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

Abstract

Several factors influencing the mechanical strength of fiber Bragg grating (FBG) sensorsduring their fabrication were examined and FBG sensors were made under controlled UV laserconditions. A chemical stripping technique to remove the acrylate coating of the fiber andH2 loading treatment to increase the photosensitivity of the optical fibers at a wavelengthrange of 240–250 nm showed negligible impact on the mechanical strength of the fiberoptic sensor. The UV laser beam width exposed on the fiber was controlled up to60 µm so as to reduce the damaged areas induced from laser exposure. Also the pulsefluence and the total dose of a pulsed KrF excimer laser were varied in order toinvestigate their influence on the mechanical strength. Finally FBG sensors withdifferent reflectivities were fabricated with only slight strength degradation suchthat they could be used in a structure with 2.54% measurement range of strain.