• Korean Journal of Optics and Photonics
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• v.9 no.3
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• pp.199-204
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• 1998

To increase the storage density in hologram recording, a simple scheme to obtain rotational, angular and spatial multiplexing efficiently at the same time is proposed and experimented. Both rotational multiplexing and angular multiplexing are obtained by controlling the reference beam directly by use of a pair of wedge prisms, while spatial multiplexing is obtained by shifting the recording medium in the recording plane. It is possible to get both an acute-angle geometry, in which the angle between the signal and reference beams is less than 90$^{\circ}$, and a 90$^{\circ}$ geometry, in which the angle is approximately 90$^{\circ}$. In experiment, 180 holograms were multiplexed with an acute-angle geometry where a photopolymer was used for the recording medium, and 147 holograms with 90$^{\circ}$ geometry where a Fe-doped LiNbO$_3$ crystal was used. The proposed scheme makes it easy it easy to realize a practical holographic memory system by simplifying the control of three complex mechanical motions that are necessary for the three multiplexing techniques.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.663-668
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• 2003

We studied a localized hologram recording method that can be used in a disk-shaped medium. In this method, the reference beam is focused by use of a cylindrical lens to get a thin spot in the medium, and then a hologram is recorded in that spot by illuminating the signal beam. Many localized holograms are multiplexed by shifting the medium by a distance more than the thin spot size of the reference beam. This method does not need recording-time scheduling for uniform diffraction efficiencies. We show that a minimal required thickness of the recording medium exists for a given spot size of the signal beam. We performed experiments for data storage and retrieval, and obtained a storage density of 20 bits/${\mu}{\textrm}{m}$$^2$ and a raw-bit error rate (RBER) of 2.5${\times}$10$^{-3}$ , when a 2 mm-thick Fe-doped LiNbO$_3$ crystal was used.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.10
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• pp.51-60
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• 1999

For an effective phase-multiplexing in holographic memory system, four types of phase code used as reference beam are generated. In case of $32 {\times} 32$ address beam, a phase error with 0%, 5%, 10% 15%, 20%, and 25% error rate, is purposely added to the real phase values in order to consider the practical SLM's nonlinear characteristics of phase modulation in computer simulation, cross talks and SNRs are comparatively analysed for these phase-codes by the auto and cross-correlation. Pseudo-Random(PSR) Phase Code has the lowest cross-correlation mean value of 0.067 among four types of Phase Code, which means the SNR of the PSR is higher than other Phase Codes. Also, the standard deviation of the PSR phase code indicating the degree of recalled data degradation is the lowest value of 0.0113.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.1C
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• pp.1-8
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• 2003

In this paper, performance of the CPC(complex phase code) which is recently proposed as a practical phase encoding method for phase-code multiplexes holographic memory system is comparatively analyzed with those of the conventional phase codes such as PR(pure random code), RCE(random code with equality), WHM(Walsh Hadamard Matrix). In computer simulation, the size of an address bean is fixed at 32$\times$32 pixels and 0%-25% phase-error ratio in a pixel are intentionally added to the real phase values to consider the nonlinear phase-modulation characteristics of the practical spatial light modulator. From comparative analysis of crosstalks and signal-to-noise ratios for these phase codes by calculating auto-correlation and cross-correlation, it is found that the CPC have the lowest cross-correlation mean value of 0.021, the lowest standard deviation of 0.0113 and the highest signal-to-noise ratio(SNR) of 27.4 among the four types of phase code. In addition, from the calculation of the number of all possible address beams for these four types of phase code as the size of the address beam is fixed to 3232 pixels, the CPC is found to have 6.334$\times$10$^{49}$ address beams, which are relatively higher number than that of the conventional phase codes.

• Journal of Broadcast Engineering
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• v.16 no.3
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• pp.403-415
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• 2011

In this paper, we proposed a hardware architecture to generate digital holograms at high speed. It used the modified computer-generated hologram (CGH) algorithm and adapted the pipeline-based hardware to be able to remove memory bottleneck problem. It uses not the method which generates a hologram by accumulating intermittent holograms but the one which independently generates a pixel of a final hologram and uses the appropriate CGH algorithm for the selected method. Based on the CGH algorithm we proposed the architecture of the digital hologram generator which consists of input interface part, calculating part, and normalizing part. The hardware can decrease memory usage because it repeatedly use object light sources which is stored in the internal buffer. It is also operationally parallelized by vertically adding unit cells. It can generate 86 frames of HD digital hologram per 1 second for 1K light sources.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.11
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• pp.86-94
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• 2012

In this paper we propose a hardware architecture of high-speed CGH (computer generated hologram) generation processor, which particularly reduces the number of memory access times to avoid the bottle-neck in the memory access operation. For this, we use three main schemes. The first is pixel-by-pixel calculation rather than light source-by-source calculation. The second is parallel calculation scheme extracted by modifying the previous recursive calculation scheme. The last one is a fully pipelined calculation scheme and exactly structured timing scheduling by adjusting the hardware. The proposed hardware is structured to calculate a row of a CGH in parallel and each hologram pixel in a row is calculated independently. It consists of input interface, initial parameter calculator, hologram pixel calculators, line buffer, and memory controller. The implemented hardware to calculate a row of a $1,920{\times}1,080$ CGH in parallel uses 168,960 LUTs, 153,944 registers, and 19,212 DSP blocks in an Altera FPGA environment. It can stably operate at 198MHz. Because of the three schemes, the time to access the external memory is reduced to about 1/20,000 of the previous ones at the same calculation speed.

• Korean Journal of Optics and Photonics
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• v.10 no.6
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• pp.473-481
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• 1999

We propose a new scheme of hologram multiplexing that can improve the crosstalk noise in the conventional phase-code multiplexing. Our method is based on the idea that the separate holograms to be stored in a certain region of the photorefractve material should have relative phase other than $180^{\circ}$. To demonstrate the new idea we fabricate a phase spatial light modulator using piezo-electric material. The experimental result shows that the crosstalk noise in the restored holograms is reduced much in our method. We also computer simulate the hologram multiplexing and compare the result with the experimental data.l data.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.275-276
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• 2007

A multiplex recording and reading technique in photopolymer are presented In order to record the polarization gratings, polarization-sensitive materials, in which linear birefringence is induced by irradiating the polarized light, are necessary. We checked orthogonal and independence of laser. The value of the photoinduced linear polarization had effect on diffraction properties in the holographic gratings. The grating strengths of two polarization are investigated and the relevant parameters for equal diffraction intensity readout are optimized.

• Journal of Korea Society of Digital Industry and Information Management
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• v.9 no.1
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• pp.151-163
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• 2013

Recently the attention on digital hologram that is regarded as to be the final goal of the 3-dimensional video technology has been increased. Digital hologram is calculated by modeling the interference phenomenon between an object wave and a reference wave. The modeling for digital holograms is called by computer generated hologram (CGH) Generally, CGH requires a very large amount of calculation. So if holograms are generated in real time, high-speed method should be needed. In this paper, we analyzed CGH equation, optimized it for mapping general purpose graphic processing unit (GPGPU), and proposed a optimized CGH calculation technique for GPGPU by resource allocation and various experiments which include block size changing, memory selection, and hologram tiling. The implemented results showed that a digital hologram that has $1,024{\times}1,024$ resolution can be generated during approximately 24ms, using 1K point clouds. In the experiment, we used two GTX 580 GPGPU of nVidia Inc.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.1
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• pp.18-26
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• 2016

The semiconductor industry is one of the key industries of Korea, which has continued growing at a steady annual growth rate. Important technology for the semiconductor industry is high integration of devices. This is to increase the memory capacity for unit area, of which key is photolithography. The photolithography refers to a technique for printing the shadow of light lit on the mask surface on to wafer, which is the most important process in a semiconductor manufacturing process. In this study, the width and step-height of wafers patterned through this process were measured to ensure uniformity. The widths and inter-plate heights of the specimens patterned using photolithography were measured using transmissive digital holography. A transmissive digital holographic interferometer was configured, and nine arbitrary points were set on the specimens as measured points. The measurement of each point was compared with the measurements performed using a commercial device called scanning electron microscope (SEM) and Alpha Step. Transmission digital holography requires a short measurement time, which is an advantage compared to other techniques. Furthermore, it uses magnification lenses, allowing the flexibility of changing between high and low magnifications. The test results confirmed that transmissive digital holography is a useful technique for measuring patterns printed using photolithography.