Juwan Kim

Intersection collision avoidance using Wireless sensor network

In this study, we propose intersection collision avoidance system in preventing traffic crashes at typical urban intersections. The proposed intersection crash prevention system would display the crash warning messages to the drivers when crash-prone conditions are detected through the sensor system installed along intersection approaches. It would further change the traffic signal setting in real-time, if necessary. To support the service, the intersection collision avoidance system introduces reliable MAC and accurate speed measurement mechanism.

Modeling of Traveling Wave Electro-absorption Modulator for High Speed Optical Communication Systems

Recently, researches for high-speed optical devices have been increased to provide mass data transmission and high-speed optical communication. Optical modulator in the transmission link is one of the crucial devices to modulate the optical signals in the optical transmission and the properties can affect a great effect to the whole optical communication system. Therefore, the properties of the modulators are very important and characterization of optical modulator should be required to ensure the high-speed optical communication applications. In this paper, the microwave characteristics of high-speed traveling wave electro-absorption modulator were modeled and analyzed using the equivalent circuit model.

Augmented reality using GPS

This paper describes a prototype system to be developing using GPS (Global Positioning System) as a tracker in order to combine real images with virtual geographical images in real time. To cover long distances, this system is built using a monitor-based configuration and divided into two parts. One is the real scene acquisition system that includes a vehicle, a wireless CCD camera, a GPS attitude determination device and a wireless data communication device. The other is the processing and visualization system that includes a wireless data communication device, a PC with a video overlay card and a 3D graphics accelerator. The pilot area of the current system is the part of SERI (Systems Engineering Research Institute) which is the institute we are working for now. And virtual objects are generated with 3D modeling data of the main building, the new building to be planned, and so on in SERI. The wireless CCD camera attached to a vehicle acquires the real scenes. And GPS attitude determination device produces a wireless CCD cameras position and orientation data. And then this information is transmitted to the processing and visualization part by air. In the processing and visualization system, virtual images are rendered using the received information and combined with the real scenes. Applications are an enhanced birds-eye view and disaster rescue work such as earthquake.

The thickness effect of SiO x layer in CIGS thin-film solar cells fabricated on stainless-steel substrate

We have investigated the thickness effect of SiO<inf>x</inf> layer in the CIGS thin-film solar cells fabricated on stainless-steel substrate. After a SiO<inf>x</inf> layer with a thickness of 1 or 2-µm was deposited on the substrate by using plasma-enhanced chemical vapor deposition, Na-doped Mo layer and Mo layer were coated on it. A CIGS thin-film solar cell on the stainless-steel substrate without the SiO<inf>x</inf> layer showed an efficiency of 7.47 %, the solar cell with the 1 µm-thick SiO<inf>x</inf> showed an efficiency of 11.82 %, and the solar with the 2 µm-thick SiO<inf>x</inf> showed the efficiency of 12.43%. The efficiency of CIGS solar cell with 2 µm-thick SiO<inf>x</inf> was higher than those of others with the thinner SiO<inf>x</inf> barrier.

Photoreflectance characteristics and photovoltaic performance of CBD-CdS/Cu(In, Ga)Se 2 thin-film solar cells

We have investigated the photoreflectance characteristics and the photovoltaic performance of Cu(In, Ga)Se2 (CIGS) thin-film solar cells that have CdS layers prepared by chemical bath deposition (CBD). The CdS was deposited on CIGS by three different conditions. (I) CdSO4 0.014 M, thiourea 0.014 M, NH4OH(30%) 60 ml, (II) CdSO4 0.0015 M, thiourea 0.074 M, NH4OH(30%) 56 ml, and (III) CdSO4 0.0015 M, thiourea 0.05 M, NH4OH(30%) 80 ml. The efficiencies of the solar cells fabricated in processes I, II, and III were 12.17 %, 14.47 %, and 14.97 %, respectively. Quantum efficiency spectra of the solar cells in the region of the CdS band gap showed consistent results with photoreflectance observations. The photoreflectance spectra of the solar cells indicate that different states were formed in CdS depending on the conditions of CBD processes.

Analog RF-optic performance of 60 GHz electroabsorption duplexer module

We proposed the vertical mode coupling structure (VMCS) for monolithic integration of optoelectronic devices. The electroabsorption duplexer (EAD) chip was fabricated by monolithically integrating both a waveguide photodiode (PD) and an electroabsorption modulator (EAM) in association with traveling wave electrodes. Using an EAD we presented a transceiver (TRx) module for dual functions of both electrical-to-optical (E/O) and optical-to-electrical (O/E) conversions at 60GHz band. The responsivity and the extinction ration of the EAD were 0.72 A/W and 20 dB at -4 Vdc, respectively. The coupling loss between the optical fiber and the device facet was as small as 1.96 dB. The small signal 3 dB bandwidth of E/O and O/E response was 25 GHz and 8 GHz, respectively. We also investigated the issues of RF packaging in which the optoelectronic and electronic amplifier devices were co-packaged in a single housing.