• Korean Journal of Optics and Photonics
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• v.27 no.6
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• pp.203-211
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• 2016

We have studied the hybrid method for reconstructing apodized chirped fiber Bragg gratings, using both an analytic estimation of grating parameters and an optimization algorithm. The Hilbert transform of the reflection spectrum was utilized to estimate grating parameters, and then the layer-peeling algorithm was used to obtain refined parameter values by the differential-evolution optimization process. Calculations for a fiber Bragg grating with wavelength chirp rate 2 nm/cm were obtained with an accuracy of $6{\times}10^{-5}nm/cm$ for the chirp rate and $3{\times}10^{-9}nm/cm$ for the index modulation, with much improved calculation speed and high reliability.

• Transactions of the Society of Information Storage Systems
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• v.2 no.3
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• pp.189-195
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• 2006

Bragg detuning effect if, one of the serious problems if the photopolymer is used for the recording material of holography memories. And the critical reasons of that are known as the bulk refractive index change and shrinkage of recording material. However, the trials for analyzing the effect are mainly on the K-sphere and biased on the transmission hologram. So, we approached Bragg detuning effect numerically and applied the method to the transmission holograms and the reflection holograms all together. We simulated it with MATLAB. As a result, the bulk refractive index change causes+Bragg detuning effect on the transmission holograms and the reflection holograms. But the shrinkage leads to+Bragg detuning effect on the transmission hologram and-Bragg detuning effect on the reflective hologram. Compared to experimental result, the bulk refractive index change(${\fallingdotseq}4{\times}10^{-4}$) and the ratio of shrinkage to the thickness of the material(${\fallingdotseq}1.67{\times}10^{-3}$) could be matched with Bragg detuning effect on the transmission hologram and the reflection hologram.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2003.08a
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• pp.249-253
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• 2003

심해로부터 해안으로 전파해오는 파랑은 해저지형 또는 구조물 등의 영향을 받아 반사, 쇄파 등과 같은 변형을 겪게 되며, 이와 같은 파랑은 연안침식 및 해안구조물의 안전과 설계에 영향을 미친다. 수중방파제(submerged breakwater)는 입사하는 파랑에너지를 대규모로 감소시켜 연안침식을 방지할 뿐만 아니라 방파제를 수중에 건설함으로써 해역환경의 개선을 가능하게 한다. 또한, Bragg반사를 이용하여 수중방파제를 건설할 경우, 연안의 불필요한 침식 및 퇴적현상을 최소화할 수 있을 뿐만 아니라 입사파에 의해 발생하는 해안구조물의 손상을 사전에 방지 할 수 있다. 아울러, 항만의 정온도를 향상시키는데 효과적으로 이용할 수 있다. (중략)

• Korean Journal of Optics and Photonics
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• v.26 no.2
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• pp.83-87
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• 2015

This study was focused on developing an optical sensor that monitors ultraviolet (UV) light. Recently, we proposed and demonstrated a novel, highly sensitive UV sensor based on a fiber Bragg grating (FBG). To ensure that the incident UV light is focused on the FBG surface, the sensor was coated with an azobenzene polymer material that acts as a UV-induced stretchable functional material, in combination with a cylindrical focal lens. In this study we have improved the sensitivity of the sensor by employing a cylindrical focal mirror as a curved reflector, to refocus the UV light passing through the FBG. We considered the performance of several different types of reflectors and chose the optimal radius of curvature for the reflector. Compared to the UV sensor without an auxiliary device, the sensitivity of the FBG sensor with a focal lens and a curved reflector was 15 times as high.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4C
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• pp.430-436
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• 2009

In this paper, we propose and describe our implementation of an automatic control system for the center wavelength of a fiber Bragg grating. The proposed system consists of a Fabry-Perot filter and cantilever structure controlled by a step motor interfacing computer. We consider the change of the center wavelength and the reflective spectrum shape for a given FBG according to the translation distance of the push stick and the cantilever thickness variation. The proposed system can control the center wavelength of a FBG with a resolution of 0.01 nm by applying compression or extension to the FBG. The proposed system has characteristics that keep the desired wavelength of the FBG with a variation of environmental conditions.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2303-2305
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• 2005

현재 광통신 분야는 보다 많은 정보를 동시에 전송하기 위해 다양한 다중화 방식들을 요구 받고 있다. 광섬유 Bragg 격자 소자를 이용한 모든 광 분기/결합 장치는 분기/결합할 수 있는 신호가 광섬유 격자 소자의 Bragg파장에 의해 정해지므로 하나의 광섬유 격자 소자는 고정된 한 채널만을 분기, 결합할 수 있다는 단점을 지니고 있다. 그러나 광섬유 격자에 온도와 스트레인(strain) 같은 외부 물리량을 가하게 되면 광섬유 격자의 주기가 변하게 되어 반사파장이 고정되지 않고 파장을 가변 할 수 있는 장점을 가지게 된다. 이에 본 논문에서는 광섬유 격자 소자에 가해진 온도, 스트레인에 의해 Bragg파장이 변화하는 성질을 이용하여 파장 가변형 Bragg 격자를 제작 및 실험을 통하여 전광필터 특성에 대하여 제시하였다.

• Information and Communications Magazine
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• v.17 no.12
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• pp.67-73
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• 2000

• Proceedings of the Korea Water Resources Association Conference
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• 2003.05b
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• pp.1043-1046
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• 2003

• Journal of the Korean Society of Radiology
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• v.12 no.1
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• pp.17-22
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• 2018

Multilayer mirrors are optical elements that can replace single crystal optical elements such as silicon or germanium, and they have artificial diffraction plane of a thickness of several nanometers. We examined the first Bragg angle and the reduction of reflectivity by variation of layer thickness in a W/Si multilayer mirror of small d-spacing. A W/Si multilayer mirror for an incidence angle of $0.55^{\circ}$ and an energy of 17.5 keV was designed and showed a maximum reflectivity of 72.67%. When the thickness of tungsten or silicon layer was simultaneously changed, the first Bragg angle was shifted and the reflectivity was reduced. When there was a change in thickness for one layer of W/Si multilayer, no change in the reflectivity was showed but the unevenness of the envelope was observed. Reduction of reflectivity was also observed at random Gaussian thickness variations. It is possible to predict the tolerance of multilayer mirror by examining the reflectivity degradation according to the thickness change in the W/Si multilayer mirror of small d-spacing.

• Composites Research
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• v.18 no.1
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• pp.16-22
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• 2005

Application fields on structural health monitoring of fiber Bragg gratings (FBGs) are gradually expanded even to a primary structure as well as a secondary structure and a specimen. For the reason, verification for the reliability of FBGs such as signal characteristics and mechanical strength becomes much more important. In this study, mechanical strength characteristics of FBGs with their fabrication process and reflectivity are investigated with various grating lengths. From the results of tension tests, it is shown that the mechanical strength of optical fibers decreases about $50\%$ just by jacket stripping and the amount of decrease is dependent on stripping methods. About $55\%$ of mechanical strength of stripped optical fibers decreases if gratings are formed in the core and it is regardless of grating lengths and reflectivity. However, the width of strength distribution increases relative to increases in reflectivity.