Embedded fiber bragg gratings in photonic crystal fiber for cure cycle monitoring of carbon fiber-reinforced polymer materials

We report on the use of a fiber Bragg grating (FBG) based sensor written in a photonic crystal fiber (PCF) to monitor the cure cycle of composite materials. The PCF under study has been specifically designed to feature a high phase modal birefringence sensitivity to transverse strain and a very low sensitivity to temperature. We exploit these particular properties to measure strain inside a composite material in the out-of-plane direction. The embedded FBG sensor has been calibrated for transverse and axial strain as well as for temperature changes. These FBGs have then been used as embedded sensors during the manufacturing of a composite material in order to monitor how strain develops inside the composite during the cure cycle. We show that our sensors allow gaining insight in the composite cure cycle in a way that would be very difficult to achieve with any other sensor technology