Composite materials with embedded photonic crystal fiber interferometric sensors

A feasibility study of smart composite materials with embedded photonic crystal fiber (PCF) sensors for measurements of local and average strain and temperature is presented in this paper. For this purpose a composite material sample with embedded fiber sensors is fabricated and characterized. For temperature independent local strain measurements a short length PCF modal interferometer is utilized, while for an average strain measurement a polarization maintaining PCF Sagnac interferometric sensor is used. The strain and temperature sensitivities of a buffer coated and a buffer stripped PM-PCF Sagnac fiber loop mirror sensors are measured in free space and compared to those for similar sensors embedded in the composite material. It is found that the Sagnac interferometer with an acrylate coated PCF embedded in the composite material shows the same response as the one in free space while the unbuffered PCF Sagnac interferometric sensor which is temperature insensitive in free space shows significant temperature sensitivity when embedded in the composite material sample. A fiber Bragg grating array is also embedded in the composite material for comparison of the strain and temperature measured by the PCF modal interferometers. The results obtained in this study demonstrate that PCF sensors are a feasible technology that can be adapted for composite material strain measurement.