• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.110-111
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• 2000

A novel 2$\times$2 switching characteristics are investigated. This switching characteristics are obtained in the multimode interference waveguide structure. For analysis, beam propagation method (BPM) based on mode propagation theory is used. As a result, the extinction ratio of higher than 11.74dB is achieved.

• Korean Journal of Optics and Photonics
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• v.5 no.2
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• pp.260-265
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• 1994

In the three-level atom interacting with a single mode radiation field, two-photon excitation between the ground state and the upper most excited state is investigated. Using the resolvant theory, the effective resolvant, containing the ground state and the final excited state, is found and the coupling constant and the detuning being taken as parameters, the excitation mechanism is analyzed. In particular. by introducing an ensemble of effective two-level atoms, a consistent interpretation in terms of inteference phenomena is pursued. rsued.

• Journal of KSNVE
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• v.9 no.3
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• pp.509-516
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• 1999

The ESPI (Electronic Speckle Pattern Interferometry) algorithm has been simulated to calculate vibrational modes of a thin right-angled STS304 plate. The phase transformation of the reference wave of the ESPI is carried out only one time during vibration in order to clarify ESPI speckle patterns. Two dimensional vibrational modes are calculated from one ESPI pattern before vibration onset and two ESPI patterns during vibrations but with and without the phase transformation. The ESPI harmonic results are compared with those derived from the finite element method (FEM), and they agree very well. Additionally a phase unwrapping algorithm has been newly developed to derive a displacement map from an ESPI phase map.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.7
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• pp.79-87
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• 1997

Untill now, the most well-known cofiguration for waveguide grating router(WGR) is composed of radiative star couplers and arrayed waveguide grating(AWG), which usually suffer form the rdiation loss of around 3dB or more. Therefore, te improved design of WGRs is needed to reduce the loss. In ths paper, we propose a novel WGR composed of multimode interference couplers which have good unifiormity, fabrication tolerance, and very low excess loss, and suggest the efficient algorithm to find the proper path length differences of AWG for given channel spacing and channel assignment to each output prot. The simulated spectral responses of the proposed WGR using the finite difference beam propagation method (BPM) show that the excess loss is less than 0.3dB and the crosstalk less than -25dB in case of 4x4 WGR, and the excess loss less than 0.4dB and the crosstalk less than -25dB in case of 8x8 WGR for all the channel wavelengths.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.49 no.8
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• pp.467-472
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• 2000

A three-level decoupled sliding mode controller is developed to achieve asymptotic stability for a class of sixth-order nonlinear systems. The sixth-order system is decoupled into three subsystems according to the structure of the whole system. Each subsystem has a separate control target in the form of a sliding surface. The information of the third sliding surface is transferred to the second one through an intermediate variable and the information of the second sliding surface is transferred to the first one through another intermediate variable. Consequently, the controller designed on the basis of the first sliding surface can make three subsystems move toward their sliding surfaces, respectively. The three-level decoupled sliding mode controller is applied to the double-inverted pendulum problem where the zero stable states are required.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.223-223
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• 2011

헬리콘 플라즈마는 자기장을 이용하여 높은 전자밀도를 가지게 하는 플라즈마 소스이다. 이러한 장점에도 불구하고, 전자석의 크기 때문에 설치가 어렵고, 전자석을 작동시키기 위해 추가 파워에 대한 비용이 필요하며, 플라즈마의 균일도가 좋지 않아 공정에서는 많이 사용되지 못하였다. 이러한 난점은 UCLA의 Chen이 영구자석을 이용한 새로운 개념의 소스를 개발함으로써 풀릴 수 있다. 이 소스는 헬리콘 플라즈마의 높은 저항을 이용하여 여러 개의 헬리콘 소스를 병렬로 연결이 가능하게끔 한다. 본 연구에서는 우선 Helic Code를 이용하여 floating metal end plate의 위치에 따른 플라즈마의 loading resistance를 계산한 후, 플라즈마의 internal 및 external parameter를 각각 single Langmuir probe와 VI-probe를 이용하여 측정하여 비교해 보았다. 헬리콘 플라즈마의 파장에 따른 보강간섭 조건을 맞췄을 경우, 헬리콘 모드로 전환이 낮은 파워에서 이루워지는 것을 external parameter를 통해 확인해 보았다.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.242-243
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• 2001

고출력 펨토초 레이저 기술은 커렌즈 모드록킹 기술, Ti：sapphire 이득매질의 개발, chirped pulse amplification (CPA) 등의 도움으로 1980년대 후반부터 급속히 발전해 왔다. 생성된 펨토초 펄스의 시간적 특성을 정확히 알아내기 위한 방법들도 많이 연구되어 주파수 분해 괌게이팅(FROG)이나 주파수위상 간섭계(SPIDER) 등의 방법들이 기존의 자체상관계를 대체하게 되었다. 극초단 레이저 펄스는 넓은 스펙트럼을 갖고 첨두출력이 높기 때문에 매질이나 광학계를 지나면서 군지연분산, 자체위상변조 등의 효과에 의한 시간적 위상변화가 쉽게 생긴다. (중략)

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.34-35
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• 2001

The wavelength demultiplexer is an essential component in optical transmission systems using wavelength-division multiplexing(WDM), which can increase the number of channels and information capacity of optical fibers. For optical telecommunication, much attention has been given to demultiplexing two wavelengths in the 1.3${\mu}{\textrm}{m}$ of low dispersion band and 1.55${\mu}{\textrm}{m}$ of low loss window. Various integrated-optical devices have been proposed to perform this function, including conventional directional couplers, asymmetric Y-branching devices, asymmetric Mach-Zehnder interferometers and two-mode interference devices. (omitted)

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2001.11a
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• pp.124-129
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• 2001

점 용접부는 응력상태가 복잡하고, 피로균열은 판 두께, 너겟 직경, 용접 타점수, 부하 방식 등의 역학적인 인자와 재질, 화학성분, 표면 상태 등의 재료적인 인자, 그리고 용접전류, 가압력, 통전 시간등의 용접적인 인자의 영향을 동시에 받으며 3차원적으로 성장하므로 균열 성장 모드는 항상 혼합보드이고 균열이 박판 내면에서 발생. 성장하므로 검출이 곤란하여 균열 성장의 해석 및 예측이 어렵다/sup 1)/. 따라서 비접촉, 실시간, Whole-field, 레이저 파장 단위까지 측정이 가능하여 기존의 방법들의 문제점을 극복할 수 있고, 반도체와 같은 소형의 제품뿐만 아니라 기존에 측정하지 못했던 초고온, 대형 구조물의 변형도 정확하게 측정을 할 수 있는 ESPI법을 이용하여 일반가전 제품, 자동차 건축용에 많이 사용되고 있는 아연도금강판(SGCC)을 선택하여 단일 용접조건으로 점용접의 피치를 변화시켜 시험편을 제작하고 면외변위를 다각도로 측정하여 그 가능성을 검증하고자 한다.(중략)

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.12
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• pp.2032-2038
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• 1989

Single mode optical fiber interferometeric sensors using phase tracking homodyne detection are typically susceptible to environmentally indured temperature fluctuations and other types of disturbances. A simple and effective phase tracking feedback electronic circuit for compensator is described to achieve stabilizing signal output, maximum sensitivity and linearity in the fiber optic Mach-Zehnder infterferometer in the presence of differential phase drift. The phase tracking range of the piezoelectric cyclinder in the reference arm is \ulcorner.7 \ulcornerad and the prabe mass about 1 gram in the sensing arm was used for measurements of the gravity acceleration.