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9 December 1999 Modified inverted-graded-index fibers for evanescent-wave chemical sensing
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This paper deals with two novel modifications of the inverted- graded index (IGI) fibers, namely with IGI fibers with a truncated inverted-linear refractive-index profile and with a truncated inverted parabolic refractive-index profile which is localized only to part of the core. Preforms for drawing the fibers were prepared by the MCVD method by using boron oxide for decreasing the refractive index of silica. Fibers were drawn from the prepared preforms and coated with polydimethylsiloxane polymeric cladding. Fabrication of the fibers and its relation to characteristics of the prepared fibers such as refractive-index profiles are described. The experimental sensitivity of the prepared IGI fibers to changes of the refractive index of the cladding was determined in immersion experiments under the excitation of the fiber with an inclined collimated beam. Results of ray-optics theoretical analysis of these sensing structures for the above excitation conditions are given, which show the possibility of further increasing the sensitivity to refractive-index changes of the optical cladding of IGI fibers even for claddings with a refractive index value of about 1.41 (commercial PCS fibers). The obtained theoretical and experimental results show higher evanescent-wave sensitivity of the two prepared novel sensing IGI fibers in comparison with standard PCS fibers.
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Vlastimil Matejec, Ivan Kasik, Miroslav Chomat, Jiri Ctyroky, Daniela Berkova, and Ivan Huettel "Modified inverted-graded-index fibers for evanescent-wave chemical sensing", Proc. SPIE 3860, Fiber Optic Sensor Technology and Applications, (9 December 1999);

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