• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.10 s.340
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• pp.19-28
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• 2005

In this paper, we analyzed tuning characteristics of the widely tunable SGDFB laser diode integrated with SGDBR. The improved time-domain model is used to analyse the laser diode. From the numerical analysis, the length of phase control region in the SGDFB section influences on the output power and the tuning range. Also, it was confirmed that the tuning range is affected by the length of the laser diode, the residual reflectivity at the facet, and the position of the facet.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.30-35
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• 2003

In this paper, the transverse strain was measured using polarization maintaining fiber Bragg grating(PMFBG) sensor. PMFBG sensor was fabricated using phase mask and Excidmer laser. The reflected wavelength of PMFBG sensor had dual peaks due to intrinsic birefringence. To find the polarization axes, peak sensitivity was measured under compression test. The signal characteristics of PMFBG sensor were also examined in embedding condition. The embedded PMFBG sensor in epoxy block was loaded for the transverse strain measurement, The wavelength-swept fiber laser(WSFL) was used to construct the PMFBG sensor system. Experiments showed that the PMFBG sensor could successfully measure the transverse strain.

• Composites Research
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• v.17 no.4
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• pp.32-39
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• 2004

Among many fiber optic sensors, FBG sensors are being studied more actively than any other sensor due to good multiplexing capabilities. Recently, the application fields of FBG sensors are mainly focused on the composite materials through embedding rather than attaching on the surface. However, there are many limitations on the embedding FBG sensors into composite materials because of the birefringence effects which is induced when FBG sensors are not embedded parallel to the reinforcing fiber. In this study, the fabrication method of FBG sensors with various grating length that are easy to fabricate with good multiplexing capabilities and more stable from the birefringence effects are investigated. The signal characteristics of the FBG sensors are also verified through the cure monitoring of 2 kinds of composite materials.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.12
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• pp.70-77
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• 1999

A new method for fabricating long fiber Bragg gratings(FBGs) using uniform phase mask is proposed. The proposed method is characterized by forming a number of subgratings sequentially in series and varying linearly the effective refractive index of each subgrating. The reflectivity of a 200mm long uniform FBG developed fabricated by the method is about 95%. Also, the bandwidth and dispersion slope of a 250mm long linear-chirped FBG developed here are ∼0.5nm and ∼4.965ps/nm respectively.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.5
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• pp.64-71
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• 2006

We developed a fiber-optic temperature sensor system, with 10 fiber Bragg gratings, for abnormal high-temperature monitoring in power systems. We used Gaussian line-fitting algorithm to compensate the spectrum distortion in the wavelength-scanned Farby-Perot filter demodulation scheme. Compared with highest-peak-detection method, the proposed algorithm substantially reduced measurement errors. The overall measurement error was less than 1[%] compared with the reference thermocouple and the linearity error was 0.37[%].

• Korean Journal of Optics and Photonics
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• v.23 no.5
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• pp.211-216
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• 2012

We report a resonance fiber Bragg sensor interrogation based on a Fourier domain mode-locking (FDML) laser. The FDML laser is constructed based on a conventional ring laser cavity configuration with fiber Fabry-Perot tunable filter (FFP-TF). There are two sensor parts which are composed with two FBGs inside the laser cavity. Each sensor part provides a separate laser cavity for the FDML laser. The resonance frequencies of the laser cavities are 46.687 kHz and 44.340 kHz, respectively. We applied a static and a dynamic strain on the FBG sensor system. The slope coefficients of the measured relative wavelength shift and relative time interval from the static strain are found to be $0.61pm/{\mu}{\epsilon}$ and $0.8ns/{\mu}{\epsilon}$, respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.8
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• pp.51-57
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• 2004

We have analyzed the effect of out-band dispersion in the cascaded fiber Bragg Elating(FBG) based optical add-drop multiplexers(OADM) when bypassed wavelengths contain SCM signals. In order to compute this impairment the dispersion characteristics of FBG have been analytically calculated by solving their coupled wave equations, and the Fourier method is applied to IMD analysis. The out-band dispersion effects over WDM/SCM signals are analyzed under different and common system situations as: ITU channel spacing(100, 50, 25 GHz), channel density parameter, frequency extension of the SCM plan, modulation characteristics, FBG length, etc. From this results, the transport of WDM/SCM signals in future DWDM transport networks could be limited by this effect which has to be taken into account for designing future networks.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.6
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• pp.443-450
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• 2016

In this study, we propose a novel fiber optic sensor to show the measurement feasibility of distributed temperature and strains in a single sensing fiber line. Distributed temperature can be measured using optical time domain reflectometry (OTDR) with a Raman anti-Stokes light in the sensing fiber line. Moreover, the strain can be measured by fiber Bragg gratings (FBGs) in the same sensing fiber line. The anti-Stokes Raman back-scattering lights from both ends of the sensing fiber, which consists of a 4 km single mode optical fiber, are acquired and inserted into a newly formulated equation to calculate the temperature. Furthermore, the center wavelengths from the FBGs in the sensing fiber are detected by an optical spectrum analyzer; these are converted to strain values. The initial wavelengths of the FBGs are selected to avoid a cross-talk with the wavelength of the Raman pulsed pump light. Wavelength shifts from a tension test were found to be 0.1 nm, 0.17 nm, 0.29 nm, and 0.00 nm, with corresponding strain values of $85.76{\mu}{\epsilon}$, $145.55{\mu}{\epsilon}$, $247.86{\mu}{\epsilon}$, and $0.00{\mu}{\epsilon}$, respectively. In addition, a 50 m portion of the sensing fiber from $30^{\circ}C$ to $70^{\circ}C$ at $10^{\circ}C$ intervals was used to measure the distributed temperature. In all tests, the temperature measurement accuracy of the proposed sensor was less than $0.50^{\circ}C$.

• Korean Journal of Optics and Photonics
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• v.29 no.6
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• pp.241-246
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• 2018

In this paper, a low-cost optical temperature sensor is implemented, using a fiber Bragg grating (FBG) as the temperature probe and a low-cost VCSEL with temperature-dependent output wavelength as the light source. To analyze the wavelength of the reflected light from the FBG, an interrogation was applied using a method of referring to the internal temperature according to the output wavelength of the VCSEL. When the temperature of the VCSEL was adjusted from 14 to $52.2^{\circ}C$, the output wavelength varied from 1519.90 to 1524.25 nm. The degree of wavelength tuning according to temperature was $0.114nm/^{\circ}C$. The variable wavelength repeatability error according to temperature was ${\pm}0.003nm$, and the temperature measurement error was ${\pm}0.18^{\circ}C$. As a result of measuring the temperatures from 22.3 to $194.2^{\circ}C$, the value of the internal temperature change of the light source according to the applied temperature ${\Delta}T$ was $0.146^{\circ}C/{\Delta}T$, the change in reflected wavelength of the temperature probe according to applied temperature ${\Delta}T$ was measured at $16.64pm/^{\circ}C$. and the temperature measurement error of the sensor was ${\pm}1^{\circ}C$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.4
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• pp.428-435
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• 2004

With the rapid and wide-spread use of cellular telephones much attention has been focussed on propagation in the urban area crowed with buildings and houses. It is often surrounded by hills, forests, and mountains. The importance of surface scattering intereference between transmitters and receivers on the rough surfaces has been interested and investigated. Therefore, a prediction method is necessary to estimate the influence of rough surfaces on microwave radio propagation. Moreover, most of the mobile communications are performed based on the digital communication system rather than the analog one. In this case, we must pay more careful attention to the signal delay caused by the phase delay due to the multi-path propagation. In this paper we have analyzed numerically scattering of electromagnetic waves from building walls by using FVTD(Finite Volume Time Domain) method. We consider three different types of rough surfaces such as periodic, random, and composite structures. We calculate the bistatic normalized radar cross section (NRCS) for horizontal and vertical polarization, and we take account of the conventional optical reflection which corresponds to the n-th Bragg reflection for periodic structures. In addition, we investigated what conditions are needed in order to be able to ignore the higher order Bragg reflection for the periodic structures.