• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.460-465
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• 2003

Characteristics of 0.98 $\mu$m-pumped erbium-doped fiber (EDF) sources with double-pass forward (DPF) configuration are analyzed by numerical calculation. Various source characteristics such as output power, spectral width and mean-wavelength stability are investigated with the variation of EDF length, pump power and pump wavelength. Some of the numerical results are compared with experimental ones for verification. The results show that the characteristics of sources with DPF configuration can change considerably with the EDF length. It is also found that an optimum design can exist for stable mean-wavelength against fluctuations of pump power and pump wavelength.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7A
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• pp.712-718
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• 2004

We report 1.6 Tb/s (160${\times}$10 Gb/s) WDM transmission over 2,000 km of single mode fiber using distributed hybrid(distributed Raman amplifier＋Erbium-doped fiber amplifier) optical amplifiers. After transmission over 2,000 km of single mode fiber, average optical signal to noise ratios of C/L-band were 20.5 dB, 21.9 dB, respectively. The minimum Q-factors of each band were 14.65 dB (BER=5.8e-8) in C-band, 13.75 dB (BER=5.0e-7) in L-band without forward error correction. We performed 1.6 Tb/s error-free transmission over 2,000 km of single mode fiber using Reed-Solomon (255, 239) forward error correction code.

• Journal of the Optical Society of Korea
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• v.12 no.4
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• pp.255-261
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• 2008

This paper reports a side-coupled asymmetric $1{\times}2$ plastic optical fiber coupler for an optical sensor system. The dependence of the optical power coupling ratio on the coupling angle and refractive index of the adhesion layer in both the forward and backward directions was examined based on the geometrical optics. It was confirmed experimentally that the coupling ratios can be optimized by controlling the coupling angle and refractive index of the adhesion layer. A maximum forward coupling efficiency > 93% was achieved.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.2
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• pp.18-33
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• 2008

This paper presents design optimization of a new Active Twist Rotor (ATR) blade and conducts its aeroelastic analysis in forward flight condition. In order to improve a twist actuation performance, the present ATR blade utilizes a single crystal piezoelectric fiber composite actuator and the blade cross-sectional layout is designed through an optimization procedure. The single crystal piezoelectric fiber composite actuator has excellent piezoelectric strain performance when compared with the previous piezoelectric fiber composites such as Active Fiber Composites (AFC) and Macro Fiber Composites (MFC). Further design optimization gives a cross-sectional layout that maximizes the static twist actuation while satisfying various blade design requirements. After the design optimization is completed successfully, an aeroelastic analysis of the present ATR blade in forward flight is conducted to confirm the efficiency in reducing the vibratory loads at both fixed- and rotating-systems. Numerical simulation shows that the present ATR blade utilizing single crystal piezoelectric fiber composites may reduce the vibratory loads significantly even with much lower input-voltage when compared with that used in the previous ATR blade. However, for an application of the present single crystal piezoelectric actuator to a full scaled rotor blade, several issues exist. Difficulty of manufacturing in a large size and severe brittleness in its material characteristics will need to be examined.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.238-239
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• 2000

The optical fibers are an interesting medium for effective tunable optical frequency conversion in the spectral range of UV, Visible, and near-IR through the nonlinear processes. A number of papers for developing the wideband and flat-gain amplifier for the WDM system applications through the combination of EDFA or thulium-doped fluoride fiber amplifier and Raman amplifier, are reported$^{(1)}$ . Even though a variety of papers related to Raman amplifications are published, the amplification with the feedback of the residual pump is not investigated yet. Accordingly, in this paper, we report the characteristics of forward Raman amplification by the simple and double-pass fiber Raman configuration through the feedback of residual pump beam. (omitted)

• Journal of the Korean Society for Precision Engineering
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• v.30 no.10
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• pp.1017-1022
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• 2013

Currently, various optical fiber tips are used to deliver laser beam for endoscopic surgery. In this paper, we demonstrated multidirectional (forward and side) firing optical fiber tip using a femtosecond micromachining and $CO_2$ laser polishing technology. We controlled the edge width of optical fiber tip, by modulating the condition of $CO_2$ laser, to regulate the amount of side and forward emission. The distal end of the optical fiber with core/clad diameter of $400/440{\mu}m$ was microstructured with cone shape by using a femtosecond laser. And then the microstructured optical fiber tip was polished by $CO_2$ laser beam result in smoothing and specular reflection at the surface of the cone structure. Finally, we operated the LightTools simulation and good agreement was generally found between the proposed model and experimental simulation.

• Membrane and Water Treatment
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• v.2 no.1
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• pp.1-24
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• 2011

The deficiency of clean water is a major global concern because all the living creatures rely on the drinkable water for survival. On top of this, abundant of clean water supply is also necessary for household, metropolitan inhabitants, industry, and agriculture. Among many purification processes, advances in low-energy membrane separation technology appear to be the most effective solution for water crisis because membranes have been widely recognized as one of the most direct and feasible approaches for clean water production. The aim of this article is to give an overview of (1) two new emerging membrane technologies for water reuse and desalination by forward osmosis (FO) and membrane distillation (MD), and (2) the molecular engineering and development of highly permeable hollow fiber membranes, with polyvinylidene fluoride (PVDF) and polybenzimidazole (PBI) as the main focuses for the aforementioned applications in National University of Singapore (NUS). This article presents the main results of membrane module design, separation performance, membrane characteristics, chemical modification and spinning conditions to produce novel hollow fiber membranes for FO and MD applications. As two potential solutions, MD and FO may be synergistically combined to form a hybrid system as a sustainable alternative technology for fresh water production.

• Journal of the Optical Society of Korea
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• v.7 no.2
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• pp.67-71
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• 2003

For a more detailed understanding of the mechanism of an L-band erbium-doped fiber amplifier, we investigated 980 nm absorption, signal amplification and forward and backward amplified spontaneous emission along the erbium-doped fiber. In addition, we compared performances of the erbium-doped fiber amplifier with and without a fiber Bragg grating.

• International Journal of Concrete Structures and Materials
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• v.3 no.1
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• pp.33-37
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• 2009

Fiber Bragg grating (FBG) sensors already have been the focus for structural health monitoring (SHM) due to their distinguishing advantages. However, as bare optical fiber is very fragile, bare FBG strain sensor without encapsulation can not properly be applied in practical infrastructures. Therefore encapsulation techniques for making encapsulated FBG strain sensor show very important in pushing forward the application of FBG strain sensors in SHM. In this paper, a simplified approximate method to analyze the stress transferring rules for embedded FBG strain sensors in concrete monitoring is put forward according to mechanics of composite materials. Shear lag theory is applied to analyze the stress transferring rule of embedded FBG strain sensor in measured host material at the first time. The measured host objects (concrete) and the encapsulated FBG strain sensor are regarded as a composite, and then the stress transfer formula and stress transfer coefficient of encapsulated FBG strain sensor are obtained.

• Coupled systems mechanics
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• v.7 no.2
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• pp.197-209
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• 2018

Fiber-reinforced concrete (FRC) is a material with increasing application in civil engineering. Here it is assumed that the material consists of a great number of rather small fibers embedded into the concrete matrix. It would be advantageous to predict the mechanical properties of FRC using nondestructive testing; unfortunately, many testing methods for concrete are not applicable to FRC. In addition, design methods for FRC are either inaccurate or complicated. In three-point bending tests of FRC prisms, it has been observed that fiber reinforcement does not break but simply pulls out during specimen failure. Following that observation, this work is based on an assumption that the main components of a simple and rather accurate FRC model are mechanical properties of the concrete matrix and fiber pullout force. Properties of the concrete matrix could be determined from measurements on samples taken during concrete production, and fiber pullout force could be measured on samples with individual fibers embedded into concrete. However, there is no clear relationship between measurements on individual samples of concrete matrix with a single fiber and properties of the produced FRC. This work presents an inverse model for FRC that establishes a relation between parameters measured on individual material samples and properties of a structure made of the composite material. However, a deterministic relationship is clearly not possible since only a single beam specimen of 60 cm could easily contain over 100000 fibers. Our inverse model assumes that the probability density function of individual fiber properties is known, and that the global sample load-displacement curve is obtained from the experiment. Thus, each fiber is stochastically characterized and accordingly parameterized. A relationship between fiber parameters and global load-displacement response, the so-called forward model, is established. From the forward model, based on Levenberg-Marquardt procedure, the inverse model is formulated and successfully applied.