• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04b
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• pp.136-140
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• 2002

투과형 광 시야각 모드의 하나인 Fringe Field Switching (FFS) mode를 반사형 액정 디스플레이소자로 응용하여 전기 광학적 특성을 컴퓨터 시늉 하였다. FFS mode는 액정이 수평으로 균일하게 유지되면서 구동하므로, 시야각에 따른 굴절률 변화 역시 균일하게 유지된다. 이러한 특성 때문에 반사형 FFS mode는 부가적인 위상필름을 쓰지 않고, 액정층과 편광판 1매 만으로도 일정한 수준의 반사형 디스플레이 특성을 얻을 수 있다. 컴퓨터 시늉을 통해 1매 편광판과 액정층, 반사판으로 구성된 Normally Black모드의 셀 구조를 취하고, 셀 간격을 일정하게 유지하면서 액정의 ${\Delta}n$을 변화시켜 특성을 구하는 방식으로 수행하여, 입사광의 파장이 550nm일때 최적의 셀 위상차값으로 $d{\Delta}n$인 $0.1365{\mu}m$를 얻었다. 입사광원을 $0^{\circ}C$로 하고 편광판 투과율이 41%였을 때 정면 반사율은 on시 33.6%, off시 0.14%로 명암대비가 233:1이었다. 특히 시야각은 극각 $60^{\circ}C$이내의 전 방향에서 명암 대비비가 5이상의 특성을 보였다.

• Korean Journal of Optics and Photonics
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• v.14 no.5
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• pp.521-529
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• 2003

For complex-coupled (CC) DFB lasers, we found that there might be little correlation between the single mode yields at threshold and above threshold. At threshold, the single mode yield considering f number of in-phase (IP) CC DFB lasers is the same as that of anti-phase (AP) CC DFB lasers. However, the single mode yield as a function of injection current above threshold of IP CC DFB lasers is much different from that of AP CC DFB lasers. In the case of IP CC DFB lasers, the single mode yield increases as the coupling coefficient ratio (CR) increases, while, in the case of AP CC DFB lasers, the single mode yield decreases rapidly regardless of CR as the injection current increases. In the case of AR-HR combinations, the effect of AR ref1ectivity on the single mode yield increases as the coupling strength decreases. As the coupling strength decreases, the CR at which the increase rate of the single mode yield starts to decrease, increases, and the maximum single mode yield increases. Single mode yields of AR-HR and AR-AR combinations are larger than those of AR-CL and CL-CL combinations.

• Korean Journal of Optics and Photonics
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• v.13 no.2
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• pp.162-165
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• 2002

We propose an optical configuration for a transflective display mode using a transflective film and a half-wave AFLC cell whose in-plane tilt angle is 22.5。. It provides high brightness and high contrast in the reflective mode as well as in the transmissive mode.

• Korean Journal of Optics and Photonics
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• v.22 no.2
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• pp.102-107
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• 2011

In this paper, a small double ring resonator reflector was designed and fabricated using a polymer waveguide, and the measurement result was discussed. A widely tunable characteristic of the small double ring resonator caused by the Vernier effect, which results from the difference of the ring radii, was observed. The insertion loss of the double ring reflector was reduced by minimizing the device length to be as short as possible, and thus the output power and the SMSR (side mode suppression ratio) was greatly enhanced. The hybrid integrated laser based on the small double ring resonator reflector lased with the SMSR of 45 dB. In addition, the wide tuning range of 40 nm could be obtained by injecting a current of 30 mA to an electrode on top of the reflector.

• Korean Journal of Optics and Photonics
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• v.17 no.6
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• pp.548-555
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• 2006

We investigate the effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection index-coupled (IC) DFB lasers composed of two index-coupled DFB sections and a phase tuning section between them in terms of yield. In the case of weak coupling strength, as the reflectivity of both facets increases, the effect of reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases. Thus the number of mode hoping increases and yield decreases for the variation of phases of both facets. In the case of strong coupling strength, as the reflectivity of both facets increases, the spatial hole burning effect increases, so that the yield decreases. The maximum yield and the range of the phase of a phase tuning section with yield more than 40% decrease as the facet reflectivity increases irrespective of coupling strength. As the coupling strength increases, the variation of yield for the variation of the phase of a phase tuning section increases and the variation of the phase of a phase tuning section with the maximum yield for the variation of the reflectivity of both facets decreases. The yield characteristics of the cases with the coupling strengths of 2 and 3 are better than those with the coupling strengths of 1.2 and 4.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.44 no.4 s.316
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• pp.28-35
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• 2007

Airbone laser altimeters have been utilized for 3D topographic mapping of the earth, moon, and planets with high resolution and accuracy, which is a rapidly growing remote sensing technique that measures the round-trip time emitted laser pulse to determine the topography. The traveling time from the laser scanner to the Earth's surface and back is directly related to the distance of the sensor to the ground. When there are several objects within the travel path of the laser pulse, the reflected laser pluses are distorted by surface variation within the footprint, generating multiple echoes because each target transforms the emitted pulse. The shapes of the received waveforms also contain important information about surface roughness, slope and reflectivity. Waveform processing algorithms parameterize and model the return signal resulting from the interaction of the transmitted laser pulse with the surface. Each of the multiple targets within the footprint can be identified. Assuming each response is gaussian, returns are modeled as a mixture gaussian distribution. Then, the parameters of the model are estimated by LMS Method or EM algorithm However, each response actually shows the skewness in the right side with the slowly decaying tail. For the application to require more accurate analysis, the tail information is to be quantified by an approach to decompose the tail. One method to handle with this problem is proposed in this study.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.240-241
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• 2003

경계면 근처에서의 에바네슨트파의 상호작용은 입사, 반사 및 굴절된 평면파의 삼중모드로 설명한다. 경계에서 굴절률이 낮은 영역에 위치한 DCM 색소분자에 의한 자발방출은 굴절률이 높은 영역에서 입사된 삼중모드와 굴절률이 낮은 영역에서 입사한 삼중모드와 상호작용을 하며, 광 측정기에서는 이 두 모드의 선형결합을 보게된다. 자발방출에 대한 실험결과는 이러한 이론을 뒷받침 해준다. (중략)

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.1
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• pp.89-103
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• 2009

This study investigates the applicability of the time reversal concept in modem acoustics to the Lamb waves, which have been widely studied for defect detection in plate-like structures. According to conventional time reversal acoustics, an input signal can be reconstructed at an excitation point if an output signal recorded at another point is reversed in the time domain and emitted back to the original source point. However, the application of a time reversal process(TRP) to Lamb wave propagations is complicated due to velocity and amplitude dispersion characteristics of Lamb waves and reflections from the boundaries of a structure. In this study, theoretical investigations are presented to better understand the time reversibility of Lamb waves. In particular, the effects of within-mode dispersion, multimode dispersion, amplitude dispersion, and reflections from boundaries on the TRP are theoretically formulated. Simple numerical case studies are conducted to validate the theoretical findings of this study.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.413-422
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• 2003

We have calculated the power extraction efficiency and the lasing wavelength distribution of index-coupled DFB lasers at threshold for various kL and facet reflectivity combinations, and compared with those above-threshold. The power extraction efficiency increases as the asymmetry of the facet reflectivities increases. The power extraction efficiency above-threshold is slightly larger than that at threshold. Since the relative photon density around the center region increases as kL increases, the power extraction efficiency decreases. The uniformity of the distribution of lasing wavelength over the stop band increases due to the relief of mode degeneracy as the asymmetry of the facet reflectivities increases. In the case of AR-HR combination, the lasing wavelength distributions at threshold are similar to those above-threshold. However, in the case of AR-AR combination, the lasing wavelength at threshold is concentrated on both edges of the stop band, while it is concentrated only on the longer wavelength edge above-threshold. As kL increases, the range of the lasing wavelength distribution increases due to the increase of the stop band. The effect of AR reflectivity on the power extraction and the lasing wavelength distribution is very weak.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.2
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• pp.331-337
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• 1994

The scatting problem by E-polarized plane wave with obique incidence on a tapered resistive strip grating with zero resistivity(perfectly conducting) at strip-edges is analyzed by the method of moments in the spectral domain. Then the induced surface current density on the strip is expanded in a series of Chebyshev polynomials of the second kind. The expasion coefficients are calculated numerically in the spectral domain, the numerical results of the geometric-optical reflection coefficient for the tapered resistivity in this paper are compared with those for the existing uniform resistivity. And the position of sharp variation points in the magnitude of the geometric-optical reflection coefficient can be moved by varying the incident angle and the strip spacing, It is found out that these sparp variation points are due to the transition of higher mode between the propagation mode and the evanescent mode.