• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.142-148
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• 2007

A mechanically induced long-period fiber grating array was fabricated and its transmission characteristics were measured. The grating away consisted of a rubber cover and a 45 cm metal bar with 10 grating groups. Each grating group was composed of 60 gratings. The period of the grating of the grating groups was increased by $10{\mu}m$ increments from $690{\mu}m$ to $780{\mu}m$. The long period fiber grating was induced when the pressure was applied on the long period grating array and the resonant wavelength depended on the position of applied pressure. The experimental results shows that this long period fiber grating away can be used as a various band rejection filter or a fiber optic sensor.

• Journal of the Optical Society of Korea
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• v.7 no.2
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• pp.89-96
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• 2003

A new method to control the free spectral range of a long period fiber grating is proposed and theoretically analyzed. As the refractive index decreases radially outward in the silica cladding due to graded doping of fluorine, waveguide dispersion in the cladding modes was modified to result in the effective indices change and subsequently the phase matching conditions for coupling with the core mode in a long period fiber grating. Enlargement of the free spectral range in a long period fiber grating was theoretically confirmed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.8
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• pp.1791-1796
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• 2011

An optical fiber short period grating of 0.7 nm as a 3 dB wavelength linewidth was fabricated using a Gaussian distributed KrF Eximer laser and a phase mask. This grating has temperature dependancy of 0.01 nm/$^{\circ}C$ over the range of -10 $^{\circ}C$ ~ 70 $^{\circ}C$and no difference between temperature directions. An optical fiber long period grating of 14.22 nm as a 3 dB linewidth was also fabricated using a amplitude mask and has dependancy of 0.01 nm/$^{\circ}C$ over the same range.

• Korean Journal of Optics and Photonics
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• v.14 no.4
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• pp.365-368
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• 2003

We have demonstrated mechanically induced Mach-Zehnder interferometers (MZI) based on a long-period fiber grating pair. The transmission spectra, the interference fringes, and the fringe spacing of the long-period fiber grating pairs have also been investigated experimently and analytically. The fringe spacings of the fabricated LPG pairs agree well with the theoretical results.

• Korean Journal of Optics and Photonics
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• v.14 no.1
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• pp.8-11
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• 2003

For the first time to our knowledge we have developed compact mechanically-induced long-period fiber grating devices which have an excellent tunability in the center wavelength and the depth of the notch. The compactness and ease to tune allow us to include them in other optical devices or systems. The devices were characterized by measuring their transmission spectra with different grating periods and applied pressures. We have also demonstrated the EDFA gain flattening using the mechanically-induced long-period fiber grating devices.

• Journal of the Optical Society of Korea
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• v.3 no.2
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• pp.74-79
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• 1999

We present a simple design rule for a passive temperature-compensating optical package. We also present experimentally that a package fabricated by using the design rule compensates the temperature dependence of the resonant wavelength of an optical long period fiber grating by varying the strain inside the fiber, The package fabricated in this work consists of two pieced of brass tube, 10 mm long, and a piece of nylon rod, 45.4 mm long. It is shown that the package can compensate the temperature-induce wavelength shifts of the long period grating to a range of 6.8 pm/$^{\circ}C$, compared with 0..48 nm/$^{\circ}C$ for an uncompensated grating. The reduced strength of the fiber caused by exposure to ultraviolet limits the performance of the package to the range operating temperature form -3 $^{\circ}C$ to 7$0^{\circ}C$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.10
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• pp.1823-1825
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• 2007

Based on Faraday effect, the variation of current flowing through the conductor can be encoded as that of azimuth angle of light polarization propagating through the fiber coil wound onto the conductor. The amount of current can be obtained by measuring the variation of the light intensity transformed from that of the azimuth angle through a polarization analyzer. In this paper we propose a fiber-optic current sensor system that employs a fiber polarization analyzer as a sensor interrogation device. The fiber polarization analyzer was prepared by inscribing a long-period fiber grating on a high birefringent fiber. At the fixed wavelength of 1522.5 nm, the fabricated fiber device has the polarization extinction ratio of more than 25 dB. The measurement of large current up to 600 Arms was accomplished based on a simple fiber interrogation device and the measurement output of the sensor system showed a good linearity.

• Journal of the Optical Society of Korea
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• v.10 no.1
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• pp.28-32
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• 2006

We propose a new pH-sensing scheme using a methylene blue adsorption on an optical fiber cladding surface. Interactions between the silica and hydroxyl ions of a base solution induce the surface of the silica negatively charged. The charged surface attracts the positively charged chromophores of methylene blue. As the pH of the solution is reduced, the electrostatic attraction will also be reduced. This electrostatic attraction can change the transmitted light intensity of the cladding mode, since the boundary condition changes. We also carried out a simulation to verify the effect from external refractive index change around a long-period fiber grating. Our results confirm that the wavelength shift by external refractive index change is negligible compared to the transmitted light intensity variation of the cladding mode. By using a long-period grating pair, we can detect the cladding mode transmittance variations. Experimentally, we showed the possibility of pH sensing in the $1.5{\mu}m$ infrared region.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.11
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• pp.1995-1997
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• 2007

In this paper we propose a wavelength-switchable fiber ring laser that employs a polarization-dependent fiber band stop filter. The fiber filter was fabricated by inscribing a long-period fiber grating on a high birefringent fiber. Dual-wavelength switching operation was accomplished by controlling the rotatable linear polarizer which rotated the polarization plane of the light circulating through the fiber laser cavity. The amplitude variation of both laser lines was measured to be less than 0.5 dB and the signal-to-amplified spontaneous emission ratio was more than 55 dB.

• Korean Journal of Optics and Photonics
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• v.15 no.5
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• pp.409-414
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• 2004

A signal processing system of long period grating sensor that works in the optical wavelength domain is proposed. The system is based on a wavelength-swept semiconductor light source that includes an SLD and a F-P tunable filter. The hysteresis effects of PZT in the F-P filter is compensated by using an etalon filter and an athermal Fiber Bragg Grating. The detected signals from the photodiode are transmitted to a computer using an A/D converter and the result of the process is displayed in the monitor.