• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.8
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• pp.580-587
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• 2003

In this paper, we introduce a novel model to analyze the linearity of a TW-EAM (traveling-wave electroabsorption modulator). The device length, microwave loss (ML), and internal reflection (IR) due to impedance mismatch have effect on the linearity of a TW-EAM. The longer devices have characteristics of lower biases with minimum IMDS (intermodulation distortions). ML decreases the output power as well as the IMD value. Internal reflection has different nonlinear characteristics according to the wavelength of the input frequency and the device length. There is little change in SFDR (spurious-free dynamic range) due to ML or IR. As a result, for a 50 GHz band RF-optical communication system, a 0.8 mm-long TW-EAM with the lowest ML would have better properties by using n, which is caused by impedance, mismatch at the output port.

• Journal of Adhesion and Interface
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• v.13 no.2
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• pp.73-84
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• 2012

The transfer mechanism of optical information at the interface of air and glass (the air-glass IF) has been investigated by thoroughly fulfilling the theoretical and experimental analyses regarding the FTIR (Frustrated Total Internal Reflection) and moisture effects on the fingerprint onto a glass cup with water. As for the fingerprint onto a glass cup with water its image was observed to be very vivid, which turned out to be due to the difference between the two light intensities reflected on the air-glass IF and the wet fingerprint ridge by manipulating the optical theories such as Fresnel relation, Snell's law, FTIR, GT (general transmission) and so on. In addition, the experimental inspection for FTIR and moisture effects on the fingerprint image also evidenced the fact that the vivid fingerprint image originated from the moisture effect rather than the FTIR phenomenon.

• The Journal of Korean Association of Computer Education
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• v.5 no.3
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• pp.89-106
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• 2002

One of the key success factors for Computer Supported Collaborative Learning(CSCL) environments relies on collaborative reflection. Reflection refers to the active, intellectual thinking for monitoring one's own learning process and continuous internal activities of exploring oneself for new learning experiences. Also, reflective activities are closely related not only with the individual aspect of internal exploration but also with the social aspect of learner-learner interaction. This paper suggests four essential macro-level design strategies such as (1)facilitating collaborative awareness, (2)making thinking visualization, (3)negotiation-mediated knowledge construction, (4)providing metacognitive awareness cues or Questions for scaffolding collaborative reflection in the CSCL environments and made some implications for key functional features for the design and development of system components for CSCL.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.165-168
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• 2002

This paper describes the dynamics of the weak shock wave propagating inside some kinds of branched pipe bends. Computations are carried out by solving the two-dimensional, compressible, unsteady Euler Equations. The second-order TVD(Total Variation Diminishing) scheme is employed to discretize the governing equations. For computations, two types of branched pipe($90^{\circ}$ branch,$45^{\circ}$ branch) with a diameter of D are used. The incident normal shock wave is assumed at D upstream of the pipe bend entrance, and its Mach number is changed between 1.1 and 2.4. The flow fields are numerically visualized by using the pressure contours and computed schlieren images. The comparison with the experimental data performed for the purpose of validation of computational work. Reflection and diffraction of the propagating shock wave are clarified. The present computations predicted the experimented flow field with a good accuracy.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.456-461
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• 2001

This paper depicts the weak shock wave propagating inside some kinds of pipe bends. Computational work is to solve the two-dimensional, compressible, unsteady Euler Equations. The second-order TVD scheme is employed to discretize the governing equations. For the computations, the incident normal shock wave is assumed at the entrance of the pipe bend, and its Mach number is changed between 1.1 and 1.7. The turning angle and radius of the curvature of the pipe bend are changed to investigate the effects on the shock wave structure. The present computational results clearly show the shock wave reflection and diffraction occurring in the pipe bend. In particular, the vortex generation, which occurs at the edge of the bend, and its shedding mechanism are discussed in details.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.942-944
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• 2009

Blue phase shows several different reflection colors from the randomly oriented domains and crystal direction. Also there are variations in the size of domains. The domain size is dependent on the temperature gradient. With smaller cooling rate of temperature, the domain size was increased compared with rapid cooling. With injection of light of specific wavelength, we find that the diffraction patterns were occurred around the light spot in the cell of blue phase. It was supposed to be from the matching of the phase retardation and domain size. However, actually the diffraction pattern is reflecting the lattice structure in double twist of the blue phase. The lattice constant from the radius of diffraction patterns shows very similar one from the reflection spectrum, which indicates the internal lattice constant in double twist of the blues phase.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.3
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• pp.248-251
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• 2009

We have investigated the effect of the quality of 1.3 um distributed feed back laser diode (DFB-LD) on the design of anti-reflection (AR) coatings. Optimal condition of AR coating to prevent internal feedback from both facets and reduce the reflection-induced intensity noise of laser diode was simulated with Macleod Simulator. Coating materials used in this work were ${Ti_3}{O_5}$ and $SiO_2$, of which design thickness were 105 nm and 165 nm, respectively. AR coating films were deposited by Ion-Assisted Deposition system. The electrical and optical properties of 1.3 um laser diode were characterized by Bar tester and Chip tester. Threshold current and slop-efficiency of DFB-LD were 27.56 mA 0.302 W/A. Far field pattern and wavelength of DFB-LD were $22.3^{\circ}(Horizontal){\times}24.4^{\circ}$ (Vertical), 1313.8 nm, respectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.351-352
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• 2006

• Proceedings of the Optical Society of Korea Conference
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• 1991.07a
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• pp.103-108
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• 1991

결정형 光 전압/전류 센서에 있어서 내부다중반사(Multiple internal Reflection), 북굴절 및 물성의 온도의존성이 어떻게 불안정성 요인으로 작용할 수 있는지를 알아보았으며, 이들 요인들을 피해서 센서의 안정성을 높힐 수 있는 방법들을 소개하였다. 구성된 光 전압/전류센서의 간단한 동작도 보았다.

• Journal of the Optical Society of Korea
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• v.15 no.1
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• pp.9-14
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• 2011

In this study, the internal structure of an optical waveguide embedded in a flexible optical circuit board is observed with a confocal microscope. In order to increase the light reflection from an internal material interface with a very small index difference, and thus enhance the signal contrast, a theta microscopy scheme has been integrated into a conventional confocal microscope, and a high NA oil-immersion lens has been used. The interface reflectivity is increased from roughly 0.0015% to 0.025% by the proposed method, and the internal structure can thus be successfully measured.