• Journal of Radiation Industry
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• v.10 no.4
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• pp.167-171
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• 2016

The scintillation efficiency of the polystyrene based plastic scintillator depends on the ratio of the wavelength shifters, organic fluors(PPO and POPOP). Thus, 24 samples of the plastic scintillator were fabricated in order to find out the optimum ratio of the wavelength shifters in the plastic scintillator. The fabricated plastic scintillators were trimmed through a cutting and polishing process. They were used in gamma energy spectrum measurement with the $^{137}Cs$ emitting mono-energy photon with 662 keV for the comparison of the scintillation efficiency. As a result, it was found out that the scintillator sample with 1.00 g of PPO (2,5-Diphenyloxazole) and 0.50 g of POPOP (1,4-Bis(5-phnyl-2oxidazolyl)benzene) dissolved in 100 g of styrene solution has the optimum ratio in terms of the light yield of the polystyrene based plastic scintillator.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.12
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• pp.36-43
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• 2001

We evaluate the optical characteristics of planar distributed feedback (DFB) waveguides with quarter-wavelength phase-shifter. To analyze explicitly its band-pass and resonance properties, we present and newly develop a modal transmission-line theory (MTLT) based on Floquet's theorem and Babinet's principle. The numerical results reveal that this approach offers a simple and analytic algorithm to analyze either the filtering or the oscillating characteristic of DFB gratings with quarter-wavelength phase-shifter, and has a novel physical insight that may not be achieved in other approximating approaches

• ETRI Journal
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• v.24 no.5
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• pp.341-348
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• 2002

We propose an asymmetric sampled grating laser and a multi-wavelength laser array associated with it. Asymmetric sampling periods combined with an index shifter make it possible to use first order reflection for lasing operations. With the structure of our design, we achieved a simple fabrication procedure as well as a high yield without using complex and time-consuming e-beam lithography for multi-period gratings. We analyzed the effect of mirror coating by numerical analysis to improve single mode and power extraction performance. By using high reflection-antireflection coatings, we obtained high power extraction efficiency without degradation of the single mode property. For the multi-wavelength laser array, to gain wavelength control, we varied the sampling periods from one laser to an adjacent laser across the array. With this approach, we showed the feasibility of an array of up to 30 channels with 100 GHz wavelength spacing.

• Journal of Sensor Science and Technology
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• v.31 no.2
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• pp.115-119
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• 2022

A readout circuit for a mercury-cadmium-telluride (MCT)-amplified mid-wave infrared (IR) photodetector was realized and applied to noncontact chemical agent detectors based on a quantum cascade laser (QCL). The QCL emitted 250 times for each wavelength in 0.2-㎛ steps from 8 to 12 ㎛ with a frequency of 100 kHz and duty ratio of 10%. Because of the nonconstant QCL emission power during on-duty, averaging the photodetector signals is essential. Averaging can be performed in digital back-end processing through a high-speed analog-to-digital converter (ADC) or in analog front-end processing through an integrator circuit. In addition, it should be considered that the 250 IR data points should be completely transferred to a PC during each wavelength tuning period of the QCL. To average and minimize the IR data, we designed a readout circuit using the analog front-end processing method. The proposed readout circuit consisted of a switched-capacitor integrator, voltage level shifter, relatively low-speed analog-to-digital converter, and micro-control unit. We confirmed that the MCT photodetector signal according to the QCL source can be accurately read and transferred to the PC without omissions.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.880-883
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• 2002

We propose an effective wavelength converter method using frequency shifter for photonic node, and examine the scalability of Generalized Multiprotocol Label Switching (GMPLS) networks. The ana1ysis is examined based on signal to noise ratio (SNR) for present 2.4 and 10 Gbit/s Synchronous Digital Hierarchy (SDH) networks, and next generation 2.7 and 10.8 Gbit/s Optical Transport Networks (OTN) format The proposed 100 channels GMPLS networks using optical frequency shifters are shown to be applicable to transmission network spanning over 1206 km(24 nodes) in 2.7 Gbit/s trunk networks. Transmission over more than 310 km (6 nodes) is also possible in 2.7 Gbit/s Metroporitan Area Networks(MAN).

• Progress in Medical Physics
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• v.28 no.4
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• pp.226-231
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• 2017

The aim is to investigate the spectra responsibilities of QD (Quantum Dot) for the innovation of new dosimetry application for therapeutic Megavoltage X-ray range. The unique electrical and optical properties of QD are expected to make it a good sensing material for dosimeter. This study shows the spectra responsibility of toluene based ZnCd QD and PPO (2.5-diphenyloxazol) mixed liquid scintillator. The QDs of 4 sizes corresponding to an emission wavelength (ZnCdSe/ZnS:$440{\pm}5nm$, ZnCdSeS:470, 500, $570{\pm}5nm$) were utilized. A liquid scintillator for control sample was made of toluene, PPO. The Composition of QD loaded scintillators are about 99 wt% Toluene as solvent, 1 wt% of PPO as primary scintillator and 0.05, 0.1, 0.2 and 0.4 wt% of QDs as solute. For the spectra responsibility of QD scintillation, they were irradiated for 30 second with 6 MV beam from a LINAC ($Infinity^{TM}$, Elekta). With the guidance of 1.0 mm core diameter optical fiber, scintillation spectrums were measured by a compact CCD spectrometer which could measure 200~1,000 nm wavelength range (CCS200, Thorlabs). We measured the spectra responsibilities of QD loaded organic liquid scintillators in two scintillation mechanisms. First was the direct transfer and second was using wave shifter. The emission peaks from the direct transfer were measured to be much smaller luminescent intensity than based on the wavelength shift from the PPO to QDs. The emission peak was shifted from PPO emission wavelength 380 nm to each emission wavelength of loaded QD. In both mechanisms, 500 nm QD loaded samples were observed to radiate in the highest luminescence intensity. We observed the spectra responsibility of QD doped toluene based liquid scintillator in order to innovate QD dosimetry applicator. The liquid scintillator loading 0.2 wt% of 500 nm emission wavelength QD has most superior responsibility at 6 MV photon beam. In this study we observed the spectra responsibilities for therapeutic X-ray range. It would be the first step of innovating new radiation dosimetric methods for radiation treatment.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1275-1277
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• 1995

We designed and constructed an extremly high power s-band traveling wave resonator for the test of high power microwave components using 80MW pulsed klystron with $4{\mu}s$ pulse width. The 10dB directional coupler for the input power coupling was used, and the ring consists of phase shifter, tuner, H-band, and other microwave components. The designed total electrical length of the system is 10 times of the waveguide wavelength, ${\lambda}_g$=15.3cm, and the measured total insertion loss is 0.15dB. The low power test measurment showed the power multiplication of 14.69. The design goal is to achieve the peak power of 300MW, pulse width $4{\mu}s$ with 30 pulse repetition rate. In this article we discuss the treveling wave resonant ring constructed at the PAL laboratory together with the test results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.25-30
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• 2017

Millimeter wave (mmWave) bands are expected to improve date rate of 5G systems due to the wide available bandwidth. While severe path loss in those bands has impeded the utilization, short wavelength enables a large number of antennas packed in a compact form, which can mitigate the path loss. However, estimating the channel with a conventional scheme requires a huge training overhead, hence an efficient estimation scheme operating with a small overhead needs to be developed. The sparsity of mmWave channels caused by the limited scatterers can be exploited to reduce the overhead by utilizing compressed sensing. In this paper, we introduce compressed sensing techniques for mmWave channel estimation. First, we formulate wideband channel estimation into a sparse recovery problem. We also analyze the characteristics of random measurement matrix constructed using quantized phase shifters in terms of mutual incoherence.

• Korean Journal of Optics and Photonics
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• v.17 no.5
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• pp.469-474
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• 2006

A $1{\times}16$ thermo-optic switch with small excess loss using multimode interference(MMI) couplers is designed, fabricated, and measured. This paper introduces the proposed $1{\times}16$ thermo-optic switch, and discusses the measurement results. The $1{\times}16$ thermo-optic switch is farmed as 4-stage which consists of 15 unit devices. The unit devices are the $2{\times}2$ thermo-optic switches with Mach-Zehnder interferometer(MZI) structure. The characteristics of the $1{\times}16$ thermo-optic switch depends strongly on each unit device. The unit deviceconsists of two 3-dB general interference MMI couplers and two single mode waveguide arms as a phase shifter. First of all, the 3-dB optical splitter and $2{\times}2$ MZI thermo-optic switch have been tested to confirm the characteristics of the unit devices of the $1{\times}16$ MZI thermo-optic switch. Using the measurement results of the unit devices, the $1{\times}16$ MZI thermo-optic switch can be produced with better characteristics. The resultant structure of the MMI coupler with the optical light source of wavelength of 1550nm for the $1{\times}16$ thermo-optic switch is that the width and the optimized length are $25{\mu}m\;and\;1580{\mu}m$, respectively. The smallest excess loss fur the unit device is -0.5dB and the average excess loss is -0.7dB.