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3D display technology offers a more realistic visual experience by allowing users to perceive depth and spatial awareness, enhancing interactivity and immersion. Among various approaches, multiview display technology constructs 3D images by offering multiple smooth views along the horizontal plane. Metasurfaces, with ultra‐thin physical structures and flexible functional designs, are positioned to make significant contributions to the evolution of 3D display technologies. Here, a 3D multiview holographic display system based on metasurfaces is proposed. Using generalized Snell's law, a spatially multiplexed metasurface is designed with nine views and achieves 3D display by cascading the metasurface with a spatial light modulator (SLM). By projecting holograms onto different areas of the metasurface via the SLM, corresponding reconstructed images can be observed from specific designed directions. Thanks to the large numerical aperture (NA) of the metasurface, the system successfully achieves nine views within a 120° field of view (FOV, with a theoretical maximum of 180°), validated experimentally. This system promises potential applications in VR/AR display, surgical navigation, geographic information system (GIS), and other fields. [ABSTRACT FROM AUTHOR]

A single‐panel complex holographic display with a three‐phase covalent macropixel featuring ultralow noise and high‐efficiency 3D image generation is proposed. The essential feature of the proposed three‐phase covalent macropixel is the point‐symmetric covalent concatenation of sub‐pixels and an adaptive computer‐generated hologram encoding algorithm. The proposed single‐panel holographic display exhibits three times signal efficiency enhancement, 1/38 reduction of DC noise, and 1/50 reduction of conjugate noise compared to conventional holographic displays in the generation of full‐color computer‐generated hologram images. This noise reduction leads to three times the optical efficiency enhancement of holographic displays. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shenzhen University Science & Engineering is the property of Editorial Department of Journal of Shenzhen University Science & Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Augmented reality (AR) technology has been widely applied across a variety of fields, with head-up displays (HUDs) being one of its prominent uses, offering immersive three-dimensional (3D) experiences and interaction with digital content and the real world. AR-HUDs face challenges such as limited field of view (FOV), small eye-box, bulky form factor, and absence of accommodation cue, often compromising trade-offs between these factors. Recently, optical waveguide based on pupil replication process has attracted increasing attention as an optical element for its compact form factor and exit-pupil expansion. Despite these advantages, current waveguide displays struggle to integrate visual information with real scenes because they do not produce accommodation-capable virtual content. In this paper, we introduce a lensless accommodation-capable holographic system based on a waveguide. Our system aims to expand the eye-box at the optimal viewing distance that provides the maximum FOV. We devised a formalized CGH algorithm based on bold assumption and two constraints and successfully performed numerical observation simulation. In optical experiments, accommodation-capable images with a maximum horizontal FOV of 7.0 degrees were successfully observed within an expanded eye-box of 9.18 mm at an optimal observation distance of 112 mm. [ABSTRACT FROM AUTHOR]

We clarified that a ferroelectric liquid crystal (FLC) has high resolution display capability as small as 1 × 1 μm pixel pitch using an FLC pixel array with a two‐layer electrode, which has a 1 × 1‐μm‐checkered apertured electrode and a plane electrode separated by an insulation layer. By applying +2 V to the apertured electrode and −10 V to the plane electrode in the two‐layer electrode and 0 V to the transparent common electrode, a checkered pattern was clearly observed, which indicates the successful individual pixel driving with a pixel pitch of 1 × 1 μm. When fabricating 1 × 2‐μm‐pitch rectangular FLC pixels, we elucidated that the liquid crystal alignment direction should be along the shorter side of the pixels to avoid asymmetric transmittance distribution in each pixel. Moreover, we successfully reconstructed a 3D holographic image using 10 × 10 k FLC pixel array with a pitch of 1 × 1 μm driven by the two‐layer electrode with hologram‐patterned apertures. We showed that FLC is a strong candidate material for realizing spatial light modulator with extremely small pixel pitches, which is essential for holographic displays with wide‐viewing‐zone angles. [ABSTRACT FROM AUTHOR]

To facilitate the practical application of wearable holographic near‐eye displays, the propagation between non‐parallel planes is essential for the hologram generation of off‐axis projection onto the holographic‐optical‐element (HOE) based combiners. However, existing methods, particularly the angular spectrum rotation‐based approach for generating tilted plane holograms, encounter challenges such as gradient loss when integrated with the stochastic gradient descent (SGD) algorithm. In this paper, we present a novel method for generating a tilted plane hologram using multi‐depth‐SGD, effectively mitigating the gradient loss issue. [ABSTRACT FROM AUTHOR]

Fast‐switching high‐efficiency liquid crystal grating is a key component in holographic true‐3D display systems. In this paper, we present our research and development of a 10.7" liquid crystal grating with 2‐3 millisecond switching time, close‐to‐ideal deflection efficiency, and >100 polarization contrast. The high performance is achieved by optimizing the design and process of the liquid crystal grating panel as well as the optical module stack. Several key design principles are analyzed and verified. Based on the developed liquid crystal grating, a 10.4" full‐color naked‐eye holographic 3D display prototype is successfully realized. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Liquid Crystal & Displays is the property of Chinese Journal of Liquid Crystal & Displays and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the development of the information industry, the wearable three‐dimensional (3D) near‐eye display that can provide complete visual information has attracted increasing attention. Compared with other existing 3D display technologies, the holographic display is a promising true 3D display technology that can fully record and reproduce the original 3D scenes. The ability to present a continuous parallax and depth perception gives holography technology an unprecedented promise in the next‐generation 3D near‐eye display. However, currently available holographic near‐eye display systems can only provide a limited viewing area (including the field of view and eyebox), greatly restricting its practical application. Focusing on the development requirements of large viewing‐area 3D holographic near‐eye display, the reasons are introduced first why the viewing area of current holographic displays is limited and then the existing solutions from different aspects, including multiplexing‐based methods, steering viewing window methods, aperiodic wavefront modulation methods, and some emerging holographic display technologies are summarized. These various solutions are analyzed respectively, and their representative works are investigated. In addition, the different applications of holography in the near‐eye display system are also discussed. Finally, the advantages and disadvantages of these techniques are compared and perspectives are given. [ABSTRACT FROM AUTHOR]

The Maxwellian display presents always‐focused images to the viewer, alleviating the vergence‐accommodation conflict (VAC) in near‐eye displays (NEDs). However, the limited eyebox of the typical Maxwellian display prevents it from wider applications. We propose a large FOV holographic Maxwellian display system and develop a new eyebox expansion method simultaneously. The system utilizes the special structure of the grating to provide secondary diffraction of the reconstructed image. The lens behind the grating is able to converge the reconstructed images of different diffraction orders at certain intervals of the point of view, which realizes a large FOV and extends the exit pupil size at the same time. [ABSTRACT FROM AUTHOR]

We propose a holographic near‐eye display system incorporating holographic optical elements. In our design, a holographic optical element is used to replace the traditional eyepiece as a combiner for holographic near‐eye display, a tilted‐plane diffraction propagation algorithm is used to optimize the holograms, and finally an Augmented Reality near‐eye display based on the holographic optical element is realized, and the wearing scheme is demonstrated. [ABSTRACT FROM AUTHOR]

Holographic display enabled by performing both amplitude modulation (AM) and phase modulation (PM) in a single Liquid Crystal on Silicon (LCoS)‐based Spatial Light Modulator (SLM) is introduced. Light propagation is manipulated in two different directions to perform both AM and PM via liquid crystals alignment layer which can be based on technologies by using photoalignment, nano‐imprint lithography (NIL), or unique over‐driving across Liquid Crystal (LC) layer of Vam‐Vpm method which are described and proved to be effective to tune incident light, control the polarization and propagation of the light entering the liquid crystals of a single LCoS‐based SLM (LCoS‐SLM) device. These methods enable holographic display and to alleviate the issues in using two separated SLMs trying to achieve the same. Further, the design techniques and methods to suppress adjacent pixels' crosstalk due to fringe field effect (FFE) [1] in 2D array are amenable to ensure higher resolution with pixel pitch down to 1¼m for compact size and higher pixel numbers beyond 8K×4K. It mitigates to reduce chores of pixel‐to‐pixel alignment, and to enhance image clarity and quality within a single LCoS‐SLM. It will be applicable to enable holographic display with such unique LCoS‐SLM particularly for AR/VR/MR smart glasses applications [18] [19] [20] once being fabricated in the future. [ABSTRACT FROM AUTHOR]

In holographic three-dimensional (3D) display, phase-only spatial light modulators (SLMs) can only accept pure phase modulation signals, often leading to amplitude distortion in the reconstructed image and inaccurate object reconstruction. This paper presents a new modulating phase encoding method with amplitude compensation. Based on the imaging characteristics of phase digital holograms, the object light amplitude variation is extended to the nonlinear region of the first-order Bessel function to maximize the intensity of the reconstructed 3D image. The amplitude distortion of the reconstructed image is effectively eliminated by pre-distortion treatment of the light amplitude. Numerical simulations and optical experiments validate the presented method.

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.

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. [ABSTRACT FROM AUTHOR]

Complex RGB spatial light modulators are required to produce full-color holographic displays. In particular, complex spatial light modulation, which modulates the amplitude and phase of incident light is essential for noiseless dynamic computer-generated hologram synthesis. The feasibility of full-color holographic image generation through the dual-layer in-plane switching liquid crystal plane is theoretically validated and experimentally demonstrated. [ABSTRACT FROM AUTHOR]

Despite massive advancements in the telecommunications industry over the last few decades, telepresence video-based teleconferencing is still far from giving a physical co-presence experience. Applications like Skype, Zoom and WebEx are constrained as it is only able to display the head and shoulders of the users on one monitor. It offers the user flat two-dimensional (2D) upper body imageries, a fixed viewpoint, inconsistent gaze direction, and restriction. Therefore, the problem arises when video-based teleconferencing is unable to support effective communication in telepresence. Thus, this research aims to propose life-size telepresence by using a projector-based holographic display. To actualize the aim, there are three phases have been proposed in this research. The first phase is to enable the tracking technique using the Kinect sensor. The second phase is to enable networking using Agora.io. The last phase is to set up the holographic display using a projector before the evaluation phase. Based on the evaluation results, the life-size telepresence using holographic display application has succeeded in achieving the project aim and shown the life-size display increases the co-presence experience of the users and increases the efficient communication between the users. [ABSTRACT FROM AUTHOR]

Augmented reality (AR) technology has been widely applied across a variety of fields, with head-up displays (HUDs) being one of its prominent uses, offering immersive three-dimensional (3D) experiences and interaction with digital content and the real world. AR-HUDs face challenges such as limited field of view (FOV), small eye-box, bulky form factor, and absence of accommodation cue, often compromising trade-offs between these factors. Recently, optical waveguide based on pupil replication process has attracted increasing attention as an optical element for its compact form factor and exit-pupil expansion. Despite these advantages, current waveguide displays struggle to integrate visual information with real scenes because they do not produce accommodation-capable virtual content. In this paper, we introduce a lensless accommodation-capable holographic system based on a waveguide. Our system aims to expand the eye-box at the optimal viewing distance that provides the maximum FOV. We devised a formalized CGH algorithm based on bold assumption and two constraints and successfully performed numerical observation simulation. In optical experiments, accommodation-capable images with a maximum horizontal FOV of 7.0 degrees were successfully observed within an expanded eye-box of 9.18 mm at an optimal observation distance of 112 mm.

A super multi-view (SMV) near-eye display (NED) effectively provides depth cues for three-dimensional (3D) display by projecting multiple viewpoint or parallax images onto the retina simultaneously. Previous SMV NED have suffered from a limited depth of field (DOF) due to a fixed image plane. In this paper, a holographic SMV Maxwellian display based on depth segmentation is proposed to enhance the DOF. The proposed approach involves capturing a set of parallax images and their corresponding depth maps. According to the depth maps, the parallax images are segmented into N sub-parallax images at different depth ranges. These sub-parallax images are then projected onto N image-recording planes (IRPs) of the corresponding depth for hologram computation. The wavefront at each IRP is calculated by multiplying the sub-parallax images with the corresponding spherical wave phases. Then, they are propagated to the hologram plane and added together to form a DOF-enhanced hologram. The simulation and experimental results are obtained to validate the effectiveness of the proposed method in extending the DOF of the holographic SMV displays, while accurately preserving occlusion. [ABSTRACT FROM AUTHOR]

In this paper, a fast hologram calculation method based on wavefront precise diffraction is proposed. By analyzing the diffraction characteristics of the object point on the 3D object, the effective viewing area of the reproduced image is analyzed. Based on the effective viewing area, the effective hologram size of the object point is obtained, and then the accurate diffraction calculation from the object point to the wavefront recording plane (WRP) is performed. By calculating all the object points on the recorded object, the optimized WRP of the whole 3D object can be obtained. The final hologram is obtained by calculating the diffraction light field from the WRP to the holographic plane. Compared with the traditional method, the proposed method can improve the calculation speed by more than 55%, while the image quality of the holographic 3D display is not affected. The proposed calculation method provides an idea for fast calculation of holograms and is expected to contribute to the development of dynamic holographic displays. [ABSTRACT FROM AUTHOR]

Holographic display has attracted widespread interest because of its ability to show the complete information of the object and bring people an unprecedented sense of presence. The absence of ideal recording materials has hampered the realization of their commercial applications. Here we report that the response time of a bismuth and magnesium co-doped lithium niobate (LN:Bi,Mg) crystal is shortened to 7.2 ms and a sensitivity as high as 646 cm/J. The crystal was used to demonstrate a real-time holographic display with a refresh rate of 60 Hz, as that of the popular high-definition television. Moreover, the first-principles calculations indicate that the electron mobility while Bi occupying Nb-site is significantly greater than that in Li-site, which directly induces the fast response of LN:Bi,Mg crystals when the concentration of Mg is above its doping threshold.

Analytical polygon‐based computer‐generated holography (CGH) is promising because of its fast rendering speed. However, quadrilateral‐based full‐analytical CGH is infeasible. In this paper, we proposed a novel analytical CGH rendering method for quadrilateral meshes, which is compatible with modern modeling software and can simultaneously reduce the rendering load. [ABSTRACT FROM AUTHOR]

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

In this paper, we propose a method to generate multi-depth phase-only holograms using stochastic gradient descent (SGD) algorithm with weighted complex loss function and masked multi-layer diffraction. The 3D scene can be represented by a combination of layers in different depths. In the wave propagation procedure of multiple layers in different depths, the complex amplitude of layers in different depths will gradually diffuse and produce occlusion at another layer. To solve this occlusion problem, a mask is used in the process of layers diffracting. Whether it is forward wave propagation or backward wave propagation of layers, the mask can reduce the occlusion problem between different layers. Otherwise, weighted complex loss function is implemented in the gradient descent optimization process, which analyzes the real part, the imaginary part, and the amplitude part of the focus region between the reconstructed images of the hologram and the target images. The weight parameter is used to adjust the ratio of the amplitude loss of the focus region in the whole loss function. The weight amplitude loss part in weighted complex loss function can decrease the interference of the focus region from the defocus region. The simulations and experiments have validated the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A digital micromirror device (DMD) has a wide range of applications in holographic display, light field manipulation, etc., due to its high-speed refresh rates. In order to precisely control the wavefront, the influence of the micromirror array structure of the DMD requires careful analysis. Based on an accurate three-dimensional phase model of DMD, we analyzed the diffraction characteristics of DMD. The model was established by accurately describing the phase distribution along each micromirror surface direction, and the distance between the point on the micromirror and the diffraction plane. The results showed that the orders of the DMD are the results of two groups of micromirrors interfering with each other, and a slight offset occurs when the incidence angle is twice the micromirror tilt angle, which can be removed by adjusting the incidence angle. The phase distribution results showed the main order of the DMD with all micromirrors in the on state can be approximated as a plane wave, which means that the hologram can be normally loaded on the DMD without worrying about phase disturbance from the micromirror array structure. This provides great convenience for computer holography based on DMD. Numerical simulations and experiments demonstrated the effectiveness of the work. [ABSTRACT FROM AUTHOR]

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

Limited by the low space-bandwidth product of the spatial light modulator (SLM), it is difficult to realize multiview holographic three-dimensional (3D) display. To conquer the problem, a method based on the holographic optical element (HOE), which is regarded as a controlled light element, is proposed in the study. The SLM is employed to upload the synthetic phase-only hologram generated by the angular spectrum diffraction theory. Digital grating is introduced in the generation process of the hologram to achieve the splicing of the reconstructions and adjust the position of the reconstructions. The HOE fabricated by the computer-generated hologram printing can redirect the reconstructed images of multiview into multiple viewing zones. Thus, the modulation function of the HOE should be well-designed to avoid crosstalk between perspectives. The experimental results show that the proposed system can achieve multiview holographic augmented reality (AR) 3D display without crosstalk. The resolution of each perspective is 4K, which is higher than that of the existing multiview 3D display system. [ABSTRACT FROM AUTHOR]

Holographic displays have the promise to be the ultimate 3D display technology, able to account for all visual cues. Recent advances in photonics and electronics gave rise to high-resolution holographic display prototypes, indicating that they may become widely available in the near future. One major challenge in driving those display systems is computational: computer generated holography (CGH) consists of numerically simulating diffraction, which is very computationally intensive. Our goal in this paper is to give a broad overview of the state-of-the-art in CGH. We make a classification of modern CGH algorithms, we describe different algorithmic CGH acceleration techniques, discuss the latest dedicated hardware solutions and indicate how to evaluate the perceptual quality of CGH. We summarize our findings, discuss remaining challenges and make projections on the future of CGH.

In the field of holographic displays, achieving a large viewing angle (LVA) has long been an essential and formidable challenge due to the limited diffraction angle of planar spatial light modulators (SLMs). Spherical holography, which allows observation from all perspectives, represents a practical approach to achieve the LVA. However, the physical limitations of commercial SLMs constrain direct implementation, making the realization of spherical holographic displays almost impractical and thus hindering technological advancement. This paper introduces an optical solution for spherical holographic display system, enabling the accurate reproduction of ultra-wide viewing angles and large objects. Our system utilizes a novel technique involving a convex parabolic mirror to convert an incident plane wave into a spherical wave. This innovative strategy permits the use of a planar SLM to create a 360°spherical holographic display. Additionally, we address the sampling issue for generating spherical holograms by constraining the point spread function (PSF), reducing the number of samples, and adapting it for visible light. Numerical simulations and optical experiments validate our success in achieving an ultra-wide viewing angle with a 360°horizontal angle and an 80°zenith angle range. Our system outperforms the state-of-the-art holographic-optical-elements approach both in computation speed and object size. We believe that our work significantly advances spherical holographic displays and offers a practical solution with vast potential applications in medicine, geology, and astronomy. • We have achieved an optical spherical holographic display with an ultra-wide viewing angle of 360°horizontal and 80°zenith angle range. • Our system outperforms state-of-the-art holographic optical component methods in terms of computational speed and object size. • Holograms are generated 21 times faster than before, and reconstruction radii can be 20 mm or larger. [ABSTRACT FROM AUTHOR]

• A new non-zero filling method for designing holograms is proposed to avoid the influence of multi-level diffraction images and zero-order spots during the reconstruction of LC-SLM hologram. • Simulation and experiments show that the proposed method has higher quality holographic display results than the original zero filling method for 2D and 3D displays. • This method can obtain high quality 2D and 3D holographic reconstruction results, and provides a new method for high quality holographic display. A new non-zero filling method is proposed to avoid the influence of zero-level spot and multilevel diffraction images mixed on the target reproduced image due to the structure of LC-SLM used for holographic display. This method can reduce the difficulty of phase recovery due to zero filling by padding non-zero values around the target image, leading to high-quality holograms. Finally, by simulation and experimental verification of 2D and 3D holography, the results are compared, and it found that this method can improve the quality of holographic display while avoiding the influence of LC-SLM's structure. It provides a method for the phase recovery of high-quality CGH design. [ABSTRACT FROM AUTHOR]

The Maxwellian display presents always-focused images to the viewer, alleviating the vergence-accommodation conflict (VAC) in near-eye displays (NEDs). However, the limited eyebox of the conventional Maxwellian display prevents it from wider applications. In this paper, an exebox-extended holographic Maxwellian near-eye display is proposed by using a real grating and a virtual grating. A diffraction grating is used to duplicate multiple beams and produce duplicate viewpoints. A virtual grating phase is added in the hologram to steer the beams and deflect the viewpoints. The proposed method combines a slight steering with a large duplicated eyebox, realizing that the viewpoint position can be flexibly controlled. The optical experiment realizes a 49.2° FOV and 12.1 mm eyebox which contains 5 moveable viewpoints. This proposed system shows good display capabilities and has potential applications. • The proposed method combines a slight steering with a large duplicated eyebox, realizing that the viewpoint position can be flexibly controlled. • The optical experiment realizes a 49.2° FOV and 12.1 mm eyebox which contains 5 moveable viewpoints. [ABSTRACT FROM AUTHOR]

Futuristic holographic displays will essentially require broadband chiro‐optical effects for medical imaging, virtual reality, smart security, and optical encryption. However, conventional metasurfaces cannot provide such on‐chip realization of broadband chiro‐optical effects. Moreover, the simultaneous conversion of amplitude, polarization, and phase (APP) at optical wavelengths to introduce giant chirality has not been realized yet. In this paper, a planar all‐dielectric metasurface is proposed incorporating extra degrees of freedom to comprehend the conversion of APP with broadband chiro‐optical effects in terms of giant asymmetric transmission with maximum efficiency of ≈77% at the wavelength of 567 nm. The underlying mechanism behind induced chiro‐optical effects is also investigated using higher‐order multipolar dielectric resonances. Moreover, experimental validation is performed using the reproduced polarization‐encrypted meta‐holograms at broadband visible wavelengths. This work expands the scope of meta‐nanophotonics with potential applications in bioimaging and polarization‐encrypted displays for healthcare and smart security applications. [ABSTRACT FROM AUTHOR]

We propose an efficient method for synthesizing mesh-based realistic computer-generated hologram (CGH). In a previous nonanalytic mesh-based CGH synthesis, the angular spectrum of the two-dimensional (2D) plane is calculated using the fast Fourier transform (FFT) with the same size as the resolution of the final hologram. Because FFT increases the computation time as the size of the input matrix increases, the previous method has a problem: The higher the resolution of the hologram, the greater the computational load, thereby delaying synthesis time. In this study, when calculating the angular spectrum of the 2D plane in mesh-based CGH synthesis, we propose a method to calculate the angular spectrum by defining the 2D plane with an arbitrary size smaller than the resolution of the final hologram. The resolution adjustment method reduces the computation time and can be applied to occlusion culling and texturing for the realistic effect of mesh-based CGH. We describe the principle, error analysis, application of realistic effect, and experimental results of the proposed method.

In this paper, a fast hologram calculation method based on wavefront precise diffraction is proposed. By analyzing the diffraction characteristics of the object point on the 3D object, the effective viewing area of the reproduced image is analyzed. Based on the effective viewing area, the effective hologram size of the object point is obtained, and then the accurate diffraction calculation from the object point to the wavefront recording plane (WRP) is performed. By calculating all the object points on the recorded object, the optimized WRP of the whole 3D object can be obtained. The final hologram is obtained by calculating the diffraction light field from the WRP to the holographic plane. Compared with the traditional method, the proposed method can improve the calculation speed by more than 55%, while the image quality of the holographic 3D display is not affected. The proposed calculation method provides an idea for fast calculation of holograms and is expected to contribute to the development of dynamic holographic displays.

A super multi-view (SMV) near-eye display (NED) effectively provides depth cues for three-dimensional (3D) display by projecting multiple viewpoint or parallax images onto the retina simultaneously. Previous SMV NED have suffered from a limited depth of field (DOF) due to a fixed image plane. In this paper, a holographic SMV Maxwellian display based on depth segmentation is proposed to enhance the DOF. The proposed approach involves capturing a set of parallax images and their corresponding depth maps. According to the depth maps, the parallax images are segmented into N sub-parallax images at different depth ranges. These sub-parallax images are then projected onto N image-recording planes (IRPs) of the corresponding depth for hologram computation. The wavefront at each IRP is calculated by multiplying the sub-parallax images with the corresponding spherical wave phases. Then, they are propagated to the hologram plane and added together to form a DOF-enhanced hologram. The simulation and experimental results are obtained to validate the effectiveness of the proposed method in extending the DOF of the holographic SMV displays, while accurately preserving occlusion.

With the explosive developments of deep learning, learning–based computer–generated holography (CGH) has become an effective way to achieve real–time and high–quality holographic displays. Plentiful learning–based methods with various deep neural networks (DNNs) have been proposed. In this paper, we focus on the rapid progress of learning–based CGH in recent years. The generation principles and algorithms of CGH are introduced. The DNN structures frequently used in CGH are compared, including U–Net, ResNet, and GAN. We review the developments and discuss the outlook of the learning–based CGH. [ABSTRACT FROM AUTHOR]

Holographic displays have gained unprecedented attention as next-generation virtual and augmented reality applications with recent achievements in the realization of a high-contrast image through computer-generated holograms (CGHs). However, these holograms show a high energy concentration in a limited angular spectrum, whereas the holograms with uniformly distributed angular spectrum suffer from a severe speckle noise in the reconstructed images. In this study, we claim that these two physical phenomena attributed to the existing CGHs significantly limit the support of accommodation cues, which is known as one of the biggest advantages of holographic displays. To support the statement, we analyze and evaluate various CGH algorithms with contrast gradients - a change of contrast over the change of the focal diopter of the eye - simulated based on the optical configuration of the display system and human visual perception models. We first introduce two approaches to improve monocular accommodation response in holographic viewing experience; optical and computational approaches to provide holographic images with sufficient contrast gradients. We design and conduct user experiments with our prototype of holographic near-eye displays, validating the deficient support of accommodation cues in the existing CGH algorithms and demonstrating the feasibility of the proposed solutions with significant improvements on accommodative gains. [ABSTRACT FROM AUTHOR]

• A method of generating phase-only hologram of binary image based on deep learning was proposed. • The global loss training strategy was used to enhance the global learning ability of neural networks. • The stochastic homogenization training strategy was used to improve the learning efficiency of binary image features. Deep learning presents a highly effective for computer-generated holography (CGH). However, existing learning-based CGH algorithms may encounter significant obstacles in generating high-quality holograms for binary images. This study proposes a novel diffraction model-driven neural network, termed load sharing yielding holography (LSY-Holo), which leverages a dual-branch architecture and a global structural similarity index measure (Global_SSIM) loss function to generate phase-only holograms (POHs). LSY-Holo framework facilitates capturing global information, enhancing the network's performance to address the ill-posed inverse problem. To further optimize the model for binary images, the research introduces a custom Binary dataset alongside a stochastic homogenization preprocessing method (SHPM), which mitigates the prevalent issue of excessive noise in reconstructed images. Additionally, this deep learning approach is integrated with an iterative algorithm, which employs holograms rapidly generated by LSY-Holo as the initial phase of the AdamW Holography (AH) algorithm. This strategy significantly accelerates the convergence of the iterative process. LSY-Holo is further extended to 3D scenes, enabling dynamic defocusing and focusing effects at varying depths. Results from numerical simulations and full-color optical reconstruction experiments demonstrate that the proposed method can enhance image quality and effectively reduce the artifacts in reconstructed images. [ABSTRACT FROM AUTHOR]

Spherical holography technology, a 3D display technology with the advantage of an infinite viewing zone and 360°observation, has received widespread attention. However, the quality of existing computer-generated spherical holograms is limited. To address this issue, we propose a Pre-compensated annealing gradient descent method (PAGD) to quickly obtain spherical holography. Compared to traditional SGD algorithms, the PAGD algorithm significantly improves convergence speed. The annealed gradient descent helps avoid local optima during the optimization process, while pre-compensation enhances the optimizer's rate. Numerical simulations have confirmed the effectiveness of this method. The optimization rate of PAGD is 16.81 times faster than that of traditional SGD. It is noteworthy that this method has broad application prospects in spherical holographic display and three-dimensional display. • Greatly improving the optimization speed of spherical computer holography. • Pre-compensation balances the numerical range of diffraction results enhancing the efficiency of the optimizer. • Easier to overcome local minima during the optimization process. • Applying simulated annealing gradient descent to the optimization of holograms. [ABSTRACT FROM AUTHOR]

Conventional diffraction calculations typically employ complex Fourier transforms in which the source and target fields are represented by complex values. However, this approach is inefficient for certain applications. To address this problem, this study introduces diffraction calculations for three fields: real-to-complex, complex-to-real, and real-to-real. These calculations utilize a real-valued fast Fourier transform and Hermite symmetry, enabling accelerated computation by eliminating half of the spectra. This study also demonstrates the practical applications of these diffraction calculations. These applications include image reproduction in digital holography, speckle reduction in holographic projection, and accelerated hologram computation in holographic displays. • In this study, diffraction calculations in three fields are proposed. • The proposed diffractions were able to accelerate approximately 2.4 times. • The applications include digital holography and holographic displays. [ABSTRACT FROM AUTHOR]

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

• Overcomes the limitations of the original OFRAP method, which had fixed size and position requirements for the support of the target image in the space domain. • With 3D-FS-OFRAP, holograms for 3D objects can be generated quickly and in a non-iterative and parallel manner. • This paper proposes a novel 3D-FS-OFRAP method for non-iterative generation of FPOHs of 3D (dynamical) objects by combing our FS-OFRAP method, layer-based method and two different multiplexing strategies. The conventional approach to three-dimensional holographic displays involves the iterative generation of holograms, which is time-consuming and results in poor reconstruction quality. This paper proposes a novel non-iterative approach to generate 3D phase holograms using a full support optimized Fresnel random phase (FS-OFRAP) method, which combines the FS-OFRAP method and the idea of 3D object layering. The proposed method involves using the iterative Fresnel method to generate FS-OFRAPs of different planes, followed by the non-iterative generation of holograms corresponding to different layers using the 3D object layering strategy. Finally, the final phase hologram is obtained through superposition or multiplexing. Numerical and optical experiments demonstrate the effectiveness and advantages of the proposed 3D-FS-OFRAP method. This new approach has the potential to significantly improve the efficiency and quality of 3D holographic displays. [ABSTRACT FROM AUTHOR]

• Build a system that integrates salient object detection, voice interaction, holographic computation, and reconstruction modules, ultimately creating a holographic voice-interactive system. • The proposed U-blocks and U-net based reverse attention residual algorithm are used to generate more effective and accurate point cloud datasets during the acquisition phase. • In our holographic voice-interactive system, the ChatGLM model serves as the core module for voice interaction, used within our holographic display system. It converts user speech input into text information and executes corresponding operations or provides feedback based on the text content, enabling further system processing or response. • In a comparison between the wavefront-recording plane (WRP) and point cloud gridding (PCG) methods, the computation speeds of the proposed Taylor Rayleigh-Sommerfeld diffraction point cloud gridding algorithm (TRS-PCG) are faster. In recent years, intelligent voice interaction technology and holographic display technology have garnered significant attention. We propose a holographic voice-interactive system. The holographic voice interaction system can provide users with a virtual assistant proficient in accurately handling user voice queries, facilitating smoother interactions. Additionally, users can interact with virtual objects via holographic projection, enhancing realism and engagement. In this research, we introduce the U-blocks and U-net based reverse attention residual algorithm to generate more effective and accurate point cloud datasets during the acquisition phase. Furthermore, we integrate the ChatGLM pre-trained language model as the core module for voice interaction in the holographic display system, covering aspects such as text interaction and output control. Additionally, we propose a Taylor Rayleigh-Sommerfeld point cloud gridding method aimed at improving the computational speed of hologram generation. We validate the feasibility of our proposed methods through numerical simulations and optical experiments. [ABSTRACT FROM AUTHOR]

Digital micromirror devices (DMDs), owing to their rapid refresh rates, are among the most commonly used spatial light modulators in holographic three-dimensional near-eye displays. However, the modulation of DMD is typically confined to binary amplitude modulation, resulting in a noticeable presence of zero-order and conjugate noise, which significantly occupies the spatial bandwidth of the display optics and reduces the quality of optical reconstruction. To address these issues, we propose a computational framework of generating optimized binary computer-generated holograms for DMD-based holographic near-eye displays. Our work employs an iterative-based optimization strategy within a band-limited diffraction computation, thereby enhancing the display quality while achieving a considerable field of view by eliminating zero-order and conjugate noise. The proposed method is verified experimentally by displaying true three-dimensional images with low speckle noise and high contrast, opening a path towards next-generation of virtual reality/augmented reality display devices. [ABSTRACT FROM AUTHOR]

• Fringes and spatial shifting noises in DPHs' reconstructed images degrade the reconstruction quality. • The designed FCN uses DPHs generated from the diffraction field as input to produce recoded DPHs as output. • Experimental results show substantial enhancement of reconstruction quality through the proposed recoding method.. Herein, we proposed a method to recode double-phase holograms (DPHs) with a full convolutional neural network (FCN) for alleviating the fringes and spatial shifting noises in that. There are many fringes near the edge of the diffraction field due to the incomplete Fresnel zone plate, and the pixel-by-pixel encoding method of DPH will cause above fringes to appear in the reconstructed image of that as well. Besides, the spatial shifting noises generated during the conversion from complex-amplitude information to pure-phase information will also decrease the reconstruction quality and definition. Depending on the great nonlinear fitting ability of FCN, the proposed method can recode DPHs, alleviating the fringes and removing the spatial shifting noises effectively. Finally, the phase-only holograms with the resolution 2400 × 4096 have been generated in 0.06 s, which have a peak signal to noise ratio (PSNR) of 35.6 dB in the mean reconstruction quality. Optical results showed that compared with the conventional methods, the target images reconstructed by the proposed method have less noise and a higher display quality. [ABSTRACT FROM AUTHOR]