• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.440-444
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• 1996

In this paper, we report an InGaAs/InAlAs multi-quantum well (MQW) avalanche photodiode (APD) showing a performance suitable for 10 Gbps lightwave communications. In designing the device, emphasis is given on the effect of indiffusion of Be dopant from the highly doped field layer into the MQW multiplication region. It is found that a small amount of diffusion can alter the dark current and gain characteristics of the device significantly. A spacer used to restrain such indiffusion is shown effective in reducing dark current (500 nA at a gain of 10) while maintaining a high bandwidth (10 GHz at a gain of 10) devices grown by molecular beam epitaxy.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.38 no.5
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• pp.27-36
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• 2001

This paper proposes new design algorithms based on stochastic relaxation (SR) for an on-line vector quantizer (VQ) design. These proposed SR methods solve the local entrapment problems of the conventional Kohonen learning algorithm (KLA). These SR methods cover two different types depending upon the use of simulated annealing (SA) : the one that uses SA is called the OLVQ SA and the other the OLVQ SR. These methods arc combined with the KLA and therefore preserve the its convergence properties. Experimental results for Gauss Markov sources, real speech and image demonstrate that the proposed algorithms can consistently provide better codebooks than the KLA.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.1
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• pp.32-39
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• 2002

Vector quantization for image compression needs expensive encoding time to find the closest codeword to the input vector. This paper proposes a search algorithm for fast vector quantization encoding. Firstly, we derive a robust condition based on the efficient topological structure of the codebook to dramatically eliminate unnecessary matching operations from the search procedure. Then, we Propose a fast search algorithm using the elimination condition. Simulation results show that with little preprocessing and memory cost, the encoding time of the proposed algorithm is reduced significantly while the encoding quality remains the same with respect to the full search algorithm. It is also found that the Proposed algorithm outperforms the existing search algorithms.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.6
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• pp.72-80
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• 1998

A method is proposed for directional vector quantization using the wavelet packets. After partitioning the wavelet packet coefficients into 9 edges according to the corresponding directions, it encodes and transmits locally dominant edges. The directions of the edges are encoded with a variable length coding and conditional switching of codebooks, while the contents of them with the vector quantization followed by the variable length index coding. The proposed algorithm is superior to various conventional image coding algorithms in the sense of PSNR, which is relatively more significant at very low bit rate such as 0.1~0.3 bpp. As the proposed algorithm preserves the edges which is the most important for the human visual system, it also provides the reconstructed images of good subjective quality even at very low bit rate.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.10
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• pp.15-22
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• 2008

The bulk-planer MOSFET has a scaling limitation due to the short channel effect (SCE). The Double-Gate MOSFET (DG-MOSFET) is a next generation device for nanoscale with excellent control of SCE. The quantum effect in lateral direction is important for subthreshold characteristics when the effective channel length of DG-MOSFET is less than 10nm, Also, ballistic transport is setting important. This study shows modeling and design issues of nanoscale DG-MOSFET considering the 2D quantum effect and ballistic transport. We have optimized device characteristics of DG-MOSFET using a proper value of $t_{si}$ underlap and lateral doping gradient.

• Journal of Broadcast Engineering
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• v.7 no.4
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• pp.335-344
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• 2002

A sub-picture slice structure is proposed which can perform the region-of-interest coding effectively, where the subjective quality can be improved by coding the region-of-interest in higher quality than the background region. In addition, the bit allocation mechanism is Proposed where the interval between quantization parameters of the foreground and background region is fixed. And the method to reduce the boundary effect between the foreground and background region is proposed. The foreground region is better protected to the network channel error than the background region. which results in the overall subjective quality improvement in the error prone environments.

• Journal of Broadcast Engineering
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• v.2 no.1
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• pp.74-83
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• 1997

We have proposed a composite feature measure which combines the color and shape features of an image for image retrieval. We improved the performance of retrieval based on the efficient color quantization using the Lloyd-Max quanizer and on the Histogram matrix matching method which considers the spatial correlation of quantized color group. We also supplemented the color information using shape information with the Improved Moment Invarlants. We have tested our technique on Image database consisting of 200 actual trademark images. Our experimental results showed that our approach improved the performance compared to the previous method under the various situations such as rotation images, translation images, noise added images, gamma corrected images and so on. The efficiency of retrieval is found to be very high and experimental results are

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.8
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• pp.547-553
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• 2006

We present a new geometry coding method for 3D meshes, an adaptive subdivision. Previous localized geometry coding methods have demonstrated better compression ratios than the global approach but they are considered hard to use in practice partly due to time - consuming quantization. Our new localized scheme replaces this quantization with an adaptive subdivision of the localized range. The deeper level a user chooses, the closer to the original the mesh will be restored. We also present an improved connectivity coder upon the current leading Angle-Analyzer's by applying a context-modeling. As a result, our new coder provides reliable and intuitive controls between bit-rate and distortion without losing efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2C
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• pp.298-305
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• 2004

This paper presents an error compensation method for a fixed-width modified Booth multiplier that receives a W-bit input and produces a W-bit product. To efficiently compensate for the quantization error, Booth encoder outputs (not multiplier coefficients) are used for the generation of error compensation bias. The truncated bits are divided into two groups depending upon their effects on the quantization error. Then, different error compensation methods are applied to each group. By simulations, it is shown that quantization error can be reduced up to 50％ by the proposed error compensation method compared with the existing method with approximately the same hardware overhead in the bias generation circuit. It is also shown that the proposed method leads to up to 40％ reduction in area and power consumption of a multiplier compared with the ideal multiplier.

• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.481-484
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• 2005

Quantum ghost imaging uses quantum mechanically entangled photons to form an image of an object. The quantum ghost image is also obtained by means of classical coincidence measurements with a classically correlated light source[1,2]. In this work we performed classical coincidence imaging experiments with classically correlated beams in their direction of propagation. We observed the ghost interference patterns which were usually made by quantum mechanically entangled states and we also analyze in detail the mechanism of the ghost imaging with classically correlated lights. We made? the classically correlated source with an Ar laser and controlled the direction of the light by a mirror? mounted on a small speaker.