• Journal of information and communication convergence engineering
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• v.5 no.4
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• pp.320-323
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• 2007

This paper presents the resonance characteristics of the ZnO-based FBAR devices with multilayered Bragg reflectors with Cr adhesion layer inserted between $SiO_2$ and W layers. Due to the post- annealing, the return loss ($S_{11}$) and series/parallel quality factor are significantly improved when compared with the non-post annealing. This post-annealing method seems to be a very efficient way to improve the resonance characteristics of FBAR devices.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1142-1145
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• 2006

The Finite-difference time-domain (FDTD) method is used to directly solve Maxwell's equations, and the techniques required for optical simulation of Bragg reflections of cholesteric liquid crystal (ChLC) displays are introduced in this paper. The simulated results show that the color gamut of a ChLC display can be broadened by using of a circular polarizer on top surface of the ChLC film, and are examined by experiments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05a
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• pp.83-85
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• 2004

MOCVD(metalorganic chemical vapor deposition)에 의해 성장된 InGaAs/AlGaAs 물질을 이용하여 V-형 양자선 (V-groove quantum-wire) 어레이(array) 구조에서 이득 결합(gain-coupling)에 의한 분포 광귀환(distributed optical feedback) 특성을 조사하였다. 분포 귀환형 (distributed feedback, DFB) 구조를 제작하는 동안 격자 재성장(grating overgrowth)을 피하기 위하여, 새롭게 개발된 constant MOCVD 성장 방법을 적용하였고, Bragg 파장에서 DFB 방향으로 광귀환의 결과인 스펙트럼의 이득 이방성(gain asymmetry)을 실험적으로 관찰하였다.

• Journal of IKEEE
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• v.2 no.1 s.2
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• pp.108-113
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• 1998

By using an equivalent network based on Floquet's theorem and bisection principle, the optical properties of planar DFB guiding structure are evaluated. The optical parameters, such as Bragg condition and the reflectivity as a function of grating period, are numerically calculated. The numerical results reveal that this method offers a simple and convenient algorithm to analyze the optical characteristics of DFB configurations.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.12
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• pp.71-79
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• 1994

In this paper, $As_{40}Se_{50-x}S_[x}Ge_{10}$(x=0, 25, 35, at.%) bulk and thin films, to develope device of reversible hologram, proved amorphous by X-RD analysis. On the thin films with composition rate, as Se-doped-quantity increased, absorption edge shifted to long wavelength, and we found that reversible photodarkening effect occurred when thin films are exposed and annealed. Optical energy gap was larger when thin films are annealed than exposed. In this effect thin films structurally stabilized by annealing. It is to formed grating hologram by the bragg method on the $As_{40}Se_{15}S_[35}Ge_{10}$ thisn films with the best transmittance properties As polariging angle grew larger, we found that maximum diffraction efficiency became smaller, and obtained it of 4.5% on the thin fim thicknesss of 0.6 m, polarizing angle of 40$^[\circ}$ and exposing for 20sec.

• ETRI Journal
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• v.28 no.1
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• pp.1-8
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• 2006

A novel all-optical gain-controlled (AOGC) bidirectional amplifier is proposed and demonstrated in a compact structure. The AOGC function using fiber Bragg grating (FBG) pairs controls both directional signals independently, and combinations of optical interleavers and isolators suppress Rayleigh backscattering (RB) noise. The amplifier achieves high and constant gain with a wide dynamic input signal range and low noise figure. The performance does not depend on the input signal conditions, whether static-state or transient signals, or whether there is symmetric or asymmetric data traffic on bidirectional transmission. Transmission comparison experiments between invariable symmetrical and random variable asymmetric bidirectional data traffic verify that the all-optical gain control and bidirectional amplification functions are successfully combined into this proposed amplifier.

• ETRI Journal
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• v.28 no.6
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• pp.739-744
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• 2006

In this paper, we report numerically calculated results of testing a temperature-insensitive refractive sensor based on a planar-type long-period waveguide grating (LPWG). The LPWG consists of properly chosen polymer materials with an optimized thermo-optic coefficient for the core layer in a four-layer waveguide structure. The resonant wavelength shift below the spectral resolution of the conventional optical spectrum analyzer is obtained accurately over a temperature change of ${\pm}7.5^{\circ}C$ even without any temperature control. The refractive index sensitivity of the proposed grating scheme is about 0.004 per resonant wavelength shift of 0.1 nm for an optimized thermo-optic coefficient.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.413-422
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• 2002

A novel photonic bandgap(PBG) structure is proposed and measured for wide bandgap and compact circuit applications. The proposed structure realizes the ultra-wideband bandgap(2-octave) characteristics by superposing two different PBG structures into a coupled double-plane configuration. A low pass filter fabricated using 3-period of the PBG cells shows 2-octave 10 ㏈ stopband from 4.3 to 16.2 ㎓ and 0.2 ㏈ insertion loss in the passband. Moreover, we confirmed that 44∼70 % size reduction can be achieved using the proposed PBG structures. We expect this novel double-plane PBG structure is widely used for compact and wideband circuit applications, such as compact high-efficiency power amplifiers using harmonic tuning techniques.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.163-166
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• 2004

Epoxy composite reinforced with 3-D braided Glass/Aramid hybrid fabric was fabricated. FBG sensor was embedded along the braid yam in order to monitor the changes of the complicated inner region of the 3-D braid structure. The good linearity between Bragg wavelength and temperature was verified by several preliminary experiments. The strain inside 3-D braided beam was estimated using FBG sensor system, and the result was compared with the calculated value. It was found that FBG sensor system is very useful technique to investigate inside region of complicated structure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.320-325
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• 2009

In this study, a method to estimate the suspension bridge deflection is developed using mode decomposition technique. In order to examine the suspension bridge stability against these dynamic loadings, the prediction of displacement response is very important to evaluate bridge stability. However, it is recognized that any measurement of movement for suspension bridges may be difficult for the absence of proper methods to measure the displacement response on site. This study aims at suggesting a method to estimate the displacement response from the measured strain signals in an indirect way to predict the displacement response, not a direct way to measure the displacement response. Additionally, by applying the FBG sensors with multi-point measurements not influenced by electric noise, it can be expected that the technique would be applicable to infrastructures.