ewu Xu

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.

Growth and spectra characterization of Ce and Eu doped SBN crystals

Congruent Sr 0.61 Ba 0.39 Nb 2 O 6 (SBN : 61) crystals doped with Ce and/or Eu have been grown by Czochralski method, and characterized by transmission, reflection, emission, and excitation spectra. Both of the two doping ions substitute for Sr 2+ or Ba 2+ and occupy A 1 or A 2 sites in SBN. Ce 3+ and Eu 3+ are the dominant charge states. Compared with the undoped SBN, both Ce and Eu doped crystals exhibit shifts of the fundamental absorption edge towards the longer wavelength direction. Lattice distortion caused by the doping ions has been characterized by the change of lattice parameters obtained from X-ray diffraction patterns, and the width of exponential absorption band tail. In the Ce and Eu double-doped crystal, serious lattice distortion, location shift of Eu 3+ absorption, excitation, and emission peaks, and emission quenching of Eu 3+ ions have been observed. The doping defects and their effects on the lattice and energy band structures are also discussed.

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.

Faraday rotation spectra of bismuth-substituted rare-earth iron garnet crystals in optical communication band

Bismuth-substituted rare-earth iron garnet (REBIG) crystals are used in optical isolators for optical communication. However, the Faraday rotation (FR) spectra of REBIG crystals in the wavelength region of 1.3–1.6 μm have not yet been theoretically studied. To interpret the spectra, we assumed that the FR in this wavelength range was dominated by the contribution of the electric dipole transitions, and calculated the FR spectra. REBIG bulk crystals were grown from the Bi2O3 self-fluxed melt by the top-seeded solution growth method. The experimental results agreed with the theoretical calculation of FR in (HoBi)3Fe5O12, (YbBi)3Fe5O12, (YYbBi)3Fe5O12, and (TbBi)3Fe5O12. The results indicate that the theoretical analysis method of the FR spectra of REBIG in the visible range of wavelengths can be applied in the optical communication band.

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.

Influence of Ce and Co doping ions on photorefractive effect of SBN:61 crystals

Abstract Ce-, Co-, and (Ce,Co)-doped Sr0.61Ba0.39Nb2O6 (SBN:61) crystals with different concentrations were grown by Czochralski technique in the congruent composition. It is the first report of double-doped SBN crystals with Ce and Co. The doping ions Ce and Co occupy 15- (or 12-) fold coordinated and 6-fold coordinated lattice sites in crystal, respectively. A little change of the lattice constants induced by doping ions were detected by XRD experiments. Absorption spectra show that Ce3+ and Co3+ are dominant valence status in SBN:61 crystal. Ce and Co doping enhances two-beam coupling gain coefficient and photorefractive response speed, due to these doping ions donating or capturing electrons during the photorefractive process.

Growth and optical properties of a new nonlinear optical lanthanum calcium borate crystal

The monoclinic lanthanum calcium borate La 2 CaB 10 O 19 (LCB) crystal was grown from its stoichiometric melt by the top-seeded pulling method. The unpolarized transmission spectrum of a 1-mm-thick (001)-cut LCB crystal was measured in the wavelength range of 190-3100nm. The crystal exhibited a high transmittance (>80%) and a short absorption edge (<190 nm). The phase-matched second-harmonic generation (SHG) properties within the (010) plane of a 1.7-mm-thick (001)-cut LCB crystal were studied for the first time with a Spectra-Physics 3900S Ti:sapphire CW tunable laser. The room-temperature phase-matching (PM) wavelength was found to be 869 nm when the light propagation and polarization directions of the fundamental beam were parallel to the [001] and [010] axes, respectively. The full width at half maximum (FWHM) of the wavelength-tuning curve was found to be about 6 nm. The phase-matched SHG of the LCB crystal exhibited a small temperature coefficient of 0.05nm/C between 24°C and 150°C and was quite stable for generating visible light upon temperature changes.

Structural and dielectric investigation of doped Sr0.61Ba0.39Nb2O6 crystals

Undoped, Ce, and Co-doped Sr0.61Ba0.39Nb2O6 crystals were grown by the Czochralski method. The temperature dependence of dielectric constants was measured experimentally. The peak temperatures in dielectric constants of the doped crystals were detected to be lower by around 7 °C than that of the undoped crystal. Doping also results in the dispersion of ferroelectric phase transition due to the more disordered structure. Nonisoelectronic substitution of doping ions and lattice deformation are discussed by taking some properties of doping ion into account, such as radius, charge status, polarization, and concentration. The influences of the doping ions on the dielectric behaviors are also discussed. In Ce and Co double-doped crystals, the interaction between the two doping ions results in the compensation of the extra charges and counteraction of the structure deformation.