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Proceedings Paper

Long-period gratings with high insensitivity to external refractive index inscribed by using a CO2 laser in fibers with parabolic-index cladding
Author(s): Miroslav Chomát; Jiří Ctyroký; Daniela Berková; Vlastimil Matějec; Ivan Kašík; Jana Proboštová; Filip Todorov; Alexander Jančárek
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Paper Abstract

Long-period gratings (LPGs) in an optical fiber, which was designed and fabricated for achieving high insensitivity of the inscribed LPGs both to bending and to the external index of refraction, are investigated. The fiber has a double cladding, consisting of a uniform outer cladding and a graded-index inner cladding, where the index of refraction decreases approximately parabolically with radius. This fiber is referred to as the parabolic-index cladding (PIC) fiber. Results obtained in the preparation of preforms and drawing PIC fibers are given. The theoretical analysis, carried out by the mode expansion and beam propagation method, yields field distributions and effective indexes of the fundamental core mode LP01 and several low-order circularly symmetric cladding modes LP0m for several external indexes of refraction. Experiments are done with an LPG with a period of 214 μm inscribed with a CO2 laser in the PIC fiber. In experiments, transmission spectra of the LPG immersed in three liquids with refractive indexes in a relatively wide range around the index of silica (water, silica-index-matching liquid, silicone oil) are measured in a temperature range of 25-67.5°C. From experiments it follows, in agreement with the theoretical analysis, that the spectral positions of the investigated attenuation band at &lgr; ≈ 1550 nm (coupling between the LP01 and LP02 mode), determined at temperatures in the above range, are highly insensitive to the external index of refraction.

Paper Details

Date Published: 16 May 2007
PDF: 10 pages
Proc. SPIE 6585, Optical Sensing Technology and Applications, 65850F (16 May 2007); doi: 10.1117/12.723004
Show Author Affiliations
Miroslav Chomát, Institute of Photonics and Electronics (Czech Republic)
Jiří Ctyroký, Institute of Photonics and Electronics (Czech Republic)
Daniela Berková, Institute of Photonics and Electronics (Czech Republic)
Vlastimil Matějec, Institute of Photonics and Electronics (Czech Republic)
Ivan Kašík, Institute of Photonics and Electronics (Czech Republic)
Jana Proboštová, Institute of Photonics and Electronics (Czech Republic)
Filip Todorov, Institute of Photonics and Electronics (Czech Republic)
Czech Technical Univ. in Prague (Czech Republic)
Alexander Jančárek, Czech Technical Univ. in Prague (Czech Republic)


Published in SPIE Proceedings Vol. 6585:
Optical Sensing Technology and Applications
Francesco Baldini; Jiri Homola; Robert A. Lieberman; Miroslav Miler, Editor(s)

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