Hybrid fiber optic sensor system for measuring the strain, temperature, and thermal strain of composite materials

This paper proposes a hybrid optical fiber sensor system for simultaneously sensing the strain, temperature, and thermal strain of composite materials. The hybrid fiber optic sensor system involves a combination of three sensors: 1) a polarimetric sensor based on an acrylate coated polarization maintaining photonic crystal fiber (PM-PCF); 2) a coating stripped PM-PCF sensor; and 3) a fiber Bragg grating sensor (FBG). Temperature is sensed using the FBG sensor, axial strain is sensed using the acrylate coated PM-PCF sensor, and thermal strain is sensed using the coating stripped PM-PCF. The hybrid sensor system presented operates in the intensity domain by converting the polarization and wavelength information from the polarimetric sensors and the FBG, respectively, into detectable linear intensity variations. Subsequently, by deriving a characteristic matrix for the hybrid sensors, information about temperature, axial strain, and thermal strain can be simultaneously determined. An experimental demonstration of the hybrid sensor system is described based on a glass fiber reinforced composite material sample within which the three different sensors are embedded. The proposed sensor configuration can be employed in composite material structural health monitoring applications.