• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.164-164
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• 2010

점광원 가정법은 광학계의 초점거리를 LED die 표면의 중심점으로 설정하고 LED 패키지의 발산형태는 이상적인 점광원으로 가정하여 설계하는 방법이며, 가초점 설계법은 focal smear라고 불리우는 초점영역의 가초점을 기준점으로 잡아 설계를 시행하는 방법이다. 실제 LED에서 빛이 발산하는 부분은 점광원이 아닌 부피를 가지고 있는 형태이기 때문에 점이외의 면에서 발생하는 오차와 가초점 영역 설정을 통한 설계는 결과에 오차를 발생시키게 된다. 따라서 구조 분석 실험 장비를 이용한 LED내부 구조를 분석한 후 이를 시뮬레이션 설계에 적용한 결과 기존 설계법에 비해 약 5%의 오차범위를 줄일 수 있었다.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.6
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• pp.50-58
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• 2009

Micro laser fabrication techniques can potentially be used for the manufacture of microstructures on the thin flat surfaces with large diameter that are frequently used in semiconductor industries. However, the large size of wafers can cause the degraded machining accuracy of the surface because it can be tilted or distorted by geometric errors of machines or the holding fixtures, etc. To overcome these errors the off-line focusing error compensation method is proposed. By using confocal autofocus system, the focusing error profile of machined surface is measured along the pre-determined path and can be compensated at the next machining process by making the corrected motion trajectories. The experimental results for silicon wafers and invar flat surfaces show that the proposed method can compensate the focusing error within the level of below $6.9{\mu}m$ that is the depth of focus required for the laser micromachining process.

• Journal of Korea Multimedia Society
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• v.9 no.5
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• pp.585-594
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• 2006

Due to the size limit, the voice coil motor (VCM) is adopted in most of the mobile phone camera to control auto-focus instead of step motor. The optical system using the VCM has the property that the focus values are varying even though the same current is induced. It means that an error of the lens position was taken placed due to the characteristics of the VCM. In this paper, a algorithm was proposed to compensate the lens position error using the step size and the search count of each stage. In the proposed algorithm -7 step middle searching stage is inserted the conventional searching algorithm for the fast auto-focus searching and the final searing step size was set to +1 for the precise focus control, respectively. In the experimental results, the focus values was found more fast in the proposed algorithm than the conventional. And more the image quality by the proposed algorithm was superior to that of the conventional.

• Korean Journal of Optics and Photonics
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• v.34 no.1
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• pp.22-30
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• 2023

The use of segmented mirrors is one of the ways to make the primary mirror of a spaceborne satellite larger, where several small mirrors are combined into a large monolithic mirror. To align multiple segmented mirrors as one large mirror, there must be no discontinuity in the x, y-axis (tilt) and axial alignment error (piston) between adjacent mirrors. When the tilt and piston are removed, we can collect the light in one direction and get an expected clear image. Therefore, we need a precise wavefront sensor that can measure the alignment error of the segmented mirrors in nm scale. The tilt error can be easily detected by the point spread image of the segmented mirrors, while the piston error is hard to detect because of the absence of apparent features, but makes a downgraded image. In this paper we used an optical testing interferometer such as a Fizeau interferometer, which has various advantages when aligning the segmented mirror on the ground, and focused on measuring the axial displacement error of a segmented mirror as the basic research of measuring the piston errors between adjacent mirrors. First, we calculated the relationship between the axial displacement error of the segmented mirror and the surface defocus error of the interferometer and verified the calculated formula through experiments. Using the experimental results, we analyzed the measurement uncertainty and obtained the limitation of the Fizeau interferometer in detecting axial displacement errors.

• Korean Journal of Optics and Photonics
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• v.9 no.1
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• pp.1-4
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• 1998

A compact scanning confocal microscope has been constructed using a quad-detector in a CD-player. The variation of error signal on depth which obtained by a quad-detector is used in the scanning confocal microscope. Bipolar error signals, which is sensitive near a focus, give a surface following effect whiout following the surface. In the case of small depth difference, the difference of materials through the reflection signal has been identified. The image which uses reflection signal only, has been obtained with the same setup. And, the results obtained in two different way were compared and analyzed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.7
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• pp.580-583
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• 2017

To compensate the degraded SAR image due to the residual errors and the spatial variant errors remaining after the motion compensation in the airborne SAR, we have introduced the autofocus method based on the partition processing. Thus, after we perform the spatial partition for the spotlight SAR data and the time partition for the stripmap SAR data, we reconstruct the subpatch images for the partitioned data. Then, we perform the local autofocus with the suitability analysis process for the phase errors estimated by the autofocus. Moreover, if the estimated phase errors are not properly compensated for the subpatch images, we perform the phase compensation method with the weight to the estimated phase error close to the degraded subpatch image to increase the SAR image quality.

• Korean Journal of Optics and Photonics
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• v.7 no.2
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• pp.101-111
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• 1996

Optical microscopes integrated with CCD cameras are widely used for automatic inspection of precision circuit patterns fabricated on glass masks and silicon wafers. For this application it is important to position the object always is focus so that the image appears in good quality while the microscope scans the object. However, as the magnification of the microscope is taken large for fine resolution the depth of focus becomes small, often in submicron ranges, requiring special care in focusing. This study proposes a new auto-focusing method, which can be readily incorporated in existing optical configuration of microscope. This method is based on optical triangulation using a separate beam of laser and two photodiodes, eliminating focus errors caused by surface roughness and waviness. Experimental results prove that the method can produce focus error signals which are very sensitive with a resolution of 5 nm within 0.5 ${\mu}{\textrm}{m}$ accuracy.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.583-590
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• 2004

The autofocus is one of the important processes in the automated vision inspection or measurements using optical microscopes, because it influences the measuring accuracy. In this paper, we used the confocal microscope configuration based on not a pinhole but a single-mode optical fiber. A single mode fiber has the functions of source and detector by applying the reciprocal scheme. As a result, we acquired a simple system configuration and easy alignment of the optical axis. Also, we embodied a fast autofocus system by acquiring the focus error signal through a source modulation technique. The source modulation technique can effectively reduce physical disturbances compared with objective lens modulation, and it is easily applicable to general optical microscopes. The focus error signal was measured with respect to the modulation amplitude, reflectance of the specimen and inclination angle of the measuring surface. The performance of the proposed autofocus system was verified through autofocusing flat mirror surface. In addition, we confirmed that source modulation rarely degrades the depth resolution by the comparison between the FWHMs of axial response curves.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.5
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• pp.366-374
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• 2018

In cases of airborne equipped with SAR, because the occurrence of motion is inevitable, it is necessary to apply autofocus techniques to SAR images to improve the image performance degradations caused by residual errors. Herein, a robust autofocus algorithm based on the minimum entropy criteria is proposed for the real SAR data in the spotlight mode. The convergence condition of the phase error estimation is checked at every iteration and if it is violated, the size of the phase error estimation is adjusted to the convergence condition. The real SAR raw data is used to demonstrate the excellent performance of the proposed algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.316-319
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• 2018

To detect the ground moving target, forward-looking SAR images obtained from the FMCW radar can be exploited. However, the quality of the SAR image is deteriorated due to the turbulence or fluctuation because of the flight path condition during the missile movement. We herein propose an entropy-minimizing autofocus method to compensate the motion error of forward-looking SAR. In particular, owing to the geometry of the forward-looking SAR, the motion error affects the SAR image in the two-dimensional (2D) form (azimuth and time axis). Therefore, we suggest a 2D autofocus method for the motion compensation.