• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.340-346
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• 2000

Traveling wave type semiconductor optical amplifiers integrated with spot-size-converter (SSC-TW-SOA) have been extensively studied for the improvement of coupling effiClency With single-mode fiber and fO! the cost reducClon 111 a packaging In tlIis paper the slructural dependence of the spot-slZe-converter on the effective facet reflectlvllY $R_{eff}$ was experimentally as well as thcoretienlly mvestlgated. It was shown that not only a sufficient mode-conversion in a sse region along the latersl and tran~verse directions but also an introductIOn of angled-facet were very essential in order to reduce $R_{eff}$ Very small ripple less than 0.1 dB in an amplified spontaneous emission spectrum was observed with the fabncated SSC-lW-SOA which consists of the wrndow length of $20\mu\textrm{m}$, facet angle of $7^{\circ}$, and antlrelleetioll-coated facet of ] % reflectivity.tivity.

• Korean Journal of Optics and Photonics
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• v.15 no.2
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• pp.149-157
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• 2004

We have calculated the power extraction efficiency and the lasing wavelength distribution of complex-coupled(CC) DFB lasers above threshold for various｜$\chi$L｜ and facet reflectivity combinations, and we have compared the results with those at threshold. Also, we have investigated the effect of coupling coefficient ratio(CR) and the reflectivity of AR facet on the power extraction efficiency and the lasing wavelength distribution. At threshold, the single mode yield as a function of power extraction efficiency of in-phase(IP) CC DFB lasers is the same as that of anti-phase(AP) CC DFB lasers. Above threshold, however, the single mode yield as a function of power extraction efficiency of IP CC DFB lasers is much larger than that of AP CC DFB lasers. For IP CC DFB lasers, AR-HR combination has high single mode yield and large power extraction efficiency compared to other facet combinations. IP CC DFB laser with AR-HR combination for ｜$\chi$L｜of 0.8 has the highest single mode yield and largest power extraction efficiency above threshold among the cases considered. For AR-HR combination, as CR increases and the reflectivity of AR facet decreases, both single mode yield and power extraction efficiency increase due to the reduction of the spatial hole burning effect. For AR-HR combination, the lasing wavelength of CC DFB laser has distributed over the stopband of DFB. As CR increases, the lasing wavelength concentrates on the long wavelength side for IP CC DFB laser, while on the short wavelength side for AP CC DFB laser. As ｜$\chi$L｜ increases, the width of the wavelength distribution decreases and the lasing wavelength moves to the long wavelength side.

• The Journal of the Acoustical Society of Korea
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• v.27 no.3
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• pp.129-139
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• 2008

The purpose of the present work is to derive the reflection and transmission coefficients of $S_0\;and\;A_0$ mode Lamb waves in relation to the geometry of a rectangular notch when the waves propagate across the notch in an elastic plate. Firstly, the excitable modes of the Lamb wave were analyzed with respect to the plate thickness. The scattering phenomena were divided into three independent processes according to the boundary shape of the notch and the direction of the wave propagation. Linear equations for each process were derived with corresponding free or continuous boundary conditions to analyze the scattered waves. By the rule of linear superposition, the waves scattered at each process were summed for each mode. Then the steady-state reflection and transmission coefficients of the scattered waves were determined so that the difference of energy flux between the incident and the scattered waves would remain within 4%.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.279-282
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• 1999

We designed and fabricated a single polarizer mode bistable twisted nematic liquid crystal display by employing a wide-band λ/4 retardation film to enhance the dark state property. We theoretically and experimentally confirmed the necessity of a wide- band λ/4 retardation film in a single polarizer mode. We obtained brighter image than previous reflective BTN LCDs.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.112-113
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• 2000

주변의 광원을 이용하는 단일 편광판 반사형 액정 표시장치는 전력 소모의 70%이상을 차지하는 배면조명이 필요 없으므로 가볍고 얇으며, 소비전력이 적고, 큰 반사효율을 얻을 수 있는 장점으로 인해 큰 주목을 받고 있다. 현재 단일 편광판 반사형 액정 표시장치는 reflective TN(RTN)$^{(1)}$ 과 mixed-mode TN(MTN)$^{(2)}$ 과 같은 TN액정 모드를 기본적으로 사용하고 있다. 하지만 TN액정 모드를 사용한 반사형 액정 표시장치는 좁은 시야각과 느린 응답 특성 등의 문제점이 있다. 이러한 문제점들을 해결하기 위해 reflective-optically compensated bend(R-OCB)$^{(3)}$ 및 reflective homeotropic TN mode$^{(4)}$ , 반사형 BTN$^{(5)}$ 등을 이용한 반사형 액정 표시장치 등이 보고된 바 있다. (중략)

• Korean Journal of Optics and Photonics
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• v.14 no.5
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• pp.565-569
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• 2003

We designed a transflective-type LCD using a twisted VA mode. Generally, a VA mode had a blue shift due to intrinsic properties. We solved this problem using spectroscopic compensation film. We used the front scattering film and negative C-plate to improve characteristics of the viewing angle and contrast ratio. As a result, we found that proposed the transflective-type TVA mode had a contrast ratio of about 80:1, a response time of 22 ms, and a reflectance of 25% in comparison with the standard MgO reflector.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.12
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• pp.53-62
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• 1999

Center of photon mass(CPM), defined as the center of axial photon distribution, is proposed as a unified design parameter, which contains information about both threshold gain and nonuniformity of axial photon distribution in DFB lasers with low and high-reflection facets. The CPM is inversely proportional to threshold gain and is 0.5 when axial photon distribution is the most uniform. Therefore, a general rule of single-frequency leser design is that main mode CPM should be around 0.5 for-uniform axial photon distribution and side mode CPM should be minimized to maximize the threshold gain difference.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.184-188
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• 2001

본 논문에서는 다중대역 피드를 위한 직교모드 변환기를 설계하였다. 직교모드 변환기의 전체적인 모양은 사각 테이퍼진 형태이고, 18-20 GHz 에서 우원 편파와 좌원편파를 발생시키기 위해 테이퍼 부분에 2개의 측면포트를 두고, 직선포트는 30-45 GHz의 광대역에서 -20dB 이하의 반사계수를 가지도록 설계하였다. 직선포트에서의 반사계수 특성을 향상시키기 위해서 측면포트에 얇은 격막을 삽입하였다. 전체적인 설계에 상용소프트웨어인 HFSS$^{R}$를 사용하였다.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.268-269
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• 2001

반사형 액정표시장치는 저전력 휴대용 표시장치 시장이 급격하게 성장함에 따라 큰 주목을 받고 있다. 현재 반사형 액정표시장치는 밝기면에서 우수한 특성을 갖는 mixed mode TN(MTN)과 reflective TR(RTN)과 같은 단일편광자를 이용한 액정모드를 기본적으로 사용하고 있다. 그러나, 이러한 액정모드는 이중편광자를 이용한 액정모드와 비교해서 dark 상태에서 누설광이 많이 발생하여 대비비가 저하되는 단점이 있다. (중략)

• Korean Journal of Optics and Photonics
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• v.20 no.4
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• pp.217-222
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• 2009

In this paper, a low-cost hybrid-integrated tunable laser is realized using a polymer-ring resonator-based add/drop filter reflector and a reflective semiconductor optical amplifier. The add/drop filter reflector, composed of a double-ring resonator with different radii, can have characteristics of selective wavelength reflection and wide wavelength tuning with an aid of vernier effect derived from the radii difference. By hybrid-integrating the reflective semiconductor optical amplifier with the add/drop filter reflector, a tunable laser can be realized through an active alignment method. The hybrid laser exhibited a single mode lasing with side mode suppression ratio of 26 dB and full width half maximum of 0.03 nm. In addition, applying a low current as small as 25 mA onto electrodes over add/drop filter reflector, a wavelength tuning range of 17 nm could be obtained.