• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.5
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• pp.724-730
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• 2002

Digital communication systems are required to cause the minimum interference to adjacent channels, they must therefore employ the linear power amplifiers. In respect to linear power amplifiers, there are many linearization techniques. Feedforward power amplifier represent very wide bandwidth and high linearization capability. In the feedforward systems, overall efficiency is reduced due to the loss of delay line. In this paper, delay filter instead of transmission delay line adapted to get more high efficiency. Experimental results showed that ACLR (Adjacent Channel Leakage Ratio) has improved 17.43(dB), which is added 3.44(dB) by using the delay filter.

• Journal of Internet Computing and Services
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• v.10 no.2
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• pp.171-177
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• 2009

Optical packet switching(OPS) is a strong candidate for the next-generation internet, since it has a fine switching granularity at the packet level for providing flexible bandwidth, and provides seamless integration between WDM layer and IP layer. Optical packet switching have been studied in two categories: OPS in synchronous and OPS in asynchronous networks. In this article we are focused on contention resolution of OPS in asynchronous networks. The hybrid buffer have been addressed, to reduce packet loss further as one of the alternative buffer structures for contention resolution of asynchronous and variable length packets, which consists of the FDL buffer and the electronic buffer. The OPS design issue for the limited number of TWCs and internal wavelengths is important in the aspect of switch cost and resource efficiency. Therefore, an hybrid buffer structured optical packet switch and its scheduling algorithm is presented for considering the limited number of TWCs and internal wavelengths, for contention resolution of asynchronous and variable length packets. The proposed algorithm could lead to the packet loss improvement compared to the legacy LAUC-VF algorithm with only the FDL buffer.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.52 no.1
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• pp.1-11
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• 2007

Light is an environmental component inevitably regulating photosynthesis and photo-morphogenesis, which are involved in the plant growth and development. Studies were conducted at the International Rice Research Institute, Philippines in 2004 and 2005, with aims to investigate 1) morphological responses of rice plants to low radiation, 2) morphological alteration of shade-grown plants when exposed to high light intensity, and 3) photosynthetic responses of shade-grown rice plants. Reduction in solar radiation by 40% induced increases in the area on a single leaf basis, biomass partitioning to leaves, and chlorophyll meter readings but brought about retardation of tiller development and decrease in above-ground biomass production of rice varieties. When the shade-grown plants from two weeks of transplanting to panicle initiation were exposed to full solar radiation after panicle initiation, they demonstrated less increase in chlorophyll meter readings and more decrease in leaf nitrogen concentrations from panicle initiation to flowering than control plants that were grown under the ambient solar radiation for whole growth period after transplanting. Shade-grown rice plants exhibited lower carbon assimilation rates but higher internal $CO_2$ concentrations on a single leaf basis than control plants, when measurements for shade-grown rice plants were made under the shading treatments. But when the measurements for shade-grown plants were made under the full solar radiation, light-saturated carbon assimilation rates were similar to control plants. Response of photosynthetic rates to varying light intensities was not considerably different between shading treatments and control. Yield reduction was observed in the shading treatments from panicle initiation to flowering and from flowering to physiological maturity, mainly by less spikelets per panicle and poor grain filling, respectively.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.7
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• pp.341-349
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• 2001

본 논문은 N개의 노드로 구성된 파장분할다중화(Wavelength Division Multiplexing) 방식의 Passive Star형 광상호연결망에서 K개의 파장이 사용가능 할 때 패킷 전송 스케쥴링 문제를 다루고 있다. 모든 노드는 파장조율이 가능한 송신기와 특정 파장에 고정된 수신기를 각각 한 개씩 가지고 있으며, 하나의 패킷이 송신기로부터 수신기까지 전송되는 데에 걸리는 시간은 항상 일정하다고 가정한다. 최적의 패킷 전송 스케쥴이란 송신노드 입장에서 임의의 파장에서 다른 파장으로 송신기를 조율하는 데에 따른 지연시간(turning delay)을 고려하여 같은 시간에 최대한 많은 서로 다른 파장을 사용하도록 함과 동시에, 수신노드의 입장에서 수신된 패킷들의 광/전 변환에 따른 지연시간(conversion delay)을 고려하여 패킷의 수신간격을 일정하게 유지함으로써 모든 패킷이 최소시간 내에 전송될 수 있도록 언제 어떤 파장을 사용하여 패킷들을 전송할 것인지 결정하는 것을 말한다. 본 논문에서는 파장조율에 따른 지연시간을 $\delta$로 나타낼 때 모든 노드가 자기 자신을 제외한 다른 모든 노드에 주기적으로 전방송(all-to-all broadcast)을 반복하는 경우에 임의로 주어진 N, K, $\delta$의 값에 대하여 최적의 패킷 전송 스케쥴을 구할 수 있는 알고리즘을 제안하고 있다. 또한, N이 K로 나누어 떨어지면 최적의 전방송 주기는 [NK($\delta$+1)/{$N_2$-N-NK+K$^2$+K}](N-1)임을 증명하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.12
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• pp.2828-2833
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• 1997

In this paepr, we have proposed an enhanced TDM with WDM hybrid photonic switching architecture, which has much simpler configuration and requires less hard ware. the basic module consists of arrayed waveguide grating (AWG) for wavelength division, compressor and fiber delay lines for time division. When compared with other systems, we proved that the proposed switch is suitable for large capacity photonic switching system due to less complexity and lower cost in implementation than the previous ones.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4C
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• pp.524-532
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• 2004

In this paper, an incoherent holographic 3D imaging and display system based on the modified triangular and Mach-Zehnder interferometers is optically implemented and some experiments are carried out. Incoherent hologram of a 3D object is generated by using the hologram input system of modified triangular interferometer. Then this complex hologram is reconstructed by using the hologram output system of modified Mach-Zehnder interferometer in which two LCD spatial light modulators and a waveplate are inserted. From the experiment with two point sources having a depth difference of 100 mm each other, it is revealed that each point source can be independently reconstructed at its own focal position from the complex hologram, while both of the bias and conjugate image are simultaneously eliminated at the same time. And in the experiment with the real 3D object of two dices having a depth difference of 30 mm each other, it is also conformed that the bias and conjugate image can be effectively eliminated from the hologram pattern and each 3D dice can be also successfully reconstructed at its own focal position from the complex hologram. These experiment results finally suggest a possibility of implementing a new incoherent holographic 3D imaging and display system using the modified triangular and Mach-Zehender interferometers.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.11
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• pp.1190-1196
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• 2014

This paper presents the design of a Frequency Modulated Continuous Wave(FMCW) radar altimeter with wide altitude range and low measurement errors. Wide altitude range is achieved by employing the optic delay in the transmitting path to reduce the dynamic range of measuring altitude. Transmitting power and receiver gain are also controlled to have the dynamic range of the received power be reduced. In addition, low measurement errors are obtained by improving the sweep linearity using the Direct Digital Synthesizer(DDS) and minimizing the phase noise employing the reference clock(Ref_CLK) as the offset frequency of the Phase Locked Loop(PLL).

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.3-4
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• 2006

• Journal of Korean Ophthalmic Optics Society
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• v.10 no.1
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• pp.9-15
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• 2005

The polariscope to measure the microscopic stress in CR lens consists of light source polarizer, model, polarizer, CCD, computer, chrome conversion orderly and the principal-stressed difference, (${\sigma}_1-{\sigma}_2$) and the fringe order n were measured by analyzing two components of light wave $E_1$ and $E_2$ following each polarizer's steps. The two-dimensional model could be determined from the fact that the optical axes of sample concide with the principal-stress directions. The bi-refringence acted to a light wave and the phase retardation were in proportion to the principal-stressed difference(${\sigma}_1-{\sigma}_2$) and the intensity of final light wave was proportioned to $sin2({\Delta}/2)$ and when ${\Delta}/2=n{\pi}$ (n=0, 1, 2, ${\ldots}$) the extinction occurs. Photoelastic's image by microscopic stress could analyzed using chrome conversion, and the image showed clearly.

• Proceedings of the KIPE Conference
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• 2008.10a
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• pp.77-79
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• 2008

본 논문에서는 구동전압 인가 방식에 따른 면광원의 방전특성에 대해 분석한다. 2kV이상의 고전압 전원장치의 직접 이용은 구성 소자의 전압 스트레스를 증가시키며 가격 상승의 원인이 된다. 100~400V대의 전원장치에 변압기를 적용하여 구동전압을 인가하게 되면 전원 및 구동회로의 간략화를 도모할 수 있으나 변압기의 영향으로 인한 천이 지연시간, 파형왜곡의 영향으로 방전 불안정 및 광효율 저하를 야기할 수 있다. 전원 출력전압 및 변압기의 권선비에 따른 직접구동과의 비교연구를 통하여 최적 설계 방안을 도모한다.