• Smart Structures and Systems
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• v.12 no.1
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• pp.23-39
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• 2013

In this article, a smart multifunctional optical system-on-a-chip (SOC) sensor platform is presented and its application for fiber Bragg grating (FBG) sensor interrogation in optical sensor networks is investigated. The smart SOC sensor platform consists of a superluminescent diode as a broadband source, a tunable microelectromechanical system (MEMS) based Fabry-P$\acute{e}$rot filter, photodetectors, and an integrated microcontroller for data acquisition, processing, and communication. Integrated with a wireless sensor network (WSN) module in a compact package, a smart optical sensor node is developed. The smart multifunctional sensor platform has the capability of interrogating different types of optical fiber sensors, including Fabry-P$\acute{e}$rot sensors and Bragg grating sensors. As a case study, the smart optical sensor platform is demonstrated to interrogate multiplexed FBG strain sensors. A time domain signal processing method is used to obtain the Bragg wavelength shift of two FBG strain sensors through sweeping the MEMS tunable Fabry-P$\acute{e}$rot filter. A tuning range of 46 nm and a tuning speed of 10 Hz are achieved. The smart optical sensor platform will open doors to many applications that require high performance optical WSNs.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.3
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• pp.146-152
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• 2013

In this paper, we have proposed and experimentally demonstrated an intensity-based self-referencing fiber optic sensor. The proposed fiber optic sensor consists of a broadband light source (BLS), fiber Bragg grating (FBG), tunable Fabry-Perot (F-P) filter, and LabVIEW program. We define the measurement parameter (X) and the calibration parameter (${\beta}$) to determine the transfer function(H) of the self-referencing fiber optic sensor, and the validity of the theoretical analysis is confirmed by experiments. The self-referencing characteristic for the proposed system has been validated by showing that the measurement parameter (X) is invariant for BLS optical power attenuations of 0 dB, 3 dB, and 6 dB. Also, the measured result is irrelevant to the FBGs with different characteristics. This means that the proposed fiber optic sensor offers the flexibility for determining the FBGs needed for implementation. Experimental results for the proposed fiber optic sensor are in good agreement with a theoretical analysis for BLS optical power attenuations and for three FBG pairs with different characteristics. So, the proposed fiber optic sensor has several benefits, including the self-referencing characteristic and the flexibility to determine the FBGs.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.11
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• pp.17-22
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• 2005

In this study, we suggested wave-variable Bragg lattice using the characteristic of the Bragg wave that varies according to the change of the temperature imposed on the optical fiber lattice device, and experimented using a simulation test. We analyzed the results of the FBG change according to the change of the temperature obtained in the variable FEG computer simulation and experiment to suggest optimal data. Therefore, utilizing wave-variable optical filter through FBG allows us to combine other channels beyond optical fiber lattice device wave, and can be used as a helpful device in the Dense Wavelength Division Multiplexed system with a channel intervention of 0.08nm(10GHz).

• Composites Research
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• v.16 no.6
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• pp.56-61
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• 2003

In this Paper, a fiber Bragg grating(FBG) sensor system is described and FBGs are well-suited for long term and extremely severe experiments, where traditional strain gauges fail. In the system. a reflect wave-length measurement method which employs a tunable light source to find out the center wave-length of FBG sensor is used. We apply the FBG system to nuclear energy Power Plant for structural integrity test to measure the displacement of the structure under designed pressure and to check the elasticity of the structure by measuring the residual strain. The system works very well and it is expected that it can be used for a real-time strain, temperature and vibration detector of smart structure.

• Proceedings of the KAIS Fall Conference
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• 2008.05a
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• pp.167-169
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• 2008

본 논문에서는 FBG 가변 형 필터의 출력 특성에 대한 수치해석의 결과와 실험값을 비교 분석하기 위해 $25^{\circ}C$에서 $90^{\circ}C$ 까지 온도 변화에 대해 FBG 가변 형 필터의 출력스펙트럼을 측정하였다. 수치해석과 실험의 결과로부터 온도변화에 따른 선폭과 출력의 크기는 거의 변화가 없지만, 브래그 파장은 이론값과 비교적 유사하게 온도에 따라 이동함을 알 수 있었다. 또한, 온도의 상승, 하강, 유지 시에도 동일한 결과를 보였다.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.421-425
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• 2005

A distributed FBG temperature sensor system was constructed for the use in protection of electric power system. A F-P wavelength tunable filter is used converting temperature-induced wavelength variations to temporal peak locations. We used Gaussian line-fitted algorithm to alleviate the error caused by quantization and electrical noises. The experimental results showed much better accuracy than the raw peak-detection scheme.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.103-106
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• 2004

Impact location monitoring is one of the major concerns of the smart health monitoring. For this application, multipoint ultrasonic sensors are to be employed. In this study, a multiplexed FBG sensor system with wide dynamic range was proposed and stabilization controlling system was also developed for the maintenance of maximum sensitivity of sensors. For the intensity demodulation system of FBG sensors, Fabry-Perot tunable filter(FP-TF) with 23.8nm FSR(free spectral range) was used, which behaves as two separate filters between $1530 \~ 1560$ nm range. Two FBG sensors were attached on the bottom side of the graphite/epoxy composite beam specimen, and low velocity impact tests were performed to detect the one-dimensional impact locations. Impact locations were calculated by the arrival time differences of the impact longitudinal waves acquired by the two FBGs. As a result, multiplexed in-line FBG sensors could detect the moment of impact precisely and found the impact locations with the average error of 1.32mm.

• 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.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.115-118
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• 2004

In this paper, a Fiber Bragg Grating (FBG) sensor system for smart structures is described. FBGs are well-suited for long term and extremely severe experiments, where traditional strain gauges fail. In the system, a reflect wave-length measurement method which employs a tunable light source to find out the center wave-length of FBG sensor is used. We applied the FBG system to composite repairing structures and beam column joint of building structure. We also applied the system to nuclear energy power plant for structural integrity test to measure the displacement of the structure under designed pressure and to check the elasticity of the structure by measuring the residual strain. The system works very well and it is expected that it can be used for a real-time strain, temperature and vibration detectors as parts of smart structures.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.91-97
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• 2001

We present a fiber Bragg grating (FBG) sensor system for measuring static and high-speed dynamic strains with a resolution of about $5\mu$strain. This sensor system demodulates signals from the FBG sensor utilizing a compensated tunable narrow bandpass filter. We have placed a set of twelve FBGs to concrete specimen and measured its internal stress under various applied load conditions.itions.