Note: Strain sensitivity comparison between fiber Bragg gratings inscribed on 125 and 80 micron cladding diameter fibers, case study on the solidification monitoring of a photo-curable resin

The influence of fiber Bragg grating diameter when measuring strain is investigated and quantified. Two fiber Bragg gratings with bare cladding diameter of 125 ?m and 80 ?m are produced by excimer laser irradiation through a phase mask, and are used to simultaneously monitor the Bragg wavelength shift due to the strain produced by the solidification of a photo-curable resin during light exposure. It is found that the ratio of the measured strains in the two fiber Bragg gratings is close to the inverse ratio of the fiber's cladding diameter. These results represent a direct simultaneous comparison between 125 ?m and 80 ?m diameter fiber Bragg grating strain sensors, and demonstrate the feasibility of strain measurements in photo-curable resins using bare 80 ?m cladding diameter fiber Bragg gratings with an increased sensitivity and spatial resolution compared with standard 125 ?m diameter fiber Bragg gratings.