Experimental study and analysis of a polymer fiber bragg grating embedded in a composite material

The characteristics of polymer fiber Bragg gratings (FBGs) embedded in composite materials are studied in this paper and are compared with characteristics of their silica counterparts. A polymer FBG of 10 mm length which exhibits a peak reflected wavelength circa 1530 nm is fabricated and characterized for this purpose. A silica FBG with a peak reflected wavelength circa 1553 nm is also embedded in the composite material for a comparison study. The fabricated composite material sample with embedded sensors is subjected to temperature and strain changes and the corresponding effects on the embedded polymer and silica FBGs are studied. The measured temperature sensitivity of the embedded polymer FBG was close to that of the same polymer FBG in free space, while the silica FBG shows elevated temperature sensitivity after embedding. With an increase in temperature, spectral broadening was observed for the embedded polymer FBG due to the stress induced by the thermal expansion of the composite material. From the observed wavelength shift and spectral bandwidth change of the polymer FBG, temperature and thermal expansion effects in the composite material can be measured simultaneously.