A volumetric display for visual, tactile and audio presentation using acoustic trapping.

Science-fiction movies portray volumetric systems that provide not only visual but also tactile and audible three-dimensional (3D) content. Displays based on swept-volume surfaces1,2, holography3, optophoretics4, plasmonics5 or lenticular lenslets6 can create 3D visual content without the need for glasses or additional instrumentation. However, they are slow, have limited persistence-of-vision capabilities and, most importantly, rely on operating principles that cannot produce tactile and auditive content as well. Here we present the multimodal acoustic trap display (MATD): a levitating volumetric display that can simultaneously deliver visual, auditory and tactile content, using acoustophoresis as the single operating principle. Our system traps a particle acoustically and illuminates it with red, green and blue light to control its colour as it quickly scans the display volume. Using time multiplexing with a secondary trap, amplitude modulation and phase minimization, the MATD delivers simultaneous auditive and tactile content. The system demonstrates particle speeds of up to 8.75 metres per second and 3.75 metres per second in the vertical and horizontal directions, respectively, offering particle manipulation capabilities superior to those of other optical or acoustic approaches demonstrated until now. In addition, our technique offers opportunities for non-contact, high-speed manipulation of matter, with applications in computational fabrication7 and biomedicine8.

Speeding up image quality improvement in random phase-free holograms using ringing artifact characteristics.

A holographic projector utilizes holography techniques. However, there are several barriers to realizing holographic projections. One is deterioration of hologram image quality caused by speckle noise and ringing artifacts. The combination of the random phase-free method and the Gerchberg-Saxton (GS) algorithm has improved the image quality of holograms. However, the GS algorithm requires significant computation time. We propose faster methods for image quality improvement of random phase-free holograms using the characteristics of ringing artifacts.

Autoencoder-based holographic image restoration.

We propose a holographic image restoration method using an autoencoder, which is an artificial neural network. Because holographic reconstructed images are often contaminated by direct light, conjugate light, and speckle noise, the discrimination of reconstructed images may be difficult. In this paper, we demonstrate the restoration of reconstructed images from holograms that record page data in holographic memory and quick response codes by using the proposed method.

Band-limited double-step Fresnel diffraction and its application to computer-generated holograms.

Double-step Fresnel diffraction (DSF) is an efficient diffraction calculation in terms of the amount of usage memory and calculation time. This paper describes band-limited DSF, which will be useful for large computer-generated holograms (CGHs) and gigapixel digital holography, mitigating the aliasing noise of the DSF. As the application, we demonstrate a CGH generation with nearly 8K × 4K pixels from texture and depth maps of a three-dimensional scene captured by a depth camera.

Arbitrary shape surface Fresnel diffraction.

Fresnel diffraction calculation on an arbitrary shape surface is proposed. This method is capable of calculating Fresnel diffraction from a source surface with an arbitrary shape to a planar destination surface. Although such calculation can be readily calculated by the direct integral of a diffraction calculation, the calculation cost is proportional to O(N²) in one dimensional or O(N4) in two dimensional cases, where N is the number of sampling points. However, the calculation cost of the proposed method is O(N log N) in one dimensional or O(N² log N) in two dimensional cases using non-uniform fast Fourier transform.

Fast calculation of computer-generated hologram using the circular symmetry of zone plates.

Computer-Generated Holograms (CGHs) can be generated from three-dimensional objects composed of point light sources by overlapping zone plates. A zone plate is a grating that can focus an incident wave and it has circular symmetry shape. In this study, we propose a fast CGH generating algorithm using the circular symmetry of zone plates and computer graphics techniques. We evaluated the proposed method by numerical simulation.

Generation of real-time large computer generated hologram using wavefront recording method.

We report the generation of a real-time large computer generated hologram (CGH) using the wavefront recording plane (WRP) method with the aid of a graphics processing unit (GPU). The WRP method consists of two steps: the first step calculates a complex amplitude on a WRP that is placed between a 3D object and a CGH, from a three-dimensional (3D) object. The second step obtains a CGH by calculating diffraction from the WRP to the CGH. The disadvantages of the previous WRP method include the inability to record a large three-dimensional object that exceeds the size of the CGH, and the difficulty in implementing to all the steps on a GPU. We improved the WRP method using Shifted-Fresnel diffraction to solve the former problem, and all the steps could be implemented on a GPU. We show optical reconstructions from a 1,980 × 1,080 phase only CGH generated by about 3 × 10(4) object points over 90 frames per second. In other words, the improved method obtained a large CGH with about 6 mega pixels (1,980 × 1,080 × 3) from the object points at the video rate.

Scaled angular spectrum method.

The angular spectrum method (ASM) calculates diffraction calculation in a high numerical aperture, unlike Fresnel diffraction. However, this method does not allow us to calculate at different sampling rates on source and destination planes. In this Letter, we propose a scaled ASM that calculates diffraction at different sampling rates on source and destination planes using the nonuniform fast Fourier transform.

Fast high-resolution computer-generated hologram computation using multiple graphics processing unit cluster system.

To overcome the computational complexity of a computer-generated hologram (CGH), we implement an optimized CGH computation in our multi-graphics processing unit cluster system. Our system can calculate a CGH of 6,400×3,072 pixels from a three-dimensional (3D) object composed of 2,048 points in 55 ms. Furthermore, in the case of a 3D object composed of 4096 points, our system is 553 times faster than a conventional central processing unit (using eight threads).

Numerical study of color holographic projection using space-division method.

We propose a color holographic projection using the space-division method, which can reconstruct a two-dimensional color image by one hologram and avoid the superimposing of unwanted images on a wanted image. We calculated three holograms corresponding to red, green and blue, and then generated one hologram to add the three holograms. The three holograms were optimized by the Gerchberg-Saxton algorithm for improvement of reconstructed color images. We numerically evaluated the image quality of color reconstructed images in terms of the color space of YCbCr, and compared the quality of color reconstructed images by the space-division method with that of reconstructed color images using another color holographic projection method.

Time-division color electroholography using one-chip RGB LED and synchronizing controller.

We propose time-division based color electroholography with a one-chip RGB Light Emitting Diode (LED) and a low-priced synchronizing controller. In electroholography, although color reconstruction methods via time-division have already been proposed, the methods require an LCD with a high refresh rate and output signals from the LCD for synchronizing the RGB reference lights such as laser sources, which consequently increase the development cost. Instead of using such an LCD, the proposed method is capable of using a general LCD panel with a normal refresh rate of 60 Hz. In addition, the LCD panel used in the proposed method does not require the output signals from the LCD. Instead, we generated synchronized signals using an external controller developed by a low-priced one-chip microprocessor, and, use a one-chip RGB LED instead of lasers as the RGB reference lights. The one-chip LED allows us to decrease the development cost and to facilitate optical-axis alignment. Using this method, we observed a multi-color 3D reconstructed movie at a frame rate of 20 Hz.

Rapid calculation algorithm of Fresnel computer-generated-hologram using look-up table and wavefront-recording plane methods for three-dimensional display.

A rapid calculation method of Fresnel computer-generated-hologram (CGH) using look-up table and wavefront-recording plane (WRP) methods toward three-dimensional (3D) display is presented. The method consists of two steps: the first step is the calculation of a WRP that is placed between a 3D object and a CGH. In the second step, we obtain an amplitude-type or phase-type CGH to execute diffraction calculation from the WRP to the CGH. The first step of the previous WRP method was difficult to calculate in real-time due to the calculation cost. In this paper, in order to obtain greater acceleration, we apply a look-up table method to the first step. In addition, we use a graphics processing unit in the second step. The total computational complexity is dramatically reduced in comparison with conventional CGH calculations. We show optical reconstructions from a 2,048×2,048 phase-type CGH generated by about 3×10(4) object points over 10 frames per second.

Fast calculation of computer-generated-hologram on AMD HD5000 series GPU and OpenCL.

In this paper, we report fast calculation of a computer-generated-hologram using a new architecture of the HD5000 series GPU (RV870) made by AMD and its new software development environment, OpenCL. Using a RV870 GPU and OpenCL, we can calculate 1,920 x 1,024 resolution of a CGH from a 3D object consisting of 1,024 points in 30 milli-seconds. The calculation speed realizes a speed approximately two times faster than that of a GPU made by NVIDIA.

Quantitative assessment method for computer-generated holograms free from the effect of viewpoint.

A quantitative assessment method for computer-generated holograms is presented. Our scheme is based on a simple evaluation quantity reflecting the optical radiating power from the holograms; this assures the overall validity of our method as a three-dimensional (3D) display assessment technique. Moreover, the effect of location from which the 3D view is observed is ruled out from the result. This contributes to both economy of computation and conciseness of the result.

One-unit system to reconstruct a 3-D movie at a video-rate via electroholography.

We have developed a one-unit system, including creating and displaying a hologram for real-time reproduction of a three-dimensional image via electroholography. We have constructed this one-unit system by connecting a special-purpose computer for holography and a special display board with a reflective liquid crystal display as a spatial light modulator. Using this one-unit system, we succeeded in reproducing a three-dimensional image composed of 10,000 points at a speed of 30 frames per second, which is the video rate in NTSC format. In addition, we were able to control a three-dimensional image in real-time using our system.

HORN-6 special-purpose clustered computing system for electroholography.

We developed the HORN-6 special-purpose computer for holography. We designed and constructed the HORN-6 board to handle an object image composed of one million points and constructed a cluster system composed of 16 HORN-6 boards. Using this HORN-6 cluster system, we succeeded in creating a computer-generated hologram of a three-dimensional image composed of 1,000,000 points at a rate of 1 frame per second, and a computer-generated hologram of an image composed of 100,000 points at a rate of 10 frames per second, which is near video rate, when the size of a computer-generated hologram is 1,920 x 1,080. The calculation speed is approximately 4,600 times faster than that of a personal computer with an Intel 3.4-GHz Pentium 4 CPU.

Simplified electroholographic color reconstruction system using graphics processing unit and liquid crystal display projector.

We have constructed a simple color electroholography system that has excellent cost performance. It uses a graphics processing unit (GPU) and a liquid crystal display (LCD) projector. The structure of the GPU is suitable for calculating computer-generated holograms (CGHs). The calculation speed of the GPU is approximately 1,500 times faster than that of a central processing unit. The LCD projector is an inexpensive, high-performance device for displaying CGHs. It has high-definition LCD panels for red, green and blue. Thus, it can be easily used for color electroholography. For a three-dimensional object consisting of 1,000 points, our system succeeded in real-time color holographic reconstruction at rate of 30 frames per second.

Simple and fast calculation algorithm for computer-generated hologram with wavefront recording plane.

We present a simple and fast calculation algorithm for a computer-generated hologram (CGH) by use of wavefront recording plane. The wavefront recording plane is placed between the object data and a CGH. When the wavefront recording plane is placed close to the object, the object light passes through a small region on the wave recording plane. The computational complexity for the object light is very small. We can obtain a CGH to execute diffraction calculation from the wavefront recording plane to the CGH. The computational complexity is constant. The total computational complexity is dramatically reduced in comparison with conventional CGH calculations.

Special purpose computer system for flow visualization using holography technology.

We have designed a special purpose computer system for visualizing fluid flow using digital holographic particle tracking velocimetry (DHPTV). This computer contains an Field Programmble Gate Array (FPGA) chip in which a pipeline for calculating the intensity of an object from a hologram by fast Fourier transform is installed. This system can produce 100 reconstructed images from a 1024 x 1024-grid hologram in 3.3 sec. It is expected that this system will contribute to fluid flow analysis.

Development of copper recovery process from flotation tailings by a combined method of high‒pressure leaching‒solvent extraction.

Sulfide copper mineral, typically Chalcopyrite (CuFeS2), is one of the most common minerals for producing metallic copper via the pyrometallurgical process. Generally, flotation tailings are produced as a byproduct of flotation and still consist of un‒recovered copper. In addition, it is expected that more tailings will be produced in the coming years due to the increased exploration of low‒grade copper ores. Therefore, this research aims to develop a copper recovery process from flotation tailings using high‒pressure leaching (HPL) followed by solvent extraction. Over 94.4% copper was dissolved from the sample (CuFeS2 as main copper mineral) by HPL in a H2O media in the presence of pyrite, whereas the iron was co‒dissolved with copper according to an equation given as CCu = 38.40 × CFe. To avoid co‒dissolved iron giving a negative effect on the subsequent process of electrowinning, solvent extraction was conducted on the pregnant leach solution for improving copper concentration. The result showed that 91.3% copper was recovered in a stripped solution and 98.6% iron was removed under the optimal extraction conditions. As a result, 86.2% of copper was recovered from the concentrate of flotation tailings by a proposed HPL‒solvent extraction process.