Papers by Author: Jae Young Joo

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Authors: Jae Young Joo, Chang Suk Kang, Soon Sub Park, Sun Kyu Lee
Abstract: In this paper, we demonstrated the machining process of a novel Light Emitting Diodes (LED) beam shaping lens, called TIR Fresnel lens, for GaN-based blue Chip Scale Packaged (CSP) LEDs. Upon achieving a precise alignment of the tool and identifying the best manufacturing condition, we have successfully fabricated a prototype of this lens on poly methyl methacrylate (PMMA) plate. The form error of the central aspheric lens was less than 1 μm deviation, and surface quality of the Fresnel facets were sufficient for Total Internal refraction without any burr or adhesion of the machined chip. Fabricated TIR Fresnel lens reduced the viewing angle of the testing CSP LED from 140° to 17.4° in FWHM. The proposed lens produced extreme compactness as well as high collimation efficiency, thereby applicable to an ultra-thin optical system.
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Authors: Sung Hoon Kim, Dae Jun Jung, Jae Young Joo, Sung Ho Jeong
Abstract: The curing characteristics of a photocurable resin are critical factors that often decide the ultimate resolution and structural sharpness of a final product fabricated by microstereolithography (μ-STL). In this study, we investigated the curing characteristics of the FA1260T photopolymer under a visible laser light of 442nm wavelength. Modification of the curing property of the FA1260T is attempted to reduce the cure depth (Dc) by adding a radical quencher to the resin. Also, an organic solvent was used to reduce the resin viscosity for an improvement of the flatness of the liquid surface during layer-by-layer curing. As a result, the minimum Dc has been reduced over a factor of 3 with no abrupt increase. Samples of three dimensional microstructures fabricated using the modified FA1260T are presented.
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