• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.3
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• pp.343-354
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• 2012

In this paper, various spiral zeroth-order resonators are proposed for wireless power transmission. Since a zerothorder resonance(ZOR) mode of meta-material transmission lines has the characteristic of an infinite wavelength, its frequency is independent of physical length. Also, to obtain high transmission efficiencies high-Q resonators and strong coupling coefficient between coupled resonators are required. Therefore, the resonators consist of spiral inductor and lumped capacitor to use the ZOR mode and they are optimized via parametric study and circuit analysis for a high-Q resonator design. The optimized resonators are simulated and compared with a conventional spiral resonator and one of them was fabricated and measured. The fabricated one has a dimension of $20cm{\times}20cm{\times}8cm$($0.009{\lambda}_0{\times}0.009_{\lambda}_0{\times}0.004{\lambda}_0$) and the transmission efficiency of 80 % is measured at 13.56 MHz at transmitted distance of 40 cm.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.426-426
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• 2011

최근 들어 금속물질을 나노미터 단위로 구성할 수 있는 기술이 진보하면서, 금속 나노입자에 의해 발생되는 표면 플라즈몬에 대해서도 다양한 분야의 관심이 집중되고 있다. 유전체 물질을 기지상으로 하는 금속:유전체 나노복합체에서 금속 나노입자는 자유전자들의 집단 진동인 국소표면 플라즈몬 공진(Localized Surface Plasmon Resonance, LSPR)현상에 의해 국부전기장을 증대 시키고, 가시광 및 적외선 영역에서 특성 광흡수 거동을 보인다. 이와 같은 광학적 특성은 금속 나노입자들의 크기, 형태, 그리고 나노입자들의 주변을 구성하는 기지상 물질의 종류에 의해 조절된다. 금속:유전체 나노복합체에 나타나는 이러한 특성은 단순장식코팅 뿐만 아니라 광의 효율적 운용과 광을 매개로 한 기능발현을 필요로 하는 디스플레이, 광학 스위칭 소재 및 태양전지의 효율 향상을 위한 광흡수층 등 매우 다양한 응용이 가능하다. 본 연구에서는 다양한 굴절률을 갖는 재료들 중, 저굴절률을 갖는 SiO2와 고굴절률을 갖는 ZnS-SiO2를 기지상 재료로 선택하여 교번증착 스퍼터링법으로 Ag와 Au입자를 형성시켰다. Ag를 금속나노입자로 갖고, SiO2와 ZnS-SiO2를 기지상으로 하는 금속:유전체 나노복합체에서는 금속나노입자 형성에 따른 뚜렷한 표면 플라즈몬 공진 광흡수 피크가 관찰된 반면 Au나노입자는 기지상에 따라 각기 다른 광흡수 특성을 나타냈는데, SiO2기지상에서 명확한 광흡수 피크를 형성했던 경우와는 달리 ZnS-SiO2기지상에서는 특정파장에서의 흡수피크로 규정되기 어려운 넓은 파장범위에 걸친 완만한 광흡수 피크를 나타냈다. TEM 분석을 통해, ZnS-SiO2 기지상 내의 Au입자는 각각 독립되어 있는 Island형태가 아닌 유전체 기지상과 대칭적으로 혼합된 네트워크 형태의 Bruggeman 기하구조를 구성하고 있음을 확인하였고, 이는 Au입자가 형성되고 성장할 때 Au와 S의 높은 결합에너지로 인해 상당한 젖음 특성을 갖고 성장하였기 때문으로 판단됐다. 따라서 나노복합체를 구성하는 물질간의 광학적 특성뿐만 아니라 기지상 내에서의 금속입자의 성장거동에 대한 연구가 수반되었을 때, 금속:유전체 나노복합체의 표면 플라즈몬 공진 광흡수 특성을 보다 정확하게 제어할 수 있다.

• Journal of Korean Ophthalmic Optics Society
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• v.4 no.2
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• pp.45-49
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• 1999

The second harmonic, wavelength is 397nm, of the continuous wave diode laser, whose maximum power is 35mW, was generated in $LiIO_3$ crystals in a ring enhancement cavity. 5mm- and 10mm-long crystals cut $43.21^{\circ}$ for optic axis were used in this experiment. Both surfaces of those were anti-reflection coated for 794nm. In case the crystal was inserted into the cavity, the condition of separation between two concave mirrors for the optimum mode matching was found. The conversion efficiency of second harmonic generation was increased by the resonant enhancement of pumping power in the ring enhancement cavity, and the frequency of diode laser was locked to that of the counter-propagation mode generated from the surface of crystal. When the pumping power was 28 mW, the infrared buildup factor was about 45 without the crystal, and 14 with the crystal due to the transmission loss of crystal. The maximum second harmonic powers of $1.5{\mu}W$ and $6.6{\mu}W$ were obtained, and corresponding conversion efficiencies were $(6.584{\pm}0.56){\times}10^{-3}$%, $2.6{\pm}0.21){\times}10%{-2}$% in 5mm- and 10mm-long $LiIO_3$, respectively.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.674-679
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• 2003

We fabricated erbium-doped fiber ring laser with a new structure that can operate in C- & L-band wavelength region. The wave-length of the laser can be tuned continuously over 102 nm between 1510.4-1612.6 nm by insertion of the fiber Fabry-Perot tunable filter (FFP-TF) in the ring cavity. By use of the wavelength tunable characteristics of our fiber laser, we measured absorption spectra of more than fifty transition lines of the acetylene ($^{13}$ C$_2$H$_2$) molecule with high signal to noise ratio (SNR).

• Korean Journal of Optics and Photonics
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• v.1 no.1
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• pp.22-27
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• 1990

The cavity-length detuning characteristics of the hybridly mode-locked dye laser have been studied with a collinear autocorrelator. In the optimum condition, the pulse width is 0.65 ps about three times as short as that of the synchronously mode-locked dye laser. As the cavity length is increased, the pulse width becomes broader than that at the optimum cavity length because of the effect of spontaneous emission. Also, the spectrum width becomes broad, therefore the time bandwidth product ($\Deltat\Deltav$) is increased. The peak power of autocorrelation is maximum at $\Deltat=5.0\umm$ longer than the optimum cavity length. On the other hand, as the cavity length is decreased, the pulse width becomes broader and the satellite pulses appear because of the gain recovery. Also the spectrum width becomes narrower than that at the optimum cavity length. In particular, at the mismatched cavity length the center of the lasing spectrum moves to shorter wavelengths. ngths.

• The Journal of the Acoustical Society of Korea
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• v.38 no.1
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• pp.67-72
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• 2019

In this study, we investigate the echo reduction performance of miniaturinzed Helmholtz resonators using smaller than wavelength acoustic metamaterial structures. The Helmholtz resonators are formed using air structures which exhibit large impedance mismatch with the surrounding underwater environment. Using the multi-physics software package, we find that significant reduction in the sonar signature is expected and frequency tailoring is possible by controlling the degree of space coiling and inner volume of the resonators. We find that for the basic Helmholtz resonators, up to 7 dB reduction in echo is expected at 10,000 Hz while when the miniaturized Helmoholtz resonators are used, up to 14 dB reduction in echo is expected at 5,000 Hz. In addition, frequency tailoring is demonstrated by varying the internal volume of the Helmholtz resonators and broadband characteristic is shown using superposition of various degree of space coiled structures. Through this study we investigate the effectiveness of the miniaturized Helmholtz resonators formed using air structures and the echo reduction results show promisses in the application of achieving underwater stealth.

• Korean Journal of Optics and Photonics
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• v.9 no.3
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• pp.151-155
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• 1998

A new Fabry-Perot tunable filter has been built with simple construction, which does not require any additional aligning and/or beam-confining components for the reduction of the diffraction loss. For this feature, one of the two fibers for the filter is processed to have a concave mirror whose curvature is the same as that of the wavefront of the Gaussian beam from the first fiber. After high reflection coatings, the two fibers are aligned to result in an FP filter whose bandwidth, free spectral range, and insertion loss is 1.47nm, 52nm, 5.6dB respectively.

• Korean Journal of Optics and Photonics
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• v.4 no.3
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• pp.289-293
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• 1993

A Nd:YLF laser pumped by a CW GaAlAs laser diode(LD) at 792 nm has been designed and fabricated. The output power was investigated as a function of LD spectrum and pump power. A folded laser resonator was desinged to compensate for the astigmatism produced at the Brewster surface of Nd:YLF rod. We obtained output power of CW 1.1 Watt when the pumping power was 2.8 Watt and the output wavelength of LD was temperature tuned to the peak absorption line of Nd:YLF. The overall efficiency was 39 % and slope efficiency was 41 %.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.32-33
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• 2000

최근 다른 두께로 조합된 양자 우물 구조를 이용한 연구가 다음과 같이 각각 다른 목적으로 진행되고 있다. 이러한 불균일 양자 우물 구조는 주로 광대역폭 반도체 광 증폭기를 위한 구조$^{l),2)}$ 광대역폭 Superluminescent Diode에 적용하기 위한 구조, $^{3)}$ 광대역폭 및 온도 비의존성 면발광 레이저를 위한 구조$^{4)}$ 로 이용되고 있으며 10여년 전에는 파장 조절 및 파장 스위칭을 위한 구조로 연구되었다.$^{5).6)}$ 이들 소자의 실현을 위해 우선 불균일 양자 우물 구조의 특성을 알아볼 필요가 있다. 본 연구에서 사용한 양자 우물 구조는 그림 1과 같이 각 양자 우물의 두께가 다르게 분포되어 있다. 그리고 이 구조를 CBE로 성장하고 릿지형 반도체 레이저를 제작하여 공진기 길이와 주입전류에 따른 발광 파장 특성으로부터 불균일 양자 우물 구조에서의 캐리어 분포 특성을 유추하였다. (중략)

• Water for future
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• v.20 no.1
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• pp.49-54
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• 1987

A numerical analysis of the characteristics of wave reflection over rippled beds (sand bars) was carried out By Boundary Element Method(B.E.M) using linear elements. It is assumed that the incident wave is normal and oblique to the rippled beds and the wave may be and the escribed by two-dimensional linear theory. The accuracy of the computational scheme is investigated by comparing the laboratory data, the analytic measured results of the other researchers. The B.E.M results for the normal incident wave is held for the mechanism of the resonant Bragg reflection at the point where the wave length of the bottom undulation is one half the wave length of the surface wave.