• Journal of the Optical Society of Korea
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• v.2 no.2
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• pp.80-82
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• 1998

A new fiber coupling scheme using thermally over-expanded core(TOEC) fiber was proposed and demonstrated. In the coupling experiment between 1.3${\mu}{\textrm}{m}$ FP-LD and the proposed TOEC fiber with a tapered hemispherical microlens. superior performances such as a long working distance, a high coupling efficiency, and large misalignment tolerances were verified experimentally.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.27-30
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• 2002

PMFBG sensor was fabricated using phase mask and Excimer laser. The reflected wavelength of PMFBG sensor had dual peaks due to intrinsic birefringence. To discover the polarization axes, peak sensitivity was measured under compression test. The signal characteristics of PMFBG sensor were also examined in embedding condition. The embedded PMFBG sensor in epoxy block was loaded for the transverse strain measurements. Experiments showed that the PMFBG sensor could successfully measure the transverse strain. This PMFBG sensor is useful for the structures that require measuring transverse stram.

• Proceedings of the Optical Society of Korea Conference
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• 1991.06a
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• pp.102-108
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• 1991

Utilizing self-phase modulation effects of a dispersion-shifted fiber and delay-line characteristics of two gratings, mode-locked 80 ps pulses at 1.319${\mu}{\textrm}{m}$ wavelength from a Nd: YAG laser are compressed down to 2.1 ps. These pulses are further compressed down to 340 fs using higher order soliton effects in a common single mode fiber.

• Proceedings of the KIEE Conference
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• 1997.07e
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• pp.1874-1876
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• 1997

A fiber optic voltage sensor using photoelastic effect of a single-mode optical fiber, excited with a 632.8 nm He-Ne laser, is developed. The photoelastic effect is produced by piezoelectric effect for the voltage measurement. It is found that the detector output voltage is proportional to the applied voltage. Also, the frequency of the output voltage is equal to that of the applied voltage. Experimental results from a laboratory model demonstrate the feasibility of the sensor for field application in high-voltage systems.

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.251-252
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• 2008

We fabricated silica glass optical fiber containing PbSe quantum-dots (QD) of average size 3.2 nm. The response time of the PbSe-QD doped optical fiber was measured to be around 200 ps. However, after exposure to 1064 nm laser emission for 15 minutes, the response time dramatically reduced to around 2.5 ps, which may be due to photo-darkening effect.

• ETRI Journal
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• v.6 no.4
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• pp.3-8
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• 1984

Frequency division multiplexed 3ch. Color TV signals have been transmitted via optical fiber by employing $1. 3\mum$ InGaAsP DH-laser diode, graded index optical fiber and Ge-APD as optical components. Overall system margin of 20 dB was realized at weighted SNR of more than 49 dB. With this system margin, measured DG and DP were less than 10% and $5^{\circ}$respectively. Throughout this experiment, it was confirmed that multichannel TV signals could be economically transmitted over optical fiber in short haul networks. This paper describes system outlines and hardware implementation results.

• Proceedings of the KIEE Conference
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• 2002.11a
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• pp.48-50
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• 2002

편광 유지 광섬유에 새겨진 장주기 격자의 파장에 따른 편광 의존 손실을 이용하여, 광섬유 브래그 격자가 사용된 광섬유 레이저에서 공동 내부 빛의 편광을 회전시킴에 따라, 발진 파장의 스위칭 및 이중 파장 발진이 가능함을 보였다.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.833-837
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• 2007

In this study, we have fabricated a gain flattened erbium-doped optical fiber amplifier. Gain flattening filters were realized by the strain-induced long period fiber gratings, which are made of periodically arrayed metal wires. Using the filter of $550{\mu}m$ period, spontaneous emission amplified at C-band wavelength by a 980nm pumping laser was flattened within 1dB of gain ripple. The performance of the simultaneous multi channel amplification was measured using a fabry-perot laser diode. Amplification ratio was above 20dB. This amplifier can be applied to the long distance transmission system based on a wavelength division multiplexing for boosting an attenuated signal.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1076-1082
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• 2012

Today the welding for LNG carrier is known to be possible using arc and plasma arc welding process. But because of the lower energy density, arc welding is inevitable to multi-pass welding for thick plate and has a limit of welding speed compared to laser which is high energy density heat source. When thick plate is welded, weld defect by multi-pass welding and heat-affected zone by high heat-input were formed. Therefore one-pass welding by key-hole has been considered to work out the problems. It is possible for Laser, electron beam, plasma process to do key-hole welding. Nowadays, plasma process has been used for welding membrane of cargo tank for LNG carrier instead of arc process. Recently, many studies have examined to apply laser process to welding of membrane. In this paper, weldability, microstructure and mechanical properties of stainless steel for LNG carrier welded by fiber laser were compared to those by plasma. As a result, although the laser welding has several times faster speed, similar properties and smaller weld and heat affected zone were obtained. Consequently, this study proves the superiority of fiber laser welding for LNG carrier.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.792-796
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• 2003

In this paper, to detect external sound frequency on the latticed structure, fiber optic sensor net using Sagnac interferometer was fabricated and tested. The latticed structure fabricated with dimension of 50cm in width and 50cm in height, the optical fiber, 50m in length, distributed and fixed on the latticed structure. Single mode fiber, a laser with 1,550nm in wavelength, 2${\times}$2 coupler were used. External sound signal applied to the fiber optic sensor net and the detected optical signals were compared and analyzed to the detected microphone signals against time and frequency domain. Based on the experimental results, fiber optic sensor net using Sagnac interferometer detected external sound frequency, effectively. This system can be expanded to the structural health monitoring system.