Novel methods for simultaneous strain and temperature measurements with optical fiber Bragg gratings

Andreas Frank; Philipp M. Nellen; Urs J. Sennhauser

doi:10.1117/12.372987

9 December 1999 Novel methods for simultaneous strain and temperature measurements with optical fiber Bragg gratings

Andreas Frank, Philipp M. Nellen, Urs J. Sennhauser

Proceedings Volume 3860, Fiber Optic Sensor Technology and Applications; (1999) https://doi.org/10.1117/12.372987
Event: Photonics East '99, 1999, Boston, MA, United States

Abstract

We report on feasibility studies of two new approaches for simultaneous strain and temperature measurements with optical fiber Bragg gratings. In sensor applications fiber Bragg gratings cannot be thermally isolated. Therefore temperature has to be compensated or measured simultaneously with the measurand of interest. In strain sensing this is often done by measuring the wavelength response of a second Bragg grating attached to an unstrained sample specimen and comparing its response to response of the strained sample. This method is very accurate. However, often it is not possible or difficult to have unstrained samples, e.g., in rockbolt anchors with embedded fiber Bragg gratings. We propose two new simultaneous measurement concepts and compare them to known concepts. The first investigated method uses the different sensitivities to strain and temperature of the main peak of a Bragg grating in transmission compared to the back-reflected cladding modes. We will present first results of simultaneous strain and temperature measurements over a range from 2 degrees Celsius to 95 degrees Celsius up to 3500 micrometer/m in strain. This method leads to a combined resolution in temperature and strain of 4 degrees Celsius and 35 micrometer, respectively. The second method is based on two low reflectivity gratings. They are in close vicinity to each other in the fiber. Both have a small refractive index modulation of about 2 (DOT) 10^-4, but one was homogeneously post-illuminated and has an increased mean refractive index. We will present first results indicating that the additional UV-illumination changes temperature- and strain-sensitivity of the post-illuminated Bragg grating slightly.

Citation Download Citation

Andreas Frank, Philipp M. Nellen, and Urs J. Sennhauser "Novel methods for simultaneous strain and temperature measurements with optical fiber Bragg gratings", Proc. SPIE 3860, Fiber Optic Sensor Technology and Applications, (9 December 1999); https://doi.org/10.1117/12.372987

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