• Journal of the Korean Vacuum Society
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• v.9 no.2
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• pp.150-154
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• 2000

We investigated the quantum well intermixing (QWI) of a compressively strained InGaAs/InGaAsP multiple quantum well (MQW) by using impurity free vacancy diffusion technique. The samples with InGaAs/$SiO_2$ capping layer showed a higher degree of intermixing compared to that of InP/$SiO_2$ capping layer after rapid thermal annealing (RTA). Band-gap shift difference as large as 123 meV (195 nm) was observed between samples capped with InGaAs/$SiO_2$ and with InP/$SiO_2$ layer at RTA temperature of $700^{\circ}C$. Using the InGaAs/$SiO_2$ cap layer, the band-gap wavelength of MQW was changed by the intermixing from 1.55 $\mu\textrm{m}$ band to 1.3 $\mu\textrm{m}$ band with a wavelength shift of a 237 nm. The transform from MQW structure to homogenous alloy was observed above the RTA temperature of $700^{\circ}C$.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.467-472
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• 2002

In this paper, we propose a polarization-insensitive temperature sensor using a thermo-optic effect of the upper and (or) lower cladding of a planar waveguide in contact with a side-polished fiber. A microscope cover glass with thickness of a 170 ${\mu}{\textrm}{m}$ is adopted as an overlay waveguide because this waveguide opposes sudden temperature change and ensures polarization-insensitive responses. The measured polarization-dependence loss is less than 0.3 dB. The temperature can be detected as a result of the shift in coupling wavelength of the sensor. We investigate the shift in coupling wavelength as a function of the temperature variation with respect to the different thermo-optic coefficients of lower and upper claddings. We also show that the temperature sensitivity of the device can be easily controlled by the thermo-optic coefficients of lower and upper claddings of the overlay waveguide.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.7 no.1
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• pp.20-25
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• 2014

There are several severe problems for LED device, the next generation's economy green lighting: as the temperature increases, the lamp efficiency decreases; if the temperature is over $80^{\circ}C$, the lifetime of lighting decreases; Red Shift phenomenon that wavelength of spectrum line moves toward long wavelength occurs; and optical power decreases as $T_j$ increases. Thus, Heat sink design that can minimize the heat of LED device is currently in progress. While the thermal resistance of COB Type LED was reduced by direct coupling of LED chip to the board, residential 13.5W requires Heat sink in order resolve heat issue. This study designed Heat Sink suitable for residential 13.5W COB LED down-light and selected the optimum Fin thickness through flow simulation that packaged the designed Heat Sink and 13.5W COB. And finally it analyzed and evaluated the thermal modes using contacting thermometer.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.74.1-74.1
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• 2012

We observed the radio sources found from the First Look Survey (FLS) field at the 1.4 GHz radio continuum emission with the Very Large Array (VLA) using the A configuration. We identify point sources and multi component sources at ${\geq}4{\sigma}$ level. We also present the submillimeter properties of the selected radio sources in the FLS field from the Herschel/SPIRE 250/350/500/${\mu}m$ and AzTEC 1.1mm surveys. The counterparts of the radio sources at submillimeter for these called 'submillimeter galaxies (SMGs)' are detected at infrared wavelength with the Spitzer MIPS 24 & 70 ${\mu}m$ sources. Based on the MMT/HECTOSPEC red-shift survey, IRS spectroscopy, and SDSS photometric red-shift survey, the radio sources are likely to be the extragalactic sources. Here, we use the star formation rate (SFR) derived from the MIPS 24 and 70 ${\mu}m$ luminosity to compare the measured SFR from the VLA 1.4 GHz luminosity. These results show that a tight correlation between the SFR from the radio luminosity and the MIPS $24{\mu}m$ rather than that from the MIPS $70{\mu}m$ luminosity. Radio and IR correlation is also used to indicate the radio and IR properties of star-formation in the galaxies and active galactic nuclei (AGNs). Using the counterpart sources selected at IR and radio wavelengths, we employ the IR/radio flux ratios to determine the properties and population of the selected galaxies.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.9
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• pp.581-586
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• 2015

We studied optical and electrical properties of two-wavelength white tandem organic light-emitting diodes using red and blue materials. White fluorescent OLEDs were fabricated using Alq3 : Rubrene (3 vol.% 5 nm) / SH-1 : BD-2 (3 vol.% 25 nm) as emitting layer (EML). White single fluorescent OLED showed maximum current efficiency of 9.7 cd/A, and tandem fluorescent OLED showed 18.2 cd/A. Commission Internationale de l'Eclairage (CIE) coordinates of single and tandem fluorescent OLEDs was (0.385, 0.435), (0.442, 0.473) at $1,000cd/m^2$, respectively. White hybrid OLEDs were fabricated using SH-1 : BD-2 (3 vol.% 10 nm) / CBP : $Ir(mphmq)_2(acac)$ (2 vol.% 20 nm) as EML. White single hybrid OLED showed maximum current efficiency of 7.8 cd/A, and tandem hybrid OLED showed 26.4 cd/A. Maximum current efficiency of tandem hybrid OLED was more twice as high as single OLED. CIE coordinates of single hybrid OLED was (0.315, 0.333), and tandem hybrid OLED was (0.448, 0.363) at $1,000cd/m^2$. CIE coordinates in white tandem OLEDs compared to those for single OLEDs observed red shift. This work reveals that stacked white OLED showed current efficiency improvement and red shifted emission than single OLED.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.2023-2028
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• 2014

In this study, we studied the effect of $Co^{60}$ gamma-radiation on the FBGs written in photo-sensitive and commercial Ge-doped single-mode optical fibers. The FBGs were exposed to gamma-radiation up to a dose of 17.8 kGy at the dose rate of 300 Gy/min. According to the experimental data and analysis results, the lowest Bragg wavelength shift (18 pm) was obtained by a grating written in photosensitive fiber without $H_2$-loading. Also, we confirmed that the H2 loading process has considerably more influence on the Bragg wavelength shift change under gamma radiation than $GeO_2$ contents in the fiber core.

• Korean Journal of Optics and Photonics
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• v.1 no.1
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• pp.7-11
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• 1990

Resonant multi photon ionization (RMPD of Hg atoms is studied by focusing a high-power laser into the ionization cell. The intermediate resonant state is taken as $6d^1D_2$ with the 4-photon resonance wavelength of 560.7 nm. The ionization signal is measured as Hg vapor pressure (0.1-3.0 Torr), laser intensity $(10-120GW/\textrm{cm}^2)$, and laser wavelength (559-569 nm) vary. AC Stark shift and line broadening of the resonant state $(6d^1D_2)$ are observed and the shift factor is measured to be $-0.6(cm^{-1}/GW/\textrm{cm}^2$. It is also observed that the ionization signal increases as the Hg vapor pressure increases up to a certain value of pressure, however, if the pressure further increases, the signal decreases. The order of non-linearity, which discribes the laser intensity dependence of ionization rate, is measured to be 3 at the resonance, and compared with the theoretical results.esults.

• Korean Journal of Optics and Photonics
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• v.14 no.2
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• pp.184-188
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• 2003

We fabricated a P-I-i-I-N $GaAs/Al_{0.35}Ga_{0.65}As$waveguide phase modulator with significant phase shift for the TE mode but negligible for the TM mode. We selected the P-I-i-I-N structure to cause a phase shift about the TM mode. The wavelength of $\lambda=1.55$\mu\textrm{m}$ was measured for both the TE and TM modes, respectively. As a result, the measured phase shift efficiency ($\Delta\phi$) by using the Fabry-Perot resonance method was $7.9^{\circ}/V.mm$ for TE-polarized light. Also, no modulation was observed for TM-polarized light.

• 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.

• Electrical & Electronic Materials
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• v.8 no.4
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• pp.472-477
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• 1995

The degree of the photodoping process in Ag(100[.angs.])/a-Se$_{75}$Ge$_{25}$(1500[.angs.]) films has measured as a function of the photon energy between 1.5[eV] and 2.9[eV] with the exposing time. The "window" characteristics of Ag occur at 3400[.angs.] (3.65[eV]) and Ag is almost transparent in this region. It is shown that transmittance is almost constant (40-50%) for the wavelength ranges of our experiment. It is found that the energy gap of a unexposed a-Se$_{75}$Ge$_{25}$ film is 1.81[eV]. Ag photodoping process results in the photodarkening effect which the absorption edge shifts to the long wavelength. Especially, very large band shift (-0.3[eV]) is obtained by exposing He-Ne laser(6328[.angs.]).. We have obtained "the U-type property" for Ar He-Ne and semiconductor laser. It is associated with the variation of energy gap(E$_{g}$) with photo-dose and substantially is explained by DWP model.l.gap(E$_{g}$) with photo-dose and substantially is explained by DWP model.