• 한국군사과학기술학회지
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• 제14권4호
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• pp.590-597
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• 2011

The IDRS provides detection, classification and bearing/range estimation by performing wavefront curvature analysis on an intercepted active transmission from target. Especially, a estimate of the target bearing/range that significantly affects the optimal operation of own submarine is required. Target bearing/range can be estimated by wavefront curvature ranging which use the difference of time arrival at sensors. But estimation ambiguity occur in bearing/range estimation due to a number of peaks caused by high center frequency and limited bandwidth of the intercepted active transmission and distortion caused by noise. As a result the bearing/range estimation performance is degraded. To estimate target bearing/range correctly, bearing/range estimation method that eliminate estimation ambiguity is required. In this paper, therefore, for wavefront curvature ranging, NLS cost function with curve fitting method is proposed, which provide robust bearing/range estimation performance by eliminating estimation ambiguity. Through simulation the performance of the proposed bearing/range estimation methods are verified.

• Journal of the Optical Society of Korea
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• 제20권3호
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• pp.358-362
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• 2016

We present a new scheme for optical encryption of a binary image. In our method, the original binary data page is first divided into two identical pages. In each data page, the “on” and “off” pixels are represented by two discrete phases that are 90° apart. The first page corresponds to the phase conjugation of the second page, and vice versa. In addition, the wavefront of the two data pages is changed simultaneously from planar to spherical, for better encryption. The wavefront modification is represented by an extra phase shift, which is a function of position on the wavefront. In this way the two separate pages are both encrypted, and therefore the pages cannot be distinguished in a CCD. If the first page is used as an encrypted data page, then the second page is used as the decryption key, and vice versa. The decryption can be done by simply combining the two encrypted data pages. It is shown in our experiment that encryption and decryption can be fully accomplished in the optical domain.

• Current Optics and Photonics
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• 제1권1호
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• pp.1-6
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• 2017

Degradation of bit-error-rate (BER), caused by atmospheric turbulence, seriously hinders the performance of coherent Free Space Optical (FSO) communication systems. An adaptive optics system proves to be effective in suppressing the atmospheric turbulence. The holographic modal wavefront sensor (HMWFS) proposed in our previous work, noted for its fast detecting rates and insensitivity to beam scintillation, is applied to the coherent FSO communication systems. In this paper, based on our previous work, we first introduce the principle of the HMWFS in brief and give the BER of the coherent FSO with homodyne detection in theory, and then analyze the improvement of BER for a coherent FSO system based on our previous simulation works. The results show that the wavefront sensor we propose is better for weak atmospheric turbulence. The most obvious advantages of HMWFS are fast detecting rates and insensitivity to beam scintillation.

• 전자공학회논문지D
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• 제36D권4호
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• pp.34-41
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• 1999

Synthetic Aperture Radar 시스템은 레이더 또는 목적물을 일정거리 또는 시간 간격동안 움직여가면서 반사되는 신호를 측정하여 동시에 처리해 줌으로써 안테나 크기를 크게 하는 효과를 가지게 되므로 목적물의 형체를 파악하는 Imaging 시스템의 일종이다. Imaging의 성패는 어떤 Modeling 과 Inversion 과정을 거치느냐에 달려 있는데 본 논문에서는 가장 Approximation이 적은 Wavefront reconstruction 기법을 적용하여 SAR 모델에서 획득한 데이터와 같은 크기의 실제 안테나가 있다고 가정하였을 때의 데이터와 이론적이고 실험적인 Signal Subspace 비교를 수행하였다. 이 연구를 통해 새로운 기법인 Wavefront reconstruction 알고리즘을 충분히 뒷받침해 줄 수 있는 결과를 얻을 수 있다.

• 한국전자파학회논문지
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• 제27권6호
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• pp.577-580
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• 2016

모노펄스 레이더에 대한 효과적인 재밍은 전파를 왜곡시키는 것이다. 그 중 대표적인 전파왜곡 기법은 두 개의 송신기를 이용하는 크로스 아이 기법이다. 크로스 아이 기법은 모노펄스 레이더의 구현 구조에 관계없이 각도를 기만할 수 있지만, 충분한 각도기만 효과를 갖기 위해서는 두 송신기의 위상 및 진폭 정확도가 확보되어야 한다. 이러한 위상 및 진폭 정확도는 전파왜곡 시스템을 구현하는데 있어서 핵심적인 요구 성능 파라미터이고, 목표로 하는 각도 오차에 따라 그 요구값이 달라진다. 본 논문에서는 목표하는 각도 오차에 따라 필요한 최소 위상차 및 진폭비를 수식으로 유도하고 그 결과를 분석한다.

• 방송공학회논문지
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• 제22권3호
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• pp.401-404
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• 2017

360 VR 영상은 등장방형 또는 정육면체, 정십이면체 등의 입체 도형의 전개도 형태의 포맷을 가진다. 이러한 포맷들은 각각 다른 특성을 가지고 있지만, 공통적으로 해상도가 일반 2D 영상에 비해 높다는 공통점을 가지고 있다. 따라서 부호화/복호화를 할 때 시간이 많이 걸리며, 병렬 처리가 필수적으로 요구된다. 최신 2D 비디오 코덱인 HEVC에는 병렬화 기술로 Wavefront Parallel Processing(WPP) 기술이 표준으로 적용되어 있는데, 이 기술은 2D 영상을 고려하여 만들어진 기술으로 3D 영상에서 사용했을 때 최적의 성능을 보이지 않는다. 따라서, WPP를 3D 영상에 적절한 방법이 필요하며 본 논문에서는 큐브맵 포맷에서 개선된 WPP 부호화/복호화 방법을 제안한다. 실험은 HEVC 참조 소프트웨어인 HM 12.0에 적용하였고, 실험 결과 기존 WPP와 비교하여 PSNR에는 큰 손실이 없으며 15%~20% 정도의 부호화 복잡도가 추가로 감소했다. 제안하는 방법은 향후 3D VR 영상을 위한 코덱에 필수적으로 포함될 것으로 기대된다.

• Current Optics and Photonics
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• 제7권1호
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• pp.1-14
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• 2023

Wavefront-coding imaging can achieve high-quality imaging along with a wide range of defocus. In this paper, the anti-laser detection and damage performance of wavefront-coding imaging systems using different asymmetric phase masks are studied, through modeling and simulation. Based on FresnelKirchhoff diffraction theory, the laser-propagation model of the wavefront-coding imaging system is established. The model uses defocus distance rather than wave aberration to characterize the degree of defocus of an imaging system. Then, based on a given defocus range, an optimization method based on Fisher information is used to determine the optimal phase-mask parameters. Finally, the anti-laser detection and damage performance of asymmetric phase masks at different defocus distances and propagation distances are simulated and analyzed. When studying the influence of defocus distance, compared to conventional imaging, the maximum single-pixel receiving power and echo-detection receiving power of asymmetric phase masks are reduced by about one and two orders of magnitude respectively. When exploring the influence of propagation distance, the maximum single-pixel receiving power of asymmetric phase masks decreases by about one order of magnitude and remains stable, and the echodetection receiving power gradually decreases with increasing propagation distance, until it approaches zero.

• IEIE Transactions on Smart Processing and Computing
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• 제4권1호
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• pp.28-34
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• 2015

Several parallelization methods that can be applied to High Efficiency Video Coding (HEVC) decoders are evaluated. The market requirements of high-resolution videos, such as Full HD and UHD, have been increasing. To satisfy the market requirements, several parallelization methods for HEVC decoders have been studied. Understanding these parallelization methods and objective comparisons of these methods are crucial to the real-time decoding of high-resolution videos. This paper introduces the parallelization methods that can be used in HEVC decoders and evaluates the parallelization methods comparatively. The experimental results show that the average speed-up factors of tile-level parallelism, wavefront parallel processing (WPP), frame-level parallelism, and 2D-wavefront parallelism are observed up to 4.59, 4.00, 2.20, and 3.16, respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.755-759
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• 2004

The van Cittert-Zernike theorem has been used in radio astronomy. Recently, the van Cittert-Zernike theorem has been tried to 3D source reconstruction. A couple of interferometer has been used in 3D coherence imaging like Michelson Stellar Interferometer and Rotational Shearing Interferometer. We propose a new type of interferometer, which is a wavefront folding interferometer with a corner cube. By characteristics of the corner cube, it is capable of measuring both mutual intensity and cross spectral density function, and it is very easy to align and robust to disturbance. We simulate the feasibility of this interferometer setup by simulation of point source reconstruction.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.384-387
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• 1995

Two axes lateral-shearing interferometer(LSI) specially devised for production line inspection lenses is presented. The interferometer composed with four prisms and a dove prism can test the lens performance including asymmetric aspheric lens. The dove prism which rotates the input image with respect to optical axis makes it possible. The wavefront passing through the test lens is reconstsucted by the phase derivative obtained form the two axes LSI system. Zernike-polynomials fitting of this wavefront is presented for determinating quantitative aberration of aspherical lenses.