• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.34-38
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• 2004

A fiber laser of which wavelength was scanned by an intra-cavity FP (Fabry-Perot) filter was used to interrogate a fiber Bragg grating strain sensor array. We calculated the wavelength variation of the fiber laser using quadrature signal processing with an unbalanced M/Z (Mach-Zehnder) interferometer and time-delayed sampling technique. The calculated wavelengths are mapped to corresponding temporal reflection peaks from the sensor array, which enables more accurate and stable interrogation without the problems caused by the FP filter's nonlinear characteristics. Wavelength resolution of ∼20 pm was obtained in our experimental setup, which could have been greatly enhanced with faster phase modulation.

• Composites Research
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• v.17 no.2
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• pp.28-33
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• 2004

Failure detection in a cross-ply laminated composite beam under tensile loading were performed using a fiber Bragg grating (FBG) sensor. A Passive Mach-Zehnder interferometric demodulator was proposed to enhance sensitivity and bandwidth. The proposed FBG sensor system without active device such as a phase modulator is very simple in configuration, easy to implement and enables the measurement of high-frequency vibration with low strain amplitude such as impact or failure signal. Failure signals detected by a FBG sensor had offset value corresponding to the strain shift with vibration at a maximum frequency of several hundreds of kilohertz. at the instant of transverse crack propagation in the 90 degree layer of composite beam.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.4
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• pp.84-91
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• 2005

We measured the pitch of one-dimensional (ID) grating specimens using a metrological atomic force microscope (M-AFM). The ID grating specimens a.e often used as a magnification standard in nano-metrology, such as scanning probe microscopy (SPM) and scanning electron microscopy (SEM). Thus, we need to certify the pitch of grating specimens fur the meter-traceability in nano-metrology. To this end, an M-AFM was setup at KRISS. The M-AFM consists of a commercial AFM head module, a two-axis flexure hinge type nanoscanner with built-in capacitive sensors, and a two-axis heterodyne interferometer to establish the meter-traceability directly. Two kinds of ID grating specimens, each with the nominal pitch of 288 nm and 700 nm, were measured. The uncertainty in pitch measurement was evaluated according to Guide to the Expression of Uncertainty in Measurement. The pitch was calculated from 9 line scan profiles obtained at different positions with 100 ㎛ scan range. The expanded uncertainties (k = 2) in pitch measurement were 0.10 nm and 0.30 nm for the specimens with the nominal pitch of 288 nm and 700 nm. The measured pitch values were compared with those obtained using an optical diffractometer, and agreed within the range of the expanded uncertainty of pitch measurement. We also discussed the effect of averaging in the measurement of mean pitch using M-AFM and main components of uncertainty.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.43-50
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• 2004

For the simultaneous measurement of strain and damage signal a fiber Bragg grating sensor system with a dual demodulator was proposed. The dual demodulator is composed of a demodulator using a tunable Fabry-Perot filter measuring the low-frequency signal with large magnitude such as strain and the other using a passive Mach-Zehnder interferometer detecting the high-frequency signal with small amplitude such as impact or damage signal. Using the proposed fiber Bragg grating sensor system, both the strain and damage signals of a cross-ply laminated composite beam under tensile loading were simultaneously measured. The strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were accompanied with vibration at a maximum frequency of several hundreds of kilohertz at the instant of matrix crack propagation in the 90 degree layer in composite beam.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2005.11a
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• pp.3-6
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• 2005

In this thesis, We researched on the characteristics of optical tunable filter that selects the channel by the wavelength changes of transmission spectrum when we apply outer physical quantities on a fiber bragg grating by using Fabry-Perot Interformer's operational principle.

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.3-4
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• 2006

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.148-149
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• 2003

렌즈와 거울의 형상을 정밀하게 측정하고 평가하는 광학시험에 많은 형태의 광간섭계가 개발되고 사용되어왔다. 그 중, 회절격자를 광선분할기로 사용하는 광간섭계들을 통칭하여 회절격자 간섭계라 부른다. 회절격자 간섭계는 별개의 광학표면을 사용하지 않고 회절격자에서 회절된 파면을 직접 기준파면으로 사용할 수 있으므로, 격자의 형태, 주기를 선정하여 기준파면과 측정파면을 원하는 방향으로 재생하여 다양한 형태의 간섭계를 만들 수 있다.(중략)

• Journal of the Korean Society of Radiology
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• v.14 no.7
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• pp.937-946
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• 2020

The grating interferometer provides the differential phase contrast image of an phase object due to refraction of the wavefront by the object, and it needs to be converted to the phase contrast image. The line-integration process to obtain the phase contrast image from a differential phase contrast image accumulates noise and generate stripe artifacts. The stripe artifacts have noise and distortion increases to the integration direction in the line-integrated phase contrast image. In this study, we have configured and compared several machine learning methods to reduce the artifacts. The machine learning methods have been applied to simulated numerical phantoms as well as experimental data from the X-ray and neutron grating interferometer for comparison. As a result, the combination of the wavelet preprocessing and machine learning method (WCNN) has shown to be the most effective.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.95-102
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• 2004

For the simultaneous measurement of strain and damage signal, a fiber Bragg grating sensor system with a dual demodulator was proposed. One demodulator using a tunable Fabry-Perot filter can measure low-frequency signal such as strain and the other demodulator using a passive Mach-Zehnder interferometer can detect high-frequency signal such as damage signal or impact signal. Using a proposed fiber Bragg grating sensor system, both the strain and damage signal of a cross-ply laminated composite beam under tensile loading were simultaneously measured. Analysis of the strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were induced due to transverse crack propagation in the 90 degree layer of composite beam and vibration with a maximum frequency of several hundreds of kilohertz was generated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.264-267
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• 2003

Pitch measurements of 150 nm pitch one-dimensional grating standards were carried out using an contact mode atomic force microscopy(C-AFM) with a high resolution three-axis laser interferometer. It was called as 'Nano-metrological AFM' In Nano-metrological AFM, Three laser interferometers were aligned well to the end of AFM tip. Laser sources of the three-axis laser interferometer in the nano-metrological AFM were calibrated with an I$_2$-stablilzed He-Ne laser at a wavelength of 633 nm. So, the Abbe error was minimized and the result of the pitch measurement using the nano-metrological AFM has a traceability to the length standard directly. The uncertainty in the pitch measurement was estimated in accordance with the Guide to the Expression of Uncertainty in Measurement(GUM). The Primary source of uncertainty in the pitch-measurements was derived from repeatability of pitch-measurement, and its value was approx 0.186 nm. Expanded uncertainty(k=2) of less than 5.23 nm was obtained. It is suggested that the metrological AFM is a useful tool for the nano-metrological standard calibration.