• 한국초등과학교육학회지:초등과학교육
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• 제26권2호
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• pp.209-215
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• 2007

The purpose of this study was to investigate the characteristics of the contents which were presented in the physics exhibits of the following three museums; Seoul National Science Museum, National Science Museum and the Exploration Center. The main findings of this research were as follows: Firstly, it was found that 73.7% of the exhibits were composed of 'dynamic exhibits', 87.6% of the exhibits were 'active involvement type exhibits', 48.3% of the exhibits were 'interest induction type exhibits' and 42.8% of the physics exhibits were composed of exhibits related to optics. Secondly, it was found that many elementary students seemed to have difficulty in understanding and executing the activities in the physics exhibits.

• Current Optics and Photonics
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• 제1권6호
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• pp.626-630
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• 2017

GaN-based green light-emitting diode (LED) structures suffer from low internal quantum efficiency (IQE), known as the "green gap" problem. The IQE of LED structures is expected to be improved to some extent by exploiting the Purcell effect. In this study, the Purcell effect on the IQE of green LED structures is investigated numerically using a finite-difference time-domain simulation. The Purcell factor of flip-chip LED structures is found to be more than three times as high as that of epi-up LED structures, which is attributed to the high-reflectance mirror near the active region in the flip-chip LED structures. When the unmodified IQE is 20%, the relative enhancement of IQE can be greater than 50%, without utilizing the surface-plasmon coupling effect. Based on the simulation results, the "green gap" problem of GaN-based green LEDs is expected to be mitigated significantly by optimizing flip-chip LED structures to maximize the Purcell effect.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.442-445
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• 2004

The acoustic target strength (TS) of submarine is associated with its active detection, positioning and classification. That is, the survivability of submarine depends on its target strength. So it should be managed with all possible means. An anechoic coating to existing submarine or changing of curvature can be considered as major measures to reduce the TS of submarine. It is mainly based on the prediction of its TS. Under this circumstances, a study on the more accurate numerical methods becomes big topic for submarine design. In this paper, Kirchhoff approximation method was adopted as a numerical tool for the physical optics region. Secondly, the scaled models of submarine were built and tested in order to verify its performance. Through the comparison, it was found out that the Kirchhoff approximation method could be good design tool for the prediction of TS of submarine.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권8호
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• pp.487-494
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• 2000

This paper describes the design, fabrication and experiments of surface-micromachined aluminum micromirror array with hidden pin-joints. Instead of the conventional elastic spring components as connection between mirror plate and supporting structure, we used pin-joint composed of pin and staples to support the mirror plate. The placement of pin-joint under the mirror plate makes large active surface area possible. These flexureless micromirrors are driven by electrostatic force. As the mirror plate has discrete deflection angles, the device can be ap;lied to adaptive optics and digitally-operating optical applications. Four-level metal structural layers and semi-cured photoresist sacrificial layers were used in the fabrication process and sacrificial layers were removed by oxygen plasma ashing. Static characteristics of fabricated samples were measured and compared with modeling results.

• 한국컴퓨터정보학회논문지
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• 제22권11호
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• pp.31-37
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• 2017

In this paper, we propose efficient design and construction of an infrared wide angle optical system with low distortion utilizing a high resolution detector for automobile application. The operational convenience and the recognition ability have been improved significantly by applying the high resolution uncooled thermal detector with wide angle optical design. The active ahtermalization mechanism is implemented so that the adjustment of the optical component of the system is to be made automatically according to the temperature change by motorized control. The modulation transfer function (MTF) is about 50% at the Nyquist frequency close the diffraction limit. The distortion is less than 5% at the edge field. As a result, a high-resolution uncooled thermal optical system with wide field of view (FOV) is assembled, aligned and its performance is tested successfully.

• 천문학회보
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• 제36권1호
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• pp.52.2-52.2
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• 2011

The correlation between black hole mass and galaxy stellar velocity dispersion gives an important clue on the black hole growth and galaxy evolution. In the case of AGN, however, it is extremely difficult to measure stellar velocity dispersions in the optical spectra since AGN continuum dilutes stellar absorption features. In contrast, stellar velocity dispersions of active galaxies can be measured in the near-IR, where AGN-to-star flux ratio is much smaller, particularly with the laser-guide-star adaptive optics. However, it is crucial to test whether the stellar velocity dispersion measured from the near-IR spectra is consistent with that measured from the optical spectra. Using the TripleSpec at the Palomar 5-m Telescope, we obtained high quality spectra ranging from 1 to 2.4 micron for a sample of 35 nearby galaxies, for which dynamical black hole masses and optical stellar velocity dispersion measurements are available, in order to calibrate the stellar velocity dispersion in the near-IR. In this poster, we present the initial results based on 10 galaxies, with the stellar velocity dispersion measured in the H-band.

• Current Optics and Photonics
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• 제6권6호
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• pp.583-589
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• 2022

Vanadium dioxide (VO₂) is a well-known material that undergoes insulator-to-metal phase transition near room temperature. Since the conductivity of VO₂ changes several orders of magnitude in the terahertz (THz) spectral range during the phase transition, VO₂-based active metamaterials have been extensively studied. Experimentally, it is reported that the metal nanostructures on the VO₂ thin film lowers the critical temperature significantly compared to the bare film. Here, we theoretically studied such early transition phenomena by developing an analytical model. Unlike experimental work that only measures transmission, we calculate the reflection and absorption and demonstrate that the role of absorption is quite different for bare and patterned samples; the absorption gradually increases for bare film during the phase transition, while an absorption peak is observed at the critical temperature for the metamaterials. In addition, we also discuss the gap width and VO₂ thickness effects on the transition temperatures.

• Current Optics and Photonics
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• 제7권1호
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• pp.33-37
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• 2023

Real-time adaptive control of laser output polarization is presented in a 10-W-level non-polarization-maintaining (non-PM) fiber amplifier. While the output polarization from a non-PM fiber amplifier tends to be irregular, depending on output power, time, and perturbation, closed-loop polarization control can maintain the polarization extinction ratio at higher than 20 dB. Real-time polarization control can attain the target linear polarization mostly within 1.4-25 ms and shows stability against external perturbations. This approach can satisfy both linear polarization and high output power in a non-PM amplifier, and facilitates optimization of laser performance and maintenance-free operation.

• 한국광학회지
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• 제31권1호
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• pp.37-44
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• 2020

본 연구에서는 기본적인 평면 태양 전지 구조에 1차원 주기를 가지는 에미터 전극 배치를 통해 광학 및 전기적 효율을 최적화하는 설계방법을 제안한다. 에미터 전극의 주기가 줄어들면 애퍼처 비율이 감소해 빛 흡수율이 줄어들어 태양 전지 성능 저하에 영향을 끼친다. 본 연구에서는 시뮬레이션을 통해 가장 간단한 평판형 태양 전지 구조 내에서 에미터 전극 배열의 최적안을 제시하였다. 광학적 측면에서 에미터 전극이 없이 광흡수층 전면에서의 광흡수를 하는 레퍼런스 소자와 성능이 유사한 조건을 도출했다. 그리고 광흡수 및 전기적 효율 측면을 모두 고려하여 가장 효과적인 전극 구조를 제안하였다. 본 연구 결과는 광전 변환으로 생성된 전하를 전극으로 가장 효율적으로 전달할 수 있는 구조를 제안함으로써, 대체 에너지원에서 큰 비중을 차지하고 있는 태양 전지의 활용성을 높이는데 기여할 것이다.

• 한국항공우주학회지
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• 제43권5호
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• pp.472-478
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• 2015

본 논문에서는 소형 위성 카메라의 영상안정화를 위해 진동외란 보상 및 궤도상 광학정렬이 가능한 능동형 광학 보정장치의 설계에 대해 연구하였다. 능동형 광학 보정장치는 초점면부 보정장치와 부경 보정장치로 이루어져 있다. 초점면부 보정장치는 영상센서에 유입되는 진동 외란을 초점면부에서 직접 보상하는 장치이다. 또한 부경 보정장치는 초점면부 보정장치와 협력하여 궤도상에서 능동적으로 광학정렬을 수행할 수 있는 장치이다. 본 논문에서는 해상도 1 m급 소형 위성에 적용 가능한 능동형 광학 보정장치 설계를 위해 소형 고해상도 위성 카메라의 요구도를 분석하고, 진동 외란 보상과 궤도상 광학정렬이 능동적으로 가능하도록 초점면부 보정장치와 부경 보정장치의 요구도를 선정하였다. 선정된 요구도를 기준으로 본 연구에서 설계된 능동형 광학 보정장치는 초점면부에서 진동외란 보상 및 초점조절, 부경에서 틸트 및 디스페이싱 보상이 가능하므로 독립적으로 5축 제어가 가능한 시스템이다.