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언덕형 굴절률 분포를 갖는 굽은 평판도파로에서의 누설모드 해석
김경암,곽재곤,박권동,김창민 한국광학회 2002 한국광학회지 Vol.13 No.6
Circular slab waveguides are conformally mapped into straight waveguides. In the outer cladding region with monotonically increasing index profile, modified Airy functions (MAF) of traveling-wave form are introduced to express the leaky mode. Field distributions and losses calculated by the proposed method are compared with those obtained by the WKB (Wentzel-Kramers-Brillouin) method. Detailed numerical examples are presented and compared with the conventional WKB methods, demonstrating our method not only allows a converging field at turning points but also guarantees fine accuracy. 원형으로 굽은 평판 광도파로를 직선 광도파로로 등각사상화 시켰다. 단조 증가하는 굴절률 분포를 갖는 바깥쪽 클래드영역의 누설모드를 표현하기 위해 진행파형 수정된 Airy함수가 처음으로 소개되었다. 모의 전산을 통해 유도된 방법에 의한 굽음손실 및 field해 분포를 계산하고, WKB에 의한 결과와 비교하였다. 모의 전산결과 기존의 WKB 방법에 비해 회기점에서 수렴하는 해를 구할 수 있었으며, 더 정확한 굽음 손실을 계산할 수 있었다.
완전 스위칭이 가능한 Ti:LiNbO<sub>3</sub> 진행파 광변조기
곽재곤,김경암,김영문,정은주,피중호,박권동,김창민 한국광학회 2003 한국광학회지 Vol.14 No.5
Ti:LiNbO$_3$세 도파로 방향성 결합기와 CPW진행파 전극으로 구성된 완전 스위칭이 가능한 외부 광변조기를 설계, 제작하였다. 결합 모드 이론을 이용하여 세 도파로 광결합기의 스위칭 현상을 해석하였으며, 유한차분법을 이용하여 단일 모드를 갖는 광도파로의 설계 및 공정 파라미터를 도출하였으며, 이를 이용하여 광 결합길이를 계산하였다. 등각사상법과 반복이완법을 이용하여, CPW구조 진행파 전극의 특성임피던스와 M/W(Micro wave)유효굴절률 정합조건을 동시에 만족하는 설계 파라미터를 도출하였다. 제작된 세 도파로 광변조기의 삽입손실과 스위칭 전압은 약 4㏈와 19V였으며, S 파라미터를 측정하여 특성임피던스 Z$_{c}$=45 Ω M/W 유효굴절률 N$_{eff}$=2.20, 그리고 감쇠상수 $\alpha$$_{0}$=0.055/cm√GHZ 등의 진행파 전극 파라미터를 추출하였다. 추출된 진행파 전극 파라미터를 이용하여 이론적인 주파수 응답 R($\omega$)을 계산하였으며, Photo Detector로 측정된 주파수 응답과 비교하였다. 주파수 응답 측정 결과, 3㏈ 변조대역폭은 13 GHz로 측정되었다. Design of the optical modulator composed of a three-waveguide coupler and CPW traveling-wave electrodes was carried out. Switching phenomena of three-waveguide couplers were analyzed by using the coupled mode theory, and the coupling-lengths of the devices were calculated by means of the FDM. CPW traveling-wave electrodes were analysed by the CMM and SOR simulation technique in order to find the conditions of phase-velocity and impedance matching. Traveling-wave modulators were fabricated on z-cut LiNbO$_3$ substrate. Ti was in-diffused in LiNbO$_3$ to make waveguides and Au electrodes were built on the waveguides by the electrolyte technique. The fabricated modulator chip was end-polished, pig-tailed and packaged in a brass mount with K-connector. The insertion loss and the switching voltage of the optical modulator were about 4㏈ and 19V, respectively. Network analyzer was used to obtain the S parameter and the corresponding RF response. From the measurement, parameters of the traveling-wave electrodes were extracted to be Z$_{c}$= 45 Ω, N$_{eff}$=2.20, and $\alpha$$_{0}$=0.055/cm√GHZ. The measured optical response R($\omega$) was compared with the theoretically estimated one, showing both responses agree well. The measurement results revealed that 3㏈ bandwidth turned out to be about 13 GHz.
Photo-electronic Properties of Cd(Cu)S/CdS Thin Films and Diodes Prepared by CBD
조두희,김경암,송기봉 한국세라믹학회 2008 한국세라믹학회지 Vol.45 No.1
In this paper, CdS/Cd(Cu)S thin films and diodes were manufactured via a chemical bath deposition (CBD) process, and theeffects of NH4Cl and TEA(triethylamine) on the properties of the films were examined. The addition of NH 4Cl significantlyincreased the thickness of the CdS and Cd(Cu)S films, however, the adition of TEA decreased the thickness in both casesslightly. The addition of NH4Cl along with TEA increased the film thickness more effectively compared to the addition of onlyNH 4Cl. The thicknes of the CdS film prepared from an aqueous solution of 0.007 M CdSO 4, 1.3 M NH4OH, 0.03 M SC(NH2)2,0.0001 M TEA and 0.03 M NH 4Cl was 310 nm. Dark resistivity of the CdS film was 1.2 ×103 Ωcm and the photo resistivity with500 W/cm2 irradiation of white light was 20 Ωcm. The Cd(Cu)S/CdS thin film diodes prepared by CBD showed good rectifyingcharacteristics.