• 한국통신학회논문지
• /
• 제29권8C호
• /
• pp.1086-1103
• /
• 2004

Most research efforts on the OCDMA technology assume single-bit-per-symbol transmission techniques such as on-off keying. However, achieving high spectral efficiency with such transmission techniques is likely to be a challenging task due to the "unipolar" nature of optical signals. In this paper, an M-ary transmission technique using more than two equally-weighted codes is proposed for OCDMA local area networks, and ie BER performance and spectral efficiency are analyzed. Poison frame arrival and randomly generated codes are assumed for the BER analysis, and the probability of incorrect symbol detection is analytically derived. From the approximation, it is found that there exists an optimal code weight that minimizes the BER, and its physical interpretation is drawn in an intuitive and simple statement. Under the assumption of this optimized code weight and sufficiently large code dimension, it is also shown that the spectral efficiency of OCDMA networks can be significantly improved by increasing the number (M) of symbols used. Since the cost of OCDMA transceivers is expected to increase with the code dimension, we finally provide a guideline to determine the optimal number of symbols for a given code dimension and traffic load.

• 한국광학회지
• /
• 제11권6호
• /
• pp.411-417
• /
• 2000

SSC(Spot-size converter)가 집적된 1$1.3\mu{m}$ FP(Fabry-Perot)-LD(Laser Diode)에서 SSC 영역의 광도파로 구조가 단일모드광섬유와의 광결합 효율 및 정렬오차에 미치는 영향에 대해서 3차원 BPM(Beam Propagation Method)를 사용하여 알아보았다. 수지 taper의 경우 광결합효율을 향상하기 위해서는 taper 끝단에 충분한 길이의 직선도파로를 형성하는 것이 중요함을 알수 있었다. 또한 수평 taper 구조에서는 출사단 방향으로 도파로폭이 좁아지는 경우가 넓어지는 경우에 비해 유리하고, 수직 taper에 비해 완만한 도파로 경사가 필요함을 알 수있었다. 단일모드 광섬유와의 광결합 손실 및 정렬오차 허용도의 관점에서 좋은 특성을 주는 SSC 도파로 모양을 제시하였다.

• 한국광학회지
• /
• 제26권3호
• /
• pp.139-146
• /
• 2015

본 논문에서는 유전체 다층 거울을 이용해 구성된 파브리-페롯 미소공진 구조가 유기발광다이오드(OLED)의 광효율에 미치는 영향을 유한차분 시간영역법과 광선추적법을 결합해 분석하였다. SiN과 $SiO_2$ 층을 교대로 쌓아 구성한 유전체 다층박막의 적용은 미소공진 효과를 강화시켜 OLED의 발광 스펙트럼의 협소화를 유도하였고 광추출효율도 수 % 증가하였다. 유전체 다층박막의 두께를 최적화함으로써 특정 파장에 대해 미소공진 효과를 일으킬 수 있었고 이는 OLED 발광색의 순도를 증가시키는데 활용될 수 있다. 광추출효율을 극대화하는 전자수송층의 최적 두께는 발광파장에 따라 달라졌는데, 이는 유기층 물질이 보이는 굴절률의 분산 때문인 것으로 생각된다.

• 세라미스트
• /
• 제10권3호
• /
• pp.28-33
• /
• 2007

The structural and optical properties of Ni-doped transparent glass-ceramics are reviewed. The quantum efficiencies of ceramics were examined to explore suitable crystalline phase for Ni-doping in glass-ceramics. Inverse spinel $LiGa_5O_8$ have the quantum efficiency of almost 100 % at room temperature. Transparent glass ceramics containing $LiGa_5O_8$ was successfully synthesized by heat treatment of $Li_2O-Ga_2-O_3-SiO_2-NiO$ glass. Most of $Ni^{2+}$ ions in glass-ceramic were incorporated into $LiGa_5O_8$ nanocrystals. The near-infrared emission covering from the O-band to L-band (1260-1625 nm) was observed from the Ni-doped $Li_2O-Ga_2O_3-SiO_2$ glass-ceramic though it was not observed from the as-cast glass. The lifetime of the emission was about $580\;{\mu}sec$ even at 300K. The emission quantum efficiency was evaluated as about 10 % that is enough high for practical usage as gain media of optical fiber amplifiers. The figure of merit (the product of the stimulated emission cross section and lifetime) was as high as that of rare-earth-doped glasses. The broad bandwidth, high quantum efficiency and high figure of merit show that transparent glass-ceramics containing $Ni^{2+}:LiGa_5O_8$ nanocrystals are promising candidates as novel ultra-broadband gain media.

• 조명전기설비학회논문지
• /
• 제21권7호
• /
• pp.6-12
• /
• 2007

LCD(liquid crystal display) TV용 백라이트의 광원으로서 면광원이 개발되었으며, 이를 이용한 조명 기기를 제작 및 평가하였다. 면광원은 유리성형을 통하여 채널을 형성하였으며 채널의 모양을 최적화하여 면광원을 이용한 조명 기기의 효율을 향상시킬 수 있었다. 본 논문에서는 특히 현재 주로 사용되고 있는 형광등과의 비교 평가를 통하여 조명용 면광원의 광 효율 및 조도 특성에 관한 성능을 평가하였다. 채널의 구조가 최적화된 면광원을 이용하여 제작된 32"형 조명 기기의 광 효율은 72.7[1m/W]이었다.

• 제어로봇시스템학회논문지
• /
• 제14권4호
• /
• pp.353-360
• /
• 2008

The LGP with nanometer structures resulted in enhancement of optical efficiency. Its fundamental mechanism is to recycle the polarized light via one round-trip through QWP(Quarter-Wave Plate) but the maximum efficiency to reach with this method is limited up to 2. To get the larger efficiency than this limited one a LGP with nanometer-patterned grating is suggested. For its optimum design the computer simulation is performed and suggests a grating that the spatial frequency between adjacent patterns is 500nm, its height 250nm, duty cycle 50%, and its cross section is rectangular. On the basis of simulation results the LGP with nanometer-patterned grating is fabricated and its optical properties such as angular intensity distribution and CIE color coordinates are characterized. The angles of transmitted light are nearly the same as the results expected from the generalized Snell's law. Thus the Mathematica code, developed in this experiment, will be applied to designing the optimized LGP. The LGP with nanometer-patterened grating shows the enhancement of transmitted intensity distribution up to 4.9 times.

• 설비공학논문집
• /
• 제20권8호
• /
• pp.563-569
• /
• 2008

Radiative, heating is suitable for outdoor heating system in windy and cold seasons. Optimal design of the reflector is very important to maximize heat transfer to a specific target area in the open space. The geometrical optical theory can be applied to analyze efficiency of the reflector. Commercial ray tracing computer programs are available only for limited geometries of the reflector. Alternatively, it may be designed and analyzed through an approximated simple lens theory. Two types of reflectors are analyzed using either of these methods. The key issue in this paper is to propose a new illumination experimental method for determination of the radiative efficiency. Optical light source and illuminometer are employed. The calculated efficiency of the reflector is compared with experimental one for checking the reliability. The relative errors between the experimental and analytical results are less than 5%, which proves the validity of this method. Based on these methodologies, a practical reflector and heating lamp unit is developed.

• 한국입자에어로졸학회지
• /
• 제13권4호
• /
• pp.159-164
• /
• 2017

The detection efficiency and characteristics of an optical particle counter (OPC), with various sample nozzle outlet diameters, were experimentally investigated. The OPC system, which was built with original design, was made up of a diode laser, two photodetectors, and a variety of optics such as a beam splitter and a concave mirror. The cone-shaped sampling nozzle was designed to be changeable to alter the outlet diameter, within the range of 1 to 3 mm. For samples, sets of polystyrene latex (PSL) standard particle with various sizes of 1 to $3{\mu}m$, were used. As a result, detection efficiency of the OPC greatly decreased with larger nozzle outlet diameter. Moreover, increased nozzle outlet diameter means broader sample flow, thus caused light interference and multiple scattering which results in abnormal high peaks in scattered light signal. The ratio of abnormal peaks to regular signal of single particle increased with larger nozzle outlet diameter.

• 한국태양에너지학회 논문집
• /
• 제22권3호
• /
• pp.57-65
• /
• 2002

The photocatalytic degradation of TCE using solar energy in POFR was studied. The use of solar energy was investigated in plastic optica fiber photocatalytic reactor (POFR). In POFR, the main parameters of photocatalytic degradation of TCE were lihgt intensity, thickness of $TiO_2$-coated film on plastic fiber core, the same of total $TiO_2$-coated surface area with changed length. We studied the apparent photonic efficiency and photocatalytic degradation rate of TCE in POFR. The apparent photonic efficiency of various light intensities was decreased by an incresed intensities. The photocatalytic activities of $TiO_2$-coated optical fiber reactor system depended on the coating thickness, and total clad-stripped surface area of POF. Photocatalytic degradation of trichloroethylene ($C_2HCl_3$, TCE) in the gas-phase was elucidated by using $TiO_2$-coated plastic optical fiber reactor. In TCE degradation, in-situ FTIR measurement resulted in mineralization into $CO_2$.

• 한국광학회지
• /
• 제30권3호
• /
• pp.101-105
• /
• 2019

LCD의 광 효율을 향상시키기 위해 LCD backlight unit (BLU)의 광원으로 적색, 녹색, 청색의 광원을 사용하였으며, RGB 광은 lenticular lens array (LLA)를 통해 집광되어 각각 컬러 필터의 적색, 녹색, 청색 필터에 색일치되는 조건으로 광이 지나도록 설계하여 시뮬레이션하였다. 광원의 위치에 따라 Type-A와 Type-B 두 가지 방식으로 시뮬레이션을 진행하였으며, 그 결과 LLA를 사용하지 않았을 때와 비교하여 Type-A는 휘도가 210%로 상승하였으며, Type-B는 270% 상승함을 확인하였다. LLA의 최적의 조건은 렌즈의 높이가 $25{\mu}m$, 렌즈 간의 간격이 $3{\mu}m$일 때, 효율이 최대가 됨을 확인하였다.