Transverse strain measurements in polymer-embedded, polarization-maintaining Fiber Bragg Gratings

Abstract

Fiber Bragg gratings (FBGs) have numerous advantages over traditional foil strain gages, most notably in that they can be embedded in host materials and used to evaluate local deformation. Among the wide variety of grating architectures that have been studied, FBGs inscribed in polarization-maintaining (PM) or other birefringent fibers provide a unique, quantifiable response to strain transverse to the fiber axis. In this work, we show that a PM FBG can accurately predict the asymmetry in transverse strain of a host material in embedded configurations. We do this by diametrically loading an epoxy cylinder that has a uniform PM FBG embedded in the center. We use elasticity and finite element modeling (FEM) to correlate the mechanical response of an embedded fiber with that of the host. An analytical solution of the nominal relationship between Bragg wavelength and strain is included for this loading condition.