capabilities. By combining additive micro-manufacturing, TiO2 NR coating, and holographic printing, our work introduces a promising avenue for the development of advanced nanodevices with superior photocatalytic performance in sustainable energy applications.

Dynamic holographic stereogram using temporal and perspective coherence

A dynamic holographic stereogram (HS) rendering technique using temporal and perspective (TP) coherence is proposed and demonstrated. It solves the issue that previous holographic rendering methods are difficult to record HS of time-varying three-dimensional (3D) images efficiently. In our technique, a unified mathematical model is set in EPIpolar coordinates for the generation of light field images of dynamic HS. The time dimension is encoded in angular coordinates through angular multiplexing. Temporal coherence of dynamic 3D images is applied to simplify the rendering of action key frames. The action key frames are the same as conventional key frames, but have 3D information. Perspective coherence is used to render the light field images between two adjacent action key frames. Parallel computing technology combined with TP coherence is used to accelerate the rendering, which is on average 378.8% faster than traditional serial per-viewpoint rendering (PVR) algorithms. HSs with vivid and striking 3D animations are demonstrated using a custom holographic printing system, which validates the effectiveness of the proposed method. The results pave the way towards developing high-performance dynamic HSs that can be used in 3D display, visual security, and virtual/augmented reality domain.

Development of holographic printed HOE recording technology with VHG-based FOV analysis for waveguide-type NED system

We propose a holographic printing–recording technology for near-eye display through volume holographic grating analysis in hologram recording and reconstruction. Most near-eye displays are designed based on waveguide-type and analog holographic optical elements, resulting in disruption of the uniformity of the image because of the difference between the initial recording conditions and the source image. This problem can be addressed using holographic printing technology to modulate different diffraction efficiencies for each holographic element. This study uses a digital HOE screen that can fabricate and reconstruct augmented reality images of 1.17”, 1.76”, and 2.35” in a field of view of 28.07°, 41.11°, and 53.13°, respectively, at a distance of 53.33 mm from the eye. Moreover, augmented images are realized with higher diffraction efficiency than conventional methods, simplifying the design and facilitating mass production of uniformed products using digital holographic printing technology.

A study on digital holographic printing technology market and copyright protection technology trends

A study on digital holographic printing technology market and copyright protection technology trends

Characterization and design of a freeform holographic optical element

ObjectiveThe aberrations of a conventional lens holographic optical element (HOE) are considerable because of the off-axis recording and diffraction nature. A freeform HOE was introduced to alleviate these aberrations. To design and optimize the recording wavefront of a freeform HOE, it is important to figure out the imaging properties of an HOE. MethodsWe systematically derived a general characterization of the conjugate imaging equation of an elementary HOE recorded by two spherical wavefronts using the scalar diffraction theory. In our design, each patch of a freeform HOE is considered as an elementary HOE. The recording wavefronts of a freeform HOE is designed by determining each elementary HOE through the conjugate imaging equation. ResultsThe image position predicted by the imaging equation is consistent with that of the finite ray-tracing method. The error when the imaging equation is applied to off-axis object points and different reconstruction wavelengths is eliminated effectively through coordinate transformation. Furthermore, based on this equation, a freeform HOE with 3 × 3 tiling elementary HOEs is designed to eliminate distortion and astigmatism of the HOE imaging system. A holographic printer to fabricate this freeform HOE is recommended.

Sparse holographic imaging for an integrated augmented reality near-eye display.

Diffraction is the main physical effect involved in the imaging process of holographic displays. In the application of near-eye displays, it generates physical limits that constrain the field of view of the devices. In this contribution, we evaluate experimentally an alternative approach for a holographic display based mainly on refraction. This unconventional imaging process, based on sparse aperture imaging, could lead to integrated near-eye displays through retinal projection, with a larger field of view. We introduce for this evaluation an in-house holographic printer that allows the recording of holographic pixel distributions at a microscopic scale. We show how these microholograms can encode angular information that overcomes the diffraction limit and could alleviate the space bandwidth constraint usually associated with conventional display design.

Perspective clipping and fast rendering of light field images for holographic stereograms using RGBD data.

The production of holographic stereogram (HS) requires a huge amount of light field data. How to efficiently clip and render these image data remains a challenge in the field. This work focuses on the perspective clipping and fast rendering algorithm for light field images using RGBD data without explicit 3D reconstruction. The RGBD data is expanded to RGBDθ data by introducing a light cone for each point, which gives a new degree of freedom for light field image rendering. Using the light cone and perspective coherence, the visibility of 3D image points can be clipped programmatically. Optical imaging effects including mirror imaging and half mirror imaging effects of 3D images can also be rendered with the help of light cones during the light field rendering process. The perspective coherence is also used to accelerate the rendering, which has been shown to be on average 168% faster than traditional DIBR algorithms. A homemade holographic printing system was developed to make the HSs using the rendered light field images. The vivid 3D effects of the HS have validated the effectiveness of the proposed method. It can also be used in holographic dynamic 3D display, augmented reality, virtual reality, and other fields.

Design of Proxy Re-encryption Based Market System for Copyright Protection of Digital Holographic Printing Contents

Design of Proxy Re-encryption Based Market System for Copyright Protection of Digital Holographic Printing Contents

Verification of Polarization Matching on the Hologram Recording Plane for the Implementation of an Optimized Digital Hologram Printing System

Conventional studies on digital hologram printer have mainly been conducted on image generation and reconstruction such as multi-view image generation method, computer-generated hologram (CGH) and a method of displaying a wave-front for a 3D object. However, There should be a criterion to evaluate the quality of the reconstructed image because hologram printer use photosensitive recording interference patterns in holographic material. For this reason, The evaluation method of the completed hologram using a digital hologram printer is focused on how well it came out without aberration or how high intensity of light has been reconstructed. However polarization has an effect on hologram regeneration efficiency because holography uses a laser that generates electromagnetic waves. Hologram recording method is usually to match linear polarization in the same direction. but digital hologram printer composed of complex optical components that causes a phase shifting due to a setup error. it will be a problem for resulting in unwanted polarization at the final recording plane. In this paper, we analyzed the possible polarization changes and analyze the optimal polarization matching status using values from hologram results and use them as a study to improve the efficiency of hologram result from holographic printer.

Holographic printing for generating large-angle freeform holographic optical elements.

We propose a holographic printing technique for generating highly efficient large-deflection-angle freeform holographic optical elements (HOEs). For industrial device applications, the optical efficiency and deflection angle of HOEs are critical. To fabricate a high-frequency volume grating in a hogel, we design an optomechanical hogel recording system with a high angle deflection capability, which contrasts with the conventional printing scheme, the wavefront holographic printing technique featuring a paraxial deflection angle. With the proposed system, a large-deflection-angle HOE is experimentally demonstrated, and short-throw holographic caustic projection patterns are realized.

High-Resolution Phase-Only Holographic 3D Display Based on Light Field Images Rendered in the Frequency Domain

Phase-only holograms are more attractive than the amplitude holograms for the higher energy utilization and the possibility to realize on-axis holographic 3D display without conjugate image. In this study, we propose a high-resolution phase-only holographic 3D display using the light field images rendered in the frequency domain. The high-resolution phase-only hologram contains a large number of elemental phase-only holograms (EPHs), and each EPH is calculated from the light field image of the corresponding viewing point in frequency domain through weighted GS (Gerchberg-Saxton) algorithm. Parallel calculation is performed to speed up the calculation in the row direction and the previous EPH is used as the initial phase for the current EPH calculation in order to improve the display quality due to the great similarity between adjacent light field images. Two high-resolution phase-only holograms both with the size of 64 mm×64 mm and the resolution of 200k×200k pixels were calculated and printed by our homemade holographic printer. The full-parallax and high quality 3D displays were verified by optical experiments, which have the potential to be applied in holographic advertising and other fields.

Optimization of the method for color measurement and color-difference calculation of holographic prints with light pillars.

To determine the methods of color measurement and color-difference calculation for holographic prints with light pillars, 94 pairs of holographic prints constituted by 17 different products were collected. A set of color-difference comparison experiments was organized by 64 observers with normal color vision, and a total of 86 groups of visual judgments were gathered. The CIELAB and CIEDE2000 color-difference values were calculated on the basis of the analysis of the microstructures of gratings distributed on the holographic paper. The performances of the original formulas were evaluated in terms of the standardized residual sum of squares index, and then they were optimized considering the power function effects (a, b factors) together with a contribution from lightness (kL factor). Meanwhile, the color-difference threshold of the holographic prints was estimated with a goal to minimize the number of wrong decision in the visual experiment; therefore, the values were set as 2.50 and 2.00 for the original CIELAB and CIEDE2000 with the consistency of 91.5% and 98.9%, respectively. The results can also provide guidance to evaluate the color quality of the holographic prints with light pillars in the packaging and printing industries.

Design and fabrication of freeform holographic optical elements

Holographic optical elements (HOEs) have a wide range of applications, including their emerging use in virtual and augmented reality displays, but their design and fabrication have remained largely limited to configurations using simple wavefronts. In this paper, we present a pipeline for the design, optimization, and fabrication of complex, customized HOEs that enhances their imaging performance and enables new applications. In particular, we propose an optimization method for grating vector fields that accounts for the unique selectivity properties of HOEs. We further show how our pipeline can be applied to two distinct HOE fabrication methods. The first uses a pair of freeform refractive elements to manufacture HOEs with high optical quality and precision. The second uses a holographic printer with two wavefront-modulating arms, enabling rapid prototyping. We propose a unified wavefront decomposition framework suitable for both fabrication approaches. To demonstrate the versatility of these methods, we fabricate and characterize a series of specialized HOEs, including an aspheric lens, a head-up display lens, a lens array, and, for the first time, a full-color caustic projection element.

Efficient Hogel-Based Hologram Synthesis Method for Holographic Stereogram Printing

With the development of the holographic printer, printing synthetic hologram requires smaller holographic element (hogel) size to improve spatial resolution of the reconstruction. On the contrary, a larger hogel size affords higher angular resolution, but it leads to a lower lateral resolution and there exists a trade-off problem. In this paper, a hologram synthesis method based on three-dimensional (3D) rendering of computer-generated holographic stereogram (HS) is proposed to limit the spatial-angular trade-off problem. The perspectives of the 3D scene are captured by re-centering the camera method and transformed into parallax-related images by a proposed pixel re-arrangement algorithm for holographic printing. Unlike the conventional approaches, the proposed algorithm not only improves the angular resolution of the reconstruction while maintaining the hogel size fixed, but also keeps the spatial resolution without degradation. The effectiveness of the proposed method is verified by numerical simulation and an optical experiment.

Holographically Printed Freeform Mirror Array for Augmented Reality Near-Eye Display

We propose augmented reality (AR) near-eye display using a holographically printed freeform mirror array. A wide depth of field AR system is implemented by the retinal projection via a small mirror array. Since we use a holographic mirror array, more advantages over a traditional physical mirror array are achieved. Due to the see-through characteristics of the holographic optical element (HOE), the array structure does not obstruct the sight of an observer. Also, the holographic printing technique for the freeform mirror array enables a wide depth of field system without using a floating lens and compensates for the astigmatism of the HOE. The detailed design method of the freeform mirror array HOE is presented. Through the retinal image simulations and the experimental results, the feasibility of the proposed method is verified.

Use of focus stacking and SfM techniques in the process of registration of a small object hologram

In this Letter, a method for shape visualization of small objects (microscopic) in the form of a hologram is presented. It consists of a standard optical set-up for small object registration (i.e., stereoscopic or biological microscope). The focus stacking technique is used to obtain a series of images with increased depth of field and on them a shape reconstruction procedure (structure from motion, SfM) is made. With use of a dense cloud of points, a sequence of parallax-related images suitable for Geola’s digital holographic printing is generated. The holographic printer produces single-parallax holographic (full three-dimensional) images of real or virtual objects.

Holographically customized optical combiner for eye-box extended near-eye display.

We propose a customizing method of a holographic optical element (HOE) by using a holographic printer, which extends the eye-box with high field of view (FOV) for a holographic augmented reality near-eye display (AR NED). The holographic printer setup to manufacture HOE is presented and a prototype of the AR NED is implemented. To make a simple AR NED system, we propose a total internal reflection holographic printing method using an index-matching optical frame. As a result, the eye-box of the AR NED is extended in both vertical and horizontal directions and FOV of 50° is achieved at the center of the eye-box. Through the simulations and the experimental results, the feasibility of the proposed method is verified.

High Field-of-View Near-Eye Display Using Total Internal Reflection Prism and Holographic Printing Technique

High Field-of-View Near-Eye Display Using Total Internal Reflection Prism and Holographic Printing Technique

High Field-of-View Near-Eye Display Using Total Internal Reflection Prism and Holographic Printing Technique

High Field-of-View Near-Eye Display Using Total Internal Reflection Prism and Holographic Printing Technique