• 한국광학회지
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• 제11권1호
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• pp.43-46
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• 2000

Kerr 렌즈 모드록킹된 티타늄 사파이어 레이저에서 상용화된 광학부품만을 이용하여 9 fs의 펄스를 생성하였다. 공진기 내부와 출령경을 지나면서 발생하는 군속도 분산을 각각 용융 프리즘 쌍을 이용하여 보상하였고, 넓은 스펙트럼을 얻기 위하여 광대역 거울을 사용하였다. 이전에 사용했던 광대역 거울과 반사율을 비교해 봄으로서 10fs 미만의 극초단 펄스를 생성하기 위해서는 180nm 이상의 넓은 반사대역을 갖는 거울을 선택하는 것이 필수적임을 확인하였다.

• 한국통신학회논문지
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• 제35권8B호
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• pp.1150-1158
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• 2010

At present multimedia service composed of voice, data, and video service is prevalent in the Internet. As such, wide-scale penetration of Internet service imposes tremendous pressure to the network infrastructure such as the media servers and links as well as the nodes. In addition, users from a large-scale population require broad bandwidth and high level of QoS. This requires a network with reliable and scalable services to customers, which also necessitates a realistic method for the design of the a media server. In this work, we explore the influence of user's behavior about delay on the performance of media server that takes into account the system and user attributes in a realistic manner. By incorporating user's behavior about the delay-sensitivity, we present an analytic framework for the evaluation of the performance of the media server, via which we illustrate a meaningful intuition in the provision of Internet multimedia service.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2005년도 학술대회 논문집
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• pp.405-408
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• 2005

This paper presents the characteristics of antenna factors for sleeve dipole antennas with a broad bandwidth. The coupled integral equations for the unknown current distributions on each elements are derived and solved by applying Galerkin's method of moments. The flatness of antenna factor is considered by variation of the length and number of sleeve elements.

• 한국정보통신학회논문지
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• 제10권2호
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• pp.368-373
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• 2006

본 논문에서는 CPW 급전된 두 개의 슬롯이 부착된 이중공진 직사각형 슬롯안테나를 제시하였다. 이 안테나는 약 2.1GHz 및 3.3GHz에서 공진되는 이중 안테나로 각 공진 주파수에서 넓은 대역폭을 갖는다. 이들 각 공진 주파수에서 정합하기 위해 CPW inset 구조를 갖도록 하였다. 직사각형 슬롯안테나의 각 파라미터의 변화를 알아보기 위해 여러 안테나를 제작하고, 각 안테나의 특성을 직접 측정하였다. 그리고 이를 분석하여 안테나 설계방법에 대해 고찰하였다.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 1999년도 KOBA 방송기술 워크샵 KOBA Broadcasting Technology Workshop
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• pp.183-190
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• 1999

We have started the field test of the VOD service since April 1996, in Huis Ten Bosch which is one of the famous theme parks in Japan. In three years, total about 100 thousands people have used this VOD system and evaluated it. This test verifies that the VOD system which provides moving picture by MPEG2 via broad bandwidth ATM network has already reached the level of actual use. And also we get the know-how to construct contents, or how to manage network resources and server resources, and we have proposed them.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 B
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• pp.959-961
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• 2003

In this paper, we describe implemented DMAC (Direct Memory Access Controller) architecture on Altera's $Excalibur^{TM}$ that includes industry-standard $ARM922T^{TM}$ 32-bit RISC processor core operating at 200 MHz. We implemented DMAC based on AMBA (Advanced Micro-controller Bus Architecture) AHB (Advanced Micro-performance Bus) interface. Implemented DMAC has 8-channel and can extend supportable channel count according to user application. We used round-robin method for priority selection. Implemented DMAC supports data transfer between Memory-to-Memory, Memory-to-Peripheral and Peripheral-to-Memory. The max transfer count is 1024 per a time and it can support byte, half-word and word transfer according to AHB protocol (HSIZE signals). We implemented with VHDL and functional verification using $ModelSim^{TM}$. Then, we synthesized using $LeonardoSpectrum^{TM}$ with Altera $Excalibur^{TM}$ library. We did FPGA P&R and targeting using $Quartus^{TM}$. We can use implemented DMAC module at any system that needs high speed and broad bandwidth data transfers.

• 한국정밀공학회지
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• 제27권6호
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• pp.7-16
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• 2010

Physical fundamentals of ultrashort femtosecond lasers are addressed along with emerging applications for precision manufacturing and metrology. Femtosecond lasers emit short pulses whose temporal width is in the range of less than a picosecond to a few femtoseconds, thereby enabling extremely high peak-power machining with less thermal damages. Besides, the broad spectral bandwidth of femtosecond lasers constructed in the form of frequency comb permits absolute distance measurements leading to ultraprecision positioning control and dimensional metrology.

• Journal of the Optical Society of Korea
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• 제12권4호
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• pp.326-336
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• 2008

A WDM-PON has been considered as an ultimate solution for access networks. However, there were many technical and practical issues for commercial deployment. These issues were solved with wavelength locked F-P LD and the WDM-PONs employing this optical source were commercialized. These WDM-PON systems have been deployed in Korea, Europe, and US. We reviewed wavelength locking technology and WDM-PON achievements. When we inject spectrum sliced broadband light into an F-P LD, the multimode output is changed to a quasi single mode. Then, we can use the single mode light for WDM signal transmission. The broad spectral gain of the semiconductor gain medium enables a color-free operation of WDM-PON, i.e., an identical ONT can be used for each user. The wavelength locking properties depend on many parameters, especially alignment of injection wavelength to a lasing mode, passband profile of AWG and front facet reflectivity of F-P LD. However, these dependencies can be reduced by proper design of the laser and the injection bandwidth. Thus, WDM-PON systems have been achieved with color-free operation.

• Current Optics and Photonics
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• 제5권2호
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• pp.134-140
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• 2021

In this paper, I introduce a novel design method of a high performance nanophotonic beam deflector providing broadband operation, large active tunability, and signal efficiency, simultaneously. By combining thermo-optically tunable vanadium dioxide nano-ridges and a metallic mirror, reconfigurable local optical phase of reflected diffraction beams can be engineered in a desired manner over broad bandwidth. The active metagrating deflectors are systematically designed for tunable deflection of reflection beams according to the thermal phase-change of vanadium dioxide nano-ridges. Moreover, by multiplexing the phase-change supercells, a robust design of actively tunable beam splitter is also verified numerically. It is expected that the proposed intuitive and simple design method would contribute to development of next-generation optical interconnects and spatial light modulators with high performances. The author also envisions that this study would be fruitful for modern holographic displays and three-dimensional depth sensing technologies.

• 비파괴검사학회지
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• 제35권2호
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• pp.112-119
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• 2015

고해상도 분자 영상이 가능한 광음향 현미경의 공간해상도는 초음파 변환기에 의해 결정되기 때문에 높은 동작 주파수, 광대역, 높은 신호 수신 효율을 갖는 광음향 수신 변환기는 고성능 광음향 현미경에 필수적이다. Polyvinylidene fluoride (PVDF)는 이러한 광음향 수신 변환기 성능 확보가 가능한 압전소재이다. 그러나 PVDF는 낮은 음향 임피던스로 인해 사용되는 흡음층에 의해서 중심주파수 및 대역폭이 영향을 받게된다. 본 논문에서는 광음향 현미경에 적합한 PVDF 기반 고주파수 초음파 수신 변환기의 최적 흡음층 소재의 음향 임피던스가 최종 변환기 성능에 어떠한 영향을 주는지에 관한 연구를 수행하였다. 이를 위해 EPO-TEK 301, E-Solder 3022, RTV를 각각 흡음층 물질로 사용하여 고주파수 초음파 수신 변환기를 제작하고 그 음향 특성을 평가하였다. 제작된 변환기의 공간해상도를 평가하기 위해 $25{\mu}m$ 직경을 갖는 철심을 표적으로 사용하여 영상을 획득하였으며, 실험을 통해 얻은 펄스-에코 신호 크기 및 중심주파수, -6 dB 대역폭, 공간해상도 평가를 통해 PVDF의 음향 임피던스보다 약간 높은 음향 임피던스를 갖는 EPO-TEK 301이 가장 적합한 흡음층 물질임을 알 수 있었다.