• Korean Journal of Optics and Photonics
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• v.30 no.6
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• pp.249-254
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• 2019

An optical current sensor device that measures electric current by the principle of the Faraday effect was designed and fabricated. The polarization-rotated reflection interferometer and the quadrature phase interferometer were introduced so as to improve the operational stability. Complex structures containing diverse optical components were integrated in a polymeric optical integrated circuit and manufactured in a small size. This structure allows sensing operation without extra bias feedback control, and reduces the phase change due to environmental temperature changes and vibration. However, the Verdet constant, which determines the Faraday effect, still exhibits an inherent temperature dependence. In this work, we tried to eliminate the residual temperature dependence of the optical current sensor based on polarization-rotated reflection interferometry. By varying the length of the fiber-optic wave plate, which is one of the optical components of the interferometer, we could compensate for the temperature dependence of the Verdet constant. The proposed optical current sensor exhibited measurement errors maintained within 0.2% over a temperature range, from 25℃ to 85℃.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.7-15
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• 2008

In this paper, it is investigated that the limitation due to the asymmetry of optical power with respect to optical phase conjugator(OPC) in mid-span spectral inversion(MSSI) for compensating optical signal distortion due to group velocity dispersion(GVD) and nonlinearities generated in fiber by combining with lumped dispersion management(DM) technique into MSSI. Two kinds of lumped DM configuration(configuration A and configuration B) are considered and compared each other in this research. Configuration A consists of two dispersion compensating fiber(DCF) span positioned after transmitter and before receiver, respectively. Configuration B consists of two dispersion compensating fiber(DCF) span positioned before and after OPC placed at middle of total transmission link, respectively. It is confirmed that the transmission performances are more improved by the configuration A combined with MSSI than configuration B. Also, it is confirmed that the best performance of overall channels are obtained by making net residual dispersion(NRD) to have positive value in self phase modulation(SPM)-limited WDM transmission systems, irrelevant to the configuration of DM.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.5
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• pp.145-150
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• 2023

Non-uniform optical taper waveguides have been widely used as devices for high-efficiency mode coupling, as they are integrated with single-mode optical fibers or photonic crystal waveguides. In this paper, we present a new platform for chemical sensing and bio-sensing using optical taper waveguides with these characteristics. The principle of operation is based on the coupling efficiency and interference properties of optical directional coupler (DC) and multi-mode interference coupler (MMIC). First, the curvature characteristics of taper sections of DC and MMIC is explained, and the design specifications of optimized taper waveguide to increase waveguide sensitivity is selected. Next, the sensor response to the change in refractive index of sensing analyte is numerically analyzed. Numerical results show that as the length of couplers increases, the effective index per change in refractive index unit (RIU) of analyte increases, and that sensitivity can be tuned using taper DC and MMIC design techniques.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.10
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• pp.2293-2302
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• 2012

New optical transmission links technique for compensating of the distorted wavelength division multiplexed (WDM) signals due to group velocity dispersion (GVD) and self phase modulation (SPM) in single mode fiber (SMF) are proposed. The proposed optical links have optical phase conjugator (OPC) placed at nearby WDM transmitter or receiver and repeater spans with artificial distribution of SMF length and residual dispersion per span (RDPS). It is confirmed that optimal link configuration expanding effective launching power range and effective net residual dispersion (NRD) by improving system performance is that having OPC closely placed at WDM receiver and the gradually descended distribution of SMF length and RDPS of each repeater spans, related with the gradually increased optical link length. And, it is also confirmed that NRD is controlled by postcompensation in optimal optical link with OPC closely placed at WDM receiver.

• Journal of Advanced Navigation Technology
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• v.28 no.4
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• pp.552-558
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• 2024

In dispersion management, which involves additionally inserting a dispersion compensation fiber of an appropriate length to eliminate or reduce the chromatic dispersion of a single-mode fiber, determining the form of the dispersion map, which is the cumulative dispersion profile according to the transmission distance, is the most basic and important. In this paper, the various symmetric dispersion map based on trapezoids applied to dispersion-managed links combined with mid-span spectral inversion (MSSI), which compensates for the distortion caused by Kerr nonlinear effects through optical phase conjugation in the middle of the entire transmission link are proposed, and the effect of each dispersion map on distortion compensation of wavelength division multiplexed (WDM) signals is analyzed. Although the degree of compensation varies depending on the factors that determine the detailed shape of the proposed trapezoid-shaped dispersion map and RDPS (residual dispersion per span), overall, it was confirmed that distortion compensation for signals with a small extinction ratio was more effective than distortion compensation for WDM channel signals with a large extinction ratio.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.1
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• pp.89-98
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• 2002

Optical current sensor and optical voltage sensor modules were designed and fabricated to improve measurement error and insulation in automatic power distributor By using Faraday effect, optical current sensor with an $\alpha$-iron core was designed and fabricated to minimize current induction of the other phase and was optimized to maintain linearity. Optical voltage sensor was fabricated owing to the pockets effect and adopted spatial electric field type because of small room in an automatic power distributor. To connect a distributor with an external terminal for signal processing, optical multi connector was designed, fabricated and tested for coupling loss and gas leakage. The linearity of optical current sensor for applied current maintains variation of smaller than 2.5% for applied current range from 20A to 700A. The linearity of optical voltage sensor was smaller than 1% for appling voltage from 6.6kV to 19.8kV. Since the measured characteristics are good, these devices can be considered as being applicable in practice.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.54-59
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• 2008

We report on the measurements of absorption spectra from acetylene ($^{12}C_2H_2$) and hydrogen cyanide ($H^{13}C^{14}N$) for wavelength reference in the C-band (conventional band) region using a supercontinuum optical source generated from a mode-locked $Cr^{4+}$:YAG laser. The center wavelength of the mode-locked $Cr^{4+}$:YAG laser was 1510 nm and the pulse duration was 75 fs at 100 MHz repetition rate. The supercontinuum source achieved a flatness of ${\pm}5dB$ over a wavelength range of more than 400 nm, using a 20 m long photonic crystal fiber. The measured absorption spectra from acetylene ($^{12}C_2H_2$) and hydrogen cyanide ($H^{13}C^{14}N$) had more than 50 lines and were analyzed for wavelength standardization.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.209-212
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• 1997

Spectral gain variation characteristics of the silica-based erbium doped fiber amplifiers is investigated in the 1545-1557 nm wavelength region. For a given length of the erbium doped fiber, the gain($G_0$) with minimum spectral gain variation is uniquely determined. The spectral gain imbalance DG is nearly proportional to the difference between G0 and the operating gain(G) with the proportional constant of 0.1-0.2 dB/dB. For the gain flattened EDFA at the input power of -20 dBm/ch. and the gain of 21 dB, the output power and the optical signal to noise variations after 12 cascaded EDFAs were 5 dB and 3 dB, respectively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.749-751
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• 2009

Optical link design technique for compensating of distorted 40 Gbps ${\times}$ 24 channels WDM signals is researched. The considered optical link consists of optical phase conjugator (OPC) placed at 100 km and 900 km, which are non-midway of total transmission distance, and dispersion management (DM). It is confirmed that optimal net residual dispersions (NRD) are 800 ps/nm and 900 ps/nm when OPC placed at 100 km and 900 km, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.338-338
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• 2010

지난 20여년 동안 반도체 레이저 다이오드는 주로 CD (DVD) 픽업용 (파장: 640 nm 이하) 및 통신용 (파장 1550 nm) 광원 분야에서 집중적으로 개발되어 왔다. 그러나 기술의 개발과 더불어 파장조절이 비교적 자유로워지고 광출력이 증대 되면서 기존의 레이저 고유의 영역까지 그 응용분야기 확대되고 있고, 이에 따라 고출력 반도체 레이저 다이오드의 시장 규모도 꾸준히 증가되고 있는 상황이다. 고출력 반도체 레이저 다이오드는 발진 파장 및 광출력에 따라 다양한 분야에 응용되고 있으며, 특히 발진파장이 808 nm 인 고출력 레이저 다이오드의 경우 재료가공, 펌핑용 광원 (DPSSL, 광섬유 레이저), 의료, 피부미용 (점 제거), 레이저 다이오드 디스플레이 등 가장 다양한 응용분야를 가진 광원 중의 하나라고 할 수 있다. MBE(Molecular Beam Epitaxy)로 성장된 InAlAs 에피층 (epi-layer)을 사용하여 고출력을 갚는 레이저 다이오드를 제작함에 있어서, 에피층은 결함 (defect)이 없는 우수한 단결정이 요구되지만, 실제 결정 성장 과정에서는 성장온도와 Al 조성비 등의 성장 조건의 변화에 따라 전기적 광학적 특성 및 신뢰성에 큰 영향을 받는 것으로 보고되고 있다. 이에 본 연구에서는 DLTS (Deep Level Transient Spectroscopy) 방법을 이용하여 InAlAs 양자점 에피층의 깊은 준위 거동을 조사하였다. DLTS 측정 결과, 0.3eV 부근의 point defect과 0.57 ~ 0.70 eV 영역의 trap이 조사되었으며, 이는 갈륨 (Ga) vacancy와 산소 원자의 복합체에 기인한 결함으로 분석된다.