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The polyimide used for FBG re-coating
leads to a sensitivity of the FBG wavelength to humidity and enhances its
temperature sensitivity as expected. The polyimide coated FBG shows
sensitivities of 4.36×10-6 RH%-1 and 10.6×10-6 K-1.
Relative humidity changes can lead to a wavelength shift of more than 0.5 nm at
1550 nm. For applications where the narrowband filter wavelength stability is
essential like DWDM, less sensitive coatings or sealing have to be employed. In
high temperature sensor applications, where polyimide coatings are necessary
the RH cross sensitivity has to be considered.
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1.
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H.G. Limberger and D. Varelas, “Advances
in Fiber Gratings: Technology, Applications, and Reliability.”,
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Reliability, vol. CR73, addendum, 1999.
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G. Meltz, “Overview of Fiber
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A.D. Kersey, M.A. Davis, H.J. Patrick, L.
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Sensors”, Journal of Lightwave Technology 15 (8), pp. 1442-1463,
1997.
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J.L. Armstrong, M.J. Matthewson, and C.R.
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5.
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P.Kronenberg, D. Inaudi, I. F.C. Smith, “Development
of an “optical hair”-hygrometer: A novel way to measure humidity using fibre
optics”, Int. Conf. on trends in optical non-destructive testing, D.
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