• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.370-374
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• 1996

A Superstructure Grating(SSG) Distributed-Bragg-Reflector(DBR) laser has a broad tuning range with a good mode suppression ratio. However, gaps of channel are observed in the wavelength-tuning characteristics of an SSGDBR laser which employs linearly-chirped DBR mirrors. We found by numerical simulation that the gaps may be attributed to the nonuniform reflection-peak heights of a linearly-chirped DBR mirrors. We propose a nonlinearly chirped grating DBR mirror structure that makes reflection-peak heights almost uniform. Therefore a nonlinearly chirped grating structure can be employed in an extended tuning range semiconductor laser to achieve gap-free tuning and low threshold current operation simultaneously.

• Korean Journal of Optics and Photonics
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• v.30 no.2
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• pp.37-47
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• 2019

A reflecting omnidirectional optical system with four spherical and aspherical mirrors, for use with long-wavelength infrared light (LWIR) for night surveillance, is proposed. It is designed to include a collecting pseudo-Cassegrain reflector and an imaging inverse pseudo-Cassegrain reflector, and the design process and performance analysis is reported in detail. The half-field of view (HFOV) and F-number of this optical system are $40-110^{\circ}$ and 1.56, respectively. To use the LWIR imaging, the size of the image must be similar to that of the microbolometer sensor for LWIR. As a result, the size of the image must be $5.9mm{\times}5.9mm$ if possible. The image size ratio for an HFOV range of $40^{\circ}$ to $110^{\circ}$ after optimizing the design is 48.86%. At a spatial frequency of 20 lp/mm when the HFOV is $110^{\circ}$, the modulation transfer function (MTF) for LWIR is 0.381. Additionally, the cumulative probability of tolerance for the LWIR at a spatial frequency of 20 lp/mm is 99.75%. As a result of athermalization analysis in the temperature range of $-32^{\circ}C$ to $+55^{\circ}C$, we find that the secondary mirror of the inverse pseudo-Cassegrain reflector can function as a compensator, to alleviate MTF degradation with rising temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.11
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• pp.907-913
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• 2002

An experimental study on energy density distributions produced by dish solar concentrating system was performed to optimally design and rightly position a cavity receiver. This deemed also very useful to find and correct various errors associated with a concentrator. It is observed that the actual focal length is 2.17 m with a maximum energy density of 1.89 MW/$m^2$. By evaluating the position of flux centroid, it was found that there are errors within 2 cm from the target center. As a result of the percent power within radius, approximately 90% of the incident radiation is intercepted by about 0.06 m radius. The area concentration ratio normalized to 800 W/$m^2$ insolation and 90% mirror reflectivity was 347 suns. The total integrated power of 2467 W was measured under focal flux distributions, which corresponds to the intercept rate of 85.8%.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.72.2-72.2
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• 2013

An off-axis telescope has several advantages in optical performance comparing with a conventional on-axis telescope. However, in general, an off-axis telescope has a narrow field of view due to the linear astigmatism caused by the asymmetric structure. It was shown in the previous work that the linear astigmatism can be eliminated by properly configuring parameters in a confocal off-axis reflector system. Furthermore, the third order aberrations of a confocal off-axis telescope can be minimized by optimizing the shape of the mirrors. Despite many advantages, the confocal off-axis telescopes have been evaded because of difficulties of off-axis mirror fabrication, alignment process and unaccustomed off-axis baffle design. The baffle for the off-axis telescope should be designed considering that the effects of stray lights are different because of the asymmetry of off-axis system. In this poster, the design, manufacturing, and test for the baffle and housing of an off-axis telescope are presented.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.1
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• pp.75-78
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• 2002

Thirty three layer $TiO_2/SiO_2$ coating mirrors with high reflectance through a 620~820nm wavelength range have been designed and fabricated by electron beam evaporation method. Multilayer films were deposited on glass(BK7) and sequentially. The high reflector design is based on alternating high and low refractive index layers. $n_H$ and $n_L$ such that a "stopband"(or area of high reflectivity) is created that is centered around the design wavelength. ${\lambda}_0$. The measured transmittance spectrum with an incident wavelength at an incident angle of $40^{\circ}{\pm}7^{\circ}$ exhibited a reflectance of 99.9% at the wavelength of 620~820nm but high peak transmittance in the wavelength region from 700 to 740nm.

• Korean Journal of Optics and Photonics
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• v.31 no.6
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• pp.328-333
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• 2020

In this paper, we study the analysis method for the aspherical tolerance of a Korsch telescope using a Q polynomial. It is important to analyze the tolerances for evaluating quality in high-precision fabrication of aspherical reflectors for high-resolution satellites. Thus we express the aspheric surface in terms of a Q polynomial in which each coefficient term is composed independently, and analyze the tolerance of a Korsch telescope. We also analyze the tolerance using Zernike fringe sag, which expresses the shape error of an aspherical mirror. By comparing the two results, we confirm that the Q-polynomial method can be used to analyze an aspherical mirror.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.1
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• pp.35-46
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• 2004

In comparison with edge-emitting lasers(EELs), predicting the output power and slope efficiency of Vertical-Cavity Surface-Emitting Lasers(VCSELs) is very difficult due to the absorption loss in DBR layers. However, by using transfer matrix method(TMM), we've made possible to calculate such parameters of multi-layer structures like VCSELs. In this paper, we've calculated the threshold gain, threshold current and slope efficiency through the methodology based on TMM. Also TMM is the way of customizing the VCSEL structure for the desired threshold current and slope efficiency by changing the number of DBR mirror layers.

• Journal of the Korean Society of Industry Convergence
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• v.19 no.2
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• pp.62-68
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• 2016

Laser distance measuring systems are used in many fields with high precision. However, when measuring the reflector such as the mirror and the black color, a laser distance measuring system does not guarantee the measurement accuracy. In order to measure the shape of the cargo, this study proposes the radar distance measurement system. The radar distance measuring system is composed of a distance measuring unit with a 24 GHz antenna module, a signal processing and control board and the 1-axis tilting unit. And, this study developed a monitoring program to monitor the measured data. In order to evaluate performance of the developed system, the distance measurement tests are carried out. The distance error was about 6-15 cm. However, considering the size of the cargo, the precision is not a problem. And, cargo shape was measured by using the distance information measured by the 1-axis tilting unit. It could get a 2 dimension shape profile for the cargo stacked in a yard.

• Journal of Astronomy and Space Sciences
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• v.35 no.4
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• pp.253-261
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• 2018

Korea Astronomy and Space Science Institute (KASI) has been developing the space optical and laser tracking (SOLT) system for space geodesy, space situational awareness, and Korean space missions. The SOLT system comprises satellite laser ranging (SLR), adaptive optics (AO), and debris laser tracking (DLT) systems, which share numerous subsystems, such as an optical telescope and tracking mount. It is designed to be capable of laser ranging up to geosynchronous Earth orbit satellites with a laser retro-reflector array, space objects imaging brighter than magnitude 10, and laser tracking low Earth orbit space debris of uncooperative targets. For the realization of multiple functions in a novel configuration, the SOLT system employs a switching mirror that is installed inside the telescope pedestal and feeds the beam path to each system. The SLR and AO systems have already been established at the Geochang station, whereas the DLT system is currently under development and the AO system is being prepared for testing. In this study, the design and development of the SOLT system are addressed and the SLR data quality is evaluated compared to the International Laser Ranging Service (ILRS) tracking stations in terms of single-shot ranging precision. The analysis results indicate that the SLR system has a good ranging performance, to a few millimeters precision. Therefore, it is expected that the SLR system will not only play an important role as a member of the ILRS tracking network, but also contribute to future Korean space missions.