Multi-Depth Computer-Generated Hologram Based on Stochastic Gradient Descent Algorithm with Weighted Complex Loss Function and Masked Diffraction

Author(s):

Quan, Jiale; Yan, Binbin; Sang, Xinzhu; Zhong, Chongli; Li, Hui; Qin, Xiujuan; Xiao, Rui; Sun, Zhi; Dong, Yu & Zhang, Huming

Abstract:

“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.”

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Publication: Micromachines
Issue/Year: Micromachines, Volume 14; Number 3; Pages 605; 2023
DOI: 10.3390/mi14030605

Binocular holographic display based on the holographic optical element

Author(s):

Qin, Xiujuan; Sang, Xinzhu; Li, Hui; Yu, Chongxiu; Xiao, Rui; Zhong, Chongli; Sun, Zhi; Dong, Yu & Yan, Binbin

Abstract:

“Due to the limited pixel pitch of the spatial light modulator (SLM), the field of view (FOV) is insufficient to meet binocular observation needs. Here, an optimized controlling light method of a binocular holographic threedimensional (3D) display system based on the holographic optical element (HOE) is proposed. The synthetic phase-only hologram uploaded onto the SLM is generated with the layer-based angular spectrum diffraction theory, and two different reference waves are introduced to separate the left view and the right view of the3Dscene. The HOE with directional controlling light parameters is employed to guide binocular information into the left-eye and the right-eye viewing zones simultaneously. Optical experiments verify that the proposed system can achieve binocular holographic augmented reality 3D effect successfully with real physical depth, which can eliminate the accommodation-vergence conflict and visual fatigue problem. For each perspective, the FOV is 8.7 when the focal length of the HOE is 10 cm. The width of the viewing zone is 2.3 cm when the viewing distance is 25 cm.”

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Publication: Journal of the Optical Society of America A
Issue/Year: Journal of the Optical Society of America A, Volume 39; Number 12; Pages 2316; 2022
DOI: 10.1364/josaa.473989

Holographic Glasses for Virtual Reality

Author(s):

JONGHYUN KIM, NVIDIA, USA and Stanford University, USA
MANU GOPAKUMAR, SUYEON CHOI, AND YIFAN PENG, Stanford University, USA
WARD LOPES, NVIDIA, USA
GORDON WETZSTEIN, Stanford University, USA

Abstract:

“We resent Holographic Glasses, a holographic near-eye display system with an eyeglasses-like form factor for virtual reality. Holographic Glasses are composed of a pupil-replicating waveguide,
a spatial light modulator, and a geometric phase lens to create holographic images in a lightweight
and thin form factor. The proposed design can deliver full-color 3D holographic images using an optical stack of 2.5 mm thickness. A novel pupil-high-order gradient descent algorithm is presented for the correct phase calculation with the user’s varying pupil size. We implement benchtop and wearable prototypes for testing. Our binocular wearable prototype supports 3D focus cues and provides a diagonal field of view of 22.8? with a 2.3 mm static eye box and additional capabilities of dynamic eye box with beam steering, while weighing only 60 g excluding the driving board.”

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Publication: Association for Computing Machinery
Issue/Year: Association for Computing Machinery, 2022

Accommodative holography: improving accommodation response for perceptually realistic holographic displays

Author(s):

Kim, Dongyeon; Nam, Seung-Woo; Lee, Byounghyo; Seo, Jong-Mo & Lee, Byoungho

Abstract:

“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.”

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Publication: ACM Transactions on Graphics
Issue/Year: ACM Transactions on Graphics, Volume 41; Number 4; Pages 1–15; 2022
DOI: 10.1145/3528223.3530147

Hogel-free Holography

Author(s):

Chakravarthula, Praneeth; Tseng, Ethan; Fuchs, Henry & Heide, Felix

Abstract:

“Holography is a promising avenue for high-quality displays without requiring bulky, complex optical systems. While recent work has demonstrated accurate hologram generation of 2D scenes, high-quality holographic projections of 3D scenes has been out of reach until now. Existing multiplane 3D holography approaches fail to model wavefronts in the presence of partial occlusion while holographic stereogram methods have to make a fundamental trade of between spatial and angular resolution. In addition, existing 3D holographic display methods rely on heuristic encoding of complex amplitude into phase-only pixels which results in holograms with severe artifacts. Fundamental limitations of the input representation, wavefront modeling, and optimization methods prohibit artifact-free 3D holographic projections in today’s displays. To lift these limitations, we introduce hogel-free holography which optimizes for true 3D holograms, supporting both depth- and view- dependent efects for the irst time. Our approach overcomes the fundamental spatio-angular resolution trade-of typical to stereogram approaches. Moreover, it avoids heuristic encoding schemes to achieve high image idelity over a 3D volume. We validate that the proposed method achieves 10 dB PSNR improvement on simulated holographic reconstructions. We also validate our approach on an experimental prototype with accurate parallax and depth focus efects”

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Publication: ACM Transactions on Graphics
Issue/Year: ACM Transactions on Graphics, 2022
DOI: 10.1145/3516428

Varifocal diffractive lenses for multi-depth microscope imaging

Author(s):

Reda, Francesco; Salvatore, Marcella; Borbone, Fabio; Maddalena, Pasqualino; Ambrosio, Antonio & Oscurato, Stefano Luigi

Abstract:

“Flat optical elements enable the realization of ultra-thin devices able to either reproduce or overcome the functionalities of standard bulky components. The fabrication of these elements involves the structuration of material surfaces on the light wavelength scale, whose geometry has to be carefully designed to achieve the desired optical functionality. In addition to the limits imposed by lithographic design-performance compromises, their optical behavior cannot be accurately tuned afterward, making them difficult to integrate in dynamic optical systems. Here we show the realization of fully reconfigurable flat varifocal diffractive lens, which can be in-place realized, erased and reshaped directly on the surface of an azopolymer film by an all-optical holographic process. Integrating the lens in the same optical system used as standard refractive microscope, results in a hybrid microscope capable of multi-depth object imaging. Our approach demonstrates that reshapable flat optics can be a valid choice to integrate, or even substitute, modern optical systems for advanced functionalities.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 30; Number 8; Pages 12695; 2022
DOI: 10.1364/oe.455520

Speckle reduction in holographic display with partially spatial coherent illumination

Author(s):

Zhao, Zijie; Duan, Junyi & Liu, Juan

Abstract:

“A method of holographic reconstruction under partially spatial coherent illumination with different degree of coherence is proposed to suppress speckle noise based on theoretical analysis. The core factor of speckle reduction based on partially spatial coherent light is convolution operation in CGH reconstruction process. Numerical simulations and optical experiments are both performed to verify the proposed theory. The results reconstructed by proposed and traditional method are compared, and the speckle contrasts can be reduced to 0.05 and 0.08 at most in Fresnel and Fraunhofer zone respectively. The image quality is obviously improved. This method can provide further applications for three-dimensional holographic display, beam shaping and coherence degree modulation techniques.”

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Publication: Optics Communications
Issue/Year: Optics Communications, Volume 507; Pages 127604; 2022
DOI: 10.1016/j.optcom.2021.127604

Polygon-based computer-generated holography: a review of fundamentals and recent progress [Invited]

Author(s):

Zhang, Yaping; Fan, Houxin; Wang, Fan; Gu, Xianfeng; Qian, Xiaofan & Poon, Ting-Chung

Abstract:

“In this review paper, we first provide comprehensive tutorials on two classical methods of polygon-based computer-generated holography: the traditional method (also called the fast-Fourier-transform-based method) and the analytical method. Indeed, other modern polygon-based methods build on the idea of the two methods. We will then present some selective methods with recent developments and progress and compare their computational reconstructions in terms of calculation speed and image quality, among other things. Finally, we discuss and propose a fast analytical method called the fast 3D affine transformation method, and based on the method, we present a numerical reconstruction of a computer-generated hologram (CGH) of a 3D surface consisting of 49,272 processed polygons of the face of a real person without the use of graphic processing units; to the best of our knowledge, this represents a state-of-the-art numerical result in polygon-based computed-generated holography. Finally, we also show optical reconstructions of such a CGH and another CGH of the Stanford bunny of 59,996 polygons with 31,724 processed polygons after back-face culling. We hope that this paper will bring out some of the essence of polygon-based computer-generated holography and provide some insights for future research.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Volume 61; Number 5; Pages B363; 2022
DOI: 10.1364/ao.444973

Dual-task convolutional neural network based on the combination of the U-Net and a diffraction propagation model for phase hologram design with suppressed speckle noise

Author(s):

Sun, Xiuhui; Mu, Xingyu; Xu, Cheng; Pang, Hui; Deng, Qiling; Zhang, Ke; Jiang, Haibo; Du, Jinglei; Yin, Shaoyun & Du, Chunlei

Abstract:

“In this paper, a dual-task convolutional neural network based on the combination of the U-Net and a diffraction propagation model is proposed for the design of phase holograms to suppress speckle noise of the reconstructed images. By introducing a Fresnel transmission layer, based on angular spectrum diffraction theory, as the diffraction propagation model and incorporating it into U-Net as the output layer, the proposed neural network model can describe the actual physical process of holographic imaging, and the distributions of both the light amplitude and phase can be generated. Afterwards, by respectively using the Pearson correlation coefficient (PCC) as the loss function to modulate the distribution of the amplitude, and a proposed target-weighted standard deviation (TWSD) as the loss function to limit the randomness and arbitrariness of the reconstructed phase distribution, the dual tasks of the amplitude reconstruction and phase smoothing are jointly solved, and thus the phase hologram that can produce high quality image without speckle is obtained. Both simulations and optical experiments are carried out to confirm the feasibility and effectiveness of the proposed method. Furthermore, the depth of field (DOF) of the image using the proposed method is much larger than that of using the traditional Gerchberg-Saxton (GS) algorithm due to the smoothness of the reconstructed phase distribution, which is also verified in the experiments. This study provides a new phase hologram design approach and shows the potential of neural networks in the field of the holographic imaging and more.”

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Publication: Optics Express
Issue/Year: Optics Express, Volume 30; Number 2; Pages 2646; 2022
DOI: 10.1364/oe.440956

Neural 3D holography

Author(s):

Choi, Suyeon; Gopakumar, Manu; Peng, Yifan; Kim, Jonghyun & Wetzstein, Gordon

Abstract:

“Holographic near-eye displays promise unprecedented capabilities for virtual and augmented reality (VR/AR) systems. The image quality achieved by current holographic displays, however, is limited by the wave propagation models used to simulate the physical optics. We propose a neural network-parameterized plane-to-multiplane wave propagation model that closes the gap between physics and simulation. Our model is automatically trained using camera feedback and it outperforms related techniques in 2D plane-to-plane settings by a large margin. Moreover, it is the first network-parameterized model to naturally extend to 3D settings, enabling high-quality 3D computer-generated holography using a novel phase regularization strategy of the complex-valued wave field. The efficacy of our approach is demonstrated through extensive experimental evaluation with both VR and optical see-through AR display prototypes.”

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Publication: ACM Transactions on Graphics
Issue/Year: ACM Transactions on Graphics, Volume 40; Number 6; Pages 1–12; 2021
DOI: 10.1145/3478513.3480542
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