• Korean Journal of Optics and Photonics
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• v.16 no.3
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• pp.275-286
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• 2005

The performance of the InGaN LED's in terms of the photon extraction efficiency has been analyzed by the Monte Carlo photon simulation method. Simulation results show that the sidewall slanting scheme, which works well for the AlInGaP or InGaN/SiC LED, plays a very minimal role in InGaN/sapphire LED's. In contrast to InGaN/SiC LED's, the lower refractive index sapphire substrate restricts the generated photons to enter the substrate, minimizing the chances for the photons to be deflected by the slanted sidewalls of the epitaxial semiconductor layers that are usually very thin. The limited photon transmission to the sapphire substrate also degrades the. photon extraction efficiency especially in the epitaxial-side down mount. One approach to exploit the photon extraction potential of the epitaxial-side down mount may be to texture the substrate-epitaxy interface. In this case, randomized photon deflection off the textured interface directly increases the number of the photons entering the sapphire substrate, from which they easily couple out of the chip and thereby improving the photon extraction efficiency drastically.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.224-228
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• 2008

A highly sensitive integrated photonic temperature sensor was proposed and developed incorporating a polymeric microring resonator. The change in the ambient temperature was estimated by observing the shift in the resonant wavelength of the resonator induced via the thermooptic effect. For the purpose of enhancing its sensitivity, the sensor was built by implementing a polymeric resonator exhibiting a high thermooptic coefficient on a silicon substrate with a small coefficient of thermal expansion. For the range of from $20^{\circ}C$ to $30^{\circ}C$ near the room temperature, the fabricated sensor yielded a sensitivity of as high as 165 ${\pm}/^{\circ}C$ and a resolution of better than $0.1^{\circ}C$. And its performance was found to be hardly affected by the variation in the refractive index of the target analyte, which was applied to the surface of the sensor. It is hence expected that the sensor could be integrated with other refractormetric optical sensors, thereby compensating for the fatal error caused by the change in the ambient temperature.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05a
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• pp.53-56
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• 2004

The a-Si:H TFT using ferroelectric of SrTi $O_3$as a gate insulator is fabricated on glass. Dielectric characteristics of ferroelectric are superior to $SiO_2$and S $i_3$ $N_4$. Ferroelctric increases on-current, decreases thresh old voltage of TFT and also improves breakdown characteristics. The a-SiN:H has optical band gap of 2.61 eV, refractive index of 1.8~2.0 and resistivity of 10$^{13}$ - 10$^{15}$ $\Omega$cm, respectively. Insulating characteristics of ferroelectrics are excellent because dielectric constant of ferroelectric is about 60~100 and breakdown strength is over 1MV/cm. TFT using ferroelectric has channel length of 8~20${\mu}{\textrm}{m}$ and channel width of 80~200${\mu}{\textrm}{m}$. And it shows that drain current is 3.4$mutextrm{A}$ at 20 gate voltage, $I_{on}$ / $I_{off}$ is a ratio of 10$^{5}$ - 10$^{8}$ and $V_{th}$ is 4~5 volts, respectively. In the case of TFT without ferroelectric, it indicates that the drain current is 1.5 $mutextrm{A}$ at 20 gate voltage and $V_{th}$ is 5~6 volts. With the improvement of the ferroelectric thin film properties, the performance of TFT using this ferroelectric has advanced as a gate insulator fabrication technology is realized.zed.d.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.382-382
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• 2010

$TaO_2$ thin films as gate dielectrics have been proposed to overcome the problems of tunneling current and degradation mobility in achieving a thin equivalent oxide thickness. An extremely thin $SiO_2$ layer is used in order to separate the carrier in MOSFETchannel from the dielectric field fluctuation caused by phonons in the dielectric which decreases the carrier mobility. The electronic and optical properties influenced the device performance to a great extent. The atomic structure of amorphous and crystalline Tantalum oxide ($TaO_2$) gate dielectrics thin film on Si (100) were grown by utilizing atomic layer deposition method was examined using Ta-K edge x-ray absorption spectroscopy. By using X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy (REELS) the electronic and optical properties was obtained. In this study, the band gap (3.400.1 eV) and the optical properties of $TaO_2$ thin films were obtained from the experimental inelastic scattering cross section of reflection electron energy loss spectroscopy (REELS) spectra. EXAFS spectra show that the ordered bonding of Ta-Ta for c-$TaO_2$ which is not for c-$TaO_2$ thin film. The optical properties' e.g., index refractive (n), extinction coefficient (k) and dielectric function ($\varepsilon$) were obtained from REELS spectra by using QUEELS-$\varepsilon$(k, $\omega$)-REELS software shows good agreement with other results. The energy-dependent behaviors of reflection, absorption or transparency in $TaO_2$ thin films also have been determined from the optical properties.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.3
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• pp.61-64
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• 2008

Purpose: The analysis of individual eye model designed from clinical demonstration about emmetropia shows that the aberration would be changed by the wave change. Method: The model on the basis of clinical demonstration of eye ball is designed in a form of having 4 refraction surfaces and a constant refractive index. We analyzed designed twelve individual eye model into aberrations changes, as giving changes Fraunhofer lines's six wavelengths. Result: About individual eye model, change in the wavelength of the wavefront aberrations analysis using the Zernike coefficient. This data indicate that the shorter wave is, the more defocus increases and the deviation value of spherical aberration and RMS are widened. Conclusion: As quantity of defocus according to result wavelength change is shorter and shorter, inclination which is similar twelve individual eye model is bigger and bigger and individual eye model majority of cases, little change, and change is shown in part individual eye model is a significant performance degradation can be raised.

• Journal of Astronomy and Space Sciences
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• v.21 no.4
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• pp.417-428
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• 2004

We have investigated the optical property of the KAO(Korea Astronomy Observatory) wide field telescope (named NEOPAT-3; Near Earth Object and Satellite Patrol-3) and aligned optical system. The NEOPAT-3 is restricted to V,R,I-filters because of the refractive property of the correcting lens system. Because of the fast focal ratio, the optical performance of the NEOPAT-3 is very sensitive to its alignment factors of the optical system. To make the spot radius smaller than $8{\mu}m$ in rms over 2degree${\times}2$degree field, the optical system must satisfy the following conditions: 1) The tilt error between detector plane and focal plane should be less than 0.05degree. 2) The decenter error between the primary mirror and the correcting lens system should be less than 1mm. 3) The distance error between the primary mirror and the correcting lens system should be less than 2.3mm. In order to align the optical system accurately, we measured the aberrations of the telescope quantitatively by means of curvature sensing technique. NEOPAT-3 is installed temporary on the roof of the TRAO(Taeduk Radio Astronomy Observatory) main building to normalize system performance and to develop automatic observation.

• Korean Journal of Food Science and Technology
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• v.31 no.3
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• pp.600-605
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• 1999

Methyl linoleate was oxidized at 60, 90, 120 and $150^{\circ}C$, respectively, with sparging oxygen for different periods of time. On the basis of the peroxide values determined at four temperatures, four heating times were chosen for the analysis of physicochemical parameters, such as peroxide value, total oxidation products, polymer content, viscosity, refractive index and characteristics of thermal degradation by DSC (Differential Scanning Calorimeter). The content of peroxide linkage (C-O-O-C) polymer and ether or carbon to carbon linkage (C-O-C/C-C) polymer were analyzed by High Performance Size Exclusion Chromatography (HPSEC). The polymer formed at four temperatures was qualitatively identified as dimer. The polymer with peroxide linkage (C-O-O-C) were detected from methyl linoleate oxidized at $60^{\circ}C\;and\;90^{\circ}C$, but they were not detected from methyl linoleate oxidized at $120^{\circ}C\;and\;150^{\circ}C$. The enthalpy changes increased as peroxide value increased whereas maximum degradation temperature decreased. The highest correlation coefficients were obtained between maximum degradation temperature $(T_m)$, exothermic enthalpy changes and peroxide value, peroxide linkage (C-O-O-C) polymer content.

• Progress in Medical Physics
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• v.8 no.2
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• pp.67-76
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• 1997

We studied optical behavior of scintillation light generated in NaI(TI) crystal using Monte Carlo simulation method. The simulation was performed for the model of NaI(TI) scintillator (size: 60 mm ${\times}$ 60 mm ${\times}$ 6 mm) using an optical tracking code. The sensitivity as a function of surface treatment (Ground, Polished, Metal-0.95RC, Polished-0.98RC, Painted- 0.98RC) of the incident surface of the scintillator was compared. The effects of NaI(TI) scintillator thickness and the refractive index of light guide optically coupling between the NaI(TI) scintillator and photomultiplier tube (PMT) were simulated. We also evaluated intrinsic position resolution of the system by calculating the spread of scintillation light generated. The sensitivities of the system having the surface treatment of Ground, Polished, Metal-0.95RC, Polished-0.98RC and Painted-0.98RC were 70.9％, 73.9％, 78.6％, 80.1％ and 85.2％, respectively, and the surface treatment of Painted-0.98RC allowed the highest sensitivity. As increasing the thickness of scintillation crystal and light guide, the sensitivity of the system was decreased. As the refractive index of light guide increases, the sensitivity was increased. The intrinsic position resolution of the system was estimated to be 1.2 mm in horizontal and vertical directions. In this study, the performance of NaI(TI)-PMT detector system was evaluated using Monte Carlo simulation. Based on the results, we concluded that the NaI(TI)-PMT detector array is a favorable configuration for small gamma camera imaging breast tumor using Tc-99m labeled radiopharmaceuticals.

• Asian-Australasian Journal of Animal Sciences
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• v.27 no.7
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• pp.1003-1012
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• 2014

The use of a suitable methodology to quantify the phytate phosphorus ($P_{phy}$) content in both the feed and the excreta from broilers is required to enable accurate calculation of the catalytic efficiency of the phytase supplemented in the feed. This study was conducted to compare 2 analytical methodologies (colorimetry and also high-performance liquid chromatography with a refractive index detector) in order to calculate the phytase efficiency by utilizing the results from the methodology that was shown to be the most appropriate. One hundred and twenty broilers were distributed in a $(4+1){\times}2$ factorial arrangement, corresponding to 4 diets that were equally deficient in P supplemented with increasing levels of phytase (0, 750, 1,500, and 2,250 units of phytase activity - FTU - per kg of feed) plus 1 positive control diet without phytase, supplied to male and female birds. The result indicated that the colorimetric methodology with an extraction ratio of 1:20 (mass of sample in g:volume of the solvent extractor in mL) was shown to be the most adequate. There was no interaction between the phytase level and the sex of the broilers (p>0.05). Males consumed 12% more $P_{phy}$ than did females (p<0.01), but the sex of the broilers did not affect (p>0.05) the excretion and retention coefficient of $P_{phy}$. The increase in the phytase level of the diet reduced (linear, p<0.01) the $P_{phy}$ excretion. The greatest $P_{phy}$ retention was estimated at 87.85% when the diet contained 1,950 FTU/kg (p<0.01), indicating that it is possible to reduce the inorganic P in the formulation at an amount equivalent to 87.85% of the $P_{phy}$ content present in the feed, which, in this research, corresponds to a decrease in 2.86 g of P/kg of the feed.

• Journal of Korean Ophthalmic Optics Society
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• v.20 no.4
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• pp.471-476
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• 2015

Purpose: We have analyzed the transmittance distribution of various ocular lenses using local transmittance microscope to investigate the optical homogeneity of the lens. Methods: The local transmittance of the laser which is focused on the surface of the spectacle lens was measured by using the photo-detector, lock-in amplifier and motorized-stage. 25 multi-coated lenses with non-tinted of 5 groups and 45 multicoated lenses with tinted of 9 groups were analyzed as a sample respectively. Results: Average and deviation of local transmittance for nontinted lenses were measured almost uniformly with various refractive index and coating. However, deviation of transmittance of for tinted lenses was analyzed as about 3.7 times larger than that of non-tinted lenses. Inhomogeneity of local transmittance of for tinted lenses was also analyzed as about 3.1 times larger than that of non-tinted lenses. Conclusions: We could analyze that standard deviation of transmittance and inhomogeneity of local transmittance of for tinted lenses is larger than that of non-tinted lenses using the local transmittance microscope. These analysis using local transmittance microscope can be utilized as a way to evaluate lens performance and improve optical homogeneity.