Acceleration of computer-generated hologram using wavefront-recording plane and look-up table in three-dimensional holographic display

Binocular full-color holographic three-dimensional near eye display using a single SLM

A binocular full-color holographic three-dimensional near eye display system using a single spatial light modulator (SLM) is proposed. In the display system, the frequency spectrum shifting operation and color spectrum shifting operation are adopted to realize the frequency division multiplexing (FDM) and frequency superposition multiplexing (FSM) by manipulating the frequency spectrums of each color- and view-channel sub-holograms. The FDM combined with polarization multiplexing will be used to implement binocular display using a single SLM, and the FSM working with a bandpass filter for each view-channel will be used to achieve full-color display from single frame hologram. The optical analysis and experiments with 3D color objects confirm the feasibility of the proposed system in the practical application.

Real-time realistic computer-generated hologram with accurate depth precision and a large depth range

Holographic display is an ideal technology for near-eye display to realize virtual and augmented reality applications, because it can provide all depth perception cues. However, depth performance is sacrificed by exiting computer-generated hologram (CGH) methods for real-time calculation. In this paper, volume representation and improved ray tracing algorithm are proposed for real-time CGH generation with enhanced depth performance. Using the single fast Fourier transform (S-FFT) method, the volume representation enables a low calculation burden and is efficient for Graphics Processing Unit (GPU) to implement diffraction calculation. The improved ray tracing algorithm accounts for accurate depth cues in complex 3D scenes with reflection and refraction, which is represented by adding extra shapes in the volume. Numerical evaluation is used to verify the depth precision. And experiments show that the proposed method can provide a real-time interactive holographic display with accurate depth precision and a large depth range. CGH of a 3D scene with 256 depth values is calculated at 30fps, and the depth range can be hundreds of millimeters. Depth cues of reflection and refraction images can also be reconstructed correctly. The proposed method significantly outperforms existing fast methods by achieving a more realistic 3D holographic display with ideal depth performance and real-time calculation at the same time.

Superpixel-based sub-hologram method for real-time color three-dimensional holographic display with large size

One of the biggest challenges for large size three-dimensional (3D) holographic display based on the computer-generated hologram (CGH) is the trade-off between computation time and reconstruction quality, which has limited real-time synthesis of high-quality holographic image. In this paper, we propose a superpixel-based sub-hologram (SBS) method to reduce the computation time without sacrificing the quality of the reconstructed image. The superpixel-based sub-hologram method divides the target scene into a collection of superpixels. The superpixels are composed of adjacent object points. The region of the superpixel-based sub-hologram corresponding to each superpixel is determined by an approximation method. Since the size and the complexity of the diffraction regions are reduced, the hologram generation time is decreased significantly. The computation time has found to be reduced by 94.89% compared with the conventional sub-hologram method. It is shown that the proposed method implemented on the graphics processing unit (GPU) framework can achieve real-time (> 24 fps) color three-dimensional holographic display with a display size of 155.52 mm × 276.48 mm.

Review of computer-generated hologram algorithms for color dynamic holographic three-dimensional display

Holographic three-dimensional display is an important display technique because it can provide all depth information of a real or virtual scene without any special eyewear. In recent years, with the development of computer and optoelectronic technology, computer-generated holograms have attracted extensive attention and developed as the most promising method to realize holographic display. However, some bottlenecks still restrict the development of computer-generated holograms, such as heavy computation burden, low image quality, and the complicated system of color holographic display. To overcome these problems, numerous algorithms have been investigated with the aim of color dynamic holographic three-dimensional display. In this review, we will explain the essence of various computer-generated hologram algorithms and provide some insights for future research.

Polarization enlargement of FOV in Super Multi-view display based on near-eye timing-apertures

With strip-type timing-apertures attached to each eye of a viewer, more than one perspective views can be guided to either eye sequentially through different timing-apertures, thus implementing VAC-free (vergence-accommodation conflict-free) SMV (Super Multi-view) 3D (three-dimensional) display. To overcome the FOV (field of view) limitation problem due to small size of the timing-apertures along their arrangement direction, novel polarization architectures are designed to the timing-apertures in this paper. Correspondingly, the display screen of the proposed SMV display system is divided into M > 1 sub-screens along the arrangement direction of the timing-apertures, with adjacent sub-screens emitting light of mutually orthogonal polarization. At a time-point of each time period, a group of M timing-apertures, which correspond to the M sub-screens in a one-by-one manner along the arrangement direction, are turned on for creating an M-fold FOV, with each polarized timing-aperture of the group allowing light from the corresponding sub-screen passing through and blocking light from sub-screen(s) adjacent to the corresponding sub-screen. At 2T > 1 time-points of each time period, 2T groups of timing-apertures are turned on sequentially for presenting more than one two-dimensional images of the displayed scene to each eye, to implement SMV display based on persistence of vision. M stands for the FOV magnification number and T stands for the two-dimensional image number for each eye. As proof, a 3-fold FOV of 41° gets implemented experimentally with a currently available timing-aperture array of M = 3, accompanied by an effective noise-free region (ENFR) of 8.34 mm. Furthermore, the promising of freeing FOV from timing-aperture constraint fundamentally by larger M is described, out-of-screen blur along strip direction of the timing-apertures and the problem of limited ENFR are discussed.

Two-step acceleration calculation method to generate curved holograms using the intermediate plane in a three-dimensional holographic display

Nowadays, curved computer-generated holograms are widely applied to increase the field of view. However, heavy computational load restricts the development of curved computer-generated holograms. In this paper, we propose a two-step acceleration calculation method to generate curved holograms by using the intermediate plane, which is placed between the object and a curved computer-generated hologram. The first step is the calculation of the intermediate plane by an improved accurate highly compressed lookup-table method. In the second step, we execute diffraction calculation from the intermediate plane to obtain a curved computer-generated hologram. Numerical simulations and optical experiments are performed to demonstrate that the proposed method is an efficient method for reducing calculation time. Additionally, the increase of field of view using a curved hologram is also numerically demonstrated. It is expected that our method can be combined with a curved display screen to realize three-dimensional holographic displays in the future.

Speckleless color dynamic three-dimensional holographic display based on complex amplitude modulation

In this paper, we propose a method to implement a speckleless color dynamic three-dimensional holographic display by modulating amplitude and phase distribution simultaneously. Computer-generated holograms are calculated with an initial uniform phase, and the speckle noise of reconstructed images is suppressed effectively. We perform both numerical simulations and optical experiments to demonstrate the effectiveness of the proposed method. The numerical simulations show that the proposed method can achieve speckleless reconstruction and the optical experiments provide a good color dynamic display effect. It is expected that the proposed method could be widely applied to realize high-quality color dynamic holographic displays in the future.

Deep-learning-based hologram generation using a generative model

We propose a new learning and inferring model that generates digital holograms using deep neural networks (DNNs). This DNN uses a generative adversarial network, trained to infer a complex two-dimensional fringe pattern from a single object point. The intensity and fringe patterns inferred for each object point were multiplied, and all the fringe patterns were accumulated to generate a perfect hologram. This method can achieve generality by recording holograms for two spaces (16 Space and 32 Space). The reconstruction results of both spaces proved to be almost the same as numerical computer-generated holograms by showing the performance at 44.56 and 35.11 dB, respectively. Through displaying the generated hologram in the optical equipment, we proved that the holograms generated by the proposed DNN can be optically reconstructed.

GPU-accelerated calculation of computer-generated holograms for line-drawn objects

The heavy computational burden of computer-generated holograms (CGHs) has been a significant issue for three-dimensional (3D) display systems using electro-holography. Recently, fast CGH calculation methods of line-drawn objects for electro-holography were proposed, which are targeted for holography-based augmented reality/virtual reality devices because of their ability to project object contours in space with a small computational load. However, these methods still face shortcomings, namely, they cannot draw arbitrary curves with graphics processing unit (GPU) acceleration, which is an obstacle for replaying highly expressive and complex 3D images. In this paper, we propose an effective algorithm for calculating arbitrary line-drawn objects at layers of different depths suitable for implementation of GPU. By combining the integral calculation of wave propagation with an algebraic solution, we successfully calculated CGHs of 1, 920 × 1, 080 pixels within 1.1 ms on an NVIDIA Geforce RTX 2080Ti GPU.

Acceleration of fully computed hologram stereogram using lookup table and wavefront recording plane methods

Lookup table (LUT) and wavefront recording plane (WRP) methods are proposed to accelerate the computation of fully computed hologram stereograms (HSs). In the LUT method, we precalculate large and complete spherical wave phases with varying depths, and each complex amplitude distribution segment of the object point can be obtained quickly by cropping a specific and small part of the precalculated spherical wave phases. Then, each hologram element (hogel) can be calculated by superposing all the related segments. In addition, setting a WRP near the 3D scene can further accelerate computation and reduce storage space. Because the proposed methods only replace the complex calculation using referencing LUT, they are accurate and have no limitation on the size of hogel compared with some methods of paraxial approximation. Simulations and optical experiments verify that the proposed methods can reconstruct quality 3D images with reduced computational load.

Augmented reality display system using modulated moiré imaging technique

To enhance the depth rendering ability of augmented reality (AR) display systems, a modulated moiré imaging technique is used to render the true three-dimensional (3D) images for AR display systems. 3D images with continuous depth information and large depth of field are rendered and superimposed on the real scene. The proposed AR system consists of a modulated moiré imaging subsystem and an optical combiner. The modulated moiré imaging subsystem employs modulated point light sources, a display device, and a microlens array to generate 3D images. A defocussing equal period moiré imaging structure is used, which gives a chance for the point light sources to modulate the depth position of 3D images continuously. The principles of the imaging system are deduced analytically. A custom-designed transparent off-axis spherical reflective lens is used as an optical combiner to project the 3D images into the real world. An experimental AR system that provides continuous 3D images with depth information ranging from 0.5 to 2.5 m is made to verify the feasibility of the proposed technique.

Image quality improvement of holographic 3-D images based on a wavefront recording plane method with a limiting diffraction region

This study aims to improve the image quality of holographic three-dimensional (3-D) images based on the wavefront recording plane (WRP) method. In this method, we place a WRP close to the 3-D objects to reduce the propagation distance of light from the objects to the WRP. The conventional WRP method has been implemented only under conditions that did not cause aliasing noise. This study proposes a WRP method with a limiting diffraction region from the WRP to the hologram such that we can perform the WRP method under any condition. As a result, we succeeded in improving the image quality of the 3-D images based on the WRP method.