Holographic Projection System Research Articles

Learning About Lunar Phases: Exploring Taiwanese University Students’ Conceptions of and Approaches to Learning by Holographic Projection

Extant literature has preliminarily confirmed the potential benefits of holographic projections for educational purposes. Yet, students’ experiences of learning by holographic projection have rarely been addressed. The main purpose of this study was therefore to explore students’ conceptions of and approaches to learning by holographic projection. A holographic projection system was devised to assist students in learning the concept of lunar phases. This study also investigated the relationships between students’ conceptions and approaches, and determined if there were any variations based on students’ learning gains. Phenomenographic analysis was adopted to analyze 30 university students from Taiwan, and a multiple-choice conceptual test was conducted to assess their learning achievements. The main findings indicated that students with conceptions of learning by holographic projection as increasing the presence of a scene or mapping 2D images to 3D structures tended to adopt surface approaches, such as only observing the changes presented in the holographic projection, repetitively operating the system functions without intended purposes, or simply following the instruction guidelines to meet the minimal requirements. However, this study unexpectedly found that students who utilized surface approaches had significantly higher learning gains on the conceptual test than their counterparts did.

Accelerated Augmented Reality Holographic 4k Video Projections Based on Lidar Point Clouds for Automotive Head‐Up Displays

AbstractIdentifying road obstacles hidden from the driver's field of view can ensure road safety in transportation. Current driver assistance systems such as 2D head‐up displays are limited to the projection area on the windshield of the car. An augmented reality holographic point cloud video projection system is developed to display objects aligned with real‐life objects in size and distance within the driver's field of view. Light Detection and Ranging (LiDAR) point cloud data collected with a 3D laser scanner is transformed into layered 3D replay field objects consisting of 400 k points. GPU‐accelerated computing generated real‐time holograms 16.6 times faster than the CPU processing time. The holographic projections are obtained with a Spatial Light Modulator (SLM) (3840×2160 px) and virtual Fresnel lenses, which enlarged the driver's eye box to 25 mm × 36 mm. Real‐time scanned road obstacles from different perspectives provide the driver a full view of risk factors such as generated depth in 3D mode and the ability to project any scanned object from different angles in 360°. The 3D holographic projection technology allows for maintaining the driver's focus on the road instead of the windshield and enables assistance by projecting road obstacles hidden from the driver's field of view.

High-brightness holographic projection.

We propose a holographic projection system that achieves high image quality, brightness, and light efficiency. Using a novel, to the best of our knowledge, light-efficiency loss function, we are able to concentrate more light on the projection region and improve display brightness compared with conventional projectors. Leveraging emerging artificial intelligence-driven computer-generated holography and camera-in-the-loop calibration techniques, we learn a holographic wave propagation model using experimentally captured holographic images and demonstrate state-of-the-art light reallocation performance with high image quality.

Augmented Reality Holographic Visualization System for Surgery Auxiliary Visualization: Proof of Concept for Surgical Training.

An Augmented Reality (AR) system based on the holographic projection of the relevant anatomic structures is proposed for auxiliary visualization during surgeries. The current two-dimensional visualization systems require the surgeons to mentally extract the associated three-dimensional information during the interventions, which entails risks and complications. This work shows an AR holographic projection system for real-time three-dimensional representation of the relevant surgical information, thus overcoming this problem. As an initial proof of concept, the system is experimentally assessed as potential surgery training tool.Clinical Relevance- This work explores the potential of AR holographic projection systems for intraoperative assistance to the surgical team, starting from its possible use as surgery training and planning tool.

3‐3: Large‐FoV Fast LiDAR System based on Electrically Suppressed Helix Ferroelectric Liquid Crystal

With the continuing prosperity of LiDAR markets, the demand of a fast‐scanning, high‐precision and inexpensive LiDAR system is growing rapidly. In this paper, we disclose a fast‐switchable ferroelectric liquid crystal Dammann grating and polarization grating‐based holographic projection and detection system for 3D imaging devices and LiDAR with an extended field of view. The field of view of the proposed system can achieve ~80° with <0.5cm precision at a significantly lower cost. This improvement increases LiDAR versatility and performance in various scenarios.

Digital Pre-Distorted One-Step Phase Retrieval Algorithm for Real-Time Hologram Generation for Holographic Displays

In a computer-generated holographic projection system, the image is reconstructed via the diffraction of light from a spatial light modulator. In this process, several factors could contribute to non-linearities between the reconstruction and the target image. This paper evaluates the non-linearity of the overall holographic projection system experimentally, using binary phase holograms computed using the one-step phase retrieval (OSPR) algorithm, and then applies a digital pre-distortion (DPD) method to correct for the non-linearity. Both a notable increase in reconstruction quality and a significant reduction in mean squared error were observed, proving the effectiveness of the proposed DPD-OSPR algorithm.

Applying multi-focus filtering plane in double-step Fresnel diffraction method for enhanced holographic projection region

Computer-generated holography has been anticipated in augmented reality (AR) since it can fully provide multi-depth 3D information to users, but speckle noises are often accompanied as one of the most significant degradation factors. Since complex amplitude encoding can suppress speckle noises, applying double-phase encoding to a lensless holographic projection system using a double-step Fresnel diffraction (DSF) algorithm has been reported to reduce those noises. However, a single filtering focus at a virtual focal plane might significantly reduce the projection region compared to the maximum diffraction bandwidth of the spatial light modulator. In this paper, we applied multiple foci for the focal plane of the DSF method with off-axis phase encoding, which can expand the projection region and is applicable to display multi-depth images with DSF. Numerical analysis conducted for image quality compared with conventional single focus DSF algorithm shows that the speckle performance does not degrade so much as the number of foci increase. We expect the proposed method to be useful for holographic projection optical systems such as AR head-up display.

Aberration analysis of a projection-type CGH display with an expanded FOV based on the HOE screen.

This paper proposed a holographic optical element as a see-through screen for the computer-generated hologram projection system with 3D images. The proposed holographic screen consisted of a linear grating and a lens phase. The linear grating is used to redirect the information light and guide information into the observer's eye and achieve the see-through function. The lens phase is used to magnify the field of view of the holographic projection system. The aberration caused by the screen was analyzed in this paper and the aberration can be pre-corrected in the hologram calculation algorithm. Finally, the proposed system achieved 20.3 by 14.3 degrees field of view at 532 nm laser based on the spatial light modulator with 6.4 µm pixels.

Augmentation of 3D Holographic Image Graticule With Conventional Microscopy

In this paper, we report an implementation of a computer-generated holographic projection technique to display a holographic scene like a measuring graticule around the magnified sample image in a reflected bright-field microscopy. The implemented system acts as a gauging tool for lateral and longitudinal measurements of a sample that is being observed under a microscope through the assistance of a holographic measuring graticule. Numerical and experimental verifications have been performed, demonstrating the successful augmentation of a holographic projection system as a measuring tool with a conventional bright-field microscopic system.

Large field-of-view lensless holographic dynamic projection system with uniform illumination and U-net acceleration

Compared to traditional projection systems, a diffraction-based lensless projection system offers the advantages of a compact size with high design freedom. However, the existing iterative algorithms for computer-generated holograms (CGHs) in large field-of-view diffraction systems are not mature, and are characterised by long processing times, making them unsuitable for application in dynamic displays. Furthermore, most large-scale diffraction algorithms neglect the intensity and phase nonuniformity of the illuminated spherical beam. Herein, we develop a large field-of-view laser projection system with U-net acceleration. Our system has a diffractive optical element (DOE) inserted between the digital micromirror device (DMD) and the screen to reduce the intensity and phase nonuniformity introduced by the spherical wave. Structural parameters of the system are also optimized, then amplitude CGHs are loaded on the DMD sequentially. A divergent laser beam illuminates the DMD and is converted to a uniform beam by the DOE before it reaches the screen. The Gerchberg–Saxton (GS) iterative algorithm based on the scaled angular spectrum method (SASM–GS) is used to generate the amplitude CGH. However, as this process of computation includes three forward and three backward diffractions, it is time-consuming. Therefore, CGHs generated by the SASM–GS algorithm were used as labels, and a U-net model was trained using the MNIST database. Simulations revealed that the trained U-net model can accurately generate amplitude CGHs and has a certain degree of versatility. Notably, the hologram generation time of the U-net model was one-tenth that of the SASM–GS algorithm. Finally, we performed experiments to verify the efficacy of the U-net model, demonstrating the feasibility of the proposed dynamic lensless projection system.

Generation and experimental reconstruction of optimized Fresnel random phase-only holograms

In this paper, we demonstrate a method for random phase optimization in the Fresnel domain that enables the fast generation of phase-only holograms (POHs). Our proposal consists of applying the iterative Fresnel transform algorithm (IFrTA) to optimize a random phase with the parameters of a given holographic projection system. Then, the resulting optimized Fresnel random phase is used for the generation of POHs of several objects. We compare the performance of our proposed method to the direct generation of holograms using IFrTA, and quantitatively study the quality of the reconstructed object varying the generation parameters. Our results show significantly improved computation speed and minor loss of accuracy compared with the direct application of the IFrTA. We present both numerical and optical reconstructions obtained with a holographic projection scheme based on a phase-only spatial light modulator to verify the validity and effectiveness of our proposal.

An interactive holographic projection system that uses a hand-drawn interface with a consumer CPU

Holography is a promising technology for photo-realistic three-dimensional (3D) displays because of its ability to replay the light reflected from an object using a spatial light modulator (SLM). However, the enormous computational requirements for calculating computer-generated holograms (CGHs)—which are displayed on an SLM as a diffraction pattern—are a significant problem for practical uses (e.g., for interactive 3D displays for remote navigation systems). Here, we demonstrate an interactive 3D display system using electro-holography that can operate with a consumer’s CPU. The proposed system integrates an efficient and fast CGH computation algorithm for line-drawn 3D objects with inter-frame differencing, so that the trajectory of a line-drawn object that is handwritten on a drawing tablet can be played back interactively using only the CPU. In this system, we used an SLM with 1,920 times 1,080 pixels and a pixel pitch of 8 μm × 8 μm, a drawing tablet as an interface, and an Intel Core i9–9900K 3.60 GHz CPU. Numerical and optical experiments using a dataset of handwritten inputs show that the proposed system is capable of reproducing handwritten 3D images in real time with sufficient interactivity and image quality.

Holography, and the future of 3D display

The pioneers of holography, Gabor, Leith, Upatnieks, and Denisyuk, predicted very early that the ultimate 3D display will be based on this technique. This conviction was rooted on the fact that holography is the only approach that can render all optical cues interpreted by the human visual system. Holographic 3D displays have been a dream chased after for many years, facing challenges on all fronts: computation, transmission, and rendering. With numbers such as 6.6 × 1015 flops required for calculations, 3 × 1015 b/s data rates, and 1.6 × 1012 phase pixels, the task has been daunting. This article is reviewing the recent accomplishments made in the field of holographic 3D display. Specifically, the new developments in machine learning and neural network algorithms demonstrating that computer-generated holograms approach real-time processing. A section also discuss the problem of data transmission that can arguably be solved using clever compression algorithms and optical fiber transmission lines. Finally, we introduce the last obstacle to holographic 3D display, which is is the rendering hardware. However, there is no further mystery. With larger and faster spatial light modulators (SLMs), holographic projection systems are constantly improving. The pixel count on liquid crystal on silicon (LCoS) as well as microelectromechanical systems (MEMS) phase displays is increasing by the millions, and new photonic integrated circuit phased arrays are achieving real progress. It is only a matter of time for these systems to leave the laboratory and enter the consumer world. The future of 3D displays is holographic, and it is happening now.

Compression of 3D dynamic holographic scenes in the Fresnel domain

In this paper we present an optodigital protocol for the compression of 3D dynamic scenes recorded with an off-axis Fresnel holographic system. The compression protocol involves optical scaling, sampling with binary masks, and multiplexing of the optical field data obtained after a filtering process applied to Fresnel holograms. Volume reduction of up to 93.71% and a 16-fold decrease in the transfer time are achieved. Virtual-optical reconstruction is performed for different values of the parameters involved in the compression protocol. The correlation coefficient is used as a metric to measure the loss caused by the volume reduction process. Furthermore, we show that a high level of lossy compression can be achieved with this protocol, with better reconstruction quality than the MPEG-4 video compression technique. Finally, we perform the experimental reconstruction using a holographic projection system based on a phase-only spatial light modulator, thus highlighting the potential of our proposal.

Compact lensless full-color holographic projection system with digital phase

A lensless full-color holographic projection system is proposed, satisfying the requirement of compactness and flexibility. The system enables projection by illuminating a single-chip spatial light modulator (SLM) simultaneously with red (R), green (G), and blue (B) lasers, in which the SLM loads a color-multiplexed phase-only hologram. To strengthen compactness, filtering and achromatic systems are achieved by digital phase, where the digital lens phase focuses the light field onto the filter plane, and the digital blazed gratings shift the RGB images to achieve a fine alignment. Besides, the flexibility of diffraction calculation is enhanced by the cascaded D-FFT and S-FFT algorithm (CDS algorithm, where D-FFT is acronym of double fast fourier transform and S-FFT is acronym of single fast fourier transform). Both simulation and optical experiments are carried out. We conducted 2D image and animation projection and multi-image-plane projection. The results confirm the feasibility of our method.

Holographic capture and projection system of real object based on tunable zoom lens

In this paper, we propose a holographic capture and projection system of real objects based on tunable zoom lenses. Different from the traditional holographic system, a liquid lens-based zoom camera and a digital conical lens are used as key parts to reach the functions of holographic capture and projection, respectively. The zoom camera is produced by combing liquid lenses and solid lenses, which has the advantages of fast response and light weight. By electrically controlling the curvature of the liquid-liquid surface, the focal length of the zoom camera can be changed easily. As another tunable zoom lens, the digital conical lens has a large focal depth and the optical property is perfectly used in the holographic system for adaptive projection, especially for multilayer imaging. By loading the phase of the conical lens on the spatial light modulator, the reconstructed image can be projected with large depths. With the proposed system, holographic zoom capture and color reproduction of real objects can be achieved based on a simple structure. Experimental results verify the feasibility of the proposed system. The proposed system is expected to be applied to micro-projection and three-dimensional display technology.

Three-Dimensional Holographic Reconstruction of Brain Tissue Based on Convolution Propagation

In this study, a dynamic holographic projection system for brain tissue and its anatomical structures extracted from Magnetic Resonance (MR) plane slice is reported. Computer holograms are calculated using a modified Gerchberg-Saxton (GS) iterative algorithm where the projection is based on the plane wave decomposition. First, brain anatomy includes white matter (WM), grey matter (GM) and brain tissue are extracted. Then, phase holograms using the proposed method are generated. Finally, single-phase hologram for the whole brain anatomy is generated and is optically reconstructed by a phase-only spatial light modulator (SLM) at different depths. The obtained results revealed that the three-dimensional holographic projection of MR brain tissue can aid to provide better interpretation of brain anatomical structure to achieve better diagnostic results.

Holographic Projection System for Drawing Fingertip Trajectory Obtained from Depth Camera

Holographic Projection System for Drawing Fingertip Trajectory Obtained from Depth Camera

Holographic Projection System for Drawing Fingertip Trajectory Obtained from Depth Camera

Holographic Projection System for Drawing Fingertip Trajectory Obtained from Depth Camera

Holographic projection based on programmable axilens

In a traditional holographic projection system, a clear reconstructed image is formed only in the focal plane of the Fourier lens. In this paper, We propose a novel method to form simultaneously holographic reconstructed images in good focus located at different planes. The large focal depth characteristic of the programmable axilens is applied to the holographic projection. First, the iterative Fourier algorithm is employed to generate a phase hologram. A new phase distribution is formed by superimposing the axilens phase on the phase hologram, and loading onto the phase-only liquid crystal on silicon (LCoS); With the programmability of the LCoS, the different focal-depth parameters of the axilens are tuned. We could obtain the desired holographic reconstructed images when the collimated laser is used to incident the LCoS. The experimental results show that compared with the holographic projection system based on Fresnel lens, the holographic reconstructed images in good focus can be observed simultaneously on a multi-plane in a range by dynamically changing the focal depth of the axilens.