The mechanical strength of fiber Bragg gratings under controlled UV laser conditions

Abstract

Several factors influencing the mechanical strength of fiber Bragg grating (FBG) sensors during their fabrication were examined and FBG sensors were made under controlled UV laser conditions. A chemical stripping technique to remove the acrylate coating of the fiber and H2 loading treatment to increase the photosensitivity of the optical fibers at a wavelength range of 240–250 nm showed negligible impact on the mechanical strength of the fiber optic sensor. The UV laser beam width exposed on the fiber was controlled up to 60 µm so as to reduce the damaged areas induced from laser exposure. Also the pulse fluence and the total dose of a pulsed KrF excimer laser were varied in order to investigate their influence on the mechanical strength. Finally FBG sensors with different reflectivities were fabricated with only slight strength degradation such that they could be used in a structure with 2.54% measurement range of strain.