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Applications of Brillouin Dynamic Grating to Distributed Fiber Sensors
Kwang Yong Song,Hotate, Kazuo,Weiwen Zou,Zuyuan He IEEE 2017 Journal of Lightwave Technology Vol.35 No.16
<P>In the process of stimulated Brillouin scattering (SBS), acoustic waves are generated by the interference of counterpropagating optical waves via electrostriction effect. These acoustic waves not only stimulate the Brillouin scattering process, but can also play a role of moving Bragg reflector for another optical wave when a proper phase-matching condition is satisfied between the interacting optical waves. Brillouin dynamic grating (BDG) represents this secondary role of the acoustic wave, which shows a unique reflection spectrum, called BDG spectrum. The BDG spectrum generally shows higher sensitivity to the change of physical variables, such as temperature and strain than ordinary Brillouin gain spectrum (BGS), and also provides information on the waveguide parameters, such as polarization or modal birefringence with high accuracy. This paper reviews the operation principle of BDG under various conditions and the research progresses on its application to distributed fiber sensors.</P>
Analysis of Brillouin frequency shift and acoustic waves in a hollow optical fiber.
Jeong, Yoonseob,Song, Kwang-Yong,Hotate, Kazuo,Oh, K Optical Society of America 2009 Optics letters Vol.34 No.20
<P>We propose and demonstrate a new method to manipulate the Brillouin frequency shift in silica optical fiber by introducing a silica hollow optical fiber (HOF) waveguide structure. Propagation characteristics of acoustic waves guided along the HOF were theoretically analyzed, and the corresponding Brillouin frequency shifts were measured by a Brillouin optical-correlation domain-analysis system. We experimentally observed that Brillouin frequency shift v(B) monotonically increases as a function of the central air-hole radius, which showed good agreement with the simulation results. We confirmed that a precise control of Brillouin frequency shift can be obtained by controlling the waveguide parameters of the HOF.</P>
Song, Kwang Yong,Zou, Weiwen,He, Zuyuan,Hotate, Kazuo Optical Society of America 2009 Optics letters Vol.34 No.9
<P>We demonstrate the distributed measurement of Brillouin dynamic grating spectra in a polarization-maintaining fiber based on time-domain analysis. Local reflection spectra of the Brillouin dynamic grating are acquired by synchronized propagation of the pump and the probe pulses based on the map of the Brillouin frequency distribution. Large temperature sensitivity as high as -50.9 MHz/ degrees C is observed with 2 m spatial resolution in 100 m range.</P>
Analysis of Historical Documents from a Viewpoint of Paper Science
YOON-HEE HAN,TOSHIHARU ENOMAE,AKIRA ISOGAI,HIROFUMI YAMAMOTO,MICHIHISA HOTATE 한국펄프·종이공학회 2006 한국펄프종이학회 기타 간행물 Vol.- No.-
Restoration of historical documents and arts has become important to inherit cultural properties. Most of historical documents were recorded on paper. Therefore, restoration of ancient papers is demanded and techniques for this purpose must be developed and sophisticated. In our study, several nondestructive methods for analyzing ancient paper have been developed. Image analysis using fast Fourier transform with suitable modifications was applied to optical micrographs of traditionally-handmade Korean and Japanese papers. This analysis determines the angle and anisotropy of fiber orientation of paper surfaces. Fiber orientation of traditionally-handmade Korean and Japanese papers was found to show their own characteristics in accordance with the motion of a papermaking screen made of bamboo splints. Consequently, the information on fiber orientation was found to be possible to distinguish the flow-sheet forming typical of Japanese paper and still- sheet forming typical of Korean paper. Moreover, the anisotropy was always higher for the screen side than for the top side, thus meaning that surface fiber orientation is possible to distinguish the two sides of paper of which papermaking history is unknown. An application of this technique to actual historical documents evidenced that wrapping papers were used as envelops with a lateral side up, namely, after rotating 90 degrees. A variety of cultural habits in writing letters was revealed by discrimination of the two sides.