• Korean Journal of Optics and Photonics
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• v.6 no.3
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• pp.228-232
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• 1995

We have made modulation doped SMQW-PBH-DFB-LD for high speed optical communications. The waveguide and barrier layers were doped by Zn with the concentration of $1.2 \times 10^{18}cm^{-1}$. Mean threshold current and slope efficiency were 24.88 mA (minimum 16 mA) and 0.197 mW/mA (maximum 0.275 mW/mA) respectively. Linewidth enhancement factor ($\alpha$) of MD-SMQW-PBH-DFB-LD was reduced than that of SMQW-PBH-DFB-LD. Linewidth enhancement factor of 1.8 owes to the large gain coefficient of modulation doped active layer. The resonance frequency was linearly increased with the square root of optical power. The resonance frequency in small signal modulation was measured as 8 GHz and -3 dB modulation bandwidth was 10 GHzat $46mA(I_{th}+30mA)$..

• Journal of the Society of Cosmetic Scientists of Korea
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• v.21 no.2
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• pp.57-72
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• 1995

We have recently developed a novel in vitro SPF evaluation method with a high correlation coefficient (r=0.93) to in vivo SPF values(test sunscreen formulas : cress m, foundation). In this method, the in vitro SPF value was determined by the ratio of the time taken to achieve the minimal erythema dose with and without the sunscreens applied. We also reviewed the dilution and thin-layer methods for in vitro SPF evaluation, and investigated the relationship between irradiance(3$\times$10-3 2.5x 10-5W/cm2) and the degree of erythema. The degree of erythema was similar if t he radiation exposure(40mJ/cm2) was kept constant. It was obtained more than 0.90 correlation coefficient when it was compared the results by our new method with those from SPF-290 analyzer (Optometries, U.S.A.).

• Korean Journal of Optics and Photonics
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• v.10 no.6
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• pp.500-506
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• 1999

We designed and fabricated a bidirectional optical transceiver module for low cost access network. An integrated chip forming a pin-PD on an 1.3 urn FP-LD was assembled by flip-chip bonding on a Si optical bench, a single mode fiber with an angled end facet was aligned passively with the integrated chip on V-groove of Si-optical bench. Gaussian beam theory was applied to evaluate the coupling coefficients as a function of some parameters such as alignment distance, angle of fiber end facet, vertical alignment error. The theory is also used to search the bottle-neck between transmittance and receiving coupling efficiency in the bi-directional optical system. Tn this paper, we confirmed that reduction of coupling efficiency by the vertical alignment error between laser beam and fiber core axis can be compensated by controlling the fiber facet angle. In the fabrication of sub-module, a'||'&'||' we made such that the fiber facet have a corn shape with an angled facet only core part, the reflection of transmitted laser beam from the fiber facet could be minimized below -35 dE in alignment distance of 2: 30 /J.m. In the same condition, transmitted output power of -12.1 dEm and responsivity of 0.2. AIW were obtained.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.2
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• pp.280-289
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• 2004

Adequate polymerization is a crucial factor in obtaining optimal physical properties and clinical performance of resin composite restorative materials. The purpose of this study was to determine the effectiveness of shade and depth on dental composite resin polymerized with plasma arc curing unit employing FTIR and microhardness. From this experiment, the following results were obtained : 1. The light transmission and microhardness by mode 6 in plasma arc curing were similar to by 20 secs in halogen light curing. 2. The experimental groups of A1, A2, A3, A3.5 were not signifcant difference to light transmission and microhardness on surface and 2mm depth, but were significant difference on 3mm and 4mm depth. Especially light transmission and microhardness were small in darker shade and deeper thickness. 3. Compared with depth cure, uncured monomer amount increased at more than 2mm depth. 4. The light transmission by FTIR and polymerization by microhardness were significant corelation.

• Journal of the Korean Vacuum Society
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• v.10 no.1
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• pp.98-103
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• 2001

A new application of dirchroic mirror for the improvement of luminance and luminous efficacy in an AC-Plasma Display Panel (PDP) is suggested. Only about half of the Vacuum Ultraviolet (VUV) generated in the reflective PDP cell is used for the excitation of the phosphor. We are suggesting an idea of adopting a dichroic mirror which can reflect the VUV toward the phosphor which otherwise is absorbed by the front panel. The optical constants of the thin films of dirhroic mirror were determined from the photometric measurements through an iteration process of matching calculated and measured values of the reflectance and transmittance in the VUV wavelength region. From these results, we could design such a filter whose high reflection zone is centered at 147nm by a computer simulation accurately. The 147nm VUV is radiated from Xenon 3Pl state which is dominantly used to activate the phosphor in the PDP cell. The dichroic mirror was made with an electronbeam evaporator and its reflectance was measured by a reflectometer. We confirmed the usefulness of the dichroic mirror for the improvement of efficiency with experiments done by test panels. The panel with mirror shows improved luminance and luminous efficacy by 20∼30％.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.4
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• pp.793-796
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• 2010

The equalizer compensates a signal distorted by transmission lines and amplifying stages, so the signal can have uniform characteristics over all frequency range. The equalizer in ODD(Optical Disc Drive) improves the stability of the extracted clock from a received signal and the readability of an inserted disc by suppressing noise and ISI(Inter-Symbol Inference). The length of marks-spaces and track pitch on discs becomes shorter as the recording density of an optical media is higher, which causes noise and ISI. And, the sensitivity about the fluctuation of physical systems is higher as the optical devices become more complicate. This paper proposes a method to select the coefficient of built-in equalizer of ODD in order to maintain the quality of signals against noise and ISI caused by system fluctuation.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.5
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• pp.80-87
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• 1999

We propose a new recirculating fiber delay-line filter structure. In proposed system, we insert a fiber Bragg grating(FBG) into a recirculating fiber delay line and it operates as a partially reflection mirror. Therefore, the transfer function of the system is given by the recirculating delay output part and the multiple-reflected output part due to a FBG. By adjusting the parameters such as coupling coefficient, reflectivity of FBG, and gain, we can make the system operate in various filter.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.452-456
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• 1993

The quantum efficiencies of photomultiplier tubes were measured by counting the coincidence photon pairs generated in the process of spontaneous parametric down-conversion. They were measured within 3% accuracy over the range of wavelength from 560 to 850 nm without any standard light source or detector. The values for 633 nm correspond to those obtained with a calibrated laser power meter within the measurement error.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.5
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• pp.517-524
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• 2004

In this paper, we investigated the compensation characteristics of distorted NRZ format and RZ format signal dependence on dispersion variation of each transmission section in 8-channel WDM system. The WDM system have two transmission sections of unequal length with respect to optical phase conjugator(OPC) position. We select highly-nonlinear dispersion shifted fiber(HNL-DSF) as a nonlinear medium of OPC in order to convert wideband signal waves to conjugated waves. First, we confirmed that RZ is better than NRZ as a modulation format for maintenance or stable performance, when total dispersion or both sections in WDM system is different each other. Also, we confirmed that total dispersion of the short length section must be smaller than that of the long length section in order to excellently compensate for NRZ format signal.

• Korean Journal of Agricultural and Forest Meteorology
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• v.2 no.1
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• pp.9-15
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• 2000

The objective of this study is to evaluate the use of RADARSAT and Landsat TM data for the monitoring of rice growth. The relationships between backscatter coefficients($\sigma$$^{0}$ ) of RADARSAT data and digital numbers (DN) of Landsat TM and rice growth parameters were investigated. Radar backscatter coefficients were calculated by calibration process and then compared with rice growth parameters; plant height, leaf area index (LAI), and fresh and dry biomass. When radar backscatter coefficient ($\sigma$$^{0}$ ) of rice was expressed as a function of time, it is shown that the increasing trend ranged from -22--20dB to -9--8dB as growth advances. The temporal variation of backscatter coefficient was significant to interpret rice growth. According to the relationship between leaf area index and backscatter coefficient, backscatter coefficient underestimated leaf area index at the beginning of life history and overestimated, at the reproductive stage. The same increasing trend between biomass and backscatter coefficient was shown. From these results, RADARSAT data appear positive to the monitoring of rice growth. Each band of time-series Landsat TM data had a significant trend as a rice crop grows during its life cycle. Spectral indices, NDVI[(TM4-TM3)/(TM4+TM3)] and RVI(TM4/TM2), derived from Landsat TM equivalent bands had the same trend as leaf area index.