• Korean Journal of Optics and Photonics
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• v.4 no.2
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• pp.140-144
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• 1993

A computer program for computing the edge response function(ERF) from the optical transfer function( 0TF) was developed. The ERFs of un-aberrated optical system and aberrated optical system were studied by the use of that program. We calculated the ERFs of the optical systems with a single aberration and with a combined aberration. In sagittal case, the ERE of the optical system with defocus or spherical aberration was worse than that with coma. In tagential case, the ERF of the optical system with coma was worse than that with defocusing or spherical aberraion. Both the shape and the position of ERF were varied with coma, but only the position of ERF was varied with distortion, in tangential case.

• 한국정보통신설비학회:학술대회논문집
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• 2009.08a
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• pp.314-319
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• 2009

In this paper, the network performance of a turbo coded optical code division multiple access (COMA) system with cross-layer, which is between physical and network layers, concept is analyzed and simulated We consider physical and MAC layers in a cross-layer concept. An intensity-modulated/direct-detection (IM/DD) optical system employing pulse position modulation (PPM) is considered In order to increase the system performance, turbo codes composed of parallel concatenated convolutional codes (PCCCs) is utilized. The network performance is evaluated in terms of bit error probability (BEP). From the simulation results, it is demonstrated that turbo coding offers considerable coding gain with reasonable encoding and decoding complexity. Also, it is confirmed that the performance of such an optical COMA network can be substantially improved by increasing the interleaver length and the number of iterations in the decoding process. The results of this paper can be applied to implement the indoor optical wireless LANs.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.54.3-54.3
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• 2021

The Coma cluster serves as an ideal laboratory to study the cluster assembly history. It is known as a typical example of relaxed galaxy clusters. However, recent X-ray, radio and optical observations revealed a number of substructures in Coma. The NGC 4839 group is an interesting substucture in the sense that it is overlappled with the X-ray bright component in the south-west region. Recent hydrodynamical simulations in the literature suggest that the NGC 4839 group came from the north-east direction of Coma, passed the apocenter about 1 Gyr ago, and started a second infall to the Coma core recently. Interestingly a number of E+A galaxies are located along the filament connecting the NGC 4839 group and the Coma core. We are surveying a wide area covering the NGC 4839 group to search for globular clusters and use them to investigate any connection between the globular clusters and the merger scenario of the NGC 4839 group. We utilized Subaru Hyper Suprime-Cam archival images of two circular fields with diameter ~1.8 deg, covering the Coma core and the NGC 4839 group. We discuss the results with regard to the formation history of the NGC 4839 group.

• Journal of the Semiconductor & Display Technology
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• v.15 no.3
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• pp.62-66
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• 2016

Optical system needs to be aligned before its undergoing process, is usually shows coma aberrations, which occurred due to imperfection in the lens or other components results in off-axis point sources, appearing to have a tail like a comet. There are some methods to correct coma aberration. In this paper, to correct coma aberration in optical system, using a robot arm type coordinate measuring machine(CMM). CMMs are widely used to measure the form of accuracy of parts and positioning accuracy of systems. Among them, robot arm type CMM has more advantages than the others, such as its mobility and measuring range. However, robot arm type CMM has lower accuracy than cantilever type CMM. To prove robot arm type CMM's accuracy, several factors were suggested in this paper and the final measuring results were compared to a commercial cantilever type CMM. Based on this accuracy, a typical optical system was successfully aligned by using our robot arm type CMM.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.29.1-29.1
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• 2017

I present new near-infrared (NIR) photometry of globular cluster (GC) systems associated to a cD galaxy NGC 4874 in the core of the Coma cluster and 16 early-type galaxies in the Fornax and Virgo clusters of galaxies using the Infrared Channel of the Wide Field Camera 3 (WFC3/IR) on board the Hubble Space Telescope (HST). Combining these high-resolution NIR data with new HST Advanced Camera for Surveys (ACS) optical photometry for NGC 4874 and existing ACS GC catalogs from the ACS Fornax and Virgo Cluster Surveys, I have examined for the first time the GC systems in a statistically significant optical/NIR sample of galaxies spanning a wide range of luminosities and colors. A primary goal of this study is to explore empirically whether the distributions of purely optical and hybrid optical - NIR color indices for extragalactic GCs have different forms and whether the relations between these color indices are nonlinear, indicating that they behave differently with underlying metallicity. I find that some GC systems of large galaxies in our sample show color bimodalities that differ between the optical and optical - NIR colors, in the sense that they have disparate ratios of "blue" and "red" peak GCs, as well as differing ratios in their color dispersions. Consistent with these results, I find empirically that the dependence of hybrid optical-NIR color on purely optical color is nonlinear, with an inflection at intermediate metallicities. These findings underscore the importance of understanding the nature of galaxy-to-galaxy variations in the GC color distributions and color-color relations, as well as the exact forms of the color-metallicity transformations, in interpreting the observational data on GC color bimodality. Our ACS data for NGC 4874 shows that its GC system exhibits a very strong blue tilt, implying a very steep mass-metallicity scaling, and the centroid of this GC system is offset by $4{\pm}1kpc$ from the luminosity center of NGC 4874, in the direction of NGC 4872. Finally, I discuss the asymmetrical GC distribution around a dwarf elliptical galaxy in Coma that has a very high relative velocity with respect to the cluster mean at small clustercentric radius.

• Journal of the Optical Society of Korea
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• v.13 no.2
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• pp.184-192
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• 2009

There are total eight degrees of freedom in designing a three-mirror system. If we correct four kinds of third order aberrations and the system should have the specified effective focal length, the remaining three degrees of freedom can be used for selecting a suitable configuration for a specific application. We suggest an analytic design procedure for a three-mirror telescope system which has a suitably sized secondary mirror and proper separations between mirrors, and is corrected for four kinds of third order aberrations, spherical aberration, coma, astigmatism, and field curvature. Two design examples are shown. One has a compact configuration with off-axial field, the other has relatively long configuration with annular ring field.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.76.3-77
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• 2015

MIR colors are an excellent tool to investigate the transition phase of galaxy evolution in terms of star formation at various phases. The Coma supercluster is the nearest massive supercluster, hosting two main clusters, the Coma (Abell 1656) and Leo (Abell 1367) clusters, and one galaxy group, the NGC 4555 group, providing an ideal laboratory to study how galaxies evolve depending on environment. We present the results of a study for MIR properties of galaxies in the Coma supercluster using multi-wavelength data from the optical to MIR including the Sloan Digital Sky Survey Data Release 12 and the Wide-field Infrared Survey Explorer. We investigate differences in MIR properties of galaxies among three galaxy systems, and discuss the results in relation with star formation history and morphological transformation of galaxies.

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.83-84
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• 2006

• Korean Journal of Optics and Photonics
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• v.2 no.3
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• pp.127-132
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• 1991

We have obtained the analytic solutions of the four spherical mirror system free from the Seidel third order aberratios which are spherical aberration, coma, astigmatism, and distortion, Vignetting. Petzval field curvature, and optical properties according to the design parameters are numerically investigated and optimized. The numerical aperture of this system is 0.2 and the half field angle is $1.5^{\circ}$.

• Current Optics and Photonics
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• v.3 no.1
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• pp.72-77
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• 2019

This study was performed to analyze the optical aberrations of the cornea induced by myopic refractive surgery. Corneal total higher-order aberrations, spherical aberration and coma for 4-mm and 6-mm pupils were measured using a wave-front analyzer. The amount of aberrations of the oblate corneal optics by the achieved correction was found to be larger than for the prolate corneal shape with complete eye, in an emmetropia control group. The change in corneal shape acts as an optical factor that degrades the quality of the retinal image; it seems to be one of the important factors related to quality of vision.