Xinan Liang

Increasing pixel count of holograms for three-dimensional holographic display by optical scan-tiling

Abstract. We present a novel approach that utilizes both physical tiling and optical scan-tiling of high-speed electrically addressed spatial light modulator (SLM) for increasing the pixel count of hologram. Twenty-four SXGA (1280×1080) high-speed ferroelectric liquid crystal on silicon are first physically tiled to form an 8(rows)×3(columns) SLM array. This array is further tiled to form a final hologram with pixel count of 377.5 Megapixels through a 1-axis galvanometric scanning mirror. A large computer-generated hologram is calculated and fed into the individual SLMs according to the predefined sequence. Full-color and full-parallax flickless three-dimensional objects are replayed at a rate of 60 frames per second in a 10-in. display window. The launching of the hologram, laser illumination, and scanning mirror are synchronized and controlled by a field-programmable gate array.

Fast distributed large-pixel-count hologram computation using a GPU cluster

Large-pixel-count holograms are one essential part for big size holographic three-dimensional (3D) display, but the generation of such holograms is computationally demanding. In order to address this issue, we have built a graphics processing unit (GPU) cluster with 32.5 Tflop/s computing power and implemented distributed hologram computation on it with speed improvement techniques, such as shared memory on GPU, GPU level adaptive load balancing, and node level load distribution. Using these speed improvement techniques on the GPU cluster, we have achieved 71.4 times computation speed increase for 186M-pixel holograms. Furthermore, we have used the approaches of diffraction limits and subdivision of holograms to overcome the GPU memory limit in computing large-pixel-count holograms. 745M-pixel and 1.80G-pixel holograms were computed in 343 and 3326 s, respectively, for more than 2 million object points with RGB colors. Color 3D objects with 1.02M points were successfully reconstructed from 186M-pixel hologram computed in 8.82 s with all the above three speed improvement techniques. It is shown that distributed hologram computation using a GPU cluster is a promising approach to increase the computation speed of large-pixel-count holograms for large size holographic display.

Digital holographic three-dimensional display of 50-Mpixel holograms using a two-axis scanning mirror device

The current limitation in pixel count of a single spatial light modulator SLM is one of the technological hurdles that must be over- come to produce a holographic 3-D display with a large image size. A conventional approach is to tile subholograms that are predivided from a reconfigurable computer-generated hologram CGH with a high pixel count. We develop a new approach to achieve a 50 Mpixel display by tiling reconstructed subholograms computed from a predivided 3-D ob- ject. The tiling is done using a two-axis scanning mirror device with a new tiling sequence. A shutterless system design is also implemented to enable effective tiling of subholograms. A high-speed digital micromirror device DMD at 6 kHz with 19201080 pixels is utilized to reconstruct the subholograms. Our current system shows the potential to tile up to 120 subholograms, which corresponds to about 240 Mpixels. The ap- proach we demonstrate gives a scalable solution to achieve a gigapixel- level display in the future.

Development of full-color full-parallax digital 3D holographic display system and its prospects

We have developed a full-color full-parallax digital 3D holographic display system by using 24 physically tiled SLMs, an optical scan tiling approach and two sets of RGB lasers, which could display 378-Mpixel holograms at 60 Hz, with a displayed image size of 10 inch in diagonal. In this paper, we will review and compare three different holographic display systems developed by our group from various aspects, including SLMs, lasers, optics designs, hologram computation, data transmission, and system synchronization. We will also discuss the bottlenecks and prospects of further development of the system for practical applications.

Full High-Definition Digital 3D Holographic Display and Its Enabling Technologies

Holographic display is a true three-dimensional (3D) display technology presenting all depth cues without using any special glasses. In this paper, we first introduce a monochrome digital 3D holographic display system developed at Data Storage Institute (DSI), which is capable of displaying both static and dynamic 3D objects reconstructed from computer-generated holograms (CGHs). The system can also display 50-Mpixel holograms at 25 Hz refresh rate via a novel hologram tiling approach, which enables the increase of displayed image size. A futuristic vision for full high-definition (HD) digital 3D holographic display is then proposed and analyzed. The dynamic reconstruction of full-HD 3D objects from CGHs has been preliminarily demonstrated. Finally, we introduce the development trends of its enabling technologies such as highperformance computing, new algorithms, data storage and transmission, spatial light modulator (SLM) and RGB (red, green and blue) laser sources.

Large-pixel-count hologram data processing for holographic 3D display

The pixel count of hologram for a holographic 3D display system increases rapidly with the increase in reconstructed object size and viewing angle. According to our analysis, for 10 inch reconstructed object size with 5° viewing angle, a hologram with a pixel count of 378 Million is required. Such a large pixel count is a challenge for both hologram computation and hologram data transmission. The computation load is analyzed to be a few hundreds of Tflop for the object with a few million object points, and the hologram data transmission rate required is analyzed to be 22.3 Gbps and 67.0 Gbps for monochrome display and color display using time division multiplexing at 60 Hz, respectively. A computer cluster with 32.7 Tflops GPU computing ability and 60 Gbps transmission bandwidth was built to meet the hardware requirements for large-pixel-count hologram computation and transmission. A distributed computation method was implemented for computing large-pixel-count holograms. Computation time of 5.6 seconds was achieved for 378- Mpixel hologram containing information of 1.7 M object points. During the playback of holographic video using our holographic 3D display system, the hologram data was read out from SSDs, transmitted over the high speed network, and finally launched onto SLMs for reconstruction. A data transmission rate of 31.8 Gbps was achieved, which corresponded to 378-Mpixel hologram at 84 Hz for monochrome reconstruction and full color reconstruction using space division multiplexing. The increasing demand for computation power and data transmission rate of large-pixel-count hologram video displays has been effectively addressed.

Dynamic display of 3D objects in real and virtual spaces with computer-generated holography

In this paper a new holographic 3D display system based on computer-generated hologram (CGH) is developed for the reconstruction of 3D objects. A new algorithm is also developed to reduce the hologram computation time and memory usage. The dynamic 3D objects are successfully reconstructed at video rates in both real and virtual spaces.

Ray-casting CRT algorithm for holographic 3D display with full parallax occlusion effect

In this paper, a full parallax occlusion algorithm for holographic 3D display is developed and the motion parallax and dynamic occlusion effect of the reconstructed 3D object is successfully demonstrated. The ray-casting, directional clustering and vertical angle marking technologies are integrated with coherent ray tracing (CRT) hologram computation algorithm. By applying the vertical angle marking technology, only a single pass of the entire horizontal viewing angle is needed to compute full parallax occlusion. The complexity of the algorithm is reduced by about one order compared to standard occlusion algorithm which considers the entire range of combination of horizontal and vertical viewing angles for occlusion. Compared to conventional CRT computation which does not consider occlusion effect, the algorithm has also increased the computation speed to about 350%. The algorithm is able to work with any forms of 3D data. The optimal horizontal angular resolution has also been identified as 0.007 degree for our system experimentally which enables the optimization of the algorithm. Various 3D objects with full parallax occlusion effect have been reconstructed optically.

Regular effective hologram regions for computer generated holography

An effective hologram region (EHR) based approach is presented to speed up the computation of computer generated holograms (CGHs). The object space is predivided into subspaces, and an EHR for each subspace is predefined according to the maximum spatial frequency of interference fringes, light diffraction efficiency, and CGH binarization effect. To compute the hologram of an object, the object points are first categorized according to which subspace they are located in, and then their holograms are calculated using the corresponding EHRs. As each EHR usually takes up only a portion of the hologram plate, the CGH computational load is thus reduced. This new approach is highly suitable for large hologram display systems. In addition, when compared to the reconstructed image using the conventional approach, our experimental results show that more noise can be blocked off and the reconstructed image appears sharper without noticeable brightness reduction.

Determination of magneto-optical constants by measuring Kerr rotation angles of magnetic films with different sample structures

A new data analysis method is proposed to determine magneto-optical (MO) constants by measuring Kerr rotation angles on samples with different multilayer film structures. The MO film in the multilayer samples is protected by a SiO2 film with two different thicknesses. An existing algorithm is used to calculate the Kerr rotation angle based on the MO theory developed in the early 1990s. A new error function is defined to evaluate the distance from the calculated Kerr angles to the measured ones. The proposed method is developed based on the Staged Continuous Tabu Search (SCTS) algorithm to retrieve the MO constant by searching the minimum of the error function. The uniqueness and accuracy of the MO constant determined by this method are discussed, and its relative error introduced by the measurement error of Kerr rotation angles is also analyzed. Without measuring the ellipticity, the proposed method is relatively simple and can be applied to determine the MO constants for the samples with two or three layers of films.