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Proceedings Paper

Adaptive two-wave mixing wavelength demodulation of fiber Bragg grating sensor for monitoring dynamic strains
Author(s): Yi Qiao; Yi Zhou; Sridhar Krishnaswamy
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Paper Abstract

A two-wave mixing (TWM) wavelength demodulator using InP:Fe photorefractive crystal (PRC) in the C-band (1530-1570nm) is demonstrated. The system can be used as a wavelength demodulator for use with Fiber Bragg Grating (FBG) sensors to monitor dynamic strains. In this configuration, the FBG is illuminated with a broadband source, and any strain in the FBG is encoded as a wavelength shift of the light reflected by the FBG. The reflected light from the FBG is spilt into two unbalanced paths and both beams (pump and signal) mix in the PRC. Any wavelength shift of the reflected light results in an equivalent phase shift between the pump and signal beams as they travel unbalanced path lengths. Since TWM is an adaptive process, the two interfering beams are naturally in quadrature and remain in quadrature even in the presence of large quasi-static strains. We demonstrate that FBG demodulation using TWM has the ability to selectively monitor dynamic strains without the need for active compensation of large quasi-static strains that otherwise would cause the FBG sensor to drift. As TWM interferometers can be readily multiplexed at relatively low cost; the proposed technique can be used to demodulate signals from a network of FBG sensors for use in structural health monitoring.

Paper Details

Date Published: 16 May 2005
PDF: 8 pages
Proc. SPIE 5758, Smart Structures and Materials 2005: Smart Sensor Technology and Measurement Systems, (16 May 2005); doi: 10.1117/12.598041
Show Author Affiliations
Yi Qiao, Northwestern Univ. (United States)
Yi Zhou, Northwestern Univ. (United States)
Sridhar Krishnaswamy, Northwestern Univ. (United States)

Published in SPIE Proceedings Vol. 5758:
Smart Structures and Materials 2005: Smart Sensor Technology and Measurement Systems
Eric Udd; Daniele Inaudi, Editor(s)

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