Effect of transverse load on fiber bragg grating measurements (The)

Abstract

The field of communications has been revolutionized by the advent of optical fiber. Optical fiber now connects most of the world carrying a vast amount of information through a very limited physical medium. To the materials engineer, optical fiber technology has stimulated interest in a new type of micro-sensor application, where the size, weight, and the ability to integrate the sensor into a material structure play a major role. Areas of interest currently include materials characterization, cure monitoring, and structural health monitoring. The fiber Bragg grating (FBG) is such a sensor technology, creating an optical strain gauge within the core of an optical fiber through the use of a wavelength specific filter. As the FBG experiences induced strain along its major axis, its light signal indicates the amount of strain with great accuracy and sensitivity. In FBG applications, where loading may occur in all directions, complex changes take place in the FBG signal. As these changes impact the usefulness of the FBG as a strain sensor, this thesis endeavors to study and demonstrate the effect of transverse load on the FBG structure. A review of the basics of optical fiber fabrication, light transmission, and optical fiber sensor technology is presented first, followed by a detailed discussion of the FBG’s manufacturing and operation. The crux of the thesis is presented with the results of experiments conducted to characterize the FBG signal in both unloaded and transversely loaded configurations. Polarization and wavelength based experiments and analyses are conducted to detect changes in the FBG signal. The results of the study are used to propose cause and effect relationships between transverse loading, its effect on the material properties of the FBG, and changes in the FBG signal.%%%%Ph.D., Material Engineering – Drexel University, 2000