Experimental verification of response of embedded optical fiber Bragg grating sensors in non-homogeneous strain fields

One of the advantages of optical fiber sensors is their ease of embedment w ithin a structure for non-destructive strain monitoring. In particular, Bra gg grating sensors are written directly into an optical fiber hence remaini ng unobtrusive. In addition, several gratings can be written in series alon g a single fiber, permitting sensing at discrete points throughout the stra in field. However, in regions of strong strain gradients, measuring the str ain at discrete points may not be sufficient. One solution is to write a Br agg grating longer than the strain region of interest and use the change in its spectral response to determine the applied strain field as a function of position along the fiber. This paper presents an experimental verificati on of the response of an embedded optical fiber Bragg grating (OFBG) to app lied non-homogeneous strain fields. Optical fiber Bragg grating sensors wer e embedded in four epoxy specimens of different forms so as to apply known strain functions along the gauge length when the specimen is under uniaxial tension. The complete spectral response of the Bragg gratings was then mea sured as a function of increasing load. The results are compared with analy tical calculations, based on the piecewise-uniform period assumption for ch irped gratings. Finally, the use of these spectra is discussed as possible basis functions for the resolution of an arbitrary applied strain distribut ion. (C) 2000 Elsevier Science Ltd. All rights reserved.