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In a classical metasurface-based holographic display system, a clear holographic reconstruction image can be obtained only in the back-focal-plane of the lens. However, when the receiving plane deviates from the focal plane, the reconstructed holographic image suffers from degradations that limit the quality of the images. Hence, we propose a novel metasurface-based holographic display to realize clearly continuous imaging within the specified position range by superimposing the meta-axilens phase. It can effectively relieve the alignment requirements of the imaging system. Firstly, the parameters and properties of all-dielectric meta-atom is analyzed. Then we compare and demonstrate two sets of metasurface-based optical elements (meta-axicon, meta-lens, and meta-axilens), made by silicon meta-atoms working at 610 nm. Furthermore, we show that the metasurface hologram with the axilens phase can form a series of the relatively clear holographic images away from the focal plane. Our proposal suggests a method to reconstruct holographic wavefront in different planes simultaneously, and one can find their application domain, such as 3D biological imaging, spectroscopy, optical information storage, and encryption.

Holography can produce the most real three-dimensional (3D) image, and is considered as the ultimate 3D display technology. However, compared with other display technologies, it has not been practically available in video display so far due to low refresh rate. To realize dynamic holographic display, photosensitive material doped liquid crystal (LC) has been discovered and deeply investigated because of superior photorefractive and photoelectric properties. In this work, we present a dynamic holographic display using LC film doped with perovskite (CsPbBr3) nanocrystal (NC) as the photorefractive material. The dependence of diffraction efficiency and response time on doping concentration, recording beam power and applied voltage are investigated. A maximum diffraction efficiency of 18% has been achieved under a low electric field intensity of 0.45 V/μm and the shortest build-up time of grating is 5.5 ms. The system can realize a video display with 60 Hz refresh rate in red, green and blue colors, which demonstrates the feasibility of applying perovskite NC doped LC film in dynamic holographic display.

We demonstrate an interactive holographic display system for real-time drawing and erasing of 3D point-cloud images. This system detects the position of the observer’s fingertip with a motion sensor, which it uses to calculate the complex amplitude distribution for the hologram. Because the calculated distribution is added to or subtracted from the complex amplitude distribution of the previous frame, the calculation time per frame is independent of the number of points comprising the 3D point cloud. Then, the system can quickly update the hologram even when the number of points comprising the 3D point cloud is increased. Because the 3D point-cloud image reconstructed from the calculated hologram is projected at the same position as the observer’s fingertip with almost no latency, the system can draw and erase a 3D point-cloud image through interactions with the observer’s fingertip. We experimentally confirmed that the system successfully draws and erases a 3D point-cloud image.

Electromagnetic metasurfaces are structured surfaces consisting of a thin array of subwavelength elements with engineered scattering properties, thus providing a promising means of holographic display by controlling the field distributions. However, the existing metasurface holography has limited capabilities in achieving 3-D fields with simultaneous features of high spatial resolution and energy efficiency due to the design methods. In this work, we present a transmissive metasurface to achieve polarization-dependent field distributions in 3-D space with both high resolution and efficiency. In the design, a new method that utilizes dyadic Green’s function (DGF) as the rigorous propagator is used. Using the method, the sources and fields are linked directly and can be located on arbitrary 3-D points with the intermediate spaces being equal or unequal. The design is successfully validated by full-wave simulations and experimental measurements. The broadband simulation results indicate that the design has a bandwidth of 0.8 GHz. This work demonstrates a feasible and simple route of field synthesis for real-world applications that require high resolution, high efficiency, and 3-D scenarios.

AIMS AND OBJECTIVES The research aims to identify the technology of producing the holographic image and how to display it through 3D LED fans for use in the field of advertising. HYPOTHESIS AND METHODOLOGIES The research relied on the descriptive analytical approach to produce holographic images, as well as the experimental approach to reach the best methods for producing and designing a holographic display through 3D LED fans. 1. The use of 3D LED fans for a holographic display in advertising is more effective than using traditional methods. 2. Modern technology has helped to develop the concept of stereoscopic image and its spread. 3. Display product pictures through holographic technology more attractive than traditional methods. 4. Graphics and electronic montage programs have helped increase the quality of the images used in the field of advertising. 5. The angle of rotation of the subject during shooting affects the display quality. Results: 1- Displaying product pictures through holographic technology more attractive than traditional methods. 2- Graphics and electronic editing software helped in controlling the quality of the displayed images. 3- The angle of rotation of the subject during shooting affects the quality of the presentation. 4-The rotation time affects the quality of video during the presentation. 5- Image quality control has an effect on presentation.

Holographic displays promise unprecedented capabilities for direct-view displays as well as virtual and augmented reality applications. However, one of the biggest challenges for computer-generated holography (CGH) is the fundamental tradeoff between algorithm runtime and achieved image quality, which has prevented high-quality holographic image synthesis at fast speeds. Moreover, the image quality achieved by most holographic displays is low, due to the mismatch between the optical wave propagation of the display and its simulated model. Here, we develop an algorithmic CGH framework that achieves unprecedented image fidelity and real-time framerates. Our framework comprises several parts, including a novel camera-in-the-loop optimization strategy that allows us to either optimize a hologram directly or train an interpretable model of the optical wave propagation and a neural network architecture that represents the first CGH algorithm capable of generating full-color high-quality holographic images at 1080p resolution in real time.

Holography is arguably the most promising technology to provide wide field-of-view compact eyeglasses-style near-eye displays for augmented and virtual reality. However, the image quality of existing holographic displays is far from that of current generation conventional displays, effectively making today's holographic display systems impractical. This gap stems predominantly from the severe deviations in the idealized approximations of the "unknown" light transport model in a real holographic display, used for computing holograms. In this work, we depart from such approximate "ideal" coherent light transport models for computing holograms. Instead, we learn the deviations of the real display from the ideal light transport from the images measured using a display-camera hardware system. After this unknown light propagation is learned, we use it to compensate for severe aberrations in real holographic imagery. The proposed hardware-in-the-loop approach is robust to spatial, temporal and hardware deviations, and improves the image quality of existing methods qualitatively and quantitatively in SNR and perceptual quality. We validate our approach on a holographic display prototype and show that the method can fully compensate unknown aberrations and erroneous and non-linear SLM phase delays, without explicitly modeling them. As a result, the proposed method significantly outperforms existing state-of-the-art methods in simulation and experimentation - just by observing captured holographic images.

Since its discovery almost 70 years ago, the hologram has been considered to reproduce the most realistic three dimensional images without visual side effects. Holographic video has been extensively researched for commercialization, since Benton et al. at MIT Media Lab developed the first holographic video systems in 1990. However, commercially available holographic video displays have not been introduced yet for several reasons: narrow viewing angle, bulky optics and heavy computing power. Here we present an interactive slim-panel holographic video display using a steering-backlight unit and a holographic video processor to solve the above issues. The steering-backlight unit enables to expand the viewing angle by 30 times and its diffractive waveguide architecture makes a slim display form-factor. The holographic video processor computes high quality holograms in real-time on a single-chip. We suggest that the slim-panel holographic display can provide realistic three-dimensional video in office and household environments., Holographic displays that are both compact and produce realistic holograms without eyestrain are still difficult to realize. Here the authors implement a steering-backlight unit and a holographic video processor to produce a realistic holographic display in a slim panel.

This report discusses the effect of speckle size on the quality of holographic images based on a liquid-crystal-on-silicon (LCoS) spatial light modulator (SLM). Further, it proposes methods of quantifying the average speckle size and holographic image resolution. These methods enable both characteristics to be compared using the same unit (the number of pixels in the holographic image), providing an intuitive and effective comparative analysis method. In particular, by varying the LCoS resolution ratio, the change in the resolvable minimum pixels of the holographic image is interpreted in conjunction with the average speckle size; moreover, an analysis of the correlation between the latter two is presented. This approach, based on LCoS resolution division, could provide useful insights into single-SLM-based, full-color holographic displays using space division. Furthermore, it could be extended to other components, including more advanced LCoS SLMs, and used to identify the relative effects on image quality with speckles.

Displays play an extremely important role in modern information society, which creates a never-ending demand for the new and better products and technologies. The latest requirements for novel display technologies focus on high resolution and high color gamut. Among emerging technologies that include organic light-emitting diode (OLED), micro light-emitting diode (micro-LED), quantum dot light-emitting diode (QLED), laser display, holographic display and others, QLED is promising owing to its intrinsic high color gamut and the possibility to achieve high resolution with photolithography approach. However, previously demonstrated photolithography techniques suffer from reduced device performance and color impurities in subpixels from the process. In this study, we demonstrated a sacrificial layer assisted patterning (SLAP) approach, which can be applied in conjunction with photolithography to fabricate high-resolution, full-color quantum dot (QD) patterns. In this approach, the negative photoresist (PR) and sacrificial layer (SL) were utilized to determine the pixels for QD deposition, while at the same time the SL helps protect the QD layer and keep it intact (named PR-SL approach). To prove this method’s viability for QLED display manufacture, a 500-ppi, full-color passive matrix (PM)-QLED prototype was fabricated via this process. Results show that there were no color impurities in the subpixels, and the PM-QLED has a high color gamut of 114% National Television Standards Committee (NTSC). To the best of our knowledge, this is the first full-color QLED prototype with such a high resolution. We anticipate that this innovative patterning technique will open a new horizon for future display technologies and may lead to a disruptive and innovative change in display industry.

Computer generated holograms represent a novel digital media that with adequate processing tools and the advance of holographic display technologies will foster the development of true immersive video technologies applications. A digital hologram typically conveys a considerable amount of data making compression and image quality evaluation tools necessary for the development of practical applications. This paper proposes an objective evaluation of the performances of state-of-the-art compression techniques applied to digital holographic data. The experimental analysis takes into account several holographic images reconstructing the holograms from different perspectives and distances. The results of the exploratory study are reported, discussed and complemented with a statistical analysis of the hologram data under test, providing insights for computer-generated holography compression techniques design.

In this paper, a method of speckle noise suppression for holographic zoom display based on layered-pixel-scanning (LPS) algorithm is proposed. Different from the traditional algorithm, the proposed method suppresses the speckle noise based on a new algorithm design and light source optimization. The LPS algorithm is designed to calculate the phase-only hologram of the 3D object. By extracting the initial complex hologram of the 3D object and scanning the hologram by pixel, the errors of the complex amplitude can be reduced as much as possible. Then a hologram subsampling method based on the LPS algorithm generated is proposed, so the scaling of the reproduced image can be achieved easily. At the same time, the pattern with different random phase is generated and loaded on the spatial light modulator so that the reconstructed light can be optimized. When the optimized light irradiates on the phase hologram of the object, the reconstructed image with suppressed speckle noise can be displayed. The experimental results show that the proposed method has an excellent reproduction effect. Moreover, the feasibility and unique advantages of the proposed method in the holographic augmented-reality display, zoom display and multi-plane display have been proved. We believe that this method can promote the application of the holographic display.

With significant advances in holographic display technology, a plethora of interactive applications, such as tele-conferencing and tele-surgery, are well on their way to integrating holographic technologies. However, hologram-based applications will place significant demands on networking infrastructure, which are not supported today. These include support for ultra-low delays, high bandwidth, and the ability to coordinate, synchronize, and dynamically adapt multiple data streams. This article articulates these challenges and points out gaps in existing networks that solutions must address. In addition, it provides an experimental analysis of novel network architectures that address one of these challenges, namely the ability to dynamically set up new flows with very low latency incurred by the first packet.

Herein, the design and implementation of a transparent 3D touch‐enabled surface for richer user interaction with midair 3D virtual objects in a touch‐interactive pseudo‐holographic display are presented. Frustrated total internal reflection (FTIR)‐based touch sensing is used in combination with a four‐sided pyramidal pseudo‐holographic projection. The developed system allows gesture‐based control and smooth touch interaction through facile and inexpensive hardware and open‐source software tools. A software application is also developed as the interface between the touch/gesture‐sensing system and the optical display. By bringing the virtual and real world closer through touch‐based interaction, the presented system will enrich user experience and enable advances in areas such as education, entertainment, gaming, retail, and museums where holograms are currently used.

Engineered three-dimensional (3D) tissues that replicate composite in-vivo architectures have shown great potential for use in biomedical research. Cell-encapsulated hydrogel micro-scaffolds have been applied widely as basic building blocks to construct these artificial tissues. However, accurate reproduction of heterogeneous hierarchical structures and different regional mechanical properties inside a single integrated micro-scaffold that mimics physiologically relevant complex tissues presents a major challenge. Here, we propose a novel fabrication control algorithm to achieve high-accuracy photolithography of micro-scaffolds that recapitulate the high fidelity of native tissues by adjusting a 3D digital mask using holographic imaging feedback. By performing digital holographic reconstruction to express the hydrogel photocuring process in a matrix form and presetting the curing duration for each discrete point, the 3D digital mask was predefined to represent the required customized micro-scaffold. During fabrication, the UV exposure area was divided into microscaled grids with relatively uniform irradiance to control the photocuring process discretely for every local region in the entire architecture. The holographic imaging feedback allowed the curing duration of each grid to be adjusted in real-time, which enabled accurate reproduction of a 3D construct integrated with different microstructural morphologies and mechanical properties. Finally, PEGDA and GelMA, as typical biomaterials, were used to fabricate the heterogeneous hierarchical micro-scaffold. The structural accuracy was improved from 65 m to 12 m and the Youngs modulus was controlled flexibly in the 27.93.5 to 91.23.5 kPa range. With different local mechanical properties, cell migration in the micro-scaffold from soft to stiff areas is observed successfully.

Reflection and refraction images are treated as the texture of the object in computer graphics, which brings wrong depth information when focusing on the object in holographic display. In this paper, a method of ray tracing rendering with complete depth information for computer-generated hologram(CGH) is proposed. Correct depths of reflection and refraction images are calculated, and layer-based method is used to generate CGH. In experiment result, our method truthfully reconstructs the complete depth information of complex scene. Reflection or refraction images and its corresponding media surfaces can be focused on correct depth. All layer data is computed in a single ray tracing procedure, and the generation speed of 1024×1024 CGH for 3D scene divided into 10 layers is 100fps.

For augmented reality applications, the micro display panels are generally used, as a straightforward method for display engines. But there are the light efficiency and vergence accommodation conflict problems, which affect the performance and application of the AR glasses, HMD and HUDs. One way to solve the problem is to use holography display instead of direct display, which exploit the diffraction light instead of reflection light of the liquid crystal panel. One of the big problems is the form factor of holographic systems which use SLM. Most of current SLMs are composed of a driver board with FPGA and a liquid crystal on silicon panel. The FPGA driver board is big and very power consuming, which makes it better for general SLM systems that cares more about changing the driving algorithm flexibly rather than make it a wearable gadget. A compact SLM system is designed specifically for AR applications, which replaced the normally used FPGA system with a driver IC and greatly reduce they whole system size and power consumption while realize the same function for holographic display. The driver IC could receive the RGB signal or MIPI signal and transform the standard picture signal to a high frame rate color sequential signal, also the gray scale could be tuned through on chip registers either beforehand or instantly, which makes it good for liquid crystals working in different wavelength. The driver board is 2*6 cm2 with a type-C connector which could easily transmit image data from a laptop or a cellphone. This form factor is almost the same with monocular glasses. The power consumption of the driver IC is around 250mW for the driver IC comparing to the normally 5W power of FPGAs. Also, the frame rate could be from 60 to 120 Hz. A simple Fourier holography optical system is used to demonstrate the holographic display, with a lens tear apart from a smart glass on the market. The 3D holographic is displayed in the lens.

Holographic displays enable the formation of a three-dimensional particle field distribution and is promised to be one solution of the key problems in present virtual and augmented reality displays. The biggest challenge in the computer-generated holography (CGH) is the high consuming calculation time and the restricted field of view due to the micro display screen. In order to solve the above mentioned problems, we propose a method for machine learning accelerated lensless holographic projection, which is based on the reconstruction of complex amplitude image from phase-only CGH. The runtime of generating the phase-only CGH is half of traditional iterative method. The complex amplitude image can achieve the maximum diffraction bandwidth of the spatial light modulator (SLM). The feasibility of this method is verified by experiments.

Three-dimensional (3D) light-field displays (LFDs) suffer from a narrow viewing angle, limited depth range, and low spatial information capacity, which limit their diversified application. Because the number of pixels used to construct 3D spatial information is limited, increasing the viewing angle reduces the viewpoint density, which degrades the 3D performance. A solution based on a holographic functional screen (HFS) and a ladder-compound lenticular lens unit (LC-LLU) is proposed to increase the viewing angle while optimizing the viewpoint utilization. The LC-LLU and HFS are used to create 160 non-uniformly distributed viewpoints with low crosstalk, which increases the viewpoint density in the middle viewing zone and provides clear monocular depth cues. The corresponding coding method is presented as well. The optimized compound lenticular lens array can balance between suppressing aberration and improving displayed quality. The simulations and experiments show that the proposed 3D LFD can present natural 3D images with the right perception and occlusion relationship within a 65° viewing angle.

The viewing-angle enlargement of a holographic image is a crucial factor for realizing the holographic display. The numerical aperture (NA) of digital hologram other than a pixel specification has been known to determine the angular field extent of image. Here, we provide a valid foundation for the dependence of viewing angle on the hologram numerical aperture by investigating mathematically the internal structure of the sampled point spread function showing a self-similarity of its modulating curves. The enhanced-NA Fresnel hologram reconstructs the images at a viewing angle larger than a diffraction angle by a hologram pixel pitch where its angle value is expressed in terms of the NA of whole hologram aperture, which is systematically observed by optical hologram imaging. Finally, we found that the aliased replica noises generated in the enhanced-NA Fresnel diffraction regime are effectively suppressed within the diffraction scope by a digitized pixel. This characteristic enables us to overcome the image reduction and to remove the interference of high-order images, which leads to the wide viewing-angle holographic display. Optical experiments are shown to be consistent with the results of numerical simulation., Comment: 29 pages, 10 figures

The autostereoscopic 3D display has two important indicators, both the number of viewpoints and display resolution. However, it's a challenge to improve both the viewpoint and the resolution. Here, we develop a fixed-position multiview and lossless resolution autostereoscopic 3D display system that includes the dynamic liquid crystal (LC) grating screen. This display system consists of an LC display panel and an LC grating screen. The synchronization of the frame switching of the LC display panel and the LC grating screen shutter enables the preserved resolution. The “eye space” design makes the viewpoint dense enough and determines the LC grating screen's parameters. We use binocular viewpoint tracking technology to realize the LC grating screen's adaptive control based on the above work. Different binocular views are rendered in real-time according to the different positions of a single pair of stereoscopic viewpoints in the eye space, making the motion parallax possible. We present the working principle and mathematical analysis. We implement a prototype for verifying the principle. According to the experiment results analysis, this prototype can achieve viewpoint tracking and motion parallax based on resolution lossless and viewpoint dense enough.

Computer-Generated Holography (CGH) algorithms simulate numerical diffraction, being applied in particular for holographic display technology. Due to the wave-based nature of diffraction, CGH is highly computationally intensive, making it especially challenging for driving high-resolution displays in real-time. To this end, we propose a technique for efficiently calculating holograms of 3D line segments. We express the solutions analytically and devise an efficiently computable approximation suitable for massively parallel computing architectures. The algorithms are implemented on a GPU (with CUDA), and we obtain a 70-fold speedup over the reference point-wise algorithm with almost imperceptible quality loss. We report real-time frame rates for CGH of complex 3D line-drawn objects, and validate the algorithm in both a simulation environment as well as on a holographic display setup.

Phase flicker can degrade the performance of holographic applications at the device and application levels. On the device side, the meaningful phase modulation resolution is proved to be limited by the overlapping between adjacent phase levels caused by flicker. Here, the tolerance of the overlapping for different modulation levels is provided. The frame rate of the device is also constrained by the phase flicker. The balance between low flicker and fast LC response for fast frame rate is quantitatively analyzed. On the application side, the effects of real phase flicker on the performance of blazed gratings and image holograms are investigated using the temporal phase flicker profiles measured from a phase-only liquid crystal on silicon (LCOS) device; they are shown to be comparable with that introduced by quantization level and amplitude noise, respectively.

Recently, cylindrical holographic display technology as a 360-degree display technology has attracted much attention. However, all the studies are based on the field of view (FOV) in the azimuth direction, and the issue of FOV in the vertical direction has never been discussed. In this paper, a new holographic display is proposed to expand the vertical FOV by a conical holographic diffraction model, in which the object plane is the outer cylinder and the observation plane is a part of the cone. In this proposed method, the proposed diffraction model is firstly established by the Rayleigh-Sommerfeld diffraction formula, and then the convolution and FFT are used for a fast diffraction calculation. The correctness and effectiveness of our proposed method are verified by the simulation of Young's interference and the numerical reconstructions from the complex amplitude and encoded holograms, respectively. In addition, an accurate relationship between the conical inclination angle and the vertical FOV expansion is analyzed, and the simulation results show that our proposed method can significantly expand the vertical FOV by 0.4 of the original object. Therefore, the issue of the vertical FOV in cylindrical holography is deeply discussed and successfully addressed for the first time.

This work exploits deep learning to develop real-time hologram generation. We propose an original concept of introducing hologram modulators to allow the use of generative models to interpret complex-valued frequency data directly. This new mechanism enables the pre-trained learning model to generate frequency samples with variations in the underlying generative features. To achieve an object-based hologram generation, we also develop a new generative model, named the channeled variational autoencoder (CVAE). The pre-trained CVAE can then interpret and learn the hidden structure of input holograms. It is thus able to generate holograms through the learning of the disentangled latent representations, which can allow us to specify each disentangled feature for a specific object. Additionally, we propose a new technique called hologram super-resolution (HSR) to super-resolve a low-resolution hologram input to a super-resolution hologram output. Combining the proposed CVAE and HSR, we successfully develop a new approach to generate super-resolved, complex-amplitude holograms for 3D scenes.

In this paper, potential distortions corresponding to the hologram printed by a holographic wave-front printer are analyzed. Potential distortions are classified as the magnification(demagnification) distortion, barrel distortion, pincushion distortion, SLM mounting distortion, and translation distortion, respectively. These distortions are grouped as the optics distortion, SLM mounting distortion and the translation distortion depending on the process of recording the hologram in the holographic wave-front printer. In order to evaluate each distortion, a distortion analysis method based on a local spatial frequency is proposed. Through the proposed method, a diffracted wavefield reconstructed from a quantitatively distorted hologram is theoretically analyzed, and the validity of this analysis is verified by applying the numerical reconstruction method. In the numerical reconstruction, a propagation of a distorted wavefield reconstructed from the quantitatively distorted hologram is confirmed and contributed to generate the distorted reconstruction plane, such as a focal cloud plane and a convergence plane, depending on the types of distortion.

Holographic display has the potential to be utilized in many 3D application scenarios because it provides all the depth cues that human eyes can perceive. However, the shortage of 3D content has limited the application of holographic 3D displays. To enrich 3D content for holographic display, a 2D to 3D rendering approach is presented. In this method, 2D images are firstly classified into three categories, including distant view images, perspective view images and close-up images. For each category, the computer-generated depth map (CGDM) is calculated using a corresponding gradient model. The resulting CGDMs are applied in a layer-based holographic algorithm to obtain computer-generated holograms (CGHs). The correctly reconstructed region of the image changes with the reconstruction distance, providing a natural 3D display effect. The realistic 3D effect makes the proposed approach can be applied in many applications, such as education, navigation, and health sciences in the future.

In this Letter, we introduce a computer-generated hologram (CGH) optimization technique that can control the randomness of the reconstructed phase. The phase randomness significantly affects the eyebox size and depth of field in holographic near-eye displays. Our proposal is to synthesize the CGH through the sum of two terms computed from the target scene with a random phase. We set a weighting pattern for summation as the optimization variable, which enables the CGH to reflect the random phase during optimization. We evaluate the proposed algorithm on single-depth and multi-depth contents, and the performance is validated via simulations and experiments.

A lensless full-color holographic Maxwellian near-eye display using a single amplitude-type spatial light modulator is proposed in this Letter. The color holographic image is directly projected onto the retina without any eyepiece. The color crosstalk is clearly separated from the signal in the space owing to the encoded spherical wave and carrier wave. An aperture numerical filter and a real polarized filter are used at the pupil plane to accurately stop the crosstalk light. A high-quality dynamic speckless color holographic image was produced in the mid-air within a specific depth range. The horizontal eyebox expansion is achieved simply through multiple spherical wave encoding and verified through an optical experiment. The proposed display is compact and promising as the augmented reality near-eye display.

In this paper, we propose a holographic near-eye 3D display method based on large-size computer-generated hologram (CGH). The reconstructed image with a large viewing angle is obtained by using a time multiplexing and spatial tiling system. The large-size CGHs are generated and they record the information of the 3D object from different angles. The CGHs are reproduced at different moments. For a certain reconstructed moment, three spatial light modulators (SLMs) spatially spliced into a linear structure are used to load a single CGH. The diffraction boundary angle of the reconstructed light forming each image point is equal to the maximum diffraction angle of the SLM, so the viewing angle of the image generated by the CGH is enlarged. For different CGHs, the incident angle of reconstructed light is changed. Through time multiplexing, the reconstructed images of the CGHs are combined into a reconstructed image whose viewing angle is further enlarged. Due to the large viewing angle of the reconstructed image, the proposed method has unique advantages in near-eye display. The feasibility of the proposed method is proved by experimental results.

The image generated by binary computer-generated holograms (CGHs) always suffers from serious speckle noise. Thanks to the fast frame rate of the binary spatial light modulator, the speckle can be significantly suppressed by intensity accumulation, i.e., the sequential display of multiple CGHs of the same scene. If enough randomness is added to the CGHs, the speckle noise can be mostly averaged out. Intuitively, the quality of the reconstructed image should be proportional to the number of intensity accumulation. However, there is no simple method to predict the dependence of the average noise and accumulation number, and we can only know the results after finishing the full computation. In this paper, we propose an empirical formula of the average noise based on the speckle phenomenon in a laser projector. Using this model, we have confirmed that the randomness induced by random phase is equivalent to that induced by random down-sampling for the generation of binary CGHs. In addition, if the computational efficiency is a concern, the CGH calculated with iterations is not recommended for intensity accumulation display. Finally, there is an upper-quality limit of the reconstructed image by intensity accumulation. Thus, a strategy for efficient intensity accumulation is suggested. Published version

The development of environmentally robust photosensitive materials for holographic recording is crucial for applications such as outdoor LED light redirection, holographic displays and holographic sensors. Despite the progress in holographic recording materials development, their sensitivity to humidity remains a challenge and protection from the environment is required. One approach to solving this challenge is to select substrate such as cellulose acetate, which is water resistant. This work reports the development of a cellulose-based photopolymer with sensitivity of 3.5 cm2/mJ and refractive index modulation of 2.5 × 10−3 achieved in the transmission mode of recording. The suitability for holographic recording was demonstrated by recording gratings with the spatial frequency of 800 linepairs/mm. The intensity dependence of the diffraction efficiency of gratings recorded in 70 μm thick layers was studied and it was observed that the optimum recording intensity was 10 mW/cm2. The robustness of the structures was studied after immersing the layer in water for one hour. It was observed that the diffraction efficiency and the surface characteristics measured before and after exposure to water remain unchanged. Finally, the surface hardness was characterized and was shown to be comparable to that of glass and significantly higher than the one of PVA-based acrylamide photopolymer.

Due to the large pixel pitch and limited size of spatial light modulator (SLM), the field of view (FOV) of current holographic display is greatly restricted. Cylindrical holography can effectively overcome the constraints of FOV. However, the existent algorithms of cylindrical hologram are all based on the wave-optics based approach. In this paper, to the best of our knowledge, we adopt the ray-optics based approach in the generation of cylindrical computer generated hologram (CCGH) for the first time. Information of parallax images captured from three-dimensional (3D) objects using a curved camera array is recorded into a cylindrical hologram. Two different recording specific algorithms are proposed, one is based on the Fast Fourier Transform (FFT) method, and another is based on the pinhole-type integral imaging (PII) method. The simulation results confirm that our proposed methods are able to realize a fast generation of the cylindrical photorealistic hologram.

Computer holography is a technology that use a mathematical model of optical holography to generate digital holograms. It has wide and promising applications in various areas, especially holographic display. However, traditional computational algorithms for generation of phase-type holograms based on iterative optimization have a built-in tradeoff between the calculating speed and accuracy, which severely limits the performance of computational holograms in advanced applications. Recently, several deep learning based computational methods for generating holograms have gained more and more attention. In this paper, a convolutional neural network for generation of multi-plane holograms and its training strategy is proposed using a multi-plane iterative angular spectrum algorithm (ASM). The well-trained network indicates an excellent ability to generate phase-only holograms for multi-plane input images and to reconstruct correct images in the corresponding depth plane. Numerical simulations and optical reconstructions show that the accuracy of this method is almost the same with traditional iterative methods but the computational time decreases dramatically. The result images show a high quality through analysis of the image performance indicators, e.g., peak signal-to-noise ratio (PSNR), structural similarity (SSIM) and contrast ratio. Finally, the effectiveness of the proposed method is verified through experimental investigations.

Speed and enhancement are the two most important metrics for anti-scattering light focusing by wavefront shaping (WS), which requires a spatial light modulator with a large number of modulation modes and a fast speed of response. Among the commercial modulators, the digital-micromirror device (DMD) is the sole solution providing millions of modulation modes and a pattern rate higher than 20 kHz. Thus, it has the potential to accelerate the process of anti-scattering light focusing with a high enhancement. Nevertheless, modulating light in a binary mode by the DMD restricts both the speed and enhancement seriously. Here, we propose a multi-pixel encoded DMD-based WS method by combining multiple micromirrors into a single modulation unit to overcome the drawbacks of binary modulation. In addition, to efficiently optimize the wavefront, we adopted separable natural evolution strategies (SNES), which could carry out a global search against a noisy environment. Compared with the state-of-the-art DMD-based WS method, the proposed method increased the speed of optimization and enhancement of focus by a factor of 179 and 16, respectively. In our demonstration, we achieved 10 foci with homogeneous brightness at a high speed and formed W- and S-shape patterns against the scattering medium. The experimental results suggest that the proposed method will pave a new avenue for WS in the applications of biomedical imaging, photon therapy, optogenetics, dynamic holographic display, etc.

In this paper, a holographic display system with wide viewing area is proposed based on the effective area expansion of the SLM. The effective area of the SLM is calculated based on the viewing area characteristics and expanded by using two SLMs. Different from the traditional holographic system based on the parallel-arranged SLMs or curved-arranged SLMs, we calculate the effective areas of the SLMs and the effective hologram of the system can be generated based on the effective-viewing-area (EVA) algorithm. The proposed system uses a 4K SLM by seamlessly stitching the effective areas of two 2K SLMs. After the EVA is calculated, the size of the effective hologram is inversely calculated according to the EVA. So, the effective area of the hologram is increased, and the calculation of the wasted information is greatly decreased. With the proposed system, the reconstructed object with large viewing area can be realized. Moreover, the calculation time for generating the hologram is reduced significantly. Experimental results verify the feasibility of the proposed system. In the proposed system, the 2K SLMs are used as examples for splicing, when more high-performance SLMs are used, the viewing area will be further expanded, and the advantage of the calculation speed will be more obvious than the traditional splicing method. The proposed system can provide new references to the holographic display system based on multiple SLMs stitching.

Near-eye displays using holographic projection are emerging as an exciting display approach for virtual and augmented reality at high-resolution without complex optical setups --- shifting optical complexity to computation. While precise phase modulation hardware is becoming available, phase retrieval algorithms are still in their infancy, and holographic display approaches resort to heuristic encoding methods or iterative methods relying on various relaxations. In this work, we depart from such existing approximations and solve the phase retrieval problem for a hologram of a scene at a single depth at a given time by revisiting complex Wirtinger derivatives, also extending our framework to render 3D volumetric scenes. Using Wirtinger derivatives allows us to pose the phase retrieval problem as a quadratic problem which can be minimized with first-order optimization methods. The proposed Wirtinger Holography is flexible and facilitates the use of different loss functions, including learned perceptual losses parametrized by deep neural networks, as well as stochastic optimization methods. We validate this framework by demonstrating holographic reconstructions with an order of magnitude lower error, both in simulation and on an experimental hardware prototype.

In this paper, we present a concept for speckle reduction using optical superposition instead of temporal superposition. The proposed speckle reduction method does not contain any mechanical movement nor time-multiplexing technique. Therefore, the system is stable and free from the frame rate degradation or additional computation load. In addition, the angle diversity method is adopted with the proposed method to intensify the speckle reduction. In order to apply the angle diversity method, the required minimum angle difference is analyzed theoretically. To realize the proposed speckle reduction concept, the system is implemented with practical optical components. The system includes an echelon, which is a stair-shaped glass and a static diffuser. The echelon is employed to decrease the spatial coherence of the incident beam. The static diffuser imposes the band-limited random phases on each of the split beams that have passed through the echelon. Also, the static diffuser is used to combine mutually incoherent split beams into a single speckle-reduced beam. The proposed speckle-reduced light source is applied to the holographic display to demonstrate the speckle reduction effect. Experimental results show that the speckle contrast of the reconstructed image is reduced by 55%.

We propose an approach for simultaneously shaping multiple three dimensional (3D) vector curve beams. The intensity distribution and polarization state variation of each 3D vector curve beam can be tuned along arbitrary prescribed trajectories. The scheme is based on the coaxial superposition of the orthogonally polarized 3D base vector curve beams through non-iterative holographic 3D beam shaping technique. In particular, the hybrid 3D vector curve beams array is also generated with identical depth range. The transversal position of each vector beam can be governed independently. Moreover, the multiplexing of 3D vector beams is realized with different depth ranges in the focal region along the beam propagation. The numerical results are identical to the experiments. This method will be benefit to the trapping and transportation of particles.

The use of Holographic or Diffractive optics is on the rise, premium DSLR optics using this technology is an outstanding example of compact device. This technology applied to head-up display (HUD) is presented, using the windshield as a transparent holographic display, with the ability to present floating graphical object in a large field of view. Augmented Reality display will be possible, increasing considerably the User Experience and situational awareness. Additionally, the use of Holographic Optical Element reduces the size, weight and cost of the actual HUD box.

The addition of a random phase is widely utilised to diffuse object information in computer-generated hologram calculations. However, different object regions have nonuniform initial information diffusion abilities. The conventional random phase addition method always causes the excessive diffusion of information, especially for high frequency regions, which influences the reconstructed quality. In this paper, a gradient-limited random phase addition method is developed to avoid excessively diffusing object information. Herein, an image is segmented into two regions according to its frequency characteristics. Correspondingly, wide and narrow optimum ranges of a limited random phase are provided for low and high frequency regions, respectively. The numerical simulation results show that the peak signal-to-noise ratio and structural similarity index of reconstructed images increase by approximately 10% and 13%, respectively. The resolution of the reconstructed test image is improved by approximately 2 line pairs. Additionally, using in time-average method reduces the superposition number. Optical experiments are also performed to verify its feasibility.

Holography as a true three-dimensional (3-D) technique is thought to be the ultimate display technique. However, dynamic holographic materials still have problems such as slow refresh, high applied electrical field, etc., to be solved to realize video-rate 3-D display. We present silver nanoparticles (Ag NPs) doped liquid crystal films with very big birefringence and super-fast hologram refresh speed as real-time dynamic holographic medium, which can be applied in holographic video display. And the fastest response time of both build-up and self-erasure of hologram can be up to 0.1 ms, which means the material has the ability to realize a smooth holographic video-rate display. The holographic diffraction efficiency dependent on the intensity of recording light, applied electrical field, etc. is investigated. The maximum diffraction efficiency is measured up to 50% under a low applied electrical field of 0.12 V/ $\mu$ m. Real-time holographic videos at red, green, and blue colors are obtained and the process of hologram formation is analyzed, which shows that the LC films doped Ag NPs can be a good candidate for applications of large-size, real-time, color holographic true 3-D display in future.

Background Due to the restriction of display mode, in most of the virtual reality systems with multiple people in the same physical space, the program renders the scene based on the position and perspective of the one user, so that other users just see the same scene, resulting in vision disorder. Methods To improve experience of multi-user co-located collaboration, in this study, we propose a fire drill system supporting co-located collaboration, in which three co-located users can collaborate to complete the virtual firefighting mission. Firstly, with multi-view stereoscopic projective display technology and ultra wideband (UWB) technology, co-located users can roam independently and watch virtual scenes through the correct perspective view based on their own position by wearing dedicated shutter glasses, thus carrying out different virtual tasks, which improves the flexibility of co-located collaboration. Secondly, we design simulated firefighting water-gun using the micro-electromechanical system sensor, through which users can interact with virtual environment, and thus provide a better interactive experience. Finally, we develop a workbench including a holographic display module and multi-touch operation module for virtual scene assembly and virtual environment control. Results The controller can use the workbench to adjust the virtual layout in real time, and control the virtual task process to increase the flexibility and playability of system. Conclusions Our work can be employed in a wide range of related virtual reality applications. Keywords: Virtual reality, Co-located collaboration, Multi-view display, Ultra wideband, Simulated firefighting water-gun

In the point-based method, the aliasing phenomenon in the hologram plane is usually considered as a harmful phenomenon because it will degrade the reconstructed image quality. In this paper, the advantage of the aliasing phenomenon is employed to improve the reconstructed image quality of the phase-only hologram. Through analysis of the principle of this phenomenon, we proposed a method to improve the reconstructed image quality of the phase-only hologram. By controlling the strength of the aliasing, the amplitude distribution in the hologram plane can be turned into a nearly uniform distribution. It is helpful to generate an optimized phase-only hologram, which results in higher quality of the reconstructed image because the effect of lost information caused by abandon the amplitude part can be diminished. Moreover, a holographic see-through display system is designed to demonstrate the effectiveness of the proposed method.