• Journal of the Optical Society of Korea
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• 제15권1호
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• pp.4-8
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• 2011

We have evaluated the performances of bidirectional optical amplifiers which were suited for the cost-effective implementation of amplified bidirectional passive optical networks (PONs). First, we measured the maximum gains of two simple bidirectional optical amplifiers implemented without using any optical components for the suppression of reflected signals. From the results, the maximum gains of two simple bidirectional amplifiers with a broadband light source (BLS) seeded optical source were limited to be 27 dB due to the reflection-induced in-band crosstalk, when the reflectance coefficients were measured to be -33 dB in both directions. Then, we have also implemented a bidirectional optical amplifier with two band splitters for the amplified bidirectional PON where the two different wavelength bands were allocated to the downstream and upstream signals transmission. In our measurement, we confirmed that the maximum gain of bidirectional optical amplifier with two band splitters could be increased to more than 30 dB owing to the efficient suppression of in-band crosstalk.

• Journal of Electrochemical Science and Technology
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• 제14권2호
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• pp.120-130
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• 2023

PEMFC has high potential for future development due to its high energy density, eco-friendliness, and high energy efficiency. When it becomes small, light and flexible, it can be competitive as an energy source for portable devices or flexible electronic devices. However, the use of hard and heavy materials for structural rigidity and uniform contact pressure transmission has become an obstacle to reducing the weight and flexibility of PEMFCs. This review intends to provide an example of the application of a new structure and material for lightweight and flexibility. As a lightweight PEMFC, a tubular design is presented and structural advantages through numerical modeling are explained. Manufacturing methods to realize the structural advantages and possibilities of tubular PEMFCs are discussed. In addition, the materials and manufacturing processes used to fabricate lightweight and flexible PEMFCs are described and factors affecting performance are analyzed. Strategies and structural improvements of light and flexible movements are discussed according to the component parts.

• ETRI Journal
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• 제28권3호
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• pp.329-336
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• 2006

This paper investigates the problem of protecting multicast sessions in mesh wavelength-division multiplexing (WDM) networks against single link failures, for example, a fiber cut in optical networks. First, we study the two characteristics of multicast sessions in mesh WDM networks with sparse light splitter configuration. Traditionally, a multicast tree does not contain any circles, and the first characteristic is that a multicast tree has better performance if it contains some circles. Note that a multicast tree has several branches. If a path is added between the leave nodes on different branches, the segment between them on the multicast tree is protected. Based the two characteristics, the survivable multicast sessions routing problem is formulated into an Integer Linear Programming (ILP). Then, a heuristic algorithm, named the adaptive shared segment protection (ASSP) algorithm, is proposed for multicast sessions. The ASSP algorithm need not previously identify the segments for a multicast tree. The segments are determined during the algorithm process. Comparisons are made between the ASSP and two other reported schemes, link disjoint trees (LDT) and shared disjoint paths (SDP), in terms of blocking probability and resource cost on CERNET and USNET topologies. Simulations show that the ASSP algorithm has better performance than other existing schemes.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.1097-1102
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• 2009

In a railway vehicle, corrugated steel panel is widely used for the floor panel because of its high bending stiffness and light weight. However, this panel shows lower sound insulation performance than that of the plate with the same weight. Especially, in a particular frequency band, transmission loss (TL) rapidly decreases and it results in the deterioration of TL of the overall floor panel. This study identifies that the remarkable drop in TL is caused from the local resonance of the periodic corrugated structure. This study shows that the frequency band of the TL drop can be controlled by the proper design of the corrugated structure. In addition, improvement effect of TL by attaching foam and glass wool is estimated by experiment. The purpose of the study is to provide the practical information for the improvement of the sound insulation performance of the corrugated steel.

• 한국산학기술학회논문지
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• 제16권1호
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• pp.677-682
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• 2015

본 논문에서는 일반적인 광시스템에서 항상 존재하는 잡음 및 외부로부터 더해지는 잡음이 광시스템의 수신기의 성능에 미치는 영향에 대하여 고찰하였다. 광전송시스템에서 광검출기가 1 이하의 양자효율을 갖는 경우를 고려하여 온-오프 키잉 전송시에 수신기의 수신 감도를 계산하였다. m이 50이상인 경우 표준에러확률을 유지하기 위한 광시스템의 수신기 감도가 300이하로 계산되어 m가 적은 경우에 비해서 저출력 시스템을 구성할 수 있음을 확인할 수 있었다. 그러나 이러한 값도 실제 시스템에서는 큰 부담이 되는 값이므로 보다 저출력 광원을 사용하는 경우를 고려하여 수신단에 전치증폭기를 설치한 경우에 대해서도 고려하였는데, 그림 3에서 보이는 바와 같이 보다 적은 출력을 갖는 광원을 사용해도 무방하다는 결과를 얻을 수 있었다.

• 전자공학회논문지
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• 제52권11호
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• pp.115-123
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• 2015

적외선 영상은 외광의 밝기에 영향을 적게 받아서 원격 탐사 및 영상 보안 등의 응용에서 활발하게 활용되고 있다. 그러나 안개와 같은 기상 악화상황으로 인하여 해당 적외선 영상의 화질이 크게 저하되는 경우가 빈번하게 발생한다. 칼라 영상의 안개제거 기술이 다양하게 연구되어온 반면 적외선 영상의 안개제거 기술은 상대적으로 관심을 받지 못하고 있다. 본 논문에서는 근적외선 대역 영상에 대하여 적외선 영상의 통계학적 특징을 이용한 안개 제거 알고리즘을 제안한다. 기계학습 기법을 활용하여 전달량을 보정하고 다중 후처리 기법을 적용하여 정확한 전달량을 구하였다. 제안 기술을 이용하여 복원한 적외선 영상이 기존 칼라영상에 기반한 알고리즘을 적외선 영상에 적용하여 얻은 결과보다 화질이 좋다는 것을 확인하였다.

• Journal of Information Display
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• 제11권1호
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• pp.1-7
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• 2010

The intermediate connectors play crucial roles in the performance of tandem organic light-emitting diodes (OLEDs) because they are required to facilitate charge carrier transport and to guarantee transparency for light transmission and deposition compatibility. Understanding the physical properties of the intermediate connector is not only fundamentally important but is also crucial to developing high-efficiency organic devices with a tandem structure. In this study, several effective intermediate connectors in tandem OLEDs using a doped or non-doped organic p-n heterojunction were systematically investigated by studying their interfacial electronic structures and corresponding device characteristics. The working mechanisms of the intermediate connectors are discussed herein by referring to their relevant energy levels with respect to those of the neighboring organic layers. The factors affecting the operation of the intermediate connectors in tandem OLEDs, as demonstrated herein, provide guidance for the identification of new materials and device architectures for high-performance devices.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권3호
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• pp.1136-1151
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• 2018

This paper proposes a new hybrid scheme to decrease the high peak to average power ratio (PAPR) of optical orthogonal frequency division multiplexing (OFDM) signals in visible light communication (VLC) systems. The PAPR causes nonlinear signal distortions and high power requirements for the VLC transmitter (light emitting diode, LED). The proposed method is applicable for both direct current-biased optical OFDM (DCO-OFDM) and asymmetrically clipped optical OFDM (ACO-OFDM). In the proposed scheme, the PTS method is firstly modified to fit both optical OFDM approaches transmission and then combined with signal clipping method for further PAPR reduction and bit error rate (BER) improvement of the VLC system. The performance of hybrid scheme has been evaluated and compared with the original OFDM based VLC system, conventional PTS and clipping methods. The results show that the hybrid scheme outperforms other methods in terms of both the PAPR reduction and BER performance.

• 한국전자통신학회논문지
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• 제14권5호
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• pp.977-984
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• 2019

본 논문에서는 안개 성분을 포함한 실외영상의 효과적인 응용을 위하여 저 복잡도를 갖는 전달량 추정 및 픽셀 기반 JBDCP(: Joint Bright and Dark Channel Prior)를 이용한 단일 영상 기반 안개 제거 방법을 제안한다. 기존의 전달량 추정은 계산량과 메모리 요구량이 큰 정련과정을 포함하는 반면, 제안하는 안개 제거 방법은 픽셀단위 및 블록단위 dark channel 정보를 결합하여 에지 정보가 보존되는 전달량을 추정하고 복잡도를 크게 감소시킨다. 또한 픽셀 기반 JBDCP를 이용하여 영상의 각 위치마다 다른 안개값을 구함으로써 영상의 특성을 반영한 전달량 추정이 가능하다. 다양한 안개 영상에 대해 수행한 실험 결과는 제안하는 방법이 기존의 방법에 비해 저 복잡도로 실행되면서 우수한 안개 제거 성능을 보여 실시간 기기를 포함한 다양한 분야에 응용될 수 있음을 나타낸다.

• 한국ITS학회 논문지
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• 제9권2호
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• pp.60-67
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• 2010

최근에, LED를 사용한 WPAN 응용 기술에 많은 연구가 진행되고 있다. 하지만, LED를 이용한 가시광 통신은 통신을 수행하는데 약점을 가지고 있다. 시스템 성능을 저하시키는 요인으로 통신 환경에서 다른 물체에 의한 전파 지연으로 발생하는 다중 경로 페이딩을 들 수 있다. 따라서 본 논문에서 OFDM 기술은 다중 경로 페이딩과 분산을 줄이고, 고속 데이터 전송을 제공하기 위해서 적용하였다. 게다가, 광잡음에 의한 정보 손실을 줄이기 위해서 채널코딩으로써 터보 부호화 기술을 사용하였다. OFDM과 터보 부호화를 적용하므로써, 약 4 [dB] 정도의 성능향상을 보임을 알 수 있었다. 또한, 도플러 효과가 일어난다고 가정하였을 경우, 시스템 성능이 저하됨을 시뮬레이션을 통해 알 수 있었다.