• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.6
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• pp.1425-1431
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• 2013

We have measured the radiation-induced Bragg wavelength shift (BWS) of fiber Bragg grating (FBG) which was inscribed in Ge-doped core silica using a phase mask during irradiation up to a dose of 23 kGy and annealing effects after the gamma-exposure. For packaged FBG sensors, we observed the maximum radiation-induced BWS of about 91 pm during irradiation. Packaged FBG sensors also show higher radiation sensitivity above nearly a factor of two than non-packaged type sensor in the same condition.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.104-109
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• 2009

In order to apply FBG(Fiber Bragg Grating) sensor as one of reliable sensors in the commercial railway structure, the reliability of FBG sensor in the mechanical strength viewpoint have to be confirmed and the maximum strain should surpass the fracture strain of the host structure to measure the measurands until the host structures fail. In this paper, several factors that influence the mechanical failure strength of fiber Bragg grating sensors were analyzed. A set-up for dynamic tensile testing of optical glass fibers with fiber Bragg gratings was made. To increase the FBG failure strength, techniques relying on the H2 loading treatment and stripping methods were established and testified as a result of the tensile strength test of optical fibers.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.10
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• pp.90-97
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• 1996

A numerical method for scattering of electromagnetic waves from a periodic strip grating over a grounded dielectric slab is considered for TE and TM polarization cases from the viewpoints of both reflection grating problem and leaky wave antenna problem. The analysis is based on a mode expansion method, floquet's theorem, and the method of moments. Numerical results involving some combinations of geometric parameters are presented in terms of complex propagation constant (kd-$\beta$d diagram), radiation pattern, and relative scattered powers of spectral modes. In particular, the relationship between complex propagatio constnat form the viewpoint of leaky wqve antenna problem and Off-bragg and bragg blazing phenomena from the viewpoint of reflecton graing problem is investigated.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.11
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• pp.82-87
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• 1999

To temperature-compensate the Bragg wavelength of fiber grating filters two materials with different thermal expansion coefficients were depolyed for packaging. After temperature-compensation packaging the maximum difference of the Bragg wavelength in the temperature range of $-10^{\circ}C$ to $70^{\circ}C$ was 0.03nm, which is only about one thirtiety of the Bragg wavelength shift of the temperature-uncompensated fiber grating filter.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.665-668
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• 1997

We fabricated a number of optical fiber Bragg gratings by varying the UV beam parameters such as the laser energy density, pulse repetition rate and exposing time. The reflectance and the Bragg wavelength shift of the fiber Bragg gratings formed with a KrF excimer laser in real time depend strongly on the UV beam parameters. The index changes in the gratings during the exposing time are well fitted to the well known equations.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.961-963
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• 2015

In this study, we studied the effect of $Co^{60}$ gamma-radiation on the fiber Bragg gratings written by femtosecond UV laser in single mode optical fibers. The fiber Bragg gratings were exposed to gamma-radiation up to a dose of about 31.6 kGy at the dose rate of 106 Gy/min. According to the experimental data and analysis results, we confirmed Bragg gratings written by femtosecond laser have the excellent radiation-hardened characteristics for high radiation environments.

• Korean Journal of Optics and Photonics
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• v.17 no.3
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• pp.209-215
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• 2006

Circular Bragg gratings(CBGs) canbe incorporated in most of the semiconductor laser devices because of the frequency-selective property applicable as an optical narrowband-pass filter in DWDM optical communications. In this paper, the optical filtering characteristics of CBGs are evaluated by a novel and simple analytic modal transmission-line theory(MTLT), which is based on Floquet-Babinet's principle. The numerical results reveal that this method offers a simple and convenient algorithm to analyze the filtering characteristics of CBGs as well as is extended conveniently to evaluate the guiding problems of circular multi-layered periodic structures.

• Journal of Korea Water Resources Association
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• v.37 no.9
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• pp.729-736
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• 2004

Analysis of reflection of random waves propagating over rectangular submerged non-porous breakwaters was performed by using the eigenfunction expansion method. In this study, random waves were generated by superposition of several monochromatioc waves. Reflection coefficients were calculated by summing each numerical results of regular waves. Predicted results from the eigenfunction expansion method were in a good agreement with the results of laboratory measurements. Reflection coefficients of random waves were also resonated at the Bragg reflection condition.

• Journal of the Optical Society of Korea
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• v.20 no.5
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• pp.575-578
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• 2016

The thermal endurance of fiber Bragg gratings (FBGs), written with the aid of 193-nm ArF excimer laser irradiation on H₂-loaded Ge/B codoped silica fiber, and pretreated with a CO₂ laser and a subsequent slow cooling process, is investigated. These treated gratings show relatively less degradation of grating strength during the thermal annealing procedure. The thermal decay characteristics of treated and untreated fiber, recorded over a time period of 9 hours, have been compared. The effect on the Bragg transmission depth (BTD) and the center-wavelength shift, as well as the growth of refractive-index change during the grating inscription process for both treated and untreated fiber, are analyzed.

• Journal of the Korean Society of Safety
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• v.16 no.2
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• pp.121-129
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• 2001

This paper demonstrates the development of optical temperature sensor based on the etched planar waveguide Bragg grating. Topics include design and fabrication of the etched planar waveguide Bragg grating, investigation of the grating reflection characteristics, and temperature measurement capabilities. The typical bandwidth and reflectivity of the surface etched grating has been ~0.2nm and ~7%, respectively, at a wavelength of ～1552nm. The temperature-induced wavelength change of the optical sensor is found to be slightly non-linear over ～20$0^{\circ}C$ temperature range. Theoretical models for the grating response of the sensor based on waveguide and plate deformation theories agree with experiments to within acceptable tolerance.