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Proceedings Paper

Polarization-multiplexed and phase-stepped fiber optic shearography using laser wavelength modulation
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Paper Abstract

Shearography is a non-contact technique that measures deformation gradients, which can subsequently be used to evaluate out-of-plane strain components. In this paper orthogonal deformation gradients are measured quasi- simultaneously. The object under investigation is illuminated using linearly polarized light from an optical fiber. A polarization sensitive Michelson interferometer shears the speckle image from the object in orthogonal directions, for horizontally and vertically polarized light, allowing both displacement gradients to be measured independently. Laser diode injection current modulation provides a wavelength shift, which can be used to step between linear polarizations by using the birefringence of a highly-birefringent optical fiber. Wavelength modulation can also be used to phase step the interferograms produced, by using an unbalanced Michelson interferometer. If the wavelength modulation, optical fiber length and the pathlength imbalance are matched, then the polarization can be stepped between linear polarizations and the phase can be stepped by the same wavelength modulation. Images of the phase stepped correlation fringes and the wrapped phase maps illustrate the system operation.

Paper Details

Date Published: 17 August 1999
PDF: 9 pages
Proc. SPIE 3745, Interferometry '99: Applications, (17 August 1999); doi: 10.1117/12.357773
Show Author Affiliations
Roger M. Groves, Cranfield Univ. (United Kingdom)
Stephen W. James, Cranfield Univ. (United Kingdom)
Ralph P. Tatam, Cranfield Univ. (United Kingdom)

Published in SPIE Proceedings Vol. 3745:
Interferometry '99: Applications
Werner P. O. Jueptner; Krzysztof Patorski, Editor(s)

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