• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 창립 20주년기념 특별학술발표회
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• pp.133-134
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• 2009

We have presented our approach to build a 3D display system based on digital holography. For wide viewing angle, we have presented several techniques such as measurement, time-sharing display, and coherent amplification. These techniques can advance the wavefront 3D display system to next stage.

• 한국광학회지
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• 제22권3호
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• pp.129-133
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• 2011

2-파장 홀로그래피에서 수정된 화인 맵을 이용하여 2-파장 홀로그래피에서 발생하는 잡음 증폭현상을 줄이는 연구를 수행하였다. 일반 적인 화인 맵은 측정체의 단차가 2-파장 홀로그래피에 사용되는 광원의 파장보다 작은 경우에는 잡음을 잘 줄일 수 있으나, 단차가 파장 보다 큰 경우에는 측정 결과에 영향을 주어 잘못 된 측정 결과를 보인다. 이러한 오차를 줄이기 위하여 수정된 화인 맵을 이용하였으며, 그 결과 측정체의 단차가 파장 보다 큰 경우에도 측정에 영향을 주지 않고 잡음을 줄일 수 있음을 확인 하였다.

• 한국광학회지
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• 제21권4호
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• pp.146-150
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• 2010

디지털 홀로그래피에서 재생상을 재생할때 복소공액 홀로그램을 도입하여 위상 왜곡과 잡음이 제거된 재생 영상을 얻는 방법에 대하여 연구하였다. 일반적으로 디지털 홀로그램은 시료의 위상 정보 외에 위상 정보에 겹쳐져 있어 잡음으로 작용하는 허상, DC항 뿐만 아니라 측정 시스템의 위상 왜곡 현상도 모두 포함되어 기록된다. 기록된 홀로그램에서 시료의 위상 정보만을 분리하여 이를 재생하면 질 좋은 위상 재생상을 얻을 수 있다. 본 연구에서는 복소공액 홀로그램을 이용하면 off-axis 및 in-line 홀로그래피에서 위상왜곡과 측정시스템이 가지고 있는 잡음을 제거 할 수 있음을 실험적으로 확인하였다.

• 한국광학회지
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• 제18권2호
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• pp.117-121
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• 2007

In-line 디지털 홀로그래피가 가지고 있는 가장 근본적인 단점은 실상과 허상 그리고 영차 회절광이 공간적으로 분리 되지 않는 것이다. 본 연구에서는 영차 회절광은 소프트웨어를 이용하여 제거하고, 실상과 허상의 구분은 in-line 홀로그래피 현미경의 기하학적 배치를 이용하여 구분하였다. in-line 홀로그래피 현미경에서 허상의 크기는 대물렌즈와 홀로그램간의 거리에 의존한다. 본 연구에서는 허상의 크기가 대물렌즈의 후방 초점거리와 대물렌즈와 홀로그램 면까지의 거리가 일치할 때 최소가 되는 것을 알았으며, 이를 이용하여 실상과 허상을 구분하였다.

• ETRI Journal
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• 제41권1호
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• pp.84-92
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• 2019

Recent advances in digital holography in the far-infrared region of the spectrum have demonstrated the potential use of digital holography in homeland security as a tool to observe hostile environments in which smoke, flames, and dust impair vision. However, to make this application practical, it is necessary to simplify the optical setup. Here, we show an off-axis, self-reference scheme that spills the reference beam out from the object beam itself and avoids the need for a complex interferometric arrangement. We demonstrate that this scheme allows the reconstruction of high-quality holograms of objects captured under visible as well as far-infrared light exposure. This could pave the way to the industrialization of holographic systems to enable users to see through fire. Moreover, the quantitative nature of the holographic signal is preserved. Thus, the reported results demonstrate the possibility to use this setup for optical metrology.

• 한국산업정보학회논문지
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• 제17권2호
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• pp.29-32
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• 2012

Computer generated holography (CGH) is technology for generating holograms of synthetic, three dimensional (3D) objects which may not exist in the physical world. The process, however, requires heavy amount of computation as the resolution of a hologram is significantly higher than that of a typical optical image. This paper reviews four modern techniques for fast generation of digital Fresnel holograms which are important in the development of holographic video systems. The methods that will be described include the virtual window, sub-line, wavefront recording plane (WRP), and the interpolative WRP schemes. These works share the common objective to generate digital Fresnel hologram at a speed that is close to the video frame rate, and with complexity which is realizable with affordable computing and reconfigurable hardware devices. The author will present the principles and realization of these works, as well as some potential area of research in digital holography.

• Current Optics and Photonics
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• 제2권6호
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• pp.547-553
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• 2018

In this paper, a new method for spatial filtering in digital holography is proposed and verified by simulations compared to conventional methods. The new method is based on the simultaneous acquisition of two digital holograms, which can be separated by distinct spatial modulation, in a single image. Two holograms are generated by two reference waves, which have different spatial modulation orientations. Then, the overlapping region between the DC term and the object wave in the first hologram can be replaced with a less-overlapping region of the object wave in the second hologram because the whole image contains two holograms where the same objective wave has been recorded. In the simulation results, it is confirmed that the reconstructed image by the new method has better quality than for the original method.

• Current Optics and Photonics
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• 제3권2호
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• pp.119-127
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• 2019

A new secret-key-sharing cryptosystem using optical phase-shifting digital holography is proposed. The proposed secret-key-sharing algorithm is based on the Diffie-Hellman key-exchange protocol, which is modified to an optical cipher system implemented by a two-step quadrature phase-shifting digital holographic encryption method using orthogonal polarization. Two unknown users' private keys are encrypted by two-step phase-shifting digital holography and are changed into three digital-hologram ciphers, which are stored by computer and are opened to a public communication network for secret-key-sharing. Two-step phase-shifting digital holograms are acquired by applying a phase step of 0 or ${\pi}/2$ in the reference beam's path. The encrypted digital hologram in the optical setup is a Fourier-transform hologram, and is recorded on CCDs with 256 quantized gray-level intensities. The digital hologram shows an analog-type noise-like randomized cipher with a two-dimensional array, which has a stronger security level than conventional electronic cryptography, due to the complexity of optical encryption, and protects against the possibility of a replay attack. Decryption with three encrypted digital holograms generates the same shared secret key for each user. Schematically, the proposed optical configuration has the advantage of producing a kind of double-key encryption, which can enhance security strength compared to the conventional Diffie-Hellman key-exchange protocol. Another advantage of the proposed secret-key-sharing cryptosystem is that it is free to change each user's private key in generating the public keys at any time. The proposed method is very effective cryptography when applied to a secret-key-exchange cryptosystem with high security strength.

• Current Optics and Photonics
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• 제4권6호
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• pp.483-499
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• 2020

In this paper, a novel analog signature scheme is proposed by modifying an RSA-based digital signature scheme with optical phase-shifting digital holography. The purpose of the proposed method is generating an analog signature to provide data confidentiality and security during the data transfer, compared to the digital signature. The holographic encryption technique applied to a hash value reveals an analog-type of pseudo-random pattern in the analog signature scheme. The public key and secret key needed to verify the analog signature are computed from public key ciphers which are generated by the same holographic encryption. The proposed analog signature scheme contains a kind of double encryption in the process of generating signature and key, which enhances security level more than the digital signature. The results of performance simulations show the feasibility of the highly secure signature scheme, and security analysis shows high robustness against known-message attacks and chosen-message attacks. In addition, the proposed method can apply to one-time signature schemes which can be used to sign only one message and it can also apply to authentication, e-mails, electronic banking and electronic data interchange.

• Journal of the Optical Society of Korea
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• 제15권3호
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• pp.264-271
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• 2011

In this paper we examine and compare the computational speeds of three-dimensional (3D) object recognition by use of digital holography based on central unit processing (CPU) and graphic processing unit (GPU) computing. The holographic fringe pattern of a 3D object is obtained using an in-line interferometry setup. The Fourier matched filters are applied to the complex image reconstructed from the holographic fringe pattern using a GPU chip for real-time 3D object recognition. It is shown that the computational speed of the 3D object recognition using GPU computing is significantly faster than that of the CPU computing. To the best of our knowledge, this is the first report on comparisons of the calculation time of the 3D object recognition based on the digital holography with CPU vs GPU computing.