• Korean Journal of Optics and Photonics
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• v.18 no.6
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• pp.383-388
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• 2007

A color filter was demonstrated incorporating a patterned metal grating in a quartz substrate. The filter is created in a metal layer perforated with a symmetric two-dimensional array of circular holes, with the pitch smaller than the wavelength of the visible light. A finite-difference time-domain simulation was performed to analyze the device by investigating the effect of structural parameters like the grating height, the period, the hole size, and the refractive index of the hole-filling material on its performance. The device performance was especially optimized by controlling the refractive index of the material comprising the holes of the grating. And two different devices were fabricated by means of the e-beam direct writing with the following design parameters: the grating height of 50 nm, the two pitches of 340 nm for the red color and 260 nm for the green color. For the prepared device with the period of 340 nm, the center wavelength was 680 nm and the peak transmission 57%. And for the other device with the pitch of 260 nm, the center wavelength was 550 nm and the peak transmission was 50%. The filling of the hole with a material whose refractive index is matched to that of the substrate has led to an increase of ${\sim}15%$ in the transmission efficiency.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.198-199
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• 2003

광섬유 브래그 격자(Fiber Bragg Grating, FBG)는 좁은 선폭과 적은 삽입손실 등의 뛰어난 스펙트럼 특성을 가지고 있어, 고밀도 파장분할 다중화 방식을 이용한 광통신 시스템과 여러 종류의 광섬유센서에 응용되고 있다. 브래그 격자의 광학적 스펙트럼을 능동적으로 조절하기 위하여, 광섬유에 열이나 스트레인을 인가하거나, 음파와 빛의 결합을 이용한 방법이 제안되었으며, 특히 음향 광학 브래그 격자 변조기(Acousto-Optic Superlattice Modulator)는 종 방향 음파(Longitudinal Acoustic Wave)를 이용하여 파장과 크기의 조절이 가능한 사이드 밴드(Side Band)를 생성해 내었다. (중략)

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.3
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• pp.39-44
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• 2004

Fiber Bragg grating sensors are fabricated by core index modulation using UV laser and phasemask. Bragg wavelength of the grating is changed by the external strain. In this paper, a signal processing system of fiber Bragg grating sensor has studied in the optical wavelength domain. The system is based on the sweep semiconductor light source that consists of SLD, F-P tunable filter and etalon filter. The hysteresis effects of PZT in the F-P tunable filter are compensated. The long term measurement stability is obtained by controlling the temperature of F-P tunable filter and the SLD. We compare the strain data from fiber Bragg grating sensor and that from strain gauge at concrete hume pipe. We also get very good results for the long gauge displacement using fiber Bragg grating sensor which are identical to the data with short gauge length ordinary displacement sensor.

• Proceedings of the IEEK Conference
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• 2003.11a
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• pp.107-110
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• 2003

본 논문은 LTJ 적응필터의 실용적 구현에 관한 연구이다. 음성코덱(codec)을 사용하는 응용분야에서는 코덱 복호화단의 LPC 계수정보를 얻을 수 있으므로 이를 반사계수로 변환하여 사용하므로서 반사계수 적응에 소용되는 계산량을 감소시킬 수 있으며, 코덱에서는 프레임 또는 서브프레임 단위로 LPC 계수를 적응시키므로 시변 변환 영역 적응필터에 해당하는 LTJ 적응필터의 필터 계수 보상에 필요한 계산량을 감소시킬 수 있다. 실제 음성신호를 사용하여 제안된 실용적 구현 방법의 타당성을 검증하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.2
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• pp.202-207
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• 2021

One of the most important tasks in image processing is noise filtering. Noise removal in image is a difficult task due to many reasons such as nonstationary sequences and corrupted by various types of noise. Human's visual perception is heavily based on the edge information. Thus, noise filtering must preserve edges. To remove the noise, we usually use the square-shaped median filter. They possess mathematical simplicity but have the disadvantages that blur the edges. In this paper we consider a new technique for image restoration using a weighted octagonal median filter. The technique consists of simple hypothesis test for edge detection, and we use the weighted octagonal-shaped moving window. The new technique is applied to noise corrupted image and experimental results are compared to the results of the square-shaped median filter and the cross-shaped median filter.

• Korean Journal of Optics and Photonics
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• v.12 no.5
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• pp.401-405
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• 2001

We propose a novel channel-switching transmission filter using segmented chirped fiber Bragg gratings (CFBG's) each of which has separate transmission bands in the reflection spectrum of the CFBG. The segmented CFBG's are made by using specially designed slits. The separated reflection spectral bands of the segmented CFBG's are controlled by the attached fiber stretchers, and the controlled reflection bands are used to choose the channels independently. Tunability of the transmission spectra is experimentally demonstrated in WDM transmission experiments.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.10
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• pp.51-56
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• 2000

An all fiber coupler-type add/drop filter has been fabricated by writing a Bragg grating in the coupling region of a fused fiber coupler. The fused fiber coupler with 99.8% coupling ratio and 74/m coupling coefficient was used for the add/drop filter. The add/drop filter shows 99% reflectivity and 83% drop efficiency at the operating wavelength of 1536.2nm.

• Proceedings of the Optical Society of Korea Conference
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• 2006.07a
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• pp.45-46
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• 2006

• Journal of Industrial Technology
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• v.5
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• pp.27-36
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• 1985

마이크로 컴퓨터로 실현(實現)되는 디지탈 필터는 유한어장효과(有限語張效果)에 기인(基因)한 양자화(量子化)(quantization)와 잉여현상(overflow) 때문에, 이상적(理想的)인 선형(線型)필터도 비선형(非線型) 특성(特性)을 나타내어 Limit Cycle과 같은 오차의 원인이 된다. 본(本) 논문(論文)에서는 수학행렬(行列)의 안정(安定)성질을 이용한 Norm-Lyapunov 함수를 이용하여, 디지탈 필터의 안정도를 해석하였다. 잉여현상이 없는 경우에는 Jury-Lee 판별법을 적용하여 전자(前者)와 비교하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.50-57
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• 2004

For the application of structural health monitoring such as AE detection, a stabilized FBG sensor system with wide dynamic range was proposed. A tunable Fabry-Perot filter with narrow free spectral range(FSR) was used to simplify the multiplexing demodulator for FBG vibration sensors. Stabilization controlling system was also developed for the maintenance of maximum sensitivity of the sensors. In order to verify the performance of the proposed FBG vibration sensor system, we measured sensitivity, and the system showed the average sensitivity of 256 $n{\in}_{mas}/{\sqrt{Hz}}$. Finally, multi-points vibration tests using in-line FBG sensors were conducted to validate the multiplexing performance of the FBG system.