• Journal of the Korean Society for Precision Engineering
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• v.31 no.5
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• pp.367-373
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• 2014

Surface texturing is a machining process on the surface to give engineering functions. The representative process of the surface texturing is lotus effect to give hydrophobic property by the lithography and chemical etching, which is the bio mimic from the nature. Surface texturing can be manufactured by a lot of processes, in particular using mechanical method such as a precise diamond turning, grinding, rolling, embossing, vibrorolling, and abrasive jet machining (AJM). Among them, the grinding process is notable in terms of the wide range of texturing area and fast processing time. The patterning by grinding is done by the grooved grinding wheel on the work piece. In this case, the pattern shape is determined by the grinding conditions as well as the wheel dressing conditions. In this paper, experimental study on the pattern shapes were done and provide the feasibility in use for the large area patterning.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.2
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• pp.91-96
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• 2014

Aspheric lenses used in the thermal imaging are typically fabricated using expensive single-crystal materials (Ge and ZnS, etc.) by the costly single point diamond turning (SPDT) process. As a potential solution to reduce cost, compression molding method using chalcogenide glass has been attracted to fabricate IR optic. Thermal deformation of a molded lens should be compensated to fabricate chalcogenide aspheric lens with form accuracy of the submicron-order. The thermal deformation phenomenon of molded lens was analyzed ant then compensation using mold iteration process is followed to fabricate the high accuracy optic. Consequently, it is obvious that compensation of thermal deformation is critical and useful enough to be adopted to fabricate the lens by molding method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.184-187
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• 2005

This paper is described about the technique of ultra-precision machining for optical parts in HMD system. Machining technique for PMMA and BK7 with single point diamond turning machining is reported in this paper. The main factors influencing on the machined surface quality are discovered and regularities of machining process are drawn. The purpose of our research is to find the optimum machining conditions fur cutting of PMMA and grinding of BK7. Also, apply the SPDTM technique to the manufacturing of ultra precision optical components of HMD system. Aspheric PMMA lens without a polishing process, the surface roughness of 5 nm Ra, and the form error of ${\lambda}/2\;({\lambda}=632.8nm)$ for reference curved surface 30 mm has been required.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.67.2-67.2
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• 2020

Not only the magnitude of the mirror surface error, the pattern matters as it produces certain aberrations. In particular, the surface error of the freeform mirrors, which are optimized to eliminate specific aberrations, might show much higher sensitivity in optical performance. Therefore, we analyze the mirror surface error with Zernike polynomials with the goal of generating a realistic error surface. We investigate the surface error of the freeform mirror fabricated by diamond turning machine to analyze the realistic tendency of the error. The surface error with 0.22 ㎛ root-mean-square value is fitted to the Zernike terms using the incremental fitting method, which increases the number of the fitting coefficients through steps. Furthermore, optical performance via surface error pattern based on Zernike terms is studied to see the influences of each term. With this study, realistic error surface generation may allow higher accuracy not only for the feasibility test but also for all tests and predictions using optical simulations.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.83.1-83.1
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• 2013

선형비점수차를 완벽하게 제거한 비축반사경 이론을 천체 관측용 분광기의 전단 광학계 등에 응용하면 색수차가 없는 기기 제작이 가능하다. 이러한 비축 반사경은 DTM(Diamond Turning Machine)을 이용하여 알루미늄으로 만들면 제작 시간이 단축된다. 그러나 DTM을 이용해 알루미늄과 같이 무른 금속을 가공할 경우 툴마크가 발생하게 된다. 툴마크는 회절현상을 발생시키며 이러한 회절현상은 알루미늄 반사경을 이용한 광학계 개발에 제약이 된다. 툴마크는 DTM 가공 이후 연마를 통해 제거할 수 있지만 알루미늄의 무른 특성으로 인해 연마 과정에서 반사경의 형상이 변할 가능성이 크다. 이러한 알루미늄 반사경의 형상 변화를 최소화하기 위한 방법으로는 알루미늄 반사경 표면에 무전해니켈도금을 하는 것이다. 하지만 도금 과정에서 반사경의 형상이 변할 가능성이 있기 때문에 두가지 방법을 사용하여 툴마크를 제거할 계획이다. 첫 번째 방법은 DTM 가공된 알루미늄 반사경을 5 um의 무전해니켈도금 이후 연마하여 툴마크를 제거하고 반사율 증가를 위해 그 위에 다시 알루미늄 코팅을 하는 방법니다. 두 번째 방법은 100 um의 무전해니켈도금 이후 DTM 가공을 하고 다시 연마를 통해 툴마크를 제거하는 방법이다. 이번 발표에서는 툴마크를 제거하기 위한 2가지 방법의 장단점을 확인하고 툴마크를 제거한 알루미늄 반사경을 제작하기 위한 과정을 설명하였다. 본 연구에서 개발한 비축 반사경은 서울대학교 창의연구단의 광학/적외선 카메라 CQUEAN의 차세대 모델에 적용할 계획이다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.591-598
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• 2012

In this study, the cutting characteristics of bulk metallic glass (BMG) cut using a computer numerically controlled (CNC) lathe were investigated for different insert tool materials and cutting speeds. The surface roughness, chip morphology, cutting forces, and tool wear during turning of $Zr_{50}Cu_{40}Al_{10}$ BMG alloy were examined. Four kinds of tool materials were used to cut an 8-mm-diameter BMG. The examination of the surface roughnesses of the BMG specimens machined at each cutting speed showed that the surface roughness became better as the cutting speed increased, and the tool materials also influenced the surface roughness. The chip morphology investigations showed that the unoxidized BMG chips had serrated curled chips with adiabatic shear bands, while the oxidized chips exhibited local melting and tangling rather than the usual spiral-shaped chips. The cutting force induced during machining of the Zr-based BMG was the largest for the TiN-WC tool, followed by the polycrystalline diamond (PCD) tool. The cermet tool exerted the smallest cutting force.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.1
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• pp.92-99
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• 2014

An aspherical lens, which resolves several problems with a spherical lens,typically serves asa key part of an optical system. Generally, an aspherical lens is fabricated using a diamond turning machine or by mean of injection molding. However, residual stress and/or tool marks can arise when using a commercial fabricating method such as DTM or injection molding. A polishing process, thus, is commonly used to obtain a high-precision aspherical lens. In this study, a polishing method using MR fluid was applied to minimize several problems, in this case residual stress and the creation of tool marks, during the cutting process. The MR polishing system was developed to polish aspherical lenses. A series of experiments were performed to obtain a very fine surface roughness. PMMA (the lens material for molding) was used as a workpiece, and the gap size, magnetic field intensity, wheel speed and feed rate were selected as the parameters in this study. Finally, a very fine surface roughness of Ra=2.12nm was obtained after MR polishing.

• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.443-448
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• 2004

We realized the national standard of the candela, one of the SI units, by using two photometers with the spectral responsivity measured in reference to the absolute cryogenic radiometer. The external apertures of the photometers were fabricated using a diamond turning machine, and measured in terms of area with uncertainty of 0.05 %(k = 1). The candela is realized using a 1 kW FEL lamp and the characterized photometers on an optical bench. The uncertainty is budgeted to be 0.25 %(k = 1) considering the uncertainty of the spectral responsivity and the response uniformity of the detectors, the area of the external apertures, the color temperature of the lamp, and the positioning reproducibility of the photometers and the lamp. We verified the realized scale by comparing with the scale of National Institute of Standards and Technology, USA. They coincided with each other within 0.1%.

• Current Optics and Photonics
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• v.6 no.2
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• pp.171-182
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• 2022

A single-photon laser and mid-wave infrared (MWIR) common aperture optical system was designed and developed to detect and range a long-distance civil aviation aircraft. The secondary mirror of the Ritchey-Chretien (R-C) optical system was chosen as a dichroic lens to realize the design of a common aperture system for the laser and MWIR. Point spread function (PSF) ellipticity was introduced to evaluate the coupling efficiency of the laser receiving system. A small aperture stop and narrow filter were set in the secondary image plane and an afocal light path of the laser system, respectively, and the stray light suppression ability of the small aperture stop was verified by modeling and simulation. With high-precision manufacturing technology by single point diamond turning (SPDT) and a high-efficiency dichroic coating, the laser/MWIR common aperture optical system with a 𝜑300 mm aluminum alloy mirror obtained images of buildings at a distance of 5 km with great quality. A civil aviation aircraft detection experiment was conducted. The results show that the common aperture system could detect and track long-distance civil aviation aircraft effectively, and the coverage was more than 450 km (signal-to-noise ratio = 6.3). It satisfied the application requirements for earlier warning and ranging of long-range targets in the area of aviation, aerospace and ground detection systems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1189-1193
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• 2012

The Miniaturized Fingerprint Imager (MFI) is a slim optical mouse that can be used as an input device for application to wireless portable personnel communication devices such as smartphones. In this study, we have fabricated key optical components of an MFI, including the illumination optical components and imaging lens. An LED beam-shaping lens consisting of an aspheric lens and a Fresnel facet was successfully machined using a diamond turning machine (DTM). A customized V-shaped groove for beam path banding was fabricated by the bulk micromachining of silicon that was coated with aluminum using the shadow effect in thermal evaporation. The imaging lens and arrayed multilevel Fresnel lenses were fabricated by electron beam lithography and FAB etching, respectively. The proposed optical components are extremely compact and have high optical efficiency; therefore, they are applicable to ultraslim optical systems.