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Proceedings Paper

Accurate strain measurements with fiber Bragg grating sensors and wavelength references
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Paper Abstract

Fiber Bragg grating sensors are one of many fiber optic sensor technologies that are currently being used in structural health monitoring systems. The sensors operate by detecting shif in the wavelength of relfected maxima due to applied strain. This paper studies a new fiber Bragg interrogation method that utilizes a swept wavelength laser in combination with wavelength references. These include a gas cell, which is used as the long term wavelength standard and an etalon used for accurate interpolation of peak wavelengths. An etalon is essentially a filter that has a periodic response over a broad wavelength range. Since its wavelength response spacing is smaller than the gas cell, it can be used to determine the intermediate wavelengths between two gas cell absorption lines. Peak location is a key element of this interogation method and several detection algorithms are investigated. It was determined that polynomial peak fitting is the most computationally efficient method and yields a resolution of better than 0.5 pm with signal to noise ratios of 30:1 or better. With higher signal to noise ratios, polynomial peak fitting can yield a resolution of better than 0.25 pm and a resolution of bettern than 0.25 pm. Using a tunable laser, a HCN gas cell and an etalon with maxima every 140 pm, static load tests will demonstrate that a resolution of 1 pm and an accuracy of less than 5pm can be achieved. Also, this accuracy will be maintained over a long period of time as it is based on absorption lines in the gas cell. The results of this study demonstrate that absolute accurate strain measurements can be obtained with the use of wavelength references in conjunction with a suitable peak location algorithm.

Paper Details

Date Published: 27 July 2004
PDF: 8 pages
Proc. SPIE 5384, Smart Structures and Materials 2004: Smart Sensor Technology and Measurement Systems, (27 July 2004); doi: 10.1117/12.542107
Show Author Affiliations
Evangeline Rivera, Univ. of Manitoba (Canada)
Douglas J. Thomson, Univ. of Manitoba (Canada)

Published in SPIE Proceedings Vol. 5384:
Smart Structures and Materials 2004: Smart Sensor Technology and Measurement Systems
Eric Udd; Daniele Inaudi, Editor(s)

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