Holographic Three-dimensional Display Research Articles

Contactless human–computer interaction system based on three-dimensional holographic display and gesture recognition

Contactless human–computer interaction system based on three-dimensional holographic display and gesture recognition

Holographic display using layered computer-generated volume hologram.

The spatial frequency of the reconstructed image of planar computer-generated hologram(CGH) is limited by the sampling interval and the lack of thickness. To break through this limitation of planar CGH, we propose a new computer-generated volume hologram(CGVH) for full-color dynamic holographic three-dimensional(3D) display, and an iteration-free layered CGVH generation method. The proposed CGVH is equivalent to a volume hologram sampled discretely in three directions. The generation method employs the layered angular spectral diffraction to calculate the light field in the layered CGVH, and then encodes it into a CGVH. Numerical simulation results show that the CGVH can accurately reconstruct full-color 3D objects, where better imaging quality, more concentrated diffraction energy, denser reconstructed spatial frequency information, and larger viewing angle are achieved. The proposed CGVH is expected to be applied to realize dynamic modulation, wavelength multiplexing, and angle multiplexing in various optical fields in the future.

Reducing crosstalk of a multi-plane holographic display by the time-multiplexing stochastic gradient descent.

Multi-plane reconstruction is essential for realizing a holographic three-dimensional (3D) display. One fundamental issue in conventional multi-plane Gerchberg-Saxton (GS) algorithm is the inter-plane crosstalk, mainly caused by the neglect of other planes' interference in the process of amplitude replacement at each object plane. In this paper, we proposed the time-multiplexing stochastic gradient descent (TM-SGD) optimization algorithm to reduce the multi-plane reconstruction crosstalk. First, the global optimization feature of stochastic gradient descent (SGD) was utilized to reduce the inter-plane crosstalk. However, the crosstalk optimization effect would degrade as the number of object planes increases, due to the imbalance between input and output information. Thus, we further introduced the time-multiplexing strategy into both the iteration and reconstruction process of multi-plane SGD to increase input information. In TM-SGD, multiple sub-holograms are obtained through multi-loop iteration and then sequentially refreshed on spatial light modulator (SLM). The optimization condition between the holograms and the object planes converts from one-to-many to many-to-many, improving the optimization of inter-plane crosstalk. During the persistence of vision, multiple sub-hologram jointly reconstruct the crosstalk-free multi-plane images. Through simulation and experiment, we confirmed that TM-SGD could effectively reduce the inter-plane crosstalk and improve image quality.The proposed TM-SGD-based holographic display has wide applications in tomographic 3D visualization for biology, medical science, and engineering design, which need to reconstruct multiple independent tomographic images without inter-plane crosstalk.

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.

High Resolution Multiview Holographic Display Based on the Holographic Optical Element.

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.

Magneto-optical holographic 3D display with wide viewing angle using microlens array and digital mirror device

We developed a three-dimensional (3D) holographic display using the magneto-optical effect. The system uses a microlens array to reduce the area size of light reflected from pixels of a digital mirror device to approximately 1 μm and write in parallel to a magnetic recording medium as hologram data. This method makes it possible to write over a wide area even with a piezo stage that has high resolution but a narrow range of movement. The holograms, written at a pixel pitch of 1.1 um, enabled the reconstruction of 3D images with a wide viewing angle of 26.7 deg. By avoiding abrupt directional changes of the piezo stage, the image quality was improved by eliminating line defects in the written holograms; image distortion was reduced by setting the incident angle of the reference light in the program of a computer-generated hologram to match the model and the reconstructing optical system. Image distortion was reduced by improving the program of the computer-generated hologram.

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.

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

We present an erratum to our recent work [Appl. Opt.60, 7844-7848 (2021)APOPAI0003-693510.1364/AO.433422] that corrects errors in Eqs. (5) and (8). All the simulations and experiments in the original paper were performed using the correct equations, and therefore, the corrections do not affect the results and conclusions of the original paper.

Speckle reduction in holographic display with partially spatial coherent illumination

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.

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.

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.

Large field-of-view holographic display by gapless splicing of multisegment cylindrical holograms.

A holographic three-dimensional (3D) display is a recognized and ideal 3D display technology. In the field of holographic research, cylindrical holography with the merit of 360° field of view (FOV) has recently become a hot issue, as it naturally solves the problem of limited FOV in planar holography. The recently proposed approximate phase compensation (APC) method successfully obtains larger FOV and fast generation of segment cylindrical hologram (SCH) in the visible light band. However, the FOV of SCH remains limited due to its intrinsic limitations, and, to our best knowledge, the issue has not been effectively addressed. In this paper, the restricted conditions are first analyzed for the generation of SCH by the APC method. Then, an FOV expansion method is proposed for realizing a large FOV holographic display by gapless splicing of multi-SCH. The proposed method can successfully obtain larger FOV cylindrical holograms and effectively eliminate the splicing gaps; its effectiveness is verified by the results of numerical simulation and optical experiments. Therefore, the proposed method can effectively solve the FOV limitation problem of the APC method for the generation of SCH in the visible band, realize a large FOV 3D display, and provide a useful reference for holographic 3D display.

Fast calculation of computer generated hologram based on single Fourier transform for holographic three-dimensional display

We present an efficient method for the fast calculation of computer generated hologram (CGH). The 3D object is split into sub-layers according to its depth information. A 2D all-in-focus image is generated by sequential tiling all the layers in one plane. A Fourier hologram that contains all the information of 3D object is calculated from the fast Fourier transform (FFT) of the reassembled 2D image. By multiplying a pre-calculated multifocal off-axis digital phase mask (DPM) to the Fourier hologram, the content of each layer is axially relocated to different depth in the Fourier transform optical system to reconstruct the 3D object. The computation speed of the proposed method is greatly improved with only single FFT calculation process. Both of simulation and experimental results proves the validation of the proposed method.

A deep learning approach for the fast generation of acoustic holograms.

Acoustic holographic techniques are crucial in diverse applications, such as three-dimensional holographic display and particle manipulation. However, conventional methods for computer-generated acoustics holography rely heavily on iterative optimization algorithms, which are time-consuming and particularly hinder their capacity of generating a dynamic hologram in real time. Here, a deep learning approach based on U-Net is proposed to rapidly generate an acoustic hologram with optimal amplitude and phase maps. It is demonstrated that, after being trained with adequate data that are numerically synthesized by the pseudo-inverse method, the proposed deep learning approach can generate both amplitude and phase maps for new target images with an improved overall reconstruction quality. Remarkably, after the offline cost is compensated by a lower online cost for the proposed DL approach, the hologram generation speed is significantly accelerated by the proposed deep learning approach as compared with the pseudo-inverse method, especially for complicated or dynamic images. With the hierarchical feature learning capability and the fast online computational speed, the proposed deep learning approach can serve as a smart platform for rapidly generating complete maps of holograms for the sophisticated or dynamical target images, leading to the new possibility of real-time acoustic-hologram-based applications.

Enlarging field of view by a two-step method in a near-eye 3D holographic display.

The narrow field of view (FOV) has always been one of the most with limitations that drag the development of holographic three-dimensional (3D) near-eye display (NED). The complex amplitude modulation (CAM) technique is one way to realize holographic 3D display in real time with the advantage of high image quality. Previously, we applied the CAM technique on the design and integration of a compact colorful 3D-NED system. In this paper, a viewing angle enlarged CAM based 3D-NED system using a Abbe-Porter scheme and curved reflective structure is proposed. The viewing angle is increased in two steps. An Abbe-Porter filter system, composed of a lens and a grating, is used to enlarge the FOV for the first step and, meanwhile, realize complex amplitude modulation. A curved reflective structure is used to realize the FOV enlargement for the second step. Besides, the system retains the ability of colorful 3D display with high image quality. Optical experiments are performed, and the results show the system could present a 45.2° diagonal viewing angle. The system is able to present dynamic display as well. A compact prototype is fabricated and integrated for wearable and lightweight design.

Fast calculation method for parabolic-mirror-reflection holographic 3D display using wavefront segmentation.

Convex-parabolic-mirror reflection enables a very wide viewing zone in a holographic three-dimensional (3D) display. In this work, segmentation is introduced to reduce the calculation time of holograms in a convex-parabolic-mirror-reflection holographic 3D display. Wavefront segmentation can practically limit the lateral spread of the wavefront to be considered, which enables the application of geometrical approximation and conventional diffraction theories such as Fresnel diffraction. Thus, diffraction calculation via the convex parabolic mirror can be derived analytically and calculated rapidly using fast Fourier transform (FFT). Our proposed FFT-based method can calculate the diffraction integral 7000 times faster than our previous method, which involved calculating directly the diffraction integral without FFT. In addition, numerical simulation and an optical experiment are presented to verify our proposal.

Binocular dynamic holographic three-dimensional display for optical see-through augmented reality using two spatial light modulators

In this paper, a binocular see-through holographic three-dimensional (3D) display system based on two spatial light modulators (SLMs) is proposed and implemented, where the SLMs are used to load the phase-only holograms of the left and right 3D perspective images of a volumetric scene for optical holographic reconstruction with correct depth cues, respectively. Moreover, two beam splitters are employed to achieve the functions of directional light-guide devices and optical combiners simultaneously for providing binocular augmented reality (AR) sensation. Optical experiments demonstrate that the proposed system can successfully present binocular holographic AR 3D images with both binocular parallax and accommodation effect, which enables observation free of the accommodation-vergence conflict and visual fatigue problem. Furthermore, the capability of dynamic display with the proposed system is also tested in the experiments by synchronously refreshing the SLMs with the sequential holograms, and the captured videos demonstrate that the proposed system shows a promising potential for the real-time binocular AR true 3D display products.

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

In this paper, we propose a fast calculation method using look-up table and wavefront-recording plane. Wavefront-recording plane method consists of two steps: the first step is the calculation of a wavefront-recording plane which is placed between the object and the hologram. In the second step, we obtain the hologram by executing diffraction calculation from the wavefront-recording plane to the hologram plane. The first step of the previous wavefront-recording plane method is time consuming. In order to obtain further acceleration to the first step, we propose high compressed look-up table method based on wavefront-recording plane. We perform numerical simulations and optical experiments to verify the proposed method. Numerical simulation results show that the calculation time reduces dramatically in comparison with previous wavefront-recording plane method and the memory usage is very small. The optical experimental results are in accord with the numerical simulation results. It is expected that proposed method can greatly reduce the computational complexity and could be widely applied in the holographic field in the future.

Performance improvement of projection-type multiview holographic three-dimensional display using spatial light modulators

Projection-type multiview holographic three-dimensional (3D) display using a single spatial light modulator (SLM) and a directional diffractive device (DDD) composed of pixelated gratings is able to present 3D scenes with wide viewing angle and significantly reduced data volume. However, there are still several limitations on the display performance, such as finite number of viewpoints and low resolution for each view. In this paper, we propose an optimization method of projection-type multiview holographic 3D display by using multiple SLMs and a large-area DDD, where the total valid pixels used for multiview 3D display are substantially increased thanks to the seamless mosaic of holographic reconstructed images of multiple computer-generated holograms (CGHs) displaying on the SLMs so that the display performance can be noticeably improved. Two verification experiments are performed by combining two phase-only SLMs with an 8-view and a 4-view DDDs, respectively. The experimental results confirm that the crosstalk-free multiview holographic 3D displays with more viewpoints or higher resolution are successfully achieved, verifying the effectiveness of the proposed method.

Holographic three-dimensional display based on optimizing arrangement of holograms

We present a simple yet effective method to realize holographic three-dimensional (3D) display by optimizing arrangement of holograms. After a 3D object is divided into a set of layers in axial direction, these layers are calculated into corresponding sub-holograms by Fraunhofer diffraction. The hologram uploaded on SLM consists of sub-holograms side-by-side. Both simulations and experiments are carried out to verify the feasibility of the proposed method. The difference between Fresnel diffraction and Fraunhofer diffraction in the proposed method is analyzed. Aiming at the problems exposed in the experiments, reconstructed results are discussed and further improved by optimizing arrangement of sub-holograms. The process of 3D modeling is simple and the computational complexity is accordingly reduced. This method may provide a promising solution in future holographic 3D realization.