• Korean Journal of Optics and Photonics
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• v.30 no.4
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• pp.133-141
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• 2019

Revision of the International System of Units (SI) in terms of fundamental constants was achieved by the 26th General Conference on Weights and Measures (CGPM) in November 2018. Four base units (kilogram, ampere, kelvin, and mole) of SI were redefined by fixing the values of the Planck constant h, elementary charge e, Boltzmann constant k, and Avogadro constant $N_A$ respectively. In this paper the scientific principle for redefining the kilogram from the Planck constant with the Kibble balance is explained as an example. The revised SI takes effect on May 20, 2019.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.5
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• pp.296-302
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• 1999

$CdIn_2S_4 and CdIn_2S_4 : Co^{2+}$ singlecrystals of thenormal spinel structure were grown by the C.T.R. method. The optical energy band structure of these compounds had a indirect band gap at the fundamental optical absorption band edge. The direct and the indirect energy gaps are found to be 2.325 and2.179eV for $Cdln_2S_4$ , and 2.303 and 2.169eV for $CdIn_2S_4 and CdIn_2S_4 : Co^{2+}$ at 5K, respectivly. The fundamental absorption band edge of these single crystals shift to a shorter wavelength region with decreasing temperature, and the temperature dependence of the optical energy gaps in these compounds satisfy Varshni equation. The Varshni constants$\alpha and \beta$ of the direct energy gap are given by $13.39{\times}10_{-4}eV/K$ and 509 K for $Cdln_2S_4$ and $29.73{\times}10_{-4} eV/K$ and 1398K for $CdIn_2S_4 and CdIn_2S_4 : Co^{2+}$. The Varshni constants ${\alpha}and {\beta}$ of the indirect energy gap are given by 9.68${\times}10^{-4}$ eV/K 308K for $Cdln_2S_4$ and $13.33{\times}10_{-4}eV/K$ and 440K for $CdIn_2S_4 : Co^{2+}$ respectivly. The impurity optical absorption peaks due to cobalt dopant are observed in $CdIn_2S_4 : Co^{2+}$ single crystal. These impurity optical absorption peaks can be attributed to the electronic transitions between the split energy levels of $Co_{2+}$ ions located at $T_d$ symmetry site of $Cdln_2S_4$ host lattece.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.203.2-203.2
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• 2013

Hydrothermally grown ZnO nanorods were synthesized with various Sn contents on quartz substrates, ranging from 0 to 2.5 at% in increment 0.5 at%. Scanning electron microscopy (SEM) and ultraviolet (UV)- visible spectroscopy were used to determine the effect of Sn doping on the structural and optical properties. In the SEM images, the nanorods have hexagonal wurzite structure and the diameter of the nanorods increase with increase in the Sn contents. The optical parameters of the Sn-doped ZnO nanorods such as the absorption coefficients, optical bandgaps, Urbach energies, refractive indices, dispersion parameters, dielectric constants, and optical conductivities were gained from the transmittance and reflectance results. In the PL spectra, the NBE peaks in the UV region decrease and blue-shift with increase in the Sn contents. In addition, the DLE peaks in the visible region of the nanorods shift toward low-energy region when the ZnO nanorods doped with various Sn contents.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.8
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• pp.80-86
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• 1997

H:LiNbO$_{3}$ optical modulator buffered by parylene layer, which has a merits in the bandwidth, power consumption and fabrication as compared with conventional SiO$_{2}$ buffered optical modulator, is proposed and analyzed. The dependences of velocity matching condition, charcteristics impedance, and driving voltage on dielectric constants, thickness of buffer layer, and electrode configurations are demonstrated with finite element calculation. And we performed the physical and chemical test of parylene buffer layer deposited on LiNbO$_{3}$ and under Au electrodes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.12
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• pp.1051-1057
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• 2000

A traveling-wave CPW(coplanar waveguide) electrode with abruptly broken input/output-taper for LiNbO$_3$optical modulator was designed and fabricated. The electrical characteristics of traveling-wave electrode on z-cut LiNbO$_3$crystal with SiO$_2$buffer layers were measured by network analyzer. To confirm the possibility of the electro-optic modulator electrode, detailed calculations of the impedance, microwave effective index and attenuation constants are presented as a function of the microwave electrode thickness, but the buffer layer thickness is fixed as 1${\mu}{\textrm}{m}$. These characteristics are discussed from the viewpoint of the device optimization and are expected to be design guides for the LiNbO$_3$modulator’s electrodes.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.323-326
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• 1999

This paper describes a point matching method that is based on an expansion of the electromagnetic field in terms of a series of Bessel and modified Bessel functions multiplied by trigonometric functions. In this method, the electric and magnetic fields inside the waveguide core are matched to those outside the core at matching points on the boundary to yield matrix equations. As an example applying this method, the paper presents the results of the computation in the form of curves of the propagation constants in a semicircular optical waveguide, be formed by annealing for reduced insertion(radiation) loss when connected to optical fiber. The propagation curves are presented in a form of refractive index independent. Also, it presents relative energy distributions between inside the core and outside the core of various modes and presents field distributions.

• Journal of the Korean Vacuum Society
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• v.6 no.1
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• pp.50-60
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• 1997

Undoped, cobalt-doped and erbium-doped $ZnAl_2S_4, ;ZnAl_2Se_4, ;CdAl_2S_4, ;and;CdAl_2Se_4$ single crystals were grown by the chemical transport reaction method. The crystal structures, the lattice constants, the optical energy gaps, and the photoluminescence properties of these single crystals were investigated. Also, the optical transition mechanisms by the impurities of cobalt and erbium were identified from these results.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.18-19
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• 2003

비정질 As$_2$S$_3$박막에 레이저광의 조사에 대한 투과율 변화는 굴절률과 흡수계수 변화 등의 비선형 광학 특성에 대한 많은 정보를 제공해준다. 투과 스펙트럼을 측정하여 비정질 As$_2$S$_3$ 박막의 광학 상수를 결정하는 일은 간단하면서도 신뢰도 높은 값들을 얻을 수있게 한다. 본 실험에서는 비정질 As$_2$S$_3$ 박막을 진공 증착법을 이용하여 제작하고, 스펙트로포터미터를 사용하여 박막이론에 따른 굴절률, 흡수계수, 박막의 두께 및 조사된 레이저광에 의한 광학적 상수의 변화등을 측정하였다. (중략)

• Bulletin of the Korean Chemical Society
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• v.12 no.5
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• pp.540-544
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• 1991

Thin film being formed on the surface of cobalt in the early stage of electrochemically induced passivation was studied by the three-parameter ellipsometry. The growth of the passive film was complete in a few seconds from the onset of the passivating potential, and was followed by a slight decrease in the thickness in 4-40 seconds. The optical constants of the passive film changed gradually during the changes in the thickness. The thickness and the optical properties at the steady state of passivation depended on the potential of the electrode. From the coulometric data and the optical properties, the composition of the passive films was deduced to be close to those of CoO, ${Co_3}{O_4}$ and ${Co_2}{O_3}$ depending on the potential. Cathodic reduction in the presence of EDTA was found to be an efficient way to obtain film-free reference surface of cobalt.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.34-35
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• 2003

광통신 분야에서 광신호의 장거리 전송에 따른 세기 감소를 보강하기 위해 쓰이는 광섬유증폭기는 현재 1.3 $\mu\textrm{m}$ 대역, 1.45 $\mu\textrm{m}$ 대역 및 1.5 $\mu\textrm{m}$ 대역에서 작동하는 희토류 이온 첨가 광섬유 광증폭기가 개발되어 쓰이고 있다. 한편 ETRI에서는 기존 광통신에 쓰이는 광 증폭기에 추가해 더 넓은 파장대를 광통신에 쓸 수 있도록 하는 새로운 파장대역의 광 증폭기 구현을 가능케하고 나아가 광통신 용량을 기존보다 휠씬 더 큰 10 Tbps급 이상으로 늘이기 위해 1.6 $\mu\textrm{m}$ 파장대인 U 밴드대 광증폭기용 광섬유인 Pr 첨가 셀레나이드 유리 조성의 신소재를 개발하였는데, 본 연구에서는 Ge-Sb-Ga-Se 계열의 Pr 첨가 셀레나이드 유리의 굴절률을 분광타원 법 (spectroscopic ellipsometry)을 사용하여 결정하였다. (중략)