• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.154-160
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• 1997

On the base of the fractional Fourier transform(FRT) which is known as a generalized form of the conventional Fourier transform, the fractional correlation has been implemented. Shift-variance property of the fraction correlation has been evaluated and compared with the shift-invariance of the conventional correlation. The fractional correlation operation has been implemented by using a planar optics configuration which integrates all of the optical components on a single glass substrate. A good agreement between the experimental and calculated results has been obtained.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.296-297
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• 2003

본 연구에서는 푸리에 변환법에 의한 위상정보 추출 기술을 개발하고, 주파수 영역에서의 창함수 필터에 따른 위상추출 특성을 분석하였다. 푸리에 변환법은 위상이동법과는 달리 정현파 패턴이 투영된 하나의 영상만을 이용하여 3차원 형상정보를 추출할 수 있는 장점이 있다. 획득된 영상은 오일러 공식으로부터 다음과 같이 표현할 수 있다. (중략)

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.94-95
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• 2003

광학식 3차원 형상측정 기술은 산업현장과 의료분야 등에서 광범위하게 사용되어지고 있으며, 이에 대한 연구도 활발히 진행되고 있다. 본 연구에서는 푸리에 변환법에 의한 위상정보 추출 기술을 개발하고, 주파수 영역에서의 창함수 필터에 따른 위상추출 특성을 분석하였다. 광조사 장치로는 LCD 프로젝터를 이용한 투영방식(그림 1)과 레이저 간섭계 투영방식(그림 2)을 사용하였다. (중략)

• Korean Journal of Optics and Photonics
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• v.28 no.1
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• pp.1-8
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• 2017

A method for inspecting defects in display substrates utilizing Fourier optics is proposed in this paper. A cost-effective inspection system can be realized with the proposed method, because it does not require a high-magnification microscope. Also, the proposed method can avoid tight tolerance for variations in displacement between substrate and camera, which is stems from shallow depth of field of the high-magnification microscope. In addition, possible damage caused by collisions between substrate and the inspection equipment can be avoided. The decision algorithm can be simpler than for a conventional inspection system, because spatial shift of periodic substrate patterns does not affect the intensity distribution of the diffracted light, by the Fourier transform property. The proposed method is explained with numerical studies, and experiments are carried out to check its feasibility for color-filter substrates of a liquid-crystal display.

• Korean Journal of Optics and Photonics
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• v.27 no.3
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• pp.101-105
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• 2016

In this study we propose the novel optimization method of the phase-only computer-generated hologram (CGH), to improve calculation speed compared to the conventional method. While the conventional method is calculated using numerical analysis, the novel method is calculated using the phase-shift characteristic of Fourier transformation. In addition, the selectivity of noise filtering lets it decrease the calculation time. The validity of the reconstructed image using the novel method is verified by comparing simulation results to ideal and conventional data, and the improvement of texture and sharpness of the reconstructed image is confirmed by simulation.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.199-203
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• 1997

Fine displacement of spherical suface was detected and analyzed by Twyman-Green interferometer and the interferogram analysis using Fourier transform method. The surface profile was obtained from single interferogram by introducing the carrier freguency to the interferogram. The interferogram was processed in the spatial frequency domain by fast Fourier transform, and the phase distribution was obtained by inverse Fourier transform. The 3-dimensional distribution for the surface displacement was obtained. It was compared with the calculated surface displacement and the error was less than λ/10.

• Proceedings of the Optical Society of Korea Conference
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• 2009.02a
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• pp.117-118
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• 2009

• Proceedings of the Optical Society of Korea Conference
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• 2007.02a
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• pp.46-47
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• 2007

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.266-271
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• 2003

The reflectance spectrum of optical films thicker than a few microns shows an intensity oscillation due to interference. Since the spectral period of the oscillation is inversely related to film thickness, the thickness of an optical film can be determined from the spectral frequency of the oscillation. For rapid data processing, the spectral frequency is obtained by use of a Fast Fourier Transformation technique. The conventional method of applying a Fast Fourier Transformation to the reflectance spectrum versus photon energy is modified so as to clear the ambiguity in choosing the proper effective refractive index value and to prevent the broadening of the Fourier transformed peak due to the refractive index dispersion. This technique of modified Fast Fourier Transformation is suggested by the authors for the first time to their knowledge. From the analysis of the calculated reflectance spectrum of a 30-${\mu}{\textrm}{m}$-thick dielectric film. it is shown to improve the accuracy in determining film thickness by a great amount. The improved accuracy of the modified Fast Fourier Transformation is also confirmed from the analysis of the reflectance spectra of a sample with 80-${\mu}{\textrm}{m}$-thick cover layer and 13-${\mu}{\textrm}{m}$-thick spacer layer on a PC substrate.

• Information and Communications Magazine
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• v.10 no.5
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• pp.53-70
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• 1993

위상 복원 문제는 어떤 신호의 푸리에 변환의 크기로부터 푸리에 위상, 또는 그 신호 자체를 구하는 문제로서 신호처리, 천문학, X-선 결정학, 전자현미경학, 광학, synthetic aperture radar 등과 같은 많은 물리학의 분야에서 일어난다. 일반적으로, 이 위상 복원 문제는 유일한 해를 갖지 않기 때문에, 이 문제를 풀기 위하여 사전 정보로 주어지는 원하는 신호의 성질을 제한조건으로 주어 이 문제가 유일한 해를 갖도록 한 뒤 이 원하는 신호를 구하는 방법을 사용해왔다. 이 논문에서는 위상 복원 문제를 소개하고, 이 문제의 중요성, 기본 이론 등을 알아보고, 지금까지 제안이 되었던 방법들을 분야별로 묶어 신호처리의 관점에서 소개한다. 먼저 수학적인 기초에 대하여 소개하고, 푸리에 변환의 크기를 보존하는 변환들에 대하여 알아본 뒤, 위상 복원 문제를 풀기 위하여 제안이 되었던 방법들을 1)하나의 푸리에 변환의 크기가 주어졌을 때의 위상 복원, 2)더해지는 기준 신호가 있을 때의 위상 복원, 3)곱해지는 신호(윈도우)를 이용한 위상 복원으로 나누어 소개한다.