Investigation on the fiber sensor for real-time monitoring the curing process of composite material through measuring the speckle spatial spectrum (SSS) of fiber

A new sort of optic fiber sensor was designed, by measuring the speckle spatial spectrum at the end face of which, the variation of refractive index of resin surrounding the embedded optical fiber can be obtained by means of the method developed here. The variation of speckle spatial spectrum depended on the variation of resin refractive index occurred in its curing process was calculated, and the relation between refractive index and cutoff frequency was given. The instrument error of the sensor was estimated. It was found that this sort of fiber sensor can be used to detect not only the gel point and end point in the curing process of resin, but also the temperature variation or vibration occurred in a structure and caused by the environment factors.