• Korean Journal of Optics and Photonics
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• v.13 no.1
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• pp.15-20
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• 2002

We demonstrate a widely-tunable wavelength converter based on four-wave mixing in a semiconductor-fiber ring laser with no external pump light. Applying 10 GHz short pulses at -8 dBm as a probe signal, we achieve continuous wavelength tuning over the semiconductor optical amplifier gain-bandwidth reaching 30 nm down- and 17 m up-wavelength conversion. In addition to the wide tuning capability, the converter shows high-speed conversion and low saturation power capabilities.

• Korean Journal of Acupuncture
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• v.28 no.3
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• pp.13-23
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• 2011

Objectives : The aim of this study was to develop the combined medical stimulus system consisted of the PEMFs (Pulsed electromagnetic fields) and LED which are able to stimulate local point such as acupoints and trigger points. Methods : To evaluate the therapeutic effect on the musculoskeletal disorders and the possibility of alternative method on manual acupuncture, we compared the fatigue recovery of two groups by analyzing the EMG and peak torque (non-stimulation and, stimulation group) after strenuous knee exercise. We chose the LR9 as a stimulation point. Results : The median frequency (MF) and fatigue index (F.I) of the stimulation group were recovered faster than those of the non-stimulation group. Also the peak torques of both groups were not restored until after 20 minutes. However, the peak torque of the stimulation group was regained higher than that of the non-stimulation group. Conclusions : We confirmed that the proposed combined stimulus system had useful effects as treatment instrument of musculoskeletal disorder using non-invasive method of PEMFs and LED.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.1
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• pp.85-90
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• 2006

This paper presents experimental results relating to the preliminary breakdown characteristics in $SF_6/CO_2$ gas mixtures under a highly non-uniform electric field. The impulse pre-breakdown developments are investigated by the measurements of corona current and light emission images. As a result, the preliminary breakdown development mechanisms for both the positive and negative polarities were fundamentally same. The first streamer corona was initiated at the tip of needle electrode, and the leaders developed with a stepwise propagation and bridged the test gap. The pause time of leader pulses in the positive polarity was significantly shorter than that in the negative polarity. Also, the time interval between the first streamer corona onset and breakdown in the negative polarity was much longer than that in the positive polarity. The discharge channel path in the positive polarity was zigzag, and the leader channel in the negative polarity was thicker and brighter than that in the positive polarity.

• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.462-467
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• 2016

Dispersion management (DM) combining with mid-spans spectral inversion (MSSI) is one of the various techniques compensating for the distorted optical signals. For the flexible implementation of this configured link, the compensation characteristics in the optical link with artificial distribution of the gradually ascending and descending of single mode fiber (SMF)'s lengths and residual dispersion per span (RDPS) as the number of fiber spans are assessed as a function of the control positions of net residual dispersion (NRD). It is confirmed that the best compensation is obtained by distributing gradually ascending or descending of SMF's lengths and RDPS capable to place NRD control position at fiber span, in which optical pulse width is most narrow.

• Korean Journal of Optics and Photonics
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• v.9 no.3
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• pp.168-174
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• 1998

We have measured nonlinear refractive index and nonlinear absorption coefficient of optical materials by using a far-field phase modulation technique. The phase variation of the probe beam in the nonlinear material is transformed into the spatial phase modulation in the far-field so that the spatial distribution of the optical intensity in conjunction with the computer simulation analysis can give the nonlinear optical constants. We have obtained the nonlinear refractive indices and nonlinear absorption coefficient of $CS_2$ and $BaF_2$ by fitting the experimental values and numerical simulation analysis of far-field measurements. The nonlinear refractive indices of $CS_2$ and $BaF_2$were obtained as $1.2{\times}10^{-11}$ esu and $1.0{\times}10^{-13}$ esu, respectively at 616 nm, and the nonlinear absorption coefficient of BaF$_2$as $5.0{\times}10^{-11}$cm/W at 308nm. These measured values were in good agreement with previous reports.

• Information and Communications Magazine
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• v.11 no.2
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• pp.77-89
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• 1994

High speed optical fiber transmission technology has been remarkably improved during the past 20 years. This paper presents recent research status and future technological issues for the future information society, that is, the Tb/s transmission by frequency division multiplexing and the ultra long-distance by optical soliton transmission. Erbium-doped fiber amplifier and recent optical technology have brought optical transmission system of up to 10 Gb/s to the point of commercialization. Taking into account the future super information highway, that is, B-ISDN network, ultra wide-band picture-based information can be provided for many subscribers via existing optical fiber cables. However, to achieve the high speed transmission, the technologies must be developed not only for transmission lines but also for transmission nodes. Since the conventional signal transmission/processing technique using electronics has the limit in its speed, novel photonic technology is being developed for this purpose. On the other hand, optical solitons propagate stably through optical fibers, without pulse broadening effect of the fiber dispersion. Since the pulse broadening effect becomes serious as the transmission speed increases, optical solitons is the important technologies to realize the high speed, long distance transmission.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.12
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• pp.51-57
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• 2004

A simple fiber length measurement technique has been demonstrated by using a self-seeding laser oscillation of a Fabry-Perot laser diode. We induced a self-seeding laser oscillation through a closed-loop by adjusting the modulation frequency of a Fabry-Peort laser diode when the output optical pulse of the laser reinjected into the laser after passing through the closed-loop. The length of a fiber-under-test was calculated from the difference between my two modulation frequencies at which self-seeding laser oscillation occurs at a specific mode. We have experimentally confirmed the technique for various fiber lengths from 0.1 km to 75 km. The relative error between the measurement result of the proposed technique and that of a commercial instrument was less than 0.24 %. The repeatability of the proposed technique was better than 0.1 %.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.2
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• pp.117-122
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• 2020

In this paper, we study the electromagnetic interference in adjacent antenna aperture of multi-function radar for Integrated MAST of naval ship, which is operating plural radars, with test result of two different X-band antennas. Two antennas is placed in the test fixture copying the part of Integrated MAST for the experiment. The test figure is modeled to see the electromagnetic interference when antenna beam is steered by using electromagnetic analysis tool. Also, 6 test scenarios is determined to verify experimentally and each test scenario is run in an anechoic chamber. At the test antenna #1 radiates a pulse signal and the signal from the antenna #2 is stored and analyzed in the optic data format through a receiving device. Based on the result, the effect of electromagnetic interference is suggested when multi-function radars in the Integrated MAST are operating in adjacent distance.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.80-80
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• 1999

플라즈마 디스플레이 패널(PDP)의 공정을 간단히 하기 위하여 포토레지스트, ITO, 격벽재료를 Ar+ laser(λ-514 nm, CW)와 Nd:YAG laser(λ=532, 266nm, pulse)로 직접 패터닝 하였다. 레이저에 의한 포토레지스트의 패턴결과, 아르곤 이온 레이저의 포토레지스트 가공의 반응 메카니즘은 레이저 빔의 열에 의한 시료 표면의 국부적인 온도상승에 의한 용융작용이며, 그 결과 식각 후 형성된 패턴의 단면 모양도 레이저빔의 profile과 같은 가우시안 형태를 나타낸다. Nd:YAG 레이저의 4고조파(532nm)를 이용한 경우 200$\mu\textrm{m}$/sce의 주사속도에서 포토레지스트를 패턴하기 위한 임계에너지(threshold energy fluence) 값은 25J/cm2이며, 약 40J/cm2의 에너지 밀도에서 하부기판의 손상이 발생하기 시작하였다. 글미 1은 Nd:YAG 레이저 4고조파를 이용하여 포토레지스트를 식각한 경우 SEM 표면사진(위)과 단차특정기에 의한 단면형상(아래)이다. ITO 막의 레이저에 의한 직접 패턴 결과, ITO 막은 레이저 펄스에 의한 급속 가열 및 증발에 의한 메커니즘으로 식각이 이루어지며, 레이저 파장에 따른 광흡수 정도의 차이에 의해 2고조파 (532nm)에서 ITO 막의 가공 품질이 4고조파(266nm)에 비해 우수하며 패턴의 폭도 출력에 따라 제어가 용이하였다. 그림 2는 Nd:YAG 레이저 2고조파를 이용하여 ITO를 식각한 경우 SEM표면 사진(위)과 단차측정기에 의한 단면형상(아래)이다. 격벽 재료의 레이저에 의한 직접 패턴 결과, Ar+ 레이저(514nm)는 출력 밀도 32NW/cm2에서 격벽을 유리 기판의 경계면까지 식각하였다. Nd:YAG 레이저(532nm)는 laser fluence가 6.5mJ/cm2에서 격벽을 식각하기 시작하였으며, 19.5J/cm2에서 유리기판의 rudraus(격벽 두께 130$\mu\textrm{m}$)까지 식각하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.59-59
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• 2010

ZnO는 II-VI 족 화합물 반도체로써 상온에서 큰 엑시톤 결합에너지 (~60 meV) 를 가지며 밴드갭이 3.37 eV인 직접 천이형 반도체로 잘 알려진 물질이다. 이러한 ZnO의 물리적 특성은 광학소자로 상용화된 GaN와 유사하기 때문에 LED나 LD등의 광 소자 재료로 주목 받고 있다. 또한 ZnO는 3족 원소 (In, Ga, Al)를 도핑 함으로써 전기적 특성 제어가 가능한 장점을 가지고 있다. 본 연구는 펄스레이저 증착법 (Pulsed Laser Deposition)을 이용하여 Si (111) 기판 위에 ZnO:In 박막을 성장 시켰으며, 도핑된 indium 양에 따른 ZnO 박막의 배향성 변화를 관찰 하였다. X-선 회절 분석법 (X-ray diffraction), 탐침형 원자현미경 (Atomic Force Microscope) 그리고 투과전자 현미경 (Transmission Electron Microscope)을 측정하였다. XRD 측정 결과 un-doped ZnO 박막은 (002) 방향으로 c-축 우선성장 하였다. 그러나 ZnO 박막내의 Indium 양이 증가 할수록 (002) 방향에서 (101), (102), (103) 등의 (101) 방향으로 성장이 변화 하였으며 5 at.% 이상에서는 (100) 방향의 성장이 관찰 되었다. TEM 측정 결과 un-doped ZnO 박막은 columnar 구조로 성장 되었으나, Indium 양이 증가할수록 column의 size가 감소하며, 5 at.% 이상에서 columnar 구조 성장이 거의 관찰되지 않는다. AFM 결과에서는 Indium 양이 증가 할수록 박막의 표면거칠기와 결정립 크기가 감소하였다.