• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.2
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• pp.44-50
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• 2012

When the fiber Bragg gratings are embedded in a fiber-optic Sagnac loop for measuring temperature or strain, it is difficult to separate the Bragg wavelengths. The transmitted light is mixed with the reflected Bragg wavelengths in the photo-detector, working as noises. To suppress the noises, we placed the FBG sensors and a fiber-optic attenuator at asymmetric positions in the loop. With the arrangement the reflected light became much bigger than the transmitted light, enabling the separation of the reflected Bragg wavelengths with almost the same signal-to-noise ratio of the FBG sensors outside the loop.

• Laser Solutions
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• v.15 no.1
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• pp.15-19
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• 2012

The fabrication of internal diffraction gratings with photoinduced refractive index modification in transparent materials was demonstrated using low-density plasma formation excited by a femtosecond (130 fs) Ti: sapphire laser (${\lambda}_p$=800 nm). The refractive index modifications with diameters ranging from $1{\mu}m$ to $3{\mu}m$ were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than $2.0{\times}10^{13}W/cm^2$. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which low-density plasma occurred.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.9
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• pp.87-92
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• 1998

TM mode coupling coefficients for a generic five-layer DFB structure with trapezoidal and triangular gratings are calculated using the extended additional layer method. To determine the unperturbed field distributions of TM modes, a grating region is replaced by a new uniform layer whose inverse dielectric constant is the average value of the inverse dielectric constant of grating region in both longitudinal and transverse directions. Based on the self-consistent check, the validity of this method is established by comparing the results calculated by partitioning the grating region up to six uniform layers.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10b
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• pp.545-549
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• 1993

an alignment system in the X-and Y-directions an X-Y-.theta. stage driven by piezoelectric actuators is presented. A pair of quadruple gratings and a quadruple photo-detector are used. The difference between the two 0-th order moire signals in reflection with a relative spatial phase of 180.deg. is used in each direction to control the alignment of the X-Y-.theta. stage. The stage is aligned at the position where the difference is zero. The quadruple gratings are 10 mm * 10 mm, and of a binary square-type with a 1/2 duty cycle. Their pitches are 16 .mu.m. Alignment accuracy of .+-.20nm was obtained in this system.

• Journal of Sensor Science and Technology
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• v.27 no.2
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• pp.82-85
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• 2018

This paper proposes a new temperature-compensative displacement sensor with a pair of fiber Bragg gratings (FBG) attached to the inner and outer surfaces of an elastic metal band. The sensor can be also used as a temperature sensor with high sensitivity. The FBG pair shifted Bragg wavelengths in the same direction according to changes in the temperature. However, because the pressure of the metal band shifted a pair of Bragg wavelengths in the opposite direction, the displacement sensor could compensate for the effect of the temperature change in the proposed FBG pair. Results of the experiments showed that the two FBG displacement sensors responded linearly and symmetrically with respect to the displacement, and the displacement could be obtained using the difference between the two Bragg wavelengths.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.12
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• pp.1014-1017
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• 2009

In this study, we studied the nature of thin films formed by holographic photodoping chalcogenide thin films with for use in programmable metallization cell devices(PMC), a type of ReRAM. We formatted straight conduction pathway from the internal interferences of the diffraction gratings which is builded by the holographic lithography method. We investigated the resistance change of solid-electrolyte chalcogenide thin films varied in the applied voltage bias direction from about $1\;M{\Omega}$ to several hundreds of $\Omega$. The switching characteristics of the devices applied holographic lithography method was more improved than ultraviolet exposure condition. As a result of improved resistance change effects, we can analogize that the diffraction gratings is a kind of pattern for straight conduction pathway formation inside the chalcogenide thin films.

• Proceedings of the KIEE Conference
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• 1998.11c
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• pp.993-995
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• 1998

We fabricated fiber gratings with three different Ge-doped fibers exposed to 60atm pressure of Hz gas at 90"C for different times and studied the effects of Ge-doping concentration and $H_2$ loading time on the growth of gratings. According to experiments. the growing effect of hydrogen loading on high Ge-doped fiber was great.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.71-74
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• 2007

The objective of this presentation is to introduce a recent development of a magnetostrictive grating technique using an optimal yoke to efficiently generate and measure SH (Shear-Horizontal) waves in a plate. Gratings are effective means to generate frequency-tuned waves, but the gap between magnetostrictive gratings inevitably obstructs magnetic flow. Because magnetic field is the main physical quantity to actuate and sense ultrasonic waves, the transducer performance is most significantly influenced by the magnetic field distribution in the strips. Thus, wave transduction efficiency can be substantially improved if better magnetic flow is formed in the strips. To improve the efficiency, the topology optimization method was used to determine an optimal yoke configuration. A series of experiments on an aluminum plate were conducted using a grating with and without the designed yoke; when the yoke was used, the signal outputs increased up to 60 %.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.1 no.1
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• pp.75-78
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• 2008

In this paper, we proposed a novel encoder/decoder for an optical CDMA(code division multiple access) system by using an array of SSFBGs(superstructured fiber Bragg gratings). The feasibility of the system is shown by the simulations. The Q-factor for the system was 14.53 dB when the well-known Gold codes are used.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.4
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• pp.1081-1085
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• 2008

To measure the curvature, in this paper, we investigate an optical curvature sensor based on the fiber Bragg gratings. We observed the variation of the Bragg resonant wavelength shift to measure the curvature change. From the experimental results, we knew that the Brags resonant wavelength shift was lineally increased with the increase of the curvature from $0\;m^{-1}$ to $10\;m^{-1}$. It's slope is about $8.8\;pm/m^{-1}$. On the other hand, the spectral reflection decreased with the increase of the curvature.