• Korean Journal of Optics and Photonics
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• v.11 no.1
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• pp.43-46
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• 2000

We generated 9-fs pulses from a Kerr-lens mode-locked Ti:sapphire laser only using commercial optical components. Two sets of prisms pair made of fused silica were used to compensate group delay dispersion inside and outside the laser oscillator respectively, and broadband mirrors were used to obtain a broad spectrum. By comparison between reflectance curves of the broadband mirrors and those of previous ones, broadband mirrors which have high reflectance bandwidth of over 180 nm were found to be essential to produce sub-IO-fs pulses. ulses.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.8B
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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.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.11a
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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.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.2
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• pp.368-373
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• 2006

In this paper, a CPW fed rectangular slot antenna loaded with two slots for dual band operation is presented. This antenna operates at about 2.1GHz and 3.3GHz with the broad bandwidth at these frequencies. a CPW inset structure is used to match the antenna at the two seperated frequencies. Some prototypes of the proposed dual frequency antenna have been implemented. Experimental results are presented and discussed.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1999.06a
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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.

• Proceedings of the KIEE Conference
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• 2003.11c
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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.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.6
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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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• v.12 no.4
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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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• v.5 no.2
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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.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.2
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• pp.112-119
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• 2015

Photoacoustic microscopy is capable of providing high-resolution molecular images, and its spatial resolution is typically determined by ultrasonic transducers used to receive the photoacoustic signals. Therefore, ultrasonic transducers for photoacoustic microscopy (PAM) should have a high operating frequency, broad bandwidth, and high signal-reception efficiency. Polyvinylidene fluoride (PVDF) is a suitable material. To take full advantage of this material, the selection of the backing material is crucial, as it influences the center frequency and bandwidth of the transducer. Therefore, we experimentally determined the most suitable backing material among EPO-TEK 301, E-Solder 3022, and RTV. For this, three PVDF high-frequency single-element transducers were fabricated with each backing material. The center frequency and -6 dB bandwidth of each transducer were ascertained by a pulse-echo test. The spatial resolution of each transducer was examined using wire-target images. The experimental results indicated that EPO-TEK 301 is the most suitable backing material for a PAM transducer. This material provides the highest signal magnitude and a reasonable bandwidth because a large portion of the energy propagates toward the front medium, and the PVDF resonates in the half-wave mode.