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Proceedings Paper

Novel Bragg grating distributed-strain sensor based on phase measurements
Author(s): Shang Yuan Huang; Myo Myint Ohn; Raymond M. Measures
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Paper Abstract

We recently disclosed that the shape of the intensity spectrum reflected from a Bragg grating can serve as an indicator of strain gradient across this grating. However, in principle, to map the strain field distribution, both the intensity spectrum (Iota) ((lambda) ) and the phase spectrum (Psi) ((lambda) ) are needed. In this paper, we propose a method based on phase measurements. It relies on the correlation between the wavelength-dependent penetration depth of light in a nonuniform (chirped) grating and the phase delay of the reflected wave. If we know that the nonuniform strain field to be measured is a monotonic function of position along the grating (which is the most practical case), then the measured grating phase-spectrum (Psi) ((lambda) ) can be used to evaluate the penetration depth and consequently the distribution of the grating optical pitch-lengths, i.e. the strain distribution over the grating. Theory reveals that the phase slope spectrum d(Psi) ((lambda) )/d(lambda) induced by a grating can directly yield the strain field profile. For example, a linear phase slope spectrum indicates a linear chirp in the grating due to a constant strain gradient; and the strain gradient can be easily obtained from the dispersion constant d2(Psi) ((lambda) )/d(lambda) 2. The validity of this method is also discussed in this paper.

Paper Details

Date Published: 20 April 1995
PDF: 12 pages
Proc. SPIE 2444, Smart Structures and Materials 1995: Smart Sensing, Processing, and Instrumentation, (20 April 1995); doi: 10.1117/12.207678
Show Author Affiliations
Shang Yuan Huang, Univ. of Toronto (Canada)
Myo Myint Ohn, Univ. of Toronto (Canada)
Raymond M. Measures, Univ. of Toronto (Canada)

Published in SPIE Proceedings Vol. 2444:
Smart Structures and Materials 1995: Smart Sensing, Processing, and Instrumentation
William B. Spillman Jr., Editor(s)

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