• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1220-1225
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• 2009

In this paper, a tunable fiber feedback laser based on the use of Sagnac loop filter and fiber Bragg grating (FBG) is proposed. The Sagnac loop filter using a high birefringence fiber provides precise 0.33-nm channel spacing as a multi-wavelength grid filter. Ni-Cr wire wound on the FBG is useful to induce the thermo-optic effect of the fiber. Two types of FBG structures, which have a different length of wire, are demonstrated to show the wavelength shift and separation. To tune FBG by resistant heat, some current is supplied into the wire. When the wavelength matched with one of the cavity modes of Sagnac loop filter, the mode-locked lasing is occurred. The electrical power sensitivity of the resonant wavelength is measured to 1.75pm/mW. This laser configuration can be applied the electrical power system for monitoring the power fluctuation.

• Steel and Composite Structures
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• v.35 no.3
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• pp.439-447
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• 2020

This paper presents two sets of full three-dimensional thermoelastic finite element analyses of superimposed thermo-mechanically loaded Spar Wingskin Joints made with laminated Graphite Fiber Reinforced Plastic composites. The study emphasizes the influence of residual thermal stresses and material anisotropy on the inter-laminar delamination behavior of the joint structure. The delamination has been pre-embedded at the most likely location, i.e., in resin layer between the top and next ply of the fiber reinforced plastic laminated wingskin and near the spar overlap end. Multi-Point Constraint finite elements have been made use of at the vicinity of the delamination fronts. This helps in simulating the growth of the embedded delamination at both ends. The inter-laminar thermoelastic peel and shear stresses responsible for causing delamination damage due to a combined thermal and a static loading have been evaluated. Strain energy release rate components corresponding to the Mode I (opening), Mode II (sliding) and Mode III (tearing) of delamination are determined using the principle of Virtual Crack Closure Technique. These are seen to be different and non-self-similar at the two fronts of the embedded delamination. Residual stresses developed due to the thermoelastic anisotropy of the laminae are found to strongly influence the delamination onset and propagation characteristics, which have been reflected by the asymmetries in the nature of energy release rate plots and their significant variation along the delamination front.

• Steel and Composite Structures
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• v.33 no.5
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• pp.729-746
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• 2019

The nonlinear behavior of single- and multi-story steel plate shear walls (SPSWs) strengthened with three different patterns of fiber reinforced polymer (FRP) laminates (including single-strip, multi-strip and fully FRP-strengthened models) is studied using the finite element analysis. In the research, the effects of orientation, width, thickness and type (glass or carbon) of FRP sheets as well as the system aspect ratio and height are investigated. Results show that, despite an increase in the system strength using FRP sheets, ductility of reinforced SPSWs is decreased due to the delay in the initiation of yielding in the infill wall, while their initial stiffness does not change significantly. The content/type/reinforcement pattern of FRPs does affect the nonlinear behavior characteristics and also the mode and pattern of failure. In the case of multi-strip and fully FRP-strengthened models, the use of FPR sheets almost along the direction of the infill wall tension fields can maximize the effectiveness of reinforcement. In the case of single-strip pattern, the effectiveness of reinforcement is decreased for larger aspect ratios. Moreover, a relatively simplified and approximate theoretical procedure for estimating the strength of SPSWs reinforced with different patterns of FRP laminates is presented and compared with the analytical results.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.10
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• pp.256-263
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• 2014

We have designed and made three kinds of FBG(Fiber Bragg Grating) Acoustic Transducer using Hopper type WDM on the use of recently developed FBG in Korea. The newly designed three kinds of FBG Acoustic Transducer using Hopper type WDM have an excellent merit of practical use with simple structure of sensors arm as well as the merit with existing fiber sensors. It was possible to detect sound waves in the range of 10 Hz to 18 kHz through the newly designed three kinds of FBG Acoustic Transducer and also, possible to detect its signal within the maximum range of 8.6 m by the use of most suitable resonance condition of the transducer. Especially, we can expect the utilization of low-frequency signal detection instead of existing acoustic sensor in the environment of electric noise and inferior condition. Furthermore, they can be developed as the high-sensibility and multi-point signal detection system through the sensor array system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.535-541
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• 2005

This paper proposes a hybrid optical lines composed of single-mode fiber(SMF) and multi-mode fiber(MMF) for gigabit-capable Passive Optical Network(GPON) using a WDM method with a single light source per each channel, and reports the results of transmission performance the proposed lines. The transmission link uses a direct modulated DFB-LD for high speed downstreams at the optical line terminal(OLT) of central office(CO) and a low cost SFP type transceiver for low-speed upstream in optical network unit(ONU). To split or combine the transmission channels, wavelength MUX/DEMUX are used in the optical line section, and MMFs not longer than 1 km are attached to the SMF lines at the ONU side of the WDM-PON links. We have performed the transmission experiment on the downstream of 2.5 Gbit/s, and 1.25 Gbit/s, and the upstream of 1.25 Gbit/s, and 622 Mbit/s which are recommended by ITU-T G.984.2. The transmission margin and feasibility of the proposed links have been tested to be suitable up to 2.5 Gbit/s transmission.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1668-1670
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• 2002

Since more than two decades, the conventional PD detecting systems have been employed in order to detect the partial discharges occurring inside the HV power apparatus for their diagnosis by use of different type of detection such as acoustic and UHF detection method. Regardless of their wide on-site application, a certain number of technical inconveniences have been disclosed as follows : multistage amplification. large volume, susceptible to external noise and high price. In this respect, the optical measurement techniques are widely proposed in these days in this concerned field ascribed to the following advantages : immune to external EMI noise and broad band response of the Pockels cell covering from DC to GHz. However, the reliability of several proposed techniques enabling to measure the electric field inside the large high power apparatus has not yet been well approved In this work, an optical measuring system, based on the Pockels effect, has been developed for measuring the field variation due to the corona discharges occurring in air and in oil. This system consists of He-Ne laser, single mode optical fiber, multi mode optical fiber, polarizing film, Y-cut LiNbO3 cell, photo detector, digital oscilloscope and personal computer with GPIB. For this purpose, optical probe has been specially designed and realized and put into the needle-plane electrode. Afterward, same measurement is carried out in oil. We demonstrate the characteristic of the optical measuring system and the measurement results.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1770-1772
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• 2003

본 연구는 국내에서 최초로 제안되고 적용가능성이 입증되어 설계, 제작된 Probe-type Pockets sensor(HY-Pockets Sensor)를 GIS등의 고전압 장비들에 응용한 레이저 부분방전 진단 시스템 개발을 목표로 하고 있다. 이러한 목적으로, 170kV 급 실 규모 GIS내부의 전류 도체에 다양한 곡률 반경의 침 전극을 부착시켜 부분 방전에 기인된 불평등 전계를 형성시켜 개발된 센서의 실규모 적용 가능성을 고찰하였다. 본 레이저 계측 시스템은 He-Ne laser, single multi-mode optical fiber, $2{\times}2$ 50/50 laser to single mode fiber coupler, probe-type Pockets sensor, photo detector 등으로 구성하여 레이저의 진행을 유도하고, 신호의 특성을 분석하였다. probe-type Pockets sensor로부터 의 출력 신호는 photo detector를 통해 전기적 신호로 변환되어 digital oscilloscope에 의해 측정되고, 또한 PC를 통해 데이터의 저장과 통계적, 분석적 처리 과정을 수행하게 된다. 본 연구의 결과로서 부분방전원에서 생성된 방전 신호에 대한 거리에 따른 센서 감도 결정, 그에 대한 센서 감도의 보정 향상, 전계의 세기의 변화에 따른 센서의 선형성 등이 도출되었고, 이러한 실험결과를 통해 실 GIS(170kv급) 내부에서 발생하는 부분방전의 검출에 본 레이저 부분방전 진단 시스템의 적용 가능성이 제시 되었다.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.1
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• pp.39-45
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• 2015

Applications of smart sensors have been extended to safety systems in the aerospace, transportation and civil engineering fields. In particular, structural health monitoring techniques using smart sensors have gradually become necessary and have been developed to prevent dangers to human life and damage to assets. Generally, smart sensors are based on electro-magnets and have several weaknesses, including electro-magnetic interference and distortion. Therefore, fiber optic sensors are an outstanding alternative to overcome the weaknesses of electro-magnetic sensors. However, they require expensive devices and complex systems. This paper proposes a new, affordable and simple sensor system that uses a single fiber to monitor pressures at multiple-points. Moreover, a prototype of the sensor system was manufactured and tested for a feasibility study. Based on the results of this experimental test, a relationship was carefully observed between the bend loss conditions and light-intensity. As a result, it was shown that impacts at multiple-points could be monitored.

• Korean Journal of Optics and Photonics
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• v.33 no.5
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• pp.210-217
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• 2022

In this paper, a study is conducted on the acceptable tolerance of an alignment device to reduce the optical loss caused by the alignment tolerance of a window hermetic optical connector. To increase the transmission distance of optical signals and fiber-optic communication systems, it is necessary to maintain and improve the high optical efficiency of the connectors used to bond optical fibers. In the case of the window hermetic optical connector, the optical system is aligned through an alignment device. At this time, since the two connectors are used together, each component is fixed, and further alignment is impossible. The alignment tolerance of the housing system and pin used to align the optical system of the connector causes optical loss, leading to serious problems in the fiber-optic communication system. Thus, to find the acceptable tolerance required for manufacturing the optical-connector alignment device, tolerance analysis is performed on the components of the optical connector, such as the ball lens and the window. We also implement single-mode and multimode optical-connector systems, respectively. Based on the results, we determine an acceptable tolerance value for the alignment device.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.3
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• pp.355-360
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• 2012

The characteristics of power generation were investigated by changing the electrical conductivity from 10 to 40mS/cm using air-cathode microbial fuel cell, which had graphite fiber fabric(GFF) anode. There were three kinds of cathode used: one was carbon cloth cathode coated with Pt, another was carbon nanotube(CNT) cathode with non-precious catalyst of Fe-Cu-Mn, and the other was carbon nanotube(CNT) cathode without any catalyst. When it was operated in batch mode, power density of 1369.5mW/$m^2$ was achieved at conductivity of 20mS/cm. Power density from MFC with CNT cathode coated with multi-catalyst of Fe-Cu-Mn was shown about 985.55mW/$m^2$, which was 75.1% compared the power density of carbon cloth coated with Pt. This meant that CNT cathode coated with multi-catalyst of Fe-Cu-Mn could be an alternative of carbon cloth cathode.