• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.260-261
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• 2007

본 논문에서는 800MHz와 1.9GHz 대역의 시스템에 적용할 수 있는 20dB 방향성 결합기를 8층 PCB 기판에 내장하여 소형화 및 저가화 할 수 있도록 설계하였다. 방향성 결합기는 4층과 6층에 coupled line으로 적층함으로써, 다층 PCB기판을 최대한 활용하여 공간을 최소화하였다. 또한, 고유전율을 가진 필름을 이용하여, coupled line의 끝에 내장형 고용량 커패시터를 연결하여 설계하였다. 6 $\times$ 6 $\times$ 0.7 (height)$mm^3$ 크기로 설계된 방향성 800MHz 결합기의 경우 -20dB의 coupling 특성, -0.6dB의 transmission 특성, -25dB의 isolation 특성을 나타내었다. 패키징 기판에 내장된 방향성 결합기는 단말기 및 통신시스템의 소형화에 크게 기여할 수 있을 것이다.

• Proceedings of the Optical Society of Korea Conference
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• 1991.06a
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• pp.22-22
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• 1991

광의 병렬처리 능력을 잘 활용한 1$\times$4 매트릭스 스위치의 구조와 전극구조를 설계하고 스위치 특성을 조사하기 위하여 beam propagation method(BPM)를 이용하여 수치계산을 하였다. 기존의 매트릭스 스위치는 대부분의 경우 방향성 결합기를 스위치 element로 이용하여 왔으나 이 결합기는 소자의 길이가 길기 때문에 단일 LinBO3 웨이퍼상에 집적할 수 있는 매트릭스 스위치의 크기가 제한되는 단점이 있다. 본 연구에서는 두 도파로 사이에 세 번째 도파로를 삽입하여 두 도파로를 결합시키는 세 도파로 결합기를 스위치 element로 사용하여 세 개의 스위치 element를 LiNbO3기판위에 직렬로 집적시킨 1$\times$4 매트릭스 스위치를 구성하였다. 스위치 element와 1$\times$4 매트릭스 스위치를 구성하였다. 스위치 element와 1$\times$4 매트릭스 스위치의 특성을 BPM을 사용하여 수치계산할 때 단일 모드 도파로의 유효 굴절을 분포는 n(X) = nm + $\Delta$ncosh-2(2x/w)의 형태로 가정했으며, 사용된 파라미터의 값은 각각 nm=2.1455, $\Delta$n=0.003, W=5$mu extrm{m}$, d=5$\mu\textrm{m}$, λ=1.3$\mu\textrm{m}$ 이고 S-파라메터의 값은 0.95927이므로 단일 모드 도파로가 된다. 계산결과 스위치 element의 결합길이는 3810$\mu\textrm{m}$이며 도파로의 길이가 결합길이와 같을 때 전극에 인가된 전압에 의한 도파로의 굴절을 섭등의 함수로 출력광의 세기를 계산한 결과 스위칭 전압은 14.85volt이고 crosstalk는 -18.9dB였다. 이 스위치 element로 구성된 1$\times$4 매트릭스 스위치는 스위칭 전압을 세 개의 전극에 적절한 조합으로 인가함으로써 한 입력 도파로에 결합된 광이 내개의 출력 도파로중 한 도파로에 스위칭 된다. 한편 수치계산의 결과를 실험적으로 확인하기 위해 스위치 element와 1$\times$4 매트릭스 스위치를 z-cut의 LinbO3 결정에 Ti을 열확산시켜 제작한 소자의 스위칭 특성을 발표할 예정이다.

• Journal of KSNVE
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• v.7 no.6
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• pp.931-936
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• 1997

Optical fiber sensor is a subject which has been attracted considerable attention in recent years. Detection of sound pressure with optical fibers positioned in the arms of a Mach-Zehnder interferometer is presented in this paper. A fiber length of the order of 150m is wounded is made by hollow cylinder type. To increase the sound signal 3${\times}3$ directional coupler is used. Fiber optic hydrophone is the underwater tank with 2kHz sound source. Finally, it is shown that the fiber optic hydeophone can stably detec 2kHz sound.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.335-339
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• 2000

A $1.31/1.55\mu\textrm{m}$ coarse WDM opncal dIrectional coupler that conslsls of two idenlical straight channel waveguides in BK7 glass has been fabricated. The separatIOn between two channel waveguides is $8\mu\textrm{m}$ and the wavegu.ide width is $4\mu\textrm{m}$ . Especlally, we assumed that the index profile is Gaussian function and complementary error function in the width direction and depth direction, respectrvely. This directional coupler operating at $1.31/1.55\mu\textrm{m}$ with crosstalk of 18dB is demonstrated and has the 16 mm long length with 12.6 mm coupling region.region.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.9
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• pp.685-691
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• 1991

A broad-band 3-dB directional coupler is implemented by using cascaded exponential transmission line as branch lines. Compared with that of the uniform transmission line, the bandwidth of the proposed 3-dB branch-line directional cpoupler increases 2.96 times.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.224-229
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• 2003

We realized a depolarizer based on two 2$\times$2 directional couplers and single mode optical fiber. A reduction method for the degree of polarization is demonstrated by using computer simulation, which is verified experimentally. The degree of polarization is -20 dB for the polarized input beam of spectral width less than 0.05 nm. The experimental results verify that the polarization noise, which is due to the change of the input polarization state, can be reduced by making the fiber-ring delay-line length greater thanthecoherencelengthofthesource.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.555-562
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• 2004

We propose a hybrid method combining the implicit with the explicit methods in order to reduce the calculation time and improve the convergence problem of the 3-dimensional finite-difference beam propagation method. The numerical simulation of a directional coupler is carried out by the proposed method. It is found from the simulation results that the calculation speed of our method is 10 times faster than that of direct solving techniques.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.05a
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• pp.113-116
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• 1993

A guided - wave electro - optical modulatored directional coupler $2{\times}2$ was fabricated on X-cut $LiNbO_3$ by proton exchange wi th self-aligned method. The Electode pattern was formed by the four extra gap electrode separtion within self-aligned electrode mask. Initial cross over state turned that by controlling the anneal ing process and self-aligned electrodes are used in fabricating the electro-optical modulatored directional coupler $2{\times}2$. The modulatored directional coupler $2{\times}2$ has very good figures of merits: the measured crosstalk was -28.2 dB and the modulating valtage of 3.2[V].

• Restorative Dentistry and Endodontics
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• v.34 no.4
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• pp.350-355
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• 2009

Bond strength depends on characteristics of bonding surface and restorative technique. The majority of studies dealing with dentin bond strength were carried out on flat bonding surface, therefore, difference of bond strength between axial wall and pulpal wall is not clear yet. This study evaluated bonding difference between cavity walls in class I composite resin restoration with different filling techniques. Twenty extracted caries-free human third molars were used. Cavities were prepared in 6 ${\times}$4 ${\times}$3 mm box-type and divided into four groups according to filling technique and bonding surface: Group I; bulk filling - pulpal wall, Group II; bulk filling - axial wall, Group III; incremental filling - pulpal wall, Group IV; incremental filling - axial wall. Cavities were filled with Filtek $Z250^{(R)}$(3M/ESPE., USA) and Clearfill SE $bond^{(R)}$(Kuraray, Japan). After 24 hour-storage in $37^{\circ}C$water, the resin bonded teeth were sectioned bucco-lingualy at the center of cavity. Specimens were vertically sectioned into 1.0 ${\times}$1.0 mm thick serial sticks perpendicular to the bond surface using a low-speed diamond saw (Accutom 50, Struers, Copenhagen, Denmark) under water cooling. The trimmed specimens were then attached to the testing device and in turn, was placed in a universal testing machine (EZ test, Shimadzu Co., Kyoto, Japan) for micro-tensile testing at a cross-head speed of 1 mm/min. The results obtained were statistically analyzed using 2-way ANOVA and t-test at a significance level of 95%. The results were as follows: 1. There was no significant difference between bulk filling and incremental filling. 2. There was no significant difference between pulpal wall and axial wall, either. Within the limit of this study, it was concluded that microtensile bond strength was not affected by the filling technique and the site of cavity walls.

• Journal of the Korean Chemical Society
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• v.25 no.6
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• pp.367-375
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• 1981

Single crystals of Potassium Sulfate ($K_2SO_4$) have been grown from the saturated solution by the evaporation method at the optimum conditions. Radiation damages in the crystal by ${\gamma}$-irradiation of about $12{\times}10^6$ Roentgen have given rise to paramagnetic centers or paramagnetic defects. Electron spin resonance (ESR) spectra of the centers are obtained with the X-band EPR spectrometer at room temperature. The ESR peaks of the paramagnetic species are found to be anisotropic but the peak of $SO_3-$ radical is an isotropic of Gaussian shape at g = 2.0036. A number of ESR spectra of the crystal for angular variation of the anisotropic peaks are recorded at various orientations of rotation about a, b and c crystallographic axes respectively. The g-values are calculated from the line position between anisotropic peaks and the isotropic one and then principal g-values and its direction cosines of the species are obtained by diagonalization of 9 matrix elements of the corresponding g-values. All the paramagnetic defects are identified by the characteristic principal g-values and its direction cosines.