• Current Optics and Photonics
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• v.7 no.3
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• pp.263-272
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• 2023

A collimator refers to an optical system that images a collimated beam at a desired point. A resolution target located at a near distance can be converted into a virtual image located at a long distance. To test the resolution for mobile cameras, a large target is placed at a long distance. If a collimator system is used, the target can be placed at a near distance. The space required for a resolution inspection can thus be drastically reduced. However, to inspect a mobile camera, the exit pupil of the collimator system and the entrance pupil of the mobile camera must match, and the stop of the collimator system must be located on the last surface. Because a collimator system cannot be symmetrical with respect to the stop, the distortion becomes extremely large, which can be corrected by combining the collimator symmetrically with respect to the object plane. A novel system was designed to inspect an optical lens on a mobile phone. After arranging the refractive power, lenses were added using the equivalent lens design method. The distortion was reduced to less than 1%. This optical system satisfies a half-field angle of 45° and an optical performance sufficient for inspection.

• Current Optics and Photonics
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• v.3 no.1
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• pp.46-53
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• 2019

Monte Carlo simulations were performed for a three-dimensional tissue model with and without an embedded large vessel, to understand how varying vessel geometry affects surface light distribution. Vessel radius was varied from 1 to 5 mm, and vessel depth from 2 to 10 mm. A larger difference in surface fluence rate was observed when the vessel's radius increased. For vessel depth, the largest difference was seen at a depth of approximately 4 mm, corresponding to human wrist region. When the vessel was placed at depths greater than 8 mm, very little difference was observed. We also tested the feasibility of using two source-detector pairs, comprising two detectors distinctly spaced from a common source, to noninvasively measure blood-scattering changes in a large vessel. High sensitivity to blood-scattering changes was achieved by placing the near detector closer to the source and moving the far detector away from the source. However, at longer distances, increasing noise levels limited the sensitivity of the two-detector approach. Our results indicate that the approach using two source-detector pairs may have potential for quantitative measurement of scattering changes in the blood while targeting large vessels near the human wrist region.

• Transactions of the Society of Information Storage Systems
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• v.3 no.3
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• pp.135-138
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• 2007

Using a Shack-Hartmann sensor and sub-wavelength sized pinhole point source, we develope an optical testing system that measures the wavefront error of high numerical aperture and small sized optical components. The subwavelength sized pinhole generates perfect spherical waves with large diffraction angle and this makes possible to test high numerical aperture optics. The Shack-Hartmann sensor reconstructs the wavefront and calculates the aberrations. We make a home-made reference plane wave source which generates nearly perfect plane waves and the calibration with this plane source gives the overall uncertainty of the optical testing system 0.010 $\lambda$ rms.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.324-331
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• 2002

The fundamentals of light-emitting diode lamp design are presented. The shapes of the reflecting cup and lens employed in LED lamps can be flexibly adjusted, over a relatively large range, by using a few parameters. The analysis of the designed lamps by Monte Carlo photon simulation shows that diverse far-field beam patterns required in various application areas can be achieved.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.10
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• pp.845-850
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• 2016

A direct laser lithography system is widely used to fabricate various types of DOEs (Diffractive Optical Elements) including lenses made as CGH (Computer Generated Hologram). However, a parametric study that uniformly and precisely fabricates the diffractive patterns on a large area (up to $200mm{\times}200mm$) has not yet been reported. In this paper, four parameters (Focal Position Error, Intensity Variation of the Lithographic Beam, Patterning Speed, and Etching Time) were considered for stabilization of the direct laser lithography system, and the experimental results were presented.

• Proceedings of the KOSOMBE Conference
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• v.1994 no.12
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• pp.26-27
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• 1994

The first step implementation of a hospital-wide Picture Archiving Communications System (PACS) at a newly built hospital Samsung Medical Center (SMC), is described. Current clinical operation encompasses the fiber optics delivery of direct-interfaced magnetic resonance imager (LRI), X-ray computed tomography (CT). digital subtraction angiography (DSA) and computed radiography (CR) digital images via high performance file server to the departments of radiology, neurosurgery, orthopedics surgery, neurology, emergency room and the surgical intensive care unit.

• Korean Journal of Optics and Photonics
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• v.8 no.2
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• pp.128-133
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• 1997

The effects of twist induced birefringence on the polarization properties of Er and Nd fiber laser with a linear type cavity were experimentally observed and theoretically analyzed. As the twist rate increases, the polarization states of the polarization eigenmodes are found to be always linear, and their frequencies gradually coincide with each other, and their polarization directions rotate at about half of twist rate at large twist rates.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.105-109
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• 2001

The micro optical parts such as ferrules are required to be manufactured within very small tolerances, as the slight deviation of the tolerance would give very large amount of loss in communication efficiency. For efficient optical communication, outer diameter, fiber diameter, fiber separation and eccentricity are significant parameters to be inspected., Thus we developed an automatic inspection system to evaluate shape parameters of the optical fiber connectors(ferrule) upto submicron accuracy using machine vision. new optical probe of multi fields of views has been developed and the image processing and data analysis algorithms have been complemented in real time basis. The developed system is successfully used in the practical ferrule manufacturing industry, and about 0.1$\mu\textrm{m}$ accuracy can be obtained with very fast inspection time.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.40-40
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• 2014

Through KASI, Korean astronomers will have access to the Gemini Observatory starting in 2015. Gemini operates two optical/infrared 8m-class telescopes: one on the northern hemisphere in Hawaii, one on the southern hemisphere in Chile. Both are equipped with state of the art instruments and adaptive optics systems that will be presented. Gemini also offers the opportunity for instrument development and welcomes visiting instruments. In terms of operations, Gemini offers to its partners three ways of applying for time: through semester-basis calls for standard programs, through yearly calls for Large and Long Programs, and through monthly calls for fast turnaround programs. Gemini operates in queue mode (observing for the principal investigators and allowing flexibility in the time domain), as well as in the classical visitor mode (where principal investigators come to the telescope). I will explain the requirements and advantages of all these modes as well as a full update on the Gemini Observatory.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.140-144
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• 2007

As an electron scanning microscopes has traditionally required a considerably large room equipped with several service and pipe lines due to its inherent size. As an alternative, a small sized SEM, simply called a mini-SEM, is introduced even if the performance in terms of magnification and resolution is a little inferior to a classical thermal SEM. However, the size and fabrication cost is dramatically reduced, dedicating to opening a new market. The optical system in the mini-SEM is redesigned and specimen stage is quitely reduced and vertical axis is excluded. The design tools and calibration techniques to develope the mini-SEM are introduced and its performance is verified through numerical analysis experiments.